Astrophysics

Cosmology, galaxies, stellar physics, and astronomical instrumentation

Includes:Cosmology and Nongalactic Astrophysics(astro-ph.CO)Astrophysics of Galaxies(astro-ph.GA)Solar and Stellar Astrophysics(astro-ph.SR)High Energy Astrophysical Phenomena(astro-ph.HE)Earth and Planetary Astrophysics(astro-ph.EP)Instrumentation and Methods for Astrophysics(astro-ph.IM)

Trending in Astrophysics

Dissecting the Hubble tension: Insights from a diverse set of Sound Horizon-free H0 measurements

The Hubble tension is commonly framed as a discrepancy between local, late-time measurements favoring $H_0 \approx 73$ km s$^{-1}$ Mpc$^{-1}$ and early-time, Sound-Horizon-based measurements favoring $H_0 \approx 67$ km s$^{-1}$ Mpc$^{-1}$. We challenge this viewpoint by analyzing 83 Sound-Horizon-independent $H_0$ measurements, categorized into four classes: Distance Ladder measurements using local calibrators; Local One-Step $Λ$CDM measurements assuming the standard expansion history; Pure Local One-Step measurements independent of $H(z)$ shape; and CMB Sound Horizon free measurements using CMB data without the Sound Horizon scale. We find that the 29 Distance Ladder measurements yield $H_0 = 72.74 \pm 0.40$ km s$^{-1}$ Mpc$^{-1}$ ($χ^2_ν\equiv χ^2/d.o.f= 0.74$), while the 54 One-Step measurements collectively yield $H_0 = 68.67 \pm 0.46$ km s$^{-1}$ Mpc$^{-1}$ ($χ^2_ν= 0.85$), a $6.7σ$ tension exceeding the Planck--SH0ES discrepancy. This tension remains significant at $4.5σ$ after accounting for correlations. Among One-Step categories, Local One-Step $Λ$CDM measurements favor the lowest value ($H_0 = 67.18 \pm 0.90$ km s$^{-1}$ Mpc$^{-1}$), Pure Local One-Step yield an intermediate value ($H_0 = 70.38 \pm 1.00$ km s$^{-1}$ Mpc$^{-1}$), and CMB Sound Horizon Free measurements give $H_0 = 68.71 \pm 0.63$ km s$^{-1}$ Mpc$^{-1}$. Thus, that the Hubble tension is better characterized as a discrepancy between the Distance Ladder and all other methodologies, rather than an early-vs-late-time split. We also identify a $2.4σ$ internal tension among One-Step measurements: analyses assuming $Λ$CDM systematically recover lower $H_0$ values by about 3.2 km s$^{-1}$ Mpc$^{-1}$ compared to model-independent methods. This suggests either unrecognized systematics/physics in the Distance Ladder or deviations from $Λ$CDM in the late-time Universe.

2601.00650

Jan 2026Cosmology and Nongalactic Astrophysics

Dynamical Dark Energy Imprints in the Lyman-Alpha Forest

The nature of dark energy (DE) remains elusive, even though it constitutes the dominant energy-density component of the Universe and drives the late-time acceleration of cosmic expansion. By combining measurements of the expansion history from baryon acoustic oscillations, supernova surveys, and cosmic microwave background data, the Dark Energy Spectroscopic Instrument (DESI) Collaboration has inferred that the DE equation of state may evolve over time. The profound implications of a time-variable, ``dynamical" DE (DDE) that departs from a cosmological constant motivate the need for independent observational tests. In this work, we use cosmological hydrodynamical simulations of structure formation to investigate how DDE affects the properties of the Lyman-Alpha ``forest'' of absorption features produced by neutral hydrogen in the cosmic web. We find that DDE models consistent with the DESI constraints induce a spectral tilt in the forest transmitted flux power spectrum, imprinting a scale- and redshift-dependent signature relative to standard Lambda-CDM cosmologies. These models also yield higher intergalactic medium temperatures and reduced Lyman-Alpha opacity compared to Lambda-CDM. We discuss the observational implications of these trends as potential avenues for independent confirmation of DDE.

2601.00767

Jan 2026Cosmology and Nongalactic Astrophysics

Irradiated Atmosphere V: Effects of Vertical-Mixing induced Energy Transport on the Inhomogeneity

Atmospheric variations over time and space boost planetary cooling, as outgoing internal flux responds to stellar radiation and opacity. Vertical mixing regulates this cooling. Our study examines how gravity waves or large-scale induced mixing interact with radiation transfer, affecting temperature inhomogeneity and internal flux. Through the radiative-convective-mixing equilibrium, mixing increases temperature inhomogeneity in the middle and lower atmospheres, redistributing internal flux. Stronger stellar radiation and mixing significantly reduce outgoing flux, slowing cooling. With constant infrared (IR) opacity, lower visible opacity and stronger mixing significantly reduce outgoing flux. Jensen's inequality implies that greater spatial disparities in stellar flux and opacity elevate the ratio of the average internal flux in inhomogeneous columns relative to that in homogeneous columns. This effect, particularly pronounced under high opacity contrasts, amplifies deep-layer temperature inhomogeneity and may enhance cooling. However, with mixing, overall cooling is weaker than without, as both the averaged internal flux of the inhomogeneous columns and that of the homogeneous column decline more sharply for the latter. Thus, while vertical mixing-induced inhomogeneity can enhance cooling, the overall cooling effect remains weaker than in the non-mixing case. Therefore, vertical mixing, by regulating atmospheric structure and flux, is key to understanding planetary cooling.

2601.00606

Jan 2026Earth and Planetary Astrophysics

Callisto's Nonresonant Orbit as an Outcome of Circum-Jovian Disk Substructure

The Galilean moons of Io, Europa, and Ganymede exhibit a 4:2:1 commensurability in their mean motions, a configuration known as the Laplace resonance. The prevailing view for the origin of this three-body resonance involves the convergent migration of the moons, resulting from gas-driven torques in the circum-Jovian disk wherein they accreted. To account for Callisto's exclusion from the resonant chain, a late and/or slow accretion of the fourth and outermost Galilean moon is typically invoked, stalling its migration. Here, we consider an alternative scenario in which Callisto's nonresonant orbit is a consequence of disk substructure. Using a suite of N-body simulations that self-consistently account for satellite-disk interactions, we show that a pressure bump can function as a migration trap, isolating Callisto and alleviating constraints on its timing of accretion. Our simulations position the bump interior to the birthplaces of all four moons. In exploring the impact of bump structure on simulation outcomes, we find that it cannot be too sharp nor flat to yield the observed orbital architecture. In particular, a "Goldilocks" zone is mapped in parameter space, corresponding to a well-defined range in bump aspect ratio. Within this range, Io, Europa, and Ganymede are sequentially trapped at the bump, and ushered across it through resonant lockstep migration with their neighboring, exterior moon. The implications of our work are discussed in the context of uncertainties regarding Callisto's interior structure, arising from the possibility of non-hydrostatic contributions to its shape and gravity field, unresolved by the Galileo spacecraft.

