Circumgalactic Medium Of Galaxies Research Articles

High resolution modelling of [CII], [CI], [OIII], and CO line emission from the interstellar medium and circumgalactic medium of a star-forming galaxy at z ∼ 6.5

The circumgalactic medium (CGM) is a crucial component of galaxy evolution, but thus far its physical properties are highly unconstrained. As of yet, no cosmological simulation has reached convergence when it comes to constraining the cold and dense gas fraction of the CGM. Such components are also challenging to observe directly, as they require sub-millimetre (sub-mm) instruments with a high sensitivity to extended and mostly diffuse emission. We present a state-of-the-art theoretical effort at modelling the [CII] 158 μm, [CI](1−0) 609 μm, [CI](2−1) 370 μm, CO(3−2) 867 μm, and [OIII] 88 μm line emissions that arise from the interstellar medium (ISM) and CGM of galaxies, with the goal of studying the contribution from different cold (T < 104 K) components of galaxy halos. We used the high-resolution cosmological zoom-in simulation PONOS (mgas = 883.4 M⊙), which represents a typical star-forming galaxy system at z = 6.5, composed of a main disc with stellar mass M* = 2 × 109 M⊙ that is undergoing a major merger. We adopted different modelling approaches based on the photoionisation code CLOUDY. Our fiducial model uses radiative transfer post-processing with RAMSES-RT and KROME (KRAMSES-RT) to create more realistic far-ultraviolet (FUV) radiation fields, which we then compared to other sub-grid modelling approaches adopted in the literature. We find significant differences in the luminosity and in the contribution of different gas phases and galaxy components between the different modelling approaches. [CII] is the least model-dependant gas tracer, while [CI](1−0) and CO(3−2) are very model-sensitive. In all models, we find a significant contribution to the emission of [CII] (up to ∼10%) and [OIII] (up to ∼21%) from the CGM. Our fiducial global radiative transfer (RT) model produces a lower density, T ∼ 104 K tail of [CII] emission that is not seen in the other more simplistic models and that resides entirely in the CGM, ionised by the FUV background and producing the extended halos observed in [CII] at high-z. Notably, [CII] and [OIII] trace different regions of the CGM: [CII] arises from an accreting filament and from the tidal tails connecting the main disc and its merging satellites, while [OIII] traces a puffy halo surrounding the main disc, probably linked to supernova feedback. We discuss our results in the context of sub-mm observations. Using simulated spectra and mock maps, we show that, despite the rather compact angular extent of PONOS’s CGM, deep ALMA observations would not detect this component, even in [CII] which is the brightest available tracer. Instead, a next generation single-dish observatory such as the Atacama Large Aperture Submillimeter Telescope (AtLAST) could detect PONOS’ CGM in [CII] at a high signal-to-noise ratio, and possibly even in [OIII].

The Circumgalactic Medium of Extreme Emission Line Galaxies at z∼2: Resolved Spectroscopy and Radiative Transfer Modeling of Spatially Extended Lyα Emission in the KBSS-KCWI Survey* *Based on data obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous

The resonantly scattered Lyα line illuminates the extended halos of neutral hydrogen in the circumgalactic medium of galaxies. We present integral field Keck Cosmic Web Imager observations of double-peaked, spatially extended Lyα emission in 12 relatively low-mass (M ⋆ ∼ 109 M⊙) z ∼ 2 galaxies characterized by extreme nebular emission lines. Using individual spaxels and small bins as well as radially binned profiles of larger regions, we find that for most objects in the sample the Lyα blue-to-red peak ratio increases, the peak separation decreases, and the fraction of flux emerging at line center increases with radius. We use new radiative transfer simulations to model each galaxy with a clumpy, multiphase outflow with radially varying outflow velocity, and self-consistently apply the same velocity model to the low-ionization interstellar absorption lines. These models reproduce the trends of peak ratio, peak separation, and trough depth with radius, and broadly reconcile outflow velocities inferred from Lyα and absorption lines. The galaxies in our sample are well-described by a model in which neutral, outflowing clumps are embedded in a hotter, more highly ionized inter-clump medium (ICM), whose residual neutral content produces absorption at the systemic redshift. The peak ratio, peak separation, and trough flux fraction are primarily governed by the line-of-sight component of the outflow velocity, the H i column density, and the residual neutral density in the ICM respectively. The azimuthal asymmetries in the line profile further suggest nonradial gas motions at large radii and variations in the H i column density in the outer halos.

