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Understanding how galaxies interact with the circumgalactic medium (CGM) requires determining how galaxies' morphological and stellar properties correlate with their CGM properties. We report an analysis of 66 well-imaged galaxies detected in Hubble Space Telescope and Very Large Telescope MUSE observations and determined to be within ±500 km s−1 of the redshifts of strong intervening quasar absorbers at 0.2 ≲ z ≲ 1.4 with H  i column densities |$N_{\rm H I} \gt 10^{18}\, \rm cm^{-2}$|⁠. We present the geometrical properties (Sérsic indices, effective radii, axis ratios, and position angles) of these galaxies determined using galfit. Using these properties along with star formation rates (SFRs, estimated using the H α or [O  ii ] luminosity) and stellar masses (M * estimated from spectral energy distribution fits), we examine correlations among various stellar and CGM properties. Our main findings are as follows: (1) SFR correlates well with M *, and most absorption-selected galaxies are consistent with the star formation main sequence of the global population. (2) More massive absorber counterparts are more centrally concentrated and are larger in size. (3) Galaxy sizes and normalized impact parameters correlate negatively with N HI, consistent with higher N HI absorption arising in smaller galaxies, and closer to galaxy centres. (4) Absorption and emission metallicities correlate with M * and specific SFR, implying metal-poor absorbers arise in galaxies with low past star formation and faster current gas consumption rates. (5) SFR surface densities of absorption-selected galaxies are higher than predicted by the Kennicutt–Schmidt relation for local galaxies, suggesting a higher star formation efficiency in the absorption-selected galaxies. [ABSTRACT FROM AUTHOR]

Our ability to interpret observations of galaxies and trace their stellar, gas, and dust content over cosmic time critically relies on our understanding of how the dust abundance and properties vary with environment. Here, we compute the dust surface density across cosmic times to put novel constraints on simulations of the build-up of dust. We provide observational estimates of the dust surface density consistently measured through depletion methods across a wide range of environments, going from the Milky Way up to z  = 5.5 galaxies. These conservative measurements provide complementary estimates to extinction-based observations. In addition, we introduce the dust surface density distribution function – in analogy with the cold gas column density distribution functions. We fit a power law of the form log  f (ΣDust) = −1.92 × log ΣDust − 3.65, which proves slightly steeper than that for neutral gas and metal absorbers. This observed relation, which can be computed by simulations predicting resolved dust mass functions through 2D projection, provides new constraints on modern dust models. [ABSTRACT FROM AUTHOR]

We model the kinematics of the high- and intermediate-velocity clouds (HVCs and IVCs) observed in absorption towards a sample of 55 Galactic halo stars with accurate distance measurements. We employ a simple model of a thick disc whose main free parameters are the gas azimuthal, radial, and vertical velocities (v ϕ, v R, and v z), and apply it to the data by fully accounting for the distribution of the observed features in the distance–velocity space. We find that at least two separate components are required to reproduce the data. A scenario where the HVCs and the IVCs are treated as distinct populations provides only a partial description of the data, which suggests that a pure velocity-based separation may give a biased vision of the gas physics at the Milky Way's disc–halo interface. Instead, the data are better described by a combination of an inflow component and an outflow component, both characterized by rotation with v ϕ comparable to that of the disc and v z of |$50\!-\!100\, {\rm km\, s}^{-1}$|⁠. Features associated with the inflow appear to be diffused across the sky, while those associated with the outflow are mostly confined within a bicone pointing towards (l  = 220°, b  = +40°) and (l  = 40°, b  = −40°). Our findings indicate that the lower (⁠|$|z| \lesssim 10\, {\rm kpc}$|⁠) Galactic halo is populated by a mixture of diffuse inflowing gas and collimated outflowing material, which are likely manifestations of a galaxy-wide gas cycle triggered by stellar feedback, that is, the galactic fountain. [ABSTRACT FROM AUTHOR]

