MIPS 24 μm observations of the hubble deep field south: probing the IR-radio correlation of galaxies at z > 1

Abstract

We present MIPS 24 μm observations of the Hubble Deep Field South taken with the Spitzer Space Telescope. The resulting image is 254 arcmin^2 in size and has a sensitivity ranging between ~12 and ~30 μJy rms, with a median sensitivity of ~20 μJy rms. A total of 495 sources have been cataloged with a signal-to-noise ratio greater than 5σ. The source catalog is presented as well as source counts which have been corrected for completeness and flux boosting. The IR sources are then combined with MUSYC optical/NIR and ATHDFS radio observations to obtain redshifts and radio flux densities of the sample.We use the IR/radio flux density ratio (q_(24)) to explore the IR–radio correlation for this IR sample and find q_(24) = 0.71 ± 0.31 for sources detected in both IR and radio. The results are extended by stacking IR sources not detected in the radio observations and we derive an average q_(24) for redshift bins between 0 < z < 2.5. We find that the high-redshift (z > 1) sources have an average q_(24) ratio which is better fit by local LIRG SEDs rather than local ULIRG SEDs, indicating that high-redshift ULIRGs differ in their IR/radio properties. So, ULIRGs at high-redshift have SEDs different from those found locally. Infrared-faint radio sources are examined, and while nine radio sources do not have an MIPS detection and are therefore radio-loud active galactic nuclei (AGNs), only one radio source has an extreme IRAC 3.6μm to radio flux density ratio indicating it is a radio-loud AGN at z > 1.

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