A closer view of the radio-FIR correlation: disentangling the
  contributions of star formation and AGN activity
  We extend the Unified Radio Catalog, a catalog of sources detected by various
(NVSS, FIRST, WENSS, GB6) radio surveys, and SDSS, to IR wavelengths by
matching it to the IRAS Point and Faint Source catalogs. By fitting each
NVSS-selected galaxy's NUV-NIR spectral energy distribution (SED) with stellar
population synthesis models we add to the catalog star formation rates, stellar
masses, and attenuations.We further add information about optical emission line
properties for NVSS-selected galaxies with available SDSS spectroscopy. Using
an NVSS 20cm (F_{1.4GHz} ge 2.5mJy) selected sample, matched to the SDSS
spectroscopic ("main" galaxy and quasar) catalogs and IRAS data (0.04<z le 0.2)
we perform an in depth analysis of the radio-FIR correlation for various types
of galaxies, separated into i) quasars, ii) star forming, iii) composite, iv)
Seyfert, v) LINER and vi) absorption line galaxies using the standard optical
spectroscopic diagnostic tools. We utilize SED-based star formation rates to
independently quantify the source of radio and FIR emission in our galaxies.
Our results show that Seyfert galaxies have FIR/radio ratios lower than, but
still within the scatter of, the canonical value due to an additional (likely
AGN) contribution to their radio continuum emission. Furthermore, IR-detected
absorption and LINER galaxies are on average strongly dominated by AGN activity
in both their FIR and radio emission; however their average FIR/radio ratio is
consistent with that expected for star forming galaxies. In summary, we find
that most AGN-containing galaxies in our NVSS-IRAS-SDSS sample have FIR/radio
flux ratios indistinguishable from those of the star-forming galaxies that
define the radio-FIR correlation. Thus, attempts to separate AGNs from
star-forming galaxies by their FIR/radio flux ratios alone can separate only a
small fraction of the AGNs, such as the radio-loud quasars.
