Towards an Empirical Understanding of Gas Accretion and Star Formation in Galaxies
February 24, 2010
Abstract: The most fascinating aspect of nearby galaxies is the intricately interwoven system of correlations between their global properties. These correlations form the basis of the so-called “scaling laws”, which are fundamental because they provide a quantitative means of characterizing the physical properties of galaxies and their systematics. Theoreticians currently enjoy a rich and diverse array of scaling laws that describe the stellar components of galaxies. Very few well-established scaling laws exist describing how the cold gas is correlated with the other global physical properties of galaxies. This constitutes a serious deficiency in our knowledge, because the gas is the reservoir of material out of which stars are forming at the present day. As such, the gas ought to be much more sensitively linked to formation processes (e.g. accretion) that are occurring now, rather than integrated over timescales of many gigayears, as is the case for the stars. In my talk, I will describe a two-pronged approach for tackling this problem: 1) Theoretical: we are extending existing semi-analytic models of galaxy formation to model how the condensed baryons in disk galaxies are partitioned between atomic gas, molecular gas and stars and to characterize the cold gas scaling properties of galactic disks 2) Observational: I will describe two large programs at Arecibo and at the IRAM 30m telescope to measure accurate and homogeneous HI and molecular gas masses for unbiased samples of galaxies drawn from the Sloan Digital Sky Survey. I will discuss how these surveys are turning up galaxies that are caught in the act of forming their disks at the present day.