Classical bulges, supermassive blackholes and AGN feedback: Extension to low-mass galaxies

TL;DR

This paper extends empirical models to predict the relationship between supermassive black holes and galaxy properties in low-mass galaxies, highlighting a new linear sequence with lower amplitude and implications for galaxy evolution and feedback.

Contribution

It introduces a model predicting SMBH and bulge relations in low-mass galaxies, revealing a new linear sequence and its role in feedback processes at high redshift.

Findings

Predicted a $M_{BH}$-$M_*$ relation with a lower amplitude in low-mass galaxies.

Identified a new linear sequence at $M_* < 10^{10.5} M_\odot$.

Suggested SMBH feedback heats circum-galactic medium, affecting star formation.

Abstract

The empirical model of Lu et al. 2014a for the relation between star formation rate and halo mass growth is adopted to predict the classical bulge mass ($M_{\rm cb}$) - total stellar mass ($M_\star$) relation for central galaxies. The assumption that the supermassive black hole (SMBH) mass ($M_{\rm BH}$) is directly proportional to the classical bulge mass, with the proportionality given by that for massive galaxies, predicts a $M_{\rm BH}$ - $M_\star$ relation that matches well the observed relation for different types of galaxies. In particular, the model reproduces the strong transition at $M_\star=10^{10.5}$ - $10^{11}M_{\odot}$, below which $M_{\rm BH}$ drops rapidly with decreasing $M_\star$. Our model predicts a new sequence at $M_\star <10^{10.5}M_{\odot}$, where $M_{\rm BH} \propto M_\star$ but the amplitude is a factor of $\sim 50$ lower than the amplitude of the sequence at $M_\star>10^{11}M_{\odot}$. If all SMBH grow through similar quasar modes with a feedback efficiency of a few percent, the energy produced in low-mass galaxies at redshift $z\gtrsim 2$ can heat the circum-galactic medium up to a specific entropy level that is required to prevent excessive star formation in low-mass dark matter halos.