Instrumentation and Methods for Astrophysics
Low-Noise SiPM Light Readout and ASIC-Based Charge Readout of a Liquid Argon Time Projection Chamber for MeV Gamma-Ray Measurements
Satoshi Takashima, Hirokazu Odaka, Shota Arai et al. (+25 more)
We have developed a compact
liquid argon time projection chamber (LArTPC), NanoGRAMS, as a technology demonstrator for the Gamma-Ray and AntiMatter Survey (GRAMS). LArTPCs have the potential to enable Compton cameras with unprecedented effective area in the MeV gamma-ray band. NanoGRAMS has an active volume of $5.12 \times 5.12 \times 10~\mathrm{cm^3}$ and is equipped with a low-noise scintillation and charge readout system. The scintillation light is detected by an array of 16 SiPMs ($6 \times 6~\mathrm{mm^2}$ each), whose signals are summed and amplified by a low-noise transimpedance amplifier operable at
liquid argon temperature. Ionization electrons are read out with $3.2\,\mathrm{mm}$-pitch pixels and processed by VATA-SGD ASICs, with synchronization provided by an FPGA-based data acquisition system. We irradiated the detector with a $^{60}\mathrm{Co}$ source (1173 and $1332\,\mathrm{keV}$) and successfully detected both 1-hit and 2-hit events. The collected charge was converted to deposited energy using a phenomenological recombination model, and the detector response was evaluated with a Geant4-based Monte Carlo simulation. The reconstructed energy spectrum shows Compton edges at 963 and $1118\,keV$, consistent with the expected values. For 2-hit events, the sequence of interactions was identified, and the reconstructed back-projection image agrees with the source position. These results demonstrate the feasibility of NanoGRAMS as a Compton camera for MeV gamma-ray imaging spectroscopy.
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All authors Satoshi Takashima, Hirokazu Odaka, Shota Arai, Kentaro Shirahama, Ryutaro Tatsumi, Hodaka Kawamura, Masashi Tanaka, Shintaro Arai, Tsuguo Aramaki, Aya Bamba, Lorenzo Fabris, Georgia Karagiorgi, Haruki Kuramoto, Jonathan LeyVa, John W. Mitchell, Aiko Miyamoto, Reshmi Mukherjee, Kaito Murakami, Azuki Nagao, Arathi Suraj, Sayana Takatsuka, Chihiro Watanabe, Shin Watanabe, Yutaro Yano, Kazushi Yawata, Hiroki Yoneda, Kohei Yorita, Jiancheng Zeng
High Energy Astrophysical Phenomena
Chandra and XMM-Newton X-ray Study on the Core-collapse Supernova Remnant N63A in an H II Region
Hanxiao Chen, Yang Chen, Lei Sun et al. (+1 more)
N63A is one of the brightest
supernova remnants (SNRs) in the Large Magellanic Cloud and provides an excellent laboratory for studying SNR
evolution in an H II region. We present a detailed X-ray analysis of N63A using Chandra and XMM-Newton observations, combining both imaging and high-resolution spectroscopy. Our global spectral fitting reveals three distinct thermal
plasma components with temperatures $kT$$\sim$0.3, 0.7, and 1.5 keV. Spatially-resolved spectroscopy with Chandra shows substantial variations in physical parameters across the remnant, with the eastern lobes of the optical nebula exhibiting significantly higher ionization timescales than the western region. These multi-temperature
plasma components indicate that N63A is evolving in a cloudy interstellar medium: the low-temperature component arises from evaporated dense cloudlets that are engulfed by the blast wave, the intermediate-temperature component represents shocked inter-cloud medium, and the highest-temperature component likely results from the shocks reflected by the clouds. We estimate a Sedov age of approximately 4.5 kyr and an explosion energy of about $4\times10^{51}$ erg. Comparison of the observed abundance ratios and masses of metal elements with the nucleosynthesis models constrains the progenitor mass to approximately $20 M_{\odot}$, supporting a single-
star core-collapse origin for N63A.
