Molecular Gas and Star Formation in Local Early-Type Galaxies

TL;DR

This study investigates molecular gas presence and star formation in local early-type galaxies, revealing diverse gas morphologies, external origins, and atypical star formation behaviors, challenging traditional galaxy evolution models.

Contribution

First complete large CO survey of local early-type galaxies, revealing high detection rates and diverse gas morphologies, with implications for galaxy evolution.

Findings

22% detection rate of molecular gas in early-type galaxies

External origin of gas in over a third of systems

Early-type galaxies show diverse star formation behaviors

Abstract

The molecular gas content of local early-type galaxies is constrained and discussed in relation to their evolution. First, as part of the Atlas3D survey, we present the first complete, large (260 objects), volume-limited single-dish survey of CO in normal local early-type galaxies. We find a surprisingly high detection rate of 22%, independent of luminosity and at best weakly dependent on environment. Second, the extent of the molecular gas is constrained with CO synthesis imaging, and a variety of morphologies is revealed. The kinematics of the molecular gas and stars are often misaligned, implying an external gas origin in over a third of the systems, although this behaviour is drastically diffferent between field and cluster environments. Third, many objects appear to be in the process of forming regular kpc-size decoupled disks, and a star formation sequence can be sketched by piecing together multi-wavelength information on the molecular gas, current star formation, and young stars. Last, early-type galaxies do not seem to systematically obey all our usual prejudices regarding star formation, following the standard Schmidt-Kennicutt law but not the far infrared-radio correlation. This may suggest a greater diversity in star formation processes than observed in disk galaxies. Using multiple molecular tracers, we are thus starting to probe the physical conditions of the cold gas in early-types.