Intermediate- and high-velocity clouds (IVCs, HVCs) are a potential source of fuel for star formation in the Milky Way (MW), but their origins and fates depend sensitively on their distances. We search for IVCs and HVCs in HST high-resolution ultraviolet spectra of 55 halo stars at vertical heights |$|z|\gtrsim \,1$| kpc. We show that IVCs (40 ≤ | |$v$| LSR| < 90 |${\rm km\, s}^{-1}$|⁠) have a high detection rate – the covering factor, f c – that is about constant (f c = 0.90 ± 0.04) from |$z$|  = 1.5 to 14 kpc, implying IVCs are essentially confined to | |$z$| | ≲ 1.5 kpc. For the HVCs (90 ≤ | |$v$| LSR| ≲ 170 |${\rm km\, s}^{-1}$|⁠), we find f c increases from f c ≃ 0.14 ± 0.10 at | |$z$| | ≲ 2–3 kpc to f c = 0.60 ± 0.15 at 6 ≲ | |$z$| | ≲ 14 kpc, the latter being similar to that found towards QSOs. In contrast, the covering factor of very high-velocity clouds (VHVCs; | |$v$| LSR| ≳ 170 |${\rm km\, s}^{-1}$|⁠) is |$f_c \lt 0.04$| in the stellar sample compared to 20 per cent towards QSOs, implying these clouds must be at d ≳ 10–15 kpc (| |$z$| | ≳ 10 kpc). Gas clouds with | |$v$| LSR| > 40 |${\rm km\, s}^{-1}$| at | b | ≳ 15° have therefore | |$v$| LSR| decreasing with decreasing | |$z$| |. Our findings are consistent with a Galactic rain and/or fountain origin for these clouds. In the latter scenario, VHVCs may mostly serve as fuel for the MW halo. In view of their high covering factors and since all the IVCs and some HVCs are found in the thick disc, they appear good candidates as gas reservoirs to help sustain star formation in the MW. [ABSTRACT FROM AUTHOR]

The primordial abundances of light elements produced in the standard theory of Big Bang nucleosynthesis (BBN) depend only on the cosmic ratio of baryons to photons, a quantity inferred from [...]

We report the detection of absorption from interstellar C2 and C3 towards the moderately reddened star Sk 143, located in the near ‘wing’ region of the SMC, in optical spectra obtained with the European Southern Observatory Very Large Telescope (VLT)/Ultraviolet and Visual Echelle Spectrograph. These detections of C2 (rotational levels J = 0–8) and C3 (J = 0–12) absorption in the SMC are the first beyond our Galaxy. The total abundances of C2 and C3 (relative to H2) are similar to those found in diffuse Galactic molecular clouds – as previously found for CH and CN – despite the significantly lower average metallicity of the Small Magellanic Cloud. Analysis of the rotational excitation of C2 yields an estimated kinetic temperature Tk ∼ 25 K and a moderately high total hydrogen density nH ∼ 870 cm−3 – compared to the T01 ∼ 45 K and nH ∼ 85–300 cm−3 obtained from H2. The populations of the lower rotational levels of C3 are consistent with an excitation temperature of about 34 K. [ABSTRACT FROM PUBLISHER]

We present observations of the intervening O vi absorption-line system at towards the quasi-stellar object (QSO) PKS 0405−123 obtained with the Far Ultraviolet Spectroscopic Explorer and Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. In addition to strong O vi, with , and moderate H i, with , this absorber shows absorption from C iii, N iv, O iv and O v, with upper limits for another seven ions. The large number of available ions allows us to test ionization models usually adopted with far fewer constraints. We find that the observed ionic column densities cannot be matched by single-temperature collisional ionization models, in or out of equilibrium. Photoionization models can match all of the observed column densities, including O vi. If one assumes photoionization by an ultraviolet (UV) background dominated by QSOs, the metallicity of the gas is , while if one assumes a model for the UV background with contributions from ionizing photons escaping from galaxies the metallicity is . Both give and to , though a solar C/O ratio is not ruled out. The choice of ionizing spectrum is poorly constrained and leads to systematic abundance uncertainties of ≈0.5 dex, despite the wide range of available ions. Multiphase models with a contribution from both photoionized gas (at ) and collisionally ionized gas [at K] can also match the observations for either assumed UV background giving very similar metallicities. We do not detect Ne viii or Mg x absorption. The limit on Ne viii/O vi (3σ) is the lowest yet observed. Thus, this absorber shows no firm evidence of the ‘warm-hot intergalactic medium’ at thought to contain a significant fraction of the baryons at low redshift. The O vi in this system is not necessarily a reliable tracer of the warm-hot intergalactic medium given the ambiguity in its origins. We present limits on the total column of warm-hot gas in this absorber as a function of temperature. This system would be unlikely to provide detectable X-ray absorption in the ions O vii or O viii even if it resided in front of the brighter X-ray sources in the sky. [ABSTRACT FROM AUTHOR]

