Dynamics of Companion Galaxies of Early-Type Galaxies

TL;DR

This study estimates the dynamical masses of early-type galaxies using satellite galaxy dynamics, revealing that ETGs likely have more elliptical satellite orbits and higher mass-to-baryon ratios compared to spiral galaxies.

Contribution

It introduces a simple model linking satellite orbital shapes to dynamical mass estimates, providing new insights into the orbital characteristics of satellite galaxies around ETGs.

Findings

ETGs have higher dynamical mass-to-baryon ratios than spiral galaxies.

Satellite orbits around ETGs tend to be more elliptical.

Dynamical mass estimates depend on satellite orbital shape.

Abstract

We estimated the dynamical masses of 115 early-type galaxies (ETGs) by analyzing the dynamics of satellite and companion galaxies of these ETGs. We selected galaxies with absolute magnitudes between -22 and -25 in the $K_s$-band from the Extragalactic Distance Database (EDD). We also selected 216 spiral galaxies for comparison. We employed a simple model to simulate the observed dynamical mass from satellite galaxies at various distances. Our simulations showed that the dynamical masses derived from satellite galaxies with elliptical orbits would be smaller than those with circular orbits even they contain the same dark mass halos. Therefore, relationships between the observed $M_\mathrm{dyn}/M_\mathrm{b}$ distributions and distances would depend on orbital shapes. From the relationships between our observed $M_\mathrm{dyn}/M_\mathrm{b}$ distributions and distances, we suggest that the satellite galaxies of the ETGs have relatively more elliptical orbits than those of the spiral galaxies have and the $M_\mathrm{dyn}/M_\mathrm{b}$ of the ETGs are greater than that of the spiral galaxies.