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Clouds and other data artefacts frequently limit the retrieval of key variables from remotely sensed Earth observations. We train a natural language processing (NLP)-inspired algorithm with high-fidelity ocean simulations to accurately reconstruct masked or missing data in sea surface temperature (SST) fields—one of 54 essential climate variables identified by the Global Climate Observing System. We demonstrate that the resulting model, referred to as Enki, repeatedly outperforms previously adopted inpainting techniques by up to an order of magnitude in reconstruction error, while displaying exceptional performance even in circumstances where the majority of pixels are masked. Furthermore, experiments on real infrared sensor data with masked percentages of at least 40% show reconstruction errors of less than the known uncertainty of this sensor (root mean square error (RMSE) ≲0.1 K). We attribute Enki’s success to the attentive nature of NLP combined with realistic SST model outputs—an approach that could be extended to other remotely sensed variables. This study demonstrates that systems built upon Enki—or other advanced systems like it—may therefore yield the optimal solution to mitigating masked pixels in in climate-critical ocean datasets sampling a rapidly changing Earth.

We present the host galaxies of four apparently nonrepeating fast radio bursts (FRBs), FRB 20181223C, FRB 20190418A, FRB 20191220A, and FRB 20190425A, reported in the first Canadian Hydrogen Intensity Mapping Experiment (CHIME/FRB) catalog. Our selection of these FRBs is based on a planned hypothesis testing framework where we search all CHIME/FRB Catalog-1 events that have low extragalactic dispersion measure ( 10°) and saved baseband data. We associate the selected FRBs with galaxies with moderate to high star formation rates located at redshifts between 0.027 and 0.071. We also search for possible multimessenger counterparts, including persistent compact radio and gravitational-wave sources, and find none. Utilizing the four FRB hosts from this study, along with the hosts of 14 published local Universe FRBs ( z < 0.1) with robust host association, we conduct an FRB host demographics analysis. We find all 18 local Universe FRB hosts in our sample to be spirals (or late-type galaxies), including the host of FRB 20220509G, which was previously reported to be elliptical. Using this observation, we scrutinize proposed FRB source formation channels and argue that core-collapse supernovae are likely the dominant channel to form FRB sources. Moreover, we infer no significant difference in the host properties of repeating and apparently nonrepeating FRBs in our local Universe FRB host sample. Finally, we find the burst rates of these four apparently nonrepeating FRBs to be consistent with those of the sample of localized repeating FRBs observed by CHIME/FRB. Therefore, we encourage further monitoring of these FRBs with more sensitive radio telescopes.

FRB 20220610A is a high-redshift fast radio burst (FRB) that has not been observed to repeat. Here, we present rest-frame UV and optical Hubble Space Telescope observations of the field of FRB 20220610A. The imaging reveals seven extended sources, one of which we identify as the most likely host galaxy with a spectroscopic redshift of z = 1.017. We spectroscopically confirm three additional sources to be at the same redshift and identify the system as a compact galaxy group with possible signs of interaction among group members. We determine the host of FRB 20220610A to be a star-forming galaxy with a stellar mass of ≈10 ^9.7 M _⊙ , mass-weighted age of ≈2.6 Gyr, and star formation rate (integrated over the last 100 Myr) of ≈1.7 M _⊙ yr ^−1 . These host properties are commensurate with the star-forming field galaxy population at z ∼ 1 and trace their properties analogously to the population of low- z FRB hosts. Based on estimates of the total stellar mass of the galaxy group, we calculate a fiducial contribution to the observed dispersion measure from the intragroup medium of ≈90–182 pc cm ^−3 (rest frame). This leaves a significant excess of ${515}_{-272}^{+122}$ pc cm ^−3 (in the observer frame); further observation will be required to determine the origin of this excess. Given the low occurrence rates of galaxies in compact groups, the discovery of an FRB in one demonstrates a rare, novel environment in which FRBs can occur. As such groups may represent ongoing or future mergers that can trigger star formation, this supports a young stellar progenitor relative to star formation.

