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The halo of gas around a galaxy at redshift 1 is clumpy and anisotropic, with little variation in gas velocity, suggesting that it consists of entrained recycled material. Clumpy and anisotropic gas around a galaxy Star-forming galaxies are surrounded by haloes of gas that has been enriched with the 'metals' created in stars and supernovae. These haloes extend out at least 100 kiloparsecs, but the structure of the gas is poorly constrained. Sebastian Lopez and collaborators use a bright gravitationally lensed arc as a back light to study Mg ɪɪ absorption in a galaxy at a redshift of 0.98. They find that the absorption strength decreases with increasing distance from the galaxy, which is in good agreement with the limited results from earlier studies. However, they find that the gas is not isotropically distributed, and that the velocity varies little over a large area. Every star-forming galaxy has a halo of metal-enriched gas that extends out to at least 100 kiloparsecs 1 , 2 , 3 , as revealed by the absorption lines that this gas imprints on the spectra of background quasars 4 . However, quasars are sparse and typically probe only one narrow beam of emission through the intervening galaxy. Close quasar pairs 5 , 6 , 7 and gravitationally lensed quasars 8 , 9 , 10 , 11 have been used to circumvent this inherently one-dimensional technique, but these objects are rare and the structure of the circumgalactic medium remains poorly constrained. As a result, our understanding of the physical processes that drive the recycling of baryons across the lifetime of a galaxy is limited 12 , 13 . Here we report integral-field (tomographic) spectroscopy of an extended background source—a bright, giant gravitational arc. We can thus coherently map the spatial and kinematic distribution of Mg ɪɪ absorption—a standard tracer of enriched gas—in an intervening galaxy system at redshift 0.98 (around 8 billion years ago). Our gravitational-arc tomography unveils a clumpy medium in which the absorption strength decreases with increasing distance from the galaxy system, in good agreement with results for quasars. Furthermore, we find strong evidence that the gas is not distributed isotropically. Interestingly, we detect little kinematic variation over a projected area of approximately 600 square kiloparsecs, with all line-of-sight velocities confined to within a few tens of kilometres per second of each other. These results suggest that the detected absorption originates from entrained recycled material, rather than in a galactic outflow.

Present-day galaxies are surrounded by cool and enriched halo gas extending for hundreds of kiloparsecs. This halo gas is thought to be the dominant reservoir of material available to fuel future star formation, but direct constraints on its mass and physical properties have been difficult to obtain. We report the detection of a fast radio burst (FRB 181112), localized with arcsecond precision, that passes through the halo of a foreground galaxy. Analysis of the burst shows that the halo gas has low net magnetization and turbulence. Our results imply predominantly diffuse gas in massive galactic halos, even those hosting active supermassive black holes, contrary to some previous results.

An incidental spectrum of the poorly studied long-period variable EF Aquilae shows [O III] emission indicative of a symbiotic star. Strong GALEX detections in the UV reinforce this classification, providing overt evidence for the presence of the hot subluminous companion. Recent compilations of the photometric behavior strongly suggest that the cool component is a Mira variable. Thus EF Aql appears to be a member of the rare symbiotic Mira subgroup.

An incidental spectrum of the poorly studied long-period variable EF Aquilae shows [O III] emission indicative of a symbiotic star. Strong GALEX detections in the UV reinforce this classification, providing overt evidence for the presence of the hot subluminous companion. Recent compilations of the photometric behavior strongly suggest that the cool component is a Mira variable. Thus EF Aql appears to be a member of the rare symbiotic Mira subgroup.

The intergalactic medium (IGM) accounts for ≳ 90% of baryons at all epochs and yet its three dimensional distribution in the cosmic web remains mostly unknown. This is so because the only feasible way to observe the bulk of the IGM is through intervening absorption line systems in the spectra of bright background sources, which limits its characterization to being one-dimensional. Still, an averaged three dimensional picture can be obtained by combining and cross-matching multiple one-dimensional IGM information with three-dimensional galaxy surveys. Here, we present our recent and current efforts to map and characterize the IGM in the cosmic web using galaxies as tracers of the underlying mass distribution. In particular, we summarize our results on: (i) IGM around star-forming and non-star-forming galaxies; (ii) IGM within and around galaxy voids; and (iii) IGM in intercluster filaments. With these datasets, we can directly test the modern paradigm of structure formation and evolution of baryonic matter in the Universe.

The intergalactic medium (IGM) accounts for ~90% of baryons at all epochs and yet its three dimensional distribution in the cosmic web remains mostly unknown. This is so because the only feasible way to observe the bulk of the IGM is through intervening absorption line systems in the spectra of bright background sources, which limits its characterization to being one-dimensional. Still, an averaged three dimensional picture can be obtained by combining and cross-matching multiple one-dimensional IGM information with three-dimensional galaxy surveys. Here, we present our recent and current efforts to map and characterize the IGM in the cosmic web using galaxies as tracers of the underlying mass distribution. In particular, we summarize our results on: (i) IGM around star-forming and non-star-forming galaxies; (ii) IGM within and around galaxy voids; and (iii) IGM in intercluster filaments. With these datasets, we can directly test the modern paradigm of structure formation and evolution of baryonic matter in the Universe.

