arXiv subjects

Jane C. Charlton

Publications and source records attributed to Jane C. Charlton.

At least 37 records · Page 2Linked to original sources

arXiv2020

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 $\langle z_{abs}\rangle=0.25$ 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 ($T\sim10^4$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 ($-2<$[Si/H]$<0$), where the mean group ($-0.54\pm0.22$) and isolated ($-0.77\pm0.14$) 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.

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arXiv2020

Solar-Metallicity Gas in the Extended Halo of a Galaxy at $z \sim 0.12$

We present the detection and analysis of a weak low-ionization absorber at $z = 0.12122$ along the blazar sightline PG~$1424+240$, using spectroscopic data from both $HST$/COS and STIS. The absorber is a weak Mg II analogue, with incidence of weak C II and Si II, along with multi-component C IV and O VI. The low ions are tracing a dense ($n_{H} \sim 10^{-3}$ cm$^{-3}$) parsec scale cloud of solar or higher metallicity. The kinematically coincident higher ions are either from a more diffuse ($n_{H} \sim 10^{-5} - 10^{-4}$ cm$^{-3}$) photoionized phase of kiloparsec scale dimensions, or are tracing a warm (T $\sim 2 \times 10^{5}$ K) collisionally ionized transition temperature plasma layer. The absorber resides in a galaxy overdense region, with 18 luminous ($> L^*$) galaxies within a projected radius of $5$ Mpc and $750$ km s$^{-1}$ of the absorber. The multi-phase properties, high metallicity and proximity to a $1.4$ $L^*$ galaxy, at $ρ\sim 200$ kpc and $|Δv| = 11$ km s$^{-1}$ separation, favors the possibility of the absorption tracing circumgalactic gas. The absorber serves as an example of weak Mg II - O VI systems as a means to study multiphase high velocity clouds in external galaxies.

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arXiv2019

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 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.

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arXiv2019

Kinematics of the OVI Circumgalactic Medium: Halo Mass Dependence and Outflow Signatures

We probe the high-ionization circumgalactic medium by examining absorber kinematics, absorber-galaxy kinematics, and average absorption profiles of 31 OVI absorbers from the "Multiphase Galaxy Halos" Survey as a function of halo mass, redshift, inclination, and azimuthal angle. The galaxies are isolated at $0.12<z_{\rm gal}<0.66$ and are probed by a background quasar within $D\approx 200$ kpc. Each absorber-galaxy pair has Hubble Space Telescope images and COS quasar spectra, and most galaxy redshifts have been accurately measured from Keck/ESI spectra. Using the pixel-velocity two-point correlation function (TPCF) method, we find that OVI absorber kinematics have a strong halo mass dependence. Absorbers hosted by $\sim L^{\ast}$ galaxies have the largest velocity dispersions, which we interpret to be that the halo virial temperature closely matches the temperature at which the collisionally ionized OVI fraction peaks. Lower mass galaxies and group environments have smaller velocity dispersions. Total column densities follow the same behavior, consistent with theoretical findings. After normalizing out the observed mass dependence, we studied absorber-galaxy kinematics with a modified TPCF and found non-virialized motions due to outflowing gas. Edge-on minor axis gas has large optical depths concentrated near the galaxy systemic velocity as expected for bipolar outflows, while face-on minor axis gas has a smoothly decreasing optical depth distribution out to large normalized absorber-galaxy velocities, suggestive of decelerating outflowing gas. Accreting gas signatures are not observed due to "kinematic blurring" in which multiple line-of-sight structures are observed. These results indicate that galaxy mass dominates OVI properties over baryon cycle processes.

