Ultra-Deep Ks-band imaging of the HST Frontier Fields (KIFF)

This release provides reduced Ks–band mosaics from the “KIFF” project: Ks-band Imaging of the Hubble Frontier Fields. The first two fields, Abell 2744 and MACS-0416, were observed with HAWK-I on UT4 in P92 (092.A-0472) and the second two fields, Abell S1063, and Abell 370, were observed in P95 (095.A-0533). The quality of the final mosaics are quite uniform between all of the survey fields, reaching point source limiting magnitudes of Ks~26.0 (AB, 5σ) and with superb image quality, FWHM~0.”4 for point sources. This data release also includes the two northern Frontier Fields clusters, MACS-0717 and MACS- 1149, which were observed with shorter integrations with the Keck/MOSFIRE instrument in 2015 and 2016. The final mosaics of the 0717 and 1149 fields have image quality ~0.”4 and 0.”5 and reach limiting depths Ks=25.5 and 25.1, respectively. The Ks -band at 2.2 μm crucially fills the gap between the reddest HST filter (1.6 μm ∼ H band) and the Spitzer/IRAC 3.6 μm passband. The deep Ks-band images provide important constraints on both the redshifts and the stellar population properties of galaxies extending well below the characteristic stellar mass across most of the age of the universe, down to, and including, the redshifts of the targeted galaxy clusters (z ~ 0.5).