TY - JOUR
T1 - The Relationship between Galaxy ISM and Circumgalactic Gas Metallicities
AU - Kacprzak, Glenn G.
AU - Pointon, Stephanie K.
AU - Nielsen, Nikole M.
AU - Churchill, Christopher W.
AU - Muzahid, Sowgat
AU - Charlton, Jane C.
N1 - Funding Information:
Australian Research Council through a Discovery Project DP170103470.
Publisher Copyright:
© 2019. The American Astronomical Society. All rights reserved..
PY - 2019/12/1
Y1 - 2019/12/1
N2 - We present interstellar matter (ISM) and circumgalactic medium (CGM) metallicities for 25 absorption systems associated with isolated star-forming galaxies (="$\left\langle z\right\rangle =0.28$" SRC="apjab4c3cieqn1.gif"/>) with 9.4 ≤ log(M ∗/M o˙) ≤ 10.9 and with absorption detected within (200 kpc). Galaxy ISM metallicities were measured using Hα/[N ii] emission lines from Keck/ESI spectra. CGM single-phase low-ionization metallicities were modeled using Markov Chain Monte Carlo 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 (1σ scatter 0.19 dex). CGM metallicity shows no dependence with stellar mass and exhibits a scatter of ∼2 dex. 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 (<2.3σ significance). 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(H i), 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(H i) < 17.2) reside along the galaxy major axis while high column density systems (logN(H i) ≥ 17.2) reside along the minor axis. This suggests N(H i) 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. On the other hand, we should replace integrated line-of-sight, single-phase metallicities with multiphase, cloud-cloud metallicities, which could be more indicative of the physical processes within the CGM.
AB - We present interstellar matter (ISM) and circumgalactic medium (CGM) metallicities for 25 absorption systems associated with isolated star-forming galaxies (="$\left\langle z\right\rangle =0.28$" SRC="apjab4c3cieqn1.gif"/>) with 9.4 ≤ log(M ∗/M o˙) ≤ 10.9 and with absorption detected within (200 kpc). Galaxy ISM metallicities were measured using Hα/[N ii] emission lines from Keck/ESI spectra. CGM single-phase low-ionization metallicities were modeled using Markov Chain Monte Carlo 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 (1σ scatter 0.19 dex). CGM metallicity shows no dependence with stellar mass and exhibits a scatter of ∼2 dex. 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 (<2.3σ significance). 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(H i), 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(H i) < 17.2) reside along the galaxy major axis while high column density systems (logN(H i) ≥ 17.2) reside along the minor axis. This suggests N(H i) 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. On the other hand, we should replace integrated line-of-sight, single-phase metallicities with multiphase, cloud-cloud metallicities, which could be more indicative of the physical processes within the CGM.
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U2 - 10.3847/1538-4357/ab4c3c
DO - 10.3847/1538-4357/ab4c3c
M3 - Article
AN - SCOPUS:85077441338
SN - 0004-637X
VL - 886
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 91
ER -