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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 22 July

Cosmology and Nongalactic Astrophysics

The correlation between voids identified in 3D large-scale-structure and 2D weak-lensing maps

Y.Fang, C. T. Davies, N. Hamaus et al. (+1 more)

We investigate the correspondence between voids identified in the 3D halo distribution and those detected in WL convergence maps. We used 108 realizations of the full-sky lensing simulations, populated with a source galaxy redshift distribution consistent with the Dark Energy Survey Year 3 sample. Catalogs of 3D halo voids and WL voids were constructed using the VIDE and tunnel algorithms, respectively. The spatial association between the two populations was quantified by measuring the angular excess number density of halo voids around WL void centers. We detected a statistically significant (S/N >= 25) positive correlation between WL voids and low-redshift halo voids (0 < z_hv < 0.5) at small angular separations, indicating that WL voids trace genuine underdensities in the large-scale matter distribution. The correlation amplitude closely depends on the WL void selection scheme and decreases when stringent peak-amplitude thresholds are applied, thereby reducing the number of detected WL voids and broadening their effective sizes. The signal also displays a strong redshift dependence: halo voids at higher redshift exhibit weaker correlations because of the declining efficiency of the WL kernel, while WL voids identified from higher-redshift source bins produce stronger correlations due to the increased contribution from line-of-sight structures. We additionally examined the impact of halo-void morphology and found that rounder voids with a weaker alignment along the line of sight display marginally stronger associations with WL voids. Our results provide new insights into the contribution of 3D structure to WL-selected underdensities and offer guidance for future observational analyses seeking to interpret WL voids as tracers of the matter field.
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All authors Y.Fang, C. T. Davies, N. Hamaus, J. J. Mohr

Cosmology and Nongalactic Astrophysics

What could an emerging Big Bang Nucleosynthesis discrepancy be hinting at?

Vivian Poulin, Julien Froustey, Cyril Pitrou et al. (+1 more)

The latest measurement of the primordial deuterium abundance is in $\sim 2\sigma$ tension with several state-of-the-art predictions of standard Big Bang nucleosynthesis (BBN), when using the baryon density inferred from the $\Lambda$CDM model fit to cosmic microwave background (CMB) data. This tension increases to $\sim 3\sigma$ for models attempting to solve the Hubble tension, such as early dark energy (EDE), which generally predict a larger baryon density than in $\Lambda$CDM. We test whether this discrepancy could be pointing to a non-standard expansion history during BBN. We compute light-element abundances with PRIMAT and compare $\Lambda$CDM, a $\Delta N_{\rm eff}$ extension, and a very early dark energy (vEDE) component. For vEDE, we sample $\Delta H/H$, the fractional increase of the expansion rate while deuterium burning is freezing out and helium-4 fusion is mostly over. The Bayesian analysis using BBN plus the CMB baryon-density constraint in the EDE cosmology gives $\Delta H/H = 0.087^{+0.036}_{-0.037}$ during the deuterium burning epoch, i.e. at a temperature $T_{\rm D}\simeq0.03\,{\rm MeV}$, and no residual tension. The vEDE component preserves the observed deuterium abundance at the larger CMB baryon density while only mildly affecting helium-4. By contrast, extra radiation raises the helium-4 abundance too efficiently and does not reconcile the baryon density determinations. Together with inflation, dark energy, and EDE, our results hint at the presence of another light scalar field in cosmology.
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All authors Vivian Poulin, Julien Froustey, Cyril Pitrou, Tristan L. Smith

Astrophysics of Galaxies

A Naked Dwarf: Molecular Gas in the Completely Stripped HI Tail of VCC 1249

Bumhyun Lee, Aeree Chung, Paolo Serra et al. (+12 more)

We present the first observational hints of the severe removal of both molecular and HI gas from the dwarf galaxy VCC 1249. This extreme stripping event is thought to be driven by the combined effects of tidal interaction and ram pressure. Using deep CO (2$-$1) observations from the James Clerk Maxwell Telescope (JCMT), we obtained marginal CO detections in three regions within the stripped HI tail, with molecular masses of $\sim$10$^{5}$ to 10$^{6}$$M_{\odot}$, comparable to typical masses of giant molecular clouds. In contrast, we did not find CO emission within the stellar disk of VCC 1249. This indicates the severe removal of cold gas, which likely caused the sudden cessation of star formation in the galaxy. This identifies VCC 1249 as a unique laboratory for witnessing the rapid, environmentally-driven quenching of a dwarf galaxy. Our findings provide a critical observational link between gas removal mechanisms and the dramatic phase transition of cluster dwarfs from star-forming to quiescent systems.
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All authors Bumhyun Lee, Aeree Chung, Paolo Serra, Nikki Zabel, Sungsoon Lim, Hyein Yoon, A. Boselli, Matteo Fossati, Yongjung Kim, Tomonari Michiyama, Juan Molina, Kana Morokuma-Matsui, Jaehyun Lee, Jeong Hwan Lee, Se-Heon Oh

High Energy Astrophysical Phenomena

Time-evolving Diagnostic of the Ionized Absorbers in NGC 4051. II. High-throughput Time-resolved Spectroscopy

Alfredo Luminari, Fabrizio Nicastro, Roberto Serafinelli et al. (+5 more)

Active Galactic Nuclei (AGNs) are one of the most powerful sources in the Universe. The accretion-liberated energy can strongly impact the surrounding environment, up to the host galaxy and beyond. Notwithstanding their ubiquitous presence, nuclear outflows are poorly characterised, mainly due to the degeneracy between their number density $n_e$ and radial location $r$, intrinsic in the photoionisation equilibrium models which are usually employed to fit the observations. This degeneracy prevents a self-consistent determination of the gas energetics and, therefore, of the efficiency in transporting the AGN energy outwards. We analyse a joint XMM-Newton and NuSTAR observation of the bright, highly-variable AGN NGC 4051. The high flux allows to perform time-resolved spectroscopy and, thus, to study the evolution of its three main ionised absorbers. Since the timescale of the gas ionisation variability depends on its number density, constraining it allows to break the density-distance degeneracy. We employ the Time-Evolving PhotoIonisation Device (TEPID) to model the temporal evolution of the outflows. We split the observation in 37 time-resolved spectra, each few kiloseconds long (total duration 160 ksec), and we fit them jointly with the time-resolved ionised spectra. We fully constrain $n_e=10^7 cm^{-3}$ and $r=10^4$ gravitational radii for the absorber with the highest opacity and intermediate ionisation. This distance is the same of the optical and UV Broad Line Region and of the soft X-ray emission lines. The fastest and most ionised absorber is at $r<600 r_G$, cospatial with the broad component of the Fe K$\alpha$ line. The slowest and least ionised absorber is at $r \geq 3.8 \cdot 10^5 r_G$, the same distance of the cold torus and the narrow Fe K$\alpha$. The total energy outflow rate is below $10^{-4} L_{bol}$, ruling out a meaningful mechanical impact on the host galaxy.
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All authors Alfredo Luminari, Fabrizio Nicastro, Roberto Serafinelli, Riccardo Middei, Yair Krongold, Elias Kammoun, Luigi Piro, Francesca Diaferia