2601.00786

Jan 2026Earth and Planetary Astrophysics

The impact of cosmic voids on AGN activity

From the Eagle project, we study the properties of galaxies hosting AGN in cosmic voids and their surrounding structures, filaments and walls, at $z=0$, comparing them to non-AGN galaxies in similar environments. We found that the AGN fraction decreases as a function of void-centric distance, with void galaxies displaying the highest AGN fraction (12\%), and galaxies in denser environments, showing the lowest AGN fraction (6.7\%), consistent with observations. The AGN fraction is particularly high in most massive void galaxies when controlling for stellar mass. When comparing AGN host galaxies to inactive ones, we find that AGN galaxies tend to have slightly more massive SMBHs, higher specific star formation rates, and reside in higher-mass haloes at a given stellar mass than non-AGN galaxies. At $\rm M_{*} > \rm 10^{10.2} \rm M_{\odot}$, AGN hosts in voids tend to have slightly more massive SMBHs than those in denser environments. Otherwise, the AGN population does not show a clear trend in relation to the global environment. In contrast, non-AGN void galaxies host more massive SMBHs, slightly higher sSFRs, and are located in more massive haloes than those in denser environments. Analysing the recent merger histories of both AGN and non-AGN populations, we find that a larger fraction of massive AGN galaxies have undergone major mergers compared to non-AGN galaxies, regardless of environment. Notably, AGN galaxies in voids show a higher frequency of recent mergers, especially major mergers, than their counterparts in other environments, especially at high stellar mass. Our results suggest that the evolution of SMBHs in voids is closely related to that of their host galaxies and their surrounding environment, while the most recent AGN activity is more strongly linked to recent interactions.

2601.00594

Jan 2026Astrophysics of Galaxies

A free-floating-planet microlensing event caused by a Saturn-mass object

A population of free-floating planets is known from gravitational microlensing surveys. None have a directly measured mass, owing to a degeneracy with the distance, but the population statistics indicate that many are less massive than Jupiter. We report a microlensing event -- KMT-2024-BLG-0792/OGLE-2024-BLG-0516, which was observed from both ground- and space-based telescopes -- that breaks the mass-distance degeneracy. The event was caused by an object with 0.219^{+0.075}_{-0.046} Jupiter masses that is either gravitationally unbound or on a very wide orbit. Through comparison with the statistical properties of other observed microlensing events and predictions from simulations, we infer that this object likely formed in a protoplanetary disk (like a planet), not in isolation (like a brown dwarf), and dynamical processes then ejected it from its birth place, producing a free-floating object.

2601.000571

Dec 2025Earth and Planetary Astrophysics

A New Empirical Fit to Galaxy Rotation Curves

We present a new empirical model for galaxy rotation curves that introduces a velocity correction term ω, derived from observed stellar motion and anchored to Keplerian baselines. Unlike parametric halo models or modified gravity theories, this approach does not alter Newtonian dynamics or invoke dark matter distributions. Instead, it identifies a repeatable kinematic offset that aligns with observed rotation profiles across a wide range of galaxies. Using SPARC data [1], we demonstrate that this model consistently achieves high fidelity fits, often outperforming MOND and CDM halo models in RMSE and R-squared metrics without parametric tuning. The method is reproducible, minimally dependent on mass modeling, and offers a streamlined alternative for characterizing galactic dynamics. While the velocity correction ω lacks a definitive physical interpretation, its empirical success invites further exploration. We position this model as a local kinematic tool rather than a cosmological framework, and we welcome dialogue on its implications for galactic structure and gravitational theory. Appendix B presents RMSE and R2 comparisons showing that this method consistently outperforms MOND and CDM halo models across a representative galaxy sample.

2601.00522

Jan 2026Astrophysics of Galaxies

Betelgeuse: Detection of the Expanding Wake of the Companion Star

Recent analyses conclude that Betelgeuse, a red supergiant star (HD 39801), likely has a companion object with a period of about 2000 days orbiting at only 2.3 stellar radii, deep in the chromosphere of the supergiant. A probable detection of such a companion, named Siwarha, has just occurred from speckle imaging. This study finds that Betelgeuse spectra in the optical region and ultraviolet exhibit signatures of variable circumstellar absorption and chromospheric outflows. These variations are consistent with the ~ 2000-day period of the companion object. Circumstellar absorption evident in optical Mn I lines, and mass outflow marked by ultraviolet Fe II, Si I, and Mg I lines increase after the transit of the companion across the disk of Betelgeuse. Following the eclipse of the companion, the absorption and outflow slowly decrease in advance of the next transit. The occurrence and variation of this plasma appear consistent with the presence of a trailing and expanding wake caused by a companion star orbiting within the atmosphere of Betelgeuse.

2601.00470

Jan 2026Solar and Stellar Astrophysics

Hadronic Origin of Sub-PeV Gamma-Ray Emission from LHAASO J0621+3755

Very High Energy (VHE) gamma rays are primarily estimated to arise from high-energy electromagnetic interactions in pulsars and their halo through electron inverse Compton (IC) scattering. Hadronic channels like neutral pion decay have also been proposed to produce TeV-PeV gamma rays from the Pulsar halo. The neutral pions are expected to be generated from cosmic ray (CR) protons interacting with the ambient/cloud. The recent observations of sub-PeV gamma rays from the halo of pulsar PSR J0622+3749 by the Large High Altitude Air Shower Observatory Kilometre-Square Array (LHAASO-KM2A) detector provide a platform to explore different channels of their production. Previous studies support consistency with the leptonic modeling of the halo, which attributes its origin to slow diffusion in the interstellar medium. In this work, we investigated the possibility of proton-proton channel as the origin of these photons. To explain the observed gamma rays with energy $\sim 4$ TeV by the High-Altitude Water Cherenkov (HAWC) telescope till 200 TeV by the LHAASO observatory, one requires the CR proton luminosity to be $η_p\sim 0.1$ of the pulsar PSR J0622+3749 spin-down luminosity. In this case, we have considered the protons propagating in a one-zone superdiffusion environment, specifically $α= 1$ in a cloud of gas density 1 per cm$^{3}$.

2601.00692

Jan 2026High Energy Astrophysical Phenomena

Readdressing the contribution of photonuclear reactions to the muon content of extensive air showers: a heuristic approach

The indirect ground-based observations of cosmic rays through extensive air showers in modern experiments typically involve the use of Monte Carlo simulations to determine the characteristics of the primary particles. These simulations necessitate assumptions about particle interactions at energies that have not yet been experimentally probed, which introduces systematic uncertainties in key observables, particularly the number of muons. Current research on this uncertainty primarily focuses on hadronic interaction models, the dominant source of muon production. This study presents an approach that takes into account another significant mechanism for muon generation: photonuclear reactions. A robust heuristic technique has been developed to estimate the contribution of these interactions to the total number of muons over a wide range of extensive air shower parameters (including primary particle type, energy, and slant atmospheric depth) and photonuclear interaction models, with an absolute percentage error on the order of $10\%$ in the estimated number of muons. Furthermore, several potential applications of the suggested method in relation to modern challenges in extensive air shower physics are discussed.

