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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 3 June

Astrophysics of Galaxies

Metal-Poor Gas Accretion Drives Giant Clump Formation at 0.6 < z < 2.6

Visal Sok, Adam Muzzin, Ben Forrest et al. (+20 more)

The physical properties of kiloparsec-scale clumps in high-redshift star-forming galaxies (SFGs) contain crucial constraints on how they assemble. Building on recent work that indicates the presence of a metallicity offset in clumpy galaxies compared to nonclumpy SFGs, we analyze the chemical abundance in a large sample of ${\sim}300$ SFGs between $0.6<z<2.6$ using LEGA-C, MOSDEF and CANUCS near-infrared spectroscopic observations. We find that clumpy galaxies generally have lower gas-phase metallcities compared to the mass-metallicity relation, while nonclumpy galaxies have higher metallicities. We further investigate the relationship between the resolved stellar properties of clumps and the integrated gas-phase metallicity of the host galaxies using a subset of galaxies observed in the CANUCS fields. In particular, clumps in SFGs with metallicity below the mass-metallicity relation (i.e., $\Delta Z \leq 0$) are generally younger and have higher SFRs, compared to clumps whose host galaxies have $\Delta Z > 0$. We do not find a significant mass difference between these two clump populations. Finally, we compute the merger statistic using the Gini-M20 morphological parameters and find that the majority of clumpy galaxies are not classified as mergers based on their stellar mass maps. The results suggest that the clumpy nature of cosmic noon galaxies is linked to metal-poor gas accretion events that trigger star formation and dilute metallicities.
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All authors Visal Sok, Adam Muzzin, Ben Forrest, Gillian Wilson, Jialu Chen, Vivian Yun Yan Tan, Sunna Withers, Roberto Abraham, Maruša Bradač, Vicente Estrada-Carpenter, Kartheik G. Iyer, Nicholas S. Martis, Gaël Noirot, Ghassan T. E. Sarrouh, Marcin Sawicki, Chris J. Willott, Aurélien Henry, Naadiyah Jagga, Danilo Marchesini, Ian McConachie, Katherine Myers, Nelson Nunes, Luke Robbins

Astrophysics of Galaxies

Strong environmental AGN enhancement among DSFGs in z > 2 protoclusters

Monica Natalia Isla Llave, Fabio Vito, Alberto Traina et al. (+17 more)

Galaxy protoclusters (PCs) at z > 2 are dense regions in which cold gas availability and elevated galaxy interaction rates trigger intense, often dust-obscured, star formation. These mechanisms are also expected to promote super-massive black hole (SMBH) growth, but this effect remains unclear, largely due to heterogeneous galaxy selections and active galactic nuclei (AGN) identification methods in previous studies. We quantitatively assess the impact of PC environment on SMBH growth by measuring the incidence of X-ray AGN among dusty star-forming galaxies (DSFGs) in PCs and in a homogeneously selected control field sample, and investigate the physical mechanisms driving any difference. We consider ALMA-detected DSFGs in sub-mm/mm continuum of seven PCs at 2 < z < 4.5, and construct a selection-matched control sample from the COSMOS survey. We statistically compare X-ray AGN incidence and host galaxy physical properties obtained through uniform spectral energy distribution fitting. We find a significant enhancement of X-ray AGN fraction in PCs by ~2.7x (Poisson significance p = 3e-4). Similar values are found in two redshift bins: ~2.7x at z = 2-3 (p = 0.003) and ~2.6x at z = 3-4.5 (p = 0.03). PC and field DSFG samples are well matched in stellar mass, star-formation rate, and dust mass, ruling out selection effects or systematically higher host masses as the driver. Our results provide quantitative evidence that the dense PC environment enhances AGN incidence and SMBH growth in DSFGs beyond what host galaxy properties alone predict, likely through increased gas availability and interaction-driven fueling. This work is a first step toward a homogeneous assessment of environmental effects on SMBH growth across cosmic time.
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All authors Monica Natalia Isla Llave, Fabio Vito, Alberto Traina, Cristian Vignali, Olga Cucciati, Benjamin Forrest, Gayathri Gururajan, Brian Lemaux, Sylvia Adscheid, Sebastiano Cantalupo, Kazuki Daikuhara, Marta Galbiati, Roberto Gilli, Tadayuki Kodama, Stefano Marchesi, Maurillio Pannella, Antonio Pensabene, Maria del Carmen Polletta, Rhythm Shimakawa, Paolo Tozzi

Astrophysics of Galaxies

Little red dots as a cosmological probe: constraining $H_0$ with quasi-periodic pulsations

Zijian Zhang, Kohei Inayoshi, Masamune Oguri et al. (+4 more)

The James Webb Space Telescope (JWST) has uncovered a population of “little red dots” (LRDs) at $z \gtrsim 4$, potentially representing early supermassive black holes embedded in dense gaseous envelopes. The recent discovery of the lensed LRD RXJ2211-RX1 reveals significant variability on rest-frame timescales of decades, which may be interpreted as quasi-periodic variation that has a potential physical parallel to stellar pulsations. In this work, we derive an idealized, self-consistent period-luminosity-temperature ($P$-$L$-$T_{\rm eff}$) relation based on the hydrostatic envelope model. If this theoretical relation holds and can be empirically validated/calibrated, it would offer a novel framework for constraining the Hubble constant ($H_0$). The current sparse sampling of \tgta\ yields a preliminary $H_0 = 120.7_{-46.5}^{+47.0} \text{ km s}^{-1}\text{ Mpc}^{-1}$ as a proof-of-concept, with the error budget dominated by the uncertainty of the pulsation period. Our forecasting analysis shows that continuous monitoring over a 10-year baseline can reduce the $H_0$ uncertainty to 3-20%, depending on the intrinsic pulsation period, while the systematic uncertainty floor remains to be fully characterized. This method offers a potential independent probe to measure luminosity distances in the early universe.
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All authors Zijian Zhang, Kohei Inayoshi, Masamune Oguri, Linhua Jiang, Fengwu Sun, Mingyu Li, Xiaojing Lin

Cosmology and Nongalactic Astrophysics

The free-streaming length of dark matter from JWST observations of 28 strong gravitational lenses