High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Dark Matter Weather: Probing Sub-GeV Interactions with Earth-Shielding Modulation

Tetiana Kozynets, Rebecca Leane and Juri Smirnov

Daily modulation from Earth shielding provides a powerful search handle for sub-GeV dark matter (DM) in low-threshold experiments. We use this effect as a probe of interaction structure in scenarios where DM couples to both electrons and nuclei. Nuclear scattering in the Earth alters the incident DM flux, while electron scattering produces the observable ionization signal, so the total rate and modulation pattern encode different aspects of the underlying interactions. We develop this two-interaction framework for argon and xenon targets and introduce a new statistical analysis that tests the modulation shape, including the location-dependent exposure of underground detectors to different Earth-crossing trajectories, alone and in combination with the ionization spectrum. We demonstrate the method for liquid-noble detectors at underground sites SURF (USA), LNGS (Italy), and SUPL (Australia), and apply it to DarkSide-50 data as a concrete case study. Our results show that Earth-scattering modulation can help disentangle electron and nuclear DM interactions and provide a validation handle for low-threshold liquid-noble searches.
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High Energy Astrophysical Phenomena

Polarization of impulsive relativistic jets propagating in a stratified medium

Gal Birenbaum, Paz Beniamini and Jonathan Granot

Gamma-ray bursts (GRBs) and at least some tidal disruption events (TDEs) are highly energetic transients involving impulsive relativistic jets. As these jets propagate into their surrounding media, they drive a relativistic forward shock into it, which radiates multi-wavelength polarized synchrotron emission, known as an afterglow. Analyzing the afterglow light curve along with its polarization curve can shed light on the geometrical properties of the GRB or TDE system such as the magnetic field structure behind the shock, the jet angular structure and even distinguish between proposed scenarios of delayed radio emission seen in some TDEs. While most afterglow polarization measurements are for long GRBs, whose massive star progenitor winds are expected to form a stratified external medium, the polarization from such environments is largely unexplored. Similarly, stratified media surround jetted TDEs. In this work we explore how shock propagation into a stratified medium affects the observed afterglow polarization from impulsive relativistic jets. We find that for both top hat and structured jets, in most cases the polarization levels are reduced and its temporal signature evolves on longer time scales compared to a uniform external medium. The polarization peaks at times close to a geometrical break in the light curve, indicating measurements during this time probe the maximal levels of polarization possible for the system. In addition, observationally capturing the polarization evolution time scales can assist in constraining our viewing angle and the external medium stratification. Such composite models, that account for more realistic systems that are motivated by light curve fittings, will allow us to complement afterglow light curves better and promote joint modeling of these observables.
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Solar and Stellar Astrophysics

A dust-free hierarchically nested supermassive-star model for James Webb Space Telescope Little Red Dots

Pau Amaro Seoane

Observations by the James Webb Space Telescope reveal a population of high-redshift objects, the little red dots. These sources exhibit optical reddening alongside blue ultraviolet continua, host broad Balmer lines indicative of active black holes, and lack detectable x-ray emission. Their cosmic abundance at early epochs exceeds standard Eddington-limited growth timescales. Prevailing models invoke specific dust geometries to reconcile these traits. We propose a dust-free physical framework. We evaluate the concept that the dust-poor subset of little red dots represents the observational manifestation of hierarchically nested supermassive stars. A primary radiation-dominated envelope traps a nuclear star cluster. Plunging stars drive a magnetic dynamo that inflates the envelope. This produces the red optical continuum. Unobscured infalling stars yield the blue ultraviolet excess. Trapped stellar debris sediments to form a high-density secondary core within this Compton-thick host. This nested topology thermalizes x-rays and powers the broad hydrogen $\alpha$ features. The central seed accretes at the global radiation limit of the host envelope. This kinetic bypass shortens the assembly timescale from hundreds of millions of years to tens of millions of years.
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High Energy Astrophysical Phenomena

The Origin of the Magnetic Flux Driving TDE Jets

Nimrod Tripto, Julian Krolik and Tsvi Piran

Tidal Disruption Events (TDEs) occur when a star approaches a black hole closely enough to be torn apart by tidal forces, after which the stellar debris begins to orbit the black hole. Over the past decade, hundreds of TDEs have been identified, with many more expected from upcoming surveys. A small subset of these events launch transient, highly luminous relativistic jets (10^47-10^48 erg/s isotropic-equivalent). These are generally interpreted in terms of the Blandford–Znajek mechanism, implying the presence of substantial magnetic flux near the black hole horizon. The question arises: What is the origin of this flux? In this paper, we investigate three candidate sources: stellar magnetic fields, magnetic flux from large radii around the black hole (the Lasso mechanism), and magnetic flux stored in the inner portion of a pre-existing accretion disk. We find that: observed stellar magnetic fields are insufficient to power these jets; the Lasso mechanism requires shallow radial magnetic field profiles and a mechanism to trap the magnetic flux brought by the debris in the vicinity of the black hole; pre-existing magnetic flux near the black hole in an accretion disk is the most plausible source.
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Cosmology and Nongalactic Astrophysics

Gravitational Lensing Predictions from Wave Simulations of Fuzzy Dark Matter

Jiajun Zhou, Zhengxiang Li, Amruth Alfred et al. (+3 more)

