BlueTides simulation: establishing black hole-galaxy relations at high-redshift

TL;DR

This study uses the BlueTides simulation to analyze black hole-galaxy scaling relations at high redshift, finding they are consistent with local universe relations but with larger scatter influenced by gas content and star formation activity.

Contribution

First to establish high-redshift black hole-galaxy relations using a large cosmological hydrodynamic simulation, revealing their early development and factors affecting scatter.

Findings

Black hole-galaxy relations at z=8 match local measurements.

Intrinsic scatter is larger at high redshift, influenced by gas fractions.

High gas content increases scatter, but relations tighten when such systems are excluded.

Abstract

The scaling relations between the mass of supermassive black holes ($M_{\bullet}$) and host galaxy properties (stellar mass, $M_{\star}$, and velocity dispersion, $\sigma$), provide a link between the growth of black holes (BHs) and that of their hosts. Here we investigate if and how the BH-galaxy relations are established in the high-$z$ universe using \textsc{BlueTides}, a high-resolution large volume cosmological hydrodynamic simulation. We find the $M_{\bullet}-M_{\star}$ and $M_{\bullet}-\sigma$ relations at $z=8$: $\log_{10}(M_{\bullet}) = 8.25 + 1.10 \ \log_{10}(M_{\star}/10^{11}M_{\odot})$ and $\log_{10}(M_{\bullet}) = 8.35 + 5.31 \ \log_{10}(\sigma/200kms^{-1})$ at $z=8$, both fully consistent with the local measurements. The slope of the $M_{\bullet}-\sigma$ relation is slightly steeper for high star formation rate and $M_{\star}$ galaxies while it remains unchanged as a function of Eddington accretion rate onto the BH. The intrinsic scatter in $M_{\bullet}-\sigma$ relation in all cases ($\epsilon \sim 0.4$) is larger at these redshifts than inferred from observations and larger than in $M_{\bullet}-M_{\star}$ relation ($\epsilon \sim 0.14$). We find the gas-to-stellar ratio $f=M_{\rm gas}/M_{\star}$ in the host (which can be very high at these redshifts) to have the most significant impact setting the intrinsic scatter of $M_{\bullet}-\sigma$. The scatter is significantly reduced when galaxies with high gas fractions ($\epsilon = 0.28$ as $f<10$) are excluded (making the sample more comparable to low-$z$ galaxies); these systems have the largest star formation rates and black hole accretion rates, indicating that these fast-growing systems are still moving toward the relation at these high redshifts. Examining the evolution (from $z=10$ to 8) of high mass black holes in $M_{\bullet}-\sigma$ plane confirms this trend.