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arXiv2019

Relationship between the Metallicity of the Circumgalactic Medium and Galaxy Orientation

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 HST/COS and from Keck/HIRES or VLT/UVES we measure column densities of, or determine limits on, CGM absorption lines. We then use a Monte-Carlo Markov chain approach with Cloudy to estimate the metallicity of cool (T$\sim$$10^4$K) CGM gas. We also use HST images to determine host galaxy inclination and quasar--galaxy azimuthal angles. Our sample spans a HI column density range of $13.8$ cm s$^{-1}<{\log N_{HI}}<19.9$ cm s$^{-1}$. We find (1) while the metallicity distribution appears bimodal, a Hartigan dip test cannot rule out a unimodal distribution ($0.4σ$). (2) CGM metallicities are independent of halo mass, spanning three orders of magnitude at fixed halo mass. (3) The CGM metallicity does not depend on the galaxy azimuthal and inclination angles regardless of HI column density, impact parameter and galaxy color. (4) 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.

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arXiv2019

Detection of Metal-Rich, Cool-Warm Gas in the Outskirts of Galaxy Clusters

We present an ultraviolet quasar absorption line analysis of metal lines associated with three strong intervening H I absorbers (with $N$(H I) $>$ 10$^{16.5}$ cm$^{-2}$) detected in the outskirts of Sunyaev-Zel'dovich (SZ) effect-selected galaxy clusters ($z_{\rm cl} \sim 0.4 - 0.5$), within clustocentric impact parameters of $ρ_{cl}$ $\sim$ $(1.6 - 4.7)r_{500}$. Discovered in a recent set of targeted far-UV $HST$/COS spectroscopic observations, these absorbers have 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 $n_{H} \sim 10^{-3} - 10^{-4}$ 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 $T \sim 10^4$ 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 AGN feedback.

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arXiv2019

C IV absorbers tracing cool gas in dense galaxy group/cluster environments

We present analysis on three intervening H I-C IV absorption systems tracing gas within galaxy group/cluster environments, identified in the $HST$/COS far-UV spectra of the background quasars PG $1148+549$ ($z_{abs}=0.00346$), SBS~$1122+594$ ($z_{abs}=0.00402$) and RXJ~$1230.8+0115$ ($z_{abs}=0.00574$). The ionization models are consistent with the origin of metal lines and H I from a cool and diffuse photoionized gas phase with $T \lesssim 4 \times 10^{4}$ K and $n_{\mathrm{H}} \lesssim 5 \times 10^{-4}$ cm$^{-3}$. The three absorbers have $89$, $51$ and $17$ galaxies detected within $1$ Mpc and $|Δv| < 600$ km s$^{-1}$. The RXJ~$1230.8+0115$ sightline traces the outskirt regions of the Virgo cluster where the absorber is found to have super-solar metallicity. The detection of metal lines along with H I has enabled us to confirm the presence of cool, diffuse gas possibly enriched by outflows and tidal interactions in environments with significant galaxy density.

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arXiv2018

The Relation Between Galaxy ISM and Circumgalactic OVI Gas Kinematics Derived from Observations and $Λ$CDM Simulations

We present the first galaxy-OVI absorption kinematic study for 20 absorption systems (EW>0.1~Å) associated with isolated galaxies (0.15$ 33^{\circ}$). OVI absorption along the galaxy major axis is not correlated with galaxy rotation kinematics, with only 1/10 systems that could be explained with rotation/accretion models. This is in contrast to co-rotation commonly observed for MgII absorption. OVI along the minor axis could be modeled by accelerating outflows but only for small opening angles, while the majority of the OVI is decelerating. Along both axes, stacked OVI profiles reside at the galaxy systemic velocity with the absorption kinematics spanning the entire dynamical range of their galaxies. The OVI found in AMR cosmological simulations exists within filaments and in halos of ~50 kpc surrounding galaxies. Simulations show that major axis OVI gas inflows along filaments and decelerates as it approaches the galaxy while increasing in its level of co-rotation. Minor axis outflows in the simulations are effective within 50-75 kpc beyond that they decelerate and fall back onto the galaxy. Although the simulations show clear OVI kinematic signatures they are not directly comparable to observations. When we compare kinematic signatures integrated through the entire simulated galaxy halo we find that these signatures are washed out due to full velocity distribution of OVI throughout the halo. We conclude that OVI alone does not serve as a useful kinematic indicator of gas accretion, outflows or star-formation and likely best probes the halo virial temperature.