2512.12481

Dec 2025High Energy Astrophysical Phenomena

A Spatially Resolved Evolutionary Sequence of Multi-wavelength AGN Host Galaxies

We study the spatially resolved star formation, gas ionisation, and outflow properties of 1813 active galactic nuclei (AGNs) from the MaNGA survey, which we classify into infrared (IR), broad-line (BL), narrow-line (NL), and radio (RD) AGNs based on their mid-infrared colours, optical spectra, and/or radio photometry. We also provide estimations of AGN power at different wavelengths. AGN incidence is found to increase with stellar mass following a power-law, with the high-mass end dominated by RDAGNs and the low-mass end dominated by NLAGNs. Compared to their mass-matched non-AGN counterparts, we find that IRAGNs, BLAGNs, and NLAGNs on average show enhanced specific star formation rates, younger stellar populations, and harder ionisation towards the centre. RDAGNs, in contrast, show radial profiles similar to quiescent galaxies. [OIII] outflows are more common and stronger in BL/IRAGNs, while RDAGNs on average show no outflow features. The outflow incidence increases with [OIII] luminosity, and the features in BL/IRAGNs on average extend to ~2 kpc from the nuclei. We further discuss a possible evolutionary sequence of AGNs and their host galaxies, where AGNs with strong emission lines or dust tori are present in star-forming galaxies. Later, young compact radio jets emerge, the host galaxies gradually quench, and the AGN hosts eventually evolve into globally quiescent systems with larger radio jets that prevent further gas cooling.

2512.11694

Dec 2025Astrophysics of Galaxies

GLIMPSE-D: An Exotic Balmer-Jump Object at z=6.20? Revisiting Photometric Selection and the Cosmic Abundance of Pop III Galaxies

We present deep JWST/NIRSpec G395M spectroscopy of GLIMPSE-16043, a promising $z\sim6$ Pop III candidate originally identified through NIRCam photometry as having weak [OIII]$λ\lambda4959,5007$ emission. Our follow-up reveals clear [OIII] emission, ruling out a genuine zero-metallicity nature. However, the combination of the measured line fluxes and photometry indicates that its spectral energy distribution requires an extraordinarily strong Balmer jump ($-1.66 \pm 0.47$ mag) and H$α$ equivalent width ($3750\pm1800$ Å), features that cannot be reproduced by current stellar+nebular or pure nebular photoionization models. The only models approaching the observations to almost within $1σ$ involve a hot ($T_{\rm eff}\!\simeq\!10^{4.7}$ K) single blackbody embedded in a low-$T_{\rm e}$ nebular environment, suggestive of scenarios such as a tidal-disruption event or a microquasar with strong disk winds. This cautions that photometric Pop~III selections are vulnerable to contamination when the rest-frame optical continuum is undetected. Motivated by this, we refine the photometric Pop III selection criteria to exclude the locus of extreme Balmer-jump objects. The revised criteria also recover the recently reported spectroscopic candidate AMORE6, demonstrating that the updated selection preserves sensitivity to genuine Pop III-like sources while removing key contaminants. Applying the refined criteria across legacy survey fields and five newly released CANUCS lensing cluster fields, we revisit the Pop III UV luminosity function and estimate the Pop III cosmic star-formation rate density to be $\approx[10^{-6}$--$10^{-4}]$~$M_{\odot}$~yr$^{-1}$~cMpc$^{-3}$ at $z\simeq6$--7, falling in the range of current theoretical predictions.

2512.11790

Dec 2025Astrophysics of Galaxies

The Effect of a Non-universal Extinction Curve on the Wesenheit Function and Cepheid Distances

The Wesenheit function is widely used to reduce the effects of interstellar reddening in distance measurements. Its construction, however, relies on the assumption of a universal extinction curve and on fixed values of the total-to-selective extinction ratio, Rv. Recent studies have shown that Rv varies significantly across the Milky Way and between different galaxies, raising concerns about systematic biases in Wesenheit magnitudes and period-Wesenheit relations. In this work, we discuss the impact of non-universal extinction on Wesenheit indices by combining the Rv-dependent extinction curve with a grid of stellar atmosphere models. We compute the integrated extinction in optical and near-infrared passbands, derive Rv-dependent R coefficients for multiple Wesenheit indices, and examine how changes in Rv propagate into Wesenheit magnitudes and Cepheid distances in our Galaxy. We find that the R coefficients in the Wesenheit functions vary strongly with Rv. For classical Cepheids in the Milky Way disk, variations of Rv within the typical observed range (2.6-3.6) can lead to substantial differences in the Wesenheit function, reaching +-0.7 mag from the mean for the Gaia-based Wesenheit index W_G and resulting in distance errors of almost 40%. Near-infrared Wesenheit indices are much less sensitive to Rv changes. Our results clearly show that accounting for variable Rv is essential when applying period-Wesenheit relations, particularly in the optical regime, or that near or mid infrared based distances should be used. While we present this effect for classical Cepheids, it applies to all pulsating stars for which period-Wesenheit relations are used to infer distances.

2512.11758

Dec 2025Astrophysics of Galaxies

Rapid sinking and efficient mergers of supermassive black holes in compact high-redshift galaxies

We present a cosmological zoom-in simulation targeting the high redshift compact progenitor phase of massive galaxies, with the most massive galaxy reaching a stellar mass of $M_{\star}=8.5\times 10^{10} \ M_{\odot}$ at $z=5$. The dynamics of supermassive black holes (SMBHs) is modelled from seeding down to their coalescence at sub-parsec scales due to gravitational wave (GW) emission by utilising a new version of the KETJU code, which combines regularised integration of sufficiently massive SMBHs with a dynamical friction subgrid model for lower-mass SMBHs. All nine massive galaxies included in this study go through a gas-dominated phase of early compaction in the redshift range of $z\sim 7-9$, starting at stellar masses of $M_\star\gtrsim 10^8\ \mathrm{M}_\odot$ and ending at a few times $M_{\star}\sim 10^9\ \mathrm{M}_\odot$. The sizes, masses and broad band fluxes of these compact systems are in general agreement with the population of systems observed with JWST known as `Little Red Dots'. In the compact phase, the stellar and SMBH masses grow rapidly, leading to a sharp decline in the central gas fractions. The outer regions, however, remain relatively gas-rich, leading to subsequent off-centre star formation and size growth. Due to the very high central stellar densities ($ρ_{\star}\gtrsim 10^{13}\,\mathrm{M_\odot/kpc^3}$), the SMBHs merge rapidly, typically just $\sim 4-35\ \mathrm{Myr}$ after the SMBH binaries have become bound. Combining KETJU with the phenomenological PhenomD model resolves the complete evolution of the GW emission from SMBH binaries through the Pulsar Timing Array frequency waveband up to the final few orbits that produce GWs observable with the future LISA mission.

