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Large fractions of metals are missing from the observable gas-phase in the interstellar medium (ISM) because they are incorporated into dust grains, a phenomenon called dust depletion. The study of the depletion of metals into dust grains in the ISM is important to investigate the origin and evolution of metals and cosmic dust. Here we aim at characterizing the dust depletion of several metals from the Milky Way to distant galaxies. We collect measurements of ISM metal column densities from absorption-line spectroscopy in the literature, and in addition, we determine Ti and Ni column densities from a sample of 70 damped Lyman-α absorbers (DLAs) towards quasars, observed at high spectral resolution with the Very Large Telescope (VLT) Ultraviolet and Visual Echelle Spectrograph (UVES). We use ISM relative abundances to estimate the dust depletion of 18 metals (C,

Among active galactic nuclei, blazars show extreme variability properties. We here investigate the case of the BL Lac object S4 0954+65 with data acquired in 2019–2020 by the Transiting Exoplanet Survey Satellite (TESS) and by the Whole Earth Blazar Telescope (WEBT) Collaboration. The 2-min cadence optical light curves provided by TESS during three observing sectors of nearly one month each, allow us to study the fast variability in great detail. We identify several characteristic short-term time-scales, ranging from a few hours to a few days. However, these are not persistent, as they differ in the various TESS sectors. The long-term photometric and polarimetric optical and radio monitoring undertaken by the WEBT brings significant additional information, revealing that i) in the optical, long-term flux changes are almost achromatic, while the short-term ones are strongly chromatic; ii) the radio flux variations at 37 GHz follow those in the optical with a delay of about three weeks; iii) the range of variation of the polarization degree and angle is much larger in the optical than in the radio band, but the mean polarization angles are similar; iv) the optical long-term variability is characterized by a quasi-periodicity of about one month. We explain the source behaviour in terms of a rotating inhomogeneous helical jet, whose pitch angle can change in time.

The chemical composition of gas in galaxies can be measured in great detail using absorption spectroscopy. By studying gas in galaxies in this way, it is possible to investigate small and faint galaxies, which are the most numerous in the universe. In particular, the chemical distribution of gas in absorbing systems gives us insight into cycles of gas in and around galaxies. In this work we study chemical enrichment within 64 damped Lyman-α absorption systems (DLAs) for redshifts in the range 1.7 < z < 4.2. We use high-resolution spectra from VLT/UVES to infer dust depletion from relative abundances of several metals. Specifically, we performed a component-by-component analysis within DLAs, and characterised variations in their chemical enrichment. Unlike hydrogen, the metal columns can be characterised according to their individual components. We used them to derive the dust depletion, which is an indicator of chemical enrichment. Our main results are as follows. Firstly, we find that some DLAs are chemically diverse within themselves (with the measure of dust depletion [Zn/Fe]fit ranging up to 0.62 dex within a single system), suggesting that the absorbing gas within these galaxies is chemically diverse. Secondly, although we do not find a clear trend of decreasing dust depletion with redshift, we do see that the most chemically enriched systems are at lower redshifts. We also observe evidence for dust-poor components at all redshifts, which may be due to the accretion of pristine gas onto galaxies. By combining the chemical and kinematic properties of the individual gas components, we observe potential signatures of infalling gas with low depletion at velocities below ∼100 km s−1, and outflows with high depletion and velocities of ∼600 km s−1. Finally, we find over-abundances of α-elements (an enhancement of ∼0.3 dex) and under-abundances of Mn in several gas components, which is likely a signature of core-collapse supernovae nucleosythesis in the ISM. We observe these effects mostly at lower levels of chemical enrichment.

Here we explore the efficiency and fidelity of a purely astrometric selection of quasars as point sources with zero proper motions in the Gaia data release 2 (DR2). We have built a complete candidate sample including 104 Gaia-DR2 point sources, which are brighter than 20th magnitude in the Gaia G-band within one degree of the north Galactic pole (NGP); all of them have proper motions that are consistent with zero within 2σ uncertainty. In addition to pre-existing spectra, we have secured long-slit spectroscopy of all the remaining candidates and find that all 104 stationary point sources in the field can be classified as either quasars (63) or stars (41). One of the new quasars that we discover is particularly interesting as the line-of-sight to it passes through the disc of a foreground (z = 0.022) galaxy, which imprints both NaD absorption and dust extinction on the quasar spectrum. The selection efficiency of the zero-proper-motion criterion at high Galactic latitudes is thus ≈60%. Based on this complete quasar sample, we examine the basic properties of the underlying quasar population within the imposed limiting magnitude. We find that the surface density of quasars is 20 deg−2 (at G <  20 mag), the redshift distribution peaks at z ∼ 1.5, and only eight systems (13-3+5%) show significant dust reddening. We then explore the selection efficiency of commonly used optical, near-, and mid-infrared quasar identification techniques and find that they are all complete at the 85−90% level compared to the astrometric selection. Finally, we discuss how the astrometric selection can be improved to an efficiency of ≈70% by including an additional cut requiring parallaxes of the candidates to be consistent with zero within 2σ. The selection efficiency will further increase with the release of future, more sensitive astrometric measurements from the Gaia mission. This type of selection, which is purely based on the astrometry of the quasar candidates, is unbiased in terms of colours and intrinsic emission mechanisms of the quasars and thus provides the most complete census of the quasar population within the limiting magnitude of Gaia.