D. Gilman, A. M. Nierenberg, T. Treu et al. (+24 more)

The formation of gravitationally bound overdensities of dark matter (DM), or halos, is a generic prediction of theories with particle DM. We present a measurement of halo properties in 28 quadruple image strong lens systems recently observed by JWST, and use these observations to constrain the free-streaming length, $\lambda_{\rm{FS}}$, of DM, a quantity that depends on the DM particle mass and formation mechanism. We improve on previous lensing analyses by simultaneously reconstructing extended lensed arcs with image positions and relative magnifications, enhancing sensitivity to perturbations by halos. Our analysis rules out deviations from the predictions of cold dark matter (CDM) on scales above $10^{7.2} M_{\odot}$ and $10^{7.4} M_{\odot}$ for subhalo abundance predicted by cosmological $N$-body simulations and semi-analytic models, respectively. These bounds correspond to upper limits $\lambda_{\rm{FS}}<6.0 \ \rm{kpc}$ and $\lambda_{\rm{FS}}<7.0 \ \rm{kpc}$, and lower limits on the mass of a spin–1/2 thermal relic DM particle $m_{\rm{therm}}>7.4 \ \rm{keV}$ and $m_{\rm{therm}}>6.5 \ \rm{keV}$. Conversely, assuming a negligible free-streaming length, as predicted by CDM, we measure a projected mass in subhalos around elliptical galaxies $1.7_{-1.2}^{+2.6} \times 10^7 \ \mathrm{M}_{\odot} \ \rm{kpc^{-2}}$ at $95 \%$ confidence. These inferences confirm key predictions of the CDM paradigm.
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All authors D. Gilman, A. M. Nierenberg, T. Treu, K. N. Abazajian, T. Anguita, V. N. Bennert, A. J. Benson, S. Birrer, S. G. Djorgovski, X. Du, C. Gannon, S. F. Hoenig, R. E. Keeley, A. Kusenko, H. R. Larsson, M. Malkan, T. Morishita, V. Motta, L. A. Moustakas, P. Mozumdar, H. Paugnat, W. Sheu, D. Sluse, D. Stern, M. Stiavelli, D. Williams, K. C. Wong

Instrumentation and Methods for Astrophysics

UK White Paper on Space-based total solar eclipse observations: structure and dynamics of the solar atmosphere

Lucie M. Green, Nicola Baresi, Huw Morgan et al. (+19 more)

Our Sun is uniquely placed to enable a detailed study of astrophysical plasmas and how they are governed by the magnetic fields that thread through them. On the one hand, magnetic fields confine plasma and determine plasma heating, flows, and energisation. On the other hand, magnetic fields and their evolution give rise to the most violent eruptions in the Solar System. Understanding the details of how energy is built up and released, and the impact of these physical processes on the plasma, remain key open questions that directly map to UKRI's science strategy through the STFC Solar System Advisory Panel's roadmap for Solar System research goals: What are the causes, consequences and predictability of solar magnetic variability and the solar cycle? What are the structures, dynamics and energetics of the Sun? What are the underlying processes that drive Sun-planet connections? And what are the fundamental processes at work in the Solar System? As laid out in this White Paper, the Moon-Enabled Sun Occultation Mission (MESOM) directly addresses these questions and in doing so delivers several Pillars of the National Space Strategy.
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All authors Lucie M. Green, Nicola Baresi, Huw Morgan, Matt Gunn, Amir Caspi, Daniel B. Seaton, Giulio Del Zanna, Yeimy J. Rivera, Francisco Javier Bailen, David Orozco Suarez, Anthony R. Yeates, Peter Wyper, Nawin Ngampoopun, Nathalia Alzate, Simone Di Matteo, Erika Palmerio, Richard J. Morton, Eleanna Asvestari, Manuela Temmer, Greta Cappello, Teodora Mihailescu, Karl Battams

Instrumentation and Methods for Astrophysics

GREX-PLUS Science Book v2

GREX-PLUS Science Team: Shunsuke Baba, Sirio Belli, Pietro Benotto et al. (+51 more)

GREX-PLUS (Galaxy Reionization EXplorer and PLanetary Universe Spectrometer) is a mission candidate for a JAXA strategic L-class mission to be launched in the 2030s. Its primary science goals are two-fold: galaxy formation and evolution, and planetary system formation and evolution. The GREX-PLUS spacecraft will carry a telescope with a 1 m primary mirror aperture cooled down to 50 K. The two science instruments will be onboard: a wide-field camera in the 2–8 $\mu$m wavelength band and a high-resolution spectrometer with a wavelength resolution of 30,000 in the 10–18 $\mu$m band. The GREX-PLUS wide-field camera aims to detect the first generation of galaxies at redshift $z>15$. The GREX-PLUS high-resolution spectrometer aims to identify the location of the water “snowline” in protoplanetary disks. Both instruments will provide unique datasets for a broad range of scientific topics, including galaxy mass assembly, the origin of supermassive blackholes, infrared background radiation, molecular spectroscopy in the interstellar medium, transit spectroscopy of exoplanet atmospheres, planetary atmospheres in the Solar System, and so on. This document is the second version of a collection of scientific themes that can be achieved with GREX-PLUS. Each section in Chapters~2 and 3 is based on presentations at several GREX-PLUS Science Workshops.
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All authors GREX-PLUS Science Team: Shunsuke Baba, Sirio Belli, Pietro Benotto, Ivan Delvecchio, Yoshinobu Fudamoto, Yuka Fujii, Yuichi Harikane, Yasuhiro Hirahara, Akio K. Inoue, Yoshiyuki Inoue, Hajime Kawahara, Taiki Kawamuro, Yui Kawashima, Lucas Kimmig, Tadayuki Kodama, Mitsuru Kokubo, Hiroyuki Kurokawa, Katsunori Kusakabe, Kosei Matsumoto, Noriyuki Matsunaga, Taro Matsuo, Yoshiki Matsuoka, Shuji Matsuura, Toru Misawa, Shota Miyazaki, Alessia Moretti, Kumiko Morihana, Takashi Moriya, Kentaro Nagamine, Kimihiko Nakajima, Hideko Nomura, Shota Notsu, Takafumi Ootsubo, Kazumasa Ohno, Giorgia Peluso, Bianca M. Poggianti, Mario Radovich, Giulia Rodighiero, Hideo Sagawa, Kazuhiro Shimasaku, Takashi Shimonishi, Ken-ichi Tadaki, Kosuke Takahashi, Michihiro Takami, Shuya Tan, Takumi Tanaka, Tsuyoshi Terai, Yoshiki Toba, Roberta Tripodi, Francesco Valentino, Benedetta Vulcani, Taihei Yano, Chikako Yasui, Stefano Zibetti

Cosmology and Nongalactic Astrophysics

Compressed Gaussian likelihood for the Planck low-$\ell$ data

Nanoom Lee

We present a compressed Gaussian likelihood for the Planck CMB low-$\ell$ E-mode polarization data, constructed from the SRoll2 likelihood which provides the tightest constraint on the reionization optical depth $\tau$ to date. The non-Gaussian form of CMB low-$\ell$ TT and EE likelihoods makes them incompatible with Fisher matrix analyses that require an analytic Gaussian $\chi^2$, such as the Fisher-bias formalism and Fisher forecasts. We show that the $\chi^2$ of an offset log-normal likelihood takes a Gaussian form in the log-transformed power spectrum amplitudes, and can therefore serve as a proxy for the true Gaussian likelihood of this variable in Fisher matrix analyses, without any explicit change of variables. Building on this, we compress the SRoll2 likelihood into a small number of piecewise offset log-normal functions and validate it against the full SRoll2 likelihood via MCMC combined with Planck and ACT DR6 data, finding excellent agreement across all $\Lambda$CDM parameters and in extended cosmological models. We further demonstrate that Fisher matrix uncertainty estimates from our compressed likelihood agree well with the full MCMC posteriors. We release our compressed likelihood planck-gaussian-lowl, a lightweight Python package incorporating the compressed low-$\ell$ TT likelihood from previous work, allowing a straightforward incorporation of the Planck CMB low-$\ell$ data into any Gaussian-likelihood-based analysis. The package is publicly available at \href{https://github.com/nanoomlee/planck-gaussian-lowl}{github.com/nanoomlee/planck-gaussian-lowl}.
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Astrophysics of Galaxies