In the cold dark matter paradigm, ultra-light particles are emerging as strong contenders to conventional massive particles. A unique prediction of dark matter comprising such ultra-light particles, known as fuzzy dark matter (FDM), is the presence of strong density modulations throughout galactic halos due to wave interference, which – when approximated by a Gaussian random field (GRF) – have been proposed to account for the inability to reproduce the observed positions (when measured at sufficient precisions) and flux ratios of multiply-lensed images of quasars. Here, we predict for the first time the properties of gravitationally lensed images generated from 3-D density fields obtained by wave simulations that directly evolve the Schrödinger–Poisson equations. Using a novel framework to project these evolved density fields along various axes of the 3-D halo, we obtain the distribution of perturbations to the positions of lensed images. As an exacting test, we find that particles of mass $10^{-22}$ eV can reproduce the positions of the quadruply-lensed radio jets in system HS 0810+2554 to a level better than that of either the GRF approximation or, to a greater extent, an NFW best-fit solution, both of which rely on accurately capturing the global 3-D density field of dark matter halos. Our work highlights the importance of wave simulations for making accurate FDM lensing predictions and the potential for high-resolution observations of lensed systems to serve as a direct probe of the nature of dark matter.
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All authors Jiajun Zhou, Zhengxiang Li, Amruth Alfred, Ran Gao, Jeremy Lim, Zong-Hong Zhu

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th

New Type IIB Poly-instanton Effects and Axion Quintessence

Luca Caraffi, Federico Carta and Michele Cicoli

Previous studies of poly-instantons in type IIB Calabi-Yau orientifolds found that these effects arise when Euclidean D3-branes wrap rigid cycles with a Wilson line. In this work, we extend this result through a general analysis of instanton zero modes, revealing the existence of new poly-instanton effects for rigid cycles with a deformation, provided that O3-planes are localised on the worldvolume of the Euclidean D3-brane. We provide concrete Calabi-Yau examples with explicit orientifold involution and brane setup. One of them is particularly well suited for realising axion hilltop quintessence. In particular, the double exponential suppression of poly-instanton effects allows to reproduce the observed vacuum energy for natural values of the underlying parameters.
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Astrophysics of Galaxies

Two stellar clocks, one history: a Gaia colour-magnitude-diagram reconstruction of the solar-neighbourhood star-formation history tested against white dwarfs

Michele Cignoni, Pier Giorgio Prada Moroni, Martina Gabbanini et al. (+2 more)

The solar-neighbourhood star-formation history (SFH) can be constrained from the colour-magnitude diagram (CMD) of non-degenerate stars and tested independently with the white-dwarf luminosity function (WDLF). These two tracers sample complementary evolutionary phases and provide a consistency check on both the recovered SFH and the adopted WD cooling models. We reconstruct the local SFH from the Gaia DR3 CMD and test whether the resulting history reproduces the observed 40 pc WDLF. We fit non-degenerate stars in a cylinder of radius 200 pc and vertical extent $\pm40$ pc using the SFERA synthetic-population code. The fit is performed with the PISA and PARSEC stellar libraries. Each CMD-derived solution is then used to generate a synthetic WD population for comparison with the 40 pc WDLF, adopting the same initial-final mass relation and four WD cooling model sets: BaSTI, MIST, La Plata, and Montreal. The two CMD-based solutions agree on the main features of the local SFH: low activity at the oldest ages, an early episode around 9-11 Gyr ago, reduced activity between about 4 and 9 Gyr, and enhanced star formation over the last few Gyr. The predicted WDLFs reproduce the bright and intermediate part of the observed distribution for all cooling grids, but differ substantially around the WDLF maximum and along the faint tail. MIST and BaSTI shift too much weight to magnitudes fainter than the observed maximum, whereas La Plata gives the closest match to the faint tail but leaves larger residuals around the maximum. Montreal provides the best overall compromise. On this cooling scale, progressively removing the oldest synthetic WDs shows that the faint tail disfavours a substantial contribution from WDs with total ages older than about 11 Gyr.
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All authors Michele Cignoni, Pier Giorgio Prada Moroni, Martina Gabbanini, Scilla Degl'Innocenti, Antonio Tinarelli

Solar and Stellar Astrophysics

A Framework for Linking Pre- and Post-Common Envelope Binary Properties with Star Clusters: The First Demonstration with a Massive White Dwarf+M Dwarf Binary in Alessi 12

Steffani M. Grondin, Maria R. Drout, Jason Nordhaus et al. (+12 more)

Common envelope (CE) evolution is a critical phase in the lives of binary stars, producing close binaries that are progenitors of type Ia supernovae and gravitational wave sources. Despite its importance, CE evolution remains poorly understood, largely due to the scarcity of systems with constrained pre- and post-CE properties. Here, we present a star cluster-based framework for reconstructing the evolutionary histories of white dwarf+main-sequence (WD+MS) post-CE binaries, where cluster membership can provide an independent age constraint and/or rule out a merger origin for the WD. We demonstrate this method with Alessi12-PCE, the first such binary in an open cluster with precisely determined pre- and post-CE properties. We classify the companion as an M4V and measure a WD mass of $1.06 \pm 0.02 M_{\odot}$, making it the most massive WD+MS binary associated with a cluster. A 6.99-hour periodicity detected in a light curve is confirmed as the binary orbital period via radial velocity monitoring. Combined with the WD mass, WD cooling age, and Alessi 12 cluster age, stellar evolution models imply a $5.40 \pm 0.10 M_{\odot}$ WD progenitor that entered a CE on the asymptotic giant branch (AGB). CE evolution models where convection is the dominant physical mechanism that sets $\alpha_{\text{CE}}$ reproduce the observed orbital separation in exactly two scenarios: either a mid-AGB interaction with $\alpha_{\text{CE}}\approx0.99$, or a late-AGB interaction with $\alpha_{\text{CE}}\approx0.05$. Applicable to other post-CE binaries in star clusters, our new framework enables empirical constraints on CE physics inaccessible from field binaries alone.
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All authors Steffani M. Grondin, Maria R. Drout, Jason Nordhaus, Philip S. Muirhead, Bailey Filer, Alexander Laroche, Jeremy J. Webb, Floor S. Broekgaarden, Ryan Chornock, Kyle Kremer, Natalie LeBaron, Raffaella Margutti, Nikki Noughani, Huei Sears, Pier-Emmanuel Tremblay

Instrumentation and Methods for Astrophysics

Structural, thermal and optical tolerance analysis of SHARP, a near infrared spectrograph for next generation telescope

