▪ Abstract  Observations of damped Lyα systems offer a unique window on the neutral-gas reservoirs that gave rise to galaxies at high redshifts. This review focuses on critical properties such as the H I and metal content of the gas and on independent evidence for star formation. Together, these provide an emerging picture of gravitationally bound objects in which accretion of gas from the IGM replenishes gas consumed by star formation. Other properties such as dust content, molecular content, ionized-gas content, gas kinematics, and galaxy identifications are also reviewed. These properties point to a multiphase ISM in which radiative and hydrodynamic feedback processes are present. Numerical simulations and other types of models used to describe damped Lyα systems within the context of galaxy formation are also discussed.

Low-resolution spectroscopy of gamma-ray burst optical afterglows: Biases in the swift sample and characterization of the absorbers http:

We present evidence for variations in the fine-structure constant from Keck/HIRES spectra of 143 quasar absorption systems over the redshift range 0.2 < z abs < 4.2. This includes 15 new systems, mostly at high-z (z abs > 1.8). Our most robust estimate is a weighted mean ∆α/α = (−0.57 ± 0.11) × 10 −5 . We respond to recent criticisms of the many-multiplet method used to extract these constraints. The most important potential systematic error at low-z is the possibility of very different Mg heavy isotope abundances in the absorption clouds and laboratory: higher abundances of 25,26 Mg in the absorbers may explain the low-z results. Approximately equal mixes of 24 Mg and 25,26 Mg are required. Observations of Galactic stars generally show lower 25,26 Mg isotope fractions at the low metallicities typifying the absorbers. Higher values can be achieved with an enhanced population of intermediate mass stars at high redshift, a possibility at odds with observed absorption system element abundances. At present, all observational evidence is consistent with the varying-α results.Another promising method to search for variation of fundamental constants involves comparing different atomic clocks. Here we calculate the dependence of nuclear magnetic moments on quark masses and obtain limits on the variation of α and mq/ΛQCD from recent atomic clock experiments with hyperfine transitions in H, Rb, Cs, Hg + and an optical transition in Hg + .

Combining high time and frequency resolution full-polarisation spectra of Fast Radio Bursts (FRBs) with knowledge of their host galaxy properties provides an opportunity to study both the emission mechanism generating them and the impact of their propagation through their local environment, host galaxy, and the intergalactic medium. The Australian Square Kilometre Array Pathfinder (ASKAP) telescope has provided the first ensemble of bursts with this information. In this paper, we present the high time and spectral resolution, full polarisation observations of five localised FRBs to complement the results published for the previously studied ASKAP FRB 181112. We find that every FRB is highly polarised, with polarisation fractions ranging from 80 – 100%, and that they are generally dominated by linear polarisation. While some FRBs in our sample exhibit properties associated with an emerging archetype (i.e., repeating or apparently non-repeating), others exhibit characteristic features of both, implying the existence of a continuum of FRB properties. When examined at high time resolution, we find that all FRBs in our sample have evidence for multiple sub-components and for scattering at a level greater than expected from the Milky Way. We find no correlation between the diverse range of FRB properties (e.g., scattering time, intrinsic width, and rotation measure) and any global property of their host galaxy. The most heavily scattered bursts reside in the outskirts of their host galaxies, suggesting that the source-local environment rather than the host interstellar medium is likely the dominant origin of the scattering in our sample.

We investigate the properties of damped Lyman α systems (DLAS) in semi‐analytic models, focusing on whether the models can reproduce the kinematic properties of low‐ionization metal lines described by Prochaska & Wolfe. We explore a variety of approaches for modelling the radial distribution of the cold neutral gas associated with the galaxies in our models, and find that our results are very sensitive to this ingredient. If we use an approach based on work by Fall & Efstathiou, in which the sizes of the discs are determined by conservation of angular momentum, we find that the majority of the DLAS correspond to a single galactic disc. These models generically fail to reproduce the observed distribution of velocity widths. In alternative models in which the gas discs are considerably more extended, a significant fraction of DLAS arise from lines of sight intersecting multiple gas discs in a common halo. These models produce kinematics that fit the observational data, and also seem to agree well with the results of recent hydrodynamical simulations. Thus we conclude that cold dark matter based models of galaxy formation can be reconciled with the kinematic data, but only at the expense of the standard assumption that DLAS are produced by rotationally supported gas discs whose sizes are determined by conservation of angular momentum. We suggest that the distribution of cold gas at high redshift may be dominated by another process, such as tidal streaming caused by mergers.

The discovery of metal-poor stars (where metal is any element more massive than helium) has enabled astronomers to probe the chemical enrichment history of the Milky Way. More recently, element abundances in gas inside high-redshift galaxies has been probed through the absorption lines imprinted on the spectra of background quasars, but these have typically yielded measurements of only a few elements. Furthermore, interpretation of these abundances is complicated by the fact that differential incorporation of metals into dust can produce an abundance pattern similar to that expected from nucleosynthesis by massive stars. Here we report the observation of over 25 elements in a galaxy at redshift z = 2.626. With these data, we can examine nucleosynthetic processes independent of the uncertainty arising from depletion. We find that the galaxy was enriched mainly by massive stars (M > 15 solar masses) and propose that it is the progenitor of a massive elliptical galaxy. The detailed abundance patterns suggest that boron is produced through processes that act independently of metallicity, and may require alternative mechanisms for the nucleosynthesis of germanium.

Abstract. Accretion disk outflows are an important part of the quasar phenomenon. They might play a major role in distributing metals to the galactic surroundings, halting growth of the central black hole and providing kinetic energy "feedback" to regulate star formation in the host galaxies. Some models of galaxy evolution indicate that feedback requires kinetic energy luminosities, L K , that are ∼5% of the quasar bolometric; LK /L =Ṁw v 2 /2ηṀacc c 2 ∼ 5% is possible ifṀw ∼Ṁacc (with v ∼ 0.1c, and η ∼ 0.1). Here we describe results from two studies designed to test the theoretical energetics of radiatively driven outflows and derive observational constraints on the outflow geometry and physical properties emphasizing weaker outflow features like NALs and mini-BALs. Outflow Models: We are testing basic ideas about quasar outflows using the numerical code cloudy, which iterates to solve the equations of motion and mass continuity with self-consistent treatments of the temperature, ionization, excitation, opacities, and (importantly) the line overlap caused by velocity shifts in a moving medium. The radiative force is determined precisely from the line+continuum opacities and the transmitted spectrum at each location in the flow. The simple 1-D geometry allows us to examine a wide range of circumstances (launch radius, density at launch, metallicity, L/L Edd , incident spectral shape with or without a separate X-ray/far-UV shielding medium, etc.) and thereby determine what ranges of flow speeds, column densities, mass loss rates, and kinetic energy yields are possible with radiative driving. Early results suggest that, with the right initial conditions, flows driven by radiative forces can indeed reach speeds of order 0.1c with L K yields high enough to be important for feedback to galaxy evolution. 399https://www.cambridge.org/core/terms. https://doi

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