SMUGGLE-Ring: Evolutionary link between nuclear star cluster and nuclear disk

SungWon Kwak, Mathias Schultheis, Ivan Minchev et al. (+8 more)

We present a high-resolution hydrodynamical simulation of the formation and evolution of nuclear structures in a Milky Way-mass galaxy using the SMUGGLE model. The system naturally develops a bar in isolation of $\approx5$ kpc in length, driving sustained gas inflows toward the center that lead to the formation of a nuclear stellar disk (NSD) and a nuclear star cluster (NSC). By only considering stars born after bar formation, we can cleanly isolate the nuclear structures and recover a clear inside-out growth of the NSD. In line with observations, we find that stellar feedback induces repeated shocks that regulate the size of the nuclear gas disk and drive gas from its outer edge toward the NSC region. Over time, the NSD and NSC share similar mass growth and star formation histories, except during the accretion of a massive star cluster. Our results suggest that both the evolutionary timescale of the bar (and thus of the NSD) and the accretion history of star clusters are essential for obtaining tighter scaling relations for nuclear structures and their host galaxies. Finally, our results favor a lower bulge mass for the Milky Way than that of our model ($B/D\approx 0.045$) to explain the compact size of its nuclear disk.
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All authors SungWon Kwak, Mathias Schultheis, Ivan Minchev, Cristina Chiappini, Woong-Tae Kim, Seungwon Baek, Federico Marinacci, Mark Vogelsberger, Laura V. Sales, Hui Li, Matthias Steinmetz

Solar and Stellar Astrophysics

Three Extremely Metal-Poor stars: discovery of a new CEMP-no star

Partha Pratim Goswami and Aruna Goswami

We have conducted detailed high-resolution spectroscopic studies on three extremely metal-poor (EMP) stars HE 0401-0138, HE 1153-0518 and HE 1246-1344. For the stars HE 0401-0138 and HE 1246-1344, we have estimated the abundances of C, Na, Mg, Ca, Sc, Ti, Cr, Mn, Co, Ni, Sr and Ba along with the upper limits for Li, O, La, Ce, Pr, Nd, Sm, and Eu. For HE 1153-0518, abundances of seven light elements from C through Ni and two heavy elements, Y and Ba, have been derived, together with upper limits for Li, O, and La. Based on their observed abundance patterns, HE 0401-0138 and HE 1246-1344 are classified as normal EMP stars, whereas HE 1153-0518 is identified as a newly discovered CEMP-no star. HE 1153-0518 shows strong carbon enhancement with a high absolute carbon abundance, extreme sodium enrichment, very low neutron-capture element abundances, and a very low carbon isotopic ratio (12C/13C = 2.0). Its spectral energy distribution shows clear infrared excess, indicating the presence of circumstellar dust. The abundance pattern of HE 1153-0518 suggests enrichment by early nucleosynthetic processes, such as faint core-collapse supernovae with mixing and fallback, while the possibility of binary interaction and subsequent internal mixing cannot be ruled out. The discovery and detailed study of HE 1153-0518 add an important object to the small population of high-A(C) CEMP-no stars and provide valuable constraints on early chemical enrichment pathways and the nature of the first generations of stars.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Mapping the star formation peak with LIGO A# and Next-Generation detectors

Divyajyoti, Stephen Fairhurst, Mark Hannam et al. (+1 more)

Measuring the redshift evolution of star formation rate density is crucial in understanding the origin and evolution of galaxies and large scale structure in the universe. It is currently measured with electromagnetic probes, however, these probes often track luminosity, which is then converted to star formation rate (SFR) depending on various factors such as initial mass function, dust extinction, etc. Gravitational waves provide an independent method to constrain SFR at high redshifts by tracking the redshift evolution obtained from analysis of binary black hole mergers. In this study we explore three population models for star-formation combined with an inverse time-delay model and demonstrate that it is possible to obtain bounds on the peak of redshift distribution with a network of upgraded LIGO detectors (such as LIGO-A#). For a year of observation, using simulated signals with a merger rate peak at $z_\text{peak}=1.5$, a network of LIGO detectors at A# sensitivity is able to constrain the peak of merger rate with a precision of $\pm 0.1$. Further, we obtain the results with a next-generation network (of Cosmic Explorer and Einstein Telescope) and conclude that the redshift distribution will be extremely well measured, with a precision of $\pm 0.02$, with future detectors.
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All authors Divyajyoti, Stephen Fairhurst, Mark Hannam, Mukesh Kumar Singh

High Energy Astrophysical Phenomena

Early Multiwavelength Observations of AT 2026fgk: The Luminous Afterglow to Sub-luminous GRB 260310A, Identified Independently of a Gamma-ray Trigger

