AAS 205th Meeting, 9-13 January 2005
Session 122 HI and Galactic Disks
Oral, Wednesday, January 12, 2005, 10:00-11:30am, Pacific Salon 1

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[122.01] Linking Gas Fractions to Bimodalities in Galaxy Properties

S. J. Kannappan (UT Austin)

Galaxies over four decades in stellar mass are shown to obey a strong correlation between u-K colors and atomic-gas-to-stellar mass ratios (G/S), using stellar mass-to-light ratios derived from optical colors. The correlation holds for G/S ranging from nearly 10:1 to 1:100 for a sample obtained by merging the SDSS DR2, 2MASS, and HYPERLEDA HI catalogs. This result implies that u-K colors can be calibrated to provide ``photometric gas fractions'' for statistical applications.

This technique is applied to a sample of ~35,000 SDSS-2MASS galaxies to examine the relationship of gas fractions to observed bimodalities in galaxy properties as a function of color and stellar mass. The recently identified transition in galaxy properties at stellar masses ~2--3\times1010 Msun corresponds to a shift in gas richness, dividing low-mass late-type galaxies with G/S ~ 1:1 from high-mass galaxies with intermediate-to-low G/S. Early-type galaxies below the transition mass also show elevated G/S, consistent with formation scenarios involving mergers of low-mass gas-rich systems and/or cold-mode gas accretion.

SJK acknowledges support from an NSF Astronomy and Astrophysics Postdoctoral Fellowship.

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© 2004. The American Astronomical Society.