Identification and follow-up observations of the host galaxies of fast radio bursts (FRBs) not only help us understand the environments in which the FRB progenitors reside, but also provide a unique way of probing the cosmological parameters using the dispersion measures (DMs) of FRBs and distances to their origin. A fundamental requirement is an accurate distance measurement to the FRB host galaxy, but for some sources viewed through the Galactic plane, optical/near-infrared spectroscopic redshifts are extremely difficult to obtain due to dust extinction. Here we report the first radio-based spectroscopic redshift measurement for an FRB host galaxy, through detection of its neutral hydrogen (H i ) 21 cm emission using MeerKAT observations. We obtain an H i –based redshift of z = 0.0357 ± 0.0001 for the host galaxy of FRB 20230718A, an apparently nonrepeating FRB detected in the Commensal Real-time ASKAP Fast Transients survey and localized at a Galactic latitude of –0.°367. Our observations also reveal that the FRB host galaxy is interacting with a nearby companion, which is evident from the detection of an H i bridge connecting the two galaxies. A subsequent optical spectroscopic observation confirmed an FRB host galaxy redshift of 0.0359 ± 0.0004. This result demonstrates the value of H i to obtain redshifts of FRBs at low Galactic latitudes and redshifts. Such nearby FRBs whose DMs are dominated by the Milky Way can be used to characterize these components and thus better calibrate the remaining cosmological contribution to dispersion for more distant FRBs that provide a strong lever arm to examine the Macquart relation between cosmological DM and redshift.

We present an analysis of Hubble Space Telescope COS/G160M observations of C IV in the inner circumgalactic medium (CGM) of a novel sample of eight z ∼ 0, L ≈ L ^⋆ galaxies, paired with UV-bright QSOs at impact parameters ( R _proj ) between 25 and 130 kpc. The galaxies in this stellar-mass-controlled sample (log _10 M _⋆ / M _⊙ ∼ 10.2–10.9 M _⊙ ) host supermassive black holes (SMBHs) with dynamically measured masses spanning log _10 M _BH / M _⊙ ∼ 6.8–8.4; this allows us to compare our results with models of galaxy formation where the integrated feedback history from the SMBH alters the CGM over long timescales. We find that the C IV column density measurements ( N _C IV ; average log _10 N _C IV,CH = 13.94 ± 0.09 cm ^−2 ) are largely consistent with existing measurements from other surveys of N _C IV in the CGM (average log _10 N _C IV,Lit = 13.90 ± 0.08 cm ^−2 ), but do not show obvious variation as a function of the SMBH mass. By contrast, specific star formation rate (sSFR) is highly correlated with the ionized content of the CGM. We find a large spread in sSFR for galaxies with log _10 M _BH / M _⊙ > 7.0, where the CGM C IV content shows a clear dependence on galaxy sSFR but not M _BH . Our results do not indicate an obvious causal link between CGM C IV and the mass of the galaxy’s SMBH; however, through comparisons to the EAGLE, Romulus25, and IllustrisTNG simulations, we find that our sample is likely too small to constrain such causality.

Poststarburst galaxies are believed to be in a rapid transition between major merger starbursts and quiescent ellipticals, where active galactic nucleus (AGN) feedback is suggested as one of the processes responsible for the quenching. To study the role of AGN feedback, we constructed a sample of poststarburst candidates with AGN and indications of ionized outflows in optical. We use MUSE/VLT observations to spatially resolve the properties of the stars and multiphase gas in five of them. All galaxies show signatures of interaction/merger in their stellar or gas properties, with some at an early stage of interaction with companions ∼50 kpc, suggesting that optical poststarburst signatures may be present well before the final starburst and coalescence. We detect narrow and broad kinematic components in multiple transitions in all the galaxies. Our detailed analysis of their kinematics and morphology suggests that, contrary to our expectation, the properties of the broad kinematic components are inconsistent with AGN-driven winds in three out of five galaxies. The two exceptions are also the only galaxies in which spatially resolved NaID P-Cygni profiles are detected. In some cases, the observations are more consistent with interaction-induced galactic-scale flows, an often overlooked process. These observations raise the question of how to interpret broad kinematic components in interacting and perhaps also in active galaxies, in particular when spatially resolved observations are not available or cannot rule out merger-induced galactic-scale motions. We suggest that NaID P-Cygni profiles are more effective outflow tracers, and use them to estimate the energy that is carried by the outflow.