K. -R. Hinds, A. Y. Q. Ho, Y. Wagh et al. (+103 more)

The origins of sub-luminous ($L_\mathrm{\gamma,\mathrm{iso}} < 10^{49.5}$\,erg\,s$^{-1}$) gamma-ray bursts (GRBs) associated with broad-lined Type~Ic supernovae (Ic-BL SNe) are poorly understood, in part due to the low discovery rate and faint afterglows. Here we present the identification of the optical afterglow of Fermi-GBM-detected GRB\,260310A (AT\,2026fgk) as a rapidly rising ($>1\,$mag\,d$^{-1}$), red ($g-r=0.4$\,mag) transient using the Gravitational-wave Optical Transient Observatory, Large Array Survey Telescope, and Zwicky Transient Facility (ZTF) data streams. We present multiwavelength follow-up observations from the first 50\,days, which reveal that GRB 260310A/AT\,2026fgk was sub-luminous ($L_\mathrm{\gamma,iso}=10^{48.8}\,$erg\,s$^{-1}$); it was the most nearby ($z=0.153$) afterglow identified blindly by an optical survey; and that it is one of the brightest afterglows ever observed at X-ray, optical, and radio (cm to mm) wavelengths. We spectroscopically confirm an underlying Ic-BL SN with properties typical of GRB-SNe ($M_\mathrm{ej}\approx3\,M_\odot$, $E_{\rm K}\approx 10^{52}\,$erg). With basic modeling of the afterglow, including the long optical rise ($\approx10^{3}\,$s), we infer either a low initial Lorentz factor ($\Gamma_0\approx40$) or a slightly off-axis viewing angle ($\lesssim3^\circ$). The host galaxy's mass and star formation rate are similar to the hosts of other sub-luminous GRBs. ZTF's flux-limited survey gives a volumetric rate of AT\,2026fgk-like events of $0.30^{+1.37}_{-0.29}\,$Gpc\,$^{-3}$\,yr$^{-1}$, which is consistent with the on-axis, high luminosity ($L_{\rm \gamma,iso}>10^{49.5}$\,erg\,s$^{-1}$) long-GRB rate. The similarity in the rates strongly constrains the prevalence of low-$\Gamma_0$ bursts and the beaming of the initial relativistic material in GRBs.
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All authors K. -R. Hinds, A. Y. Q. Ho, Y. Wagh, R. Jayaraman, D. A. Perley, G. Waratkar, A. Bochenek, B. P. Gompertz, C. Fremling, J. Rastinejad, N. Sarin, G. Schroeder, R. A. Perley, G. P. Srinivasaragavan, K. Ackley, T. Ahumada, M. F. Aller, I. Andreoni, A. Aryan, S. Belkin, E. C. Bellm, S. Ben-Ami, T. de Boer, M. Bremer, R. P. Breton, S. B. Cenko, K. C. Chambers, T. -W. Chen, C. T. Christy, G. Corcoran, L. Cotter, M. W. Coughlin, F. Cuadra, V. D'Elia, K. De, V. S. Dhillon, Dimple, M. J. Dyer, A. R. Escorial, D. K. Galloway, S. Garrappa, J. H. Gillanders, M. A. Gurwell, X. J. Hall, M. E. Huber, S. Ibrahim, J. C. Jaimes, P. Jakobsson, E. Kammoun, M. Kasliwal, G. K. Keating, T. Killestein, R. Konno, R. Kotak, D. Kovaleva, A. Krassilchtchikov, A. Kraus, A. Kumar, R. R. Laher, A. Levan, J. Lyman, A. Martin-Carrillo, Z. McGrath, P. Minguez, G. Mo, M. Nicholl, K. Noysena, A. Nugent, L. K. Nuttall, P. O'Brien, D. O'Neill, E. O. Ofek, G. S. H. Paek, P. V. de la Parra, D. Polishook, A. Ruiz Del Pozo, G. Pugliese, J. Purdum, M. Pursiainen, G. Ramsay, R. Rao, A. C. Readhead, P. Rekhi, R. Riddle, S. Rose, B. Rusholme, A. Sasli, D. Schiminovich, E. Segre, C. Sevilla, Y. M. Shani, M. Shrestha, S. J. Smartt, K. W. Smith, J. Sollerman, N. Sravan, S. Srivastav, D. Steeghs, R. Stein, T. Surti, K. Ulaczyk, J. C. Vel'azquez, R. Wainscoat, J. L. Wise, D. Xu, S. Yang

Astrophysics of Galaxies

New Measurements of Distances to Galaxies in the NGC 1052 Field with the Hubble and James Webb Space Telescopes: Testing the Bullet-Dwarf Origin of the Trail

Yimeng Tang, Gagandeep S. Anand, Aaron J. Romanowsky et al. (+2 more)

NGC 1052-DF2 and DF4 are two ultra-diffuse galaxies deficient in dark matter (DM), and reported as part of a remarkable linear trail of dwarf galaxies in the NGC 1052 field. Recently, NGC 1052-DF9 has been identified as the third galaxy missing DM along the trail. This structure may have been formed in a high-velocity head-on collision between two gas-rich dwarfs, known as the "bullet-dwarf" scenario. However, the trail overlaps in projection with a foreground system, the NGC 1035 group at $\sim13$ Mpc, raising suspicions that the trail is an artifact of this superposition. DF2 and DF4 have been found to be at distances of $21.7\pm1.2$ and $20.0\pm1.6$ Mpc, respectively, using the tip of the red giant branch (TRGB) method with deep Hubble Space Telescope (HST) imaging, but the distances to other trail dwarfs remain unknown. In this Letter, we use HST imaging to obtain surface brightness fluctuation (SBF) distance estimates for eight candidate trail dwarfs, as well as for the giant galaxies NGC 1052 and NGC 1035. We find that the dwarfs are all at $\sim$20 Mpc, and are not associated with the foreground NGC 1035 group. However, for DF2, we derive an SBF distance of $17.7\pm1.4$ Mpc, inconsistent with the published HST TGRB distance ($21.7\pm1.2$ Mpc). Meanwhile, James Webb Space Telescope (JWST) observations of DF2 offer a second, and potentially more accurate, TRGB distance of $17.6\pm0.6$ Mpc. While this value matches our SBF result, it is clear that uniform JWST imaging of the remaining trail dwarfs is critically needed.
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All authors Yimeng Tang, Gagandeep S. Anand, Aaron J. Romanowsky, Pieter G. van Dokkum, Kevin A. Bundy

Cosmology and Nongalactic Astrophysics

CMB Bounds on Primordial Black Holes via Radiation Capture

Marzieh Farhang and S. M. S. Movahed

We explore the capture of neutrinos and photons in the cosmic neutrino and photon background by primordial black holes (PBHs). We model this phenomenon as a gravitational interaction that effectively modifies the continuity equations for radiation and PBH densities and the cosmic expansion history. We find that the observability of this modified cosmic history is highly sensitive to PBH mass, and only extraordinarily massive PBHs would leave observable trace on the temperature and E-mode polarization of the cosmic microwave background (CMB). Specifically, Planck data restrict PBH abundance to $f_{\rm pbh}\lesssim 10^{-1}$ for PBH masses above $10^{15} M_\odot$, getting considerably tighter for higher masses. We expect substantial improvement as high-resolution measurements of larger CMB multipoles become available. A future cosmic-variance-limited experiment, with $\ell_{\rm max}=7000$, would set $f_{\rm pbh}\lesssim 10^{-1}-8\times 10^{-5}$ (for the fiducial $\Lambda$CDM cosmology) across $10^{13}-10^{18}M_\odot$. These constraints would be comparable to the current limits at the high-mass end of the spectrum [Carr et al, 2026]. The gravitational interaction of PBHS with the cosmic background radiation and its imprints on CMB would thus provide an independent complementary probe of extraordinarily massive PBH abundance.
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Earth and Planetary Astrophysics

The ALMA Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO): Formaldehyde (H$_2$CO) emission and its links to disk properties

Ella Chevalier, Ke Zhang, Miguel Vioque et al. (+7 more)

Protoplanetary disks are rotating structures of gas and dust surrounding young stars, serving as the birth places of planets. Understanding the chemical evolution of organic materials in these disks is key for tracing the origins of organics in planetary systems. Formaldehyde (H$_2$CO) is the most commonly detected organic molecule in protoplanetary disks. In this study, we investigate the emission of H$_2$CO and its link to disk properties, using a sample of 20 Class II disks in the Lupus and Upper Sco star-forming regions spanning over 1-6 Myr. We analyze the H$_2$CO lines at 218.222 and 290.623 GHz observed as part of the AGE-PRO ALMA Large Program. Within this sample we achieve a detection rate of H$_2$CO of 45% (9/20), and set robust upper limits for the non-detections. We measure the excitation temperature and column density of the H$_2$CO gas in the sources with H$_2$CO detections. We combine our sample with 13 additional disks with archival H$_2$CO detections and search for correlations between H$_2$CO properties and disk parameters. Notably, we find strong correlations between H$_2$CO line luminosity and dust radius, gas radius, dust mass, gas mass, stellar mass, and stellar luminosity. This suggests that H$_2$CO emission is brighter for extended massive dust disks where H$_2$CO can form via CO ice hydrogenation on grain surfaces. We find that the H$_2$CO excitation temperature is also correlated with stellar mass and stellar luminosity, so more massive and luminous stars could increase H$_2$CO excitation.
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All authors Ella Chevalier, Ke Zhang, Miguel Vioque, Nicolás T. Kurtovic, Paola Pinilla, James Miley, Dingshan Deng, John Carpenter, Carolina Agurto-Gangas, Anibal Sierra

