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  • A Rest-frame K-band View of Bulge Growth in Massive Star-forming Galaxies at z ∼ 2
    We study bulge formation in 16 massive dusty star-forming galaxies at z ∼ 2 by combining JWST MIRI F770W imaging, NIRCam imaging in eight bands, and Atacama Large Millimeter/submillimeter Array (ALMA) 870 μm data. At the median redshift of z = 2.18, the F770W band probes the rest-frame 2.4 μm light, close to the rest-frame K band, and traces the stellar mass distribution with much less dust attenuation than the NIRCam bands. The effective radii measured in F770W agree with those of the 870 μm dust emission, with a median ratio of 0.95, and are typically 23% smaller than those in F444W. The rest-frame K-band imaging is, therefore, essential to measure the true extent of the stellar mass, which is as compact as the dusty star-forming regions. In stacks of the 16 galaxies at a matched resolution, the 870 μm and F770W profiles agree closely out to 8 kpc, and a bulge plus disk decomposition of the F770W stack gives a bulge-to-total ratio of 0.50. Fitting the spectral energy distributions (SEDs) in radial bins with CIGALE, we find that the attenuation decreases from AV = 3.7 mag at the center to 1.9 mag at r ≳ 7 kpc, while the specific star formation rate profile is flat. In most of the galaxies, the bulge is already in place inside the dusty core. In two galaxies, by contrast, the 870 μm emission is 3–6 times more compact than the F770W light, which suggests that they are still in the bulge-building compaction phase. Our sample may, thus, catch massive galaxies in several phases of bulge formation.

  • Hydrogen and Helium Dissolution, Outgassing, and Loss in Evolving Sub-Neptune Magma Oceans: Examining Demographic Features and Radius Evolution
    Sub-Neptunes’ molten interiors are expected to accommodate large quantities of volatiles, potentially altering their radius evolution. Previous studies have examined this effect in isolation with simplified evolution modeling, often assuming idealized interior and atmospheric conditions. To address this limitation, we introduce SEAMIST, a unified evolution model for sub-Neptunes and super-Earths that self-consistently combines, for the first time, interior structure, cooling, rock/iron solidification, boil-off, photoevaporation, H/He dissolution, and atmospheric composition. SEAMIST considers both a partially soluble case, in which hydrogen partitions into the magma ocean with a fraction set by mantle-envelope boundary conditions, and a fully miscible case, in which hydrogen may fully dissolve into the magma ocean at high temperatures. We identify a novel catastrophic boil-off mechanism, triggered by a positive feedback between hydrogen outgassing and mass loss that can operate billions of years after disk dispersal. In partially soluble models, the impact of H/He dissolution on radius evolution is modest. This contrasts with previous expectations, as we find that increasing hydrogen abundance from outgassing enhances mass-loss efficiency, counterbalancing volatile replenishment from the rock/iron interior. Fully miscible hydrogen, in contrast, enhances envelope survival around low-mass stars and produces helium-dominated envelopes. Overall, at intermediate to low masses, mass–radius curves from partially soluble models match observed distributions. The fully miscible case predicts a radius peak and excess planets around low stellar masses that appear inconsistent with current observations, although it reproduces the observed radius “cliff” near 4R⊕ at higher masses. Our results suggest that high metallicity may explain the cliff, although alternatives cannot be ruled out.

  • The Flare and Spiral Structure of the Milky Way’s Disk as Traced by Young Giant Stars
    We explore the three-dimensional structure of a sample of ∼16,000 young giant stars in the Galactic disk out to ∼8 kpc in heliocentric distance. This population traces a thin disk with a local vertical scale height of hZ⊙ = 74 ± 5 pc, which progressively thickens toward the outer Galaxy with a prominent Galactic flare, rising exponentially with a radial scale length of hfl = 3.5 ± 0.4 kpc. Our analysis incorporates both the survey selection function and the vertical displacements caused by the Galactic warp and corrugations, which, if neglected, would lead to significant biases in the derived disk scale height. In the Galactic plane, the young giants trace coherent spiral arm segments, extending previous maps based on upper main sequence (UMS) and OB stars by 2–4 kpc, depending on the considered direction. The obtained map supports a pitch angle of roughly 20° for the Perseus Arm, and shows that the Local/Orion Arm stretches at least 10 kpc in length. Unlike earlier and more local maps based on UMS and OB stars, where the relatively small sampled portion of the Perseus Arm appeared as a short, nearly straight feature, our map reveals it as an extended structure with a gentle curvature, as expected for spiral arms on large scales. In the inner Galaxy, we also identify a new segment likely associated with the Scutum Arm, clearly detached from the Sagittarius-Carina Arm in the fourth Galactic quadrant.

  • COOL-LAMPS. IX. A Rare Duo of Quasars Each Lensed by a Single Massive Galaxy Cluster
    Wide-separation lensed quasars (WSLQs) are rare systems that arise from the chance alignment of two objects: a galaxy cluster and a background quasar. After two decades, only seven WSLQs have been found. Here, we report the discovery of COOL J1153+0755 by the COOL-LAMPS collaboration in DECaLS imaging and its confirmation with follow-up observations with the Magellan Telescopes and the Nordic Optical Telescope. This system features two multiply imaged quasars each lensed into four images by the same z = 0.4301 cluster: a classic broad-line Type I quasar at z = 1.524 (COOL J1153A) and a dust-obscured Type II quasar at z = 1.939 (COOL J1153B), with maximum image separations of and , respectively. We construct a lens model to estimate a projected cluster mass of M( < 500 kpc) ∼ 3.3 × 1014M⊙ and relative time delays between the three brightest images of each quasar of Δt A3, A1 ∼ 800, Δt A2, A1 ∼ 1200, Δt B1, B3 ∼ 800, and Δt B2, B3 ∼ 1000 days. COOL J1153A resides in a dense environment with three nearby galaxies, two of which are also strongly lensed. We identified COOL J1153+0755 without making a morphological cut in the DECaLS catalog; none of its multiple images are classified as point sources in those data, implying that morphology-based selection would miss such systems. COOL J1153+0755 expands the WSLQ sample from seven to eight systems (nine individual quasars), adding two powerful laboratories for probing black hole-galaxy coevolution at Cosmic Noon and for time-delay cosmography constraints on the Hubble constant, H0.

  • Persistent Radio Sources and Multiwavelength Counterparts of Fast Radio Bursts: Magnetar Wind Nebulae and Bow Shocks in Massive Binary Systems
    Fast radio bursts (FRBs) are millisecond-duration pulses originating from cosmological distances. Multiwavelength counterparts associated with FRBs are important for unveiling their physical origins. Recent observations provide strong evidence that the sources of some active FRBs are residing in massive-star binaries. In this paper, we study the electromagnetic counterparts of FRBs, including persistent radio sources (PRSs) and multiwavelength emission from magnetar wind nebulae (MWNe) or bow shocks in massive binary systems. We find that the PRSs with luminosity 1038–1039 erg s−1 can be generated by young MWNe. The age of magnetars is a few decades. The observed long-term variation of flux density for PRSs can be explained by the internal magnetic field decay of magnetars. The bow shock radiation can account for the less luminous PRSs with luminosity ≲1036 erg s−1. Magnetically powered nebulae may yield detectable keV synchrotron self-Compton (SSC) X-rays out to ≲20 Mpc, whereas rotation-powered systems mainly produce GeV SSC emission detectable only within ≲0.1 Mpc. For active magnetars in massive binaries, enhanced wind interaction can generate synchrotron X-rays detectable within ≲50 Mpc and GeV–TeV inverse-Compton emission detectable within ≲1–0.1 Mpc.