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All authors Hanxiao Chen, Yang Chen, Lei Sun, Jianbin Weng
Solar and Stellar Astrophysics
Bayesian Inference of Stellar r-Process Abundances
Jan Kuske, Almudena Arcones and Isak Svensson
The abundances of heavy elements observed in metal-poor, r-process-enhanced
stars provide unique information about the astrophysical conditions in which the rapid
neutron-capture process (r-process) occurs. We present a
Bayesian framework to infer these conditions from
stellar abundance patterns. Building on a large site-independent r-process survey, we use a Markov chain Monte Carlo (MCMC) sampler to fit observed abundances with weighted superpositions of abundances from nucleosynthesis calculations, each parameterized by an initial electron fraction,
entropy, and expansion timescale. Applying this framework to the nearly complete r-process template
star HD222925, we find that two components are required: A heavier H-component producing elements from the second to the third peak and a lighter L-component producing elements from the first to the second peak. Increasing the number of components does not significantly improve the agreement with observations. Extending the analysis to the limited-r
stars HD128279 and HD122563, and to the
solar r-process residuals, we find that their abundances can be reproduced by almost the same two components, albeit with different relative weights. Moreover, the lightest
neutron-capture elements ($Z \lesssim 35$) in the Sun require additional contributions absent in HD222925. Residual discrepancies are concentrated in elements sensitive to observational systematics (e.g., Ag and Cd) or
nuclear-physics inputs (around the third peak). Our study highlights the power of combining
stellar abundances with nucleosynthesis calculations to constrain the astrophysical conditions of the r-process, and motivates further improvements in both observational data and
nuclear-physics inputs.
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Solar and Stellar Astrophysics
Direct detections of white dwarfs in four WD+dM post-common envelope binaries within 20 pc
Mairi W. O'Brien, David J. Wilson, Pier-Emmanuel Tremblay et al. (+5 more)
Characterising post-common envelope binaries (PCEBs) containing a white
dwarf and a main-sequence companion is essential for improving theories of binary
evolution. This paper presents the first direct spectroscopic confirmations of the white
dwarf components in four PCEB systems within 20 pc of the Sun: G 203-47, GJ 207.1, LHS 1817, and Wolf 1130. To detect the white
dwarfs we obtained near-UV spectroscopy from STIS on the Hubble Space
Telescope, fitting with white
dwarf models and M
dwarf proxy spectra. We provide estimates of the white
dwarf effective temperatures, which range from approximately 5300 K to 6300 K. We compare these parameters to those determined from modelling with photometry alone, and find a 5 - 8 per cent discrepancy, due to emission features. Notably, 27 years after its initial detection, we confirm the presence of a white
dwarf in G 203-47, which is the ninth closest white
dwarf to the Sun. Using Swift XRT data, we find that despite the 14.9-day orbital period of G 203-47, it is not tidally locked, possessing a rotation period likely exceeding 100 days, and making it a rare example of a long-period PCEB formed via a brief common envelope interaction. We update the local white
dwarf space density to (5.2 $\pm $0.4) $\times$ 10$^{-3}$ pc$^{-3}$, and compare our results to models from the Binary Populations and Spectral Synthesis (BPASS) framework, finding a good agreement with the predicted and observed numbers of PCEBs within 20 pc.
