44 research outputs found
MAGIICAT V. Orientation of Outflows and Accretion Determine the Kinematics and Column Densities of the Circumgalactic Medium
We investigate the dependence of gas kinematics and column densities in the
MgII-absorbing circumgalactic medium on galaxy color, azimuthal angle, and
inclination to trace baryon cycle processes. Our sample of 30 foreground
isolated galaxies at , imaged with the Hubble Space
Telescope, are probed by background quasars within a projected distance of
kpc. From the high-resolution ( km s)
quasar spectra, we quantify the extent of the absorber velocity structure with
pixel-velocity two-point correlation functions. Absorbers with the largest
velocity dispersions are associated with blue, face-on ()
galaxies probed along the projected minor axis (), while
those with the smallest velocity dispersions belong to red, face-on galaxies
along the minor axis. The velocity structure is similar for edge-on () galaxies regardless of galaxy color or azimuthal angle, for red
galaxies with azimuthal angle, and for blue and red galaxies probed along the
projected major axis (). The cloud column densities for
face-on galaxies and red galaxies are smaller than for edge-on galaxies and
blue galaxies, respectively. These results are consistent with biconical
outflows along the minor axis for star-forming galaxies and accreting and/or
rotating gas, which is most easily observed in edge-on galaxies probed along
the major axis. Gas entrained in outflows may be fragmented with large velocity
dispersions, while gas accreting onto or rotating around galaxies may be more
coherent due to large path lengths and smaller velocity dispersions. Quiescent
galaxies may exhibit little-to-no outflows along the minor axis, while
accretion/rotation may exist along the major axis.Comment: 12 pages, 6 figures, 1 table. Accepted for publication in Ap
Low Mass Group Environments have no Substantial Impact on the Circumgalactic Medium Metallicity
We explore how environment affects the metallicity of the circumgalactic
medium (CGM) using 13 low mass galaxy groups (2-5 galaxies) at identified near background quasars. Using quasar spectra
from HST/COS and from Keck/HIRES or VLT/UVES we measure column densities of, or
determine limits on, CGM absorption lines. We use a Markov chain Monte Carlo
approach with Cloudy to estimate metallicities of cool (K) CGM gas
within groups and compare them to CGM metallicities of 47 isolated galaxies.
Both group and isolated CGM metallicities span a wide range ([Si/H]),
where the mean group () and isolated () CGM
metallicities are similar. Group and isolated environments have similar
distributions of {\HI} column densities as a function of impact parameter.
However, contrary to isolated galaxies, we do not find an anti-correlation
between {\HI} column density and the nearest group galaxy impact parameter. We
additionally divided the groups by member luminosity ratios (i.e.,
galaxy-galaxy and galaxy-dwarf groups). While there was no significant
difference in their mean metallicities, a modest increase in sample size should
allow one to statistically identify a higher CGM metallicity in galaxy-dwarf
groups compared to galaxy-galaxy groups. We conclude that either environmental
effects have not played an important role in the metallicity of the CGM at this
stage and expect that this may only occur when galaxies are strongly
interacting or merging, or that some isolated galaxies have higher CGM
metallicities due to past interactions. Thus, environment does not seem to be
the cause of the CGM metallicity bimodality.Comment: 14 pages, 5 figures, 2 figure sets, 1 machine-readable tabl
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 (=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.Comment: 10 pages, 6 figures, 1 table. Accepted to ApJ on October 7, 201
A Complex Multiphase DLA Associated with a Compact Group at z=2.431 Traces Accretion, Outflows, and Tidal Streams
As part of our program to identify host galaxies of known z=2-3 MgII
absorbers with the Keck Cosmic Web Imager (KCWI), we discovered a compact group
giving rise to a z=2.431 DLA with ultra-strong MgII absorption in quasar field
J234628+124859. The group consists of four star-forming galaxies within 8-28
kpc and km s of each other, where tidal streams are weakly
visible in deep HST imaging. The group geometric centre is D=25 kpc from the
quasar (D=20-40 kpc for each galaxy). Galaxy G1 dominates the group
(, M yr) while G2,
G3, and G4 are less massive (,
M yr). Using a VLT/UVES quasar spectrum covering the HI Lyman
series and metal lines such as MgII, SiIII, and CIV, we characterised the
kinematic structure and physical conditions along the line-of-sight with
cloud-by-cloud multiphase Bayesian modelling. The absorption system has a total
and an -weighted mean metallicity of
, with a very large MgII linewidth of km s. The highly kinematically complex profile is
well-modelled with 30 clouds across low and intermediate ionisation phases with
values and
. Comparing these properties to the
galaxy properties, we infer a wide range of gaseous environments, including
metal-rich outflows, metal-poor IGM accretion, and tidal streams from
galaxy--galaxy interactions. This diversity of structures forms the intragroup
medium around a complex compact group environment at the epoch of peak star
formation activity. Surveys of low redshift compact groups would benefit from
obtaining a more complete census of this medium for characterising evolutionary
pathways.Comment: 29 pages, 10 figures. Accepted for publication in MNRAS 28 June 202