March 2025 · 10 Articles · Pages 1–148
March 2025
Open Access10 Articles · Pages 1–148
We present deep 21-cm observations of the edge-on spiral galaxy NGC 4565 obtained with the Jansky Very Large Array, achieving a column density sensitivity of 2 × 10^18 cm^−2. We detect anomalous neutral hydrogen emission extending up to 15 kpc above the galactic midplane, exhibiting systematic velocity offsets relative to the disk rotation. The kinematics and spatial distribution of this extraplanar gas are consistent with cold-mode accretion from the circumgalactic medium, providing observational support for theoretical predictions of filamentary gas infall fueling ongoing disk star formation.
We present a comprehensive analysis of transit timing variations in the TRAPPIST-1 system combining archival Spitzer observations with 18 new JWST/NIRSpec transit light curves. The extended temporal baseline of over eight years enables refined dynamical mass determinations for all seven planets with precisions of 3–8%. The updated densities confirm that planets d, e, and f require substantial volatile envelopes or water-rich interiors, while planets b and c are consistent with desiccated rocky compositions. Our N-body integrations place new constraints on orbital eccentricities and the system’s long-term dynamical stability.
We present deep optical spectroscopy of 11 ultra-diffuse galaxies (UDGs) in the Coma cluster obtained with Gemini/GMOS, achieving sufficient signal-to-noise for Lick index and full-spectrum fitting analysis. The UDGs exhibit uniformly old stellar populations (ages > 8 Gyr) with sub-solar metallicities spanning −1.2 < [Fe/H] < −0.5. We find a mass-metallicity relation offset below that of normal dwarf galaxies, suggesting that UDGs experienced early truncation of star formation. Stellar velocity dispersions indicate dark matter halo masses of 10^11–10^12 solar masses, classifying these objects as failed L-star galaxies.
We present coordinated radio, optical, UV, and X-ray observations of the black hole X-ray binary MAXI J1820+070 spanning its complete 2018 outburst cycle. Simultaneous multi-wavelength light curves and spectral analysis track the source through hard, intermediate, and soft spectral states. We detect correlated optical/X-ray variability on sub-second timescales during the hard state, consistent with jet synchrotron emission, and observe discrete relativistic ejection events in VLBI radio imaging coincident with the hard-to-soft state transition. Our broadband spectral modeling constrains the black hole spin and inner disk geometry across the outburst evolution.
We present chemical abundances for 86 red giant branch stars in the Sculptor and Fornax dwarf spheroidal galaxies derived from VLT/FLAMES medium-resolution spectroscopy. We measure [Fe/H], [alpha/Fe], and neutron-capture element ratios spanning a metallicity range of −3.0 < [Fe/H] < −0.5. The alpha-element knee occurs at significantly lower metallicity in both dwarfs compared to the Milky Way halo, reflecting their lower star formation efficiencies. We detect a steep rise in [Ba/Fe] at [Fe/H] > −1.5 in Fornax attributed to s-process enrichment from AGB stars, constraining the timescale of chemical evolution in low-mass galaxies.
We measure the baryon acoustic oscillation feature in the two-point correlation function of 1.4 million quasars from the DESI Year-1 spectroscopic survey in the redshift range 0.8 < z < 2.1. Splitting the sample into four redshift bins, we obtain distance measurements with 1.5–2.8% precision, representing the most precise BAO constraints at z > 1 to date. Combined with CMB and Type Ia supernova data, our results are consistent with a flat Lambda-CDM cosmology and place new constraints on time-varying dark energy models, with the dark energy equation of state parameter w = −1.03 ± 0.05.
We perform three-dimensional radiation hydrodynamic simulations of massive protostellar disks to investigate the conditions under which gravitational fragmentation produces bound companions. Our simulations span disk-to-star mass ratios of 0.1–0.5 and include realistic dust opacity models and radiative cooling. We find that fragmentation occurs only when the Toomre Q parameter drops below 0.9 over spatial scales exceeding the local Jeans length, and that the resulting fragments have initial masses of 3–20 Jupiter masses. The majority of fragments migrate inward and are tidally disrupted, but 15% survive to form wide-orbit companions, consistent with the observed frequency of giant planets at separations beyond 50 au.
We report the detection of a compact double radio source at 1.4 and 5.5 GHz located behind the merging galaxy cluster 1E 0657−56 (the Bullet Cluster). The observed Faraday rotation measure of 4,300 rad/m^2 is among the highest measured through any galaxy cluster, implying magnetic field strengths of 10–30 microgauss in the post-shock region. Combined with X-ray surface brightness constraints from Chandra, our measurement provides a direct probe of the magnetic field amplification associated with the cluster merger shock front.
We present the optical identification of the Fermi-LAT unassociated source 4FGL J1653.4−0158 as a redback millisecond pulsar binary. Time-resolved photometry and spectroscopy obtained with the Magellan/IMACS instrument reveal a 4.2-hour orbital period, a tidally distorted companion star with a spectral type of G5, and radial velocity variations yielding a minimum neutron star mass of 1.6 solar masses. The optical light curve exhibits asymmetric heating consistent with an intrabinary shock, confirming the redback classification and adding to the growing census of spider pulsar systems identified through multi-wavelength follow-up of gamma-ray sources.
The formation of kilometer-sized planetesimals from micrometer-sized dust grains remains a central challenge in planet formation theory. This review examines the physical processes governing grain growth, including coagulation, fragmentation, and radial drift, and evaluates proposed solutions to the meter-size barrier such as streaming instability, pressure bump trapping, and porous aggregate growth. We synthesize observational constraints from millimeter-wavelength spectral indices, polarimetric signatures, and resolved disk substructures observed by ALMA, and discuss how these data inform and constrain theoretical models of the earliest stages of planet assembly.