Spitzer catalog of Herschel-selected ultrared dusty star-forming galaxies at z ~ 3-6

The largest Herschel extragalactic surveys, HerMES and HATLAS, have selected a large number of luminous infrared galaxies. While most of them are dusty star-forming galaxies (DSFGs) at z~1-2, selecting those with "ultrared" colors (SPIRE S500 > S350 > S250) is extremely efficient for identifying a tail extending towards higher redshift (z > 4). The space density and physical properties of the highest-redshift starbursts provide some of the most stringent constraints on galaxy-formation models. We will present a large Spitzer follow-up program of 300 Herschel ultrared DSFGs. We have obtained high-resolution ALMA and NOEMA data for a subset (~60), which allow us to securely identify the Spitzer/IRAC counterparts and determine whether these galaxies are gravitationally lensed or unlensed. For the rest of the sources, we identify the most probable Spitzer counterparts and their nature (lensed/unlensed) based on the SCUBA-2 positions and presence/absence of optical/near-IR low-z foreground objects identified in SDSS and VIKING etc. surveys. With multi-wavelength ancillary data, we have performed spectral energy distribution (SED) modeling to derive their physical properties and compare with the more numerous z ~ 2 DSFG population. Based on the subset with high-resolution interferometry data, a significant fraction (~0.5) of the ultrared sources are unlensed, intrinsically luminous DSFGs. The median values of the stellar mass, SFR, LIR, Av and dust mass derived from the SED ftting are all higher than those of the z ~ 2 DSFG population. We will also talk about the redshift distribution, SFR surface density, and contribution to cosmic SFR density and their implications on the formation and evolution of DSFGs. A photometric catalog of the Spitzer/IRAC data for the "ultrared" sources as well as the Spitzer-Herschel cross-matched sources in the IRAC fields will be made publicly available.