In this thesis we study the relationship between the intergalactic medium (IGM) and galaxies at z<1, in a statistical manner. Galaxies are mostly surveyed in emission using optical spectroscopy, while the IGM is mostly surveyed in absorption in the ultra-violet (UV) spectra of background quasi-stellar objects (QSOs). We present observational results investigating the connection between the IGM and galaxies using two complementary methods: • We use galaxy voids as tracers of both underdense and overdense regions. We use archival data to study the properties of H I absorption line systems within and around galaxy voids at z<0.1. Typical galaxy voids have sizes 10 Mpc and so our results constrain the very large-scale association. This sample contains 106 H I absorption systems and 1054 galaxy voids. • We use a sample of H I absorption line systems and galaxies from pencil beam surveys to measure the H I–galaxy cross-correlation at z<1. Our sample is composed of a combination of archival and new data taken by the author and collaborators. This survey covers transverse separations between H I and galaxies from ∼ 100 kpc (proper) up to ∼ 10 Mpc, filling the gap between the very large scales and those associated with the so-called circumgalactic medium (CGM). This sample contains 654 H I absorption systems and 17509 galaxies. Our results hint towards a picture in which there are at least three types of association between the diffuse gas in the Universe and galaxies at z 1: • One-to-one direct association because galaxies do contain diffuse gas. • Indirect association because both the IGM and galaxies trace the same over-dense underlying dark matter distribution. We provide quantitative evidence for this association. Moreover, we show that not all galaxies are related to the diffuse gas in the same way. In particular, a non negligible fraction of ‘non-star-forming’ galaxies might reside in environments devoid of diffuse H I. • No association because there are regions in the Universe that contain a significant amount of diffuse gas but that are devoid of galaxies. In these regions, only the IGM follows the underdense underlying dark matter distribution because galaxies are not present. We provide quantitative evidence for this scenario.

We examine to what extent disk and outflow models can reproduce observations of H I gas within a few virial radii of galaxies in pairs and groups. Using highly-sensitive HST/COS and FOS spectra of the Q0107 quasar triplet covering Ly\\(\\alpha\\) for z\\(\\lesssim\\)1, as well as a deep galaxy redshift survey including VIMOS, DEIMOS, GMOS and MUSE data, we test simple disk and outflow models against the H I absorption along three lines-of-sight (separated by 200-500 kpc) through nine galaxy groups in this field. These can be compared with our previous results in which these models can often be fit to the absorption around isolated galaxies. Our models can reproduce \\(\\approx\\) 75\\(\\%\\) of the 28 identified absorption components within 500 km/s of a group galaxy, so most of the H I around groups is consistent with a superposition of the CGM of the individual galaxies. Gas stripped in interactions between galaxies may be a plausible explanation for some of the remaining absorption, but neither the galaxy images nor the galaxy and absorber kinematics provide clear evidence of such stripped material, and these unexplained absorbers do not preferentially occur around close pairs of galaxies. We find H I column densities typically higher than at similar impact parameters around isolated galaxies (\\(\\approx\\) 2.5\\(\\sigma\\)), as well as more frequent detections of O VI than around isolated galaxies (30\\(\\%\\) of sightlines to 7\\(\\%\\)).

We present GeMS/GSAOI observations of five fast radio burst (FRB) host galaxies with sub-arcsecond localizations. We examine and quantify their spatial distributions and locations with respect to their host galaxy light distributions, finding a median host-normalized offset of 2.09 r_e and in fainter regions of the host. When combined with the FRB sample from Mannings et al. (2021), we find that FRBs are statistically distinct from Ca-rich transients in terms of light and from SGRBs and LGRBs in terms of host-normalized offset. We further find that most FRBs are in regions of elevated local stellar mass surface densities in comparison to the mean global values of their hosts. This, in combination with the combined FRB sample trace the distribution of stellar mass, points towards a possible similarity of the environments of CC-SNe and FRBs. We also find that 4/5 FRB hosts exhibit distinct spiral arm features, and the bursts originating from such hosts tend to appear on or close to the spiral structure of their hosts, with a median distance of 0.53 kpc. With many well-localized FRB detections looming on the horizon, we will be able to better characterize the properties of FRB environments relative to their host galaxies and other transient classes.

The repeating fast radio burst FRB20190520B is an anomaly of the FRB population thanks to its high dispersion measure (DM\\(=1205\\,\\)pc/cc) despite its low redshift of \\(z_\\mathrm{frb}=0.241\\). This excess has been attributed to a large host contribution of \\(DM_{host}\\approx 900\\,\\)pc/cc, far larger than any other known FRB. In this paper, we describe spectroscopic observations of the FRB20190520B field obtained as part of the FLIMFLAM survey, which yielded 701 galaxy redshifts in the field. We find multiple foreground galaxy groups and clusters, for which we then estimated halo masses by comparing their richness with numerical simulations. We discover two separate \\(M_{halo} >10^{14}\\,M_\\odot\\) galaxy clusters, at \\(z=0.1867\\) and \\(z=0.2170\\), respectively, that are directly intersected by the FRB sightline within their characteristic halo radius \\rvir{}. Subtracting off their estimated DM contributions as well that of the diffuse intergalactic medium, we estimate a host contribution of \\(DM_{host}=430^{+140}_{-220}\\,\\)pc/cc or \\(DM_{host}=280^{+140}_{-170}\\,\\)pc/cc (observed frame) depending on whether we assume the halo gas extends to \\(r_{200}\\) or \\(2\\times r_{200}\\). This significantly smaller \\(DM_{host}\\) -- no longer the largest known value -- is now consistent with H\\(\\alpha\\) emission measures of the host galaxy without invoking unusually high gas temperatures. Combined with the observed FRB scattering timescale, we estimate the turbulent fluctuation and geometric amplification factor of the scattering layer to be \\(\\tilde{F} G\\approx4.5 - 11\\,(\\mathrm{pc^2\\;km})^{-1/3}\\), suggesting most of the gas is close to the FRB host. This result illustrates the importance of incorporating foreground data for FRB analyses, both for understanding the nature of FRBs and to realize their potential as a cosmological probe.