On the radial profile of gas-phase Fe/{\alpha} ratio around distant
  galaxies
  This paper presents a study of the chemical compositions in cool gas around a
sample of 27 intermediate-redshift galaxies. The sample comprises 13 massive
quiescent galaxies at z=0.40-0.73 probed by QSO sightlines at projected
distances d=3-400 kpc, and 14 star-forming galaxies at z=0.10-1.24 probed by
QSO sightlines at d=8-163 kpc. The main goal of this study is to examine the
radial profiles of the gas-phase Fe/{\alpha} ratio in galaxy halos based on the
observed Fe II to Mg II column density ratios. Because Mg+ and Fe+ share
similar ionization potentials, the relative ionization correction is small in
moderately ionized gas and the observed ionic abundance ratio N(Fe II)/N(Mg II)
places a lower limit to the underlying (Fe/Mg) elemental abundance ratio. For
quiescent galaxies, a median and dispersion of log <N(Fe II)/N(Mg II)>
=-0.06+/-0.15 is found at d<~60 kpc, which declines to log <N(Fe II)/N(Mg II)>
<-0.3 at d>~100 kpc. On the other hand, star-forming galaxies exhibit log <N(Fe
II)/N(Mg II)> =-0.25+/-0.21 at d<~60 kpc and log <N(Fe II)/N(Mg II)>
=-0.9+/-0.4 at larger distances. Including possible differential dust depletion
or ionization correction would only increase the inferred (Fe/Mg) ratio. The
observed N(FeII)/N(Mg II) implies super-solar Fe/{\alpha} ratios in the inner
halo of quiescent galaxies. An enhanced Fe abundance indicates a substantial
contribution by Type Ia supernovae in the chemical enrichment, which is at
least comparable to what is observed in the solar neighborhood or in
intracluster media but differs from young star-forming regions. In the outer
halos of quiescent galaxies and in halos around star-forming galaxies, however,
the observed N(Fe II)/N(Mg II) is consistent with an {\alpha}-element enhanced
enrichment pattern, suggesting a core-collapse supernovae dominated enrichment
history.
