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

We present near-IR photometry and spectroscopy of 30 extremely luminous radio and mid-IR selected galaxies. With bolometric luminosities exceeding ∼ 1013 L 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 Hβ, [OIII]λλ4959, 5007 and Hα in six, 15 and 13 galaxies respectively, with 10 Lyα and five Civ lines additionally detected in the UVB arm. We use the broad [OIII]λ5007 emission lines as a proxy for the bolometric AGN luminosity, and derive lower limits to supermassive black hole masses of 107.9-109.4M with expectations of corresponding host masses of 1010.4-1012.0M .We measure λEdd > 1 for eight of these sources at a 2σ 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 AV = 2.68 mag. Due to non-detections and uncertainties in our Hβ emission line measurements, we simulate a broad Hβ line of FWHM = 1480 kms−1 to estimate extinction for all sources with measured Hα emission. We then use this to infer a mean AV = 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.