MUSE Analysis of Gas around Galaxies (MAGG) – V. Linking ionized gas traced by C iv and Si iv absorbers to Ly α emitting galaxies at z ≈ 3.0–4.5

ABSTRACT We study the connection between Ly α emitters (LAEs) and metal-enriched ionized gas traced by C iv absorption at redshift z ≈ 3–4 in 28 quasar fields with high-resolution spectroscopy from the MUSE Analysis of Gas Around Galaxies survey. In a sample of 220 C iv absorbers, we identify 143 LAEs connected to C iv gas within a line-of-sight separation $\pm 500\rm \, km\, s^{-1}$, equal to a detection rate of 36 ± 5 per cent once we account for multiple LAEs connected to the same absorber. The luminosity function of LAEs associated with absorbers has an ≈2.4 higher normalization than the field. The analysis of the LAE–C iv correlation function suggests that metal-enriched gas arises both in the haloes of the LAEs and from locations not connected to galaxies. C iv absorbers with higher equivalent width are more often associated with LAEs and C iv systems are twice less likely, especially at low equivalent width, to be found near LAEs than strong H i absorbers. The covering fraction in groups is up to ≈3 times larger than for isolated galaxies. Similar results are found using Si iv as tracer of ionized gas. We propose three components to model the gas environment of LAEs: (i) the circumgalactic medium of galaxies, accounting for the strongest correlations between absorption and emission; (ii) overdense gas filaments connecting galaxies, driving the excess of LAEs at a few times the virial radius and the modulation of the luminosity and cross-correlation functions for strong absorbers; (iii) an enriched and more diffuse medium, accounting for weaker C iv absorbers farther from galaxies.

The Bimodal Absorption System Imaging Campaign (BASIC). I. A Dual Population of Low-metallicity Absorbers at z < 1

The bimodal absorption system imaging campaign (BASIC) aims to characterize the galaxy environments of a sample of 36 H i-selected partial Lyman limit systems (pLLSs) and Lyman limit systems (LLSs) in 23 QSO fields at z ≲ 1. These pLLSs/LLSs provide a unique sample of absorbers with unbiased and well-constrained metallicities, allowing us to explore the origins of metal-rich and low-metallicity circumgalactic medium (CGM) at z < 1. Here we present Keck/KCWI and Very Large Telescope/MUSE observations of 11 of these QSO fields (19 pLLSs) that we combine with Hubble Space Telescope/Advanced Camera for Surveys imaging to identify and characterize the absorber-associated galaxies at 0.16 ≲ z ≲ 0.84. We find 23 unique absorber-associated galaxies, with an average of one associated galaxy per absorber. For seven absorbers, all with <10% solar metallicities, we find no associated galaxies with within ρ/R vir and ∣Δv∣/v esc ≤ 1.5 with respect to the absorber. We do not find any strong correlations between the metallicities or H i column densities of the gas and most of the galaxy properties, except for the stellar mass of the galaxies: the low-metallicity ([X/H] ≤ −1.4) systems have a probability of for having a host galaxy with within ρ/R vir ≤ 1.5, while the higher metallicity absorbers have a probability of . This implies metal-enriched pLLSs/LLSs at z < 1 are typically associated with the CGM of galaxies with , whereas low-metallicity pLLSs/LLSs are found in more diverse locations, with one population arising in the CGM of galaxies and another more broadly distributed in overdense regions of the universe. Using absorbers not associated with galaxies, we estimate the unweighted geometric mean metallicity of the intergalactic medium to be [X/H] ≲ −2.1 at z < 1, which is lower than previously estimated.