H. Mahmoodzadeh, P. Saracco, I. DI Antonio et al. (+15 more)

The design and verification of cryogenic near-infrared spectrographs require rigorous multidisciplinary analyses to ensure optical performance under realistic operational conditions. In this work, we present a structural-thermal-optical performance (STOP) analysis of the SHARP instrument, a multi-mode spectrograph designed for use with upcoming multi-conjugate adaptive optics (MCAO) systems on Extremely Large Telescopes (ELTs). Transient and steady-state thermal simulations were performed using Ansys to model the cooldown process and temperature distribution within the opto-mechanical structure. The resulting temperature fields were mapped to structural models through linear interpolation, enabling the evaluation of thermal stresses and deformations of optical elements. Optical sensitivity and tolerance analyses were carried out using Ansys Zemax OpticStudio, with Monte Carlo simulations applied to assess robustness against decenter, tilt, and despace errors. Results indicate that SHARP maintains RMS spot radius values within acceptance threshold, and that the inclusion of compensators significantly enhances compliance with the Ensquared Energy (EE) requirement across all channels. The analysis confirms that SHARP can achieves its optical performance goals while remaining within mechanical and thermal constraints, providing a validated framework for the development of next-generation cryogenic astronomical instrumentation.
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All authors H. Mahmoodzadeh, P. Saracco, I. DI Antonio, P. Conconi, D. Scaccabarozzi, B. Saggin, E. Molinari, C. Arcidiacono, I. Arosio, E. Cascone, V. Cianniello, V. De Caprio, G. Di Rico, B. Di Francesco, C. Eredia, P. Franzetti, M. Fumana, E. Portaluri

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Black hole-neutron star binaries with high spins and large mass asymmetries: III. Properties of the ejected material and its electromagnetic signatures

Konrad Topolski, Samuel D. Tootle, Paramvir Singh et al. (+2 more)

Compact binary systems consisting of a black hole (BH) and a neutron star (NS) are expected to provide detectable signals both in the gravitational wave and in the electromagnetic channels, thus representing excellent sources for multi-messenger astronomy. In this third paper in a series, we report on the geometric and thermodynamic properties of the purely dynamical ejecta component modeled in our general-relativistic magnetohydrodynamical simulations of BHNS systems over a comprehensive binary parameter space consisting of large mass ratio and high BH spin. The tidal disruption and dynamical mass ejection is studied by monitoring the transfer of energy and angular momentum to matter for the particular case of a highly unequal-mass binary with large BH spin, extending known results for low-mass-ratio, irrotational BHNS binaries. By varying the binary parameters, we investigate their influence on the geometric, thermodynamic, and kinematic properties of the ejected matter. Furthermore, we employ the nuclear-reaction network SkyNet to obtain the elemental abundances resulting from the r-process active in the ejecta and study how they depend on the properties of the progenitor objects. Finally, using the radiative-transfer code POSSIS, we compute the kilonova light-curves from the results of our simulations, discuss their bolometric and optical/near-infrared evolution, and compare them with the AT2017gfo data and upper-limits for S190814bv, finding overall consistency.
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All authors Konrad Topolski, Samuel D. Tootle, Paramvir Singh, Mattia Bulla, Luciano Rezzolla

High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Earth rotation turns event timing into a geometric probe of UHE neutrino origin

Andrew Cheek, João Paulo Pinheiro and Jordi Salvado

It has been proposed that the ultra-high-energy (UHE) event $\rm KM3-230213A$ detected by KM3NeT could be explained by dark matter (DM) decay. Prima facie this seems unlikely because the arrival direction of the event is opposite to the Galactic Centre. We develop a per-event test statistic to quantitively assess this possibility and forecast the required future events to exclude the DM hypothesis in favour of an isotropic signal. For the single event observed, the DM decay hypothesis is disfavoured but not excluded ($p\text{-value}_{\rm DM}\simeq0.13$–$0.15$). We emphasise how including the time-averaged detector visibility helps discrimination despite reducing the proportion of visible sky, reducing the number of events for exclusion from $\sim33$–$43$ to $\sim22$–$27$. Moving beyond this, we perform a fully time-resolved forecast and find that the required number of events for exclusion reduces by $40\%$, $\sim14$–$16$. The time variation in the signal provides vital information allowing one to exclude or confirm the DM hypothesis with much fewer events. Our results are robust against DM decay channels and halo distributions and can readily be applied to other relics distributed similarly. Our framework allows one to turn event timing into a probe of signal geometry and is generic to any UHE equatorial neutrino telescopes.
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Astrophysics of Galaxies

Outflows in the Early Universe: Neutral gas Absorption in Galaxies at z > 3 from low-resolution JWST Spectroscopy

Matteo Sapori, Sirio Belli, Letizia Bugiani et al. (+14 more)

Recent JWST/NIRSpec observations have shown that Na I D absorption tracing neutral gas outflows is widespread in massive galaxies at Cosmic Noon ($z\sim2$-$3$), but their prevalence at higher redshift remains largely unexplored. Here we investigate whether similar outflows are already in place during the first 2 Gyr of cosmic history ($z>3$), using a sample of 811 galaxies at $3<z<7$ from the public DAWN JWST Archive and the Mirage or Miracle survey, with secure spectroscopic redshifts and continuum SNR$>5$ in their JWST/NIRSpec PRISM low-resolution spectra ($R\sim100$). We derived physical properties and star formation histories via Prospector SED fitting and isolated the Na I D feature in each spectrum by subtracting the best-fit stellar continuum. We detect an excess of Na I D absorption in 20 galaxies, almost all at $3<z<5$ with stellar mass $>10^{10} M_\odot$, an overall detection fraction of $\sim2.5\%$. The detection fraction rises steeply with stellar mass and quiescence, reaching $\sim11\%$ among the most massive galaxies and $\sim43\%$ among massive quenched systems. The Na I D equivalent widths are large, spanning 4 to 16 Angstrom, and are highest in dusty star-forming galaxies. In previous medium-resolution observations, EWs above 5 Angstrom were mostly found in outflowing gas; we thus interpret our detections as mostly tracing neutral outflows, despite the lack of kinematic information at PRISM resolution. A stacking analysis confirms these trends and provides average Na I D EWs for different subsamples. Under conservative assumptions, we estimate mass outflow rates of 4 to 12 $M_\odot$ yr$^{-1}$, exceeding the current star formation rate for about 30% of the detected galaxies. We conclude that neutral outflows are likely already present and important in massive galaxies during the first 2 Gyr of cosmic history.
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All authors Matteo Sapori, Sirio Belli, Letizia Bugiani, Amir H. Khoram, Caterina Liboni, Gabriel Maheson, Gabriel Brammer, Rebecca Davies, Pratika Dayal, Anna de Graaff, Joel Leja, Rohan Naidu, Pascal Oesch, Stefano Sotira, Sandro Tacchella, Bingjie Wang, Katherine E. Whitaker

