CO Excitation and Line Energy Distributions in Gas-selected Galaxies
  While emission-selected galaxy surveys are biased towards the most luminous
part of the galaxy population, absorption selection is a potentially unbiased
galaxy selection technique with respect to luminosity. However, the physical
properties of absorption-selected galaxies are not well characterised. Here we
study the excitation conditions in the interstellar medium (ISM) in damped
Ly$\alpha$ (DLA) absorption-selected galaxies. We present a study of the CO
spectral line energy distribution (SLED) in four high-metallicity
absorption-selected galaxies with previously reported CO detections at
intermediate ($z \sim 0.7$) and high ($z \sim 2$) redshifts. We find further
evidence for a wide variety of ISM conditions in these galaxies. Two out of the
four galaxies show CO SLEDs consistent with that of the Milky Way inner disk.
Interestingly, one of these galaxies is at $z \sim 2$ and has a CO SLED below
that of main-sequence galaxies at similar redshifts. The other two galaxies at
$z>2$ show more excited ISM conditions, with one of them showing thermal
excitation of the mid-$J$ (J$=3, 4$) levels, similar to that seen in two
massive main-sequence galaxies at these redshifts. Overall, we find that
absorption selection traces a diverse population of galaxies.