2512.11665

Dec 2025Astrophysics of Galaxies

One-loop power spectrum corrections in interacting dark energy cosmologies

Interacting Dark Energy (IDE) models offer a promising avenue to explore possible exchanges of energy and momentum between dark matter and dark energy, providing a dynamical extension of the standard $Λ$CDM paradigm. Such interactions modify the growth of cosmic structures, imprinting distinctive signatures on the matter power spectrum that can be tested through large-scale structure (LSS) observations. In this work, we compute the one-loop corrections to the matter power spectrum in IDE models. We then reinterpret these results within the standard framework of the Effective Field Theory of Large-Scale Structure (EFTofLSS), which provides a consistent description of mildly non-linear scales and allows for reliable comparisons with observational data. We investigate two commonly studied forms of the coupling function, $Q$, namely $Q = ξ\mathcal{H} ρ_{\rm m}$ and $Q = ξ\mathcal{H} ρ_{\rm DE}$, and introduce a novel interaction term, $Q = Γ\, ρ_{\rm m} \, ρ_{\rm DE} \, θ_{\rm m}$, characterized by the non-linear coupling constant $Γ$, which links the interaction strength to the velocity divergence of dark matter. This coupling function is proposed to isolate the effects solely of the IDE model on mildly non-linear scales. Using Full-Shape (FS) measurements of the galaxy power spectrum from BOSS DR12, we constrain the interaction rate $Γ$, the cosmological parameters, and the bias parameters. We find $Γ= 0.0039 \pm 0.0082$, which is highly consistent with the $Λ$CDM model. This work opens the possibility of testing IDE models at mildly non-linear scales, potentially providing new insights for this class of models beyond the standard $Λ$CDM framework.

2512.11678

Dec 2025Cosmology and Nongalactic Astrophysics

A Critical Evaluation of the Physical Nature of the Little Red Dots

Little Red Dots (LRDs) are a newly identified class of active galactic nuclei (AGNs) uncovered by JWST deep surveys. Their enigmatic properties challenge the canonical AGN paradigm and have stimulated ideas on early massive black hole (BH) formation. In this review, we summarize how early BHs shape the characteristic features of LRDs, how their nuclear environments differ from those of normal AGNs, and how future observations can distinguish between competing scenarios. Our main conclusions are as follows: (1) LRDs show broad-line emission consistent with mass accretion onto BHs with $M_{\rm BH}\simeq 10^{6-7}~M_\odot$, suggesting that AGN activity is a plausible origin of their dominant red optical emission. (2) Stellar components can reproduce the continuum energetics through dusty star formation. However, the required stellar mass would be too large to remain consistent with other LRD properties. Therefore, a purely stellar origin is unlikely to be the dominant power source, although star formation may still contribute to the UV emission. (3) The coexistence of broad-line emission with Balmer absorption and break features on LRD spectra, neither of which can be explained by stellar populations, suggests that nuclear BHs are enshrouded by dense gas with a high covering fraction. (4) Gas-enshrouded AGNs can produce red optical spectra without requiring dust reddening through a combination of gas attenuation and thermal self-emission with an effective temperature of $T_{\rm eff}\simeq 5000~{\rm K}$, which also accounts for the flat infrared continuum. (5) From the spectral features and redshift evolution, LRDs are likely a transient phase in early BH growth, possibly the first accretion episodes of newborn BHs. (6) Testing models for LRD spectra and origins through time variability, ionizing sources, post-LRD objects, and low-redshift analogs is particularly promising.

2512.031301

Dec 2025Astrophysics of Galaxies

Tracing Quenching in Nearby Galaxies Through Inner Surface Mass Density and Cold Gas Content

The inner stellar mass surface density within 1 kpc, Sigma1, has emerged as a suitable proxy for bulge growth and galaxy quenching. However, the dependence of cold gas content on Sigma1 has not been thoroughly explored. In this paper, we examine the relationship between Sigma1, as well as the mass-relative parameter delSigma1, and the atomic (fHI) and molecular (fH2) cold gas fractions in massive, nearby galaxies. We utilize a sample of 341 galaxies with HI data and 201 galaxies with H2 data from the xGASS and xCOLDGASS surveys, spanning 0.02 <= z <= 0.05 and a stellar mass range of 10^10 <= M_*/M_odot <= 10^11.5. While we observe that a decline in both fHI and fH2 is associated with increasing Sigma1, we find that fH2 shows a sharper decline above a threshold value of delSigma1 = 0. In addition, the fraction of galaxies with AGN activity (Seyferts and LINERs) increases with delSigma1, with the greatest increase occurring between 0 <= delSigma1 <= 0.2 dex. We propose an evolutionary track in the plane of fH2-delSigma1, whereby molecular gas depletion at fixed mass coincides with a rise in AGN activity. Our results suggest that central bulge growth is more tightly coupled to the depletion of molecular gas rather than atomic gas, with AGN feedback possibly contributing to this process. Our work highlights the utility of Sigma1 and delSigma1 as tracers of quenching in massive galaxies.

2511.18227

Nov 2025Astrophysics of Galaxies

Euclid Quick Data Release (Q1): Hunting for luminous z > 6 galaxies in the Euclid Deep Fields -- forecasts and first bright detections

The evolution of the rest-frame ultraviolet luminosity function (UV LF) is a powerful probe of early star formation and stellar mass build-up. At z > 6, its bright end (MUV < -21) remains poorly constrained due to the small volumes of existing near-infrared (NIR) space-based surveys. The Euclid Deep Fields (EDFs) will cover 53 deg^2 with NIR imaging down to 26.5 AB, increasing area by a factor of 100 over previous space-based surveys. They thus offer an unprecedented opportunity to select bright z > 6 Lyman break galaxies (LBGs) and constrain the UV LF's bright end. With NIR coverage extending to 2um, Euclid can detect galaxies out to z = 13. We present forecasts for the number densities of z > 6 galaxies expected in the final EDF dataset. Using synthetic photometry from spectral energy distribution (SED) templates of z = 5--15 galaxies, z = 1--4 interlopers, and Milky Way MLT dwarfs, we explore optimal selection methods for high-z LBGs. A combination of S/N cuts with SED fitting (from optical to MIR) yields the highest-fidelity sample, recovering >76% of input z > 6 LBGs while keeping low-z contamination <10%. This excludes instrumental artefacts, which will affect early Euclid releases. Auxiliary data are critical: optical imaging from the Hyper Suprime-Cam and Vera C. Rubin Observatory distinguishes genuine Lyman breaks, while Spitzer/IRAC data help recover z > 10 sources. Based on empirical double power-law LF models, we expect >100,000 LBGs at z = 6-12 and >100 at z > 12 in the final Euclid release. In contrast, steeper Schechter models predict no z > 12 detections. We also present two ultra-luminous (MUV < -23.5) candidates from the EDF-N Q1 dataset. If their redshifts are confirmed, their magnitudes support a DPL LF model at z > 9, highlighting Euclid's power to constrain the UV LF's bright end and identify the most luminous early galaxies for follow-up.

