Spitzer IRS 16 micron Observations of the GOODS Fields

TL;DR

This paper presents 16 micron imaging of the GOODS fields using Spitzer, catalogs sources, compares photometry with other surveys, and analyzes galaxy counts and contributions to the extragalactic background light.

Contribution

It provides a new 16 micron catalog for GOODS fields, validates photometry, and analyzes galaxy properties and background light contributions.

Findings

Detected about 1300 sources in GOODS fields.

Galaxy counts agree with previous surveys, with improved uncertainties.

Lower limit on galaxy contribution to background light at 16 microns is 2.2 nW/m^2/sr.

Abstract

We present Spitzer 16 micron imaging of the Great Observatories Origins Deep Survey (GOODS) fields. We survey 150 square arcminutes in each of the two GOODS fields (North and South), to an average 3 sigma depth of 40 and 65 micro-Jy respectively. We detect about 1300 sources in both fields combined. We validate the photometry using the 3-24 micron spectral energy distribution of stars in the fields compared to Spitzer spectroscopic templates. Comparison with ISOCAM and AKARI observations in the same fields show reasonable agreement, though the uncertainties are large. We provide a catalog of photometry, with sources cross correlated with available Spitzer, Chandra, and HST data. Galaxy number counts show good agreement with previous results from ISOCAM and AKARI, with improved uncertainties. We examine the 16 to 24 micron flux ratio and find that for most sources it lies within the expected locus for starbursts and infrared luminous galaxies. A color cut of S_{16}/S_{24}>1.4 selects mostly sources which lie at 1.1<z<1.6, where the 24 micron passband contains both the redshifted 9.7 micron silicate absorption and the minimum between PAH emission peaks. We measure the integrated galaxy light of 16 micron sources, and find a lower limit on the galaxy contribution to the extragalactic background light at this wavelength to be 2.2\pm 0.2$ nW m^{-2} sr^{-1}.