tag:blogger.com,1999:blog-65667776513959312722024-02-06T19:43:13.221-08:00Post-quench Galaxies: Literature ReviewShort summaries of seminal articles about post-quenched galaxies and/or galaxy evolution are provided below, as well as a link to a PDF for the full article. Anonymoushttp://www.blogger.com/profile/13337278557841102817noreply@blogger.comBlogger5125tag:blogger.com,1999:blog-6566777651395931272.post-56432409693234451632014-03-15T09:09:00.000-07:002014-03-15T09:09:12.594-07:00Schawinski et al. Article - Evolution of Early and Late Types Through the Green Valley
<br />
<div style="margin-bottom: 0in;">
<b>Title</b>: The Green Valley is a Red
Herring: Galaxy Zoo reveals two evolutionary pathways towards
quenching of star formation in early- and late-type galaxies</div>
<div style="margin-bottom: 0in;">
<br /></div>
<div style="margin-bottom: 0in;">
</div>
<div style="margin-bottom: 0in;">
<b>Authors</b>: K. Schawinski, M. Urry,
B. Simmons, L. Fortson, S. Kaviraj, W. Keel, C. Lintott, K. Masters,
R. Nichol, M. Sarzi, S. Ramin, E. Treister, K. Willett, I. Wong, and
S. Yi</div>
<div style="margin-bottom: 0in;">
<br /></div>
<div style="margin-bottom: 0in;">
</div>
<div style="margin-bottom: 0in;">
<b>First Author's Institution: </b>Institute
for Astronomy, Department of Physics, ETH Zurich</div>
<div style="margin-bottom: 0in;">
<br /></div>
<div style="margin-bottom: 0in;">
To read the full article, please click <a href="http://arxiv.org/pdf/1402.4814v1.pdf" target="_blank">here</a>. </div>
<div style="margin-bottom: 0in;">
<br /></div>
<div style="margin-bottom: 0in;">
<br /></div>
<h3 style="margin-bottom: 0in;">
Article Summary:</h3>
<div>
<br /></div>
<div>
<div style="margin-bottom: 0in;">
The green valley has long been thought
of as the crossroads of galaxy evolution – creating a divide
between the star-forming galaxies of the blue cloud and
passively-evolving galaxies of the red sequence. The intermediate
color of green valley galaxies is thought of as an indicator that
star formation in these samples was recently quenched, and studying
this region between the two main populations will lead to a better
understanding of the evolutionary pathways of galaxies, possibly even
predicting what may happen to our own Milky Way. Galaxies spend most
of their life on what is dubbed the Main Sequence, where there is a
tight correlation between stellar mass and star formation rate (SFR). It is believed that certain processes can cause them to leave the main sequence and begin to
travel through the green valley. Most galaxies were presumed to
follow a similar tract through this desolate region of color space,
progressing through it in a relatively short timescale to keep the scarcity of galaxies observed in this region. In recent years,
the Galaxy Zoo project has brought a new tool to the galaxy evolution
table – a plethora of morphological classifications of galaxies
imaged by the Sloan Digital Sky Survey (SDSS), allowing astronomers
to inquire as to the effects of morphology on a galaxy's transition
through the green valley. A recent study done by Schawinski et al.
using data from the SDSS, Galaxy Evolution Explorer (GALEX), and
Galaxy Zoo has found that different morphological characteristics
will alter the movement of a galaxy through the green valley into its
quiescent fate.
</div>
<div style="margin-bottom: 0in;">
<br /></div>
<div style="margin-bottom: 0in;">
This study acquired a sample of
mass-limited galaxies in the local universe from the SDSS, with redshifts ranging
from z=0.02 to z=0.05. To gain a better understanding of star formation histories, ultraviolet
photometry from the GALEX was found for 71% of their sample. Galaxy Zoo
classifications were used to determine the morphology of the sample,
where morphology was assigned when volunteers agreed on the
classification at a rate of 80% or more. This resulted in the
classification of 18% early types, 34% late types, 45% intermediate
types (galaxies that did not receive at least 80% votes for early or late type), and 3% merging, where these classification follow the
morphology of Hubble's Tuning Fork (see <b>figure 1</b>). The science team believes the relatively
high number of intermediate types most likely results from the
abundance of systems in which the bulge or disk do not clearly
dominate rather than poor imaging data. </div>
<div style="margin-bottom: 0in;">
<br /></div>
<div style="margin-bottom: 0in;">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhZbcaOB2QD7k2J1oNxe246j0UWba2Q6sXKE_OcdCmT49oHVP4dXlJyfYwXpkdDFBO3uiYAYIdPxQmvhNzo1gspFsqYkFuGBztl3VpygcUO7iCtalQtoEx3xEV-f81zl9ImDa0gqYeqRi8/s1600/Screen+Shot+2014-03-14+at+4.46.19+PM.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhZbcaOB2QD7k2J1oNxe246j0UWba2Q6sXKE_OcdCmT49oHVP4dXlJyfYwXpkdDFBO3uiYAYIdPxQmvhNzo1gspFsqYkFuGBztl3VpygcUO7iCtalQtoEx3xEV-f81zl9ImDa0gqYeqRi8/s1600/Screen+Shot+2014-03-14+at+4.46.19+PM.png" height="209" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><b>Figure 1. </b>Example <i>gri</i> images ordered by Galaxy Zoo classifications. The left, center, and right columns show blue cloud, green valley, and red sequence galaxies, respectively. The top, center, and bottom rows show early-type, intermediate-type, and late-type galaxies, respectively. </td></tr>
</tbody></table>
<div style="margin-bottom: 0in;">
<br /></div>
<div style="margin-bottom: 0in;">
Though most late-type galaxies of the
sample inhabited the blue cloud and most early types were in the red
sequence, this study found that both early-type and late-type
galaxies spanned almost the entire color range, and within a given
morphological class, the green valley was nothing more than a
collection of outliers. </div>
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: right; margin-left: 1em; text-align: right;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjiKXgrwnQULTbK7StvCjhzJRCjADYM1aYy6cAzWjGWtTe0wRRueoZfZClE_z3FH4fSwW6E5JR6rDAEIRTeT5Z8r31RLq3fhzIhIkvb1z9DqFY4DQhRxs2YIw47xpWhRpIi0eubkItbdLM/s1600/Screen+Shot+2014-03-14+at+4.56.11+PM.png" imageanchor="1" style="clear: right; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjiKXgrwnQULTbK7StvCjhzJRCjADYM1aYy6cAzWjGWtTe0wRRueoZfZClE_z3FH4fSwW6E5JR6rDAEIRTeT5Z8r31RLq3fhzIhIkvb1z9DqFY4DQhRxs2YIw47xpWhRpIi0eubkItbdLM/s1600/Screen+Shot+2014-03-14+at+4.56.11+PM.png" height="297" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="font-size: 13px; text-align: center;"><b>Figure 2. </b>Reddening-corrected u-r color-mass diagram for the sample. <br />This figure shows two important findings - that both early and late type<br />galaxies span almost the entire color range, and that the green valley<br />is only defined in the all-galaxy color panel. </td></tr>
</tbody></table>
<div style="margin-bottom: 0in;">
The bimodality of galaxy colors is a result
of the superposition of the two populations; late types are mostly in
the blue cloud and decrease smoothly to the red sequence, and a few
early types reach all the way to the blue cloud. <b>Figure 2</b> shows a
stellar mass-color contoured plot after dust extinction corrections,
and indicates the position of the green valley in relation to the
blue cloud and red sequence. </div>
<div style="margin-bottom: 0in;">
<br /></div>
<div style="margin-bottom: 0in;">
<span style="font-style: normal;">Using
ultraviolet and optical photometry, star formation rates (SFRs) were
analyzed to find that early-type galaxies are quenched much more
rapidly than their late-type counterparts. Late-type galaxies were
still blue in the ultraviolet through the green valley, indicating
that they were still undergoing star formation as they were being
quenched. Transitions through the green valley were found to be
highly dependent on morphology, with early-type galaxies exhibiting
quenching on timescales as short as 250 Myr. If this process took
longer, like the 1-3 Gyr track estimated for late-type galaxies,
there would be a build-up of early-types in the green valley that are
not accounted for in observations. Perhaps early-type galaxies
transition through the green valley as fast as star formation would
allow. </span>
</div>
<div style="margin-bottom: 0in;">
</div>
<div style="margin-bottom: 0in;">
<br /></div>
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhjhOZhoRXK6TsLOrNLRPHlHBvaLEsTqzUehtimfouDeCSLgwrA9JmPeYEeNwxAFfPKB_0UxkIe07B_gkiqxDoBnezEFZlE07GlIjQ8lMIlDT-H9VzhUbm4UemyS9VR73sx7Sp-ayjoWWU/s1600/Screen+Shot+2014-03-14+at+5.56.33+PM.png" imageanchor="1" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhjhOZhoRXK6TsLOrNLRPHlHBvaLEsTqzUehtimfouDeCSLgwrA9JmPeYEeNwxAFfPKB_0UxkIe07B_gkiqxDoBnezEFZlE07GlIjQ8lMIlDT-H9VzhUbm4UemyS9VR73sx7Sp-ayjoWWU/s1600/Screen+Shot+2014-03-14+at+5.56.33+PM.png" height="306" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><b>Figure 3. </b>UV-optical dust corrected color-color diagrams of green valley<br />galaxies. Color-coded evolutionary tracks using different quenching<br /> timescales are overplotted on the green valley early- and late-type plots. <br />Emission line-selected AGN in host galaxies are marked with green<br />points. These signatures would only appear after a few megayears after<br />the occurrence of a quenching event. </td></tr>
</tbody></table>
<div style="margin-bottom: 0in;">
Investigation
of local environment, gas supply for star formation, and black hole
activity was done to see if these factors could have contributed to
the very different star formation histories of late-type and
early-type galaxies. A catalogue of galaxy halo masses and
information as to whether the green valley galaxies in question were
central or satellites in their clusters was used to investigate the
differences in galactic environments. Schawinski et al. found that
there were striking differences in environments for galaxies of both
populations traveling through the green valley. Though early types
were found in both low- and high-mass haloes, late types had a
dramatic split. Blue cloud late types were mostly in low-mass
haloes, but those in the green valley and red sequence were almost
exclusively in high-mass halos. This is a possible indication that
late-type quenching is caused by environmental processes. In
accordance with the large percentage of late types in the green
valley relative to early types, it was found that late types have
large gas reservoirs relative to early types to fuel star formation
and slow the evolution through the green valley. Lastly, the growth
of supermassive black holes was investigated to see how these
culprits of quenching may differ in early and late types. <b>Figure
3</b> indicates samples in the green valley that had Active Galactic
Nuclei (AGN) activity. Since
several hundred Myr or more must elapse between the end of star
formation in early types and the detection of an optical AGN, it is
likely that AGN are not responsible for the rapid quenching of star
formation in early types and rather an after-effect of the event that
triggered quenching. </div>
<div style="margin-bottom: 0in;">
<br /></div>
<div style="margin-bottom: 0in;">
<span style="font-style: normal;">Schawinski
et al. concluded with discussion on the evolutionary tracks related
to the end of star formation for late and early types. Morphological
classifications of SDSS images in Galaxy Zoo as well as ultraviolet
photometric analysis to probe star formation histories have led to
conclusions on how early- and late-type galaxies transition through
the green valley. <b>Figure 4 </b>and <b>figure 5</b> show cartoons of the predicted
evolutionary sequence through the green valley for early- and
late-type galaxies. </span>
</div>
<div style="margin-bottom: 0in;">
<br />
</div>
<div style="margin-bottom: 0in;">
</div>
<div style="margin-bottom: 0in;">
This
study concluded that late-type galaxies initiate their quenching
processes when they are cut off from reservoirs of cosmic gas fueling
their ongoing star formation. This can happen when the galactic halo
reaches a critical mass that prevents further accretion or if cooling
the hot halo gas becomes inefficient. Though the star formation rate
begins to decline, the stellar mass may continue to increase as the
remaining gas reservoirs are converted to stars. Slowly, the galaxy
moves out of the blue cloud and into the green valley, with certain
physical processes possibly accelerating the gas-depletion process.
Black hole accretion may appear in late types after the galaxies have
been quenched. This process occurs over several gigayears.
</div>
<div style="margin-bottom: 0in;">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-cyLfY7wxo_r3GE8tMStxfU0-rIo3ob9KqSz4-zp4CwkhREHMpBLrKq8kSQpJHs3iAE8DkLR6uozFCebXq8o6wCLjzU9O3I9KONUJQfyzrPPBC2owOQStsliOEADTYxO3WnyM2ikCH14/s1600/Screen+Shot+2014-03-14+at+6.04.16+PM.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-cyLfY7wxo_r3GE8tMStxfU0-rIo3ob9KqSz4-zp4CwkhREHMpBLrKq8kSQpJHs3iAE8DkLR6uozFCebXq8o6wCLjzU9O3I9KONUJQfyzrPPBC2owOQStsliOEADTYxO3WnyM2ikCH14/s1600/Screen+Shot+2014-03-14+at+6.04.16+PM.png" height="438" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><b>Figure 4. </b>Cartoon showing the evolution of late-type galaxies from the blue cloud, through the green valley, and into the red sequence. </td></tr>
</tbody></table>
<div class="separator" style="clear: both; text-align: center;">
</div>
<div style="margin-bottom: 0in;">
As
for early-type galaxies, quenching of star formation is triggered by
the rapid destruction of galaxy gas reservoirs, and happens too quick
to be due to gas exhaustion by star formation alone. These galaxies
immediately leave the main sequence as the SFR approaches zero and
stellar mass ceases to increase. As fast as stellar evolution
allows, these galaxies move through the green valley and into the red
sequence, typically on timescales of about 1 Gyr. Since there are
very few observed blue early types, it is thought this process is
initiated by a merging event of two late types and the morphology transforms as the
galaxy color and SFR do. After the quenching event, visible
radiation from black hole accretion can be seen, and the rapid
destruction of gas reservoirs suggests the involvement of unusually
strong stellar processes or AGN feedback.
