A Comparison Between the Morphologies and Structures of Dwarf Galaxies with and without Active Massive Black Holes

TL;DR

This study compares the structures of dwarf galaxies with and without active massive black holes, revealing that AGN hosts typically have (pseudo)bulges, unlike many non-AGN dwarf galaxies.

Contribution

It provides the first detailed comparison of morphological features between dwarf galaxies with and without active black holes, highlighting the association with (pseudo)bulges.

Findings

AGN hosts almost always have (pseudo)bulges.

Non-AGN hosts often lack detectable bulges.

AGN hosts have more luminous central point sources.

Abstract

We study the morphologies and structures of 57 dwarf galaxies that are representative of the general population of dwarf galaxies, and compare their demographics to a sample of dwarf galaxies hosting optically-selected AGNs. The two samples span the same galaxy stellar mass ($10^9 \lesssim M_\star/M_\odot \lesssim 10^{9.5}$) and color range, and the observations are well-matched in physical resolution. The fractions of irregular galaxies (14\%) and early-types/ellipticals ($\sim 18\%$) are nearly identical among the two samples. However, among galaxies with disks (the majority of each sample), the AGN hosts almost always have a detectable (pseudo)bulge, while a large fraction of the non-AGN hosts are pure disk galaxies with no detectable (pseudo)bulge. Central point sources of light consistent with nuclear star clusters are detected in many of the non-AGN hosts. In contrast, central point sources detected in the AGN hosts are on average more than two orders of magnitude more luminous, suggesting the point sources in these objects are dominated by AGN light. The preference for (pseudo)bulges in dwarf AGN hosts may inform searches for massive black holes in dwarf galaxies and attempts to constrain the black hole occupation fraction, which in turn has implications for our understanding of black hole seeding mechanisms.