Galaxies 09: Assembly, Gas Content and Star Formation History of Galaxies
Eric Murphy
Caltech
The Far-Infrared--Radio Correlation at High-z: From ALMA to the SKA
Using improved estimates for the IR luminosities of 24~$\mu$m detected sources in GOODS-North, where deep 70~$\mu$m data have been taken as part of the FIDEL survey, we search for, and do not find, significant evidence for evolution in the FIR-radio correlation out to $z\sim2$.
While evolution in the FIR/radio ratios with redshift is not observed, we expect the FIR-radio correlation to deviate as the importance of cosmic-ray electron cooling from Inverse Compton (IC) scattering off of the CMB, whose energy density goes as $U_{\rm CMB} \sim(1+z)^4$, becomes increasingly important relative to synchrotron cooling by a galaxy's internal magnetic field.
To combat IC losses off of the CMB at $z \gtrsim 3$, magnetic field strengths need to reach values in excess of $\gtrsim$50~$\mu$G.
The existence of strong magnetic fields in galaxies at such early epochs relative to the field strengths in galaxies today is unexpected;
magnetic fields are thought to build up over time and not decay quickly.
However, a strong (84~$\mu$G) field has recently been detected at $z\approx0.7$, and radio quiet QSOs at $z\sim6$ appear to lie on the canonical FIR-radio relationship.
After deriving a realistic sensitivity goal for the SKA, we show how the combination of these deep radio continuum surveys with data from future FIR/submm/mm facilities such as $Herschel$, ALMA, CCAT, SPICA, and eventually CALSITO/SAFIR, will help characterize the star-forming, AGN, and magnetic field properties of IR bright ($L_{\rm IR} \gtrsim 10^{11}~L_{\odot};~{\rm SFR} \gtrsim 25~M_{\odot}~{\rm yr}^{-1}$) galaxies at all redshifts.
Furthermore, 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, we argue that deep radio continuum surveys at frequencies larger than $\gtrsim$10~GHz may prove to be the best probe for characterizing the star formation history of the Universe.
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