</div>
<div style="margin-bottom: 0in;">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiA69leRCM8jvAeK413ajqJ2YXODQFlGgMIEFXzbwglh8VFQzADybG3irXfRda_S8L7YcyMxCu14TFBsgvAdbq0QAnOBtY1fzUCwpu7cedvMmkI-eRH7ImikXeLvIPwbSi_OmPMjGz8pPo/s1600/Screen+Shot+2014-03-14+at+6.04.26+PM.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiA69leRCM8jvAeK413ajqJ2YXODQFlGgMIEFXzbwglh8VFQzADybG3irXfRda_S8L7YcyMxCu14TFBsgvAdbq0QAnOBtY1fzUCwpu7cedvMmkI-eRH7ImikXeLvIPwbSi_OmPMjGz8pPo/s1600/Screen+Shot+2014-03-14+at+6.04.26+PM.png" height="420" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><b>Figure 5. </b>Cartoon showing the evolution of early-type galaxies from the blue cloud, through the green valley, and into the red sequence. </td></tr>
</tbody></table>
<div style="margin-bottom: 0in;">
<br /></div>
</div>
Anonymoushttp://www.blogger.com/profile/08361708343929797925noreply@blogger.com15tag:blogger.com,1999:blog-6566777651395931272.post-21947674897753747852013-08-15T10:12:00.000-07:002013-08-22T14:41:09.462-07:00Wong et al. Article -- Galaxy Zoo: Building the Low-mass End of the Red Sequence with Local Post-starburst Galaxies<b>Title: </b>Galaxy Zoo: building the low-mass end of the red sequence with local post-starburst galaxies<br />
<br />
<b>Authors: </b>O. I. Wong, K. Schawinski, S. Kaviraj, K. L. Masters, R. C. Nichol, C. Lintott, W. C. Keel, D. Darg, S. P. Bamford, D. Andreescu, P. Murray, M. J. Raddick, A. Szalay, D. Thomas and J. VandenBerg<br />
<br />
<b>First Author’s Institution: </b>CSIRO Astronomy & Space Science, Astronomy Department, Yale University<br />
<br />
To read the full article, please click <a href="https://vault.it.northwestern.edu/let412/GZQuench" target="_blank">here</a>.<br />
<br />
<h3>
<b>Article Summary + Additional Background Information:</b></h3>
<br />
Galaxies were once believed to be isolated and unevolving systems in our universe. In the past few decades this viewpoint has drastically changed; observations suggest that galaxies are strongly affected by gravitational interactions from the other galaxies in their nearby environment, and these interactions potentially are the main drivers of galaxy evolution. Studying collisions, tidal interactions, and their effects are exceptionally important for further probing the important processes of galaxy evolution. <br />
<br />
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: right; margin-left: 1em; text-align: right;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh2mAPslBptd4COswAybweJj6dqO54Si2N6Vcf1HgFYVxQyFDfd64WOB4U4xgjNtm6VyWHFuTMdrsv0swsryrlEe4kSgaSCawqSCkHBPgRopf68vSePAAK9xHOCiq96bsX7xg9OVwN6SxA/s536/Galaxy_color-magnitude_diagram.jpg" imageanchor="1" style="clear: right; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" height="385" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh2mAPslBptd4COswAybweJj6dqO54Si2N6Vcf1HgFYVxQyFDfd64WOB4U4xgjNtm6VyWHFuTMdrsv0swsryrlEe4kSgaSCawqSCkHBPgRopf68vSePAAK9xHOCiq96bsX7xg9OVwN6SxA/s400/Galaxy_color-magnitude_diagram.jpg" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><b>Figure 1. </b>A color-luminosity graph indicates the location of the blue cloud, green valley, and red sequence. The blue cloud is populated by star forming, spiral galaxies (late type) while the red sequence contains non-star forming, passively evolving elliptical galaxies (early type). Post-starburst galaxies transitioning from the blue cloud to the red sequence inhabit the green valley. </td></tr>
</tbody></table>
<br />
<br />
<br />
<br />
<br />
There are two basic types of galaxies recognized by Hubble’s “tuning fork” classification scheme: blue, star-forming spiral galaxies (late type) and red, quiescent elliptical galaxies (early type). Spiral galaxies tend to have younger stellar populations emitting higher-energy (bluer) light, while elliptical galaxies are littered with older stars emanating lower-energy (red) light. Through galaxy collisions, star-forming spiral galaxies in the ‘blue cloud’ are believed to develop into passively evolving elliptical galaxies in the ‘red sequence’, as illustrated in <b>Fig</b><b>ure 1</b>. During this transition galaxies occupy the sparser ‘green valley’. <br />
<br />
During galactic interactions, <a href="http://ned.ipac.caltech.edu/level5/Struck/frames.html" target="_blank">the probability of a star-star collision is on the order of 1 part in a quadrillion</a>. The dark matter halos of galaxies, which make up about 80% of the galaxy mass, do not interact other than gravitationally. However, the interstellar gas in galaxies does interact, causing a period of abnormally high star formation called a starburst. This influx of gas also fuels the supermassive black holes at the center of galaxies, generating an active galactic nuclei (AGN). The process of two galaxies colliding and merging is extremely slow by terrestrial standards, occurring over hundreds of millions to billions of years. To study these transitional galaxies, astronomers turn to the <a href="http://www.galaxyzoo.org/" target="_blank">Galaxy Zoo project</a> for information about the aftermath of galactic interactions. This provides a way to understand the evolutionary path from the blue cloud to the red valley. <br />
<br />
Galaxies that have recently quenched star formation are called post-quenched or post-starburst galaxies (PSGs). A recent study of local PSGs using the photometric and spectroscopic data from the <a href="http://www.sdss.org/" target="_blank">Sloan Digital Sky Survey</a> (SDSS) in conjunction with the results from the Galaxy Zoo project led to a better understanding of this transitional period of galaxy evolution. PSGs are also called ‘E+A’ or ‘K+A’ galaxies, because they are galaxies that have ceased current star formation but still exhibit the spectral signature of recently formed stars (i.e., stars with stellar type 'A', as shown in <b>Figure 2</b>).<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiQhyphenhyphenvKdw38aFQ1SxANd-rEvqRjGYtD9Cq-JVpKSw3yHTmeqcOq07qNyx8I_yYtOlL6CSPOdHuCfeaBFHSgcTT2B2Yx40H8B-UHfHYCGvWXJLWRoyZSfMLCjR2HlsW4MP3BSvdzeAoWmao/s961/tremontiPSBstellartype.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="432" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiQhyphenhyphenvKdw38aFQ1SxANd-rEvqRjGYtD9Cq-JVpKSw3yHTmeqcOq07qNyx8I_yYtOlL6CSPOdHuCfeaBFHSgcTT2B2Yx40H8B-UHfHYCGvWXJLWRoyZSfMLCjR2HlsW4MP3BSvdzeAoWmao/s640/tremontiPSBstellartype.jpg" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><b>Figure 2. </b>Comparison of a typical post-starburst galaxy spectrum with a normal star forming galaxy and a spectrum of a star with stellar type 'A'.</td></tr>
</tbody></table>
<br />
<br />
Using the SDSS, one of the largest and most complete samples of local PSGs was assembled, allowing volunteers of the Galaxy Zoo citizen science project to investigate the visual properties of these galaxies. The galaxies selected were in the nearby universe, with redshifts of 0.02 < z < 0.05, and with a z band magnitude of Mz < -19.5 mag. The z band was chosen for selection purposes because it is the reddest waveband provided by the SDSS and provides the closest proxy to stellar mass. This selection reduced the Malmquist bias – which is the preferential detection of intrinsically bright objects. Since the PSGs are galaxies with recently truncated star formation that still exhibit strong Balmer absorption from young stars, they were identified as having Hα emission line weaker than four times the rms level and Hδ equivalent width wider than 3 angstroms. Of the 47,573 galaxies in the selected volume 80 matched the criterion of PSGs. 12 of the PSGs selected are presented in <b>Figure 3</b>. <br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiSz56gYQ7WT2UsC32q7kfjNem-WJ18rjyYCgSjqL6nN0AzCjNUZXOdI7UkvrlkOi__SmFWSovQj-aZP5dIEoHrz0xRLZu_GfjK1Ng98FeP6OE5PyP4E9XD0sZGxzCNfoGeKoUuM2_xtBQ/s1080/SDSScolorimages2.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="204" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiSz56gYQ7WT2UsC32q7kfjNem-WJ18rjyYCgSjqL6nN0AzCjNUZXOdI7UkvrlkOi__SmFWSovQj-aZP5dIEoHrz0xRLZu_GfjK1Ng98FeP6OE5PyP4E9XD0sZGxzCNfoGeKoUuM2_xtBQ/s640/SDSScolorimages2.jpg" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><b>Figure 3. </b>This image shows the SDSS images of 12 PSGs in the sample. The left-hand panel shows four examples of early-type PSGs, the center panel intermediate-type PSGs, and the right panel late-type PSGs. </td></tr>
</tbody></table>
<br />
About 74% of the PSGs were neither early or late type galaxies, and were therefore classified as intermediate type. About 16% and 10% of the PSGs were classified as early and late types, respectively. This suggests that the PSGs in the sample are an evolutionary stepping-stone from blue, star forming spiral galaxies to red, quiescent elliptical galaxies. Quantification of merger properties from Galaxy Zoo results concluded that most of the PSG samples did not have signs of an actively merging system, though many of the samples were asymmetrical or disturbed. <br />
<br />
Additionally, using the SDSS modelMag tool, the u – r color was determined for these galaxies (where u and r are the bluest and middle band magnitudes used by SDSS, respectively). The magnitudes were corrected to take out the effects of absorption by methods used in Calzetti et al. (2000), which accounted for both warm dust (T~40-55 K) and cool dust (T~20-23 K). Most of the PSGs lay in the color range 1.8 < u - r < 2.3, which is the ‘green valley’ between the ‘blue cloud’ (late type galaxies) and the ‘red sequence’ (early type galaxies). <br />
<br />
This study also looked at the environment around the local PSGs to correlate galaxy density with evolutionary processes. The environment of the PSG samples was determined by measuring the number and proximity of galaxies around the point in space where the samples lay. Half of the PSGs resided in low-density environments, while 26 and 24 percent resided in medium- and high-density environments, respectively. <br />
<br />
Since most of the PSG sample consisted of intermediate-type morphologies, further investigation of stellar structure was required to reveal if the PSGs have intermediate-type morphologies due to past interactions or are similar in structure to the early- or late-type galaxies within the same volume. To determine this, the SDSS fracDev parameter was used. This gives the fraction of light fitted by a de Vaucouleurs profile, which describes how the surface brightness of an elliptical galaxy varies as a function of the radius from the galactic center. Using this parameter, the authors found that the structural stellar morphologies of the PSGs in the ‘green valley’ more closely resemble the morphologies of low-mass early-type galaxies, even though star formation has only recently been truncated. <br />
<br />
