The Role of Cold Gas in Massive Galaxy Evolution

Book excerpt: Finally, in Chapter 4 we demonstrate the utility of scaling relations derived from large datasets by using the gas fraction scaling relation to select an anomalous sample of massive HI-rich galaxies with surprisingly low levels of star formation. We obtain HI imaging of these galaxies to ascertain why so much of their cold gas content is not participating in star formation. All of the galaxies we observe exhibit extended HI disks whose gas surface densities are below the threshold required for star formation. Since this type of galaxy is most prevalent at stellar masses above the transition mass noted in Kauffmann et al. (2003), it is possible that the processes inhibiting star formation in these galaxies contribute to the change in star-forming properties above the transition mass.