Hubble Space Telescope Images Research Articles

Star cluster classification using deep transfer learning with PHANGS-HST

ABSTRACT Currently available star cluster catalogues from the Hubble Space Telescope (HST) imaging of nearby galaxies heavily rely on visual inspection and classification of candidate clusters. The time-consuming nature of this process has limited the production of reliable catalogues and thus also post-observation analysis. To address this problem, deep transfer learning has recently been used to create neural network models that accurately classify star cluster morphologies at production scale for nearby spiral galaxies (D ≲ 20 Mpc). Here, we use HST ultraviolet (UV)–optical imaging of over 20 000 sources in 23 galaxies from the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) survey to train and evaluate two new sets of models: (i) distance-dependent models, based on cluster candidates binned by galaxy distance (9–12, 14–18, and 18–24 Mpc), and (ii) distance-independent models, based on the combined sample of candidates from all galaxies. We find that the overall accuracy of both sets of models is comparable to previous automated star cluster classification studies (∼60–80 per cent) and shows improvement by a factor of 2 in classifying asymmetric and multipeaked clusters from PHANGS-HST. Somewhat surprisingly, while we observe a weak negative correlation between model accuracy and galactic distance, we find that training separate models for the three distance bins does not significantly improve classification accuracy. We also evaluate model accuracy as a function of cluster properties such as brightness, colour, and spectral energy distribution (SED)-fit age. Based on the success of these experiments, our models will provide classifications for the full set of PHANGS-HST candidate clusters (N ∼ 200 000) for public release.

Multiple Stellar Populations in Metal-poor Globular Clusters with JWST: A NIRCam View of M92

Recent work on metal-intermediate globular clusters (GCs) with [Fe/H] = −1.5 and −0.75 has illustrated the theoretical behavior of multiple populations in photometric diagrams obtained with the JWST. These results are confirmed by observations of multiple populations among the M dwarfs of 47 Tucanae. Here we explore multiple populations in metal-poor GCs with [Fe/H] = −2.3. We take advantage of synthetic spectra and isochrones that account for the chemical composition of multiple populations to identify photometric diagrams that separate the distinct stellar populations of GCs. We derive high-precision photometry and proper motion for main-sequence (MS) stars in the metal-poor GC M92 from JWST and Hubble Space Telescope images. We identify a first-generation (1G) and two main groups of second-generation (2GA and 2GB) stars and investigate their kinematics and chemical composition. We find isotropic motions with no differences among the distinct populations. The comparison between the observed colors of the M92 stars and the colors derived by synthetic spectra reveals that the helium abundances of 2GA and 2GB stars are higher than those of the 1G by ΔY ∼ 0.01 and 0.04, respectively. The m F090W versus m F090W − m F277W color–magnitude diagram shows that below the knee MS stars exhibit a wide color broadening due to multiple populations. We constrain the amount of oxygen variation needed to reproduce the observed MS width, which is consistent with results on red giant branch stars. We conclude that multiple populations with masses of ∼0.1–0.8 M ⊙ share similar chemical compositions.

Multiphase Gas Interactions on Subarcsec Scales in the Shocked Intergalactic Medium of Stephan’s Quintet with JWST and ALMA

We combine James Webb Space Telescope (JWST) and Hubble Space Telescope imaging with Atacama Large Millimeter Array CO(2–1) spectroscopy to study the highly turbulent multiphase intergalactic medium (IGM) in Stephan’s Quintet on 25–150 pc scales. Previous Spitzer observations revealed luminous H2 line cooling across a 45 kpc-long filament, created by a giant shock wave, following the collision with an intruder galaxy, NGC 7318b. We demonstrate that the Mid-Infrared Instrument/F1000W/F770W filters are dominated by 0–0 S(3) H2 and a combination of polycyclic aromatic hydrocarbon and 0–0 S(5) H2 emission. These observations reveal the dissipation of kinetic energy as massive clouds experience collisions, interactions, and likely destruction/recycling within different phases of the IGM. In 1 kpc-scaled structure, warm H2 was seen to form a triangular-shaped head and tail of compressed and stripped gas behind a narrow shell of cold H2. In another region, two cold molecular clumps with very different velocities are connected by an arrow-shaped stream of warm, probably shocked, H2 suggesting a cloud–cloud collision is occurring. In both regions, a high warm-to-cold molecular gas fraction indicates that the cold clouds are being disrupted and converted into warm gas. We also map gas associated with an apparently forming dwarf galaxy. We suggest that the primary mechanism for exciting strong mid-IR H2 lines throughout Stephan’s Quintet is through a fog of warm gas created by the shattering of denser cold molecular clouds and mixing/recycling in the post-shocked gas. A full picture of the diverse kinematics and excitation of the warm H2 will require future JWST mid-IR spectroscopy. The current observations reveal the rich variety of ways that different gas phases can interact with one another.