2511.02926

Nov 2025Astrophysics of Galaxies

5,882 papers

Local simulations of common-envelope dynamical inspiral. Impact of rotation, accretion, and stratification

Common envelope evolution (CEE) is a crucial phase in binary stellar evolution. Current global three-dimensional simulations lack the resolution to capture the small-scale dynamics around the embedded companion, while local wind-tunnel simulations always approximate the companion's orbital motion as linear rather than as rotation around the center of mass. We investigate how rotation, accretion, and stratification influence small-scale gas dynamics, gravitational drag and lift forces, and the spin-up rate of the companion. We perform three-dimensional local hydrodynamic simulations of a $0.2\, M_\odot$ compact companion plunging into the envelope of a $2\, M_\odot$ red giant in a reference frame rotating at the companion's orbital angular velocity, using the Athena++ code. The presence of stratification generates an inward-directed force, partially opposed by a rotation-induced outward lift force. Both the resulting inward directed force and the drag force, strongly influenced by stratification, would affect the evolution of the binary separation. We propose revised semi-analytical prescriptions for both drag and lift forces. Without accretion and for sufficiently small gravitational softening radii, a quasi-hydrostatic bubble forms around the companion, while accretion prevents its formation and converts kinetic energy into heat that could contribute to the envelope ejection. Drag and lift forces are only marginally affected by accretion. The companion spin-up rate varies non-monotonically in time, first increasing and then decreasing as it plunges deeper into the envelope. These results motivate future magnetohydrodynamic simulations to investigate how accretion, rotation, and stratification affect magnetic amplification, and how magnetic fields, in turn, influence mass and angular momentum accretion rates, as well as the drag and lift force exerted on the companion.

2601.04188Jan 2026

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GRB 180728A and SN 2018fip: the nearest high-energy cosmological gamma-ray burst with an associated supernova

The long GRB 180728A, at a redshift of $z = 0.1171$, stands out due to its high isotropic energy of $E_{γ,iso} \sim 2.5 \times 10^{51}$ erg, in contrast with most events at redshift $z<0.2$. We analyze the properties of GRB 180728A's prompt emission, afterglow, and associated supernova SN 2018fip, comparing them with other GRB-SN events. This study employs a dense photometric and spectroscopic follow-up of the afterglow and the SN up to 80 days after the burst, supported by image subtraction to remove the presence of a nearby bright star, and modelling of both the afterglow and the supernova. GRB 180728A lies on the $E_{p,i}-E_{γ,iso}$ plane occupied by classical collapsar events, and the prompt emission is one of the most energetic at $z < 0.2$ after GRB 030329 and GRB 221009A. The afterglow of GRB 180728A is less luminous than that of most long GRBs, showing a shallow early phase that steepens around 5 hours (0.2 days). The GRB exploded in an irregular, low-mass, blue, star-forming galaxy, typical of low-z collapsar events. Because of the relatively faint afterglow, the light curve bump of SN 2018fip dominates the optical emission already after $\sim$3 days and is one of the best sampled to date. The strong suppression below $\sim$ 4000 angstrom and a largely featureless continuum in the early 6--9 days spectra favor aspherical two-component ejecta with a high-velocity collimated component ($> 20,000 km s^{-1}$), dominant early-on, and a more massive, low-velocity component, which dominates at much later epochs. Our findings indicate that asymmetries need to be considered in order to better understand GRB-SNe. In any case, SN 2018fip shares many characteristics with typical GRB-SNe. Its kinetic energy is below the common range of $10^{52}-10^{53}$ erg and does not correlate with the high energy of the GRB, highlighting the diversity of the GRB-SN energy budget partition.

2601.04179Jan 2026

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Radio Activity from the Rapidly Rotating T dwarf 2MASS 2228-4310

We present the detection of 2MASS J22282889-4310262 (2M2228), a T6/T6.5 brown dwarf, using the Karl G. Jansky Very Large Array (VLA) archival data observed at C band (4-8 GHz) over two observing epochs ($2\times96$ minutes). 2M2228 is detected at time and frequency averaged Stokes I and V peak flux densities of $67.3\pm4.9\ μ \rm{Jy beam}^{-1}$ and $14.4\pm3.0\ μ\text{Jy beam}^{-1}$ in the first epoch and $107.2\pm5.2\ μ\rm{Jy\ beam}^{-1}$ and $-20.7\pm1.2\ μ\text{Jy beam}^{-1}$ in the second epoch. This discovery constitutes the eighth and, notably, the most rapidly rotating T dwarf detected to date at radio wavelengths. Our observations reveal highly polarised bursts at fractional polarisation ratios $f_\text{c}>50$%. Using Stokes I light curves, we measure occurrence intervals of $\sim47$ and $\sim58$ minutes in the two observing epochs respectively with the first burst aligning within a half period timescale of the the previously measured mid infrared photometric period of $85.8\pm0.32$ minutes. We attribute the emission to the electron cyclotron maser emission (ECME) and constrain the magnetic field strength to $B\gtrsim1.4$ kG. We emphasise that the periods inferred are provisional considering the short observing durations. The combination of previously demonstrated atmospheric stability and newly detected radio emission in 2M2228 makes it a promising laboratory for testing magnetospheric currents-driven auroral models and for guiding future coordinated James Webb Space Telescope (JWST) and radio observations to probe the link between auroral activity and atmospheric dynamics in T-type brown dwarfs.

2601.04158Jan 2026

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A spectroscopically confirmed, strongly lensed, metal-poor Type II supernova at z = 5.13

Observing supernovae (SNe) in the early Universe (z > 3) provides a window into how both galaxies and individual stars have evolved over cosmic time, yet a detailed study of high-redshift stars and SNe has remained difficult due to their extreme distances and cosmological redshifting. To overcome the former, searches for gravitationally lensed sources allow for the discovery of magnified SNe that appear as multiple images - further providing the opportunity for efficient follow-up. Here we present the discovery of "SN Eos": a strongly lensed, multiply-imaged, SN II at a spectroscopic redshift of z = 5.133 +/- 0.001. SN Eos exploded in a Lyman-α emitting galaxy when the Universe was only ~1 billion years old, shortly after it reionized and became transparent to ultraviolet radiation. A year prior to our discovery in JWST data, archival HST imaging of SN Eos reveals rest-frame far ultraviolet (~1,300Å) emission, indicative of shock breakout or interaction with circumstellar material in the first few (rest-frame) days after explosion. The JWST spectroscopy of SN Eos, now the farthest spectroscopically confirmed SN ever discovered, shows that SN Eos's progenitor star likely formed in a metal-poor environment (<= 0.1 Z_{\odot}), providing the first direct evidence of massive star formation in the metal-poor, early Universe. SN Eos would not have been detectable without the extreme lensing magnification of the system, highlighting the potential of such discoveries to eventually place constraints on the faint end of the cosmic star-formation rate density in the very early Universe.

2601.04156Jan 2026

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Implications of Non-equatorial Relativistic Accretion Flows for Ultra-Fast Inflows in AGNs

Motivated by a number of X-ray observations of active galactic nuclei (AGNs) that exhibit a potential signature of ultra-fast inflows (UFIs), we consider in this work a scenario that UFIs can be physically identified as weakly-magnetized hydrodynamic accretion flows that is guided and channeled by poloidal magnetic field into low-to-mid latitude above the equatorial disk. In the context of general relativistic hydrodynamics (GRHD) under a weak-field limit in Kerr spacetime, we present a set of preliminary results by numerically calculating the physical property of GRHD flows (e.g. kinematics and density distribution) in an effort to simulate redshifted absorption line spectra. Our model demonstrates that such GRHD accretion off the equatorial plane (i.e. $v \gsim 0.1c$ where $c$ is the speed of light in the vicinity of AGN closer than $\sim 100$ \sw radii) can manifest itself as UFIs in the form of redshifted absorption signature assuming the observed characteristics such as column density of $N_H \sim 10^{23}$ cm$^{-2}$ and ionization parameter of $\log (ξ\rm{[erg~cm~s^{-1}])} \sim 3$ as also seen in recent multi-epoch {\it NuSTAR} observations among other data.

