The Far‐ and Mid‐Infrared/Radio Correlations in theSpitzerExtragalactic First Look Survey

Using the SPITZER SPACE TELESCOPE and the VLA, we present the first DIRECTevidence that the well-known far-infrared/radio correlation is valid tocosmologically significant redshift. We also confirm, with improved statisticscompared with previous surveys, a similar result for the Mid-IR/radiocorrelation. We explore the dependence of monochromatic q_{24} and q_{70} on z.The results were obtained by matching Spitzer sources at 24 and 70 microns withVLA 1.4 GHz micro-Jy radio sources obtained for the SPITZER FLS. Spectroscopicredshifts have been obtained for over 500 matched IR/radio sources usingobservations at WIYN, Keck and archival SDSS data extending out to z > 2. Wefind that q_{24} shows significantly more dispersion than q_{70}. By comparingthe observed fluxes at 70, 24 and 4.5 microns with a library of SED templates,we find that the larger dispersion in q_{24} is predictable in terms ofsystematic variations in SED shape throughout the population. Although themodels are not able to encompass the full range of observed behavior (both thepresence of either extremely flat or extremely steep IR SEDs), the fittingparameters were used to `k-correct' the higher-z galaxies which resulted in areduced scatter in q. For comparison, we also corrected these data using theSED for M82. The results for 24 and 70 microns provide strong consistentevidence for the universality of the mid-IR/radio and far-IR/radio correlationsout to redshifts of at least z = 1.Comment: 9-pages, 3-figures: Accepted For publication APJS (Spitzer Special Suppliment--Se pt 2004