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arXiv2018

Direct Measurement of Quasar Outflow Wind Acceleration

We search for velocity changes (i.e., acceleration/deceleration) of narrow absorption lines (NALs) that are intrinsic to the quasars, using spectra of 6 bright quasars that have been observed more than once with 8-10m class telescopes. While variations in line strength and profile are frequently reported (especially in broader absorption lines), definitive evidence for velocity shifts has not been found with only a few exceptions. Direct velocity shift measurements are valuable constraints on the acceleration mechanisms. In this study, we determine velocity shifts by comparing the absorption profiles of NALs at two epochs separated by more than 10 years in the observed frame, using the cross-correlation function method and we estimate the uncertainties using Monte Carlo simulations. We do not detect any significant shifts but we obtain 3$σ$ upper limits on the acceleration of intrinsic NALs (compared to intervening NALs in same quasars) of $\sim$0.7 km s$^{-1}$ yr$^{-1}$ ($\sim$0.002 cm s$^{-2}$). We discuss possible scenarios for non-detection of NAL acceleration/deceleration and examine resulting constraints on the physical conditions in accretion disk wind.

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arXiv2018

Understanding the strong intervening OVI absorber at z$_{abs}$ ~0.93 towards PG1206+459

We have obtained new observations of the partial Lyman limit absorber at \zabs$=0.93$ towards quasar PG~1206+459, and revisit its chemical and physical conditions. The absorber, with $ N(HI) \sim 10^{17.0}$ ~\sqcm\ and absorption lines spread over $\gtrsim$1000~\kms\ in velocity, is one of the strongest known OVI absorbers at $\log N(OVI)=$15.54$\pm$0.17. Our analysis makes use of the previously known low-(e.g. \MgII), intermediate-(e.g. SiIV), and high-ionization (e.g., CIV, NV, NeVIII) metal lines along with new $HST/$COS observations that cover OVI, and an $HST/$ACS image of the quasar field. Consistent with previous studies, we find that the absorber has a multiphase structure. The low-ionization phase arises from gas with a density of $\log (n_{\rm H}/\rm cm^{-3})\sim-2.5$ and a solar to super-solar metallicity. The high-ionization phase stems from gas with a significantly lower density, i.e. $\log (n_{\rm H}/\rm cm^{-3}) \sim-3.8$, and a near-solar to solar metallicity. The high-ionization phase accounts for all of the absorption seen in CIV, NV, and OVI. We find the the detected \NeVIII, reported by \cite{Tripp2011}, is best explained as originating in a stand-alone collisionally ionized phase at $T\sim10^{5.85}~\rm K$, except in one component in which both OVI and NeVIII can be produced via photoionization. We demonstrate that such strong OVI absorption can easily arise from photoionization at $z\gtrsim1$, but that, due to the decreasing extragalactic UV background radiation, only collisional ionization can produce large OVI features at $z\sim0$. The azimuthal angle of $\sim88$\degree\ of the disk of the nearest ($\rm 68~kpc$) luminous ($1.3L_*$) galaxy at $z_{\rm gal}=0.9289$, which shows signatures of recent merger, suggests that the bulk of the absorption arises from metal enriched outflows.

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arXiv2018

Spectroscopic Observations of the Outflowing Wind in the Lensed Quasar SDSS J1001+5027

We performed spectroscopic observations of the small-separation lensed quasar SDSS J1001+5027, whose images have an angular separation $θ\sim 2.^{\!\!\prime\prime}86$, and placed constraints on the physical properties of gas clouds in the vicinity of the quasar (i.e., in the outflowing wind launched from the accretion disk). The two cylinders of sight to the two lensed images go through the same region of the outflowing wind and they become fully separated with no overlap at a very large distance from the source ($\sim 330$ pc). We discovered a clear difference in the profile of the CIV broad absorption line (BAL) detected in the two lensed images in two observing epochs. Because the kinematic components in the BAL profile do not vary in concert, the observed variations cannot be reproduced by a simple change of ionization state. If the variability is due to gas motion around the background source (i.e., the continuum source), the corresponding rotational velocity is $v_{rot}\geq 18,000$ km/s, and their distance from the source is $r\leq 0.06$ pc assuming Keplerian motion. Among three MgII and three CIV NAL systems that we detected in the spectra, only the MgII system at $z_{abs} = 0.8716$ shows a hint of variability in its MgI profile on a rest-frame time scale of $Δt_{rest}$ $\leq 191$ days and an obvious velocity shear between the sightlines whose physical separation is $\sim 7$ kpc. We interpret this as the result of motion of a cosmologically intervening absorber, perhaps located in a foreground galaxy.