A New Sample of Transient Ultraluminous X-Ray Sources Serendipitously Discovered by Swift/XRT

Ultraluminous X-ray sources (ULXs) are our best laboratories for studying extreme super-Eddington accretion. Most studies of these objects are of relatively persistent sources; however, there is growing evidence to suggest a large fraction of these sources are transient. Here we present a sample of five newly reported transient ULXs in the galaxies NGC 4945, NGC 7793, and M81 serendipitously discovered in Swift/XRT observations. Swift monitoring of these sources have provided well-sampled lightcurves, allowing for us to model the lightcurves with the disk-instability model of Hameury & Lasota, which implies durations of 60–400 days and that the mass-accretion rate through the disk is close to or greater than the Eddington rate. Of the three source regions with prior Hubble Space Telescope imaging, color–magnitude diagrams of the potential stellar counterparts show varying ages of the possible stellar counterparts. Our estimation of the rates of these sources in these three galaxies is 0.4–1.3 yr−1. We find that, while persistent ULXs dominate the high end of galaxy luminosity functions, the number of systems that produce ULX luminosities are likely dominated by transient sources.

The Dimorphos Boulder Swarm

We present deep Hubble Space Telescope images taken to examine the ejecta from the DART spacecraft impact into asteroid Dimorphos. The images reveal an extensive population of comoving boulders, the largest of which is ∼7 m in diameter (geometric albedo 0.15 assumed). Measurements of 37 boulders show a mean sky-plane velocity dispersion of 0.30 ± 0.03 m s−1, only slightly larger than the 0.24 m s−1 gravitational escape velocity from the Didymos–Dimorphos binary system. The total boulder mass, M b ∼ 5 × 106 kg (density 2200 kg m−3 assumed), corresponds to about 0.1% of the mass of Dimorphos, and the boulders collectively carry about 3 × 10−5 of the kinetic energy delivered by the DART spacecraft impact. The sky-plane distribution of the boulders is asymmetric, consistent with impact into an inhomogeneous, likely rubble-pile, body. Surface boulder counts on Didymos show that the observed boulder swarm could be ejected from as little as 2% of the surface of Dimorphos (for example, a circular crater at the impact point about 50 m in diameter). The large, slow-moving boulders are potential targets to be investigated in situ by the upcoming ESA HERA mission.

3D Spectroscopy with GTC-MEGARA of the Triple AGN Candidate in SDSS J102700.40+174900.8

Triple–active galactic nucleus (AGN) systems are expected to be the result of the hierarchical model of galaxy formation. Since there are very few of them confirmed as such, we present the results of a new study of the triple AGN candidate SDSS J102700.40+174900.8 (center nucleus) through observations with the GTC-MEGARA Integral Field Unit. 1D and 2D analysis of the line ratios of the three nuclei allow us to locate them in the EW(Hα) versus [N ii]/Hα diagram. The central nucleus is found to be a retired galaxy (or fake AGN). The neighbors are found to be a strong AGN (southeastern nucleus, J102700.55+174900.2), compatible with a Seyfert 2 (Sy2) galaxy, and a weak AGN (northern nucleus, J102700.38+174902.6), compatible with a LINER2. We find evidence that the neighbors constitute a dual AGN system (Sy2–LINER2) with a projected separation of 3.98 kpc in the optical bands. The Hα velocity map shows that the northern nucleus has an Hα emission with a velocity offset of ∼−500 km s−1, whereas the southeastern nucleus has a rotating disk and Hα extended emission at kiloparsec scales. Chandra archival data confirm that the neighbors have X-ray (0.5–2) keV and (2–7) keV emission, whereas the center nucleus shows no X-ray emission. A collisional ring with knots is observed in Hubble Space Telescope images of the southeastern nucleus. These knots coincide with star formation regions that, along with the ring, are predicted in a head-on collision. In this case, the morphology changes are probably due to a minor merger that was produced by the passing of the northern through the southeastern nucleus.