The Macquart relation describes the correlation between the dispersion measure (DM) of fast radio bursts (FRBs) and the redshift z of their host galaxies. The scatter of the Macquart relation is sensitive to the distribution of baryons in the intergalactic medium including those ejected from galactic halos through feedback processes. The variance of the distribution in DMs from the cosmic web (DM _cosmic ) is parameterized by a fluctuation parameter F . In this work, we present a new measurement of F using 78 FRBs of which 21 have been localized to host galaxies. Our analysis simultaneously fits for the Hubble constant H _0 and the DM distribution due to the FRB host galaxy. We find that the fluctuation parameter is degenerate with these parameters, most notably H _0 , and use a uniform prior on H _0 to measure ${\mathrm{log}}_{10}F\gt -0.86$ at the 3 σ confidence interval and a new constraint on the Hubble constant ${H}_{0}={85.3}_{-8.1}^{+9.4}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ . Using a synthetic sample of 100 localized FRBs, the constraint on the fluctuation parameter is improved by a factor of ∼2. Comparing our F measurement to simulated predictions from cosmological simulation (IllustrisTNG), we find agreement between redshifts 0.4 < z and z < 2.0. However, at z < 0.4, the simulations underpredict F , which we attribute to the rapidly changing extragalactic DM excess distribution at low redshift.

We report on contemporaneous optical observations at ≈10 ms timescales from the fast radio burst (FRB) 20180916B of two repeat bursts (FRB 20201023 and FRB 20220908) taken with the ‘Alopeke camera on the Gemini-North telescope. These repeats have radio fluences of 2.8 and 3.5 Jy ms, respectively, approximately in the lower 50th percentile for fluence from this repeating burst. The ‘Alopeke data reveal no significant optical detections at the FRB position and we place 3 σ upper limits to the optical fluences of

We present Keck Cosmic Web Imager Ly α integral field spectroscopy of the fields surrounding 14 damped Ly α absorbers (DLAs) at z ≈ 2. Of these 14 DLAs, nine have high metallicities ([M/H] > − 0.3), and four of those nine feature a CO-emitting galaxy at an impact parameter ≲30 kpc. Our search reaches median Ly α line flux sensitivities of ∼2 × 10 ^−17 erg s ^−1 cm ^−2 over apertures of ∼6 kpc and out to impact parameters of ∼50 kpc. We recover the Ly α flux of three known Ly α -emitting H i -selected galaxies in our sample. In addition, we find two Ly α emitters at impact parameters of ≈50–70 kpc from the high-metallicity DLA at z ≈ 1.96 toward QSO B0551-366. This field also contains a massive CO-emitting galaxy at an impact parameter of ≈15 kpc. Apart from the field with QSO B0551-366, we do not detect significant Ly α emission in any of the remaining eight high-metallicity DLA fields. Considering the depth of our observations and our ability to recover previously known Ly α emitters, we conclude that H i -selected galaxies associated with high-metallicity DLAs at z ≈ 2 are dusty and therefore might feature low Ly α escape fractions. Our results indicate that complementary approaches—using Ly α , CO, H α , and [C ii ] 158 μ m emission—are necessary to identify the wide range of galaxy types associated with z ≈ 2 DLAs.

We present high-resolution 1.5–6 GHz Karl G. Jansky Very Large Array and Hubble Space Telescope (HST) optical and infrared observations of the extremely active repeating fast radio burst (FRB) FRB 20201124A and its barred spiral host galaxy. We constrain the location and morphology of star formation in the host and search for a persistent radio source (PRS) coincident with FRB 20201124A. We resolve the morphology of the radio emission across all frequency bands and measure a star formation rate (SFR) ≈ 8.9 M _⊙ yr ^−1 , approximately ≈2.5–6 times larger than optically inferred SFRs, demonstrating dust-obscured star formation throughout the host. Compared to a sample of all known FRB hosts with radio emission, the host of FRB 20201124A has the most significantly obscured star formation. While HST observations show the FRB to be offset from the bar or spiral arms, the radio emission extends to the FRB location. We propose that the FRB progenitor could have formed in situ (e.g., a magnetar born from a massive star explosion). It is still plausible, although less likely, that the progenitor of FRB 20201124A migrated from the central bar of the host. We further place a limit on the luminosity of a putative PRS at the FRB position of L _6.0GHz ≲ 1.8 ×10 ^27 erg s ^−1 Hz ^−1 , among the deepest PRS luminosity limits to date. However, this limit is still broadly consistent with both magnetar nebulae and hypernebulae models assuming a constant energy injection rate of the magnetar and an age of ≳10 ^5 yr in each model, respectively.