<a href="http://www.galaxyzooforum.org/index.php?topic=280717.0" target="_blank">Stellar mass estimates for the galaxies</a> were measured by fitting the five optical wavebands used by the SDSS to star formation history libraries created from stellar models in Maraston (1998, 2005). A majority of the PSGs in the study had stellar masses below the transition mass that separates low-mass star-forming galaxies from the high-mass passively evolving bulge-dominated galaxies. No PSGs were found with log stellar masses greater than 11.5 solar masses (i.e., greater than 10^11.5 Msun). One possible reason for this lack of high-mass PSGs is that the sample was restricted to a very local volume. These results are consistent with the idea of galaxy formation ‘downsizing’, the theory that more massive galaxies from higher density areas run through their gas quicker and evolve through the PSG phase at higher redshifts than lower mass galaxies. <b>Figure 4</b> shows the color versus stellar mass for the PSG sample. <br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgCUfoW8eSm25YOLPnGg-s17KpAOxy5F5HNAizNkqTGO2vQmSMfpLNT4YHXP1RXCvvw-RWaoxbd4O6P7pUp1jyWBpq8Pia-gbHYvrMCDQPEOf1rd61zMCgalXUZDEAxWDzvPEvSiabgkm4/s1109/colorStellarMass.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="282" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgCUfoW8eSm25YOLPnGg-s17KpAOxy5F5HNAizNkqTGO2vQmSMfpLNT4YHXP1RXCvvw-RWaoxbd4O6P7pUp1jyWBpq8Pia-gbHYvrMCDQPEOf1rd61zMCgalXUZDEAxWDzvPEvSiabgkm4/s640/colorStellarMass.jpg" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><b>Figure 4. </b>The image above shows the location of the sample PSGs on u-r color vs stellar mass graphs. The panels of the top row, from left to right, show the location of all the galaxies, early-type galaxies, intermediate-type galaxies, and late-type galaxies in the study, respectively. The bottom row of panels shows the number fraction of the PSG sample to the galaxy sample of a particular type in a given color-stellar mass bin. </td></tr>
</tbody></table>
<br />
Current models of galaxy evolution suggest that feedback from AGN could provide the means to quench and truncate the star formation history of a massive galaxy. Mergers may induce inflows of gas that fuel star formation and the central black hole, while feedback from AGNs quench star formation by reheating cold gas and expelling much of it in AGN-driven winds. This hypothesis suggests that AGN feedback may play a role in quenching star formation in PSGs. However, apart from two PSGs in this study that exhibit spectral properties of AGN called LINERs (low-ionization nuclear emission-line regions) no observations of AGN spectral signatures were found in the PSG sample. These observations coincide with the idea of 'downsizing', in which the buildup of smaller galaxies occurs at later epochs. The low-z galaxies in this sample were most likely not massive enough to host an AGN and therefore AGN feedback was not the primary quenching mechanism. For more information on AGN feedback, refer to <a href="https://www.dropbox.com/sh/uik9yxpn83yjnwb/WB1W2j6-rn" target="_blank">Schawinski et al. 2007</a>. <br />
<br />
The results of this study show that most local PSGs occupy the ‘green valley’ and are rapidly transitioning to the low-mass end of the ‘red sequence’, with duration of this transitional period on the order of 1 billion years. The structural morphology of local ‘green valley’ PSGs is very similar to that of low-mass early-type galaxies in the ‘red sequence’, even though star formation has only recently ceased. This study suggests that these galaxies changed their shape and became bulge-dominated prior to the cessation of star formation, and therefore the transition through the 'green valley' will take approximately as long as it takes for the last batch of recently-formed stars to fade. These local PSGs show that galactic interactions in recent epochs lead to the growth of the low-mass end of the 'red sequence' and agree with the idea of downsizing. <br />
<br />
Studying galaxy collisions, starburst galaxies, active galactic nuclei, and post-starburst galaxies is giving a clearer image on how galaxies evolve, and the star formation processes that occur during this transitional phase of galaxy evolution. <br />
<div>
<br /></div>
Anonymoushttp://www.blogger.com/profile/13337278557841102817noreply@blogger.com1tag:blogger.com,1999:blog-6566777651395931272.post-79369542431995366612013-08-05T16:57:00.003-07:002013-08-08T09:00:15.183-07:00Darg et al. Article -- Utilizing Galaxy Zoo to examine properties of merging galaxies<!--[if gte mso 9]><xml>
<o:DocumentProperties>
<o:Template>Normal.dotm</o:Template>
<o:Revision>0</o:Revision>
<o:TotalTime>0</o:TotalTime>
<o:Pages>1</o:Pages>
<o:Words>1302</o:Words>
<o:Characters>7422</o:Characters>
<o:Company>University of Illinois</o:Company>
<o:Lines>61</o:Lines>
<o:Paragraphs>14</o:Paragraphs>
<o:CharactersWithSpaces>9114</o:CharactersWithSpaces>
<o:Version>12.0</o:Version>
</o:DocumentProperties>
<o:OfficeDocumentSettings>
<o:AllowPNG/>
</o:OfficeDocumentSettings>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:WordDocument>
<w:Zoom>0</w:Zoom>
<w:TrackMoves>false</w:TrackMoves>
<w:TrackFormatting/>
<w:PunctuationKerning/>
<w:DrawingGridHorizontalSpacing>18 pt</w:DrawingGridHorizontalSpacing>
<w:DrawingGridVerticalSpacing>18 pt</w:DrawingGridVerticalSpacing>
<w:DisplayHorizontalDrawingGridEvery>0</w:DisplayHorizontalDrawingGridEvery>
<w:DisplayVerticalDrawingGridEvery>0</w:DisplayVerticalDrawingGridEvery>
<w:ValidateAgainstSchemas/>
<w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid>
<w:IgnoreMixedContent>false</w:IgnoreMixedContent>
<w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText>
<w:Compatibility>
<w:BreakWrappedTables/>
<w:DontGrowAutofit/>
<w:DontAutofitConstrainedTables/>
<w:DontVertAlignInTxbx/>
</w:Compatibility>
</w:WordDocument>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:LatentStyles DefLockedState="false" LatentStyleCount="276">
</w:LatentStyles>
</xml><![endif]-->
<!--[if gte mso 10]>
<style>
/* Style Definitions */
table.MsoNormalTable
{mso-style-name:"Table Normal";
mso-tstyle-rowband-size:0;
mso-tstyle-colband-size:0;
mso-style-noshow:yes;
mso-style-parent:"";
mso-padding-alt:0in 5.4pt 0in 5.4pt;
mso-para-margin-top:0in;
mso-para-margin-right:0in;
mso-para-margin-bottom:10.0pt;
mso-para-margin-left:0in;
mso-pagination:widow-orphan;
font-size:12.0pt;
font-family:"Times New Roman";
mso-ascii-font-family:Cambria;
mso-ascii-theme-font:minor-latin;
mso-fareast-font-family:"Times New Roman";
mso-fareast-theme-font:minor-fareast;
mso-hansi-font-family:Cambria;
mso-hansi-theme-font:minor-latin;}
</style>
<![endif]-->
<!--StartFragment-->
<br />
<div class="MsoNormal">
<b>Title: </b>Galaxy
Zoo: the properties of merging galaxies in the nearby Universe – local
environments, colours, masses, star formation rates, and AGN activity</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<b>Authors:</b> D. W. Darg,
S. Kaviraj, C. J. Lintott, K. Schawinski, M. Sarzi, S. Bamford, J. Silk, D.
Andreescu, P. Murray, R. C. Nichol, M. J. Raddick, A. Slosar, A. S. Szalay, D.
Thomas, and J. Vandenberg</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<b>First Author’s
Institution: </b> University of
Oxford, Department of Physics</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
To read the full article, please click <a href="https://vault.it.northwestern.edu/let412/GZQuench" target="_blank">here</a>.</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<h3>
Article Summary: </h3>
<div>
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgGOeG_rNhQFF8dt2icTPd5Da1ODUzmebOzHxDW6zsJylLfL3Do7o0ieyPAtBtcIJvP_Tvu5pB0bB-sZzsVLLeqK-pnbcDvCmJP93gSaBMOXJfogmBQAHS_6rRcjdI3cgoSnaXnGOII8eQ/s1600/antennae_hst.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgGOeG_rNhQFF8dt2icTPd5Da1ODUzmebOzHxDW6zsJylLfL3Do7o0ieyPAtBtcIJvP_Tvu5pB0bB-sZzsVLLeqK-pnbcDvCmJP93gSaBMOXJfogmBQAHS_6rRcjdI3cgoSnaXnGOII8eQ/s400/antennae_hst.jpg" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><br /></td></tr>
</tbody></table>
<div>
<br /></div>
<div class="MsoNormal">
Examining large-scale morphological properties of galaxy mergers
proved to be a trying feat until the Galaxy Zoo project was set in motion. Because of the great variety of
configurations of mergers, visually examining images of galaxies is a much
better method for identifying and classifying these specimens than using
structural parameters. Using
classifications on the Galaxy Zoo interface, one can determine how ‘merger-like’ a
Sloan Digital Sky Survey (SDSS) image appears to be based on the percentage of
volunteers that flagged the particular image as a merger. By utilizing the morphological data
from Galaxy Zoo, Darg et al. were able to delve into important properties of
merging galaxies, such as the structure of progenitor galaxies, internal properties
of interacting galaxies, time-scales of merger events, local environments of mergers, star formation
histories, and AGN activity. </div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
In this study, 3003 merging pairs were classified as well as
a redshift-matched control sample.
The galaxies lie in the relatively local universe, with redshift range
0.005 < z < 0.1. Binned
redshifts for the merger and control samples are shown in <b>figure 1</b>. Galaxies were classified both by their
morphologies (Elliptical, Spiral, Unclear but probably Elliptical, and Unclear
but probably a Spiral) and their merger stages. Mergers could either be classified as ‘separated’,
‘interacting’, or ‘approaching post-merger’. Of the 3003 samples, ~84% were classified as interacting, ~6%
as separated, and ~10% as approaching post-merger. </div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjHfeMpRxQf0oR0GlUIBjrENI2WcZbFG-IqdEZ2Cg9UD4SbIbesfxIqjEUTEBPC1p55oLgora53OWRC1MoPwhu5omU9LKjHCU8UB0M2-bweTNyxwZsJ9JQjUz4jYlHi5AZgtQ5ZSE0Cg7o/s1600/Picture+1.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="245" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjHfeMpRxQf0oR0GlUIBjrENI2WcZbFG-IqdEZ2Cg9UD4SbIbesfxIqjEUTEBPC1p55oLgora53OWRC1MoPwhu5omU9LKjHCU8UB0M2-bweTNyxwZsJ9JQjUz4jYlHi5AZgtQ5ZSE0Cg7o/s400/Picture+1.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><b>Figure 1. </b>Binned redshift distributions for the merger and control samples. </td></tr>
</tbody></table>
<br />
<div class="MsoNormal">
<br /></div>
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: right; margin-left: 1em; text-align: right;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi2Pe-WWz4pNXygpg-QF55VqwYayDqxCJqxju36G66LmYMo4WwvogHuxLKLmFcffH1d8xt-D2cX-i_DXg80-qttLFCg77E0cVYsaERHoz7Vm0yY_wcl-aR8ICOGT3iGB-hmSmRpjFmroRQ/s1600/Picture+2.png" imageanchor="1" style="clear: right; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi2Pe-WWz4pNXygpg-QF55VqwYayDqxCJqxju36G66LmYMo4WwvogHuxLKLmFcffH1d8xt-D2cX-i_DXg80-qttLFCg77E0cVYsaERHoz7Vm0yY_wcl-aR8ICOGT3iGB-hmSmRpjFmroRQ/s400/Picture+2.png" width="300" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><b>Figure 2.</b> Number density of galaxies within 2.0 Mpc <br />
of the merger and control samples. Rho symbolizes<br />
the Adaptive-Gaussian-environment parameter. White<br />
background shows galaxies in the field, dark gray shows<br />
galaxies in clusters, and light gray shows the<br />
intermediate regime. </td></tr>
</tbody></table>
<div class="MsoNormal">
Of the merging systems visually examined in this study,
there were about 3 times as many spirals than ellipticals. This is interesting given that the
ratio of spirals to ellipticals in the global galaxy population is ~1.5. One issue that Darg et al. inquired about
was the reason for this discrepancy.
