Hubble Space Telescope Research Articles

Ground-based Reconnaissance Observations of 21 Exoplanet Atmospheres with the Exoplanet Transmission Spectroscopy Imager

Abstract One of the most prolific methods of studying exoplanet atmospheres is transmission spectroscopy, which measures the difference between the depth of an exoplanet's transit signal at various wavelengths and attempts to correlate the depth changes to potential features in the exoplanet's atmosphere. Here we present reconnaissance observations of 21 exoplanet atmospheres measured with the Exoplanet Transmission Spectroscopy Imager (ETSI), a recently deployed spectrophotometer on the McDonald Observatory Otto Struve 2.1 m telescope. ETSI measurements are mostly free of systematics through the use of a novel observing technique called common-path multiband imaging (CMI), which has been shown to achieve photometric color precision on par with space-based observations (300 ppm or 0.03%). This work also describes the various statistical tests performed on the data to evaluate the efficacy of the CMI method and the ETSI instrument in combination. We find that none of the eight comparisons of exoplanet atmospheres measured with ETSI and other observatories (including the Hubble Space Telescope) provide evidence that the spectra are statistically dissimilar. These results suggest that ETSI can provide initial transmission spectroscopy observations for a fraction of the observational and monetary overhead previously required to detect an exoplanet's atmosphere. Ultimately these reconnaissance observations increase the number of planets with transmission spectroscopy measurements by ~10% and provide an immediate prioritization of 21 exoplanets for future follow-up with more precious observatories, such as the James Webb Space Telescope. The reconnaissance spectra are available through the Filtergraph visualization portal at the URL https://filtergraph.com/etsi/.

PAH Feature Ratios around Stellar Clusters and Associations in 19 Nearby Galaxies

Abstract We present a comparison of observed polycyclic aromatic hydrocarbon (PAH) feature ratios in 19 nearby galaxies with a grid of theoretical expectations for near- and mid-infrared dust emission. The PAH feature ratios are drawn from Cycle 1 JWST observations and are measured for 7224 stellar clusters and 29,176 stellar associations for which we have robust ages and mass estimates from Hubble Space Telescope five-band photometry. Though there are galaxy-to-galaxy variations, the observed PAH feature ratios largely agree with the theoretical models, particularly those that are skewed toward more ionized and larger PAH size distributions. For each galaxy we also extract PAH feature ratios for 200 pc wide circular regions in the diffuse interstellar medium, which serve as a noncluster/association control sample. Compared to what we find for stellar clusters and associations, the 3.3 μm/7.7 μm and 3.3 μm/11.3 μm ratios from the diffuse interstellar medium are ∼0.10–0.15 dex smaller. When the observed PAH feature ratios are compared to the radiation field hardness as probed by the [O iii]/Hβ ratio, we find anticorrelations for nearly all galaxies in the sample. These results together suggest that the PAH feature ratios are driven by the shape and intensity of the radiation field and that the smallest PAHs—observed via JWST F335M imaging—are increasingly “processed” or destroyed in regions with the most intense and hard radiation fields.

SKYSURF. VI. The Impact of Thermal Variations of HST on Background Light Estimates

Abstract The SKYSURF project constrained extragalactic background light and diffuse light (DL) with the vast archive of Hubble Space Telescope (HST) images. Thermal emission from HST itself introduces an additional uncertain background and hinders accurate measurement of the DL level. Here, we use archival Wide Field Camera 3 (WFC3)/IR engineering data to investigate and model changes in the temperature of various components in HSTs optical path as a function of time (solar cycle) and time of the year (Earth–Sun distance). We also specifically investigate changes in temperature with HST's orbital phase and time since Earth occultation. We investigate possible correlations between HST component temperature and year, and temperature and month. The thermal background changes by less than one Kelvin in the WFC3 pickoff mirror, one of the most important contributors to the thermal background. We model these data to describe the impact that orbital phase, year, and time of year have on the HST and WFC3 component temperatures, and use this to derive the impact on the thermal dark signal and the resulting DL measurements. Based on this improved modeling, we provide new upper limits on the level of DL of 21, 32, and 25 nW m−2 sr−1 for F125W, F140W, and F160W. Additionally, by accounting for all known sources of measurement uncertainty, we report lower limits on the level of DL of 12, 20, and 2 nW m−2 sr−1 for F125W, F140W, and F160W.

