Space Telescope Science Institute

Abstract Atmospheric characterization of exoplanets using ground-based high-resolution transmission spectroscopy has traditionally focussed on large and close-in planets, such as hot Jupiters. In this work, we aim to extend this technique to smaller and more temperate planets by studying the atmospheric composition of the temperate super-Earth planet L 98-59 d (~1.5 R⊕; ~1.9 M⊕). Using high-resolution transmission spectra obtained using IGRINS on the Gemini-South telescope, we demonstrate the feasibility for atmospheric characterization of super-Earths using ground-based facilities, and confirm the previous tentative JWST inference of hydrogen sulfide (H2S) in the atmosphere of L 98-59 d at ≲ 3.9 σ (B ~ 390). This is the first ground-based inference of a molecular species in the atmosphere of a super-Earth planet, and reveals the sensitivity of spectrographs on 8 m-class telescopes to the atmospheric characterization of such planets. By exploring a grid of atmospheric models, we find that the data favors a cloud-free atmosphere with an abundance of H2S corresponding to ~1–10 × solar metallicity. We additionally place constraints on the atmospheric abundances of other molecular species. Assuming cloud-free models, super-solar abundances for CH4 and NH3 are ruled out at 3.6σ and 4.6σ, respectively. Our results are consistent with previous suggestions that L 98-59 d is a super-Earth with possible disequilibrium production of H2S driven by volcanic outgassing from the surface. Future studies combining multiple observations with different facilities may be able to further constrain the atmospheric composition of this planet. This work underscores the promise of atmospheric characterization of super-Earth exoplanets using high-resolution spectroscopy with ground-based facilities.

ABSTRACT Recent optical surveys have identified a rare population of low-z ($z \sim 0.01 \!-\! 0.06$) extreme star-forming galaxies (xSFGs) characterized by very low metallicity, strong emission lines, extremely high specific star-formation rate, low stellar mass, and strong Ly $\alpha$ emission. Their global properties resemble recently discovered $z\gt 6$ reionization-era star-forming galaxies. We present new multifrequency radio continuum observations of eight xSFGs using the upgraded Giant Metrewave Radio Telescope at 1.25 GHz, the Karl G. Jansky Very Large Array at $1.5, 3.0, 6.0, 10.0$, and 15.0 GHz, along with archival LOw Frequency ARray data at 150 MHz for several sources. These data allow construction of the radio spectral energy distribution (radio-SED) from $\sim 1$ GHz (down to 150 MHz for some sources) to 15 GHz, spanning nearly two orders of magnitude in frequency. We find that xSFGs exhibit a flat spectral index between 6 and 15 GHz, while a subset shows spectral turnovers at $0.3 \!-\! 3$ GHz. Our Bayesian radio-SED modelling indicates that these features are consistent with a high thermal fraction combined with free–free absorption, requiring high emission measures in some systems. By comparing modelled thermal radio emission with observed H$\beta {}$ line flux density, we find evidence for dust in several xSFGs. Finally, we confirm a previously reported correlation between Lyman continuum escape fraction ($f_\mathrm{esc}^\mathrm{LyC}$), ionization state, and radio spectral index, particularly among strong leakers.

Abstract The effect of supernovae (SNe) on star formation in the interstellar medium (ISM) depends sensitively on where SNe explode with respect to ISM clouds. Observationally, SN ISM environments characterized by spatially resolved gas maps can empirically guide the placement of SNe in subgrid models, but unfortunately such measurements remain scarce, as SNe are rare and often distant. Here we demonstrate a new approach—mapping the ISM around evolved massive stars that are soon to explode. These provide a substantially larger sample of “explosion sites” (than just historical SNe) in nearby galaxies that have high-resolution atomic and molecular ISM maps from the Jansky Very Large Array and Atacama Large Millimeter/submillimeter Array. We demonstrate this technique in the well-resolved Local Group spiral M33 by analyzing the 50 pc scale projected ISM densities around red supergiants (RSGs; 8–30 M ⊙ stars) Wolf–Rayet stars (W-Rs; >30 M ⊙ stars), and supernova remnants. We find a mass-dependent correlation between stars and gas clouds, with at least 45% of W-Rs and up to 77% of RSGs having no detectable H 2 at their pixel locations. In the sample with H 2 detections, we find that more-massive younger progenitors are coincident with denser gas. We show that the density distributions for stars >15 M ⊙ are statistically distinct from random alignment of stars and gas in M33. Our work provides the first observationally derived estimate of the fraction of the SN-producing stellar population correlated with ISM density peaks. We demonstrate how this can be compared with galaxy simulations, and advocate similar comparisons to the community for constraining subgrid models.

