The black hole - host galaxy relation for very low-mass quasars

TL;DR

This study investigates the relationship between black hole and host galaxy masses in low-mass quasars at intermediate redshifts, revealing a bilinear relation consistent with local universe trends after accounting for disc components.

Contribution

It extends the black hole-host galaxy mass relation to lower black hole masses and higher redshifts, incorporating disc corrections to align with local relations.

Findings

Most low-mass quasars lie below the local relation without correction.

Correcting for disc components aligns the relation with local universe trends.

The relation holds over 3.5 dex in black hole and bulge mass after correction.

Abstract

Recently, the relation between the masses of the black hole ($M_{BH}$) and the host galaxy ($M_{host}$) in quasars has been probed down to the parameter space of $M_{BH}\sim10^8 M_\odot$ and $M_{host}\sim10^{11} M_\odot$ at z $<$ 0.5. In this study, we have investigated the $M_{BH}$ - $M_{host}$ log-linear relation for a sample of 37 quasars with low black hole masses ($10^7 M_\odot < M_{BH} < 10^{8.3} M_\odot$) at 0.5 $<$ z $<$ 1.0. The black hole masses were derived using virial mass estimates from SDSS optical spectra. For 25 quasars, we detected the presence of the host galaxy from deep near-infrared H-band imaging, whereas upper limits for the host galaxy luminosity (mass) were estimated for the 12 unresolved quasars. We combined our previous studies with the results from this work to create a sample of 89 quasars at z $<$ 1.0 having a large range of black hole masses ($10^7 M_\odot < M_{BH} < 10^{10} M_\odot$) and host galaxy masses ($10^{10} M_\odot < M_{host} < 10^{13} M_\odot$). Most of the quasars at the low mass end lie below the extrapolation of the local relation. This apparent break in the linearity of the entire sample is due to increasing fraction of disc-dominated host galaxies in the low-mass quasars. After correcting for the disc component, and considering only the bulge component, the bilinear regression for the entire quasar sample holds over 3.5 dex in both the black hole mass and the bulge mass, and is in very good agreement with the local relation. We advocate secular evolution of discs of galaxies being responsible for the relatively strong disc domination.