Constraints on f(R) gravity from thermal-Sunyaev-Zel’dovich-effect-selected SPT galaxy clusters and weak lensing mass calibration from DES and HST

We present constraints on the f(R) gravity model using a sample of 1005 galaxy clusters in the redshift range 0.25–1.78 that have been selected through the thermal Sunyaev-Zel’dovich effect from South Pole Telescope data and subjected to optical and near-infrared confirmation with the multicomponent matched filter algorithm. We employ weak gravitational lensing mass calibration from the Dark Energy Survey Year 3 data for 688 clusters at z<0.95 and from the Hubble Space Telescope for 39 clusters with 0.6<z<1.7. Our cluster sample is a powerful probe of f(R) gravity, because this model predicts a scale-dependent enhancement in the growth of structure, which impacts the halo mass function (HMF) at cluster mass scales. To account for these modified gravity effects on the HMF, our analysis employs a semianalytical approach calibrated with numerical simulations. Combining calibrated cluster counts with primary cosmic microwave background temperature and polarization anisotropy measurements from the Planck 2018 release, we derive robust constraints on the f(R) parameter fR0. Our results, log10|fR0|<−5.32 at the 95% credible level, are the tightest current constraints on f(R) gravity from cosmological scales. This upper limit rules out f(R)-like deviations from general relativity that result in more than a ∼20% enhancement of the cluster population on mass scales M200c>3×1014M⊙. Published by the American Physical Society 2025

Variable stars in the VVV globular clusters III. RR Lyrae stars in the inner Galactic globular clusters

High reddening near the Galactic plane hampers observations and proper characterization of the globular clusters (GCs) located toward the inner regions of the Milky Way. The VISTA Variables in the V'ia L'actea (VVV) survey observed the Galactic bulge and adjacent disk for several years, providing multi-epoch, near-infrared images for 41 Galactic GCs. Detecting RR Lyrae variable stars belonging to these GCs will aid in their accurate parameterization. By fully leveraging the astrometric, photometric, and variability VVV catalogs, we searched for RR Lyrae stars associated with GCs. Our selection criteria, based on proper motions, proximity to the cluster centers, and distances inferred from their period-luminosity-metallicity relations, enable us to accurately identify the RR Lyrae population in these GCs and determine color excesses and distances to these poorly studied GCs in a homogeneous manner. Since the VVV catalogs cover from the innermost regions of the GCs to their outskirts, we can provide a comprehensive picture of the entire RR Lyrae population in these GCs. We have discovered significant RR Lyrae populations in two highly reddened Galactic GCs: UKS 1 and VVV-CL160, previously unknown to host RR Lyrae stars. Additionally, we have detected one RR Lyrae candidate in each of Terzan 4 and Terzan 9, also new to RR Lyrae detection. We further confirm and increase the number of RR Lyrae stars detected in 22 other low-latitude Galactic GCs. The RR Lyrae distances place most of these GCs within the Galactic bulge, aligning well with the few GCs in our sample with reliable Gaia or Hubble Space Telescope measurements. However, most of the VVV GCs lack accurate Gaia distances, and literature distances are generally significantly smaller than those derived in this work. As a byproduct of our analysis, we have obtained the proper motions for all the VVV GCs, independently confirming Gaia results, except for two of the most reddened GCs: UKS 1 and 2MASS-GC02.

Structural decomposition of merger-free galaxies hosting luminous AGNs

ABSTRACT Active galactic nucleus (AGN) growth in disc-dominated, merger-free galaxies is poorly understood, largely due to the difficulty in disentangling the AGN emission from that of the host galaxy. By carefully separating this emission, we examine the differences between AGNs in galaxies hosting a (possibly) merger-grown, classical bulge, and AGNs in secularly grown, truly bulgeless disc galaxies. We use galfit to obtain robust, accurate morphologies of 100 disc-dominated galaxies imaged with the Hubble Space Telescope. Adopting an inclusive definition of classical bulges, we detect a classical bulge component in $53.3 \pm 0.5$ per cent of the galaxies. These bulges were not visible in Sloan Digital Sky Survey photometry, however these galaxies are still unambiguously disc-dominated, with an average bulge-to-total luminosity ratio of $0.1 \pm 0.1$. We find some correlation between bulge mass and black hole mass for disc-dominated galaxies, though this correlation is significantly weaker in comparison to the relation for bulge-dominated or elliptical galaxies. Furthermore, a significant fraction ($\gtrsim 90$ per cent) of our black holes are overly massive when compared to b the relationship for elliptical galaxies. We find a weak correlation between total stellar mass and black hole mass for the disc-dominated galaxies, hinting that the stochasticity of black hole–galaxy co-evolution may be higher in disc-dominated than bulge-dominated systems.