Modeling lens potentials with continuous neural fields in galaxy-scale strong lenses

Strong gravitational lensing is a unique observational tool for studying the dark and luminous mass distribution both within and between galaxies. Given the presence of substructures, current strong lensing observations demand more complex mass models than smooth analytical profiles, such as power-law ellipsoids. In this work, we introduce a continuous neural field to predict the lensing potential at any position throughout the image plane, allowing for a nearly model-independent description of the lensing mass. We applied our method to simulated Hubble Space Telescope imaging data containing different types of perturbations to a smooth mass distribution: a localized dark subhalo, a population of subhalos, and an external shear perturbation. Assuming knowledge of the source surface brightness, we used the continuous neural field to model either the perturbations alone or the full lensing potential. In both cases, the resulting model was able to fit the imaging data, and we were able to accurately recover the properties of both the smooth potential and the perturbations. Unlike many other deep-learning methods, ours explicitly retains lensing physics (i.e., the lens equation) and introduces high flexibility in the model only where required, namely, in the lens potential. Moreover, the neural network does not require pretraining on large sets of labeled data and predicts the potential from the single observed lensing image. Our model is implemented in the fully differentiable lens modeling code HERCULENS.

Morpho-kinematic and photoionization models of the multipolar structures in planetary nebula NGC 6572

ABSTRACT We have studied planetary nebula (PN) NGC 6572 through 3D morpho-kinematic and photoionization modelling. The 3D morphology is reconstructed from the Hubble Space Telescope images in different narrow-band filters and position–velocity spectra. The PN has a multipolar morphology consisting of highly collimated outflows. The nebular image shows signatures of multiple lobes within a spiral-ring-like structure. The multipolar structure is modelled with two bipolar shells (axes ratios ∼5.5:1 and ∼3:1), having closed and open lobes, respectively. A toroidal structure (radius:height ∼ 1:3) surrounds the shells at the waist. The toroidal axis aligns with the major axes of the bipolar shells. Our study reveals the nebula to have a history of collimated polar outflow perpendicular to a higher density equatorial wind with the outflow seemingly having episodes of changing direction of ejection. We construct a photoionization model of NGC 6572 using the optical spectra obtained at the 2 m Himalayan Chandra Telescope. For the photoionization model, we configure the input shell geometry in the form of a highly bipolar nebular shell with reference to the 3D morphology. Our photoionization model satisfactorily reproduces the observables. We estimate nebular elemental abundances, and important characteristic parameters of the central star (e.g. effective temperature, luminosity, gravity, mass, etc.) and the nebula (e.g. hydrogen density profiles, radii, etc.). We compare the resolved H β, [O iii], and [N ii] profiles obtained using the 4.2 m William Herschel Telescope with that from the photoionization model and find a good characteristic match.

Titan’s North–South Haze Asymmetry Ratio and Boundary at Visible Wavelengths over the Cassini Mission

We document the evolution of the north–south asymmetry (NSA) of Titan’s haze albedo during the Cassini mission between 2004 and 2017. We analyze coadded cube images taken at 96 distinct wavelengths between 0.35 and 1.05 μm by the Cassini Visual and Infrared Mapping Spectrometer (VIMS-V) instrument from 14 Titan flybys. Over half of a Titan year, we observe a near-complete transition in the NSA boundary latitude across the geographic equator from the southern to the northern hemisphere, including a 3 yr fading of the boundary for several years after the equinox. The fading transition of the NSA matches previous observations of a reversal of the NSA in Hubble Space Telescope images of Titan before the winter solstice between 1997 and 2000. A comparison of NSA images taken at similar times but different phase angles shows the NSA boundary is detectable, albeit with less contrast, at moderately high phase angles (∼90°). Analysis of the NSA boundary in T61 and T67 VIMS images further supports a small tilt between the superrotating atmosphere and the solid body of Titan, as suggested in a previous analysis of 0.890 μm images from the Cassini Imaging Science Subsystem.