Solar and Stellar Astrophysics

Observational signatures of thermonuclear electron-capture supernovae – Ne II line strengthening and color evolution as traces of the explosion mechanism

Alexander Holas, Fionntan P. Callan, Samuel W. Jones et al. (+7 more)

Thermonuclear electron-capture supernovae (tECSNe) are a potential fate of certain intermediate mass stars forming ONe cores at the end of their evolution. Simulations suggest that these explosions are a viable alternative to collapse, yet no synthetic observables exist that allow for their identification among observed transients. We present first of their kind synthetic observables of a tECSN simulation, aiming to establish whether these explosions can occur in nature, and investigate potential observational signatures to separate them from similar transients such as pure deflagrations in CO white dwarfs. We carry out 3D photospheric phase and 1D late phase simulations using the radiative transfer code Artis. As input, we use a tECSN explosion simulation and a CO deflagration simulation with comparable $^{56}$Ni production, both computed with the Leafs code. Both models have similar observational characteristics, akin to SNe~Iax-like events. The tECSN ejecta model are characterized by a $M(^{56}\mathrm{Ni})/M_\mathrm{ej}$ ratio $25\%$ lower than that of comparable CO deflagration models. At early times, the tECSN model shows a slower decline in the red colors compared to the CO deflagration due the greater amount of Ti and Cr synthesized in the tECSN explosion. At late times, the tECSN model exhibits an exceptionally strong $12.8\,\mu$m Ne II emission line, that strengthens substantially over time, whereas its strength remains largely unchanged in the CO deflagration. Our results suggest tECSNe could potentially result in SN~Iax-like transients. Importantly, we find no features that are in tension with existing observables. So far, there are no indicators that unambiguously and robustly separate tECSNe from deflagrations in CO white dwarfs. Nonetheless, our work highlights the potential importance of the mid-infrared wavelength range for distinguishing possible explosion mechanisms.
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All authors Alexander Holas, Fionntan P. Callan, Samuel W. Jones, Friedrich K. Roepke, Rüdiger Pakmor, Alexandra Kozyreva, Christine E. Collins, Luke J. Shingles, Stuart A. Sim, Joshua M. Pollin

Instrumentation and Methods for Astrophysics · Cross-listed from cs.LG

Identifying Gems from Roman RAPIDly

Karan Gandhi, Ashish A. Mahabal, Jacob E. Jencson et al. (+6 more)

The Nancy Grace Roman Space Telescope (Roman), set for launch as early as September 2026, will conduct wide-field infrared imaging surveys with unprecedented spatial resolution and cadence, enabling the discovery of millions of astronomical transients. Hence, it is necessary to have automated pipelines for generating alerts in place so that the telescope can begin discovering reliable transients and variable objects soon after it is launched. However, no real Roman data currently exist, making the development of such pipelines difficult. In this work, we present a machine learning model $RuBR$ and a general methodology for distinguishing genuine transient and variable detections from spurious (bogus) detections within the RAPID pipeline. In particular, we present three models using this methodology: $RuBR_{comb}$ trained and tested on combined locally injected and OpenUniverse2024 transients, $RuBR_{loc}$ trained on locally injected transients and tested on OpenUniverse2024 transients, and $RuBR_{DA}$ that combines locally injected transients with a fraction of OpenUniverse2024 transients in domain-adaptation mode for training. This paves the way for strategies to adapt the $RuBR_{comb}$ model to real observations in the absence of any ground-truth labels during the early phases of the Roman mission. While the image differencing pipeline continues to be improved, our experimental results demonstrate the effectiveness of the proposed approach and its promise for robust real-bogus classification in the Roman era.
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All authors Karan Gandhi, Ashish A. Mahabal, Jacob E. Jencson, Russ R. Laher, Ben Rusholme, Lin Yan, Ryan M. Lau, Schuyler D. Van Dyk, Mansi M. Kasliwal

Cosmology and Nongalactic Astrophysics

First Constraints on the Ellipticities of Self-Interacting Fermionic Dark Matter Admixed Neutron Stars from Continuous Gravitational-Wave Searches

Premachand Mahapatra, Andrew L. Miller and Prasanta Kumar Das

We investigate continuous gravitational-wave (CW) emission from rapidly rotating, non-axisymmetric, isolated neutron stars admixed with self-interacting fermionic dark matter (DM) and hosting DM-induced equatorial deformations (“dark mountains”). In particular, we develop a formalism that describes how DM accumulation inside the star changes its structure, how dark mountains arise from an anisotropic distribution of DM inside it, and how the star's moment of inertia and thus the amplitude of its GW emission is increased compared to that of an ordinary neutron star. Moreover, using results from all-sky searches for CWs from non-axisymmetric neutron stars performed with LIGO O3 data, we place the first constraints on the DM-induced ellipticities $\varepsilon$ of DM-admixed neutron stars across the full GW frequency range analyzed by LIGO and for a range of self-interaction strengths. With the same data, we also exclude portions of the DM-mass/self-interaction coupling strength parameter space that would have produced detectable GW signals in LIGO O3 data. We rule out at best (at worst) couplings $g\gtrsim10^{-5.5}$ ($g\gtrsim 10^{-4}$) for DM-admixed neutron stars with ellipticities $\varepsilon=10^{-7}$ ($\varepsilon=10^{-9}$) at distances $d=1$ ($d=10$) kpc away for DM masses of $m_\chi\in[0.1,10]$ GeV. Furthermore, we show that even larger regions of this parameter space will become accessible to next-generation detectors, such as Einstein Telescope and Cosmic Explorer, with exclusions as strong as $g\gtrsim10^{-6}$ for neutron stars located $d=10$ kpc away for $\varepsilon=10^{-7}$. Our results demonstrate that searches for CWs naturally provide a direct probe of dark mountains sustained by DM-admixed neutron stars.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Integrability of $R^2$ gravity cosmological models with radiation

Vsevolod R. Ivanov and Sergey Yu. Vernov

We consider cosmological $R^2$ gravity models with radiation. We find the general solution to the trace equation $\Box R=0$ in the spatially flat Friedmann-Lemaitre-Robertson-Walker (FLRW) metric. We analyze possible evolution of the Hubble parameter depending on the sign of the radiation energy density and find conditions for the existence of a bounce solution. A scalar field Lagrangian with the induced gravity term and the fourth-order monomial potential can play a role of radiation. In this case, we also obtain the general solution to the field equation. Therefore, the resulting $R^2$ gravity model with a scalar field is integrable in the spatially flat FLRW metric. Using a conformal metric transformation, we obtain a two-field chiral cosmological model that is also integrable in the spatially flat FLRW metric.
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Cosmology and Nongalactic Astrophysics

