11241(  1) - 03/30/07 11:01  - [  1]

                  HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 11241

Version: 1    Check-in Time: 30-Mar-2007 15:01:23       STScI Edit Number: 0

Title
IR Background Fluctuations in NICMOS Ultra and Hubble Fields and the Surface Density
of First-Light Galaxies
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Type             Cycle     Parallel Pointing Tolerance
AR               16        <none>
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Investigators
                                                                                     Contact?
    PI: Prof. Asantha Roshan Cooray       University of California - Irvine
   CoI: Dr. Ranga R. Chary                California Institute of Technology            N
   CoI: Mr. Ian S. Sullivan               California Institute of Technology            N
   CoI: Mr. Devdeep S. Sarkar             University of California - Irvine             N
   CoI: Prof. Elizabeth Barton            University of California - Irvine             N
   CoI: Dr. Mark Dickinson                National Optical Astronomy Observatories,     N
                                          AURA
   CoI: Dr. Harry C. Ferguson             Space Telescope Science Institute             N
   CoI: Dr. Daniel Stern                  Jet Propulsion Laboratory                     N
   CoI: Prof. Edward L. Wright            University of California - Los Angeles        N
                                                11241(  1) - 03/30/07 11:01  - [  2]


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Abstract

We propose an archival analysis of F160W and F110W NICMOS Ultra Deep Field (NUDF)
and Hubble Deep Field North (HDFN) data, combined with deep HST ACS images of the
same field, to measure clustering of unresolved IR background (IRB) present in
"empty" pixels. These clustering measurements will be used to study any indications
for the presence of an unresolved, diffuse IR background from redshifts related to
reionization and associated with redshifted UV emission from first-light galaxies
and Lyman-alpha emission from recombinations in surrounding HII halos. The IR
background from these sources are expected to peak at wavelengths between 1 and 2
microns and it's fluctuations have a clustering spectrum distinctively different
from that of low-redshift faint galaxies. We will account for the confusion from
latter with ACS detections of faint blue optical galaxies with no IR counterparts in
NICMOS images. We will cross-correlate unresolved IR fluctuations between F110W and
F160W images of the same field to determine any wavelength dependence of the IR
background and to separate various noise and systematic effects which are not common
to both passbands. We will simulate to estimate the noise floor generated by
residual flat-field errors and the pedestal effect involving varying bias in
different quadrants of the NICMOS array. For IR anisotropy power spectrum
measurements, we will borrow and implement well established techniques used with
cosmic microwave background (CMB) anisotropy maps by the CMB community. At a
wavelength of 1.25 microns, DIRBE indicates a total IRB intensity of 54 +/- 17
nW/m^2/sr or 28 +/- 15 nW/m^2/sr, while about 8 nW/m^2/sr comes from known galaxy
counts. Our clustering measurements, combined with analytical and numerical models,
will lead to a detection of the total IRB intensity from first-light galaxies
containing Pop III stars during reionization as low as 3 nW/m^2/sr. A direct
estimate on the integrated intensity, and thus the surface density of first-light
galaxies, from unresolved IR fluctuations has strong consequences for imaging
searches for high-redshift Lyman-alpha emitters and for models of galaxy formation
and evolution.
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