THE FAR-INFRARED-RADIO CORRELATION AT HIGH REDSHIFTS: PHYSICAL CONSIDERATIONS AND PROSPECTS FOR THE SQUARE KILOMETER ARRAY

I present a predictive analysis for the behavior of the far-infrared (FIR)-radio correlation as a function of redshift in light of the deep radio continuum surveys which may become possible using the Square Kilometer Array (SKA). To keep a fixed ratio between the FIR and predominantly non-thermal radio continuum emission of a normal star-forming galaxy, whose cosmic-ray electrons typically lose most of their energy to synchrotron radiation and inverse Compton (IC) scattering, requires a nearly constant ratio between galaxy magnetic field and radiation field energy densities. While the additional term of IC losses off of the cosmic microwave background (CMB) is negligible in the local universe, the rapid increase in the strength of the CMB energy density (i.e., similar to(1 + z)(4)) suggests that evolution in the FIR-radio correlation should occur with infrared (IR; 8-1000 mu m)/radio ratios increasing with redshift. This signature should be especially apparent once beyond z similar to 3 where the magnetic field of a normal star-forming galaxy must be similar to 50 mu G to save the FIR-radio correlation. At present, observations do not show such a trend with redshift; z similar to 6 radio-quiet quasars appear to lie on the local FIR-radio correlation while a sample of z similar to 4.4 and z similar to 2.2 submillimeter galaxies exhibit ratios that are a factor of similar to 2.5 below the canonical value. I also derive a 5 sigma point-source sensitivity goal of approximate to 20 nJy (i.e., sigma(rms) similar to 4 nJy) requiring that the SKA specified sensitivity be A(eff)/T-sys approximate to 15,000 m(2) K-1; achieving this sensitivity should enable the detection of galaxies forming stars at a rate of greater than or similar to 25 M-circle dot yr(-1), such as typical luminous infrared galaxies (i.e., L-IR greater than or similar to 10(11) L-circle dot), at all redshifts if present. By taking advantage of the fact that the non-thermal component of a galaxy's radio continuum emission will be quickly suppressed by IC losses off of the CMB, leaving only the thermal (free-free) component, I argue that deep radio continuum surveys at frequencies greater than or similar to 10 GHz may prove to be the best probe for characterizing the high-z star formation history of the universe unbiased by dust.