The Growth of Black Holes: Insights From Obscured Active Galaxies

TL;DR

This study analyzes a large sample of obscured active galaxies to understand black hole growth and host galaxy properties, revealing similar black hole masses across different galaxy types and evidence of galaxy-wide influence by black holes.

Contribution

It provides new insights into black hole and host galaxy characteristics in obscured active galaxies using a large SDSS sample and follow-up spectroscopy.

Findings

Black hole masses are narrowly distributed around 10^8 solar masses.

Host galaxies show diverse morphologies, from disks to ellipticals.

Evidence of galaxy-wide influence of black holes on their surroundings.

Abstract

Obscured or narrow-line active galaxies offer an unobstructed view of the quasar environment in the presence of a luminous and vigorously accreting black hole. We exploit the large new sample of optically selected luminous narrow-line active galaxies from the Sloan Digital Sky Survey at redshifts 0.1 < z < 0.45, in conjunction with follow-up observations with the Low Dispersion Survey Spectrograph (LDSS3) at Magellan, to study the distributions of black hole mass and host galaxy properties in these extreme objects. We find a narrow range in black hole mass (<log M_BH/M_sun> = 8.0 +/- 0.7) and Eddington ratio (<log L/L_Edd> = -0.7 +/- 0.7) for the sample as a whole, surprisingly similar to comparable broad-line systems. In contrast, we infer a wide range in star formation properties and host morphologies for the sample, from disk-dominated to elliptical galaxies. Nearly one-quarter have highly disturbed morphologies indicative of ongoing mergers. Unlike the black holes, which are apparently experiencing significant growth, the galaxies appear to have formed the bulk of their stars at a previous epoch. On the other hand, it is clear from the lack of correlation between gaseous and stellar velocity dispersions in these systems that the host galaxy interstellar medium is far from being in virial equilibrium with the stars. While our findings cast strong doubt on the reliability of substituting gas for stellar dispersions in high luminosity active galaxies, they do provide direct evidence that luminous accreting black holes influence their surroundings on a galaxy-wide scale.