Investigating the Electron-capture Supernova Candidate AT 2019abn with JWST Spectroscopy

Abstract The James Webb Space Telescope (JWST) has opened up a new window to study highly reddened explosive transients. We present results from late-time JWST follow-up spectroscopic observations with NIRSpec and MIRI-LRS of the intermediate-luminosity red transient (ILRT) AT 2019abn. ILRTs represent a mysterious class of transients that exhibit peak luminosities between those of classical novae and supernovae and that are known to be highly dust obscured. Similar to the prototypical examples of this class of objects, NGC 300 2008-OT and SN 2008S, AT 2019abn has an extremely red and dusty progenitor detected only in pre-explosion Spitzer/IRAC imaging at 3.6 and 4.5 μm and not in deep optical or near-infrared Hubble Space Telescope images. We find that late-time observations of AT 2019abn from NEOWISE and JWST are consistent with the late-time evolution of SN 2008S. In part because they are so obscured by dust, it is unknown what produces an ILRT, with hypotheses including high-mass stellar merger events, nonterminal stellar outbursts, and terminal supernova explosions through electron capture in super-AGB (SAGB) stars. Our JWST observations show strong mid-IR class C polycyclic aromatic hydrocarbon features at 6.3 and 8.25 μm typical of carbon-rich post-AGB sources. These features suggest that the dust around AT 2019abn is composed of carbonaceous grains, which are not typically observed around red supergiants. However, depending on the strength and temperature of hot bottom burning, SAGB stars may be expected to exhibit a carbon-rich chemistry. Thus, our JWST observations are consistent with AT 2019abn having an SAGB progenitor and exploding as an electron-capture supernova.

Discovery and Detailed Study of the M31 Classical Nova AT 2023tkw: Evidence for Internal Shocks

Abstract We present a detailed analysis of an extragalactic slow classical nova in M31 exhibiting multiple peaks in its light curve. Spectroscopic and photometric observations were used to investigate the underlying physical processes. Shock-induced heating events resulting in the expansion and contraction of the photosphere are likely responsible for the observed multiple peaks. Deviation of the observed spectrum at the peak from the models also suggests the presence of shocks. The successive peaks occurring at increasing intervals could be due to the series of internal shocks generated near or within the photosphere. Spectral modeling suggests a low-mass white dwarf (WD) accreting slowly from a companion star. The ejecta mass, estimated from spectral analysis, is ~10−4 M ⊙, which is typical for a slow nova. We estimate the binary, by comparing the archival Hubble Space Telescope data and eruption properties with stellar and nova models, to comprise a 0.65 M ⊙ primary WD and a K iii cool evolved secondary star.

Exclusion of a Direct Progenitor Detection for the Type Ic SN 2017ein Based on Late-time Observations

Abstract To date, SN 2017ein is the only Type Ic supernova with a directly identified progenitor candidate. This candidate points to a very massive (>45 M ⊙) Wolf–Rayet (WR) progenitor, but its disappearance after the explosion of SN 2017ein remains unconfirmed. In this work, we revisit SN 2017ein in late-time images acquired by the Hubble Space Telescope at 2.4–3.8 yr after peak brightness. We find this source has not disappeared, and its brightness and color remain almost the same as in the preexplosion images. Thus, we conclude that the preexplosion source is not the genuine progenitor of SN 2017ein. It is not much likelier to be a companion star of the progenitor since it has a much lower extinction than SN 2017ein; its color also seems inconsistent with a star cluster, indicated by the newly added magnitude limit in F336W, apart from F555W and F814W. We suggest, therefore, this source is an unrelated star in chance alignment with SN 2017ein. Based on the low ejecta mass, we propose that SN 2017ein is most likely originated from a moderately massive star with M ini ∼ 8–20 M ⊙, stripped by binary interaction, rather than a very massive WR progenitor.