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All authors Mairi W. O'Brien, David J. Wilson, Pier-Emmanuel Tremblay, Boris T. Gänsicke, Conor M. Byrne, Felipe Lagos-Vilches, J. Sebastian Pineda, Joaquín A. Barraza-Jorquera
High Energy Astrophysical Phenomena
Search for GeV gamma-ray emission from PSZ G181.06+48.47 galaxy cluster using Fermi-LAT data
Anuja Deshpande, Siddhant Manna and Shantanu Desai
We present a search for high energy gamma rays in the energy range from 1–300~GeV from the
galaxy cluster PSZ2~G181.06+48.47 using 17.9~years of
Fermi-LAT data. A binned likelihood analysis employing the 16-year source catalog reveals a significant $\gamma$-ray excess at the cluster position. Modelling the emission as a point source yields a detection with $\mathrm{TS}=19.0 (4.3 \sigma)$, a
photon index of $\Gamma=3.20 \pm 0.62$, and an integrated
photon flux of $(9.75\pm2.74)\times10^{-11}\,\mathrm{ph\,cm^{-2}\,s^{-1}}$, but leaves statistically significant residual emission at the cluster center. Replacing the point-source hypothesis with a RadialGaussian spatial template significantly improves the fit, with a preferred width of $\sigma=0.4^{\circ}$ and an extension significance of $\mathrm{TS}_{\rm ext}=36.8 (6.0\sigma)$. The adopted Gaussian model yields a source detection significance of $\mathrm{TS}=55.0 (7.4\sigma)$, a
photon index of $\Gamma=2.62\pm0.26$, and an integrated
photon flux of $(3.22\pm0.50)\times10^{-10}\,\mathrm{ph\,cm^{-2}\,s^{-1}}$, while reducing the residual emission at the cluster position to a level consistent with zero. The cluster spectral energy distribution shows significant emission only in the lowest energy interval (1.0–3.13~GeV), while all higher-energy bins are consistent with upper limits, indicating a soft $\gamma$-ray spectrum with no evidence for emission above $\sim5$~GeV. These results provide strong evidence that the $\gamma$-ray emission associated with PSZ2~G181.06+48.47 is spatially extended on a scale of $\sigma\approx0.4^{\circ}$ and is more consistent with diffuse intracluster emission than with a single unresolved point source.
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Solar and Stellar Astrophysics
The white dwarf population of open clusters and their tidal tails. Tracers of contamination and stellar interactions
Vikrant V. Jadhav, Pavel Kroupa, David R. Miller et al. (+3 more)
Recent
Gaia studies have identified numerous open clusters (OCs) &
tidal tail catalogues, enabling systematic searches for white
dwarfs (WDs) associated with clusters & their extended structures. We compile a literature-based sample of OC-WD pairs to validate WD membership in cluster cores & tails, investigate the initial-final mass relation (IFMR), identify WDs formed through non-canonical
evolution, and interpret the observed WD populations using a grid of N-body simulations. We combine
Gaia DR3 cluster & tail catalogues with UV-IR photometry to analyse the OC-WD pairs. WD masses, cooling ages, radii, temperatures & luminosities are estimated using colour-magnitude diagrams & spectral energy distributions. These observations are interpreted in the context of N-body simulations. We identify 235 OC-WD pairs (99 in tails) in 80 clusters. More than 28% of the pairs are likely spurious, with contamination substantially higher in the tails (>48%) than in the cluster cores (>13%), indicating significant field-
star contamination in current
Gaia-based catalogues. The Pleiade tails also show severe contamination by old WDs. Simulations predict that the fraction of core WDs increases with cluster age, reaching >10%, whereas the observed fractions remain systematically lower, consistent with the WD deficit problem. Despite the high contamination rate, most tail WDs (~83%) are consistent with having been born inside the
tidal radius. We also identify 63 candidate binary-origin WDs & 47 new IFMR candidates. WDs provide a powerful probe of contamination in cluster and tail catalogues and place important constraints on cluster detection methods & N-body simulations. Resolving the WD deficit and improving membership validation will require improved observations, membership methods, WD physics, and spectroscopic follow-up, enabling stronger constraints on dynamical cluster
evolution & the WD IFMR.
