Spitzer Space Telescope - Archive Research Proposal #40823


A SIMPLE Proof that Lyman Alpha Emitters are Galaxies in the Act of Formation

Principal Investigator: Eric Gawiser
           Institution: Rutgers

     Technical Contact: Eric Gawiser, Rutgers

Co-Investigators: 
Kamson Lai, Harvard-Smithsonian CfA                                   
Jiasheng Huang, Harvard-Smithsonian CfA                               
Giovanni Fazio, Harvard-Smithsonian CfA                               
Caryl Gronwall, Penn State                                            
Robin Ciardullo, Penn State                                           
Kevin Schawinski, Oxford                                              

Science Category: high-z galaxies (z>0.5) 
Dollars Approved: 63281 

Abstract:
Lyman Alpha Emitting galaxies (LAEs) seen at high redshift appear to be galaxies
in the act of formation. They are currently the most promising candidates for
the progenitors of typical spiral galaxies like the Milky Way. The LAEs tend to
be younger, lower in mass, and less chemically evolved than the better-studied
Lyman Break Galaxies (LBGs). Deep IRAC imaging allows us to study the star
formation history of these objects to gain a better understanding of the process
of galaxy formation. We will use archival IRAC images of the Extended Chandra
Deep Field-South from the SIMPLE (Spitzer IRAC/MUSYC Public Legacy in ECDF-S)
and GOODS Legacy Programs combined with ground- and space-based photometry in
UBVRIzJK to study the Spectral Energy Distributions of our sample of 162 Lyman
Alpha Emitters at z=3.1. 47 of these LAEs have confirmed spectroscopic
redshifts. We will perform the identical analysis on a sample of 34
spectroscopically confirmed Lyman Break Galaxies at 2.7<z<3.9 to compare the
star formation histories of these two families of high-redshift galaxies. At
this redshift, the IRAC bands trace the rest-frame optical radiation which will
reveal or eliminate the presence of an underlying population of evolved stars.
We will use models containing both young and old stellar populations in order to
search for evidence of prior epochs of star formation. If the older component is
absent in most LAEs, they can be proved to be undergoing their first burst of
star formation, meaning that they represent fundamental building blocks of
present-day galaxies. We will also use the archival MIPS GTO images of this
field to determine the fraction of LAEs and LBGs hosting low-luminosity or
heavily obscured AGN that could not be detected through X-rays in the existing
Chandra and XMM catalogs.