High Energy Astrophysical Phenomena

Revealing the Structure and Magnetization of GRB Jets with ALMA Polarization Observations

Tanmoy Laskar, Collin T. Christy, Noah Franz et al. (+9 more)

We present a systematic study of the currently available ALMA millimeter polarimetric sample of gamma-ray burst (GRB) afterglows. Our sample comprises 24 observations (20 new) of 11 long-duration GRBs spanning $\approx0.1$-87 days after the burst. We detect significant linear polarization in 8 observations across 6 events, with polarization degrees ranging from $\Pi_L\approx0.6\%$ to $2.4\%$. For the remaining observations, we place deep upper limits (median $\Pi_L\lesssim1\%$). Multi-epoch observations reveal diverse polarization evolution. GRB 190114C yields the best-sampled $\Pi_L$ for a radio afterglow to date, with early evolution favoring patchy magnetic fields in the reverse shock (RS) and later polarization broadly consistent with forward-shock (FS) models. GRB 220921A exhibits a rapid rise in polarization from $\Pi_L\lesssim0.4\%$ to $2.4\%$ over 1.9-6.8 days, inconsistent with toroidal RS magnetic-field models but broadly consistent with several FS random-field models. GRB 221009A yields the highest-significance polarization detections in the sample ($\Pi_L\approx1.4$-$1.6\%$), yet neither existing FS nor RS polarization models reproduce both the observed polarization evolution and the viewing geometry inferred from broadband afterglow modeling, with the exception of patchy fields in the RS. Deep upper limits for GRB 171205A rule out RS toroidal-field models for the published off-axis geometry, while a strong, single-epoch detection of GRB 190829A, if RS-dominated, requires a nearly on-axis geometry for toroidal-field configurations. Interpreting the observations within a patchy-field framework implies magnetic-field coherence scales of order $\theta_B\sim10^{-3}$-$10^{-2}$ rad. These observations demonstrate the diagnostic power of radio/mm polarimetry for probing the magnetic-field structure, emission region, and viewing geometry of relativistic GRB jets.
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All authors Tanmoy Laskar, Collin T. Christy, Noah Franz, Gavin Farley, Kate D. Alexander, Jonathan Granot, Ramandeep Gill, Tarraneh Eftekhari, Shiho Kobayashi, Hendrik van Eerten, Raffaella Margutti, Edo Berger

Astrophysics of Galaxies

A New Model for the Milky Way Halo Dispersion Measure with the ENGAWA Simulations: Low DMs and Large Anisotropy

Scott Lucchini, Liam Connor, Samuel McCarty et al. (+1 more)

Fast radio burst (FRB) dispersion measures (DMs) are powerful tracers of the low density universe, but interpretation is made difficult by the integrated nature of DM. In this paper, we analyze the new ENGAWA cosmological zoom-in simulation suite to constrain the DM contribution from the Milky Way (MW) halo. The ENGAWA simulations consist of four Milky Way-like galaxies with enhanced resolution in the circumgalactic medium, making them an excellent tool to probe the properties of the gaseous halo. The median all-sky DM from the galactic halos in ENGAWA span 19-39 pc cm$^{-3}$, varying even at fixed feedback strength, halo mass, and $f_\mathrm{CGM}$. These simulations show that, with enhanced circumgalactic resolution, the mean halo DM values are in general lower with more anisotropy across the sky than previous models, reaching < 10 pc cm$^{-3}$ towards the poles. Furthermore, by varying the solar position within the simulated galaxies, we have obtained an estimate of the uncertainty in DM given our location in the MW. We provide a Python package with MW halo DM values from the simulation accessible via API functions of Galactic longitude and latitude. These new, simulation-based MW halo DM estimates will provide a critical baseline for interpretations of future FRB observations and our understanding of the global gas distribution in the Universe.
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All authors Scott Lucchini, Liam Connor, Samuel McCarty, Ralf M. Konietzka

High Energy Astrophysical Phenomena

Semi-analytical Light Curve Model for Transients Preceding Binary Mergers. I: Supernova Precursor Emission from Compact Object Companions

Daichi Tsuna, Morgan Macleod and V. Ashley Villar

A binary undergoing dynamically unstable mass transfer could rapidly shrink its orbit and lead to a merger, with the whole process often observable in human timescales. We construct a semi-analytical light curve model of binary systems composed of a star and a compact object accretor, that would display long-rising accretion-powered emission prior to a final merger-driven explosion. We apply the model to the precursors of interacting supernovae (SNe) that display long-rising light curves of years, SN 2023zkd, 2023fyq and 2021qqp, demonstrating the model's capability of inferring the mass-transfer history and constraining the progenitor binary system. The model and the parameter inference framework, encapsulated in a publicly-released script, can be applied to existing long-rising precursors of SNe as well as many SN precursors to be discovered by surveys like those from the Vera C. Rubin Observatory.
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Cosmology and Nongalactic Astrophysics

Primordial black holes forming during kination: the trapped, the overdense, and the void

Cristian Joana

We study primordial black-hole (PBH) formation in a single-field model which passes from slow roll, through a transient ultra-slow-roll phase, into kination. Nonlinear numerical-relativity simulations are used to follow localised, initially sub-Hubble field fluctuations across the non-attractor transition, to determine the resulting super-Hubble curvature profiles, and subsequently to evolve their re-entry during kination. Within the set of initial configurations explored here, we find three qualitatively distinct outcomes, namely a patch which remains trapped in inflation, a positive-curvature overdensity, and a negative-curvature void bounded by an overdense shell. Each may form a PBH, although by a different physical mechanism. For one selected profile in each of the overdense and void channels, we measure collapse thresholds and compare them with thresholds for sinc profiles. The comparison shows that neither the central curvature nor the peak linear compaction alone provides a profile- or channel-independent collapse criterion. PBH abundances in non-attractor models must therefore be formulated in terms of the distribution of complete profiles, with the trapped, overdense, and void channels treated separately.
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Cosmology and Nongalactic Astrophysics