A Sensitive Search for Supernova Emission Associated with the Extremely Energetic and Nearby GRB 221009A

We report observations of the optical counterpart of the long gamma-ray burst GRB 221009A. Due to the extreme rarity of being both nearby (z = 0.151) and highly energetic (E γ,iso ≥ 1054 erg), GRB 221009A offers a unique opportunity to probe the connection between massive star core collapse and relativistic jet formation across a very broad range of γ-ray properties. Adopting a phenomenological power-law model for the afterglow and host galaxy estimates from high-resolution Hubble Space Telescope imaging, we use Bayesian model comparison techniques to determine the likelihood of an associated supernova (SN) contributing excess flux to the optical light curve. Though not conclusive, we find moderate evidence (K Bayes = 101.2) for the presence of an additional component arising from an associated SN, SN 2022xiw, and find that it must be substantially fainter (<67% as bright at the 99% confidence interval) than SN 1998bw. Given the large and uncertain line-of-sight extinction, we attempt to constrain the SN parameters (M Ni, M ej, and E KE) under several different assumptions with respect to the host galaxy’s extinction. We find properties that are broadly consistent with previous GRB-associated SNe: M Ni = 0.05–0.25 M ⊙, M ej = 3.5–11.1 M ⊙, and E KE = (1.6–5.2) × 1052 erg. We note that these properties are weakly constrained due to the faintness of the SN with respect to the afterglow and host emission, but we do find a robust upper limit on M Ni of M Ni < 0.36 M ⊙. Given the tremendous range in isotropic gamma-ray energy release exhibited by GRBs (seven orders of magnitude), the SN emission appears to be decoupled from the central engine in these systems.

Investigating the M GCS–M h Relation in the Most Massive Galaxies

The relation between the total mass contained in the globular clusters of a galaxy and the mass of its dark-matter halo has been found observationally to be nearly linear over five decades of mass. However, the high-mass end of this relation is not well determined from previous data and shows large scatter. We analyze the globular cluster systems (GCSs) of a homogeneous sample of 11 brightest cluster galaxies (BCGs) through DOLPHOT photometry of their deep Hubble Space Telescope images in the F814W filter. We standardize the definition of M GCS, the total GCS mass, by using the GC total population within a limiting radius of 0.1R virial, while the dark-matter halo mass M h is determined from the weak-lensing calibration of M h versus M bary. When these 11 BCGs are added to the previously studied homogeneous catalog of Virgo member galaxies, a total value for η = M GCS/M h is found to be (3.0 ± 1.8internal) × 10−5, slightly higher than previous estimates but with much reduced uncertainty. Perhaps more importantly, the results suggest that the relation continues to have a near-linear shape at the highest galaxy masses, strongly reinforcing the conclusion that accreted GCs make a major contribution to the GC populations at high galaxy mass.

UNCOVERing the extended strong lensing structures of Abell 2744 with the deepest JWST imaging

ABSTRACT We present a new parametric lens model for the massive galaxy cluster Abell 2744 based on new ultra-deep JWST imaging taken in the framework of the UNCOVER program. These observations constitute the deepest JWST images of a lensing cluster to date, adding to existing deep Hubble Space Telescope (HST) images and the recent JWST Early Release Science and Director’s Discretionary Time data taken for this field. The wide field of view of UNCOVER (∼45 arcmin2) extends beyond the cluster’s well-studied central core and reveals a spectacular wealth of prominent lensed features around two massive cluster sub-structures in the north and north-west, where no multiple images were previously known. We identify 75 new multiple images and candidates of 17 sources, 43 of which allow us, for the first time, to constrain the lensing properties and total mass distribution around these extended cluster structures using strong lensing (SL). Our model yields an effective Einstein radius of θE, main = 23.2 ± 2.3 arcsec for the main cluster core (for zs = 2), enclosing a mass of M(&amp;lt; θE, main) = (7.7 ± 1.1) × 1013 M⊙, and θE, NW = 13.1 ± 1.3 arcsec for the newly discovered north-western SL structure enclosing M(&amp;lt; θE, NW) = (2.2 ± 0.3) × 1013 M⊙. The northern clump is somewhat less massive with θE, N = 7.4 ± 0.7 arcsec enclosing M(&amp;lt; θE, N) = (0.8 ± 0.1) × 1013 M⊙. We find the northern sub-structures of Abell 2744 to broadly agree with the findings from weak lensing analyses and align with the filamentary structure found by these previous studies. Our model in particular reveals a large area of high magnification values between the various cluster structures, which will be paramount for lensed galaxy studies in the UNCOVER field. The model is made publicly available to accompany the first UNCOVER data release.

