Disk Growth in Bulge-Dominated Galaxies: Molecular Gas and Morphological Evolution

TL;DR

This paper investigates the presence and role of molecular gas in early-type galaxies, revealing that such gas can form cold stellar disks and may originate internally or externally, influencing galaxy evolution.

Contribution

It provides new insights into the molecular gas content and kinematics in early-type galaxies, highlighting its potential role in their morphological and stellar evolution.

Findings

Many early-type galaxies contain molecular gas.

Gas forms cold stellar disks of hundreds of pc to over 1 kpc.

Some gas originates from internal stellar mass loss, others from external sources.

Abstract

Substantial numbers of morphologically regular early-type (elliptical and lenticular) galaxies contain molecular gas, and the quantities of gas are probably sufficient to explain recent estimates of the current level of star formation activity. This gas can also be used as a tracer of the processes that drive the evolution of early-type galaxies. For example, in most cases the gas is forming dynamically cold stellar disks with sizes in the range of hundreds of pc to more than one kpc, although there is typically only 1% of the total stellar mass currently available to form young stars. The numbers are still small, but the molecular kinematics indicate that some of the gas probably originated from internal stellar mass loss while some was acquired from outside. Future studies will help to quantify the role of molecular gas (dissipational processes) in the formation of early-type galaxies and their evolution along the red sequence.