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arXiv2017

The Impact of the Group Environment on the OVI Circumgalactic Medium

We present a study comparing OVI $λλ$1031, 1037 doublet absorption found towards group galaxy environments with that of isolated galaxies. The OVI absorption in the circumgalactic medium (CGM) of isolated galaxies has been studied previously by the "Multiphase Galaxy Halos" survey, where the kinematics and absorption properties of the CGM have been investigated. We extend these studies to group environments. We define a galaxy group to have two or more galaxies having a line-of-sight velocity difference of no more than 1000 km/s and located within 350 kpc (projected) of a background quasar sightline. We identified a total of six galaxy groups associated with OVI absorption $W_{\rm r}>0.06$ Å that have a median redshift of $\langle z_{\rm gal} \rangle = 0.1669$ and a median impact parameter of $\langle D \rangle = 134.1$ kpc. An additional 12 non-absorbing groups were identified with a median redshift of $\langle z_{\rm gal} \rangle = 0.2690$ and a median impact parameter of $\langle D \rangle = 274.0$ kpc. We find the average equivalent width to be smaller for group galaxies than for isolated galaxies $(3σ)$. However, the covering fractions are consistent with both samples. We used the pixel-velocity two-point correlation function method and find that the velocity spread of OVI in the CGM of group galaxies is significantly narrower than that of isolated galaxies $(10σ)$. We suggest that the warm/hot CGM does not exist as a superposition of halos, instead, the virial temperature of the halo is hot enough for OVI to be further ionised. The remaining OVI likely exists at the interface between hot, diffuse gas and cooler regions of the CGM.

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arXiv2016

The Highly Ionized Circumgalactic Medium is Kinematically Uniform Around Galaxies

The circumgalactic medium (CGM) traced by OVI $λλ1031, 1037$ doublet absorption has been found to concentrate along the projected major and minor axes of the host galaxies. This suggests that OVI traces accreting and outflowing gas, respectively, which are key components of the baryon cycle of galaxies. We investigate this further by examining the kinematics of 29 OVI absorbers associated with galaxies at $0.13 < z_{\rm gal} < 0.66$ as a function of galaxy color, inclination, and azimuthal angle. Each galaxy was imaged with HST and the absorption was detected in COS/HST spectra of nearby ($D<200$ kpc) background quasars. We use the pixel-velocity two-point correlation function to characterize the velocity spread of the absorbers, which is a method used previously for a sample of MgII absorber--galaxy pairs. The absorption velocity spread for OVI is more extended than MgII, which suggests that the two ions trace differing components of the CGM. Also contrary to MgII, the OVI absorption velocity spreads are similar regardless of galaxy color, inclination, and azimuthal angle. This indicates that the kinematics of the high ionization gas is not strongly influenced by the present star formation activity in the galaxy. The kinematic homogeneity of OVI absorption and its tendency to be observed mainly along the projected galaxy major and minor axes is likely due to varying ionization conditions and gas densities about the galaxy. Gas in intermediate azimuthal angles may be ionized out of the OVI phase, possibly resulting in an azimuthal angle dependence on the distribution of gas in higher ionization states.