RASCAS: RAdiation SCattering in Astrophysical Simulations

Context. Resonant lines are powerful probes of the interstellar and circumgalactic medium of galaxies. Their transfer in gas being a complex process, the interpretation of their observational signatures, either in absorption or in emission, is often not straightforward. Numerical radiative transfer simulations are needed to accurately describe the travel of resonant line photons in real and in frequency space, and to produce realistic mock observations. Aims. This paper introduces RASCAS, a new public 3D radiative transfer code developed to perform the propagation of any resonant line in numerical simulations of astrophysical objects. RASCAS was designed to be easily customisable and to process simulations of arbitrarily large sizes on large supercomputers. Methods. RASCAS performs radiative transfer on an adaptive mesh with an octree structure using the Monte Carlo technique. RASCAS features full MPI parallelisation, domain decomposition, adaptive load-balancing, and a standard peeling algorithm to construct mock observations. The radiative transport of resonant line photons through different mixes of species (e.g. H I, Si II, Mg II, Fe II), including their interaction with dust, is implemented in a modular fashion to allow new transitions to be easily added to the code. Results. RASCAS is very accurate and efficient. It shows perfect scaling up to a minimum of a thousand cores. It has been fully tested against radiative transfer problems with analytic solutions and against various test cases proposed in the literature. Although it was designed to describe accurately the many scatterings of line photons, RASCAS may also be used to propagate photons at any wavelength (e.g. stellar continuum or fluorescent lines), or to cast millions of rays to integrate the optical depths of ionising photons, making it highly versatile.

Cosmological baryon transfer in the simba simulations

ABSTRACT We present a framework for characterizing the large-scale movement of baryons relative to dark matter in cosmological simulations, requiring only the initial conditions and final state of the simulation. This is performed using the spread metric that quantifies the distance in the final conditions between initially neighbouring particles, and by analysing the baryonic content of final haloes relative to that of the initial Lagrangian regions (LRs) defined by their dark matter component. Applying this framework to the simba cosmological simulations, we show that 40 per cent (10 per cent) of cosmological baryons have moved $\gt 1\, h^{-1}\, {\rm Mpc}{}$ ($3\, h^{-1}\, {\rm Mpc}{}$) by z = 0, primarily due to entrainment of gas by jets powered by an active galactic nucleus, with baryons moving up to $12\, h^{-1}\, {\rm Mpc}{}$ away in extreme cases. Baryons decouple from the dynamics of the dark matter component due to hydrodynamic forces, radiative cooling, and feedback processes. As a result, only 60 per cent of the gas content in a given halo at z = 0 originates from its LR, roughly independent of halo mass. A typical halo in the mass range Mvir = 1012–1013 M⊙ only retains 20 per cent of the gas originally contained in its LR. We show that up to 20 per cent of the gas content in a typical Milky Way-mass halo may originate in the region defined by the dark matter of another halo. This inter-Lagrangian baryon transfer may have important implications for the origin of gas and metals in the circumgalactic medium of galaxies, as well as for semi-analytic models of galaxy formation and ‘zoom-in’ simulations.

The Red Dead Redemption Survey of Circumgalactic Gas about Massive Galaxies. I. Mass and Metallicity of the Cool Phase

We present a search for HI in the circumgalactic medium (CGM) of 21 massive ($\langle \log M_\star \rangle \sim 11.4$), luminous red galaxies (LRGs) at $z\sim0.5$. Using UV spectroscopy of QSO sightlines projected within 500 kpc ($\sim R_{vir}$) of these galaxies, we detect HI absorption in 11/21 sightlines, including two partial Lyman limit systems and two Lyman limit systems. The covering factor of $\log N(HI) \ge 16.0$ gas within the virial radius of these LRGs is $f_c(\rho \le R_{vir}) = 0.27^{+0.11}_{-0.10}$, while for optically-thick gas ($\log N(HI) \ge 17.2$) it is $f_c(\rho \le R_{vir}) = 0.15^{+0.10}_{-0.07}$. Combining this sample of massive galaxies with previous galaxy-selected CGM studies, we find no strong dependence of the HI covering factor on galaxy mass, although star-forming galaxies show marginally higher covering factors. There is no evidence for a critical mass above which dense, cold ($T \sim 10^4$ K) gas is suppressed in the CGM of galaxies (spanning stellar masses $9.5 \lesssim \log M_\star \lesssim 11.8$). The metallicity distribution in LRGs is indistinguishable from those found about lower-mass star-forming galaxies, and we find low-metallicity gas with $[{\rm X/H}] \approx -1.8$ (1.5% solar) and below about massive galaxies. About half the cases show super-solar [FeII/MgII] abundances as seen previously in cool gas near massive galaxies. While the high-metallicity cold gas seen in LRGs could plausibly result from condensation from a corona, the low-metallicity gas is inconsistent with this interpretation.