Full Nonlinear Velocity Reconstruction With Transformer and Ensemble Tree Machine Learning

Yulin Gong and Rachel Bean

Accurate reconstruction of peculiar velocities from galaxy positions is important for probing the motion and evolution of large scale structure. They are sensitive to the cosmological effects of gravity and dark sector matter, and complement other velocity inference methods such as the kinematic Sunyaev-Zel'dovich (kSZ) imprinted in the CMB. We show that machine learning methods improve velocity reconstruction by capturing nonlinear contributions. Specifically, we train both a gradient boosting decision tree (GBDT) and a Transformer using multi-scale features to predict the residual between the actual velocity and the estimate from linear theory for both the line-of-sight and transverse components. We evaluate our approach in both periodic box and, more realistic, lightcone settings using mock galaxy catalogs from the AbacusSummit simulations tailored to DESI spectroscopic surveys of luminous red galaxies (LRGs) and emission line galaxies (ELGs). We also assess the impact of redshift uncertainties such as those in Rubin LSST photometry. Both models significantly outperform the linear theory with the Transformer achieving the best performance. They more accurately recover the velocity power spectrum and maintain a higher cross-correlation with the true velocities across a wider range of spatial scales. Finally, we demonstrate two applications relevant to kSZ analyses: estimating cluster pairwise velocity correlations and stacked cluster density profiles. This machine learning framework for nonlinear velocity reconstruction opens up powerful new applications of survey data from DESI, Rubin LSST, Euclid and the Roman Space Telescope.
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Earth and Planetary Astrophysics

An 800-Million-Year-Old Impact Shower on the Terrestrial Planets from the Breakup of the Eulalia Parent Body

William F. Bottke, David Vokrouhlický, Melissa Dykhuis et al. (+1 more)

Multiple studies have proposed a substantial surge in large lunar impacts approximately $800$ million years ago (Ma). Some are based on analyses of the ages of large lunar craters, such as the $93$ km Copernicus crater. Others focus on the age distributions of impact glasses returned by lunar missions. A key challenge has been identifying and testing a plausible source for this putative impact spike. Here we use collisional and dynamical models to link this event to the formation of the Eulalia asteroid family, whose primitive carbonaceous chondrite-like parent body disrupted $\sim 800$ Ma near the 3:1 mean motion resonance with Jupiter (J3:1). Our simulations indicate that approximately three-quarters of the family's fragments eventually entered the J3:1 over a $\sim 150$-million year interval. While some fragments were injected into the resonance immediately after the disruption, others migrated more gradually via non-gravitational (Yarkovsky) thermal forces. Once in the J3:1, the fragments were dynamically transported into the planet-crossing region, leading to an elevated rate of bombardment on the Moon and terrestrial planets. Our results demonstrate that the Eulalia breakup can plausibly account for the observed lunar craters formed near $800$ Ma. Intriguingly, this event may also have had widespread repercussions across the inner Solar System. On Earth, its timing coincides with significant shifts in the biosphere, possibly linked to large impacts. On Mars, these impacts might have triggered a pulse of volcanic activity. Together, they showcase how certain catastrophic collisions in the main belt can have far-reaching consequences for the history of the terrestrial planets.
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All authors William F. Bottke, David Vokrouhlický, Melissa Dykhuis, Nicolle Zellner

Earth and Planetary Astrophysics

Transport of water in a Transient, Impact-Generated Atmosphere on Mercury

Jordan K. Steckloff, David B. Goldstein, Philip L. Varghese et al. (+2 more)

Mercury's polar cold traps host water ice deposits that are likely populated with impact-delivered water via Mercury's exosphere. However, Mercury's near-sun location experiences an extremely high photodestruction rate that rapidly destroys water with a timescale of only ~3.5 hours. Here we use the PLANET DSMC code to investigate the fate of water from a single 1 km radius comet impact striking Mercury's North Pole (30 km/s at angle of 60{\deg}). We find that the evolving plume separates into four distinct phases: 1) an early plume phase in which ballistic escape and photodestruction reach their peaks, 2) a reentry phase in which water falling back toward the surface forms a self-shielded shock-topped atmosphere that migrates across the surface and ballistic loss ceases, 3) a quasi-steady phase in which a self-shielding dawn atmospheric enhancement (DAE) forms and drives, a tenuous migration of exospheric water to the cold traps with a longitudinal dependence, and finally 4) a late phase in which self-shielding ends and photodestruction dominates, effectively ending substantial water migration. In this work, we quantify the fates of the arriving water molecules, and describe some of the more important features of this highly unsteady, evolving three-dimensional atmosphere. We find that 23% of the initial water is photodestroyed, 65% of the water ballistically escapes the system (of which, 79% photodissociates prior to reaching the Hill radius), and 14% ends up in Mercury's cold traps, which is significantly more than the ~5% that migrates to the Moon's cold traps during an equivalent impact.
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All authors Jordan K. Steckloff, David B. Goldstein, Philip L. Varghese, Laurence M. Trafton, Parvathy Prem

Cosmology and Nongalactic Astrophysics

A Measurement of the Thermal and Ionization State of the IGM at $z < 0.5$

Teng Hu, Vikram Khaire, Joseph F. Hennawi et al. (+4 more)

We apply a machine-learning-based inference method that exploits the joint Doppler parameter-column density (b-NHI) distribution from Lya forest decomposition to measure the thermal and ionization state of the intergalactic medium (IGM) in four redshift bins spanning z = 0.06 to 0.48, using 82 archival quasar spectra from the Cosmic Origin Spectrograph (COS) on board Hubble Space Telescope (HST). Our results show that the low-z IGM (z < 0.5) is extremely hot and nearly isothermal, with log(T0/K) = 4.45 (+0.08 / -0.12) [T0 = 28183 (+5700 / -6804) K] and gamma = 1.06 (+0.13 / -0.09) at z = 0.1. This temperature lies approx 7sigma (and 7 times) above the canonical prediction (log T0 approx 3.60, i.e. T0 ~ 4000 K, with gamma ~ 1.6 at z = 0), where the IGM is expected to have cooled long after He II reionization. We also measure the hydrogen photoionization rate to be log (GammaHI/s^-1) = -13.70 (+0.10 / -0.08) at z = 0.1, which is about approx 4sigma below the range predicted by current UV-background synthesis models (approx -13.3). To investigate the discrepancy between these high temperatures and theoretical models, we assess the impact of small-scale turbulence. By exploring a parameter grid in turbulent velocity (vtur) and GammaHI, we find that a standard IGM thermal and ionization state combined with unresolved turbulence of vtur simeq 15 km s^-1 can successfully reproduce the observed line widths at z = 0.1. Comparisons with high-resolution Space Telescope Imaging Spectrograph (STIS) expanded data indicate that the observed line widths are unlikely to be caused by instrumental resolution effects. Our findings suggest that either new heating mechanisms or unresolved turbulence are required to explain the unexpectedly broad Lya lines observed in the low-z IGM.
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All authors Teng Hu, Vikram Khaire, Joseph F. Hennawi, Todd M. Tripp, Jose Onorbe, Michael Walther, Zarija Lukic

