Scaling relations between black holes and their host galaxies: comparing theoretical and observational measurements, and the impact of selection effects

TL;DR

This study uses high-resolution simulations to analyze black hole-host galaxy scaling relations, comparing theoretical predictions with observations, and examining how selection effects influence perceived evolution and scatter in these relations.

Contribution

It provides a detailed comparison between simulated and observed black hole-galaxy relations, highlighting the impact of selection biases and characterizing black hole growth trajectories.

Findings

Good agreement between simulations and observations at high masses.

Selection biases can lead to overestimated evolution in scaling relations.

Black holes grow faster than hosts below the local relation, then slow down after surpassing it.

Abstract

We use the high-resolution simulation MassiveBlackII to examine scaling relations between black hole mass (MBH) and host galaxy properties (sigma, M*, and LV), finding good agreement with observational data, especially at the high-mass end. The simulations have less intrinsic scatter than observations, and the MBH-LV correlation has the largest scatter, suggesting it may the the least fundamental of the three relations. We find Gaussian scatter about all three relations, except among the highest mass galaxies, which host more massive black holes. Below z~2 the slopes for the full population remain roughly z-independent, and only steepen by 50% by z~4. The normalization of the sigma, LV relations evolve by 0.3, 0.43 dex, while the MBH correlation does not evolve to at least z~2. Testing for selection biases, we find samples selected by MBH or M* have steeper slopes than randomly selected samples. If unaccounted for, such a selection function would find faster evolution than inferred from a randomly selected sample, as objects at the highend of the relation tend to evolve more rapidly. We find a potential bias among high-LBH subsamples (tending to reside in higher mass galaxies), but these bright-AGN exhibit no intrinsic bias relative to fainter ones in equivalent-mass hosts, nor is there a significant difference between active- and inactive-samples. Finally we characterize the evolution of individual black holes along the scaling planes. Below the local relation, black holes grow faster than their host (72% of black holes 0.3 dex below the mean relation have a MBH-M* trajectory steeper than the local relation), while those above have shallower trajectories (only 14% are steeper than local). Black holes tend to grow faster than their hosts until surpassing the local relation, at which point their growth is suppressed while their hosts continue to grow, returning them to the mean relation.