A systematic study of the inner rotation curves of galaxies observed as
  part of the GASS and COLD GASS surveys
  We present a systematic analysis of the rotation curves of 187 galaxies with
masses greater than 10^10 M_sol, with atomic gas masses from the GALEX Arecibo
Sloan Survey (GASS), and with follow-up long-slit spectroscopy from the MMT.
Our analysis focuses on stellar rotation curves derived by fitting stellar
template spectra to the galaxy spectra binned along the slit. In this way, we
are able to obtain accurate rotation velocity measurements for a factor of 2
more galaxies than possible with the Halpha line. Galaxies with high atomic gas
mass fractions are the most dark-matter dominated galaxies in our sample and
have dark matter halo density profiles that are well fit by Navarro, Frenk &
White profiles with an average concentration parameter of 10. The inner slopes
and of the rotation curves correlate more strongly with stellar population age
than with galaxy mass or structural parameters. At fixed stellar mass, the
rotation curves of more actively star-forming galaxies have steeper inner
slopes than less actively star-forming galaxies. The ratio between the galaxy
specific angular momentum and the total specific angular momentum of its dark
matter halo, R_j, correlates strongly with galaxy mass, structure and gas
content. Low mass, disk-dominated galaxies with atomic gas mass fractions
greater than 20% have median values of R_j of around 1, but massive,
bulge-dominated galaxies have R_j=0.2-0.3. We argue that these trends can be
understood in a picture where gas inflows triggered by disk instabilities lead
to the formation of passive, bulge-dominated galaxies with low specific angular
momentum.