The Lyman Continuum Escape Fraction of Star-forming Galaxies at 2.4 ≲ z ≲ 3.0 from UVCANDELS

Abstract The UltraViolet Imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey Fields (UVCANDELS) survey is a Hubble Space Telescope (HST) Cycle-26 Treasury Program, allocated in total 164 orbits of primary Wide-Field Camera 3 Ultraviolet and VISible light F275W imaging with coordinated parallel Advanced Camera for Surveys F435W imaging, on four of the five premier extragalactic survey fields: GOODS-N, GOODS-S, EGS, and COSMOS. We introduce this survey by presenting a comprehensive analysis of the absolute escape fraction ( f esc abs ) of Lyman continuum radiation through stacking the UV images of a population of star-forming galaxies with secure redshifts at 2.4 ≤ z ≤ 3.0. Our stacking benefits from the catalogs of high-quality spectroscopic redshifts compiled from archival ground-based data and HST slitless spectroscopy, carefully vetted by dedicated visual inspection efforts. We develop a robust stacking method to apply to 10 samples of in total 56 galaxies, and perform detailed Monte Carlo simulations of the intergalactic medium (IGM) attenuation, to take into account the sample variance of the mean IGM transmission when measuring f esc abs . The full stack at z ≈ 2.44 from 28 galaxies places a stringent 1σ upper limit of f esc abs ≲ 5 % , whereas the full stack at z ≈ 2.72 of an equal number of galaxies gives an upper limit of f esc abs ≲ 26 % at 1σ confidence level. These new F275W and F435W imaging mosaics from UVCANDELS have been made publicly available on the Barbara A. Mikulski Archive for Space Telescopes.

The Bullseye: HST, Keck/KCWI, and Dragonfly Characterization of a Giant Nine-ringed Galaxy

Abstract We report the discovery and multiwavelength follow-up of LEDA 1313424 (“Bullseye”), a collisional ring galaxy (CRG) with nine readily identified rings—the most so far reported for a CRG. These data shed new light on the rapid, multiring phase of CRG evolution. Using Hubble Space Telescope (HST) imaging, we identify and measure nine ring structures, several of which are “piled up” near the center of the galaxy, while others extend to tens of kiloparsecs scales. We also identify faint patches of emission at large radii (~70 kpc) in the HST imaging and confirm the association of this emission with the galaxy via spectroscopy. Deep ground-based imaging using the Dragonfly Telephoto Array finds evidence that this patch of emission is part of an older, fading ring from the collision. We find that the locations of the detected rings are an excellent match to predictions from analytic theory if the galaxy was a 10-ring system whose outermost ring has faded away. We identify the likely impacting galaxy via Keck/KCWI spectroscopy, finding evidence for gas extending between it and the Bullseye. The overall size of this galaxy rivals that of known giant low surface brightness galaxies (GLSBs) such as Malin I, lending credence to the hypothesis that CRGs can evolve into GLSBs as their rings expand and fade. Analysis of the H i content in this galaxy from ALFALFA finds significantly elevated neutral hydrogen with respect to the galaxy's stellar mass, another feature in alignment with GLSB systems.

Time-resolved Hubble Space Telescope UV Observations of an X-Ray Quasiperiodic Eruption Source

Abstract X-ray quasiperiodic eruptions (QPEs) are a novel mode of variability in nearby galactic nuclei whose origin remains unknown. Their multiwavelength properties are poorly constrained, as studies have focused almost entirely on the X-ray band. Here, we report on time-resolved, coordinated Hubble Space Telescope far-ultraviolet (FUV) and XMM-Newton X-ray observations of the shortest period X-ray QPE source currently known, eRO-QPE2. We detect a bright UV point source (L FUV ≈ few × 1041 erg s−1) that does not show statistically significant variability between the X-ray eruption and quiescent phases. This emission is unlikely to be powered by a young stellar population in a nuclear stellar cluster. The X-ray-to-UV spectral energy distribution can be described by a compact accretion disk ( R out = 34 3 − 138 + 202 R g ). Such compact disks are incompatible with typical disks in active galactic nuclei, but form naturally following the tidal disruption of a star. Our results rule out models (for eRO-QPE2) invoking (i) a classic active galactic nucleus accretion disk and (ii) no accretion disk at all. For orbiter models, the expected radius derived from the timing properties would naturally lead to disk-orbiter interactions for both quasi-spherical and eccentric trajectories. We infer a black hole mass of log10(M BH) = 5.9 ± 0.3 M ⊙ and an Eddington ratio of 0.13 − 0.07 + 0.18 ; in combination with the compact outer radius, this is inconsistent with existing disk instability models. After accounting for the quiescent disk emission, we constrain the ratio of X-ray to FUV luminosity of the eruption component to be L X/L FUV > 16−85 (depending on the intrinsic extinction).