The late time optical evolution of twelve core-collapse supernovae: detection of normal stellar winds

ABSTRACT We analyse the late time evolution of 12 supernovae (SNe) occurring over the last ∼41 yr, including nine Type IIP/L, two IIb, and one Ib/c, using UBVR optical data from the Large Binocular Telescope (LBT) and difference imaging. We see late time (5–42 yr) emission from nine of the eleven Type II SNe (eight Type IIP/L, one IIb). We consider radioactive decay, circumstellar medium (CSM) interactions, pulsar/engine driven emission, dust echoes, and shock perturbed binary companions as possible sources of emission. The observed emission is most naturally explained as CSM interactions with the normal stellar winds of red supergiants with mass-loss rates in the range −7.9 ≲ log10(M⊙ yr−1) ≲ −4.8. We also place constraints on the presence of any shock heated binary companion to the Type Ib/c SN 2012fh and provide progenitor photometry for the Type IIb SN 2011dh, the only one of the six SNe with pre-explosion LBT observations where the SN has faded sufficiently to allow the measurement. The results are consistent with measurements from pre-explosion Hubble Space Telescope images.

SKYSURF-4: Panchromatic Hubble Space Telescope All-Sky Surface-brightness Measurement Methods and Results

The diffuse, unresolved sky provides most of the photons that the Hubble Space Telescope (HST) receives, yet remains poorly understood. The HST Archival Legacy program SKYSURF aims to measure the 0.2–1.6 μm sky surface brightness (sky-SB) from over 140,000 HST images. We describe a sky-SB measurement algorithm designed for SKYSURF that is able to recover the input sky-SB from simulated images to within 1% uncertainty. We present our sky-SB measurements estimated using this algorithm on the entire SKYSURF database. Comparing our sky-SB spectral energy distribution (SED) to measurements from the literature shows general agreements. Our SKYSURF SED also reveals a possible dependence on the Sun angle, indicating either nonisotropic scattering of solar photons off interplanetary dust or an additional component to zodiacal light. Finally, we update the diffuse light limits in the near-IR based on the methods from Carleton et al., with values of 0.009 MJy sr−1 (22 nW m−2 sr−1) at 1.25 μm, 0.015 MJy sr−1 (32 nW m−2 sr−1) at 1.4 μm, and 0.013 MJy sr−1 (25 nW m−2 sr−1) at 1.6 μm. These estimates provide the most stringent all-sky constraints to date in this wavelength range. SKYSURF sky-SB measurements are made public on the official SKYSURF website and will be used to constrain diffuse light in future papers.

Probing sub-galactic mass structure with the power spectrum of surface-brightness anomalies in high-resolution observations of galaxy-galaxy strong gravitational lenses – I. Power-spectrum measurement and feasibility study

ABSTRACT While the direct detection of the dark-matter particle remains very challenging, the nature of dark matter could be possibly constrained by comparing the observed abundance and properties of small-scale sub-galactic mass structures with predictions from the phenomenological dark-matter models, such as cold, warm, or hot dark matter. Galaxy-galaxy strong gravitational lensing provides a unique opportunity to search for tiny surface-brightness anomalies in the extended lensed images (i.e. Einstein rings or gravitational arcs), induced by possible small-scale mass structures in the foreground lens galaxy. In this paper, the first in a series, we introduce and test a methodology to measure the power spectrum of such surface-brightness anomalies from high-resolution Hubble Space Telescope (HST) imaging. In particular, we focus on the observational aspects of this statistical approach, such as the most suitable observational strategy and sample selection, the choice of modelling techniques, and the noise correction. We test the feasibility of the power-spectrum measurement by applying it to a sample of galaxy-galaxy strong gravitational lens systems from the Sloan Lens ACS Survey, with the most extended, bright, high-signal-to-noise-ratio lensed images, observed in the rest-frame ultraviolet. In the companion paper, we present the methodology to relate the measured power spectrum to the statistical properties of the underlying small-scale mass structures in the lens galaxy and infer the first observational constraints on the sub-galactic matter power spectrum in a massive elliptical (lens) galaxy.

