We present interstellar matter (ISM) and circumgalactic medium (CGM) metallicities for 25 absorption systems associated with isolated star-forming galaxies ( ) with 9.4 ≤ log(M*/M ) ≤ 10.9 and with ...absorption detected within (200 kpc). Galaxy ISM metallicities were measured using H /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 (1 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 (<2.3 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.
ABSTRACT We report a bimodality in the azimuthal angle (Φ) distribution of gas around galaxies traced by O vi absorption. We present the mean Φ probability distribution function of 29 Hubble Space ...Telescope-imaged O vi absorbing (EW > 0.1 ) and 24 non-absorbing (EW < 0.1 ) isolated galaxies (0.08 0.67) within ∼200 kpc of background quasars. We show that equivalent width (EW) is anti-correlated with impact parameter and O vi covering fraction decreases from 80% within 50 kpc to 33% at 200 kpc. The presence of O vi absorption is azimuthally dependent and occurs between 10°-20° of the galaxy projected major axis and within 30° of the projected minor axis. We find higher EWs along the projected minor axis with weaker EWs along the project major axis. Highly inclined galaxies have the lowest covering fractions due to minimized outflow/inflow cross-section geometry. Absorbing galaxies also have bluer colors while non-absorbers have redder colors, suggesting that star formation is a key driver in the O vi detection rate. O vi surrounding blue galaxies exists primarily along the projected minor axis with wide opening angles while O vi surrounding red galaxies exists primarily along the projected major axis with smaller opening angles, which may explain why absorption around red galaxies is less frequently detected. Our results are consistent with a circumgalactic medium (CGM) originating from major axis-fed inflows/recycled gas and from minor axis-driven outflows. Non-detected O vi occurs between Φ = 20°-60°, suggesting that O vi is not mixed throughout the CGM and remains confined within the outflows and the disk-plane. We find low O vi covering fractions within of the projected major axis, suggesting that cool dense gas resides in a narrow planer geometry surrounded by diffuse O vi gas.
In this third paper of a series studying the Magellanic gas in absorption, we analyze the gas ionization level using a sample of 69 Hubble Space Telescope/Cosmic Origins Spectrograph sightlines that ...pass through or within 30degrees of the 21 cm emitting regions. We find that 81% (56/69) of the sightlines show UV absorption at Magellanic velocities, indicating that the total cross-section of the Magellanic System is approximately 11,000 deg super(2), or around one-quarter of the entire sky. Using observations of the Si III/Si II ratio together with Cloudy photoionization modeling, we calculate the total gas mass (atomic plus ionized) of the Magellanic System to be approximately 2.0 x 10 super(9) M sub(middot in circle) (d/55 kpc) super(2), with the ionized gas contributing around three times as much mass as the atomic gas. This is larger than the current-day interstellar HI mass of both Magellanic Clouds combined, indicating that they have lost most of their initial gas mass.
Abstract
We introduce a Bayesian approach coupled with a Markov Chain Monte Carlo method and the maximum-likelihood statistic for fitting the profiles of narrow absorption lines (NALs) in quasar ...spectra. This method also incorporates the overlap between different absorbers. We illustrate and test this method by fitting models to a “mini-broad” (mini-BAL) and six NAL profiles in four spectra of the quasar UM 675 taken over a rest-frame interval of 4.24 yr. Our fitting results are consistent with past results for the mini-BAL system in this quasar by Hamann et al. We also measure covering factors (
C
f
) for two narrow components in the C
iv
and N
v
mini-BALs and their overlap covering factor with the broad component. We find that
C
f
(N
v
) is always larger than
C
f
(C
iv
) for the broad component, while the opposite is true for the narrow components in the mini-BAL system. This could be explained if the broad and narrow components originated in gas at different radial distances, but it seems more likely to be due to being produced by gas at the same distance but with different gas densities (i.e., ionization states). The variability detected only in the broad absorption component in the mini-BAL system is probably due to gas motion, since both
C
f
(C
iv
) and
C
f
(N
v
) vary. We determine for the first time that multiple absorbing clouds (i.e., a broad and two narrow components) overlap along our line of sight. We conclude that the new method improves fitting results considerably compared to previous methods.