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arXiv2016

Molecular Hydrogen Absorption from the Halo of a z ~ 0.4 Galaxy

Lyman- and Werner-band absorption of molecular hydrogen (H$_2$) is detected in $\sim$50% of low redshift ($z<1$) DLAs/sub-DLAs with $N$(H$_2$) > 10$^{14.4}$ cm$^{-2}$. However the true origin(s) of the H$_2$ bearing gas remain elusive. Here we report a new detection of an H$_{2}$ absorber at $z=$ 0.4298 in the HST/COS spectra of quasar PKS 2128-123. The total $N$(HI) of 10$^{19.50\pm0.15}$ cm$^{-2}$ classifies the absorber as a sub-DLA. H$_{2}$ absorption is detected up to the $J=3$ rotational level with a total $\log N$(H$_{2}$) = 16.36$\pm$0.08 corresponding to a molecular fraction of log $f$(H$_{2}$) = $-$2.84$\pm$0.17. The excitation temperature of $T_{ex}$ = 206$\pm$6K indicates the presence of cold gas. Using detailed ionization modelling we obtain a near-solar metallicity (i.e., [O/H]= $-$0.26$\pm$0.19) and a dust-to-gas ratio of $\log κ\sim -0.45$ for the H$_{2}$ absorbing gas. The host-galaxy of the sub-DLA is detected at an impact parameter of $ρ\sim$ 48 kpc with an inclination angle of $i \sim$ 48 degree and an azimuthal angle of $Φ\sim$ 15 degree with respect to the QSO sightline. We show that co-rotating 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., 2$θ>$150 degree), much larger than the observed outflow opening angles in Seyfert galaxies, in order to intercept the QSO sightline. We thus favor a scenario in which the H$_2$ 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 $\sim$12 kpc reinforces such an idea.

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arXiv2016

Multi-Sightline Observation of Narrow Absorption Lines in Lensed Quasar SDSS J1029+2623

We exploit the widely-separated images of the lensed quasar SDSS J1029+2623 ($z_{em}$=2.197, $θ=22^{\prime\prime}\!\!.5$) to observe its outflowing wind through two different sightlines. We present an analysis of three observations, including two with the Subaru telescope in 2010 February (Misawa et al. 2013) and 2014 April (Misawa et al. 2014), separated by 4 years, and one with the Very Large Telescope, separated from the second Subaru observation by $\sim$2 months. We detect 66 narrow absorption lines (NALs), of which 24 are classified as intrinsic NALs that are physically associated with the quasar based on partial coverage analysis. The velocities of intrinsic NALs appear to cluster around values of $v_{ej}$ $\sim$ 59,000, 43,000, and 29,000 km/s, which is reminiscent of filamentary structures obtained by numerical simulations. There are no common intrinsic NALs at the same redshift along the two sightlines, implying that the transverse size of the NAL absorbers should be smaller than the sightline distance between two lensed images. In addition to the NALs with large ejection velocities of $v_{ej}$ > 1,000 km/s, we also detect broader proximity absorption lines (PALs) at $z_{abs}$ $\sim$ $z_{em}$. The PALs are likely to arise in outflowing gas at a distance of r $\leq$ 620 pc from the central black hole with an electron density of $n_e$ $\geq$ 8.7$\times$10$^{3}$ cm$^{-3}$. These limits are based on the assumption that the variability of the lines is due to recombination. We discuss the implications of these results on the three-dimensional structure of the outflow.

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arXiv2015

The Azimuthal Dependence of Outflows and Accretion Detected Using OVI Absorption

We report a bimodality in the azimuthal angle ($Φ$) distribution of gas around galaxies traced by OVI absorption. We present the mean $Φ$ probability distribution function of 29 HST-imaged OVI absorbing (EW>0.1A) and 24~non-absorbing (EW<0.1A) isolated galaxies (0.08<z<0.67) within 200kpc of background quasars. We show that EW is anti-correlated with impact parameter and OVI covering fraction decreases from 80% within 50kpc to 33% at 200kpc. The presence of OVI absorption is azimuthally dependent and occurs between $\pm10-20^{\circ}$ of the galaxy projected major axis and within $\pm30^{\circ}$ 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 OVI detection rate. OVI surrounding blue galaxies exists primarily along the projected minor axis with wide opening angles while OVI 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 CGM originating from major axis-fed inflows/recycled gas and from minor axis-driven outflows. Non-detected OVI occurs between $Φ=20-60^{\circ}$, suggesting that OVI is not mixed throughout the CGM and remains confined within the outflows and the disk-plane. We find low OVI covering fractions within $\pm10^{\circ}$ of the projected major axis, suggesting that cool dense gas resides in a narrow planer geometry surrounded by diffuse OVI gas.