JWST Imaging of Edge-on Protoplanetary Disks. IV. Mid-infrared Dust Scattering in the HH 30 Disk

Abstract We present near- and mid-infrared (IR) broadband imaging observations of the edge-on protoplanetary disk around HH 30 with the James Webb Space Telescope/Near Infrared Camera and the Mid-Infrared Instrument (MIRI). We combine these observations with archival optical/near-IR scattered light images obtained with the Hubble Space Telescope and a millimeter-wavelength dust continuum image obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) with the highest spatial resolution ever obtained for this target. Our multiwavelength images clearly reveal the vertical and radial segregation of micron-sized and submillimeter-sized grains in the disk. In the near- and mid-IR, the images capture not only bireflection nebulae separated by a dark lane but also diverse dynamical processes occurring in the HH 30 disk, such as spiral- and tail-like structures, a conical outflow, and a collimated jet. In contrast, the ALMA image reveals a flat dust disk in the disk midplane. By performing radiative transfer simulations, we show that grains of about 3 μm in radius or larger are fully vertically mixed to explain the observed mid-IR scattered light flux and its morphology, whereas millimeter-sized grains are settled into a layer with a scale height of ≳1 au at 100 au from the central star. We also find a tension in the disk inclination angle inferred from optical/near-IR and millimeter observations, with the latter being closer to exactly edge-on. Finally, we report the first detection of the proper motion of an emission knot associated with the mid-IR collimated jet detected by combining two epochs of our MIRI 12.8 μm observations.

Strong-lensing Analysis of SPT-CL J2325−4111 and SPT-CL J0049−2440, Two Powerful Cosmic Telescopes (RE > 40″) from the SPT Clusters Sample

Abstract We report the results from a study of two massive (M 500c > 6.0 × 1014 M ⊙) strong-lensing clusters selected from the South Pole Telescope cluster survey for their large Einstein radius (R E > 40″), SPT-CL J2325−4111 and SPT-CL J0049−2440. Ground-based and shallow Hubble Space Telescope (HST) imaging indicated extensive strong-lensing evidence in these fields, with giant arcs spanning 18″ and 31″, respectively, motivating further space-based imaging follow-up. Here, we present multiband HST imaging and ground-based Magellan spectroscopy of the fields, from which we compile detailed strong-lensing models. The lens models of SPT-CL J2325−4111 and SPT-CL J0049−2440 were optimized using nine and eight secure multiply imaged systems with a final image-plane rms of 0 . ″ 63 and 0 . ″ 73, respectively. From the lensing analysis, we measure a projected mass density within 500 kpc of M(<500 kpc) = (7.30 ± 0.07) × 1014 M ⊙ and M ( < 500 kpc ) = 7.1 2 − 0.19 + 0.16 × 1 0 14 M ⊙ for these two clusters, and subhalo mass ratios of 0.12 ± 0.01 and 0.2 1 − 0.05 + 0.07 , respectively. Both clusters produce a large area with high magnification (μ ≥ 3) for a source at z = 9, A | μ | ≥ 3 lens = 4.9 3 − 0.04 + 0.03 arcmin2 and A | μ | ≥ 3 lens = 3.6 4 − 0.10 + 0.14 arcmin2, respectively, placing them in the top tier of strong-lensing clusters. We conclude that these clusters are spectacular sightlines for further observations that will reduce the systematic uncertainties due to cosmic variance. This paper provides the community with two additional well-calibrated cosmic telescopes, as strong as the Frontier Fields and suitable for studies of the highly magnified background Universe.

