Spitzer Imaging of Herschel Lensed Sub-mm Galaxies

Sub-millimeter surveys have, in the last decade, revealed an unexpected population of high-redshift dust-obscured sub-mm galaxies (SMGs) which are forming stars at a tremendous rate. Due to steep number counts and the negative k-correction at sub-mm wavelengths sub-mm surveys are effective at finding intrinsically faint, gravitationally lensed galaxies. We have now produced a reliable list of about 150 bright lensed SMGs in 200 sq. deg of the Herschel-ATLAS and HerMES (the GTO program of the SPIRE Instrument team) surveys with Herschel-SPIRE. We propose Spitzer IRAC 3.6 and 4.5 micron imaging of 122 of these gravitationally lensed SMGs. The target SMGs are selected to maximally overlap with existing and planned multi-wavelength followup programs, without duplicating existing deep IRAC data. Using the proposed Spitzer data we will: (a) Extend the SEDs of z~ 1 to 5 lensed SMGs into the near-IR regime, where derived stellar masses are more reliable than those estimated at other wavelengths alone; (b) Combine with lens models from existing and planned high-resolution sub-mm imaging (SMA, CARMA, PdBI) to map the evolution of stellar mass as a function of redshift and star-formation rate (SFR); (c) Combine with existing and planned CO and CII molecular line measurements to map the evolution of dust-to-gas and stellar-to-gas mass ratios as a function of redshift and SFR; (d) Obtain snapshot statistics on the sub-mm galaxy evolution from z of 1 to 5 as a function of stellar, dust, and gas mass to study the role of mergers and AGN contribution that may regulate the starburst phenomenon; (e) Compare our results to those from numerical simulations of high-redshift starburst galaxies to investigate the physical conditions in SMGs, and their evolutionary pathways