Black Hole Growth, Baryon Lifting, Star Formation, and IllustrisTNG

TL;DR

This paper explores the relationship between black hole growth, baryon lifting, and star formation quenching in massive halos, comparing observational evidence with simulations like IllustrisTNG and EAGLE, and suggesting model improvements.

Contribution

It identifies discrepancies in black hole mass predictions between simulations and observations and proposes parameter adjustments to better reflect baryon lifting and galaxy evolution processes.

Findings

Observational data supports a linear MBH--Mhalo relation up to 10^14 MSun.

IllustrisTNG black holes are too massive at Mhalo < 10^13 MSun.

EAGLE underestimates black hole masses at Mhalo ~10^14 MSun.

Abstract

Quenching of star formation in the central galaxies of cosmological halos is thought to result from energy released as gas accretes onto a supermassive black hole. The same energy source also appears to lower the central density and raise the cooling time of baryonic atmospheres in massive halos, thereby limiting both star formation and black hole growth, by lifting the baryons in those halos to greater altitudes. One predicted signature of that feedback mechanism is a nearly linear relationship between the central black hole's mass (MBH) and the original binding energy of the halo's baryons. We present the increasingly strong observational evidence supporting a such a relationship, showing that it extends up to halos of mass Mhalo ~10^14 MSun. We then compare current observational constraints on the MBH--Mhalo relation with numerical simulations, finding that black hole masses in IllustrisTNG appear to exceed those constraints at Mhalo < 10^13 MSun and that black hole masses in EAGLE fall short of observations at Mhalo ~ 10^14 MSun. A closer look at IllustrisTNG shows that quenching of star formation and suppression of black hole growth do indeed coincide with black hole energy input that lifts the halo's baryons. However, IllustrisTNG does not reproduce the observed MBH--Mhalo relation because its black holes gain mass primarily through accretion that does not contribute to baryon lifting. We suggest adjustments to some of the parameters in the IllustrisTNG feedback algorithm that may allow the resulting black hole masses to reflect the inherent links between black hole growth, baryon lifting, and star formation among the massive galaxies in those simulations.