The repeating fast radio burst FRB 20190520B is an anomaly of the FRB population thanks to its high dispersion measure (DM = 1205 pc cm ^−3 ) despite its low redshift of z _frb = 0.241. This excess has been attributed to a large host contribution of DM _host ≈ 900 pc cm ^−3 , far larger than any other known FRB. In this paper, we describe spectroscopic observations of the FRB 20190520B 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 _⊙ galaxy clusters at z = 0.1867 and 0.2170 that are directly intersected by the FRB sight line within their characteristic halo radius r _200 . Subtracting off their estimated DM contributions, as well that of the diffuse intergalactic medium, we estimate a host contribution of ${{\rm{D}}{\rm{M}}}_{{\rm{h}}{\rm{o}}{\rm{s}}{\rm{t}}}={430}_{-220}^{+140}$ or ${280}_{-170}^{+140}\,{\rm{p}}{\rm{c}}\,{{\rm{c}}{\rm{m}}}^{-3}$ (observed frame), depending on whether we assume that the halo gas extends to r _200 or 2 × r _200 . This significantly smaller DM _host —no longer the largest known value—is now consistent with H α 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 $\widetilde{F}G\approx 4.5\mbox{--}11{({\mathrm{pc}}^{2}\,\mathrm{km})}^{-1/3}$ , suggesting that 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.

Direct observations of low-mass, low-metallicity galaxies at z ≳ 4 provide an indispensable opportunity for detailed inspection of the ionization radiation, gas flow, and metal enrichment in sources similar to those that reionized the universe. Combining the James Webb Space Telescope (JWST), Very Large Telescope/MUSE, and Atacama Large Millimeter/submillimeter Array, we present detailed observations of a strongly lensed, low-mass (≈10 ^7.6 M _⊙ ) galaxy at z = 3.98 (also see Vanzella et al.). We identify strong narrow nebular emission, including C iv λ λ 1548, 1550, He ii λ 1640, O iii ] λ λ 1661, 1666, [Ne iii ] λ 3868, [O ii ] λ 3727, and the Balmer series of hydrogen from this galaxy, indicating a metal-poor H ii region (≲0.12 Z _⊙ ) powered by massive stars. Further, we detect a metal-enriched damped Ly α system (DLA) associated with the galaxy with the H i column density of N _H I ≈ 10 ^21.8 cm ^−2 . The metallicity of the associated DLA may reach the supersolar metallicity (≳ Z _⊙ ). Moreover, thanks to JWST and gravitational lensing, we present the resolved UV slope ( β ) map at the spatial resolution of ≈100 pc at z = 4, with steep UV slopes reaching β ≈ −2.5 around three star-forming clumps. Combining with low-redshift analogs, our observations suggest that low-mass, low-metallicity galaxies, which dominate reionization, could be surrounded by a high covering fraction of the metal-enriched, neutral-gaseous clouds. This implies that the metal enrichment of low-mass galaxies is highly efficient, and further supports that in low-mass galaxies, only a small fraction of ionizing radiation can escape through the interstellar or circumgalactic channels with low-column-density neutral gas.

We report the first statistical analyses of [C ii ] and dust continuum observations in six strong O i absorber fields at the end of the reionization epoch obtained by the Atacama Large Millimeter/submillimeter Array (ALMA). Combined with one [C ii ] emitter reported in Wu et al., we detect one O i -associated [C ii ] emitter in six fields. At redshifts of O i absorbers in nondetection fields, no emitters are brighter than our detection limit within impact parameters of 50 kpc and velocity offsets between ±200 km s ^−1 . The averaged [C ii ]-detection upper limit is 50 kpc) and having larger outflow velocities within ±600 km s ^−1 . If these detections are confirmed in the future, then the mechanism of pushing metals at larger distances with higher velocities needs to be further explored from the theoretical side.