Euclid preparation

Data from the Euclid space telescope will enable cosmic shear measurements to be carried out with very small statistical errors, necessitating a corresponding level of systematic error control. A common approach to correct for shear biases involves calibrating shape measurement methods using image simulations with known input shear. Given their high resolution, galaxies observed with the Hubble Space Telescope (HST) can, in principle, be utilised to emulate Euclid observations of sheared galaxy images with realistic morphologies. In this work, we employ a GalSim-based testing environment to investigate whether uncertainties in the HST point spread function (PSF) model or in data processing techniques introduce significant biases in weak-lensing (WL) shear calibration. We used single Sérsic galaxy models to simulate both HST and Euclid observations. We then ‘Euclidised’ our HST simulations and compared the results with the directly simulated Euclid-like images. For this comparison, we utilised a moment-based shape measurement algorithm and galaxy model fits. Through the Euclidisation procedure, we effectively reduced the residual multiplicative biases in shear measurements to sub-percent levels. This achievement was made possible by employing either the native pixel scales of the instruments, utilising the Lanczos15 interpolation kernel, correcting for noise correlations, and ensuring consistent galaxy signal-to-noise ratios between simulation branches. Alternatively, a finer pixel scale can be employed alongside deeper HST data. However, the Euclidisation procedure requires further analysis on the impact of the correlated noise, to estimate calibration bias. We found that additive biases can be mitigated by applying a post-deconvolution isotropisation in the Euclidisation set-up. Additionally, we conducted an in-depth analysis of the accuracy of TinyTim HST PSF models using star fields observed in the F606W and F814W filters. We observe that F606W images exhibit a broader scatter in the recovered best-fit focus, compared to those in the F814W filter. Estimating the focus value for the F606W filter in lower stellar density regimes has allowed us to reveal significant statistical uncertainties.

Detection of Emission Line Galaxies in the Slitless Spectra of HST and CSST

Abstract Slitless spectroscopy onboard space telescopes is a powerful tool to detect emission-line objects such as emission-line galaxies (ELGs) and quasars. In this work, we present a study of ELGs observed with slitless spectroscopy by the Hubble Space Telescope (HST) in a deep field of ​​​​​​∼44 arcmin2. This is one of the deepest HST fields with a wealth of imaging and spectral data. In particular, previous VLT/MUSE observations have covered this field and identified a large number of ELGs. We reduce the HST spectra using the latest pipeline with a forward modeling algorithm and construct a sample of ELGs. By comparing with the MUSE spectra, we characterize our ELG detection in the HST spectra, including the impact of the line flux, line width, signal-to-noise ratio, etc. We find that the morphological broadening may affect the detection of ELGs, such that more compact sources are easier to be detected in slitless spectra. We discuss its implications to future slitless spectroscopic surveys that will be carried out by the China Space Station Telescope (CSST) and find that the CSST slitless spectroscopy has a capability comparable to that of HST in terms of the detection of emission lines.

Evolution of the Sérsic index up to z = 2.5 from JWST and HST

Context. The Hubble Space Telescope (HST) has long been the only instrument able to allow us to investigate the structure of galaxies up to redshift z = 3, limited to the rest-frame UV and optical. The James Webb Space Telescope (JWST) is now unveiling the rest-frame near-IR structure of galaxies, less affected by dust attenuation and more representative of their underlying stellar mass profiles. Aims. We measure the evolution with redshift of the rest-frame optical and near-IR Sérsic index (n), and examine the dependence on stellar mass and star-formation activity across the redshift range 0.5 ≤ z ≤ 2.5. Methods. For an HST-selected parent sample in the CANDELS fields we infer rest-frame near-IR Sérsic profiles for ≈15 000 galaxies in publicly available NIRCam imaging mosaics from the COSMOS-Web and PRIMER surveys. We augment these with rest-frame optical Sérsic indices, previously measured from HST imaging mosaics. Results. The median Sérsic index evolves slowly or not at all with redshift, except for very high-mass galaxies (M⋆ > 1011 M⊙), which show an increase from n ≈ 2.5 to n ≈ 4 at z < 1. High-mass galaxies have higher n than lower-mass galaxies (the sample reaches down to M⋆ = 109.5 M⊙) at all redshifts, with a stronger dependence in the rest-frame near-IR than in the rest-frame optical at z > 1. This wavelength dependence is caused by star-forming galaxies that have lower optical than near-IR n at z > 1 (but not at z < 1). Both at optical and near-IR wavelengths, star-forming galaxies have lower n than quiescent galaxies, confirming and fortifying the result that across cosmic time a connection exists between star-formation activity and the radial stellar mass distribution. Besides these general trends that confirm previous results, two new trends emerge: (1) at z > 1 the median near-IR n varies strongly with star formation activity, but not with stellar mass, and (2) the scatter in near-IR n is substantially higher in the green valley (0.25 dex) than on the star-forming sequence and among quiescent galaxies (0.18 dex) – this trend is not seen in the optical because dust and young stars contribute to the variety in optical light profiles. Our newly measured rest-frame near-IR radial light profiles motivate future comparisons with radial stellar mass profiles of simulated galaxies as a stringent constraint on processes that govern galaxy formation.