ABSTRACT
We present an ultraviolet quasar absorption line analysis of metal lines associated with three strong intervening H i absorbers (with $N(\rm {{H}\,{\small I}})$ > 1016.5 cm−2) detected in ...the outskirts of Sunyaev–Zel’dovich (SZ) effect-selected galaxy clusters (zcl ∼ 0.4–0.5), within clustocentric impact parameters of ρcl ∼ (1.6–4.7)r500. Discovered in a recent set of targeted far-UV HST/COS spectroscopic observations, these absorbers have among the highest H i column densities ever observed in the outskirts of galaxy clusters, and are also rich in metal absorption lines. Photoionization models yield single phase solutions for the three absorbers with gas densities of nH ∼ 10−3–10−4 cm−3 and metallicities of X/H > −1.0 (from one-tenth solar to near-solar). The widths of detected absorption lines suggest gas temperatures of T ∼ 104 K. The inferred densities (temperatures) are significantly higher (lower) compared to the X-ray emitting intracluster medium in cluster cores. The absorbers are tracing a cool phase of the intracluster gas in the cluster outskirts, either associated with gas stripped from cluster galaxies via outflows, tidal streams or ram-pressure forces, or denser regions within the intracluster medium that were uniformly chemically enriched from an earlier epoch of enhanced supernova and Active Galactic Nucleus (AGN) feedback.
We investigate the geometric distribution of gas metallicities in the circumgalactic medium (CGM) around 47, z < 0.7 galaxies from the "Multiphase Galaxy Halos" Survey. Using a combination of quasar ...spectra from Hubble Space Telescope (HST)/COS and from Keck/HIRES or Very Large Telescope/UVES, we measure column densities of, or determine limits on, CGM absorption lines. We then use a Markov Chain Monte Carlo approach with Cloudy to estimate the metallicity of cool (T ∼ 104 K) CGM gas. We also use HST images to determine host-galaxy inclination and quasar-galaxy azimuthal angles. Our sample spans a H i column density range of 13.8 cm−2 < < 19.9 cm−2. We find (1) while the metallicity distribution appears bimodal, a Hartigan dip test cannot rule out a unimodal distribution (0.4 ). (2) CGM metallicities are independent of halo mass, spanning three orders of magnitude at a fixed halo mass. (3) The CGM metallicity does not depend on the galaxy azimuthal and inclination angles regardless of H i column density, impact parameter, and galaxy color. (4) The ionization parameter does not depend on azimuthal angle. We suggest that the partial Lyman limit metallicity bimodality is not driven by a spatial azimuthal bimodality. Our results are consistent with simulations where the CGM is complex and outflowing, accreting, and recycled gas are well-homogenized at z < 0.7. The presence of low-metallicity gas at all orientations suggests that cold streams of accreting filaments are not necessarily aligned with the galaxy plane at low redshifts or intergalactic transfer may dominate. Finally, our results support simulations showing that strong metal absorption can mask the presence of low-metallicity gas in integrated line-of-sight CGM metallicities.
ABSTRACT Lyman- and Werner-band absorption of molecular hydrogen ( ) is detected in ∼50% of low-redshift ( ) DLAs/sub-DLAs with ( ) cm−2. However, the true origin(s) of the -bearing gas remain ...elusive. Here we report a new detection of an absorber at = 0.4298 in the Hubble Space Telescope (HST)/Cosmic Origins Spectrograph spectra of quasar PKS 2128-123. The total of cm−2 classifies the absorber as a sub-DLA. absorption is detected up to the J = 3 rotational level with a total = 16.36 0.08, corresponding to a molecular fraction of = −2.84 0.17. The excitation temperature of = 206 6 K indicates the presence of cold gas. Using detailed ionization modeling, we obtain a near-solar metallicity (i.e., O/H = −0.26 0.19) and a dust-to-gas ratio of for the -absorbing gas. The host galaxy of the sub-DLA is detected at an impact parameter of ∼ 48 kpc with an inclination angle of i ∼ 48° and an azimuthal angle of Φ ∼ 15° with respect to the QSO sightline. We show that corotating gas in an extended disk cannot explain the observed kinematics of Mg ii absorption. Moreover, the inferred high metallicity is not consistent with the scenario of gas accretion. An outflow from the central region of the host galaxy, on the other hand, would require a large opening angle (i.e., ), much larger than the observed outflow opening angles in Seyfert galaxies, in order to intercept the QSO sightline. We thus favor a scenario in which the -bearing gas is stemming from a dwarf-satellite galaxy, presumably via tidal and/or ram pressure stripping. Detection of a dwarf galaxy candidate in the HST/WFPC2 image at an impact parameter of ∼12 kpc reinforces such an idea.