We present a sample of nine fast radio bursts (FRBs) from which we derive magnetic field strengths of the host galaxies represented by normal, z < 0.5 star-forming galaxies with stellar masses M _* ≈ 10 ^8 –10 ^10.5 M _⊙ . We find no correlation between the FRB rotation measure (RM) and redshift, which indicates that the RM values are due mostly to the FRB host contribution. This assertion is further supported by a significant positive correlation (Spearman test probability P _S < 0.05) found between the RM and the estimated host dispersion measure (DM _host ; with Spearman rank correlation coefficient r _S = +0.75). For these nine galaxies, we estimate their magnetic field strengths projected along the sight line ∣ B _∥ ∣, finding a low median value of 0.5 μ G. This implies the magnetic fields of our sample of hosts are weaker than those characteristic of the solar neighborhood (≈6 μ G), but relatively consistent with a lower limit on the observed range of ≈2–10 μ G for star-forming disk galaxies, especially as we consider reversals in the B -field, and that we are only probing B _∥ . We compare to RMs from simulated galaxies of the Auriga project—magneto-hydrodynamic cosmological zoom simulations—and find that the simulations predict the observed values to within a 95% confidence interval. Upcoming FRB surveys will provide hundreds of new FRBs with high-precision localizations, RMs, and imaging follow-up to support further investigation into the magnetic fields of a diverse population of z < 1 galaxies.

We present a comprehensive catalog of observations and stellar population properties for 23 highly secure host galaxies of fast radio bursts (FRBs). Our sample comprises 6 repeating FRBs and 17 apparent nonrepeaters. We present 82 new photometric and 8 new spectroscopic observations of these hosts. Using stellar population synthesis modeling and employing nonparametric star formation histories (SFHs), we find that FRB hosts have a median stellar mass of ≈10 ^9.9 M _⊙ , mass-weighted age ≈5.1 Gyr, and ongoing star formation rate ≈1.3 M _⊙ yr ^−1 but span wide ranges in all properties. Classifying the hosts by degree of star formation, we find that 87% (20 of 23 hosts) are star-forming, two are transitioning, and one is quiescent. The majority trace the star-forming main sequence of galaxies, but at least three FRBs in our sample originate in less-active environments (two nonrepeaters and one repeater). Across all modeled properties, we find no statistically significant distinction between the hosts of repeaters and nonrepeaters. However, the hosts of repeating FRBs generally extend to lower stellar masses, and the hosts of nonrepeaters arise in more optically luminous galaxies. While four of the galaxies with the clearest and most prolonged rises in their SFHs all host repeating FRBs, demonstrating heightened star formation activity in the last ≲100 Myr, one nonrepeating host shows this SFH as well. Our results support progenitor models with short delay channels (i.e., magnetars formed via core-collapse supernova) for most FRBs, but the presence of some FRBs in less-active environments suggests a fraction form through more delayed channels.

The FLIMFLAM survey is collecting spectroscopic data of field galaxies near fast radio burst (FRB) sight lines to constrain key parameters describing the distribution of matter in the Universe. In this work, we leverage the survey data to determine the source of the excess extragalactic dispersion measure (DM), compared to Macquart relation estimates of four FRBs: FRB20190714A, FRB20200906A, FRB20200430A, and FRB20210117A. By modeling the gas distribution around the foreground galaxy halos and galaxy groups of the sight lines, we estimate DM _halos , their contribution to the FRB DMs. The FRB20190714A sight line shows a clear excess of foreground halos which contribute roughly two-thirds of the observed excess DM, thus implying a sight line that is baryon dense. FRB20200906A shows a smaller but nonnegligible foreground halo contribution, and further analysis of the intergalactic medium is necessary to ascertain the true cosmic contribution to its DM. FRB20200430A and FRB20210117A show negligible foreground contributions, implying a large host galaxy excess and/or progenitor environment excess.

We present findings of the detection of Magnesium II (Mg ii , λ = 2796, 2803 Å) absorbers from the early data release of the Dark Energy Spectroscopic Instrument (DESI). DESI is projected to obtain spectroscopy of approximately 3 million quasars (QSOs), of which over 99% are anticipated to be at redshifts greater than z > 0.3, such that DESI would be able to observe an associated or intervening Mg ii absorber illuminated by the background QSO. We have developed an autonomous supplementary spectral pipeline that detects these systems through an initial line-fitting process and then confirms the line properties using a Markov Chain Monte Carlo sampler. Based upon a visual inspection of the resulting systems, we estimate that this sample has a purity greater than 99%. We have also investigated the completeness of our sample in regard to both the signal-to-noise properties of the input spectra and the rest-frame equivalent width ( W _0 ) of the absorber systems. From a parent catalog containing 83,207 quasars, we detect a total of 23,921 Mg ii absorption systems following a series of quality cuts. Extrapolating from this occurrence rate of 28.8% implies a catalog at the completion of the five-year DESI survey that will contain over eight hundred thousand Mg ii absorbers. The cataloging of these systems will enable significant further research because they carry information regarding circumgalactic medium environments, the distribution of intervening galaxies, and the growth of metallicity across the redshift range 0.3 ≤ z < 2.5.

