Towards an Empirical Understanding of Gas Accretion and Star Formation in Galaxies

Guinevere Kauffmann (MPA Garching)

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.