Does it have to do with the environment in which these mergers take
place or differences in the internal properties of these galaxies? To parameterize the environment of
these mergers, a sophisticated measure of the number of galaxies per unit
volume called the ‘adaptive-Gaussion-environment parameter’ was used. This allowed the determination of
whether the merging galaxies and the control were located in the low-density
field, high-density clusters, or in an intermediate regime. <b>Figure 2</b> shows that both mergers and
controls peaked in a region dubbed ‘intermediate environments’. Since mergers were also found to occupy
similar if not denser environments than the control (where elliptical galaxies
are more prevalent), the role of environment in causing the high
spiral-to-elliptical ratio in mergers can be ruled out. Instead, the prevalence of spirals in
mergers likely arises from the longer time-scales of detectability for mergers
involving spirals than for mergers involving ellipticals. </div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiptaCikI8frqTmOPcdQOXM32Y1lT_lcSI11chp_odu5A3uabtR4DYaPFIu3IGNo7RXCfJAgkDEWjjaePdQGGlTRJemMxWYPUVaS9ZE6Ohh2cIusaRPkLZUITSIpsVsOCRnIrKmiBcLIcU/s1600/Picture+3.png" imageanchor="1" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiptaCikI8frqTmOPcdQOXM32Y1lT_lcSI11chp_odu5A3uabtR4DYaPFIu3IGNo7RXCfJAgkDEWjjaePdQGGlTRJemMxWYPUVaS9ZE6Ohh2cIusaRPkLZUITSIpsVsOCRnIrKmiBcLIcU/s400/Picture+3.png" width="285" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><b>Figure 3.</b> Volume-limited and non-volume limited<br />
distribution of galaxies in color space. The graphs<br />
on the left show the u-r color versus absolute<br />
magnitude. The center graphs show the frequency<br />
of ellipticals and spirals compared to the control<br />
sample (EU and SU stand for unsure but probably<br />
elliptical and unsure but probably spiral, <br />
respectively). The right graphs show the frequency<br />
of all merging samples compared to control. </td></tr>
</tbody></table>
<div class="MsoNormal">
At least one of each of the galaxies merging had spectral
data, allowing this study to do a color analysis of the samples. In accord with earlier observations,
the merging galaxies had a larger spread of colors than the control sample,
supporting the notion that ‘irregular’ morphologies have a greater spread in
color than ‘regular’ ones. A
volume limited (where only galaxies with M<sub>r</sub> < -20.55 were used)
and a non-volume limited color-magnitude diagram for the merger and control
samples can be seen in <b>figure 3</b>. A
clear bimodality between the elliptical and spiral regimes can be seen in the
binned color plots. <b>Figure 4</b> shows the mass-distributions of galaxies in both
merger and control samples. Across
almost all environments, the spiral-galaxy stellar mass distributions appear to
be the same in the mergers as in the control sample. Ellipticals mergers on the other hand appear to be slightly
more massive than their control counterparts. When morphologies are not looked at, a very similar mass
distribution for merger and control samples is attained. The fact that mergers favor spirals
(which are generally less massive) <i>yet</i>
have an overall distribution just as massive as the control sample may indicate
that galaxies involved in mergers really are more massive. </div>
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: right; margin-left: 1em; text-align: right;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh6uOsy6ZkOD7pA9p0sBxtHfuhVmboOzn2ySRZkcPJceswwbwB6-lLLxY6EGAWhQJuImuRftehetqk9AGu0i1OTUN59FU4RAD5R1U7vEo9W66mtTwDnLTlJJIHx_5Td-UiZ5kp1Nb-fYZc/s1600/Picture+4.png" imageanchor="1" style="clear: right; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh6uOsy6ZkOD7pA9p0sBxtHfuhVmboOzn2ySRZkcPJceswwbwB6-lLLxY6EGAWhQJuImuRftehetqk9AGu0i1OTUN59FU4RAD5R1U7vEo9W66mtTwDnLTlJJIHx_5Td-UiZ5kp1Nb-fYZc/s400/Picture+4.png" width="293" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><b>Figure 4.</b> Mass distributions for galaxies in all<br />
environments (top row), galaxies in the field (second<br />
row), galaxies in intermediate regimes (third row) and<br />
galaxies in dense clusters (bottom). </td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<b><br /></b>
<b><br /></b>
<b><br /></b>
<b><br /></b>
<b>Figure 5</b> shows the entire sample of
merger-pairs in a mass-color-morphology graph. Both color and morphology of the galaxies scale strongly
with mass. An interesting find is that there is a near absence of ellipticals with masses below 3 x 10<sup>10</sup>
solar masses, raising the question as to what happens to two low-mass spiral
galaxies when they merge. This may
be due to low-mass galaxies retaining a sufficient amount of gas to
reform a disc after a major merger event (gas content along with conservation
of angular momentum is what leads to a flattened-out disc shape in
galaxies). More massive galaxies
may be prone to more catastrophic angular momentum loss during a merger event,
and the remaining gas supplies may plunge into the central core and transfer
the angular momentum required for disc morphology into the stellar dispersion
of the remnant bulge. </div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhvz_BIuyG4Vn9WG5xHx9-8sie4bKxAwpE573z-CqG7jGS-XD97tRUFskFdoFayu4M-Nk1cPkrX4vHHal_6PfoFE2DYmahO_eNxsZIbDFy4w-gX1EfUNeocszs_uk_TUEIhnWxGK7_eI_w/s1600/Picture+5.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhvz_BIuyG4Vn9WG5xHx9-8sie4bKxAwpE573z-CqG7jGS-XD97tRUFskFdoFayu4M-Nk1cPkrX4vHHal_6PfoFE2DYmahO_eNxsZIbDFy4w-gX1EfUNeocszs_uk_TUEIhnWxGK7_eI_w/s640/Picture+5.png" width="510" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><b>Figure 5.</b> A mass-color-morphology diagram. The top three plots show the average stellar mass for (from left to right) spiral-spiral mergers, spiral-elliptical mergers, and elliptical-elliptical mergers. The main plot shows the u-r color of each sample, the stellar mass of each galaxy (with the more massive galaxy's value on the x-axis) and the type of galaxies that are taking part in the merger event (given by a circle, asterisk, or triangle data point). </td></tr>
</tbody></table>
<div class="MsoNormal">
Due to the importance of feedback mechanisms to a gas
retention model, the study next examined active galactic nuclei (AGN) and star
formation signatures of the mergers.
By examining the measured fluxes of emission lines in the samples, this
study was able to determine the most likely sources of these emissions and
separate their galaxies into 4 categories: star-forming, mixed (both star formation
and AGN activity), AGN (either Seyfert nuclei or LINERs), and quiescent (or
‘weak emission-line’). <b>Figure 6</b>
shows the locations of these four types of mergers in mass-color space. In this plot, galaxies characterized by
star-formation occupied the low-mass region, AGN occupied the intermediate-mass
region, and quiescent types occupied the high-mass region. This suggests that the fuel supply of
high-mass galaxies has been exhausted (as to not fuel star formation or AGN
activity) and low-mass galaxies may have insufficient mass to power AGN. Alternatively, AGN signatures in low-mass galaxies may also be obscured by high gas content and high star formation rates (SFRs). By
comparing spectral signatures to a control sample, the study determined that
mergers significantly enhance SFRs in spiral galaxies only, whereas
ellipticals live up to being ‘red and dead’ and their SFRs not as affected by
major mergers. Using H-alpha
emission strength, estimations of the SFRs (of galaxies that fell in the
star-forming category) were measured to be ~5.2 solar masses per year, which
was about twice the value of a control sample of non-merging star-forming
galaxies. The highest SFR of the
merging galaxies was ~ 95 solar masses per year. </div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh7sJwGegLTi8p1_cSqzbSeqY0bDh4aUGCwVmFOT3LaLdI-Hi5NTaOI4axS2Olyb28hgjkg87uWxtK9505FyyT9FVstJxsHd5l4OXqO07tIlZT5oJpOnutI1A2O_Wjsp9KmjkYFO1FvWTo/s1600/Picture+6.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="375" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh7sJwGegLTi8p1_cSqzbSeqY0bDh4aUGCwVmFOT3LaLdI-Hi5NTaOI4axS2Olyb28hgjkg87uWxtK9505FyyT9FVstJxsHd5l4OXqO07tIlZT5oJpOnutI1A2O_Wjsp9KmjkYFO1FvWTo/s400/Picture+6.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><b>Figure 6.</b> Color-stellar mass relation for galaxies of differing spectral types. Each plot highlights the samples that fall into each respective category. </td></tr>
</tbody></table>
<div class="MsoNormal">
The use of galaxy zoo morphology classifications allowed
this study to analyze the effects of mergers on different types of
galaxies. By estimating the
environment around mergers, the prevalence of spiral galaxies in merger
events was found to not be due to the density of the environments in which mergers occur. Therefore, internal properties of
galaxies may be the reason for the high number of spirals in mergers;
spirals have large gas reservoirs that may result in longer time-scales of
merger events, whereas when two elliptical galaxies merge one would expect them to produce comparatively faint tidal tails and little star formation, thus making them harder to detect. Since
detectability of mergers relates to their timescales and timescales relate to
internal properties of galaxies, addressing the colors, stellar masses, and spectral emission of the samples is of importance.
This study found that colors of merging galaxies scale strongly with
mass and morphology, and are spread over a larger area than control galaxies. Ellipticals are rare below a mass of ~
3 x 10<sup>10</sup> solar masses, which may be due to low-mass spiral mergers
surviving the event and having enough gas to reform their disc. Moving to the feedback mechanisms of
the merging samples, Darg et al. found that mergers induce intense
star-formation <i>only</i> when they involve
spiral galaxies, and AGN activity was not present in low-mass mergers. In star-forming mergers, the SFRs were
~2 times greater than that of a control sample of star-forming galaxies. This study also found that specific
SFRs (star-formation rates per unit stellar mass), scale down with stellar
mass, possibly due to gas supplies being continually drained as galaxies
accumulate mass. The
results generally imply that mergers affect spirals much more than ellipticals,
which in turn affects the time-scales of detectability for merger events. </div>
<!--EndFragment-->Anonymoushttp://www.blogger.com/profile/08361708343929797925noreply@blogger.com0tag:blogger.com,1999:blog-6566777651395931272.post-36682629586076206252013-06-30T22:00:00.000-07:002013-08-08T09:00:42.646-07:00Kaviraj et al. Article -- Ultraviolet Analysis of Post-Starburst Galaxies and Quenching Mechanisms<!--[if !mso]>
<style>
v\:* {behavior:url(#default#VML);}
o\:* {behavior:url(#default#VML);}
w\:* {behavior:url(#default#VML);}
.shape {behavior:url(#default#VML);}
</style>
<![endif]--><!--[if gte mso 9]><xml>
<o:DocumentProperties>
<o:Template>Normal.dotm</o:Template>
<o:Revision>0</o:Revision>
<o:TotalTime>0</o:TotalTime>
<o:Pages>1</o:Pages>
<o:Words>1051</o:Words>
<o:Characters>5992</o:Characters>
<o:Company>University of Illinois</o:Company>
<o:Lines>49</o:Lines>
<o:Paragraphs>11</o:Paragraphs>
<o:CharactersWithSpaces>7358</o:CharactersWithSpaces>
<o:Version>12.0</o:Version>
</o:DocumentProperties>
<o:OfficeDocumentSettings>
<o:AllowPNG/>
</o:OfficeDocumentSettings>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:WordDocument>
<w:Zoom>0</w:Zoom>
<w:TrackMoves>false</w:TrackMoves>
<w:TrackFormatting/>
<w:PunctuationKerning/>
<w:DrawingGridHorizontalSpacing>18 pt</w:DrawingGridHorizontalSpacing>
<w:DrawingGridVerticalSpacing>18 pt</w:DrawingGridVerticalSpacing>
<w:DisplayHorizontalDrawingGridEvery>0</w:DisplayHorizontalDrawingGridEvery>
<w:DisplayVerticalDrawingGridEvery>0</w:DisplayVerticalDrawingGridEvery>
<w:ValidateAgainstSchemas/>
<w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid>
<w:IgnoreMixedContent>false</w:IgnoreMixedContent>
<w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText>
<w:Compatibility>
<w:BreakWrappedTables/>
<w:DontGrowAutofit/>
<w:DontAutofitConstrainedTables/>
<w:DontVertAlignInTxbx/>
</w:Compatibility>
</w:WordDocument>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:LatentStyles DefLockedState="false" LatentStyleCount="276">
</w:LatentStyles>
</xml><![endif]--><!--[if !supportAnnotations]-->
<script></script>
<!--[endif]-->
<!--[if gte mso 10]>
<style>
/* Style Definitions */
table.MsoNormalTable
{mso-style-name:"Table Normal";
mso-tstyle-rowband-size:0;
mso-tstyle-colband-size:0;
mso-style-noshow:yes;
mso-style-parent:"";
mso-padding-alt:0in 5.4pt 0in 5.4pt;
mso-para-margin-top:0in;
mso-para-margin-right:0in;
mso-para-margin-bottom:10.0pt;
mso-para-margin-left:0in;
mso-pagination:widow-orphan;
font-size:12.0pt;
font-family:"Times New Roman";
mso-ascii-font-family:Cambria;
mso-ascii-theme-font:minor-latin;
mso-fareast-font-family:"Times New Roman";
mso-fareast-theme-font:minor-fareast;
mso-hansi-font-family:Cambria;
mso-hansi-theme-font:minor-latin;}
</style>
<![endif]--><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="2050"/>
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1"/>
</o:shapelayout></xml><![endif]-->
<!--StartFragment-->
<br />
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in; text-align: center;">
<div style="text-align: left;">
<b>Title</b>: UV properties of E+A galaxies:
constraints on feedback-driven quenching of star formation</div>
</div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<o:p></o:p></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<br /></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in; tab-stops: 238.5pt;">
<b>Authors</b>: S. Kaviraj, L. A.
Kirkby, J. Silk and M. Sarzi<o:p></o:p></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in; tab-stops: 238.5pt;">
<b><br /></b>
<b>Authors’ Institutions: </b>University of
Oxford Department of Physics and University of Hertfordshire Centre for
Astrophysics Research</div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<o:p></o:p></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<br />
To read the full article, please click <a href="https://vault.it.northwestern.edu/let412/GZQuench" target="_blank">here</a>. </div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<br />
<br /></div>
<h3>
<o:p>Article Summary: </o:p></h3>
<div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgZMudtqU45HArFDjH4z5LbBdiXSAmmIL_xq_-efVwg9TpoF-gTys-6ne4CZlse5Ygrk_AG-EIUCnMalsrxVaGjsouUpMS7EQYF37aYYUMasDxOSz2HmelawzRw7kRTfy9PHSv0ApQAKcQ/s1130/glx2012-02f_img01.jpeg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgZMudtqU45HArFDjH4z5LbBdiXSAmmIL_xq_-efVwg9TpoF-gTys-6ne4CZlse5Ygrk_AG-EIUCnMalsrxVaGjsouUpMS7EQYF37aYYUMasDxOSz2HmelawzRw7kRTfy9PHSv0ApQAKcQ/s400/glx2012-02f_img01.jpeg" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><b>A</b>n image of galaxy NGC 3801 combining light from across the spectrum, ranging from ultraviolet to radio. NASA's GALEX and other instruments caught this galaxy in the act of quenching its cold, gaseous fuel for new stars - possibly marking the transition from a star-forming spiral galaxy to a quiescent elliptical galaxy. According to theory, star formation will soon be quenched by the shock waves from two powerful jets shooting our of NGC 3801's central supermassive black hole, as seen in the radio emission colored green. Image courtesy of NASA/JPL-Caltech. </td></tr>
</tbody></table>
<o:p><br /></o:p>
<o:p><br /></o:p></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in; text-indent: .5in;">
The study of Post-Starburst Galaxies (PSGs) and the mechanisms that quenched
their star formation provides key insights into understanding the processes
that shape galaxy evolution. PSGs
offer a look at a valuable evolutionary link between gas-rich star-forming
galaxies and gas-poor quiescent galaxies.
A study by Kaviraj et al. in 2007 carried out the first large-scale examination
of PSGs with ultraviolet (UV) photometry.