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The study of the properties of galaxies in the first billion years after the Big Bang is one of the major topics of current astrophysics. Optical and near-infrared spectroscopy of the afterglows of long gamma-ray bursts (GRBs) provides a powerful diagnostic tool to probe the interstellar medium (ISM) of their host galaxies and foreground absorbers, even up to the highest redshifts. We analyze the VLT/X-shooter afterglow spectrum of GRB 210905A, triggered by the Neil Gehrels Swift Observatory, and detect neutral hydrogen, low-ionization, high-ionization, and fine-structure absorption lines from a complex system at z = 6.3118, which we associate with the GRB host galaxy. We use them to study the ISM properties of the host system, revealing the metallicity, kinematics, and chemical abundance pattern of its gas along the GRB line of sight. We also detect absorption lines from at least two foreground absorbers at z = 5.7390 and z = 2.8296. The total metallicity of the z ∼ 6.3 system is [M/H]tot = −1.72 ± 0.13, after correcting for dust depletion and taking α-element enhancement into account, as suggested by our analysis. This is consistent with the values found for the other two GRBs at z ∼ 6 with spectroscopic data showing metal absorption lines (GRB 050904 and GRB 130606A), and it is at the higher end of the metallicity distribution of quasar damped Lyman-α systems (QSO-DLAs) extrapolated to such a high redshift. In addition, we determine the overall amount of dust and dust-to-metal mass ratio (DTM) ([Zn/Fe]fit = 0.33 ± 0.09 and DTM = 0.18 ± 0.03). We find indications of nucleosynthesis due to massive stars and, for some of the components of the gas clouds, we find evidence of peculiar nucleosynthesis, with an overabundance of aluminum (as also found for GRB 130606A). From the analysis of fine-structure lines, we determine distances of several kiloparsecs for the low-ionization gas clouds closest to the GRB. Those are farther distances than usually found for GRB host absorption systems, possibly due to the very high number of ionizing photons produced by the GRB that could ionize the line of sight up to several hundreds of parsecs. Using the HST/F140W image of the GRB field, we show the GRB host galaxy (with a possible afterglow contamination) as well as multiple objects within 2″ from the GRB position. We discuss the galaxy structure and kinematics that could explain our observations, also taking into account a tentative detection of Lyman-α emission at z = 6.3449 (∼1200 km s−1 from the GRB redshift in velocity space), and the observational properties of Lyman-α emitters at very high redshift. This study shows the amazing potential of GRBs to access detailed information on the properties (metal enrichment, gas kinematic, dust content, nucleosynthesis...) of very high-redshift galaxies, independently of the galaxy luminosity. Deep spectroscopic observations with VLT/MUSE and JWST will offer the unique possibility of combining the information presented in this paper with the properties of the ionized gas, with the goal of better understanding how galaxies in the reionization era form and evolve.

(155140) 2005 UD has a similar orbit to (3200) Phaethon, an active asteroid in a highly eccentric orbit thought to be the source of the Geminid meteor shower. Evidence points to a genetic relationship between these two objects, but we have yet to fully understand how 2005 UD and Phaethon could have separated into this associated pair. Presented herein are new observations of 2005 UD from five observatories that were carried out during the 2018, 2019, and 2021 apparitions. We implemented light curve inversion using our new data, as well as dense and sparse archival data from epochs in 2005–2021, to better constrain the rotational period and derive a convex shape model of 2005 UD. We discuss two equally well-fitting pole solutions (λ = 116.°6, β = −53.°6) and (λ = 300.°3, β = −55.°4), the former largely in agreement with previous thermophysical analyses and the latter interesting due to its proximity to Phaethon’s pole orientation. We also present a refined sidereal period of P sid = 5.234246 ± 0.000097 hr. A search for surface color heterogeneity showed no significant rotational variation. An activity search using the deepest stacked image available of 2005 UD near aphelion did not reveal a coma or tail but allowed modeling of an upper limit of 0.04–0.37 kg s−1 for dust production. We then leveraged our spin solutions to help limit the range of formation scenarios and the link to Phaethon in the context of nongravitational forces and timescales associated with the physical evolution of the system.