Cosmology and Nongalactic Astrophysics

Neutrino mass constraints in interacting dark energy models after DESI DR2

Hui Li, Guo-Hong Du, Tian-Nuo Li et al. (+4 more)

Recent DESI observations indicate a deviation from the $\Lambda$CDM model, showing a preference for dynamical dark energy and thereby relaxing the upper limit on the neutrino mass within this framework. This deviation can also be explained by the presence of an interaction between dark energy and dark matter. In this work, we investigate the cosmological upper bounds on the total neutrino mass ($\sum m_{\nu}$) across four different interacting dark energy (IDE) models. The present analysis employs the latest DESI baryon acoustic oscillation, cosmic microwave background, and type Ia supernova datasets. These results demonstrate that the upper bounds on $\sum m_{\nu}$ exhibit profound sensitivity to the specific phenomenological formulation of the interaction term. While the I$\Lambda$CDM2 model ($Q \propto H \rho_{\mathrm{c}}$) substantially relaxes the stringent upper limit ($\sum m_{\nu} < 0.129$ eV at 95% confidence level), notably the I$\Lambda$CDM3 model ($Q \propto H_0 \rho_{\mathrm{de}}$), severely compresses the allowed parameter space, yielding a highly restrictive bound of $\sum m_{\nu} < 0.051$ eV. Furthermore, rigorous goodness-of-fit evaluations utilizing the Deviance Information Criterion and $\Delta\chi^2_{\mathrm{MAP}}$ indicate that the current observational data statistically favor these mass-suppressing IDE models. This establishes an exacerbated statistical tension between the observationally preferred IDE scenarios and the normal hierarchy lower bound ($\sim 0.06$ eV) determined by terrestrial neutrino oscillation experiments.
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All authors Hui Li, Guo-Hong Du, Tian-Nuo Li, Hai-Li Li, Lu Feng, Jing-Fei Zhang, Xin Zhang

Solar and Stellar Astrophysics

Deep Learning with Magnetic Parameter Constraints for Short-Term Prediction of Solar Active Region Vector Magnetic Fields

Yuqing Zhou, Hui Liu, Zhenyu Jin et al. (+5 more)

Forecasting the dynamic evolution of solar magnetic fields is a critical technique for enabling space weather warnings. Addressing the limitations of existing methods in predicting all vector magnetic field components and in maintaining consistency with solar surface magnetic-field-related quantities, this study proposes a deep learning prediction method that integrates dynamic masks of active regions with multiple magnetic parameter constraints. By constructing a three-channel representation of vector magnetic fields, applying dynamic masks to enhance attention to strong-field regions, and incorporating multi-parameter magnetic parameter constraints, we developed an end-to-end short-term (12-hour) predictive model of solar vector magnetic field evolution. Using SDO/SHARP vector magnetogram data, the model predicts and analyses field evolution across all components. Quantitative evaluations demonstrate that our approach achieves horizon-averaged structural similarity index measure (SSIM) of 0.912 (per-hour range: 0.909–0.916) and correlation coefficient (CC) of 0.998 for the radial component Br (root-mean-square error (RMSE) 13.0–21.0 G); the horizontal components achieve Bphi SSIM 0.760–0.800 (CC 0.910–0.945, RMSE 38.5–50.0 G) and Btheta SSIM 0.728–0.750 (CC 0.895–0.920, RMSE 38.5–49.0 G). The model maintains unsigned magnetic flux prediction errors at 7.82% (95% confidence interval (CI): +/-0.11%). These results demonstrate strong image-domain performance together with consistency under the magnetic-parameter diagnostics used here, suggesting initial potential for supporting future space weather forecasting efforts.
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All authors Yuqing Zhou, Hui Liu, Zhenyu Jin, Yuyang Li, Sizhong Zou, Jiaben Lin, Mingfu Shao, Zhuoheng Huang

Solar and Stellar Astrophysics

Full-Disk Spectroscopy of the Solar Corona Across a Solar Cycle with Hinode/EIS

James McKevitt, Ignacio Ugarte-Urra and Peter R. Young

The structure and dynamics of the solar corona evolve with the Sun's magnetic cycle, yet how this variability manifests in the disk-integrated, Sun-as-a-star observables used in stellar activity studies remains poorly constrained. We compile 18 full-disk spectroscopic mosaic scans made by Hinode/EIS spanning 2013-2024, covering solar cycle 24 and the rise of solar cycle 25, and probe coronal plasma variability through the integrated and spatially resolved intensity, Doppler velocity, and non-thermal velocity of log T~6.2 plasma in active regions and the quiet Sun. Disk-integrated coronal intensity is strongly correlated with the solar cycle, consistent with stellar observations. No clear solar-cycle variation is found in the distributions of coronal Doppler or non-thermal velocity in either active regions or the quiet Sun, though their total intensities do track the cycle. Active region intensity per unit solid angle shows a moderate correlation with solar cycle. Taken together, these results support the hypothesis that Sun-as-a-star coronal intensity variability across the solar cycle is driven primarily by the changing fraction of the disk occupied by active regions, rather than by changes in the log T~6.2 plasma properties of those regions. The well-established correlation between upflowing plasma and elevated non-thermal line broadening in active regions persists throughout the cycle, implying that the underlying kinematic properties of active region plasma are insensitive to the global magnetic field configuration, a result with direct implications for the interpretation of coronal activity cycles on solar-like stars.
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Instrumentation and Methods for Astrophysics

An update to Allocating Time on Scientific Platforms in Outer Space using five cycles of JWST General Observer programs

Christopher Williams

Allocating Time on Scientific Platforms in Outer Space (Williams, 2025 in Research Policy) explored time allocated to astronomers to use the James Webb Space Telescope (JWST). It was based on data from the first three Cycles of General Observer (GO) programs (2022, 2023 and 2024) and used multi-variable regression modelling. Analysis provided support for progress towards reducing bias in time allocation decisions in terms of Principal Investigator (PI) gen-der, institution and country. It also provided strong evidence that higher time allocation is linked to larger teams and data non-exclusivity. However, a question was raised concerning a possible swing towards long-standing PI gender bias as the Cycles progressed, i.e., that equality might only be temporary. In addition, the possibility of a Trump-era effect on time allocation bias towards USA PIs could not be tested as data predated 2025. Furthermore, changes in telescope allocation committee policy and the potential effect of telescope overhead changes were not fully assessed. The current research note provides an update by using the latest Cycles and expands the sample to Cycles 1 to 5 (n=1208 JWST programs) to provide tentative answers to these unresolved issues. While there is strong support to the overall findings for Cycles 1 to 3, we now note the emergence of USA PI and prior JWST experience as positive determinants of time allocation in regression models. The updated analysis also provides new insights concerning bias in the extra-galactic scientific categories.
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High Energy Astrophysical Phenomena