Due to the sensitivity of the UV to young stars, this study was
accurately able to reconstruct the star formation histories of 38 PSGs in the
nearby Universe by combining optical and UV data from the Sloan Digital Sky Survey
(SDSS) and Galaxy Evolution Explorer (GALEX) surveys. <o:p></o:p></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in; text-indent: .5in;">
<br /></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in; text-indent: .5in;">
PSGs,
also known as ‘E+A’ Galaxies, show strong <a href="http://dept.astro.lsa.umich.edu/~cowley/balmers.html/" target="_blank">Balmer absorption lines </a>that are
characteristic of recent star formation but lack the <a href="http://ned.ipac.caltech.edu/level5/Sept02/Kennicutt/Kenn2_4.html" target="_blank">forbidden [OII]</a> and H-alpha emission that are present
during ongoing star formation.
This indicates that these galaxies have recently had a strong episode of
star formation that was abruptly quenched. Understanding the processes that ‘quench’ these galaxies is
an important step to understanding this transitional period of galaxy
evolution. <o:p></o:p></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in; text-indent: .5in;">
<br /></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in; text-indent: .5in;">
At intermediate redshifts (z ~ 0.5), PSGs were
found to be primarily in clusters of galaxies, as opposed to in smaller groups
or in the field. For this reason,
these galaxies were believed to result from cluster-specific mechanisms such as
<a href="http://astrobites.org/2012/08/28/mixing-up-gas-in-the-wake-of-a-strangled-satellite/" target="_blank">galaxy harassment or ram-pressure stripping</a> (the stripping of galactic gas as galaxies
travel through the cluster).
However, local observations indicate that PSGs are much more common in
the field. This indicates that
other channels likely exist in the production of PSGs. Many PSGs exhibit morphological
disturbances, which may mean that their evolution is linked, at least
partially, to mergers and interactions.
Simulations support this hypothesis, indicating that gas-rich mergers
are capable of triggering strong star formation episodes. <o:p></o:p></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in; text-indent: .5in;">
<br /></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in; text-indent: .5in;">
The
criteria used in the selection of this study’s PSG sample were similar to
earlier studies: H-delta (EW)
> <complete id="goog_215141143">+</complete>5.0 Å, H-alpha (EW)
> -3.0 Å, and [OII] (EW) > -2.5 Å, where a positive or negative sign
denotes absorption or emission lines, respectively, and EW stands for <a href="http://astronomy.swin.edu.au/cosmos/E/Equivalent+Width" target="_blank">equivalent width</a>. To ensure accuracy, the sample was restricted to the redshift
range 0 < z < 0.2, a signal-to-noise ratio greater than 10, and galaxies
with evidence of an Active Galactic Nuclei (AGN) were removed. This was because
the scattered light from the AGN could contaminate the UV continuum. <o:p></o:p>The authors also checked the morphologies of the sample using the SDSS fracDev tool. They found that they have spheroidal morphologies, which provides support for the idea that PSGs are precursors of early-type galaxies.</div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in; text-indent: .5in;">
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgP02ZlzhIFozerTtOvbO45RboXtMU-zh_TpeZRLdlyKL2gIWMfo3DrEAbWbcPteX0Q_9APDnUKDgfXWtvb2x2ZYKApLPlLrOfzEQ-aSDyadAm1IhGxO-NCbWFT5EC_p_7KO873DWQjHQQ/s303/color+space.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="286" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgP02ZlzhIFozerTtOvbO45RboXtMU-zh_TpeZRLdlyKL2gIWMfo3DrEAbWbcPteX0Q_9APDnUKDgfXWtvb2x2ZYKApLPlLrOfzEQ-aSDyadAm1IhGxO-NCbWFT5EC_p_7KO873DWQjHQQ/s320/color+space.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><!--[if gte mso 9]><xml>
<o:DocumentProperties>
<o:Template>Normal.dotm</o:Template>
<o:Revision>0</o:Revision>
<o:TotalTime>0</o:TotalTime>
<o:Pages>1</o:Pages>
<o:Words>29</o:Words>
<o:Characters>166</o:Characters>
<o:Company>University of Illinois</o:Company>
<o:Lines>1</o:Lines>
<o:Paragraphs>1</o:Paragraphs>
<o:CharactersWithSpaces>203</o:CharactersWithSpaces>
<o:Version>12.0</o:Version>
</o:DocumentProperties>
<o:OfficeDocumentSettings>
<o:AllowPNG/>
</o:OfficeDocumentSettings>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:WordDocument>
<w:Zoom>0</w:Zoom>
<w:TrackMoves>false</w:TrackMoves>
<w:TrackFormatting/>
<w:PunctuationKerning/>
<w:DrawingGridHorizontalSpacing>18 pt</w:DrawingGridHorizontalSpacing>
<w:DrawingGridVerticalSpacing>18 pt</w:DrawingGridVerticalSpacing>
<w:DisplayHorizontalDrawingGridEvery>0</w:DisplayHorizontalDrawingGridEvery>
<w:DisplayVerticalDrawingGridEvery>0</w:DisplayVerticalDrawingGridEvery>
<w:ValidateAgainstSchemas/>
<w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid>
<w:IgnoreMixedContent>false</w:IgnoreMixedContent>
<w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText>
<w:Compatibility>
<w:BreakWrappedTables/>
<w:DontGrowAutofit/>
<w:DontAutofitConstrainedTables/>
<w:DontVertAlignInTxbx/>
</w:Compatibility>
</w:WordDocument>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:LatentStyles DefLockedState="false" LatentStyleCount="276">
</w:LatentStyles>
</xml><![endif]-->
<!--[if gte mso 10]>
<style>
/* Style Definitions */
table.MsoNormalTable
{mso-style-name:"Table Normal";
mso-tstyle-rowband-size:0;
mso-tstyle-colband-size:0;
mso-style-noshow:yes;
mso-style-parent:"";
mso-padding-alt:0in 5.4pt 0in 5.4pt;
mso-para-margin-top:0in;
mso-para-margin-right:0in;
mso-para-margin-bottom:10.0pt;
mso-para-margin-left:0in;
mso-pagination:widow-orphan;
font-size:12.0pt;
font-family:"Times New Roman";
mso-ascii-font-family:Cambria;
mso-ascii-theme-font:minor-latin;
mso-fareast-font-family:"Times New Roman";
mso-fareast-theme-font:minor-fareast;
mso-hansi-font-family:Cambria;
mso-hansi-theme-font:minor-latin;}
</style>
<![endif]-->
<!--StartFragment-->
<br />
<div class="MsoCaption">
<b>Figure <!--[if supportFields]><span style='mso-element:
field-begin'></span><span style="mso-spacerun: yes"> </span>SEQ Figure \*
ARABIC <span style='mso-element:field-separator'></span><![endif]-->1</b><!--[if supportFields]><span style='mso-element:
field-end'></span><![endif]-->. Position of E+A galaxies used in the study
(filled blue circles) compared to a sample of early-type galaxies from SDSS DR5
in (NUV – r) versus (g – r) color space. <o:p></o:p></div>
<!--EndFragment--></td></tr>
</tbody></table>
<br />
<br /></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in; text-indent: .5in;">
<div class="separator" style="clear: both; text-align: center;">
</div>
<br />
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in; text-indent: .5in;">
The seven photometric filters used were the five SDSS bands (u, g, r, i, z) and the two GALEX filters in the far-ultraviolet (FUV) and near-ultraviolet (NUV). <b>Figure 1</b> shows the position of the PSG sample in (NUV – r) versus (g – r) color space, compared to a sample of early-type galaxies.<br />
<br />
<b>Figure 2</b> shows the PSGs approximate ages, mass fractions (amount of stellar mass formed during the starburst compared to the mass of the galaxy), time-scales, and star formation rates (SFRs). They derive the SFR by dividing the stellar mass formed during the starburst by the estimated time-scale of the starburst. While low-luminosity PSGs have implied SFRs less than 50 solar masses per year, high-luminosity PSGs exhibit SFRs greater than 300 and even as high as 2000 solar masses per year. These SFRs are comparable to those found in Luminous Infrared Galaxies (LIRGs) and Ultra-Luminous Infrared Galaxies (ULIRGs) at low redshifts, indicating that massive LIRGs could potentially be the progenitors of massive PSGs. </div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in; text-indent: .5in;">
</div>
<br />
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj3YljU7ABxaMVGw2BkbnXddHWK6KJFAPntc1clcW8W1BtqYPzLeCRjH0X1wQU4bPOcQlhbW6oBtYYRraK3tEA6p1ONdmYqj0SRtbYqUsawKJL4GxnXNpHuHNd9VrQEqKfEUUnj7z88xiY/s426/figure+2.jpg" imageanchor="1" style="clear: right; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj3YljU7ABxaMVGw2BkbnXddHWK6KJFAPntc1clcW8W1BtqYPzLeCRjH0X1wQU4bPOcQlhbW6oBtYYRraK3tEA6p1ONdmYqj0SRtbYqUsawKJL4GxnXNpHuHNd9VrQEqKfEUUnj7z88xiY/s640/figure+2.jpg" width="352" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><!--[if gte mso 9]><xml>
<o:DocumentProperties>
<o:Template>Normal.dotm</o:Template>
<o:Revision>0</o:Revision>
<o:TotalTime>0</o:TotalTime>
<o:Pages>1</o:Pages>
<o:Words>35</o:Words>
<o:Characters>200</o:Characters>
<o:Company>University of Illinois</o:Company>
<o:Lines>1</o:Lines>
<o:Paragraphs>1</o:Paragraphs>
<o:CharactersWithSpaces>245</o:CharactersWithSpaces>
<o:Version>12.0</o:Version>
</o:DocumentProperties>
<o:OfficeDocumentSettings>
<o:AllowPNG/>
</o:OfficeDocumentSettings>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:WordDocument>
<w:Zoom>0</w:Zoom>
<w:TrackMoves>false</w:TrackMoves>
<w:TrackFormatting/>
<w:PunctuationKerning/>
<w:DrawingGridHorizontalSpacing>18 pt</w:DrawingGridHorizontalSpacing>
<w:DrawingGridVerticalSpacing>18 pt</w:DrawingGridVerticalSpacing>
<w:DisplayHorizontalDrawingGridEvery>0</w:DisplayHorizontalDrawingGridEvery>
<w:DisplayVerticalDrawingGridEvery>0</w:DisplayVerticalDrawingGridEvery>
<w:ValidateAgainstSchemas/>
<w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid>
<w:IgnoreMixedContent>false</w:IgnoreMixedContent>
<w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText>
<w:Compatibility>
<w:BreakWrappedTables/>
<w:DontGrowAutofit/>
<w:DontAutofitConstrainedTables/>
<w:DontVertAlignInTxbx/>
</w:Compatibility>
</w:WordDocument>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:LatentStyles DefLockedState="false" LatentStyleCount="276">
</w:LatentStyles>
</xml><![endif]-->
<!--[if gte mso 10]>
<style>
/* Style Definitions */
table.MsoNormalTable
{mso-style-name:"Table Normal";
mso-tstyle-rowband-size:0;
mso-tstyle-colband-size:0;
mso-style-noshow:yes;
mso-style-parent:"";
mso-padding-alt:0in 5.4pt 0in 5.4pt;
mso-para-margin-top:0in;
mso-para-margin-right:0in;
mso-para-margin-bottom:10.0pt;
mso-para-margin-left:0in;
mso-pagination:widow-orphan;
font-size:12.0pt;
font-family:"Times New Roman";
mso-ascii-font-family:Cambria;
mso-ascii-theme-font:minor-latin;
mso-fareast-font-family:"Times New Roman";
mso-fareast-theme-font:minor-fareast;
mso-hansi-font-family:Cambria;
mso-hansi-theme-font:minor-latin;}
</style>
<![endif]-->
<!--StartFragment-->
<br />
<div class="MsoCaption">
<b>Figure <!--[if supportFields]><span style='mso-element:
field-begin'></span><span style="mso-spacerun: yes"> </span>SEQ Figure \*
ARABIC <span style='mso-element:field-separator'></span><![endif]-->2<!--[if supportFields]><span style='mso-element:
field-end'></span><![endif]-->.</b> The top plot shows the age of the burst versus
the mass fraction. The middle plot
shows the binned timescale of the starburst. The lower plot shows the implied star formation rate versus
