Testing the Evolutionary Link between Type 1 and Type 2 Quasars with
  Measurements of the Interstellar Medium
  In a popular scenario for the coevolution of massive black holes and
galaxies, major mergers of gas-rich galaxies fuel vigorous star formation and
obscured (type 2) quasar activity until energy feedback from the active
galactic nucleus clears away the gas and dust to reveal an unobscured (type 1)
quasar. Under this scenario, the precursor type 2 quasars should be more
gas-rich than their type 1 counterparts, and both types of quasars are expected
to be gas-deficient relative to normal, star-forming galaxies of similar
stellar mass. We test this evolutionary hypothesis by investigating the
infrared (~ 1-500 micron) spectral energy distribution of 86 optically selected
z < 0.5 type 2 quasars, matched in redshift and [O III] luminosity to a
comparison sample of type 1 quasars. Contrary to expectations, the gas content
of the host galaxies of type 2 quasars is nearly indistinguishable from that of
type 1 quasar hosts, and neither type exhibits the predicted deficit in gas
relative to normal galaxies. The gas mass fraction of quasar hosts appears
unaffected by the bolometric luminosity of the active nucleus, although their
interstellar radiation field is preferentially higher than that of normal
galaxies, potentially implicating active galactic nucleus heating of the
large-scale galactic dust.