2601.04141Jan 2026

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Secular Excitation of Polar Neptune Orbits in Pure Disk-Planet Systems

The stellar spin-orbit angles of Neptune-sized planets present a primordial yet puzzling view of the planetary formation epoch. The striking dichotomy of aligned and perpendicular orbital configurations are suggestive of obliquity excitation through secular resonance -- a process where the precession of a hot Neptune becomes locked onto a forcing frequency, and is slowly guided into a perpendicular state. Previous models of resonant capture have involved the presence of companion perturbers to the star-planet-disk system, but in most cases, such companions are not confirmed to be present. In this work, we present a mechanism for exciting Neptunes to polar orbits in systems without giant perturbers, where photo-evaporation is the self-contained mechanism. Photo-evaporation opens a gap in the protoplanetary disk at ~1 au, and the inner disk continues to viscously accrete onto the host star, precessing quickly due to the perturbation of the outer disk. As the inner disk shrinks, it precesses more slowly, and encounters a resonance with the J2 precession of the Neptune, quickly exciting it to a polar configuration. While likely not applicable to more massive planets which trigger back-reactions onto the disk, this mechanism reproduces the obliquities of small planets in multiple respects.

2601.04140Jan 2026

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A census of star-formation and gas mass tracers in two lensed $z \sim 4$ dusty star-forming galaxies

We present new and archival Atacama Large Millimeter/submillimeter Array (ALMA) observations of two strongly lensed dusty star-forming galaxies (DSFGs) selected from the South Pole Telescope survey, SPT0418-47 $(z = 4.225)$ and SPT2147-50 $(z = 3.760)$. We study the [C II], CO(7-6), [C I](2-1), and, in SPT0418-47, $p$-H$_2$O emission, which along with the underlying continuum (rest-frame 160 $μ$m and 380 $μ$m) are routinely used as tracers of gas mass and/or star-formation rate (SFR). We perform a pixel-by-pixel analysis of both sources in the image plane to study the resolved Kennicutt-Schmidt relation, finding generally good agreement between the slopes of the SFR versus gas mass surface density using the different tracers. Using lens modeling methods, we find that the dust emission is more compact than the line emission in both sources, with CO(7-6) and [C I](2-1) similar in extent and [C II] the most extended, reminiscent of recent findings of extended [C II] spatial distributions in galaxies at similar cosmic epochs. We develop the [C I](2-1) / CO(7-6) flux density ratio as an observable proxy for gas depletion timescale ($τ_{\rm dep}$), which can be applied to large samples of DSFGs, in lieu of more detailed inferences of this timescale which require analysis of observations at multiple wavelengths. Furthermore, the extended [C II] emission in both sources, compared to the total continuum and line emission, suggests that [C II], used in recent years as a molecular gas mass and SFR tracer in high-$z$ galaxies, may not always be a suitable tracer of these physical quantities.

2601.04133Jan 2026

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Satellite-borne γ-ray astrophysics from coherent interactions in oriented crystals

High-density and high-Z crystals are a key element of most space-borne $γ$-ray telescopes operating at GeV energies (such as Fermi-LAT). The lattice structure is usually neglected in the development of a crystalline detector, although its effects on the energy deposit development should be taken into account, since the interactions of a high energy ($\sim$~GeV) photon or e$^\pm$ impinging along the axis of an oriented crystal are different than the ones observed in a fully isotropic medium. Specifically, if the angle between a photon (e$^\pm$) trajectory and the crystal axis is smaller than $\sim$ 0.1$^\circ$, a large enhancement of the pair production (bremsstrahlung) cross-section is observed. Consequently, a photon-induced shower inside an oriented crystal develops within a much more compact region than in an amorphous medium. Moreover, for photon energies above a few GeV and incidence angles up to several degrees, the pair-production cross-section exhibits a pronounced dependence on the angle between the crystal axis and the photon polarization vector. \\ In this work we show that these effects could be exploited to develop a novel class of light-weight pointing space-borne $γ$-ray telescopes, capable of achieving an improved sensitivity and resolution, thanks to a better shower containment in a smaller volume with respect to non-oriented crystalline detectors. We also show that an oriented tracker-converter system could be used to measure the polarization of a $γ$-ray source above few GeV, in a regime that remains unexplorable through any other detection technique. This novel detector concept could open new pathways in the study of the physics of extreme astrophysical environments and potentially improve the detector sensitivity for indirect Dark Matter searches in space.

2601.04129Jan 2026

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Characterizing the physical and chemical properties of the Class I protostellar system Oph-IRS 44. Binarity, infalling streamers, and accretion shocks

(Abridged) In the low-mass star formation process, theoretical models predict that material from the infalling envelope could be shocked as it encounters the outer regions of the disk. Nevertheless, only a few protostars show evidence of these shocks at the disk-envelope interface, and the main formation path of shocked-related species is still unclear. We present new ALMA observations of IRS 44, a Class I source that has previously been associated with accretion shocks, taken at high angular resolution (0.1"). We target multiple molecular transitions of CO, H2CO, and simple sulfur-bearing species. In continuum emission, the binary nature of IRS 44 is observed for the first time at sub-millimeter wavelengths. Infalling signatures are seen for the CO line and the emission peaks at the edges of the continuum emission around IRS 44 B, the same region where bright SO and SO2 emission is seen. Weak CS and H2CO emission is observed, while OCS, H2S, and H2CS transitions are not detected. IRS 44 B seems to be more embedded than IRS 44 A, indicating a non-coeval formation scenario or the rejuvenation of source B due to late infall. CO emission is tracing the outflow component at large scales, infalling envelope material at intermediate scales, and two infalling streamer candidates are identified at disk scales. Infalling streamers might produce accretion shocks when they encounter the outer regions of the infalling-rotating envelope. These shocks heat the dust and release S-bearing species as well as promoting a lukewarm chemistry in the gas phase. With the majority of carbon locked in CO, there is little free C available to form CS and H2CS in the gas, leaving an oxygen-rich environment. The high column densities of SO and SO2 might be a consequence of two processes: direct thermal desorption from dust grains and gas-phase formation due to the availability of O and S.