z-band magnitude.</div>
</td></tr>
</tbody></table>
<br />
One
of the most important aspects of starburst galaxies is the quenching mechanisms
that truncate their bursts. PSGs
experience ‘negative feedback’ that causes the star formation rate to slow down. In this study it was found that for
galaxies below a mass of 10<sup>10</sup> solar masses, the quenching efficiency decreased with an increasing galactic mass. However, for galaxies with masses greater than ~10<sup>10</sup>
solar masses, this trend was reversed; quenching efficiency increased with an
increasing galactic mass. <b>Figure 3</b>
shows the relationship between galaxy mass and quenching efficiency, with a
clear change at ~10<sup>10</sup> stellar mass. This observation suggests that there are two primary sources
for negative feedback: supernovae and AGN. In the absence of AGN, supernovae would be the primary
source of negative feedback. As
galaxies become more massive, the depth of the potential well increases, making
it more difficult for supernovae to eject gas from the system. However, for galaxies greater than ~10<sup>10</sup>
solar masses, AGN begin to appear and become the dominant source of negative
feedback. Since the mass of the
black hole scales with the central velocity dispersion, it is expected that AGN
feedback will become more effective as the galaxy mass increases. Because galaxies with ongoing AGN
activity were excluded from the sample, it is plausible that AGN feedback
processes simultaneously quench both star formation and AGN activity. Through quantitative analysis, Kaviraj
et al. were able to support these qualitative predictions. </div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<o:p></o:p></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhND6uy2esv-Sh28oaqHZVhTcBenMYPl62nKLBRa9NL3tf7FEo6c_H7uvYVwP6hufD4_mJDbjrXfgAGxQCfLAyHbiTJmr7uscfmYES6fdrw-Hu-faSwVtdQizmVm8hZwRMEbq6hfEIxF8M/s368/figure+3.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="410" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhND6uy2esv-Sh28oaqHZVhTcBenMYPl62nKLBRa9NL3tf7FEo6c_H7uvYVwP6hufD4_mJDbjrXfgAGxQCfLAyHbiTJmr7uscfmYES6fdrw-Hu-faSwVtdQizmVm8hZwRMEbq6hfEIxF8M/s640/figure+3.jpg" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><!--[if gte mso 9]><xml>
<o:DocumentProperties>
<o:Template>Normal.dotm</o:Template>
<o:Revision>0</o:Revision>
<o:TotalTime>0</o:TotalTime>
<o:Pages>1</o:Pages>
<o:Words>68</o:Words>
<o:Characters>390</o:Characters>
<o:Company>University of Illinois</o:Company>
<o:Lines>3</o:Lines>
<o:Paragraphs>1</o:Paragraphs>
<o:CharactersWithSpaces>478</o:CharactersWithSpaces>
<o:Version>12.0</o:Version>
</o:DocumentProperties>
<o:OfficeDocumentSettings>
<o:AllowPNG/>
</o:OfficeDocumentSettings>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:WordDocument>
<w:Zoom>0</w:Zoom>
<w:TrackMoves>false</w:TrackMoves>
<w:TrackFormatting/>
<w:PunctuationKerning/>
<w:DrawingGridHorizontalSpacing>18 pt</w:DrawingGridHorizontalSpacing>
<w:DrawingGridVerticalSpacing>18 pt</w:DrawingGridVerticalSpacing>
<w:DisplayHorizontalDrawingGridEvery>0</w:DisplayHorizontalDrawingGridEvery>
<w:DisplayVerticalDrawingGridEvery>0</w:DisplayVerticalDrawingGridEvery>
<w:ValidateAgainstSchemas/>
<w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid>
<w:IgnoreMixedContent>false</w:IgnoreMixedContent>
<w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText>
<w:Compatibility>
<w:BreakWrappedTables/>
<w:DontGrowAutofit/>
<w:DontAutofitConstrainedTables/>
<w:DontVertAlignInTxbx/>
</w:Compatibility>
</w:WordDocument>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:LatentStyles DefLockedState="false" LatentStyleCount="276">
</w:LatentStyles>
</xml><![endif]-->
<!--[if gte mso 10]>
<style>
/* Style Definitions */
table.MsoNormalTable
{mso-style-name:"Table Normal";
mso-tstyle-rowband-size:0;
mso-tstyle-colband-size:0;
mso-style-noshow:yes;
mso-style-parent:"";
mso-padding-alt:0in 5.4pt 0in 5.4pt;
mso-para-margin-top:0in;
mso-para-margin-right:0in;
mso-para-margin-bottom:10.0pt;
mso-para-margin-left:0in;
mso-pagination:widow-orphan;
font-size:12.0pt;
font-family:"Times New Roman";
mso-ascii-font-family:Cambria;
mso-ascii-theme-font:minor-latin;
mso-fareast-font-family:"Times New Roman";
mso-fareast-theme-font:minor-fareast;
mso-hansi-font-family:Cambria;
mso-hansi-theme-font:minor-latin;}
</style>
<![endif]-->
<!--StartFragment-->
<br />
<div class="MsoCaption">
<b>Figure <!--[if supportFields]><span style='mso-element:
field-begin'></span><span style="mso-spacerun: yes"> </span>SEQ Figure \*
ARABIC <span style='mso-element:field-separator'></span><![endif]-->3</b><!--[if supportFields]><span style='mso-element:
field-end'></span><![endif]-->. A log-log plot of galaxy mass vs time-scale
ratio. The time-scale ratio is the
ratio of the time-scale of the burst to the dynamical time-scale of the galaxy,
which describes the 'natural' time-scale over which processes such as star
formation would take place if left unhindered. Note that time-scale ratio and quenching efficiency are <i>inversely correlated</i>, so an <i>decreasing</i> slope is analogous to a <i>increasing</i> quenching efficiency. <o:p></o:p></div>
<!--EndFragment--></td></tr>
</tbody></table>
<br /></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
One
last investigation in this study was to probe the migration time from gas-rich
star-forming galaxies to gas-poor quiescent galaxies, also known as moving from
the ‘blue cloud’ to the ‘red sequence’ (see Figure 1 in the Wong et al. article
summary). Migration times were
estimated by ‘ageing’ the best-fitting star formation model of each PSG. Most galaxies complete their migration
time within 2 Gyr, with a median migration time of ~1.5 Gyr. <b>Figure 4</b> presents the migration tracks
of PSGs in color-color and color-magnitude space. </div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiSByY8l7FslKRi-kbDsBDJAPfe4v1BM1hT3SkA1XzZgpaEsThEGLOZGv0oKT3WRR8Vmtzpnj1aUMfG41tY3AMWYh43q48UGvIjgVWI-qRJ82xJOWVooG3N3wstMBu7DK9NMyKUQTyeUl0/s390/figure+4.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiSByY8l7FslKRi-kbDsBDJAPfe4v1BM1hT3SkA1XzZgpaEsThEGLOZGv0oKT3WRR8Vmtzpnj1aUMfG41tY3AMWYh43q48UGvIjgVWI-qRJ82xJOWVooG3N3wstMBu7DK9NMyKUQTyeUl0/s640/figure+4.jpg" width="441" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><!--[if gte mso 9]><xml>
<o:DocumentProperties>
<o:Template>Normal.dotm</o:Template>
<o:Revision>0</o:Revision>
<o:TotalTime>0</o:TotalTime>
<o:Pages>1</o:Pages>
<o:Words>68</o:Words>
<o:Characters>390</o:Characters>
<o:Company>University of Illinois</o:Company>
<o:Lines>3</o:Lines>
<o:Paragraphs>1</o:Paragraphs>
<o:CharactersWithSpaces>478</o:CharactersWithSpaces>
<o:Version>12.0</o:Version>
</o:DocumentProperties>
<o:OfficeDocumentSettings>
<o:AllowPNG/>
</o:OfficeDocumentSettings>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:WordDocument>
<w:Zoom>0</w:Zoom>
<w:TrackMoves>false</w:TrackMoves>
<w:TrackFormatting/>
<w:PunctuationKerning/>
<w:DrawingGridHorizontalSpacing>18 pt</w:DrawingGridHorizontalSpacing>
<w:DrawingGridVerticalSpacing>18 pt</w:DrawingGridVerticalSpacing>
<w:DisplayHorizontalDrawingGridEvery>0</w:DisplayHorizontalDrawingGridEvery>
<w:DisplayVerticalDrawingGridEvery>0</w:DisplayVerticalDrawingGridEvery>
<w:ValidateAgainstSchemas/>
<w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid>
<w:IgnoreMixedContent>false</w:IgnoreMixedContent>
<w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText>
<w:Compatibility>
<w:BreakWrappedTables/>
<w:DontGrowAutofit/>
<w:DontAutofitConstrainedTables/>
<w:DontVertAlignInTxbx/>
</w:Compatibility>
</w:WordDocument>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:LatentStyles DefLockedState="false" LatentStyleCount="276">
</w:LatentStyles>
</xml><![endif]-->
<!--[if gte mso 10]>
<style>
/* Style Definitions */
table.MsoNormalTable
{mso-style-name:"Table Normal";
mso-tstyle-rowband-size:0;
mso-tstyle-colband-size:0;
mso-style-noshow:yes;
mso-style-parent:"";
mso-padding-alt:0in 5.4pt 0in 5.4pt;
mso-para-margin-top:0in;
mso-para-margin-right:0in;
mso-para-margin-bottom:10.0pt;
mso-para-margin-left:0in;
mso-pagination:widow-orphan;
font-size:12.0pt;
font-family:"Times New Roman";
mso-ascii-font-family:Cambria;
mso-ascii-theme-font:minor-latin;
mso-fareast-font-family:"Times New Roman";
mso-fareast-theme-font:minor-fareast;
mso-hansi-font-family:Cambria;
mso-hansi-theme-font:minor-latin;}
</style>
<![endif]-->
<!--StartFragment-->
<br />
<div class="MsoCaption">
<!--[if gte mso 9]><xml>
<o:DocumentProperties>
<o:Template>Normal.dotm</o:Template>
<o:Revision>0</o:Revision>
<o:TotalTime>0</o:TotalTime>
<o:Pages>1</o:Pages>
<o:Words>40</o:Words>
<o:Characters>231</o:Characters>
<o:Company>University of Illinois</o:Company>
<o:Lines>1</o:Lines>
<o:Paragraphs>1</o:Paragraphs>
<o:CharactersWithSpaces>283</o:CharactersWithSpaces>
<o:Version>12.0</o:Version>
</o:DocumentProperties>
<o:OfficeDocumentSettings>
<o:AllowPNG/>
</o:OfficeDocumentSettings>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:WordDocument>
<w:Zoom>0</w:Zoom>
<w:TrackMoves>false</w:TrackMoves>
<w:TrackFormatting/>
<w:PunctuationKerning/>
<w:DrawingGridHorizontalSpacing>18 pt</w:DrawingGridHorizontalSpacing>
<w:DrawingGridVerticalSpacing>18 pt</w:DrawingGridVerticalSpacing>
<w:DisplayHorizontalDrawingGridEvery>0</w:DisplayHorizontalDrawingGridEvery>
<w:DisplayVerticalDrawingGridEvery>0</w:DisplayVerticalDrawingGridEvery>
<w:ValidateAgainstSchemas/>
<w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid>
<w:IgnoreMixedContent>false</w:IgnoreMixedContent>
<w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText>
<w:Compatibility>
<w:BreakWrappedTables/>
<w:DontGrowAutofit/>
<w:DontAutofitConstrainedTables/>
<w:DontVertAlignInTxbx/>
</w:Compatibility>
</w:WordDocument>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:LatentStyles DefLockedState="false" LatentStyleCount="276">
</w:LatentStyles>
</xml><![endif]-->
<!--[if gte mso 10]>
<style>
/* Style Definitions */
table.MsoNormalTable
{mso-style-name:"Table Normal";
mso-tstyle-rowband-size:0;
mso-tstyle-colband-size:0;
mso-style-noshow:yes;
mso-style-parent:"";
mso-padding-alt:0in 5.4pt 0in 5.4pt;
mso-para-margin-top:0in;
mso-para-margin-right:0in;
mso-para-margin-bottom:10.0pt;
mso-para-margin-left:0in;
mso-pagination:widow-orphan;
font-size:12.0pt;
font-family:"Times New Roman";
mso-ascii-font-family:Cambria;
mso-ascii-theme-font:minor-latin;
mso-fareast-font-family:"Times New Roman";
mso-fareast-theme-font:minor-fareast;
mso-hansi-font-family:Cambria;
mso-hansi-theme-font:minor-latin;}
</style>
<![endif]-->
<!--StartFragment-->
</div>
<div class="MsoCaption">
<b>Figure <!--[if supportFields]><span style='mso-element:
field-begin'></span><span style="mso-spacerun: yes"> </span>SEQ Figure \*
ARABIC <span style='mso-element:field-separator'></span><![endif]-->4</b><!--[if supportFields]><span style='mso-element:
field-end'></span><![endif]-->. Migration tracks for E+A galaxies in the (NUV –
r) versus (g – r) color space (top panel) and the (NUV – r) versus M(z)
color-magnitude space (bottom panel).
