Probing the M-sigma Relation in the Non-Local Universe Using Red QSOs

TL;DR

This study investigates the M-sigma relation in dust-obscured QSOs at intermediate redshifts, revealing an offset from the local relation and a trend with luminosity, suggesting complex galaxy and black hole growth histories.

Contribution

It introduces a method to measure the M-sigma relation in non-local universe dust-obscured QSOs and presents pilot results highlighting potential evolution and luminosity dependence.

Findings

Offset of 0.8 dex from local M-sigma relation in red QSOs

Higher black hole masses compared to local AGN at similar redshifts

Trend of increasing offset with AGN luminosity

Abstract

We describe a method to measure the M-sigma relation in the non-local universe using dust-obscured QSOs. We present results from a pilot sample of nine 2MASS red QSOs with redshifts 0.14<z<0.37. We find that there is an offset (0.8 dex, on average) between the position of our objects and the local relation for AGN, in the sense that the majority of red QSO hosts have lower velocity dispersions and/or more massive BHs than local galaxies. These results are in agreement with recent studies of AGN at similar and higher redshifts. This could indicate an unusually rapid growth in the host galaxies since z~0.2, if these objects were to land in the local relation at present time. However, the z>0.1 AGN (including our sample and those of previous studies) have significantly higher BH mass than those of local AGN, so a direct comparison is not straightforward. Further, using several samples of local and higher-z AGN, we find a striking trend of an increasing offset with respect to the local M-sigma relation as a function of AGN luminosity, with virtually all objects with log(L_5100/erg s^-1) > 43.6 falling above the relation. Given the relatively small number of AGN at z>0.1 for which there are direct measurements of stellar velocity dispersions, it is impossible at present to determine whether there truly is evolution in M-sigma with redshift. Larger, carefully selected samples of AGN are necessary to disentangle the dependence of M-sigma on mass, luminosity, accretion rates, and redshift.