Radio Sources in the Nearby Universe

Abstract

We identified 15,658 NVSS radio sources among the 55,288 2MASX galaxies brighter than $k_\mathrm{20fe} = 12.25$ at $\lambda = 2.16\,\mu\mathrm{m}$ and covering the $\Omega =7.016$ sr of sky defined by J2000 $\delta > -40^\circ$ and $\vert b \vert > 20^\circ$. The complete sample of 15,043 galaxies with 1.4 GHz flux densities $S \geq 2.45 \mathrm{~mJy}$ contains a 99.9% spectroscopically complete subsample of 9,517 galaxies with $k_\mathrm{20fe} \leq 11.75$. We used only radio and infrared data to quantitatively distinguish radio sources powered primarily by recent star formation from those powered by active galactic nuclei. The radio sources with $\log[L(\mathrm{W~Hz}^{-1})] > 19.3$ that we used to derive the local spectral luminosity and power-density functions account for $>99$% of the total 1.4~GHz spectral power densities $U_\mathrm{SF} = (1.54 \pm 0.20) \times 10^{19} \mathrm{~W~Hz}^{-1} \mathrm{~Mpc}^{-3}$ and $U_\mathrm{AGN} = (4.23 \pm 0.78) \times 10^{19} \mathrm{~W~Hz}^{-1} \mathrm{~Mpc}^{-3}$ in the universe today, and the spectroscopic subsample is large enough that the quoted errors are dominated cosmic variance. The recent comoving star-formation rate density indicated by $U_\mathrm{SF}$ is $\psi \approx 0.015~ M_\odot \mathrm{~yr}^{-1} \mathrm{~Mpc}^{-3}$.