2601.04108Jan 2026

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Modeling the Effect of C/O Ratio on Complex Carbon Chemistry in Cold Molecular Clouds

Elemental abundances, which are often depleted with respect to the solar values, are important input parameters for kinetic models of interstellar chemistry. In particular, the amount of carbon relative to oxygen is known to have a strong effect on modeled abundances of many species. While previous studies have focused on comparison of modeled and observed abundances to constrain the C/O ratio, the effects of this parameter on the underlying chemistry have not been well-studied. We investigated the role of the C/O ratio on dark cloud chemistry using the NAUTILUS code and machine learning techniques for molecular representation. We find that modeled abundances are quite sensitive to the C/O ratio, especially for carbon-rich species such as carbon chains and polycyclic aromatic hydrocarbons (PAHs). CO and simple ice-phase species are found to be major carbon reservoirs under both oxygen-poor and oxygen-rich conditions. The appearance of C3H4 isomers as significant carbon reservoirs, even under oxygen-rich conditions, indicates the efficiency of gas-phase C3 formation followed by adsorption and grain-surface hydrogenation. Our model is not able to reproduce the observed, gas-phase C/H ratio of TMC-1 CP at the time of best fit with any C/O ratio between 0.1 and 3, suggesting that the modeled freeze-out of carbon-bearing molecules may be too rapid. Future investigations are needed to understand the reactivity of major carbon reservoirs and their conversion to complex organic molecules.

2601.04103Jan 2026

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Dissecting the dust distribution and polarization around two B213 young stellar objects with ALMA

The earliest stages of disk formation and dust evolution during the protostellar phase remain poorly constrained. Millimeter dust emission and its polarization provide key insights into the physical processes and material distribution at the envelope-disk interface. We present ALMA polarimetric observations at 1.4 mm and 3 mm of two young stellar objects in Taurus, IRAS 04166+2706 (K04166) and IRAS 04169+2702 (K04169), probing scales from 25 au to 3000 au. We model the Stokes I emission to separate disk and envelope contributions and analyze the polarization properties to identify the dominant polarization mechanisms. K04166 shows extended Stokes I and polarized emission tracing a tentative hourglass magnetic field morphology in its envelope. In the inner envelope and disk (< 100 au), the properties of the polarized emission change, suggesting either a toroidal magnetic field or the presence of large grains. In contrast, K04169 exhibits compact Stokes I and polarized emission consistent with self-scattering from the disk. Both disks are extremely compact, but only K04166 retains a substantial envelope. Our multiscale ALMA polarimetric observations reveal a transition from magnetically aligned grains in envelopes to self-scattering in disks within the transition region of 20-50 au. These results provide important clues on dust grain growth and magnetic field morphology at the disk-envelope scales. Despite being embedded in the same filament, the two sources display striking differences, indicating that K04166 is a young embedded object with a substantial envelope threaded by relatively organized magnetic fields. Meanwhile, K04169 is more evolved, likely to be a young T-Tauri star. However, in both disks, the presence of large grains already suggests a scenario of early dust evolution in disks of the Class 0 stage.

2601.04091Jan 2026

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Spiral galaxies with flat radial abundance gradients at large radii

We consider the oxygen abundance distributions for a sample of massive spiral galaxies from the MaNGA survey in which the radial abundance gradient flattens to a constant value outside of the outer break radius, Rb,outer. The outer break radius can be considered as a dividing radius between the galaxy and the circumgalactic medium (CGM). The values of the Rb,outer range from 0.8R_{25} to 1.45R_{25}, where R_{25} is the optical radius of the galaxy. The oxygen abundances in the CGM range from 12+log(O/H) ~ 8.0 to ~ 8.5. The O/H distribution in each of our galaxies also shows the inner break in the radial abundance profile at the radius Rb,inner. The metallicity gradient in the outer part of the galaxy is steeper than in the inner part. The behaviour of the radial abundance distributions in these galaxies can be explained by assuming an interaction with (capture of the gas from) a small companion and adopting the model for the chemical evolution of galaxies with a radial gas flow. The interaction with a companion results in the mixing of gas and a flat metallicity gradient in the CGM. The capture of the gas from a companion increases the radial gas inflow rate and changes the slope of the radial abundance gradient in the outer part of the galaxy.

2601.04059Jan 2026

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Cosmological constraints on viable $f(R)$ models using weak lensing

The accelerated expansion of the Universe remains one of the central open problems in modern cosmology. While the $Λ$CDM model successfully describes a wide range of observations, the physical nature of dark energy is still unknown, motivating the study of alternative theories of gravity. Among these, $f(R)$ models provide a well-established extension of General Relativity, capable of reproducing a $Λ$CDM-like background evolution without introducing an explicit dark energy component. However, they can induce deviations in the growth of cosmic structures, making them testable through observables sensitive to cosmological perturbations. In this work, we use weak gravitational lensing to constrain several viable $f(R)$ gravity models. We analyze their impact on the matter power spectrum, as well as on the convergence and cosmic shear power spectra. Our analysis is carried out within a Bayesian framework using the \textit{Cobaya} code and its modified gravity extension, \textit{MGCobaya}, which enables consistent theoretical predictions and their comparison with current weak lensing and CMB lensing data. We find that standard cosmological parameters remain consistent with the $Λ$CDM scenario for all models considered, as expected from their background degeneracy. Nevertheless, we obtain non-trivial and model-dependent constraints on the characteristic parameters of several $f(R)$ theories.

2601.04048Jan 2026

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Two-source terrestrial planet formation with a sweeping secular resonance

The models that most successfully reproduce the orbital architecture of the Solar System terrestrial planets start from a narrow annulus of material that grows into embryos and then planets. However, it is not clear how this ring model can be made consistent with the chemical structure of the inner Solar System, which shows a reduced-to-oxidized gradient from Mercury to Mars and a parallel gradient in the asteroid belt. We propose that there were two primary reservoirs in the early inner Solar System: a narrow, refractory enriched ring inside of 1 au, and a less massive, extended planetesimal disk outside of 1 au with oxidation states ranging from enstatite chondrites to ordinary chondrites. We show through a suite of N-body simulations that an inwardly sweeping secular resonance, caused by aerodynamic drag and perturbations from a mean-motion resonant Jupiter and Saturn, gathers the outer planetesimal disk into a narrow ring that migrates radially, forms Mars, and contributes oxidized material to proto-Earth. Remaining unaccreted planetesimals can be implanted into the asteroid belt as the parent bodies of aubrites and non-carbonaceous iron meteorites, while the most reduced material is not implanted and thus unsampled in the meteorite collection. This model explains the oxidation and isotopic gradients within the inner Solar System within the context of a low-viscosity, magnetic wind-driven disk.

2601.04032Jan 2026

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HI-bearing dark galaxies predictions from constrained Local Group simulations: how many and where to find them

Dark galaxies are small, DM-dominated halos whose gas remains in hydrostatic and thermal equilibrium and has never formed stars. They are of particular interest because they represent a strong prediction of the LCDM model. As of today, only a handful of candidates have been observed, the most intriguing of which being Cloud-9. Using several state-of-the-art hydrodynamical simulations, we aim to predict the abundance of dark galaxies expected within our Local Group (LG), characterise their properties and provide guidance for their potential detection. We analyse LG simulations with constrained initial conditions, run with different codes, implementing different baryonic physics, feedback prescriptions, and employing two distinct values of SF density threshold, n_th=0.13 and 10 cm^-3, to select samples of dark and bright galaxies harboured in haloes of similar mass. We demonstrate that dark galaxies exist in such simulations, though their number is larger in simulations that use a higher, more realistic n_th. These galaxies, whose gas remains diffuse and never forms stars, predominantly inhabit less-concentrated, higher-spin DM halos than their luminous counterparts. Dark galaxies are typically found in low-density regions at the outskirts of the LG, and their evolution across z indicate that both the DM and gas densities in their surroundings were consistently lower than those found around bright galaxies, making them less susceptible to interactions, mergers, or gas inflows. We estimate that up to 8 dark galaxies should be detectable in HI emission within 2.5 Mpc of the LG, with the FAST telescope, accounting for its sky coverage and minimum M_HI and N_HI. Current hydrodynamical simulations of galaxies, combined with upcoming HI surveys, will offer a direct and powerful test of LCDM through their ability to predict and measure properties of dark galaxies within and beyond the LG.