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All authors Vikrant V. Jadhav, Pavel Kroupa, David R. Miller, Snehalata Sahu, Dinnbier Frantisek, Ladislav Šubr
Cosmology and Nongalactic Astrophysics
Cosmology from Nx2pt Analyses of SKAO Wide-Area Surveys
Ian Harrison, Ziad Sakr, Giulia Piccirilli et al. (+7 more)
SKAO surveys will provide an unprecedented window into the large-scale structure of the universe through HI 21cm
galaxy and intensity mapping surveys, and
radio continuum surveys. We present forecasts for the cosmological constraining power of “$N\times2\mathrm{pt}$” analyses – which combine
galaxy clustering,
galaxy weak
lensing,
galaxy-
galaxy lensing signals and 21cm Intensity Maps. By assuming cosmology surveys from an SKA-Mid AA4, we show that such an $N\times2\mathrm{pt}$ analysis will be able to deliver measurements of $\sim1\%$ precision on $\Lambda$CDM cosmological parameters. We also explore dynamical dark energy in the $w_0, w_a$ model, the sum of
neutrino masses $\rm M_\nu$, and the background
curvature $\Omega_{\rm k}$.
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All authors Ian Harrison, Ziad Sakr, Giulia Piccirilli, Chandra Shekhar Saraf, Jacobo Asorey, Benedict Bahr-Kalus, José Fonseca, Marina Migliaccio, David Parkinson, Cora Uhlemann
Astrophysics of Galaxies
A Compact Proto-group at $z \sim 5$: A Massive Galaxy Caught in Formation
Ronaldo Laishram, Yusei Koyama, Fengwu Sun et al. (+11 more)
We report the discovery of SCGG-z5, a compact
galaxy proto-group at $z = 4.97$ in the MACS0416 field, identified from the SAPPHIRES Early Data Release. Six members are spectroscopically confirmed via H$\alpha$ emission, spanning $4.96 \leq z_{\rm spec} \leq 4.98$ within a projected diameter of $\sim16$ pkpc. Spectral energy distribution (SED) fitting yields individual
stellar masses $8.4 \leq \log(M_*/M_{\odot}) \leq 9.8$, a total group
stellar mass of $\log(M_*/M_{\odot}) = 10.07 \pm 0.04$; three of the six members lie above or on the
star-forming main sequence at $z \sim 5$, by up to $0.5$ dex. Pixel-by-pixel analysis reveals diverse resolved radial
star-formation profiles: three members show declining specific SFR radial profiles and outward-rising
stellar age gradients, consistent with inside-out
stellar mass growth, while the most massive member shows a tentative inverted sSFR profile suggestive of reduced central
star formation. The line-of-sight velocity dispersion over all six members is $\sigma_v = 375^{+55}_{-195}$ km s$^{-1}$. The projected mass
estimator yields $\log(M_{\rm PM}/M_{\odot}) \approx 12.30^{+0.30}_{-0.25}$, consistent with a dark-matter-dominated group
halo. EAGLE simulations of structurally similar groups predict full coalescence by $z \sim 3$–$4$, with the merged remnant reaching $\log(M_*/M_{\odot}) > 11$ by $z \sim 1$, consistent with SCGG-z5 representing a rare pre-coalescence phase of early massive
galaxy formation, possibly tracing the assembly of a future brightest group or cluster
galaxy.
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All authors Ronaldo Laishram, Yusei Koyama, Fengwu Sun, Takahiro Morishita, Yoshinobu Fudamoto, Haruka Kusakabe, Jakob M. Helton, Xiaojing Lin, Tadayuki Kodama, Eiichi Egami, Kosuke Takahashi, Ryo Albert Sutanto, Novan Saputra Haryana, Zhengyi Chen
High Energy Astrophysical Phenomena
Determination of neutron star radius from pulse profile modeling using profile likelihood
Vyaas Ramakrishnan and Shantanu Desai
In recent years, NICER data have been extensively used to determine
neutron star masses and radii using pulse profile modeling. Pulse profile modeling is implemented with the X-PSI package and the best-fit parameters are typically obtained using
Bayesian inference. Using simulated data, we demonstrate the first ever application of frequentist inference to determine the
neutron star radius, where the nuisance parameters are treated using profile likelihood. We find that the profile likelihood technique can recover the true radius to $< 1\sigma$. The uncertainty in the estimated radius is also comparable to that obtained from
Bayesian analysis while being computationally much faster. Therefore, this work serves as a proof-of-principle application of frequentist inference to estimate the
neutron star radius using pulse profile modeling and complements the
Bayesian inference technique currently used. We have also made our analysis codes for frequentist inference using X-PSI publicly available.
