Spitzer Space Telescope - General Observer Proposal #40026


Characterizing the Stellar Populations in Lyman-Alpha Emitters and Lyman Break
Galaxies at 5.7<z<7 in the Subaru Deep Field

Principal Investigator: Eiichi Egami
           Institution: University of Arizona

     Technical Contact: Eiichi Egami, University of Arizona

Co-Investigators: 
Nobunari Kashikawa, NAOJ, Japan                                       
Kazuhiro Shimasaku, University of Tokyo                               
Masami Ouchi, STScI                                                   
Richard Ellis, Caltech                                                
Johan Richard, Caltech                                                
Daniel Stark, Caltech                                                 
Jean-Paul Kneib, Observatoire de Marseille                            
Jiasheng Huang, CfA                                                   
Kristian Finlator, University of Arizona                              
Romeel Dave, University of Arizona                                    

Science Category: cosmology 
 Observing Modes: IracMap 
  Hours Approved: 102.0 

Abstract:
The epoch of reionization marks a major phase transition of the Universe, during
which the intergalactic space became transparent to UV photons. Determining when
this occurred and the physical processes involved represents the latest frontier
in observational cosmology. Over the last few years, searches have intensified
to identify the population of high-redshift (z>6) galaxies that might be
responsible for this process, but the progress is hampered partly by the
difficulty of obtaining physical information (stellar mass, age, star formation
rate/history) for individual sources. This is because the number of z>6 galaxies
that have both secure spectroscopic redshifts and high-quality infrared
photometry (especially with Spitzer/IRAC) is still fairly small. Considering
that only several photometric points are available per source, and that many
model SEDs are highly degenerate, it is crucial to obtain as many observational
constraints as possible for each source to ensure the validity of SED modeling.
To better understand the physical properties of high-redshift galaxies, we
propose here to conduct HST/NICMOS (72 orbits) and Spitzer/IRAC (102 hours)
imaging of spectroscopically confirmed, bright (z<26 mag (AB)) Ly-alpha emitters
(LAEs) and Lyman-break galaxies (LBGs) at 5.7<z<7 selected from the Subaru Deep
Field. Spectroscopic redshifts remove one critical free parameter from SED
modeling while bright source magnitudes ensure high-quality photometric data.
By making accurate determinations of stellar masses, ages, and star-formation
histories, we will specifically address the following major questions: (1) Do
LAEs and LBGs represent physically different galaxy populations at z>6 as
suggested recently? (2) Is Ly-alpha emission systematically suppressed at z>6
with respect to continuum emission? (i.e., are we reaching the epoch of
incomplete reionization?), and (3) Do we see any sign of abnormally young
stellar population in any of the z>6 galaxies?