Optical and near-infrared velocity dispersions of early-type galaxies

TL;DR

This study compares optical and near-infrared velocity dispersions in early-type galaxies, finding close agreement and suggesting these galaxies are largely optically thin, with implications for understanding their dust content and structure.

Contribution

It provides a systematic, homogeneous comparison of optical and near-infrared dispersions in early-type galaxies, revealing a close correspondence contrary to previous studies.

Findings

Median fractional difference of 6.4% between dispersions

No significant correlation between dust mass and dispersion difference

Early-type galaxies are largely optically thin

Abstract

We have carried out a systematic, homogeneous comparison of optical and near-infrared dispersions. Our magnitude-limited sample of early-type galaxies in the Fornax cluster comprises 11 elliptical and 11 lenticular galaxies more luminous than MB = -17. We were able to determine the central dispersions based on the near-infrared CO absorption band head for 19 of those galaxies. The velocity dispersions range from less than 70 km/s to over 400 km/s. We compare our near-infrared velocity dispersions to the optical dispersions measured by Kuntschner (2000). Contrary to previous studies, we find a one-to-one correspondence with a median fractional difference of 6.4%. We examine the correlation between the relative dust mass and the fractional difference of the velocity dispersions, but find no significant trend. Our results suggest that early-type galaxies are largely optically thin, which is consistent with recent Herschel observations.