Ages (in Gyr) along the track are shown color-coded. <o:p></o:p></div>
<!--EndFragment--></td></tr>
</tbody></table>
</div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<a href="http://www.blogger.com/blogger.g?blogID=6566777651395931272" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="http://www.blogger.com/blogger.g?blogID=6566777651395931272" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a>In
conclusion, by combining the optical and UV data, this study was able to
reconstruct the time-scales, mass fractions, SFRs, migration times, and
quenching mechanisms in this sample of PSGs. This study suggests that supernovae are the primary
quenching mechanism for galaxies under 10<sup>10</sup> solar masses, and AGN
become the primary source of negative feedback for galaxies over ~10<sup>10</sup>
solar masses. When supernovae are
the primary source, quenching efficiency decreases with galaxy mass because the
increasing depth of the potential well makes it more difficult to eject gas
from the system. As AGN become the
dominant source of negative feedback, quenching efficiency increases with
galaxy mass, due to the AGN luminosity scaling with the mass of the black
hole. The study of PSGs helps us
understand the processes that shape galaxy evolution. Future comparative studies
of PSGs at low and high redshifts could help provide insight into the processes
that dictate galaxy evolution over cosmic time. </div>
<div>
<div>
<div class="msocomtxt" id="_com_1" language="JavaScript">
<!--[if !supportAnnotations]--></div>
<!--[endif]--></div>
</div>
<!--EndFragment-->Anonymoushttp://www.blogger.com/profile/08361708343929797925noreply@blogger.com0tag:blogger.com,1999:blog-6566777651395931272.post-66032010648221313732013-06-30T20:59:00.000-07:002013-08-08T09:00:56.661-07:00Yang et al. Article -- A Detailed Look at E+A Galaxy Evolution<!--[if !mso]>
<style>
v\:* {behavior:url(#default#VML);}
o\:* {behavior:url(#default#VML);}
w\:* {behavior:url(#default#VML);}
.shape {behavior:url(#default#VML);}
</style>
<![endif]--><!--[if gte mso 9]><xml>
<o:DocumentProperties>
<o:Template>Normal.dotm</o:Template>
<o:Revision>0</o:Revision>
<o:TotalTime>0</o:TotalTime>
<o:Pages>1</o:Pages>
<o:Words>1213</o:Words>
<o:Characters>6916</o:Characters>
<o:Company>University of Illinois</o:Company>
<o:Lines>57</o:Lines>
<o:Paragraphs>13</o:Paragraphs>
<o:CharactersWithSpaces>8493</o:CharactersWithSpaces>
<o:Version>12.0</o:Version>
</o:DocumentProperties>
<o:OfficeDocumentSettings>
<o:AllowPNG/>
</o:OfficeDocumentSettings>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:WordDocument>
<w:Zoom>0</w:Zoom>
<w:TrackMoves>false</w:TrackMoves>
<w:TrackFormatting/>
<w:PunctuationKerning/>
<w:DrawingGridHorizontalSpacing>18 pt</w:DrawingGridHorizontalSpacing>
<w:DrawingGridVerticalSpacing>18 pt</w:DrawingGridVerticalSpacing>
<w:DisplayHorizontalDrawingGridEvery>0</w:DisplayHorizontalDrawingGridEvery>
<w:DisplayVerticalDrawingGridEvery>0</w:DisplayVerticalDrawingGridEvery>
<w:ValidateAgainstSchemas/>
<w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid>
<w:IgnoreMixedContent>false</w:IgnoreMixedContent>
<w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText>
<w:Compatibility>
<w:BreakWrappedTables/>
<w:DontGrowAutofit/>
<w:DontAutofitConstrainedTables/>
<w:DontVertAlignInTxbx/>
</w:Compatibility>
</w:WordDocument>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:LatentStyles DefLockedState="false" LatentStyleCount="276">
</w:LatentStyles>
</xml><![endif]-->
<!--[if gte mso 10]>
<style>
/* Style Definitions */
table.MsoNormalTable
{mso-style-name:"Table Normal";
mso-tstyle-rowband-size:0;
mso-tstyle-colband-size:0;
mso-style-noshow:yes;
mso-style-parent:"";
mso-padding-alt:0in 5.4pt 0in 5.4pt;
mso-para-margin-top:0in;
mso-para-margin-right:0in;
mso-para-margin-bottom:10.0pt;
mso-para-margin-left:0in;
mso-pagination:widow-orphan;
font-size:12.0pt;
font-family:"Times New Roman";
mso-ascii-font-family:Cambria;
mso-ascii-theme-font:minor-latin;
mso-fareast-font-family:"Times New Roman";
mso-fareast-theme-font:minor-fareast;
mso-hansi-font-family:Cambria;
mso-hansi-theme-font:minor-latin;}
</style>
<![endif]--><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="2050"/>
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1"/>
</o:shapelayout></xml><![endif]-->
<!--StartFragment-->
<br />
<b>Title</b>: A Detailed Evolution of E+A Galaxies
into Early Types<br />
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<o:p></o:p></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<br /></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in; tab-stops: 238.5pt;">
<b>Authors</b>: Y. Yang, A.
Zabludoff, D. Zaritsky, and J. Mihos<o:p></o:p></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in; tab-stops: 238.5pt;">
<br /></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<b>Authors’ Institutions: </b>Steward
Observatory, University of Arizona and Department of Astronomy, Case Western
Reserve University<o:p></o:p></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<br /></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
To read the full article, please click <a href="https://vault.it.northwestern.edu/let412/GZQuench" target="_blank">here</a>. </div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<br /></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<br /></div>
<h3>
Article Summary:</h3>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjYVrlrP4Gu-iNm1QoVqhJUmOkctZVoUx1bcM1eSW29nTzNwQT4tUsrn9-oVLe5Wd9G0yzKdk2VND1NwywXtcdoeP2nCAJRzjPWIsRT8tt3hw8uQpoBUI3PRLk4uBKjMF4LANnvAhMzQsY/s875/756442main_p1323a-orig_full.jpeg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjYVrlrP4Gu-iNm1QoVqhJUmOkctZVoUx1bcM1eSW29nTzNwQT4tUsrn9-oVLe5Wd9G0yzKdk2VND1NwywXtcdoeP2nCAJRzjPWIsRT8tt3hw8uQpoBUI3PRLk4uBKjMF4LANnvAhMzQsY/s640/756442main_p1323a-orig_full.jpeg" width="490" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">The Hubble Space Telescope captured galaxy NGC 2936 is in a celestial dance with its elliptical companion NGC 2937. NGC 2936 used to be a flat, spiral galaxy, its stars now scrambled due to the gravitational interactions with its companion. Compressed gas during the encounter triggers a burst of star formation, visible as bluish streams along the distorted arms. These galactic interactions could possibly lead to the vibrant, star-forming, distorted spiral galaxy to evolve into a quiet elliptical galaxy like its companion. Image courtesy of NASA. </td></tr>
</tbody></table>
</div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
The
transitional period between gas-rich, star-forming galaxies to gas-poor,
passively evolving galaxies is an important phase of galaxy evolution.
Post-Starburst Galaxies (PSGs) appear to inhabit this
transitional period. To determine
what PSGs become after their young stellar populations fade away, Yang et al.
acquired detailed morphologies of 21 PSGs using high-resolution images from the
Hubble Space Telescope (<i>HST</i>) Advanced
Camera for Surveys (ACS) and Wide-Field Planetary Camera 2 (WFPC2). They used these images to measure the
morphologies, color profiles, scaling relations, and star cluster
characteristics of their PSG sample. Their results suggest that PSGs evolve
into early-type E/SO galaxies and contribute to the building up of the ‘red
sequence’.<o:p></o:p></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<br /></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
PSGs
represent the best candidates for galaxies caught in the midst of the
transformation between late and early types due to their relatively young
stellar population and lack of ongoing star formation, as suggested by their
strong Balmer absorption lines and absence of emission lines such as [O <sub>II</sub>]
and H-alpha. Since PSGs reside in low-density
environments, the abrupt end to their star formation is likely due to
galaxy-galaxy interactions rather than cluster-specific mechanisms such as <a href="http://astrobites.org/2012/08/28/mixing-up-gas-in-the-wake-of-a-strangled-satellite/" target="_blank">ram pressure stripping and strangulation</a>.
This theory is supported by significant fractions of PSGs having merger
features. <o:p></o:p></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<br /></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
The
21 PSGs in the sample were spectroscopically identified from 11,113 galaxy
spectra of the Las Campanas Redshift Survey (LCRS). The 21 PSGs have redshifts
between 0.07 and 0.18. The
high-resolution <i>HST</i> images, such as
those presented in <b>figure 1</b>, enabled small- and large-scale interaction features
to be identified. The morphologies
of PSGs in this study were very diverse, including train wrecks, barred
galaxies, blue cores, and relaxed-looking disky galaxies. Over half of the PSGs had identifiable
tidal or disturbed features. Five
of the galaxies in the sample had interacting, companion galaxies within ~30
kpc. One of the samples even had a
binary PSG system in which both of the galaxies were tidally disturbed. These findings support the idea that
galaxy interactions and mergers trigger the PSG phase. In addition, morphological analysis determined that six of
the PSGs had distinct, compact blue cores and seven of the galaxies had dust
features such as lanes and filamentary structures. <o:p></o:p></div>
<div class="separator" style="clear: both; text-align: center;">
<br /></div>
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhuC5k8bP9K9IOGzMPKDR4cgAUpkjYlohhOmeMXV34Mt60QEOZflpdmqHLRosQWaMxQ7S9pvmlpq6CNNYt8NjuYblNR0nT_r1t8f1_1kFUPcNxcA7M16tf780hLHVNy944kjIqT3zCMVAk/s241/figure+1.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="396" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhuC5k8bP9K9IOGzMPKDR4cgAUpkjYlohhOmeMXV34Mt60QEOZflpdmqHLRosQWaMxQ7S9pvmlpq6CNNYt8NjuYblNR0nT_r1t8f1_1kFUPcNxcA7M16tf780hLHVNy944kjIqT3zCMVAk/s400/figure+1.jpg" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><!--[if gte mso 9]><xml>
<o:DocumentProperties>
<o:Template>Normal.dotm</o:Template>
<o:Revision>0</o:Revision>
<o:TotalTime>0</o:TotalTime>
<o:Pages>1</o:Pages>
<o:Words>43</o:Words>
<o:Characters>248</o:Characters>
<o:Company>University of Illinois</o:Company>
<o:Lines>2</o:Lines>
<o:Paragraphs>1</o:Paragraphs>
<o:CharactersWithSpaces>304</o:CharactersWithSpaces>
<o:Version>12.0</o:Version>
</o:DocumentProperties>
<o:OfficeDocumentSettings>
<o:AllowPNG/>
</o:OfficeDocumentSettings>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:WordDocument>
<w:Zoom>0</w:Zoom>
<w:TrackMoves>false</w:TrackMoves>
<w:TrackFormatting/>
<w:PunctuationKerning/>
<w:DrawingGridHorizontalSpacing>18 pt</w:DrawingGridHorizontalSpacing>
<w:DrawingGridVerticalSpacing>18 pt</w:DrawingGridVerticalSpacing>
<w:DisplayHorizontalDrawingGridEvery>0</w:DisplayHorizontalDrawingGridEvery>
<w:DisplayVerticalDrawingGridEvery>0</w:DisplayVerticalDrawingGridEvery>
<w:ValidateAgainstSchemas/>
<w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid>
<w:IgnoreMixedContent>false</w:IgnoreMixedContent>
<w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText>
<w:Compatibility>
<w:BreakWrappedTables/>
<w:DontGrowAutofit/>
<w:DontAutofitConstrainedTables/>
<w:DontVertAlignInTxbx/>
</w:Compatibility>
</w:WordDocument>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:LatentStyles DefLockedState="false" LatentStyleCount="276">
</w:LatentStyles>
</xml><![endif]-->
<!--[if gte mso 10]>
<style>
/* Style Definitions */
table.MsoNormalTable
{mso-style-name:"Table Normal";
mso-tstyle-rowband-size:0;
mso-tstyle-colband-size:0;
mso-style-noshow:yes;
mso-style-parent:"";
mso-padding-alt:0in 5.4pt 0in 5.4pt;
mso-para-margin-top:0in;
mso-para-margin-right:0in;
mso-para-margin-bottom:10.0pt;
mso-para-margin-left:0in;
mso-pagination:widow-orphan;
font-size:12.0pt;
font-family:"Times New Roman";
mso-ascii-font-family:Cambria;
mso-ascii-theme-font:minor-latin;
mso-fareast-font-family:"Times New Roman";
mso-fareast-theme-font:minor-fareast;
mso-hansi-font-family:Cambria;
mso-hansi-theme-font:minor-latin;}
</style>
<![endif]-->
<!--StartFragment-->
<br />
<div class="MsoCaption">
<b>Figure <!--[if supportFields]><span style='mso-element:
field-begin'></span><span style="mso-spacerun: yes"> </span>SEQ Figure \*
ARABIC <span style='mso-element:field-separator'></span><![endif]-->1</b><!--[if supportFields]><span style='mso-element:
field-end'></span><![endif]-->.
Examples of 3 PSGs used in the study. The left column shows dim tidal features using high-contrast
R-band, the middle column shows images for the WFPC2 sample, and the right
column show residual R-band images subtracted from the smooth symmetric model
components<o:p></o:p></div>
<!--EndFragment--></td></tr>
</tbody></table>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<br /></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
PSGs
tend to be bulge-dominated systems.
The median bulge fraction (B/T), which gives the ratio of the bulge
luminosity to the total luminosity of the galaxy, was 0.59. This is consistent with that of S0
galaxies, with an average B/T of 0.63.
<a href="http://astronomy.swin.edu.au/cosmos/S/Surface+Brightness+Profiles" target="_blank">Sérsic profiles</a>, represented by an r<sup>1/n</sup> profile describing
how the intensity of a galaxy varies with distance from its center, were also
obtained to further investigate PSG bulge characteristics. Disk galaxies and spheroidals generally
have Sérsic indices of n=1 and n=4, respectively, yet most of the PSGs had
indices with n>5 and a couple with indices n>10. This indicates that the luminosity of PSGs
is highly concentrated, potentially due to substructures near their centers
such as bright nuclei, bars, and rings.
