NRAO/Socorro Colloquium Series

Martin Bureau

University of Oxford

Molecular gas and star formation in early-Type Galaxies

Despite pervasive residual star formation, early-type galaxies are generally considered "red and dead", composed exclusively of old stars with no star formation. Here, their molecular gas content is constrained and discussed in relation to their evolution, supporting the continuing importance of minor mergers and/or cold gas accretion. First, as part of the Atlas3D survey, the first complete, large, volume-limited survey of CO in normal early-type galaxies is presented. At least of 23% of local early-types possess a substantial amount of molecular gas, the necessary ingredient for star formation, independent of mass and environment. Second, using CO synthesis imaging, the extent of the molecular gas is constrained 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 all systems, more than half in the field, while external gas accretion is shut down in clusters. 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. Fourth, early-type galaxies do not seem to systematically obey all our usual prejudices regarding star formation (e.g. Kennicutt-Schmidt law, far infrared-radio continuum correlation), suggesting a greater diversity of star formation processes than observed in disk galaxies. Lastly, a first step toward constraining the physical properties of the molecular gas in early-type galaxies is taken, by modeling the line ratios of density-and opacity-sensitive molecules in a few objects. Taken together,these observations provide a much greater understanding of the gas cycle in local early-type galaxies, and argue for the continuing importance of (minor) mergers and cold gas accretion. In the future, spatially-resolved ALMA observations of high-density molecular gas tracers will probe the interstellar medium and star formation laws locally, in a regime entirely different from that normally probed in spiral galaxies.

January 27, 2012
11:00 am

Array Operations Center Auditorium

All NRAO employees are invited to attend via video, available in Charlottesville Room 230, Green Bank Room 137 and Tucson N525.

Local Host: Lisa Young