ABSTRACT
We present here results from a survey of intervening C iv absorbers at z < 0.16 conducted using 223 sightlines from the Hubble Spectroscopic Legacy Archive. Most systems (83%) out of the ...total sample of 69 have simple kinematics with 1 or 2 C iv components. In the 22 C iv systems with well constrained H i column densities, the temperatures from the b-values imply predominantly photoionized plasma (T ≤ 105 K) and non-thermal dynamics. These systems also have solar or higher metallicities. We obtain a C iv line density of $\mathrm{ d}\mathcal {N}/\mathrm{ d}X = 5.1\pm 1.0$ for $\log N(\rm {C}\, \rm {{iv}})~(\rm {cm}^{-2})\ge 12.9$, and $\Omega _{\rm {C}\, \rm {\rm {iv}}}=(8.01\pm 1.62) \times 10^{-8}$ for $12.9 \le \log N(\rm {C}\, \rm {{iv}})~(\rm {cm}^{-2}) \le 15.0$. The C iv bearing diffuse gas in the z < 0.16 Universe has a metallicity of (2.07 ± 0.43) × 10−3 Z⊙, an order of magnitude more than the metal abundances in the IGM at high redshifts (z ≳ 5), and consistent with the slow build-up of metals in the diffuse circum/intergalactic space with cosmic time. For z < 0.015 (complete above L > 0.01L⋆), the Sloan Digital Sky Survey provides a tentative evidence of declining covering fraction for strong C iv (N > 1013.5 cm−2) with ρ (impact parameter) and ρ/Rvir. However, the increase at high separations suggests that strong systems are not necessarily coincident with such galaxies. We also find that strong C iv absorption at z < 0.051 is not coincident with galaxy overdense regions complete for L > 0.13L⋆.
ABSTRACT
As part of our program to identify host galaxies of known z = 2–3 Mg ii absorbers with the Keck Cosmic Web Imager (KCWI), we discovered a compact group giving rise to a z = 2.431 DLA with ...ultrastrong Mg ii absorption in quasar field J234628+124859. The group consists of four star-forming galaxies within 8–28 kpc and v ∼ 40–340 km s−1 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 (1.66L*, SFRFUV = 11.6 M⊙ yr−1) while G2, G3, and G4 are less massive (0.1–0.3L*, SFRFUV = 1.4–2.0 M⊙ yr−1). Using a VLT/UVES quasar spectrum covering the H i Lyman series and metal lines such as Mg ii, Si iii, and C iv, we characterized the kinematic structure and physical conditions along the line of sight with cloud-by-cloud multiphase Bayesian modelling. The absorption system has a total $\log (N({{{\rm H}\,\rm{\small I}}})/{\rm cm}^{-2})=20.53$ and an $N({{{\rm H}\,\rm{\small I}}})$-weighted mean metallicity of log (Z/Z⊙) = −0.68, with a very large Mg ii linewidth of Δv ∼ 700 km s−1. The highly kinematically complex profile is well modelled with 30 clouds across low- and intermediate-ionization phases with values ${13\lesssim \log (N({{{\rm H}\,\rm{\small I}}})/{\rm cm}^{-2})\lesssim 20}$ and −3 ≲ log (Z/Z⊙) ≲ 1. 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 characterizing evolutionary pathways.
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