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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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<title>Tim Carleton</title>
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<ul>
<li><a href="index.html">Home</a></li>
<li ><a href="aboutme.html">About Me</a></li>
<li "current_page_item"><a
href="research.html">Research</a></li>
<li><a href="cv3.pdf"?>CV</a></li>
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<h2>Research</h2>
</div>
<div id="content-header">
My research is focused the
interplay between internal and external
factors affecting galaxy evolution
between z=1 and today, with a focus on dwarf galaxies.
Dwarf galaxies have a very wide range of properties and are affected by a
variety of physical processes. They are the most abundant galaxies in the
Universe, and there is a lot we still a lot we still don't understand about them!
<p>
For my research, I often combine observational data (often from HST or JWST) with simulation data
to best study my particular research problem.
</p>
</div>
<h3>Ultra-Diffuse Galaxies</h3>
<p>
A large population of
extremely extended dwarf galaxies (dubbed
'Ultra-Diffuse Galaxies,' or UDGs) has been
identified by recent surveys with high
sensitivity limits. Understanding the formation of
these unusual galaxies is compelling, both on
its own right as well as within the broader context of
dwarf galaxy fromation and evolution.
</p>
<h3>Dwarf Galaxy Globular Clusters</h3>
<p>
One of the most interesting properties of UDGs is their significant globular cluster populations.
While some have speculated that this is connected witih their dark matter halo properties, the globular cluster-dark matter halo
connection is poorly understood for dwarf galaxies. Understanding the connection between globular clusters and dwarf galaxies
can give us insight to the process of globular cluster formation, as well as the dark matter halos of dwarf galaxies.
</p>
<h3>Exragalactic Background Light and SKYSURF</h3>
<p>
When we point our telescopes at the night sky, we can see many different types of stars and galaxies, as well as many diffuse
light foregrounds, like Zodiacal Light and Diffuse Galactic Light. When all the light from
all of these objects and foregrounds is summed together, it should equal the total amount of light we see. However, some studies indicate
that that is not the case, suggesting that some other light source is missing from our understanding. <a href=http://skysurf.asu.edu/>SKYSURF</a> is a large archival
HST project to study this discrepancy - both in terms of better constraining the light from exragalactic sources (the Extragalactic Background
Light) and measuring the total level of incoming light.
</p>
<!--<h3>The UVJ Diagram & the 3D-HST survey</h3>
<p>
The location of a galaxy in <it>U-V</it>
vs. <it>V-J</it> color-color space has proven
extremely valuable in separating red dusty
galaxies from red quiescent galaxies,
particularly at high redshift. The 3D-HST
survey provides deep spectroscopic follow-up
of a large number of star-forming and
quiescent galaxies using the HST grism. These
observations, in addition to providing a direct
calibration of the star-formation properties
of UVJ-classified galaxies, can illuminate the
how emission line-based properties of high-z
galaxies compare with their light-weighted
stellar populations.
</p>
<h3>Satellite Quenching at high
redshift</h3>
<p>
It is well known that environment plays an
important role in shutting down
star formation (or quenching) in dwarf galaxies.
While many physical mechanisms (e.g. ram-pressure
stripping, strangulation, starvation...) have been put
forward to explain this process,
observational evidence is only beginning to settle the
question which of these effects are at play in
low mass (M<sub>*</sub></sub>~10<sup>8</sup>
M<sub>⊙</sub>) dwarfs in the local
universe, and the relative importance of each effect. Observations of
satellite-quenching in similar dwarfs at high-z provide an
important piece of our understanding of the
mechanisms at play during the decline in star-formation.
</p>
<h3>CO-H<sub>2</sub> Conversion Factor</h3>
<!--<span class="image image-right"><img
src="images/cgasphibbsksaco.png" alt=""/></span>--!>
<p>
<!--Molecular gas is the principal
fuel in the star formation process, so understanding the
molecular gas content of high-redshift
galaxies goes a long way in building our
understanding of this process at
high-z. A crucial component of
interpreting observations of molecular gas
at high-z is the CO-H<sub>2</sub> Conversion
Factor (α<sub>CO</sub>) relating the
observed CO luminosity to the molecular gas
mass.
Using data from the <a
href="http://www.iram-institute.org/EN/content-page-279-7-158-240-279-0.html">
PHIBSS</a> and <a
href="http://www.iram-institute.org/EN/content-page-298-7-158-240-298-0.html">
COLD GASS</a> programs, I have investigated
the impact of metallicity and density
on the galaxy-wide α<sub>CO</sub>
value. My research, which found that α<sub>CO</sub> values do
not significantly evolve from <it>z</it>=1 to <it>z</it>=0,
demonstrates that molecular gas conditions have not significantly
evolved over the past 8 billion years.--!>
<!--By comparing the observed CO luminosities
to the observed star-formation rates, we are
able to gain insight into the structure of
star-formation in these galaxies.
I am interested in the molecular gas content
of galaxies and how it influences galaxy evolution.
The molecular gas content of galaxies is
primarily studied through emission of carbon
monoxide (CO). However, the conversion between
the optically thick CO luminosity and the
total molecular gas mass
(α<sub>CO</sub>) relies on a number of
assumptions. Because of its importance in
understanding molecular gas, a full
understanding of α<sub>CO</sub> and its
dependencies is critical for our theory of
galaxy evolution.
Using the Kennicutt-Schmidt law, I measure the
molecular gas content in high-redshift in
order to study how α<sub>CO</sub> varies
with redshift.--!>
</div>
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