Cosmic Evolution of Black Holes and Spheroids. II: Scaling Relations at z=0.36

TL;DR

This study investigates the evolution of black hole and spheroid scaling relations at z=0.36, revealing that spheroids grow significantly over time and challenging the assumption of universal tight relations.

Contribution

It provides new observational evidence that spheroids at z=0.36 do not follow pure luminosity evolution, indicating additional growth mechanisms like mergers are involved.

Findings

Spheroids at z=0.36 are less luminous and have lower velocity dispersions than local counterparts.

Spheroids need to grow about 60% in stellar mass to match local scaling relations.

Evolution follows M/M_sph ~ (1+z)^{1.5+-1.0}.

Abstract

We combine Hubble Space Telescope images of a sample of 20 Seyfert galaxies at z=0.36 with spectroscopic information from the Keck Telescope to determine the black hole mass - spheroid luminosity relation (M-L), the Fundamental Plane (FP) of the host galaxies and the M-sigma relation. Assuming pure luminosity evolution, we find that the host spheroids had smaller luminosity and stellar velocity dispersion than today for a fixed M. The offsets correspond to Delta log L_B,0=0.40+-0.11+-0.15 (Delta log M = 0.51+-0.14+-0.19) and Delta log sigma = 0.13+-0.03+-0.05 (Delta log M = 0.54+-0.12+-0.21), respectively for the M-L and M-sigma relation. A detailed analysis of known systematic errors and selection effects shows that they cannot account for the observed offset. The data are inconsistent with pure luminosity evolution and the existence of universal and tight scaling relations. To obey the three local scaling relations by z=0 the distant spheroids have to grow their stellar mass by approximately 60% (\Delta log M_sph=0.20+-0.14) in the next 4 billion years. The measured evolution can be expressed as M/ M_sph ~ (1+z)^{1.5+-1.0}. Based on the disturbed morphologies of a fraction of the sample (6/20) we suggest collisional mergers with disk-dominated systems as evolutionary mechanism.