The road towards precision measurements of $H_0$ with bright sirens in the Einstein Telescope era

Chiara De Leo, Elsa M. Teixeira and Vivian Poulin

Gravitational-wave standard sirens provide an independent probe of cosmic expansion since their luminosity distances are inferred directly from the gravitational-wave signal and, for bright sirens (BSs), the source redshifts are obtained through the identification of electromagnetic counterparts. In this work, we forecast the constraining power of future bright siren catalogues on the Hubble constant using simulated binary-neutron-star mergers detected by the Einstein Telescope with associated electromagnetic counterparts. We construct mock catalogues with different numbers of events and redshift distributions, with GW170817 as a reference BS, and analyse the resulting constraints within a flat $\Lambda$CDM cosmology. We find that, when bright sirens are used as a standalone probe, most of the information on $H_0$ is provided by low-redshift events, with the improvement in precision saturating for sources above $z \sim 1$; beyond that redshift, the constraining power of BSs is increasingly limited by the degeneracy with $\Omega_m$, which prevents further gains in precision on $H_0$. In this case, approximately $90$ low-redshift BSs are required to reach $\sigma_{H_0} \sim 1\,{\rm km\,s^{-1}\,Mpc^{-1}}$, while about $45$ are sufficient for $\sigma_{H_0} \sim 2\,{\rm km\,s^{-1}\,Mpc^{-1}}$. When external BAO information is included to reduce the $H_0 - \Omega_m$ degeneracy, intermediate-redshift sirens become more informative and the required number of events decreases substantially, to roughly $20$ and $15$ BSs for $\sigma_{H_0} \sim 1\,{\rm km\,s^{-1}\,Mpc^{-1}}$ and $\sigma_{H_0} \sim 2\,{\rm km\,s^{-1}\,Mpc^{-1}}$, respectively. These results highlight the importance of both electromagnetic counterpart identification and complementary background probes in making BSs a competitive, distance-ladder-independent test of the Hubble tension.
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Astrophysics of Galaxies

Estimating Cluster Galaxy Infall Time from Phase Space in TNG

Cameron Lawlor-Forsyth

Using the TNG300 and TNG-Cluster simulations, phase space-based estimates for galaxy infall time onto clusters with $M_{\mathrm{h}} \geqslant 10^{14}~M_{\odot}$ are determined for all simulation snapshots with $z \leqslant 1$. These infall time estimates are consistent with previous work in the literature, and can be readily applied to observations of cluster galaxies, where no other estimate is feasible, based only on the galaxy's position in projected phase space. The analysis pipeline used to produce these infall time estimates is publicly released, as are the resulting data products, as well as a tutorial that outlines their use. It is anticipated that both the data products and the provided tutorial will facilitate future research within the community which require infall time estimates, and will provide an additional baseline for studies investigating the orbital histories of galaxies in dense environments like galaxy clusters.
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Astrophysics of Galaxies

Spectral Data-cube Cleaning for CCAT Deep Spectroscopic Survey. I. Effect of correlated noise and filtering on the power spectrum

A. Dev, C. Karoumpis, Y. Okada et al. (+8 more)

The Epoch of Reionization Spectrometer (EoR-Spec) on the Fred Young Submillimeter Telescope (FYST) will conduct the CCAT Deep Spectroscopic Survey (DSS) to perform line-intensity mapping of redshifted [C II] emission. Atmospheric $1/f$ noise and instrumental systematics affect power-spectrum recovery. We present realistic end-to-end simulations to quantify these effects and evaluate a Filter-and-Bin (F&B) pipeline. The simulated observations include instrument response, astrophysical emission, atmospheric noise, and observing strategy. The pipeline suppresses atmospheric $1/f$ noise by about four orders of magnitude at low temporal frequencies while leaving only minor residual correlated noise. For a single EoR-Spec module operating at 50% observing efficiency, the DSS is expected to detect the combined [C II] + CO power spectrum on shot-noise-dominated scales ($k > 0.1\,\mathrm{Mpc}^{-1}$). With two modules operating at full efficiency, detections are achievable over all targeted spatial scales. The transfer function exceeds 80% at $k \gtrsim 0.5\,\mathrm{Mpc}^{-1}$ but falls below 20% at $k \lesssim 0.1\,\mathrm{Mpc}^{-1}$, indicating significant suppression of large-scale modes. These results demonstrate that the F&B pipeline is effective for recovering the shot-noise regime, while improved map-making techniques will be required for accurate large-scale clustering measurements.
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All authors A. Dev, C. Karoumpis, Y. Okada, K. Basu, F. Bertoldi, D. Chung, J. Clarke, R. Freundt, T. Nikola, T. Oak, D. Riechers

High Energy Astrophysical Phenomena

Pulsar glitches in the presence of vortex traps

Anantharaman Sekharipuram Viswanathan, Dipankar Bhattacharya, M. Ali Alpar et al. (+1 more)

Pulsar glitches are thought to originate when angular momentum is transferred to the crust of the neutron star from the superfluid enclosed within, mediated by vortex avalanches. This idea has been qualitatively validated in the existing literature by simulating a star with a small number ($\sim 10^{3}$) of superfluid vortices, subject to deceleration and uniform pinning. Here, we employ the Barnes-Hut approximation to simulate up to $10^{5}$ vortices in a reasonable time. Using the new setup, we probe glitches that originate in the presence of inhomogeneous pinning. The inner crust of a neutron star is expected to crack as the star spins down, relieving stresses and resulting in rearrangements within the crustal lattice. These regions become centres for pinning with large pinning energies. Many such vortex traps are expected to exist in mature pulsars like Vela. We simulate one such star and find that the rise of the glitch is now staggered, a clear signature of the trap network. In young to middle-aged stars like PSR J0537-6910, we expect quakes which result in new traps and also unpin the vortices in existing ones. We observe that such a configuration involving the simultaneous release of several traps could introduce a bimodality in the glitch-size distribution, a feature that has previously been reported for PSR J0537-6910. Our simulations also indicate that macroscopic inhomogeneities in the distribution of vortices could spontaneously develop in a star with uniform pinning sites.
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All authors Anantharaman Sekharipuram Viswanathan, Dipankar Bhattacharya, M. Ali Alpar, Erbil Gügercinoğlu

