The AKARI Deep Field-South: Spitzer 24- and 70-μm observations, catalogues and counts

The AKARI Deep Field-South (ADF-S) is as ~12 deg 2 region near the South Ecliptic Pole that has been observed with deep scans in the far-infrared by the AKARI satellite. As such it is becoming one of the key extragalactic survey fields. We here present complementary observations of the ADF-S conducted by the Spitzer Space Telescope at wavelengths of 24 and 70 μm. We extract source catalogues at each of these wavelengths reaching depths of ~0.2 mJy at 24 μm and ~20 mJy at 70 μm. We also apply a K-to-24 μm colour criterion to select objects with galaxy-like colours in the 24-μm survey. Completeness corrections as a function of flux density are derived for both catalogues by injecting artificial sources of known flux density into the maps, and we find that our surveys are 50 per cent complete at 0.26 and 24 mJy at 24 and 70 μm, respectively. We can thus produce number counts as a function of flux density for the ADF-S at 24 and 70 μm. These are combined with existing literature counts and compared to four different number count models derived from galaxy evolution models. One complicating factor for the ADF-S counts is the presence of a foreground galaxy cluster at z = 0.04 in the field. We examine the ranges of flux densities to which this cluster might make a contribution to the counts and find hints that the 24-μm luminosity function of the cluster galaxies might be enhanced above that of field galaxies. Full catalogues for these ADF-S Spitzer surveys at 24 and 70 μm are made available as part of this paper.