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Research Interests:
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Galaxy formation, with particular interest in the merger statistics of dark matter
halos, the galaxies contained within them, and how to connect DM halos to observable
galaxies, and their properties (SFR, gas mass, stellar mass, metallicity, etc.).
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How mass accretion histories and merger statistics govern the morphologies and
other properties of observed galaxies. How do disks survive in an LCDM universe?
Current Research:
I am currently working on several
projects simultaneously, all involving the study of halo mergers based on a
cosmological LCDM simulation.
a) I am studying the instantaneous merger
rate of dark matter halos as a function of redshift. How much higher
is the merger rate into bright galaxies at z=3 compared to z=0? Is
this consistent with LBGs at z~3 being heavily dominated by merging
galaxies? Does this agree with observations of "merger fraction" vs. z?
b) Motivated in part by my recent work on
the merger rates of relatively large mergers
into the main progenitor of Milky-Way sized halos (See
Stewart et. al. 2008) I am working on using number density matching to
the observed luminosity function (Conroy & Wecshler 2008) to assign
galaxy stellar masses to dark matter halos at z=0-2. Then try to use
observations to assign gas masses to these galaxies and look at gas rich/gas poor
merger statistics. Can this explaing disk survival?
c) There appears to be a universal merger rate of halos,
self-similar across host halo mass, and possibly self-similar across
redshift. I wish to investigate this universality. Given a fit to
dN/dz, can you then analytically integrate/differentiate to create any merger rate
information you need, given a merger ratio, halo mass, redshift?
<Figure at right: an example merger tree from an N-Body
simulation. Numbers on the left represent epoch a=1/(1+z), with time
running downward. Black lines denote isolated field halos, while red
lines denote subhalos that have fallen within the virial radius of a larger,
more massive halo.>
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