Astrophysics of Galaxies

Gas accretion onto the Milky Way: high-velocity cloud survival and the revival of the terminal-velocity paradigm

Michael M. Schulreich, Dieter Breitschwerdt and Jürgen Kerp

The terminal-velocity paradigm has long been used to interpret the motion and infer the distances of HVCs accreting onto the Milky Way, yet its validity under realistic Galactic conditions remains uncertain. We investigate its dynamical limits by combining analytical modelling with three-dimensional hydrodynamical simulations of clouds moving through a stratified Milky Way halo. We derive a generalized equation of motion including gravity, ram-pressure drag, a phenomenological mass-exchange model capturing mass loss and growth, and Bernoulli-driven cloud expansion. Analytical solutions for constant-property clouds provide a reference framework, while the full evolution is assessed using simulations with adiabatic physics, radiative cooling, and thermal conduction. Terminal velocity is a local equilibrium but not a global attractor: dense clouds remain quasi-ballistic over most of their trajectories and approach terminal motion only shortly before reaching the Galactic disc. Hydrodynamical effects further limit the paradigm. In adiabatic flows, instabilities rapidly disrupt the cloud, rendering the terminal-velocity description inapplicable. Radiative cooling instead promotes condensation and momentum loading, maintaining strong coupling to the background gas and restoring a terminal-velocity-like regime over extended periods, while thermal conduction mainly affects small-scale structure. Synthetic observables, including position–velocity diagrams, optical extinction, and soft X-ray emission, reproduce key features of observed HVCs such as velocity bridges and compression-driven emission. We also provide direct measurements of the effective drag coefficient for infalling clouds, finding values of order unity but strongly time-dependent. Overall, the terminal-velocity paradigm is a conditional description governed by cloud structure, mass exchange, and the ambient medium.
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Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det

Overview and design optimization of a custom hybrid X-ray telescope for the International Axion Observatory (IAXO)

Yue Yu, Jooyun Woo, Ipek Altunyurt et al. (+34 more)

We present the design optimization for maximizing the effective area of a custom X-ray optic for the International Axion Observatory (IAXO) and BabyIAXO, including its novel hybrid configuration that enables full coverage of the 700-mm-diameter magnetic bore with minimal stress imposed on the mirrors; shell layout optimized for axion spectra and spatial distribution; and the coating recipes that enhance reflectivity in the energy range of interest. We evaluate how these design choices improve the observation signal-to-noise ratio (SNR) of BabyIAXO and IAXO by calculating the broad-band effective area and simulating the point spread function (PSF) and focal spot at the detector plane. The cost-effective and scalable optic offers an energy response from 0.03–15 keV, achieving an effective area that exceeds 2400 cm$^2$ near 1 keV - the peak of the ABC axion spectrum - and remains above 1700 cm$^2$ around 3 keV - the peak of the Primakoff axion spectrum. It yields a half-power diameter (HPD) of $\sim 46^{\prime\prime}$ for an on-axis point source at infinity, and a focal-spot HPD of $\sim 120^{\prime\prime}$ for the radial distribution expected for axion signals within the approximately $3^{\prime}$-radius solar core. A relatively generous fabrication-error budget is also summarized. The custom optic, accounting for fabrication errors, is anticipated to deliver a more than $55$-fold enhancement in the SNR.
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All authors Yue Yu, Jooyun Woo, Ipek Altunyurt, Stefano Basso, Vadim Burwitz, Francisco R. Candón, Juan Francisco Castel Pablo, Marta M. Civitani, Todd Decker, Klaus Desch, Desiree Della Monica Ferreira, Javier Galan, Maurizio Giannotti, Louis Helary, Peter L. Henriksen, Alba María Huerva, Igor G. Irastorza, Eftychia Kotsiou, Axel Lindner, Frank Marutzky, Sonny Massahi, Sam Moseley, Takashi Okajima, Johanna von Oy, Diego Paredes-Sanz, Giancarlo Parodi, Kerstin Perez, Michael J. Pivovaroff, David Reuther, Anacorina Romero, Jaime Ruz, Vyshnavi Sabbi, Tobias Schiffer, Uwe Schneekloth, Daniele Spiga, Marcela Stern, Julia K. Vogel

Instrumentation and Methods for Astrophysics

The High-Speed FPGA Readout System for the Advanced X-ray Imaging Satellite (AXIS)

Declan O'Neill, Jill Juneau, Peter Orel et al. (+17 more)

The Advanced X-ray Imaging Satellite (AXIS) is a Probe-class mission concept designed to deliver arcsecond spatial resolution, high-sensitivity spectral imaging across the 0.3-10 keV band. The X-ray Astronomy and Observational Cosmology (XOC) Group at Stanford, in collaboration with the MIT Kavli Institute (MKI) and MIT Lincoln Laboratory (MIT-LL), is developing the AXIS X-ray camera, including both the detector and the front-end readout electronics required to meet the mission's demanding performance goals. The telescope's focal plane detector consists of four 1440x1440 pixel charge-coupled devices (CCDs) developed by MIT-LL, each featuring 16 parallel output channels. These outputs are amplified by a high-speed, low-power, low-noise application-specific integrated circuit (ASIC) - the Multi-Channel Readout Chip (MCRC) - developed at Stanford. Following amplification, the analog signals are digitized and processed to construct a pixel array, prior to event detection. Here, we present the field-programmable gate array (FPGA) architecture developed to enable high-speed, parallelized readout of these CCD channels. The FPGA samples 16 analog-to-digital converter (ADC) channels at 50 MHz, performs preprocessing of pixel data, which is then streamed via User Datagram Protocol (UDP) over a 1 Gb Ethernet link to the back-end system for event reconstruction. Our design demonstrates the goal readout performance for AXIS (20 frames per second) and provides a framework for future high-throughput X-ray observatories.
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All authors Declan O'Neill, Jill Juneau, Peter Orel, Sven Herrmann, Gregory Prigozhin, Eric D. Miller, Steven W. Allen, Marshall W. Bautz, Tanmoy Chattopadhyay, Kevan Donlon, Robert Goeke, Catherine E. Grant, Beverly LaMarr, Christopher Leitz, R. Glenn Morris, Abigail Y. Pan, Tonya L. Peshel, Artem Poliszczuk, Haley R. Stueber, Keith Warner

