Glenn G. Kacprzak

We present a spectroscopic survey of field galaxies and lensed sources in the vicinity of the strong lensing galaxy cluster known as the Carousel lens at z=0.49. Using both Gemini/GMOS slitmask spectra and deep VLT/MUSE observations, we bring the total number of lensed sources up to 12, including three which were not previously known from imaging observations but are apparent in the MUSE data as emission-line sources. Of these sources, 10 have confident redshifts, and an additional 2 have tentative redshifts from likely Ly α emission (including seven new redshifts determined here adding to those presented previously in Sheu et al. (2024). In total, we identify 42 images of these 12 sources. This lens system is remarkably symmetric and well-modeled by a simpler lens model than typical cluster lenses, and the large number of sources and their large range of redshifts make this cluster ideal for constraining cosmological parameters such as w and Ω m as well as the cluster density profile. Additionally, we present a catalog of 57 unlensed field galaxies with confident redshifts, of which 49 are associated with the cluster. We measure a cluster velocity dispersion of about 1100 km s from which we estimate a halo mass M 200 c ∼ 1.2 × 10 15 M ⊙ .

Interactions between galaxies and their CGM can be observationally traced by extended tidal-like features. Interacting absorption-selected galaxies are galaxies that exhibit diffuse extended structures such as tidal features due to gravitational influence of other galaxies, and are associated with quasar absorbers. We report an analysis of 17 interacting galaxies associated with either H i or Mg ii absorbers and their tidal features at 0.1≲z≲ 0.6 selected from a total sample of 3658 galaxies. These were detected in HST and VLT MUSE observations and spectroscopically confirmed to be associated with strong intervening quasar absorbers. We estimated stellar masses (M*) of the tidal structures from spectral energy distribution fits and analyzed the kinematics of these structures using emission lines detected in the MUSE data. Our main findings are as follows: (1) Interacting absorbing galaxies exhibiting tidal features have enhanced star formation rates (SFR), specific star formation rates (sSFR), SFR surface densities, dust reddening, while exhibiting comparable emission metallicities to absorbing galaxies without tidal interactions. (2) The tidal features have higher sSFR but lower SFR and lower dust reddening than their host galaxies. (3) There is no significant difference in Mg ii λ 2796 rest-frame equivalent width between interacting and non-interacting absorbing galaxies. However, absorbing galaxies with tidal features are more massive and are located at greater distances from quasar sightlines, possibly tracing more extended CGM. Together, these results highlight the CGM’s influence traced by tidal features on the stellar and kinematic properties of the interacting absorbing galaxies.

We investigate the origin of intervening cool Mg II absorption detected in the spectra of background quasars and the nature of associated galaxies across a broad redshift range of 0.3 ≤ z ≤ 1.6, and a largely unexplored galactrocentric distance of ≲20 kpc. Using nebular [O II ] λλ 3727, 3729 emission lines identified in DESI fibre spectra centred on quasars, we detect 342 galaxies at a typical detection rate of ∼0.45% at z ≲ 1, which increases with the Mg II equivalent width ( W ₂₇₉₆ ). A significant fraction (74%) of these galaxies are associated with strong absorbers with W ₂₇₉₆ ≥ 2 Å. These absorbers trace galaxies spanning stellar masses of 8.4 ≤ log( M _★ / M _⊙ )≤11.6 and star formation rates (SFRs) of −1 ≤ log(SFR [ M _⊙ yr ⁻¹ ]) ≤ 2.7, located at projected galactocentric distances of 4−24 kpc. We find that the average Mg II absorber strength increases from 2.1 Å to 2.8 Å between redshifts of z ∼ 0.4 and 1.2, indicating evolution in the cool gas content of galaxy halos. The relatively constant absorber strength with galactocentric distance implies a clumpy structure of cool gas in the circumgalactic medium (CGM). Further, we find a positive correlation between W ₂₇₉₆ versus stellar mass ( M _★ ), and the SFR, suggesting that the distribution of metal-enriched cool gas in the CGM is closely tied to the properties of the host galaxies. The redshift evolution of gas-phase metallicity suggests that strong Mg II absorbers trace the general population of star-forming galaxies. The velocity dispersion of the cool gas increases with halo mass, and the wide range of the line-of-sight velocity offset (−389 to 364 km s ⁻¹ ) between the galaxy systemic velocity and absorbers highlights the dynamical nature of CGM. However, the majority of this gas remains gravitationally bound to the dark matter halos, consistent with a picture of gas recycling via galactic fountains.