Extreme Circumgalactic H i and C iii Absorption around the Most Massive, Quenched Galaxies

Abstract Luminous red galaxies (LRGs) are the most massive galaxies at z ∼ 0.5 and, by selection, have negligible star formation (SF). These objects have halo masses between those of L * galaxies, whose circumgalactic media (CGMs) are observed to have large masses of cold gas, and clusters of galaxies, which primarily contain hot gas. Here, we report detections of strong and extended metal (C iii 977) and H i lines in the CGM of two LRGs. The C iii lines have equivalent widths (EWs) of ∼1.8 and ∼1.2 Å, and velocity spreads of ∼796 and ∼1245 , exceeding all such measurements from local ∼L * galaxies (maximal C iii EWs ∼1 Å). The data demonstrate that a subset of halos hosting very massive, quenched galaxies contain significant complexes of cold gas. Possible scenarios to explain our observations include that the LRGs’ CGMs originate from past activity (e.g., SF or active galactic nuclei driven outflows) or from the CGMs of galaxies in overlapping subhalos. We favor the latter scenario, in which the properties of the CGMs are more tightly linked to the underlying dark matter halo than properties of the targeted galaxies (e.g., SF).

Resonant line transfer in a fog: using Lyman-alpha to probe tiny structures in atomic gas

Motivated by observational and theoretical work which both suggest very small scale ($\lesssim 1\,$pc) structure in the circum-galactic medium of galaxies and in other environments, we study Lyman-$\alpha$ (Ly$\alpha$) radiative transfer in an extremely clumpy medium with many "clouds" of neutral gas along the line of sight. While previous studies have typically considered radiative transfer through sightlines intercepting $\lesssim 10$ clumps, we explore the limit of a very large number of clumps per sightline (up to $f_{\mathrm{c}} \sim 1000$). Our main finding is that, for covering factors greater than some critical threshold, a multiphase medium behaves similar to a homogeneous medium in terms of the emergent Ly$\alpha$ spectrum. The value of this threshold depends on both the clump column density and on the movement of the clumps. We estimate this threshold analytically and compare our findings to radiative transfer simulations with a range of covering factors, clump column densities, radii, and motions. Our results suggest that (i) the success in fitting observed Ly$\alpha$ spectra using homogeneous "shell models" (and the corresponding failure of multiphase models) hints towards the presence of very small-scale structure in neutral gas, in agreement within a number of other observations; and (ii) the recurrent problems of reproducing realistic line profiles from hydrodynamical simulations may be due to their inability to resolve small-scale structure, which causes simulations to underestimate the effective covering factor of neutral gas clouds.

DUST IN THE CIRCUMGALACTIC MEDIUM OF LOW-REDSHIFT GALAXIES

Using spectroscopically selected galaxies from the Sloan Digital Sky Survey we present a detection of reddening due to dust in the circumgalactic medium of galaxies. We detect the mean change in the colors of "standard crayons" correlated with the presence of foreground galaxies at z ~0.05 as a function of angular separation. Following Peek & Graves (2010), we create standard crayons using passively evolving galaxies corrected for Milky Way reddening and color-redshift trends, leading to a sample with as little as 2% scatter in color. We devise methods to ameliorate possible systematic effects related to the estimation of colors, and we find an excess reddening induced by foreground galaxies at a level ranging from 10 to 0.5 millimagnitudes on scales ranging from 30 kpc to 1 Mpc. We attribute this effect to a large-scale distribution of dust around galaxies similar to the findings of Menard et al. 2010. We find that circumgalactic reddening is a weak function of stellar mass over the range $6 \times 10^9 M_\odot$ -- $6 \times 10^{10} M_\odot$ and note that this behavior appears to be consistent with recent results on the distribution of metals in the gas phase.

PROPERTIES OF QSO METAL-LINE ABSORPTION SYSTEMS AT HIGH REDSHIFTS: NATURE AND EVOLUTION OF THE ABSORBERS AND NEW EVIDENCE ON ESCAPE OF IONIZING RADIATION FROM GALAXIES

