The Relationship Between Galaxy ISM and Circumgalactic Gas Metallicities
  We present ISM and CGM metallicities for 25 absorption systems associated
with isolated star-forming galaxies (<z>=0.28) with 9.4<log(M*/Msun)<10.9 and
with absorption detected within 200kpc. Galaxy ISM metallicities were measured
using Ha/[NII] emission lines from Keck/ESI spectra. CGM single-phase
low-ionization metallicities were modeled using MCMC and Cloudy analysis of
absorption from HST/COS and Keck/HIRES or VLT/UVES quasar spectra. We find that
the star-forming galaxy ISM metallicities follow the observed stellar mass
metallicity relation (scatter 0.19dex). CGM metallicity shows no dependence
with stellar mass and exhibits a scatter of ~2dex. All CGM metallicities are
lower than the galaxy ISM metallicities and are offset by log(dZ)=-1.17+/-0.11.
There is no obvious metallicity gradient as a function of impact parameter or
virial radius (<2.3 sigma). There is no relationship between the relative
CGM-galaxy metallicity and azimuthal angle. We find the mean metallicity
differences along the major and minor axes are -1.13+/-0.18 and -1.23+/-0.11,
respectively. Regardless of whether we examine our sample by low/high
inclination or low/high impact parameter, or low/high N(HI), we do not find any
significant relationship with relative CGM-galaxy metallicity and azimuthal
angle. We find that 10/15 low column density systems (logN(HI)<17.2) reside
along the galaxy major axis while high column density systems (logN(HI)>17.2)
reside along the minor axis. This suggest N(HI) could be a useful indicator of
accretion/outflows. We conclude that CGM is not well mixed, given the range of
galaxy-CGM metallicities, and that metallicity at low redshift might not be a
good tracer of CGM processes. Furthermore we should replace integrated
line-of-sight, single phase, metallicities with multi-phase, cloud-cloud
metallicities, which could be more indicative of the physical processes within
the CGM.
