Spitzer Space Telescope - General Observer Proposal #30000


Gotcha!  Using Swift GRBs to Pinpoint the Highest Redshift Galaxies

Principal Investigator: Edo Berger
           Institution: Carnegie Observatories

Co-Investigators: 
Lennox Cowie, U. Hawaii                                               
Ranga-Ram Chary, Spitzer Science Center                               
Shirnivas Kulkarni, Caltech                                           
Derek Fox, Pennsylvania State U.                                      
Paul Price, U. Hawaii                                                 
Patrick McCarthy, Carnegie Institution of Washington                  
Brian Schmidt, Australian National University                         
Alicia Soderberg, Caltech                                             
Bradley Cenko, Caltech                                                
Michael Rauch, Carnegie Institution of Washington                     
Michael Gladders, Carnegie Institution of Washington                  
Amy Barger, U. Wisconson, Madison                                     
Bruce Peterson, Australian National University                        
George Djorgovski, Caltech                                            
Eran Ofek, Caltech                                                    

Science Category: high-z galaxies (z>0.5) 
 Observing Modes: IracMap 
  Hours Approved: 20.4 

Abstract:
While there is convincing evidence that the Universe was reionized
between redshifts of 6.5 and 15, the role of galaxies in this process
is still not understood.  Several star-forming galaxies at z~6 have
been identified in recent deep, narrow-field surveys, but the
expensive observations along with cosmic variance and contamination
make it difficult to assess their contribution to reionization, or to
significantly increase the sample.  It has now been demonstrated that
gamma-ray bursts (GRBs) exist at z>6, and we have already obtained HST
and Spitzer observations of the host galaxy of GRB050904 at z=6.295
using our Cycle 14 program.  GRBs have the advantage of being an
uncontaminated signpost for star-formation, and their afterglows are
sufficiently bright even at z>6 to allow photometric selection (via
the Ly-alpha drop out technique) with 2-5 meter telescopes.
Spectroscopic confirmation, including detailed information on the host
ISM, is also likely (as demonstrated in the case of GRB050904).  Using
our approved TOO programs at an extensive range of facilities (2-5m
telescopes up to Keck/Magellan/Gemini), we can rapidly find afterglows
at z>6 and easily distinguish them from dusty low redshift bursts.
This approach is highly efficient compared to current techniques,
especially at z>7.  Our large allocation on Keck/Magellan/Gemini will
also be used to obtain spectroscopy of the afterglows and host
galaxies.  Here we request to continue our program of imaging
GRB-selected z>6 galaxies with NICMOS (z>6), and Spitzer/IRAC to
characterize their properties (SFR, age, morphology, extinction), and
begin to address their role in reionization.  These observations are
requested as >2 month TOOs, allowing flexibility of scheduling and at
the same time taking a unique and timely advantage of the exquisite
performance of three of NASA's premier missions.

This is an HST Cycle 15 Approved HST/Spitzer proposal.