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Cosmology and Nongalactic Astrophysics
Reconstruction of Primordial Power Spectrum from Gravitational Waves of High-Redshift Black Hole Binaries
Qianhang Ding, Xinpeng Wang, Masahide Yamaguchi et al. (+1 more)
High-
redshift binary black hole (BBH) events are promising candidates for
primordial black holes (PBHs) detectable by next-generation gravitational wave (GW) detectors. A redshifted mass distribution of detected PBH candidates can be obtained from GW observations, from which the underlying PBH mass function can be reconstructed. In this work, we develop a framework that applies the gradient-descent method to the observed redshifted mass distribution and reconstructs the PBH mass function and, subsequently, the
primordial power spectrum (PPS) on small scales. As an illustrative application, we analyze BBH events in the LIGO–Virgo–KAGRA (LVK) catalogs under a specified PBH selection criterion. We find a regularization-stable candidate bump-like enhancement of order $\mathcal{O}(10^{-2})$ in the reconstructed PPS, centered around $k_{\mathrm{peak}}\simeq 5.7\times 10^5~\mathrm{Mpc}^{-1}$ under the adopted assumptions. Our results demonstrate the feasibility of reconstructing the small-scale PPS from high-
redshift BBH observations with next-generation GW detectors.
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All authors Qianhang Ding, Xinpeng Wang, Masahide Yamaguchi, Ying-li Zhang
Cosmology and Nongalactic Astrophysics
O5 dark-siren forecasts for modified GW propagation: background robustness of the $\Xi$ posterior
Zhaorui Zhang and Hong-Bo Jin
Binary black hole mergers without electromagnetic counterparts are expected to dominate O5 gravitational-wave catalogs. Recent CHIMERA~2.0 forecasts typically fix $\Omega_m$ to a CMB-informed value and use spectroscopic hosts when available, but the corresponding sensitivity of the $\Xi$ posterior has not been assessed for pure dark sirens on the public O5 mock catalog. We analyze 300 O5-sensitivity mock events without
galaxy catalogs, varying $\Omega_m$ over $[0.20,\,0.35]$ (including Planck $0.315$), and compare fixed-background inference with joint $(H_0,\,\Omega_m,\,\Xi)$ inference. The marginalized $\Xi$ posterior is $0.9783 \pm 0.3548$ and shows no change across this interval. Only GW luminosity distances enter the analysis, so the likelihood constrains $\Xi\, D_L^{\rm EM}(H_0,\,\Omega_m)$; when $\Omega_m$ is changed, $H_0$ shifts to compensate and the $\Xi$ marginal remains unchanged. Joint inference gives $\Xi^{\rm joint} = 0.9550 \pm 0.3710$, with $|\rho| \lesssim 0.05$ for the $\Omega_m$–$\Xi$ and $H_0$–$\Xi$ pairs, whereas $\rho_{H_0 \Omega_m} \simeq -0.4$ and the $H_0$ median moves by $\simeq 4.2\,{\rm km\,s^{-1}\,Mpc^{-1}}$ over the adopted $\Omega_m$ range.