We use medium- and high-resolution spectroscopy of close pairs of quasars to analyze the circumgalactic medium (CGM) surrounding 32 damped Ly α absorption systems (DLAs). The primary quasar sightline in each pair probes an intervening DLA in the redshift range 1.6 < z _abs < 3.5, such that the secondary sightline probes absorption from Ly α and a large suite of metal-line transitions (including O i , C ii , C iv , Si ii , and Si iv ) in the DLA host galaxy’s CGM at transverse distances 24 kpc ≤ R _⊥ ≤ 284 kpc. Analysis of Ly α in the CGM sightlines shows an anticorrelation between R _⊥ and H i column density ( N _HI ) with 99.8% confidence, similar to that observed around luminous galaxies. The incidences of C ii and Si ii with N > 10 ^13 cm ^−2 within 100 kpc of DLAs are larger by 2 σ than those measured in the CGM of Lyman break galaxies (C _f ( N _C _II ) > 0.89 and ${{\rm{C}}}_{f}({N}_{\mathrm{Si}{\rm\small{II}}})={0.75}_{-0.17}^{+0.12}$ ). Metallicity constraints derived from ionic ratios for nine CGM systems with negligible ionization corrections and N _HI > 10 ^18.5 cm ^−2 show a significant degree of scatter (with metallicities/limits across the range $-2.06\lesssim \mathrm{log}Z/{Z}_{\odot }\lesssim -0.75$ ), suggesting inhomogeneity in the metal distribution in these environments. Velocity widths of C iv λ 1548 and low-ionization metal species in the DLA versus CGM sightlines are strongly (>2 σ ) correlated, suggesting that they trace the potential well of the host halo over R _⊥ ≲ 300 kpc scales. At the same time, velocity centroids for C iv λ 1548 differ in DLA versus CGM sightlines by >100 km s ^−1 for ∼50% of velocity components, but few components have velocities that would exceed the escape velocity assuming dark matter host halos of ≥10 ^12 M _⊙ .

The Dragonfly galaxy (MRC 0152-209), the most infrared-luminous radio galaxy at redshift z ∼ 2, is a merger system containing a powerful radio source and large displacements of gas. We present kiloparsec-resolution data from the Atacama Large Millimeter/submillimeter Array and the Very Large Array of carbon monoxide (6−5), dust, and synchrotron continuum, combined with Keck integral field spectroscopy. We find that the Dragonfly consists of two galaxies with rotating disks that are in the early phase of merging. The radio jet originates from the northern galaxy and brightens when it hits the disk of the southern galaxy. The Dragonfly galaxy therefore likely appears as a powerful radio galaxy because its flux is boosted into the regime of high- z radio galaxies by the jet–disk interaction. We also find a molecular outflow of (1100 ± 550) M _⊙ yr ^−1 associated with the radio host galaxy, but not with the radio hot spot or southern galaxy, which is the galaxy that hosts the bulk of the star formation. Gravitational effects of the merger drive a slower and longer-lived mass displacement at a rate of (170 ± 40) M _⊙ yr ^−1 , but this tidal debris contains at least as much molecular gas mass as the much faster outflow, namely M _H2 = (3 ± 1) × 10 ^9 ( α _CO /0.8) M _⊙ . This suggests that both the active-galactic-nucleus-driven outflow and mass transfer due to tidal effects are important in the evolution of the Dragonfly system. The Keck data show Ly α emission spread across 100 kpc, and C iv and He ii emission across 35 kpc, confirming the presence of a metal-rich and extended circumgalactic medium previously detected in CO(1–0).

