The black hole masses of extremely luminous radio-WISE selected galaxies

Abstract

We present near-IR photometry and spectroscopy of 30 extremely luminous radio and mid-IR selected galaxies. With bolometric luminosities exceeding $\sim 10^{13}$ ${\mathrm{L}}_{\odot }$ and redshifts ranging from $z=0.880-2.853$, we use VLT instruments X-shooter and ISAAC to investigate this unique population of galaxies. Broad multi-component emission lines are detected in 18 galaxies and we measure the near-IR lines $\mathrm{H}{\hat{\mathrm{I}}}^2$, $\text{[OIII]}\hat{\mathrm{I}}»\hat{\mathrm{I}}»4959,5007$ and $\mathrm{H}\hat{\mathrm{I}}\pm$ in six, 15 and 13 galaxies respectively, with 10 $\mathrm{Ly}\hat{\mathrm{I}}\pm$ and five CIV lines additionally detected in the UVB arm. We use the broad $\text{[OIII]}\hat{\mathrm{I}}»5007$ emission lines as a proxy for the bolometric AGN luminosity, and derive lower limits to supermassive black hole masses of $10^{7.9}$-$10^{9.4}$ ${\text{M}}_{\odot }$ with expectations of corresponding host masses of $10^{10.4}$-$10^{12.0}$ ${\text{M}}_{\odot }$. We measure $\hat{\mathrm{I}}{»}_{\mathrm{Edd}}$ > 1 for eight of these sources at a $2\ddot{I}ƒ$ significance. Near-IR photometry and SED fitting are used to compare stellar masses directly. We detect both Balmer lines in five galaxies and use these to infer a mean visual extinction of $A_V$ = 2.68 mag. Due to non-detections and uncertainties in our $\mathrm{H}{\hat{\mathrm{I}}}^2$ emission line measurements, we simulate a broad $\mathrm{H}{\hat{\mathrm{I}}}^2$ line of FWHM = 1480 $\mathrm{km}{\mathrm{s}}^{-1}$ to estimate extinction for all sources with measured $\mathrm{H}\hat{\mathrm{I}}\pm$ emission. We then use this to infer a mean $A_V=3.62$ mag, demonstrating the highly-obscured nature of these galaxies, with the consequence of increasing our estimates of black-hole masses by an 0.5 orders of magnitude in the most extreme and obscured cases.

Accepted for publication in MNRAS. 14 pages (+8 page appendix), 11 figures and 9 tables