<o:p></o:p></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<br /></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
To
quantify asymmetric features, this study calculated the concentration index ‘C’
and rotational asymmetry index ‘A’ to be able to place the sample galaxies on a
C-A plane, as shown in <b>figure 2</b>. In
general, PSGs have high concentration indices consistent with those of
spheroids, but considerably larger asymmetry indices than ellipticals due to
structures that arose from the starburst or recent merger. Therefore, PSGs would be
morphologically classified as early-type galaxies once the disruptions and
tidal features dissipate or fade. </div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<o:p></o:p></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEinv6PjfOS6mwaADjldjQKz1xvalNh-6qMjaQe9y65qZoBo9trf6dN1U3Wd3wr1tAULxXicVI8z7K0FjvoCT0mvj0QoocKVDKaKs1Lk_-M8Pu_K2awq-zGfF4qb_2bdeRSLMkklcm48lrA/s398/figure+2.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="255" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEinv6PjfOS6mwaADjldjQKz1xvalNh-6qMjaQe9y65qZoBo9trf6dN1U3Wd3wr1tAULxXicVI8z7K0FjvoCT0mvj0QoocKVDKaKs1Lk_-M8Pu_K2awq-zGfF4qb_2bdeRSLMkklcm48lrA/s400/figure+2.jpg" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><!--[if gte mso 9]><xml>
<o:DocumentProperties>
<o:Template>Normal.dotm</o:Template>
<o:Revision>0</o:Revision>
<o:TotalTime>0</o:TotalTime>
<o:Pages>1</o:Pages>
<o:Words>46</o:Words>
<o:Characters>265</o:Characters>
<o:Company>University of Illinois</o:Company>
<o:Lines>2</o:Lines>
<o:Paragraphs>1</o:Paragraphs>
<o:CharactersWithSpaces>325</o:CharactersWithSpaces>
<o:Version>12.0</o:Version>
</o:DocumentProperties>
<o:OfficeDocumentSettings>
<o:AllowPNG/>
</o:OfficeDocumentSettings>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:WordDocument>
<w:Zoom>0</w:Zoom>
<w:TrackMoves>false</w:TrackMoves>
<w:TrackFormatting/>
<w:PunctuationKerning/>
<w:DrawingGridHorizontalSpacing>18 pt</w:DrawingGridHorizontalSpacing>
<w:DrawingGridVerticalSpacing>18 pt</w:DrawingGridVerticalSpacing>
<w:DisplayHorizontalDrawingGridEvery>0</w:DisplayHorizontalDrawingGridEvery>
<w:DisplayVerticalDrawingGridEvery>0</w:DisplayVerticalDrawingGridEvery>
<w:ValidateAgainstSchemas/>
<w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid>
<w:IgnoreMixedContent>false</w:IgnoreMixedContent>
<w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText>
<w:Compatibility>
<w:BreakWrappedTables/>
<w:DontGrowAutofit/>
<w:DontAutofitConstrainedTables/>
<w:DontVertAlignInTxbx/>
</w:Compatibility>
</w:WordDocument>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:LatentStyles DefLockedState="false" LatentStyleCount="276">
</w:LatentStyles>
</xml><![endif]-->
<!--[if gte mso 10]>
<style>
/* Style Definitions */
table.MsoNormalTable
{mso-style-name:"Table Normal";
mso-tstyle-rowband-size:0;
mso-tstyle-colband-size:0;
mso-style-noshow:yes;
mso-style-parent:"";
mso-padding-alt:0in 5.4pt 0in 5.4pt;
mso-para-margin-top:0in;
mso-para-margin-right:0in;
mso-para-margin-bottom:10.0pt;
mso-para-margin-left:0in;
mso-pagination:widow-orphan;
font-size:12.0pt;
font-family:"Times New Roman";
mso-ascii-font-family:Cambria;
mso-ascii-theme-font:minor-latin;
mso-fareast-font-family:"Times New Roman";
mso-fareast-theme-font:minor-fareast;
mso-hansi-font-family:Cambria;
mso-hansi-theme-font:minor-latin;}
</style>
<![endif]-->
<!--StartFragment-->
<br />
<div class="MsoCaption">
<b>Figure <!--[if supportFields]><span style='mso-element:
field-begin'></span><span style="mso-spacerun: yes"> </span>SEQ Figure \*
ARABIC <span style='mso-element:field-separator'></span><![endif]-->2</b><!--[if supportFields]><span style='mso-element:
field-end'></span><![endif]-->. C-A classification the the 21 PSGs (filled
circles) as well as 113 local elliptical, intermediate spiral, and late-type
spirals (oval, plus sign, and spiral, respectively). The dashed line provides a rough division of early and late
types on the CA plane. <o:p></o:p></div>
<!--EndFragment--></td></tr>
</tbody></table>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<br /></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
The
color morphologies of the PSGs were just as diverse as their structural
morphologies. Radial color
profiles can depend on dust content and spatial distributions, ages, and
<a href="https://edocs.uis.edu/jmart5/www/rrlyrae/metals.htm" target="_blank">metallicities</a> of stellar populations, which in turn depend on the evolutionary
history of the galaxies. For
example, if galaxy-galaxy interactions are responsible for creating a PSG, then
the young stellar population is expected to be concentrated in the center,
yielding a positive color gradient (i.e., redder color with increasing
radius). If mechanisms such as ram
pressure stripping are responsible for producing the PSG, color profiles may be
more uniform. </div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<span style="text-indent: 0.5in;"><br /></span></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<span style="text-indent: 0.5in;">High-resolution
color distributions in this study indicate that a significant fraction of the PSGs
have positive color gradients and sometimes distinct blue cores.</span><span style="text-indent: 0.5in;"> </span><span style="text-indent: 0.5in;"><b>Figure 3</b> shows that twelve PSGs had a
positive color gradient, five had a negative color gradient (bluer with
increasing radius), and five had flat or mixed color profiles.</span><span style="text-indent: 0.5in;"> </span><span style="text-indent: 0.5in;">Of the five with negative color
gradients, three show clear dust signatures, which may mean that the red cores
in these galaxies arise from increasing dust extinction toward the center.</span><span style="text-indent: 0.5in;"> </span><span style="text-indent: 0.5in;">Early-type galaxies typically have
slightly negative color profiles.</span><span style="text-indent: 0.5in;"> </span><span style="text-indent: 0.5in;"><a href="http://cas.sdss.org/dr3/en/proj/advanced/galaxies/tuningfork.asp" target="_blank">E/S0</a>s
in the local universe have negative color gradients that originate from their
metallicity gradients; their stellar populations become more metal-rich and
redder towards the center.</span><span style="text-indent: 0.5in;"> </span><span style="text-indent: 0.5in;">Over
time, the PSGs with positive color gradients may begin to exhibit negative
color gradients if their young stellar populations are more metal-rich than the
underlying old populations and these young stars run through their lifecycle. This
possibly suggests that PSGs are the precursors of E/SO galaxies.</span><span style="text-indent: 0.5in;"> </span><span style="text-indent: 0.5in;"> </span></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEib10af3bhILBpH5JpLiW8V_kiMFvZwe82Co1mafBx3xh7W8FllQjpOhsvBo0G4ak8cdd_i23i-e8YMg9h9kBDPNY81tSOEPeDgMqfu910vEdbFywNkO3ZNw5fsN71h_IKoCn1dwEDkDio/s398/figure+3.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEib10af3bhILBpH5JpLiW8V_kiMFvZwe82Co1mafBx3xh7W8FllQjpOhsvBo0G4ak8cdd_i23i-e8YMg9h9kBDPNY81tSOEPeDgMqfu910vEdbFywNkO3ZNw5fsN71h_IKoCn1dwEDkDio/s640/figure+3.jpg" width="420" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><!--[if gte mso 9]><xml>
<o:DocumentProperties>
<o:Template>Normal.dotm</o:Template>
<o:Revision>0</o:Revision>
<o:TotalTime>0</o:TotalTime>
<o:Pages>1</o:Pages>
<o:Words>32</o:Words>
<o:Characters>185</o:Characters>
<o:Company>University of Illinois</o:Company>
<o:Lines>1</o:Lines>
<o:Paragraphs>1</o:Paragraphs>
<o:CharactersWithSpaces>227</o:CharactersWithSpaces>
<o:Version>12.0</o:Version>
</o:DocumentProperties>
<o:OfficeDocumentSettings>
<o:AllowPNG/>
</o:OfficeDocumentSettings>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:WordDocument>
<w:Zoom>0</w:Zoom>
<w:TrackMoves>false</w:TrackMoves>
<w:TrackFormatting/>
<w:PunctuationKerning/>
<w:DrawingGridHorizontalSpacing>18 pt</w:DrawingGridHorizontalSpacing>
<w:DrawingGridVerticalSpacing>18 pt</w:DrawingGridVerticalSpacing>
<w:DisplayHorizontalDrawingGridEvery>0</w:DisplayHorizontalDrawingGridEvery>
<w:DisplayVerticalDrawingGridEvery>0</w:DisplayVerticalDrawingGridEvery>
<w:ValidateAgainstSchemas/>
<w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid>
<w:IgnoreMixedContent>false</w:IgnoreMixedContent>
<w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText>
<w:Compatibility>
<w:BreakWrappedTables/>
<w:DontGrowAutofit/>
<w:DontAutofitConstrainedTables/>
<w:DontVertAlignInTxbx/>
</w:Compatibility>
</w:WordDocument>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:LatentStyles DefLockedState="false" LatentStyleCount="276">
</w:LatentStyles>
</xml><![endif]-->
<!--[if gte mso 10]>
<style>
/* Style Definitions */
table.MsoNormalTable
{mso-style-name:"Table Normal";
mso-tstyle-rowband-size:0;
mso-tstyle-colband-size:0;
mso-style-noshow:yes;
mso-style-parent:"";
mso-padding-alt:0in 5.4pt 0in 5.4pt;
mso-para-margin-top:0in;
mso-para-margin-right:0in;
mso-para-margin-bottom:10.0pt;
mso-para-margin-left:0in;
mso-pagination:widow-orphan;
font-size:12.0pt;
font-family:"Times New Roman";
mso-ascii-font-family:Cambria;
mso-ascii-theme-font:minor-latin;
mso-fareast-font-family:"Times New Roman";
mso-fareast-theme-font:minor-fareast;
mso-hansi-font-family:Cambria;
mso-hansi-theme-font:minor-latin;}
</style>
<![endif]-->
<!--StartFragment-->
<br />
<div class="MsoCaption">
<b>Figure <!--[if supportFields]><span style='mso-element:
field-begin'></span><span style="mso-spacerun: yes"> </span>SEQ Figure \*
ARABIC <span style='mso-element:field-separator'></span><![endif]-->3</b><!--[if supportFields]><span style='mso-element:
field-end'></span><![endif]-->. Redshifted radial color profiles of the 20 PSGs
. A positive slope means the
galaxies are bluer towards the center and a negative slope means the galaxies
are redder towards the center. <o:p></o:p></div>
<!--EndFragment--></td></tr>
</tbody></table>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<span style="text-indent: 0.5in;"><br /></span></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<span style="text-indent: 0.5in;">Half of the PSGs with positive color
gradients also had compact, almost stellar-like, blue cores that were distinct
from the other parts of the galaxy.</span><span style="text-indent: 0.5in;">
</span><span style="text-indent: 0.5in;">Though their origins are not fully understood, blue cores are common in
early-type galaxies at higher redshifts (z > 0.5), when field spheroids were
assembling.</span><span style="text-indent: 0.5in;"> </span><span style="text-indent: 0.5in;">Therefore, the
blue-core PSGs may be the local analogs to these higher redshift blue-core
spheroids.</span><span style="text-indent: 0.5in;"> </span><span style="text-indent: 0.5in;">Three of the six PSGs
with blue cores also had <a href="http://astrobites.org/glossaries/galaxy-and-agn-types/" target="_blank">LINER</a> (low-ioniation emission line region) spectral
signatures, indicative of Active Galactic Nuclei (AGN) activity being the potential mechanism for quenching
star formation in these PSGs.</span><span style="text-indent: 0.5in;"> </span></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in; text-indent: .5in;">
<o:p></o:p></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<br /></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
To
further determine if of the data supports the idea that PSGs evolve into
early-type galaxies, this study compared scaling relations between PSG and
early-type galaxies. The
fundamental plane is an empirical relation between the effective radius, the
central velocity dispersion, and the mean surface brightness. PSGs stand apart from E/S0s in the fundamental
plane, which implies that the stellar populations of PSGs are different from
those of E/S0s. On average, the
mass to luminosity ratio (<i>M/L</i>) of PSGs
is 3.8 times smaller than that of E/S0s.
In PSGs, smaller or less massive galaxies appear to have a smaller <i>M/L</i>. This trend arises naturally from merger scenarios, where
low-mass galaxies have higher gas fractions and could produce relatively larger
populations of young stars. <o:p></o:p></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<br /></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
Properties
of newly formed star clusters in the PSGs were analyzed to determine if they
are consistent with those of early-type galaxies. High-resolution images were required to identify star
clusters in the PSG sample. At
least nine of the PSGs had a population of unresolved compact sources. The colors and luminosities of the
young star clusters are consistent with the ages inferred from the PSG spectra
(0.01-1 Gyr), signifying that these clusters likely arose during the
interaction/starburst phase. Though
it is uncertain how many of these clusters will survive to the E/S0 phase, it
is at least possible that the young star clusters in PSGs can evolve into the
globular cluster systems seen in E/S0s. <o:p></o:p></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
<br /></div>
<div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in;">
To
summarize, using high spatial resolution <i>HST</i>
ACS and WFPC2 images to derive morphological properties, color profiles,
scaling relations, and characteristics of young star clusters, this study
suggests that PSGs are caught in the act of transforming from gas-rich
late-type galaxies to gas-poor early-type galaxies. Further investigation of PSGs is critical to better
understanding of the origin of the red sequence of galaxies. <o:p></o:p></div>
<!--EndFragment-->Anonymoushttp://www.blogger.com/profile/08361708343929797925noreply@blogger.com0