Anisotropic thermal conduction plays an important role in various astrophysical systems. One of the most stringent tests of thermal conduction can be found in supernova remnants. In this paper we study anisotropic thermal conduction and examine the physical nature of the flux of thermal conduction in the classical and saturated limits. We also present a temporally second-order accurate implicit–explicit scheme for the time-update of thermal conduction terms within a numerical magnetohydrodynamics (MHD) scheme. Several useful tests are presented showing that the method works well. We also present a convergence study of the hot gas produced in thermally conducting, magnetized supernova remnants and show that the resolutions used here provide reasonably accurate results. [ABSTRACT FROM AUTHOR]

We present a large number of 2.5D simulations of supernova remnants expanding into interstellar media having a range of densities, temperatures and magnetic field strengths. The simulations include equilibrium cooling and anisotropic, flux-limited thermal conduction along magnetic field lines. The volume of hot gas produced during the remnant's evolution is shown to be strongly influenced by the inclusion of thermal conduction, supporting prior results by Slavin & Cox and Tilley & Balsara. The magnetic field has also been shown to play an extremely important role in reheating the gas at later epochs when the hot gas bubble collapses on itself. Low-density, strongly magnetized runs show the greatest effect of this reheating. The four-volumes and three-areas of gas with characteristic temperatures that cause it to emit in O vi, O vii and O viii have also been catalogued and their dependence on interstellar parameters has been documented. The results reveal the importance of magnetic tension forces as well as the anisotropic thermal conduction along field lines for the production of these ions. Simulated luminosities and linewidths of O vi, O vii and O viii as well as their dosages have been catalogued. Simulated linewidths of radioactive species, 26Al and 60Fe, ejected by supernovae have also been catalogued and found to be less than 200 km s−1 for most of the remnants' evolution. These results enable us to understand why INTEGRAL has thus far been unable to detect very large linewidths for these radioactive species in certain star-forming regions. [ABSTRACT FROM AUTHOR]

We explore the role of anisotropic thermal conduction on the evolution of supernova remnants (SNRs) through interstellar media with a range of densities via numerical simulations. We find that a remnant expanding in a dense environment can produce centre-bright hard X-ray emission within 20 kyr, and centre-bright soft X-ray emission within 60 kyr of the supernova event. In a more tenuous environment, the appearance of a centre-bright structure in hard X-rays is delayed until about 60 kyr. The soft X-ray emission from such a remnant may not become centre bright during its observable lifetime. This can explain the observations that show that mixed-morphology SNRs preferentially occur close to denser, molecular environments. Remnants expanding into denser environments tend to be smaller, making it easier for thermal conduction to make large changes in the temperatures of their hot gas bubbles. We show that the lower temperatures make it very favourable to use high-stage ions as diagnostics of the hot gas bubbles in SNRs. In particular, the distribution of O viii transitions from shell bright at early epochs to centre bright at later epochs in the evolution of an SNR expanding in a dense interstellar medium when the physics of thermal conduction is included. [ABSTRACT FROM AUTHOR]

The cosmic abundance of lithium continues to represent a conundrum, as predictions from BBN theory are inconsistent with measurements in the atmospheres of the lowest-metallicity stars. While there are worries that modifications of the stellar Li abundances may play a role in this discrepancy, no satisfactory solution has yet been found. We suggest an alternate approach to studying the cosmic abundance of Li: measurements of interstellar gas-phase Li in low-metallicity environments. [ABSTRACT FROM PUBLISHER]