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arXiv2015

An Extreme Metallicity, Large-Scale Outflow from a Star-Forming Galaxy at z ~ 0.4

We present a detailed analysis of a large-scale galactic outflow in the CGM of a massive (M_h ~ 10^12.5 Msun), star-forming (6.9 Msun/yr), sub-L* (0.5 L_B*) galaxy at z=0.39853 that exhibits a wealth of metal-line absorption in the spectra of the background quasar Q 0122-003 at an impact parameter of 163 kpc. The galaxy inclination angle (i=63 degree) and the azimuthal angle (Phi=73 degree) imply that the QSO sightline is passing through the projected minor-axis of the galaxy. The absorption system shows a multiphase, multicomponent structure with ultra-strong, wide velocity spread OVI (logN = 15.16\pm0.04, V_{90} = 419 km/s) and NV (logN = 14.69\pm0.07, V_{90} = 285 km/s) lines that are extremely rare in the literature. The highly ionized absorption components are well explained as arising in a low density (10^{-4.2} cm^{-3}), diffuse (10 kpc), cool (10^4 K) photoionized gas with a super-solar metallicity ([X/H] > 0.3). From the observed narrowness of the Lyb profile, the non-detection of SIV absorption, and the presence of strong CIV absorption we rule out equilibrium/non-equilibrium collisional ionization models. The low-ionization photoionized gas with a density of 10^{-2.5} cm^{-3} and a metallicity of [X/H] > -1.4 is possibly tracing recycled halo gas. We estimate an outflow mass of ~2x10^{10} Msun, a mass-flow rate of ~54 Msun/yr, a kinetic luminosity of ~9x10^{41} erg/s, and a mass loading factor of ~8 for the outflowing high-ionization gas. These are consistent with the properties of "down-the-barrel" outflows from infrared-luminous starbursts as studied by Rupke et al. Such powerful, large-scale, metal-rich outflows are the primary means of sufficient mechanical and chemical feedback as invoked in theoretical models of galaxy formation and evolution.

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arXiv2014

HST/COS detection of a Ne VIII absorber towards PG 1407+265: An unambiguous tracer of collisionally ionized hot gas?

We report the detection of Ne VIII in a z_abs = 0.59961 absorber towards the QSO PG 1407+265 (z_em = 0.94). Besides Ne VIII, absorption from HI Lyman series lines (HI 1025 - 915), several other low (C II, N II, O II, and S II), intermediate (C III, N III, N IV, O III, S IV, and S V) and high (S VI, O VI, and Ne VIII) ionization metal lines are detected. Disparity in the absorption line kinematics between different ions implies that the absorbing gas comprises of multiple ionization phases. The low and the intermediate ions (except S V) trace a compact (~ 410 pc), metal-rich (Z ~ Z_sun) and over-dense (log n_H ~ -2.6) photoionized region that sustained star-formation for a prolonged period. The high ions, Ne VIII and O VI, can be explained as arising in a low density (-5.3 < log n_H < -5.0), metal-rich (Z > Z_sun) and diffuse (~ 180 kpc) photoionized gas. The S V, S VI and C IV (detected in the FOS spectrum) require an intermediate photoionization phase with -4.2 < log n_H < -3.5. Alternatively, a pure collisional ionization model, as used to explain the previous known Ne VIII absorbers, with 5.65 < log T < 5.72, can reproduce the S VI, O VI, and Ne VIII column densities simultaneously in a single phase. However, even such models require an intermediate phase to reproduce any observable S V and/or C IV. Therefore, we conclude that when multiple phases are present, the presence of Ne VIII is not necessarily an unambiguous indication of collisionally ionized hot gas.

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