Using Voigt-profile-fitting procedures on Keck High Resolution Spectrograph spectra of nine QSOs, we identify 1099 C iv absorber components clumped in 201 systems outside the Lyman forest over 1.6 ≲ z ≲ 4.4. With associated Si iv, C ii, Si ii and N v where available, we investigate the bulk statistical and ionization properties of the components and systems and find no significant change in redshift for C iv and Si iv while C ii, Si ii and N v change substantially. The C iv components exhibit strong clustering, but no clustering is detected for systems on scales from 150 km s−1 out to 50,000 km s−1. We conclude that the clustering is due entirely to the peculiar velocities of gas present in the circumgalactic media of galaxies. Using specific combinations of ionic ratios, we compare our observations with model ionization predictions for absorbers exposed to the metagalactic ionizing radiation background augmented by proximity radiation from their associated galaxies and find that the generally accepted means of radiative escape by transparent channels from the internal star-forming sites is spectrally not viable for our stronger absorbers. We develop an active scenario based on runaway stars with resulting changes in the efflux of radiation that naturally enable the needed spectral convergence, and in turn provide empirical indicators of morphological evolution in the associated galaxies. Together with a coexisting population of relatively compact galaxies indicated by the weaker absorbers in our sample, the collective escape of radiation is sufficient to maintain the intergalactic medium ionized over the full range 1.9 < z ≲ 4.4.

GALACTIC AND CIRCUMGALACTIC O VI AND ITS IMPACT ON THE COSMOLOGICAL METAL AND BARYON BUDGETS AT 2 &lt;z≲ 3.5

We present the first results from our NASA Keck Observatory Database of Ionized Absorbers toward Quasars (KODIAQ) survey which aims to characterize the properties of the highly ionized gas of high redshift galaxies and their circumgalactic medium (CGM) at 2<z<4. We select absorbers optically thick at the Lyman limit ({\tau}LL > 1, log N(HI) > 17.3) as probes of these galaxies and their CGM where both transitions of the O VI doublet have little contamination from the Ly {\alpha}, {\beta} forests. We found 20 absorbers that satisfy these rules: 7 Lyman limit systems (LLSs), 8 super-LLSs (SLLSs) and 5 damped Ly{\alpha} (DLAs). The O VI detection rate is 100% for the DLAs, 71% for the LLSs, and 63% for the SLLSs. When O VI is detected, log N(OVI)=14.9+/-0.3, an average O VI column density substantially larger and with a smaller dispersion than found in blind O VI surveys at similar redshifts. Strong O VI absorption is therefore nearly ubiquitous in the CGM of z~2-3 galaxies. The total velocity widths of the O VI profiles are also large (200<Dv(OVI)<400 km/s). These properties are quite similar to those seen for O VI in low z star-forming galaxies, and therefore we hypothesize that these strong CGM O VI absorbers (with {\tau}LL > 1) at 2<z<3.5 also probe outflows of star-forming galaxies. The LLSs and SLLSs with no O VI absorption have properties consistent with those seen in cosmological simulations tracing cold streams feeding galaxies. When the highly ionized (Si IV and O VI) gas is taken into account, we determine that the {\tau}LL > 1 absorbers could contain as much as 3-14% of the cosmic baryon budget at z~2-3, only second to the Ly{\alpha} forest. We conservatively show that 5-20% of the metals ever produced at z~2-3 are in form of highly ionized metals ejected in the CGM of galaxies.

QSO ABSORPTION SYSTEMS DETECTED IN Ne VIII: HIGH-METALLICITY CLOUDS WITH A LARGE EFFECTIVE CROSS SECTION

Using high-resolution, high signal-to-noise ultraviolet spectra of the zem = 0.9754 quasar PG1148+549 obtained with the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope, we study the physical conditions and abundances of Ne viii+O vi absorption line systems at zabs = 0.68381, 0.70152, 0.72478. In addition to Ne viii and O vi, absorption lines from multiple ionization stages of oxygen (O ii, O iii, O iv) are detected and are well aligned with the more highly ionized species. We show that these absorbers are multiphase systems including hot gas (T ≈ 105.7 K) that produces Ne viii and O vi, and the gas metallicity of the cool phase ranges from Z = 0.3 Z☉ to supersolar. The cool (≈104 K) phases have densities nH ≈ 10−4 cm−3 and small sizes (<4 kpc); these cool clouds are likely to expand and dissipate, and the Ne viii may be within a transition layer between the cool gas and a surrounding, much hotter medium. The Ne viii redshift density, /, requires a large number of these clouds for every L > 0.1 L* galaxy and a large effective absorption cross section (≳ 100 kpc), and indeed, we find a star-forming ∼L⋆ galaxy at the redshift of the zabs = 0.72478 system, at an impact parameter of 217 kpc. Multiphase absorbers like these Ne viii systems are likely to be an important reservoir of baryons and metals in the circumgalactic media of galaxies.