The Microjansky Radio Galaxy Population

We use highly spectroscopically complete observations of the radio sourcesfrom the VLA 1.4 GHz survey of the HDF-N region to study the faint radio galaxypopulation and its evolution. We spectrally classify the sources into fourspectral types: absorbers, star formers, Seyfert galaxies, and broad-line AGNs,and we analyze their properties by type. We supplement the spectroscopicredshifts with photometric redshifts measured from the rest-frame UV to MIRspectral energy distributions. Using deep X-ray observations of the field, wedo not confirm the existence of an X-ray-radio correlation for star-forminggalaxies. We also do not observe any correlations between 1.4 GHz flux and Rmagnitude or redshift. We find that the radio powers of the host galaxies risedramatically with increasing redshift, while the optical properties of the hostgalaxies show at most small changes. Assuming that the locally determinedFIR-radio correlation holds at high redshifts, we estimate total FIRluminosities for the radio sources. We note that the FIR luminosity estimatesfor any radio-loud AGNs will be overestimates. Considering only the radiosources with quasar-like bolometric luminosities, we find a maximum ratio ofcandidate highly-obscured AGNs to X-ray-luminous (>10^42 ergs/s) sources ofabout 1.9. We use source-stacking analyses to measure the X-ray surfacebrightnesses of various X-ray and radio populations. We find the contributionsto the 4-8 keV light from our candidate highly-obscured AGNs to be very small,and hence these sources are unable to account for the light that has beensuggested may be missing at these energies.