The environments of deflectors in strong-lensing systems affect our ability to test cosmological models and constrain evolutionary properties of galaxies. Here, we measure the deflector scale (Einstein mass) and deflector environment (halo mass) of 89 spectroscopically confirmed strong lenses in the ASTRO3D Galaxy Evolution With Lenses ( AGEL ) survey. We classify the deflector scale by measuring θ _E to determine the mass enclosed by the Einstein radius, M ( < θ _E ). We quantify deflector environment by using photometric redshifts to determine the galaxy surface density to the fifth-nearest neighbor Σ ₅ ( z ). We find that 47.2% of our deflectors are embedded in cluster environments, whereas only 9.0% have cluster-scale Einstein radii (masses). We measure a weak correlation ( r = 0.38) between Einstein mass and Σ ₅ ( z ), suggesting that the assumption of single galaxy-scale deflectors in lens modeling is overly simplified. We hypothesize that the weak correlation results from galaxy-scale bias in the original AGEL selection and the observational challenge of detecting faint arcs with large Einstein radii. Comparing number densities, N _gal , between AGEL and control fields, we find that AGEL deflectors are in systematically denser environments. Our study provides a method to identify strong lenses as a function of deflector environment and approximate the impact of large-scale environment in lens modeling. We provide the measured lensing parameters for our 89 AGEL systems as well as z _phot and r -mag (AB) maps of the line of sight. ^{11 11} These resources will be made publicly available at the Harvard Dataverse: doi: 10.7910/DVN/GYDQQP .

Quasar sightline observations reveal that low ionization state gas corotates with the galaxy disk and often at subcentrifugal velocities, suggesting that the gas is spiraling toward the galaxy disk. However, while observations ubiquitously detect O vi absorption around low-redshift, ∼ L ^* star-forming galaxies, the relationship between O vi and the galaxy disk, especially the kinematics, is not well established. This work focuses on the O vi kinematics and its comparison with that of the low ions and galactic disk rotation. We present observations of 18 pairs of quasars and z ≈ 0.2 star-forming galaxies. All quasar sightlines intersect the circumgalactic medium (CGM) within 45° from the galaxy major axes. We show that while individual O vi velocity components do not correlate with disk rotation, the bulk of the O vi gas in individual sightlines rarely counterrotates. We then match O vi velocity components with those of low ions by minimizing the difference of their velocity centroids. The O vi velocity components with successful low-ion matches are typically found at small sightline impact parameters and are more likely to corotate with the disk. We suggest that the low-ion-matched O vi velocity components trace the gas cospatial with the low ions near the extended disk plane in the inner CGM, whereas those without low-ion matches represent the gas at large 3D radii. While the gas at large radii is theoretically expected to kinematically correlate with the disk angular momentum, this correlation is expected to be weaker due to the higher turbulent to mean rotation velocity ratio at large radii, consistent with our results.

Next-generation surveys such as the Euclid survey, the Legacy Survey of Space and Time (LSST), and the China Space Station Telescope (CSST) survey are expected to discover ~10^5 galaxy-galaxy scale strong gravitational lenses. This motivates the development of scalable and robust lens modeling approaches that can efficiently and reliably learn from wide-field survey datasets before high-resolution follow-up. We design a scalable, Bayesian, Lenstronomy-based pipeline and apply it to a sample of sixteen lens candidates observed with the Parallel Imager for Southern Cosmology Observations (PISCO) on the Magellan telescope. PISCO provides four-band imaging (z, i, r, g) with colours, depth and seeing conditions comparable to LSST. To fully exploit the constraining power of this dataset, our pipeline performs simultaneous multi-band modeling, using a common mass profile across all four bands while allowing independent light profiles in each. This approach leverages color information to provide joint constraints on the lens mass and yields reduced uncertainties compared to single-band analyses. Fifteen out of sixteen PISCO lens candidates are successfully recovered with interpretable lensing configurations, including DESJ0533-2536, the first reported hyperbolic-umbilic galaxy-galaxy scale strong lensing candidate. We further assess how much model complexity can be reliably constrained given the resolution and seeing of PISCO-like data. Overall, our results demonstrate that scalable, multi-band lens modeling of ground-based data can extract meaningful constraints on mass and source morphology, providing a practical pathway to maximize the scientific return from large samples in upcoming surveys.