MIPS 24 Micron Observations of the Hubble Deep Field South: Probing the IR-Radio Correlation of Galaxies at z > 1

TL;DR

This study uses Spitzer MIPS 24 micron data of the Hubble Deep Field South to analyze the IR-radio correlation of galaxies at redshifts greater than 1, revealing differences in IR/radio properties of high-z ULIRGs compared to local ones.

Contribution

First detailed IR-radio correlation analysis at z > 1 using MIPS 24 micron data combined with optical/NIR and radio observations.

Findings

High-redshift (z > 1) ULIRGs have IR/radio SEDs different from local ULIRGs.

Average q_24 ratio for z > 1 sources is consistent with local LIRGs.

Most radio sources without IR detection are radio-loud AGN.

Abstract

We present MIPS 24 micron 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 to ~30 microJy rms, with a median sensitivity of ~20 microJy rms. A total of 495 sources have been cataloged with a signal-to-noise ratio greater than 5 sigma. 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 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 a MIPS detection and are therefore radio-loud AGN, only one radio source has an extreme IRAC 3.6 micron to radio flux density ratio indicating it is a radio-loud AGN at z > 1.