Abstract Galaxy mergers have long been proposed as a mechanism for funneling gas toward galactic centres, potentially triggering accretion onto supermassive black holes (SMBHs) and igniting active galactic nuclei (AGN). While simulations often support this scenario, observational studies have yielded conflicting results regarding the AGN-merger connection. In this study, we analyze 31 galaxies from cosmological zoom-in simulations spanning redshifts 0.5 < z < 3. We identify mergers using detailed merger trees based on six-dimensional dark matter particle information and identify AGN activity through SMBH accretion histories. To bridge the gap between simulations and observations, we generate mock JWST-like images and extract non-parametric morphological parameters. Employing a k-nearest neighbours (KNN) classifier in a five-dimensional space (four morphological parameters and redshift), we identify mergers in the mock-observed dataset. Our analysis reveals a statistically significant enhancement of AGN activity in merging systems, particularly at lower redshifts (0.5 < z < 0.9), where central gas reservoirs are more depleted. This supports the view that mergers contribute more significantly to AGN triggering in environments with low internal gas reservoirs, while their impact may be less pronounced in gas-rich systems. However, when relying solely on morphological classifications from mock observations, the observed AGN-merger connection weakens, especially at higher redshifts. This underscores the challenges in detecting merger-induced AGN activity observationally and highlights the importance of combining simulations with realistic mock observations to fully understand the AGN-merger relationship.

Abstract Background stars observed through a circumstellar disk provide valuable benchmarks for investigating the disk’s extinction properties. The HD 163296 system is an excellent case study due to its large disk, the clearly visible extinction effects in JWST/NIRCam data, and the presence of numerous background sources within or around its disk. We present the measured contrasts and astrometry of sources surrounding HD 163296 from Cycle 1 JWST/NIRCam coronagraphic observations, which will serve as a useful reference for future studies of the disk’s extinction characteristics.

The main sequence of star-forming galaxies (SFGMS or MS) is a fundamental scaling relation that provides a global framework for studying galaxy formation and evolution, as well as an insight into the complex star formation histories (SFHs) of individual galaxies. In this work, we combine large-area pre-JWST surveys (COSMOS2020, CANDELS), which probe high- M ★ sources (> 10 9 M ⊙ ), with SHARDS/CANDELS FAINT and JWST data from CANUCS, CEERS, JADES, and UNCOVER, to obtain a high- z , star formation rate (SFR) and stellar mass ( M ★ ) complete sample spanning both high- and low- M ★ regimes. Completeness in both M ★ and the SFR is key to avoiding biases introduced by low-mass, highly star-forming objects. Our combined dataset is 80% complete down to 10 7.6 M ⊙ at z ∼ 1 (10 8.8 M ⊙ at z ∼ 9). The overall intrinsic MS slope (based on the SFR 100 and M ★ derived with Dense Basis and nonparametric SFHs) shows little evolution up to z ∼ 5, with values ∼0.7 − 0.8. The slope in the low- M ★ regime becomes steeper than that in the high- M ★ end at least up to z ∼ 5, but the strength of this change is highly dependent on the assumptions made on the symmetry of the uncertainties in M ★ and SFR. If real, the steepening suggests reduced star formation efficiency or declining gas content with decreasing M ★ . The transition between the low- M ★ regime and the canonical MS occurs around 10 9.5 M ⊙ , independent of z . This critical value may coincide with the assembly of galaxies’ disks, which can provide a mechanism for self-regulation that stabilizes them against feedback. The intrinsic scatter is compatible with canonical estimates, also at low- M ★ , ranging from 0.2 − 0.3 dex. This is indicative of rapid variations in star formation being averaged out over ≲100 Myr.

Using JWST/MIRI observations, we report the detection of CO$_2$ ice in the dusty torus of the planetary nebula NGC 6302, an environment generally considered hostile to fragile molecular species and ices due to intense UV irradiation. This detection accompanies cold (20-50 K) gas-phase CO$_2$ along the same sightlines. The ice absorption profile exhibits a double-peak profile, a characteristic of pure, crystalline CO$_2$ ice. The CO$_2$ gas-to-ice ratio is more than an order of magnitude higher than in young stellar objects, pointing to distinct ice formation or processing mechanisms in evolved stellar environments. This discovery demonstrates that the dusty torus provides sufficient shielding to harbour ice chemistry, and that ice-mediated surface reactions must be incorporated into chemical models of planetary nebulae.