A variable active galactic nucleus at z = 2.06 triply-imaged by the galaxy cluster MACS J0035.4−2015

ABSTRACT We report the discovery of a triply imaged active galactic nucleus (AGN), lensed by the galaxy cluster MACS J0035.4−2015 (zd = 0.352). The object is detected in Hubble Space Telescope imaging taken for the RELICS program. It appears to have a quasi-stellar nucleus consistent with a point-source, with a de-magnified radius of re ≲ 100 pc. The object is spectroscopically confirmed to be an AGN at zspec = 2.063 ± 0.005 showing broad rest-frame UV emission lines, and detected in both X-ray observations with Chandra and in ALCS ALMA band 6 (1.2 mm) imaging. It has a relatively faint rest-frame UV luminosity for a quasar-like object, MUV, 1450 = −19.7 ± 0.2. The object adds to just a few quasars or other X-ray sources known to be multiply lensed by a galaxy cluster. Some diffuse emission from the host galaxy is faintly seen around the nucleus, and there is a faint object nearby sharing the same multiple-imaging symmetry and geometric redshift, possibly an interacting galaxy or a star-forming knot in the host. We present an accompanying lens model, calculate the magnifications and time delays, and infer the physical properties of the source. We find the rest-frame UV continuum and emission lines to be dominated by the AGN, and the optical emission to be dominated by the host galaxy of modest stellar mass $M_{\star }\simeq 10^{9.2}\, \mathrm{M}_{\odot }$ . We also observe some variation in the AGN emission with time, which may suggest that the AGN used to be more active. This object adds a low-redshift counterpart to several relatively faint AGN recently uncovered at high redshifts with HST and JWST.

A spectacular jet from the bright 244–440 Orion proplyd: The MUSE NFM view

In this work we present the highest spatial and spectral resolution integral field observations to date of the bipolar jet from the Orion proplyd 244–440 using Multi-Unit Spectroscopic Explorer (MUSE) narrow-field mode (NFM) observations on the Very Large Telescope (VLT). We observed a previously unreported chain of six distinct knots in a roughly S-shaped pattern, and by comparing them with Hubble Space Telescope (HST) images we estimated proper motions in the redshifted knots of 9.5 mas yr−1 with an inclination angle of 73°, though these quantities could not be measured for the blueshifted lobe. Analysis of the [Fe II] and [Ni II] lines suggests jet densities on the order of ~105 cm−3. We propose that the observed S-shaped morphology originates from a jet launched by a smaller source with M★ &lt; 0.2 M⊙ in orbital motion around a larger companion of M★ ≃ 0.5 M⊙ at a separation of 30–40 au. The measured luminosities of the knots using the [O I]λ6300 Å and [S II]λ6731 Å lines were used to estimate a lower limit to the mass-loss rate in the jet of 1.3 × 10−11 M⊙ yr−1 and an upper limit of 10−9 M⊙ yr−1, which is typical for low-mass driving sources. While the brightness asymmetry between the redshifted and blueshifted lobes is consistent with external irradiation, further analysis of the [Ni II] and [Fe II] lines suggests that photoionization of the jet is not likely to be a dominant factor, and that the emission is dominated by collisional excitation. The dynamical age of the jet compared to the anticipated survival time of the proplyd demonstrates that photoevaporation of the proplyd occurred prior to jet launching, and that this is still an active source. These two points suggest that the envelope of the proplyd may shield the jet from the majority of external radiation, and that photoionization of the proplyd does not appear to impact the ability of a star to launch a jet.