Bridging Roche Lobe Overflow and micro-TDEs: The Runaway Evolution of Eccentric Mass Transfer in Star-Black Hole Binaries

Tian-Shun Chen and Dong Lai

Binary systems may undergo mass transfer while maintaining significant orbital eccentricities. Stellar-mass black holes (sBHs) can strip stars on eccentric orbits and produce micro-tidal disruption events (micro-TDEs). While previous hydrodynamical studies have focused on compact systems on the verge of disruption, the transition between self-regulated eccentric mass transfer and runaway disruption remains poorly understood. We present SPH simulations of a Sun-like star interacting with a $10\,M_\odot$ sBH across a range of initial eccentricities ($e_0=0.30$–$0.70$) and pericenter distances ($b_0=3.33$–$3.57$ in units of the tidal radius), tracking the systems for tens to over 100 orbital periods. Our results reveal that these binaries can evolve along two distinct pathways, dictated by the competition between mass-transfer-driven stellar expansion and orbital widening: (i) Runaway disruption ($b_0\lesssim 3.45$), in which mass loss at pericenter drives adiabatic expansion of the stellar envelope, leading to unstable Roche-lobe overflow and runaway disruption of the star. The stripped debris forms a thick accretion flow with hyper-Eddington accretion rates onto the sBH, potentially powering fast X-ray/UV or blue/optical transients. (ii) Stable mass transfer ($b_0\gtrsim 3.57$), in which the binary settles into a long-lived, stable mass-transfer phase lasting up to 150 orbits (the limit of our simulation), regulated by orbital expansion from pericenter mass loss. These eccentric mass-transfer events could manifest observationally as repeating, quasi-periodic flares.
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Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

The geometry of lunar gravitational wave detection

Jacopo Tissino, Filippo Santoliquido, Francesco Iacovelli et al. (+9 more)

The Lunar Gravitational Wave Antenna (LGWA) is a planned gravitational wave detector on the Moon, targeting the deci-Hertz band and expected to deliver breakthrough discoveries across several science cases, including the Moon's interior structure and astrophysics. In this work, we show that adopting a frame comoving with the Solar System barycenter (SSB), but with its origin at a location that minimizes timing uncertainty, reduces the sampling time by an order of magnitude. We present a systematic post-processing procedure to identify the optimal origin within the Solar System for any given signal. We explore alternative timing parametrizations beyond the merger time, and find that they have only a minor impact on parameter uncertainties. Using the stellar-mass black hole binary GW250114 as a case study, we illustrate how these geometrical considerations translate into improved parameter constraints. Two minutes before its merger, the LGWA would have measured its chirp mass to a precision of 0.0002 solar masses (90% symmetric) and constrained its sky position to within 65 square degrees (90% HPD area); these constraints are tighter than those obtained by the LIGO-Virgo-KAGRA (LVK) detectors, despite a lower signal-to-noise ratio. We connect our results to an analytical approximation proposed by Wen and Chen, which relates the area spanned by the orbital motion of a detector to its efficacy in constraining the sky position of a source. We verify its qualitative validity for compact binary sources with a series of injections, identifying the regimes in which its underlying assumptions break down. Our results demonstrate that inference for long-duration GW signals with the LGWA must be treated as a geometrical problem, in which detector motion, reference-frame choice, and signal evolution jointly determine both parameter constraints and computational efficiency.
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All authors Jacopo Tissino, Filippo Santoliquido, Francesco Iacovelli, Ulyana Dupletsa, Tito Dal Canton, Matteo Ballelli, Ansh Chopra, Luis Enrique Espinosa Castro, Laura Pezzella, Matteo Schulz, Izumi Takimoto Schmiegelow, Jan Harms

Instrumentation and Methods for Astrophysics

Posterior sampling in the Age of Emulators

Andreas Nygaard, Luca Janken, Steen Hannestad et al. (+1 more)

We investigate posterior sampling strategies for cosmological parameter inference using fully differentiable neural-network likelihood emulators, which provide both rapid likelihood evaluations and automatic differentiation. We compare Metropolis–Hastings (MH), the Metropolis-Adjusted Langevin Algorithm (MALA), Hamiltonian Monte Carlo (HMC), the No U-Turn Sampler (NUTS), and Affine Invariant Ensemble Sampling (AIES) using likelihood emulators constructed with the CLiENT framework. The methods are tested on emulators of both the $\Lambda$CDM model and a sterile-neutrino extension. While NUTS generally converges in the fewest samples, its higher computational cost reduces this advantage when performance is measured by wall time. As a result, MALA and even standard MH remain highly competitive. We further find that whitening and covariance adaptation substantially improve sampling efficiency. The TensorFlow implementations developed for this work are released as the BEST (Batched Emulator Sampling with TensorFlow) package, providing a general framework for sampling arbitrary TensorFlow likelihood functions. The package is available through PyPI as 'best-inference' and on GitHub (at https://github.com/AndreasNygaard/best-inference.git).
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All authors Andreas Nygaard, Luca Janken, Steen Hannestad, Thomas Tram

High Energy Astrophysical Phenomena

$E_{\rm peak}$-$\alpha$ Correlation in Time Resolved GRB Spectra: A Bottom-Up Approach with Optically Thin Inverse Compton Scattering Model

Pragyan Pratim Bordoloi, Ayush Shivkumar and Shabnam Iyyani

Gamma-ray bursts (GRBs) are the brightest explosions in the Universe, yet the origin of their emission remains uncertain. Time-resolved spectral analysis offers key insights into the evolution of spectral shapes, constraining both radiation mechanisms and emission-site microphysics. Observationally, GRB spectra are well described by the empirical Band function, characterized by the peak energy ($E_{\mathrm{peak}}$) and low-energy spectral index ($\alpha$). We investigate the temporal evolution of spectra produced by optically thin inverse-Compton scattering (ICS) within a standard fireball jet framework, focusing on the scenarios that can produce the two commonly observed spectral evolution patterns: hard-to-soft evolution and intensity tracking, within a single emission pulse. The evolution is analysed using both Bayesian block and constant-fluence binning, with the observed spectrum modeled consistently using the Band function. Using this bottom-up approach, we find that optically thin ICS yields a positive $E_{\mathrm{peak}}$-$\alpha$ correlation, with $\alpha$ evolving from hard (Planck-like, $> +0.5$) to softer ($< -0.67$) values. Such hard $\alpha$ values are inconsistent with standard synchrotron emission. This characteristic evolution in the $E_{\mathrm{peak}}$-$\alpha$ plane, therefore, provides a diagnostic signature of optically thin ICS as the dominant radiation mechanism during the prompt phase of GRBs. Furthermore, this type of smooth evolution of $\alpha$ within a single pulse does not require invoking a transition between different radiation mechanisms, unless additional observational evidence supports such a change.
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