Abstract The X-ray source around supermassive black holes in active galactic nuclei (AGN) has been dubbed the corona by analogy to the solar (and stellar) corona. Both stellar and AGN coronae are orders of magnitude hotter than their counterpart optical source; the stellar photosphere and accretion disk respectively. Both coronae vary on short time scales down to seconds. The coronal activity in the Sun is well imaged and its activity has been shown to be driven by magnetic energy converted into heat through the process of magnetic reconnection. While it has been theorized that AGN corona are also magnetically driven, the driving mechanism of AGN coronal activity has not been directly observed. A smoking gun of magnetic reconnection is when a coronal flare’s temporal evolution in hard and soft X-rays follows the Neupert Effect. These flares result in both a solar coronal mass ejection, and energetic particles streaming down along magnetic field lines to the photosphere. Here, we report the detection of the Neupert Effect in an AGN corona, providing the first direct evidence for magnetic reconnection in AGN. Our measurements indicate a magnetic field loop height of up to 30 gravitational radii, and a distance of about 400 gravitational radii between the corona and the UV emitting accretion disk. The present findings thus enable the application of solar coronal physics to the less accessible AGN corona.

Abstract Stellar feedback drives multiphase gas outflows from starburst galaxies, but the interpretation of dust emission in these winds remains uncertain. To investigate this, we analyze new JWST mid-infrared images tracing polycyclic aromatic hydrocarbon (PAH) emission at 7.7 and 11.3 μ m from the outflow of the prototypical starburst M82 out to 3.2 kpc. We find that PAH emission shows significant correlations with CO, H α , and X-ray emission within the outflow, though the strengths and behaviors of these correlations vary with gas phase and distance from the starburst. PAH emission correlates strongly with cold molecular gas, with PAH–CO scaling relations in the wind nearly identical to those in galaxy disks despite the very different conditions. The H α –PAH correlation indicates that H α traces the surfaces of PAH-bearing clouds, consistent with arising from ionized layers produced by shocks. Meanwhile, the PAH–X-ray correlation disappears once distance effects are controlled for past 2 kpc, suggesting that PAHs are decoupled from the hot gas and the global correlation merely reflects the large-scale structure of the outflow. The PAH-to-neutral gas ratio remains nearly flat to 2 kpc, with variations following changes in the radiation field. This implies that the product of PAH abundance and dust-to-gas ratio does not change significantly over the inner portion of the outflow. Together, these results demonstrate that PAHs robustly trace the cold phase of M82’s wind, surviving well beyond the starburst and providing a powerful, high-resolution proxy for mapping the life cycle of entrained cold material in galactic outflows.

Abstract We introduce a new photometric catalog of RR Lyrae (RRL) variables (∼300,000) mainly based on data available in public datasets. We also present the largest and most homogeneous spectroscopic dataset of RRLs and blue horizontal branch (BHB) stars ever collected. This includes radial velocity measurements (∼16,000) and iron abundances (Δ S method for 8140 RRLs, plus 547 from literature). Elemental abundances based on high-resolution spectra are provided for 487 RRLs and 64 BHB stars. We identified candidate RRLs associated with the main Galactic components and their iron distribution function (IDF) becomes more metal rich when moving from the halo ([Fe/H] = −1.56) to the thick disk (TCD; [Fe/H] = −1.47) and thin disk (TND; [Fe/H] = −0.73). Furthermore, halo RRLs and RRLs in retrograde orbits are α enhanced ([ α /Fe]=0.27, σ = 0.18), while TCD RRLs are either α enhanced ([Fe/H] ≤ −1.0) or α poor ([Fe/H] > −1.0), and TND RRLs are mainly α poor ([ α /Fe] = −0.01, σ = 0.20). We also identified RRLs associated with the main stellar streams—Gaia–Sausage–Enceladus (GSE); Sequoia, Helmi, and Sagittarius—and we found that their IDFs are quite similar to halo RRLs. However, GSE RRLs lack the metal-poor/metal-rich tails and their α -element distribution is quite compact. The iron radial gradient in Galactocentric distance for TND, TCD, and halo RRLs is negative and it decreases from −0.026, to −0.010, and to −0.002 dex kpc −1 . The iron radial gradient based on dry halo (halo without substructures) RRLs is, within the errors, equal to the global halo. We also found a strong similarity between iron and [ α /Fe] radial gradients of Milky Way RRLs and M31 globular clusters throughout the full range of galactocentric distances covered by the two samples.