High Energy Astrophysical Phenomena

Probing the High-Energy Emission of the VHE-emitting Changing-Look Blazar B2 1420+32

Anjum Peer, Zahir Shah, Sikandar Akbar et al. (+2 more)

We present a multi-wavelength temporal and spectral study of the changing-look blazar B2~1420+32 using Fermi-LAT, Swift-XRT, and Swift-UVOT data from MJD~58818–60721. The source reached a peak 0.1–300~GeV photon flux of $(4.62 \pm 0.29) \times 10^{-6}\,\mathrm{ph\,cm^{-2}\,s^{-1}}$ around MJD~60488, about 60 times the 4FGL-DR4 average, during which the photon index hardened to $2.19 \pm 0.14$; the flux–index evolution shows only weak evidence for global harder-when-brighter behaviour. The fractional variability is strongly energy dependent, largest in $\gamma$-rays, substantial in the optical/UV, and low in X-rays. Strong $\gamma$-ray–optical/UV correlations and a moderate $\gamma$-ray–X-ray correlation indicate that the X-ray emission tracks the $\gamma$-ray variability less closely than the optical/UV emission. The X-ray spectra are best described by a log-parabola, and the negative curvature measured in four of the five states suggests that the X-ray band samples the transition between the high-energy tail of the synchrotron component and the onset of the inverse-Compton component. We identified five activity states and modelled the high-energy (X-ray and $\gamma$-ray) component of their broadband spectral energy distributions (SEDs) using synchrotron self-Compton (SSC), external Compton (EC), and SSC+EC scenarios. The SSC-only and EC-only models either require physically disfavoured parameters or fail to reproduce the VHE emission, whereas SSC+EC provides the most self-consistent description, with a seed-photon temperature of $\sim 10^{3}$~K favouring an infrared torus origin. The brighter states require larger bulk Lorentz factors and higher jet powers, while the magnetic field varies only modestly, indicating that the flux evolution is governed by a combination of Doppler boosting and jet energetics.
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All authors Anjum Peer, Zahir Shah, Sikandar Akbar, Bari Maqbool, Ranjeev Misra

Cosmology and Nongalactic Astrophysics

The burgeoning rise of the 21-cm forest I: constraints on the optical depth of the intergalactic medium at $5.38 < z < 5.84$

Chanasorn Kongprachaya, Gianni Bernardi, Emilio Ceccotti et al. (+3 more)

The redshifted 21-cm line is a promising probe of the Epoch of Reionization, during which the first generation of stars ionized the InterGalactic Medium (IGM). We aimed to constrain the IGM neutral Hydrogen fraction and spin temperature via redshifted 21-cm absorption against high-redshift radio sources. We analysed an 18-hour observation of the radio-loud quasar PSO J352.4034-15.3373 ($z = 5.84$) in the 203-222.5 MHz band. We obtained a continuum image with a $0.66$ mJy/beam rms noise and a spectrum with $3.6$ mJy/beam rms noise per 390 kHz-wide channel. We fit the quasar spectrum with a power-law continuum modified by an intervening 21-cm absorption, testing two scenarios: an island model, a residual cold neutral Hydrogen patch surviving at the end of reionization, and a global model, approximating the overall decline of the IGM HI fraction and spin temperature with redshift. Combining archival data spanning 150 MHz to 3.0 GHz with our measurements, we determined a quasar flux density of $86.8 \pm 1.1$ mJy at 200 MHz and a spectral index of $-0.88 \pm 0.02$ across the full frequency range. We found no evidence for the 21-cm absorption from intervening neutral Hydrogen at $5.38<z<5.84$. Assuming the island model, we set a 95% confidence lower limit on the IGM spin temperature of $1.73$ K in residual HI regions. Assuming the global model, we constrained the 21-cm optical depth to $\tau_{21}< 0.02$ (95% C.L.). These results provide constraints on the 21-cm optical depth near the end of reionization, over the $5.38 < z < 5.84$ range, and confirm that the IGM was heated above the adiabatic cooling limit ($\sim 0.8$ K at $z = 5.68$), consistent with theoretical predictions and with 21-cm power spectrum measurements at higher redshifts. Our results also disfavour the presence of extremely cold HI regions at $z < 5.84$ and open the way to future 21-cm absorption from high-redshift sources.
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All authors Chanasorn Kongprachaya, Gianni Bernardi, Emilio Ceccotti, Andrei Mesinger, Benedetta Ciardi, Oleg M. Smirnov

Instrumentation and Methods for Astrophysics

Fast, low-noise CCD systems for future strategic X-ray missions

Haley R. Stueber, Tanmoy Chattopadhyay, Tonya L. Peshel et al. (+12 more)

Future strategic X-ray missions, such as those targeted by the Great Observatories Maturation Program (GOMaP), require fast, low-noise X-ray imaging spectrometers. To achieve the speed and noise capabilities required by such programs, our Stanford team, in collaboration with the MIT Kavli Institute (MKI) and MIT Lincoln Laboratory (MIT-LL), is developing enhanced X-ray charge-coupled devices (CCDs) and readout systems that leverage tailored application-specific integrated circuits (ASICs). Here, we report the energy resolution and noise performance achieved using some of the latest MIT-LL CCDs in conjunction with Stanford-developed Multi-Channel Readout Chip (MCRC) ASICs. Additionally, we present a new sampling method for simultaneous optimization of the output gate (OG), reset gate (RG), and reset drain (RD) biases which, in combination with new integrated fast summing well (SW) and RG clock operation modes, enables the data rates and noise required for future X-ray telescopes. Finally, we present noise power spectral density (PSD) and waveform analysis methods and posit a physical model for characterizing and understanding output stage noise behavior.
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All authors Haley R. Stueber, Tanmoy Chattopadhyay, Tonya L. Peshel, Abigail Y. Pan, Steven W. Allen, Marshall W. Bautz, Kevan Donlon, Catherine E. Grant, Sven Herrmann, Beverly J. LaMarr, Eric D. Miller, R. Glenn Morris, Peter Orel, Artem Poliszczuk, Gregory Y. Prigozhin