2601.04024Jan 2026

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Stellar-mass black holes on the millimetre fundamental plane of black hole accretion

Recent work revealed the existence of a galaxy "millimetre fundamental plane of black hole accretion", a tight correlation between nuclear $1$mm luminosity, intrinsic $2$ - $10$keV X-ray luminosity and supermassive black hole mass, originally discovered for nearby low- and high-luminosity active galactic nuclei. Here we use mm and X-ray data of $5$ X-ray binaries (XRBs) to demonstrate that these stellar-mass black holes also lie on the mm fundamental plane, as they do at radio wavelengths. One source for which we have multi-epoch observations shows evidence of deviations from the plane after a state change, suggesting that the plane only applies to XRBs in the hard state, as is true again at radio wavelengths. We show that both advection-dominated accretion flows and compact jet models predict the existence of the plane across the entire range of black hole masses, although these models vary in their ability to accurately predict the XRB black hole masses.

2601.04007Jan 2026

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Investigation of the dynamics and origin of the NEA pair 2021 PH27 and 2025 GN1

We analyse the association between the NEAs 2021 PH27 and 2025 GN1, which share similar heliocentric Keplerian elements and the same taxonomic classification. First, we confirm the spectral similarity by getting independent colours measurements of 2025 GN1 and confirming that they are both X-type. From numerical integration of the orbits up to 100 kyr in the past, taking into account relativistic corrections, we found that the two asteroids experienced five similar flybys with Venus, but none of them were closer than the Roche limit. The perihelion distance also reached values between 0.1 and 0.08 au about 17/21 kyr and 45/48 kyr ago, but still well outside the Roche limit with the Sun. So, the origin of the pair by tidal disruption of a progenitor rubble-pile asteroid appears unlikely. On the other hand, we found periods lasting several thousand years where the perihelion was below 0.1 au, and this can lead to thermal fracturing of the surface. We found that the rotation period of the primary and the mass ratio secondary/primary make the pair indistinguishable from the binary systems known among the NEAs, and the YORP effect can double the rotation period of 2021 PH27 in $150 \pm 50$ kyr. So it is plausible that the pair was formed by the rotational disintegration of a rubble-pile asteroid due to anisotropic gas emission or the YORP effect, which formed a binary system that later dissolved due to the internal dynamics of the pair. We are unable to give a value for the separation age; we can only say that it occurred more than 10.5 kyr ago and may have occurred between 17/21 kyr ago during the last and longer phase of lower perihelion distance. In this scenario, little meteoroids released in space due to the fragmentation event are still near the pair's orbit and can generate a meteor shower in Venus' atmosphere.

2601.03990Jan 2026

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The Gaia All-Sky Stellar Parameters Service (GASPS)

Temperature and luminosity are the two key diagnostics of a star, yet these cannot come directly from survey data, but must be imputed by comparing those data to models. SED fitting offers a high-precision method to obtain both parameters for stars where both their distance and extinction are well known. The recent publication of many all-sky or large-area surveys coincides the publication of parallaxes and 3D extinction cubes from the Gaia satellite, making it possible to perform SED fitting of truly large ($>10^8$) numbers of Galactic stars for the first time. The analysis of this data requires a high level of automation. Here, we describe the ongoing Gaia All-Sky Stellar Parameters Service (GASPS): the fitting of 240 million SEDs from Gaia DR3 and the extraction of temperatures and luminosities for the corresponding stars using the PySSED code. We demonstrate the quality of the initial results, and the promise that these data show, from wavelength-specific information such as the ultraviolet and infrared excess of each star, to stellar classification, to expansion of the project beyond our own Galaxy, and mineralogical mapping of the Milky Way's interstellar medium.

2601.03978Jan 2026

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2601.03966

Can Dynamic Spectrum Sharing Protect Passive Radio Sciences?

Dynamic Spectrum Sharing (DSS) is increasingly promoted as a key element of modern spectrum policy, driven by the rising demand from commercial wireless systems and advances in spectrum access technologies. Passive radio sciences, including radio astronomy, Earth remote sensing, and meteorology, operate under fundamentally different constraints. They rely on exceptionally low interference spectrum and are highly vulnerable to even brief radio frequency interference. We examine whether DSS can benefit passive services or whether it introduces new failure modes and enforcement challenges. We propose just-in-time quiet zones (JITQZ) as a mechanism for protecting high value observations and assess hybrid frameworks that preserve static protection for core passive bands while allowing constrained dynamic access in adjacent frequencies. We analyze the roles of propagation uncertainty, electromagnetic compatibility constraints, and limited spectrum awareness. Using a game theoretic framework, we show why non-cooperative sharing fails, identify conditions for sustained cooperation, and examine incentive mechanisms including pseudonymetry-enabled attribution that promote compliance. We conclude that DSS can support passive radio sciences only as a high-reliability, safety-critical system. Static allocations remain essential, and dynamic access is viable only with conservative safeguards and enforceable accountability.

2601.03966Jan 2026

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Formation of multi-planetary systems via pebble accretion in externally photoevaporating discs in stellar clusters

In this paper, we investigate how external photo-evaporation influences the formation, dynamical evolution and the resultant planetary architecture of multi-planet systems born in stellar clusters. We use a model of N-body simulations of multiple planet formation via pebble accretion coupled with a 1-D viscous disc subject to external photo-evaporation. We found that external photo-evaporation reduces the planet growth by reducing the pebble mass reservoir in discs containing multiple planetary embryos across a wide range of disc masses, and is particularly effective in suppressing planet growth in less initially massive discs (< 0.1 M$_{\odot}$). However, in more initially massive ($\geq$ 0.1 M$_{\oplus}$) discs planets lost due to planet-planet interactions dominate the outcome for final resultant total planet mass, masking the effects of external photo-evaporation in curbing the planet mass growth. In terms of the final resulting planetary architectures, the signature of external photo-evaporation is visible in less massive (< 0.1 M$_{\odot}$) discs, with fewer numbers and lower masses of planets surviving in discs irradiated with stronger external FUV radiation. External photo-evaporation also leaves a signature for the wide orbit (> 10 au) terrestrial planets (0.1 - 1 M$_{\oplus}$), with fewer planets populating this region for stronger FUV field. Finally, the 1st-order resonant pairs fraction decreases with stronger FUV radiation, although the resonant pairs occur rarely regardless of the FUV radiation environment, due to the small number of planets that survive gravitational encounters.

2601.03963Jan 2026

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