Stellar Occultation Observations of (38628) Huya and Its Satellite: A Detailed Look into the System

Abstract The physical and orbital parameters of trans-Neptunian objects provide valuable information about the solar system’s formation and evolution. In particular, the characterization of binaries provides insights into the formation mechanisms that may be playing a role at such large distances from the Sun. Studies show two distinct populations, and (38628) Huya occupies an intermediate position between the unequal-sized binaries and those with components of roughly equal sizes. In this work, we predicted and observed three stellar occultation events by Huya. Huya and its satellitewere detected during occultations in 2021 March and again in 2023 June. Additionally, an attempt to detect Huya in 2023 February resulted in an additional single-chord detection of the secondary. A spherical body with a minimum diameter of D = 165 km can explain the three single-chord observations and provide a lower limit for the satellite size. The astrometry of Huya’s system, as derived from the occultations and supplemented by observations from the Hubble Space Telescope and Keck Observatory, provided constraints on the satellite orbit and the mass of the system. Therefore, assuming the secondary is in an equatorial orbit around the primary, the limb fitting was constrained by the satellite orbit position angle. The system density, calculated by summing the most precise measurement of Huya’s volume to the spherical satellite average volume, is ρ 1 = 1073 ± 66 kg m−3. The density that the object would have assuming a Maclaurin equilibrium shape with a rotational period of 6.725 ± 0.01 hr is ρ 2 = 768 ± 42 kg m−3. This difference rules out the Maclaurin equilibrium assumption for the main body shape.

A Population Analysis of 20 Exoplanets Observed from Optical to Near-infrared Wavelengths with the Hubble Space Telescope: Evidence for Widespread Stellar Contamination

We present a population study of 20 exoplanets, ranging from Neptune-like to inflated hot-Jupiter planets, observed during transit with the Space Telescope Imaging Spectrograph (STIS) and Wide Field Camera 3 (WFC3) instruments on board the Hubble Space Telescope (HST). To obtain spectral information from the near-ultraviolet to the near-infrared, we reanalyzed 16 WFC3 and over 50 STIS archival data sets with our dedicated HST pipeline. We also include 24 WFC3 data sets previously reduced with the same software. Across our target sample, we observe significant divergence among multiple observations conducted with the same STIS grating at various epochs, while we do not detect variations in the WFC3 data sets. These results are suggestive of stellar contamination, which we have investigated further using known Bayesian tools and other tailored metrics, facilitating a more objective assessment of stellar activity intensity within each system. Our findings reveal that stellar activity contaminates up to half of the studied exoplanet atmospheres, albeit at varying extents. Accounting for stellar activity can significantly alter planetary atmospheric parameters like molecular abundances (up to 6 orders of magnitude) and temperature (up to 145%), contrasting with the results of analyses that neglect activity. Our results emphasize the importance of considering the effects of stellar contamination in exoplanet transit studies; this issue is particularly true for data sets obtained with facilities that do not cover the optical and/or UV spectral range where the activity is expected to be more impactful but also more easily detectable. Our results also provide a catalog of potentially active stars for further investigation and monitoring.

Unveiling the nature of the donor stars of the ultraluminous X-ray sources in NGC 1559

Context. X-ray data provide insights into accretion processes and the compact objects of ultraluminous X-ray sources (ULXs), while optical and IR observations help identify the donor star and surrounding environment. Together, these approaches shed light on the origins of the high X-ray luminosities observed in ULXs Aims. This study examines the optical and IR properties of eight ULXs in NGC 1559 using archival data from the Hubble Space Telescope and the James Webb Space Telescope. To constrain the nature of the donor stars of the ULXs, photometric results were obtained from the temporal analysis, spectral energy distributions (SEDs), and color-magnitude diagrams (CMDs). Furthermore, the long-term and spectral characteristics of one ULX, X-1, were investigated. Methods. ULX counterparts were determined from astrometric calculations. The long-term light curves and SEDs were constructed to interpret the origin of the optical and IR emissions. The masses and ages of donor star candidates were determined using CMDs. To constrain the mechanism of X-ray emission, the time-averaged spectrum and long-term light curve of X-1 were obtained. Results. Unique optical and IR counterparts for ULXs X-14 and X-24 were determined, while only optical counterparts were detected for X-1 and X-18. Our findings indicate that the optical emission originates from the donor stars of X-14 and X-24, whereas for X-1 and X-18 it is dominated by the accretion disk. In addition, X-1 exhibits long-term X-ray variability spanning orders of magnitude.