This study addresses how the incidence rate of strong O vi absorbers in a galaxy’s circumgalactic medium (CGM) depends on galaxy mass and, independently, on the amount of star formation in the galaxy. We use Hubble Space Telescope/Cosmic Origins Spectrograph absorption spectroscopy of quasars to measure O vi absorption within 400 projected kpc and 300 km s ^−1 of 52 galaxies with M _* ∼ 3 × 10 ^10 M _⊙ . The galaxies have redshifts 0.12 < z < 0.6, stellar masses 10 ^10.1 M _⊙ < M _* < 10 ^10.9 M _⊙ , and spectroscopic classifications as star-forming or passive. We compare the incidence rates of high column density O vi absorption ( N _O _VI ≥ 10 ^14.3 cm ^−2 ) near star-forming and passive galaxies in two narrow ranges of stellar mass and, separately, in a matched range of halo mass. In all three mass ranges, the O vi covering fraction within 150 kpc is higher around star-forming galaxies than around passive galaxies with greater than 3 σ -equivalent statistical significance. On average, the CGM of star-forming galaxies with M _* ∼ 3 × 10 ^10 M _⊙ contains more O vi than the CGM of passive galaxies with the same mass. This difference is evidence for a CGM transformation that happens together with galaxy quenching and is not driven primarily by halo mass.

We combine data sets from the CGM ^2 and CASBaH surveys to model a transition point, R _cross , between circumgalactic and intergalactic media (CGM and IGM, respectively). In total, our data consist of 7244 galaxies at z < 0.5 with precisely measured spectroscopic redshifts, all having impact parameters of 0.01–20 comoving Mpc from 28 QSO sightlines with high-resolution UV spectra that cover H i Ly α . Our best-fitting model is a two-component model that combines a 3D absorber–galaxy cross-correlation function with a simple Gaussian profile at inner radii to represent the CGM. By design, this model gives rise to a determination of R _cross as a function of galaxy stellar mass, which can be interpreted as the boundary between the CGM and IGM. For galaxies with 10 ^8 ≤ M _⋆ / M _⊙ ≤ 10 ^10.5 , we find that R _cross ( M _⋆ ) ≈ 2.0 ± 0.6 R _vir . Additionally, we find excellent agreement between R _cross ( M _⋆ ) and the theoretically determined splashback radius for galaxies in this mass range. Overall, our results favor models of galaxy evolution at z < 0.5 that distribute T ≈ 10 ^4 K gas to distances beyond the virial radius.

We present the discovery of an as yet nonrepeating fast radio burst (FRB), FRB 20210117A, with the Australian Square Kilometre Array Pathfinder (ASKAP), as a part of the Commensal Real-time ASKAP Fast Transients Survey. The subarcsecond localization of the burst led to the identification of its host galaxy at z = 0.214(1). This redshift is much lower than what would be expected for a source dispersion measure (DM) of 729 pc cm ^−3 , given typical contributions from the intergalactic medium and the host galaxy. Optical observations reveal the host to be a dwarf galaxy with little ongoing star formation—very different to the dwarf host galaxies of the known repeating FRBs 20121102A and 20190520B. We find an excess DM contribution from the host and attribute it to the FRB’s local environment. We do not find any radio emission from the FRB site or host galaxy. The low magnetized environment and the lack of a persistent radio source indicate that the FRB source is older than those found in other dwarf host galaxies, establishing the diversity of FRB sources in dwarf galaxy environments. We find our observations to be fully consistent with the “hypernebula” model, where the FRB is powered by an accretion jet from a hyperaccreting black hole. Finally, our high time resolution analysis reveals burst characteristics similar to those seen in repeating FRBs. We encourage follow-up observations of FRB 20210117A to establish any repeating nature.

We conducted a deep spectroscopic survey, named SSA22-HIT, in the SSA22 field with the DEep Imaging MultiObject Spectrograph (DEIMOS) on the Keck telescope, designed to tomographically map high- z H i gas through analysis of Ly α absorption in background galaxies’ spectra. In total, 198 galaxies were spectroscopically confirmed at 2.5 < z < 6 with a few low- z exceptions in the 26 × 15 arcmin ^2 area, of which 148 were newly determined in this study. Our redshift measurements were merged with previously confirmed redshifts available in the 34 × 27 arcmin ^2 area of the SSA22 field. This compiled catalog containing 730 galaxies of various types at z > 2 is useful for various applications, and it is made publicly available. Our SSA22-HIT survey has increased by approximately twice the number of spectroscopic redshifts of sources at z > 3.2 in the observed field. From a comparison with publicly available redshift catalogs, we show that our compiled redshift catalog in the SSA22 field is comparable to those among major extragalactic survey fields in terms of a combination of wide area and high surface number density of objects at z > 2. About 40% of the spectroscopically confirmed objects in SSA22-HIT show reasonable quality of spectra in the wavelengths shorter than Ly α when a sufficient amount of smoothing is adopted. Our data set enables us to make the H i tomographic map at z ≳ 3, which we present in a parallel study.