On the Reionization-era Globular Cluster in the Low-mass Galaxy Eridanus II

Using color–magnitude diagrams from deep archival Hubble Space Telescope imaging, we self-consistently measure the star formation history of Eridanus II (Eri II), the lowest-mass galaxy (M ⋆(z = 0) ∼ 105 M ⊙) known to host a globular cluster (GC), and the age, mass, and metallicity of its GC. The GC (∼13.2 ± 0.4 Gyr, 〈[Fe/H]〉 = −2.75 ± 0.2 dex) and field (mean age ∼13.5 ± 0.3 Gyr, 〈[Fe/H]〉 = −2.6 ± 0.15 dex) have similar ages and metallicities. Both are reionization-era relics that formed before the peak of cosmic star and GC formation (z ∼ 2–4). The ancient star formation properties of Eri II are not extreme and appear similar to z = 0 dwarf galaxies. We find that the GC was ≲4 times more massive at birth than today and was ∼10% of the galaxy's stellar mass at birth. At formation, we estimate that the progenitor of Eri II and its GC had M UV ∼ −7 to −12, making it one of the most common type of galaxy in the early universe, though it is fainter than direct detection limits, absent gravitational lensing. Archaeological studies of GCs in nearby low-mass galaxies may be the only way to constrain GC formation in such low-mass systems. We discuss the strengths and limitations in comparing archaeological and high-redshift studies of cluster formation, including challenges stemming from the Hubble Tension, which introduces uncertainties into the mapping between age and redshift.

The Mass of the Black Hole in NGC 5273 from Stellar Dynamical Modeling

We present a new constraint on the mass of the black hole in the active S0 galaxy NGC 5273. Due to the proximity of the galaxy at 16.6 ± 2.1 Mpc, we were able to resolve and extract the bulk motions of stars near the central black hole using adaptive-optics-assisted observations with the Gemini Near-infrared Integral Field Spectrograph, as well as constrain the large-scale kinematics using archival Spectroscopic Areal Unit for Research and Optical Nebulae spectroscopy. High-resolution Hubble Space Telescope imaging allowed us to generate a surface-brightness decomposition, determine approximate mass-to-light ratios for the bulge and disk, and obtain an estimate for the disk inclination. We constructed an extensive library of dynamical models using the Schwarzschild orbit-superposition code FORSTAND, exploring a range of disk and bulge shapes, halo masses, etc. We determined a black hole mass of M • = [0.5–2] × 107 M ⊙, where the low side of the range is in agreement with the reverberation mapping measurement of M • = [4.7 ± 1.6] × 106 M ⊙. NGC 5273 is one of the few nearby galaxies that hosts a broad-lined active galactic nucleus, allowing a crucial comparison of black hole masses derived from independent mass-measurement techniques.

TDCOSMO

Strong-lensing time delays enable the measurement of the Hubble constant (H0) independently of other traditional methods. The main limitation to the precision of time-delay cosmography is mass-sheet degeneracy (MSD). Some of the previous TDCOSMO analyses broke the MSD by making standard assumptions about the mass density profile of the lens galaxy, reaching 2% precision from seven lenses. However, this approach could potentially bias the H0 measurement or underestimate the errors. For this work, we broke the MSD for the first time using spatially resolved kinematics of the lens galaxy in RXJ1131−1231 obtained from the Keck Cosmic Web Imager spectroscopy, in combination with previously published time delay and lens models derived from Hubble Space Telescope imaging. This approach allowed us to robustly estimate H0, effectively implementing a maximally flexible mass model. Following a blind analysis, we estimated the angular diameter distance to the lens galaxy Dd = 865−81+85 Mpc and the time-delay distance DΔt = 2180−271+472 Mpc, giving H0 = 77.1−7.1+7.3 km s−1 Mpc−1 – for a flat Λ cold dark matter cosmology. The error budget accounts for all uncertainties, including the MSD inherent to the lens mass profile and line-of-sight effects, and those related to the mass–anisotropy degeneracy and projection effects. Our new measurement is in excellent agreement with those obtained in the past using standard simply parametrized mass profiles for this single system (H0 = 78.3−3.3+3.4 km s−1 Mpc−1) and for seven lenses (H0 = 74.2−1.6+1.6 km s−1 Mpc−1), or for seven lenses using single-aperture kinematics and the same maximally flexible models used by us (H0 = 73.3−5.8+5.8 km s−1 Mpc−1). This agreement corroborates the methodology of time-delay cosmography.