The low-mass end of the Mbh/Mhost relation in quasars

TL;DR

This study extends the Mbh-Mhost relation in quasars to lower black hole masses (~10^7 Msun), confirming it remains linear and consistent with relations in inactive galaxies, based on imaging and analysis of 26 quasars.

Contribution

It provides the first measurement of the Mbh-Mhost relation slope in quasars at low black hole masses, extending the known parameter space.

Findings

The relation holds over 2 dex in both parameters.

The slope is consistent with a linear relation.

No evidence found for black holes below the relation.

Abstract

The Mbh-Mhost relation in quasars has been probed only in a limited parameter space, namely at Mbh~10^9 Msun and Mhost~10^12 Msun. Here we present a study of 26 quasars lying in the low-mass end of the relation, down to Mbh~10^7 Msun. We selected quasars from the SDSS and HST-FOS archives, requiring modest Mbh (as derived through the virial paradigm). We imaged our sources in H band from the Nordic Optical Telescope. The quasar host galaxies have been resolved in 25 out of 26 observed targets. Host galaxy luminosities and stellar masses are computed, under reasonable assumptions on their star formation histories. Combining these results with those from our previous studies, we manage to extend the sampled parameter space of the Mbh-Mhost relation in quasars. The relation holds over 2 dex in both the parameters, similarly to what observed in low-luminosity AGN and in quiescent galaxies. For the first time, we are able to measure the slope of the Mbh-Mhost relation in quasars. We find that it is consistent with the linear case (similarly to what observed in quiescent galaxies). We do not find any evidence of a population of massive black holes lying below the relation.