The Dark Energy Spectroscopic Instrument (DESI) Survey has obtained a set of spectroscopic measurements of galaxies to validate the final survey design and target selections. To assist in these tasks, we visually inspect DESI spectra of approximately 2500 bright galaxies, 3500 luminous red galaxies (LRGs), and 10,000 emission-line galaxies (ELGs) to obtain robust redshift identifications. We then utilize the visually inspected redshift information to characterize the performance of the DESI operation. Based on the visual inspection (VI) catalogs, our results show that the final survey design yields samples of bright galaxies, LRGs, and ELGs with purity greater than 99%. Moreover, we demonstrate that the precision of the redshift measurements is approximately 10 km s ^−1 for bright galaxies and ELGs and approximately 40 km s ^−1 for LRGs. The average redshift accuracy is within 10 km s ^−1 for the three types of galaxies. The VI process also helps improve the quality of the DESI data by identifying spurious spectral features introduced by the pipeline. Finally, we show examples of unexpected real astronomical objects, such as Ly α emitters and strong lensing candidates, identified by VI. These results demonstrate the importance and utility of visually inspecting data from incoming and upcoming surveys, especially during their early operation phases.

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

We performed an out-of-distribution (OOD) analysis of ∼12,000,000 semi-independent 128 × 128 pixel2 sea surface temperature (SST) regions, which we define as cutouts, from all nighttime granules in the MODIS R2019 Level-2 public dataset to discover the most complex or extreme phenomena at the ocean’s surface. Our algorithm (ULMO) is a probabilistic autoencoder (PAE), which combines two deep learning modules: (1) an autoencoder, trained on ∼150,000 random cutouts from 2010, to represent any input cutout with a 512-dimensional latent vector akin to a (non-linear) Empirical Orthogonal Function (EOF) analysis; and (2) a normalizing flow, which maps the autoencoder’s latent space distribution onto an isotropic Gaussian manifold. From the latter, we calculated a log-likelihood (LL) value for each cutout and defined outlier cutouts to be those in the lowest 0.1% of the distribution. These exhibit large gradients and patterns characteristic of a highly dynamic ocean surface, and many are located within larger complexes whose unique dynamics warrant future analysis. Without guidance, ULMO consistently locates the outliers where the major western boundary currents separate from the continental margin. Prompted by these results, we began the process of exploring the fundamental patterns learned by ULMO thereby identifying several compelling examples. Future work may find that algorithms such as ULMO hold significant potential/promise to learn and derive other, not-yet-identified behaviors in the ocean from the many archives of satellite-derived SST fields. We see no impediment to applying them to other large remote-sensing datasets for ocean science (e.g., SSH and ocean color).

The reionization of helium at z ~ 3 is the final phase transition of the intergalactic medium and supposed to be driven purely by quasars. The He ii transverse proximity effect—enhanced He ii transmission in a background sightline caused by the ionizing radiation of a foreground quasar—therefore offers a unique opportunity to probe the morphology of He ii reionization and to investigate the emission properties of quasars, e.g., ionizing emissivity, lifetime and beaming geometry. We use the most-recent HST/COS far-UV dataset of 22 He ii absorption spectra and conduct our own dedicated optical spectroscopic survey to find foreground quasars around these He ii sightlines. Based on a set of 66 foreground quasars, we perform the first statistical analysis of the He ii transverse proximity effect. Despite a large object-to-object variance, our stacking analysis reveals an excess in the average He ii transmission near the foreground quasars at 3σ significance. This statistical evidence for the transverse proximity effect is corroborated by a clear dependence of the signal strength on the inferred He ii ionization rate at the background sightline. Our detection places, based on the transverse light crossing time, a geometrical limit on the quasar lifetime of tQ > 25 Myr. This evidence for sustained activity of luminous quasars is relevant for the morphology of H i and He ii reionization and helps to constrain AGN triggering mechanisms, accretion physics and models of black hole mass assembly. We show how future modeling of the transverse proximity effect can additionally constrain quasar emission geometries and e.g., clarify if the large observed object-to-object variance can be explained by current models of quasar obscuration.