Spitzer Space Telescope - Archive Research Proposal #50805


Comparing the Stellar Populations of Star-forming Galaxies at z=2

Principal Investigator: Eric Gawiser
           Institution: Rutgers

     Technical Contact: Eric Gawiser, Rutgers

Co-Investigators: 
Kamson Lai, Harvard-Smithsonian CfA                                   
Jia-Sheng Huang, Harvard-Smithsonian CfA                              
Giovanni Fazio, Harvard-Smithsonian CfA                               
Kevin Schawinski, Oxford University                                   
Caryl Gronwall, Penn State University                                 
Robin Ciardullo, Penn State University                                
Nicholas Bond, Rutgers University                                     
Lucia Guaita, P.U. Catolica                                           
Nelson Padilla, P.U. Catolica                                         

Science Category: high-z galaxies (z>0.5) 
Dollars Approved: 75000 

Abstract:
Published results from our Cycle 4 Archival program show that Lyman Alpha
Emitting galaxies (LAEs) at z=3.1 appear to be galaxies in the act of formation.
These objects are currently our most promising candidates for the progenitors of
present-day L* galaxies like the Milky Way, as they are younger, lower in mass,
and less chemically evolved than z~3 Lyman Break Galaxies (LBGs). Deep IRAC
images allow us to study the star formation history of these objects through
multi-band spectral energy distribution (SED) fitting. By doing this with a
sample of z=3.1 LAEs, we have begun to place constraints on the process of
galaxy formation in the early universe. Here we propose to extend our study to
lower redshifts, using a sample of LAEs at z=2.1, along with a
continuum-selected sample of spectroscopically-confirmed star-forming galaxies
(SFGs) between 1.5<z<3. To do this, we will combine archival IRAC data from the
GOODS and SIMPLE (Spitzer IRAC/MUSYC Public Legacy in E-CDFS) surveys of the
Extended Chandra Deep Field South with ground- and space-based photometry in
UBVRIzJK. We will perform a uniform two-population SED analysis using the
Maraston models, a Salpeter IMF, and the Calzetti dust law. This will enable us
to directly compare the star formation histories of LAEs to those of
continuum-selected SFGs at both z=2 and z=3, probe the evolution in these
objects, and determine which have properties most consistent with being the
progenitors of z=0 L* galaxies. In addition, we will subdivide our galaxy
samples into those detected at 8 microns with IRAC and those present in the 24
micron public FIDEL image of the field. This will test whether MIR-detected
galaxies at z~2 are as massive as those at z~3. Finally, we will use the FIDEL
24 and 70 micron images to determine the fraction of SFGs and LAEs that host
low-luminosity or heavily obscured AGN, which cannot be detected in Chandra and
XMM imaging.