# Black hole masses of tidal disruption event host galaxies II

## TL;DR

This study analyzes the properties of host galaxies of tidal disruption events, revealing differences in black hole masses, galaxy luminosities, and emission characteristics between optical and X-ray selected samples, and providing insights into their accretion processes.

## Contribution

It provides new spectroscopic measurements of TDE host galaxies, compares optical and X-ray selected hosts, and explores their black hole and galaxy properties with statistical analysis.

## Key findings

- Optical hosts are mostly quiescent galaxies with black hole masses peaking near 10^6 M_sun.
- X-ray hosts include less luminous, lower mass galaxies with different black hole mass distributions.
- X-ray emission regions are smaller and have lower Eddington ratios compared to optical TDEs.

## Abstract

We present new medium resolution, optical long-slit spectra of a sample of 6 UV/optical and 15 X-ray selected tidal disruption event candidate host galaxies. We measure emission line ratios from the optical spectra, finding that the large majority of hosts are quiescent galaxies, while those displaying emission lines are generally consistent with star-formation dominated environments; only 3 sources show clear evidence of nuclear activity. We measure bulge velocity dispersions using absorption lines and infer host black hole (BH) masses using the M-$\sigma$ relation. While the optical and X-ray host BH masses are statistically consistent with coming from the same parent distribution, the optical host distribution has a visible peak near $M_{\rm BH} \sim 10^6 M_\odot$, whereas the X-ray host distribution appears flat in $M_{\rm BH}$. We find a subset of X-ray selected candidates that are hosted in galaxies significantly less luminous (M$_{\rm g}$$\sim$-16) and less massive (stellar mass$\sim$10$^{8.5-9}$M$_{\odot}$) than those of optical events. Using statistical tests we find suggestive evidence that, in terms of black hole mass, stellar mass and absolute magnitude, the hard X-ray hosts differ from the UV/optical and soft X-ray samples. Similar to individual studies, we find that the emission region size for the X-ray sample is much smaller than the optical emission region, consistent with a compact accretion disk. We find a typical Eddington ratio of the X-ray emission is $\sim$0.01, as opposed to the optical events which have L$_{\rm BB}$$\sim$L$_{\rm Edd}$.