Galaxy-catalog analyses on the same events at fixed $\Omega_m = 0.3$ reach $\sim 7.5\%$ precision on $\Xi$, compared with $\pm 36.3\%$ here; the larger uncertainty is driven mainly by missing host
redshifts. Sub-percent $\Xi$ tests will therefore still require measured
redshifts even if dark sirens dominate the detection rate.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Evading Cosmological Strong Coupling in Non-minimally Coupled Vector Gravity
Antonio De Felice, Seishi Enomoto, Nagisa Hiroshima et al. (+1 more)
Recent analyses of Proca theories with non-minimal
curvature couplings have uncovered an additional scalar degree of freedom with an identically vanishing propagation speed, $c_s^2=0$, signaling a scale-dependent strong-coupling problem. In this Letter, we show that an additional derivative interaction can lift this zero-speed degeneracy and restore a non-degenerate quadratic dynamics for the scalar perturbations. In an open region of parameter space, the scalar kinetic
matrix is positive definite and the high-frequency propagation speeds are real and positive. At quadratic order, this removes the specific signature of strong coupling associated with the $c_s^2=0$ mode. We also uncover a non-uniform limit as the temporal vector condensate approaches zero: at fixed nonzero $A_0$, the formal extreme-ultraviolet regime develops a ghost, while the kinetic structure of the exactly vanishing-condensate branch is different. The momentum scale at which this ghost appears is pushed toward increasingly high values as $A_0\to0$. Whether the ghost scale ultimately lies above the EFT cutoff depends on an independent determination of the EFT cutoff. Finally, we identify a stable de Sitter fixed point with $A_0\neq0$, surrounded by a finite region in which the scalar no-ghost and high-frequency stability conditions remain satisfied.
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All authors Antonio De Felice, Seishi Enomoto, Nagisa Hiroshima, Atsushi Naruko
Cosmology and Nongalactic Astrophysics
The Environmental Dependence of Halo Intrinsic Alignments: Stronger Signals in Underdense Regions
Masaya Ichikawa, Jingjing Shi, Toshiki Kurita et al. (+3 more)
The intrinsic
alignment (IA) of
galaxies and the dark matter
haloes that host them is one of the leading astrophysical systematics for weak-
lensing cosmology, yet how the IA signal depends on the large-scale environment in which
haloes reside is not yet fully characterised. We use the high-resolution $N$-body simulations of the Dark Quest suite to measure the environmental dependence of the IA of dark matter
haloes over the
redshift range $z=0.1$–$1.5$. We quantify each
halo's environment through the overdensity $\delta_8$, defined from the number of neighbouring
haloes within $8\, h^{-1}Mpc$, and we isolate the environmental effect from its degeneracy with the
halo-mass dependence by comparing the most overdense and most underdense
haloes constructed to share the same
halo-mass distribution. We find that
haloes in underdense environments exhibit systematically larger IA amplitudes $A_{\rm IA}$ than
haloes of the same mass in overdense environments, by a factor of $\sim1.5$–$1.8$, and that this trend persists across the mass and
redshift ranges probed, strengthening towards low
redshift. Using an orientation-only (unit-ellipticity)
estimator, we further show that this environmental contrast is driven by a combination of two effects:
haloes in underdense regions are both intrinsically less spherical and more strongly aligned with the large-scale
tidal field than their overdense counterparts of the same mass. These results indicate that the large-scale environment is a non-negligible variable in modelling
halo and
galaxy alignments, and may be a particularly important factor for beyond-two-point weak-
lensing analyses.
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All authors Masaya Ichikawa, Jingjing Shi, Toshiki Kurita, Masahiro Takada, Takahiro Nishimichi, Linda Blot
Astrophysics of Galaxies
Distance Estimates to Five Bok Globules Using Gaia DR3 Parallaxes and Near-Infrared Photometry: Validation with 3D Dust Maps
Rajat Subhra Paul and Himadri Sekhar Das
Accurate distances to small, opaque Bok globules are difficult to obtain due to their compact sizes and lack of embedded standard candles. We estimate distances to five globules – CB4, CB24, CB56, CB60, and CB188 – using a near-infrared (NIR) extinction technique applied to 2MASS photometry, combined with
stellar distances from
Gaia DR3 parallaxes. Extinction-distance profiles reveal distinct rises marking each cloud, yielding median distances of 766~pc (CB4), 354~pc (CB24), 483~pc (CB56), 1143~pc (CB60), and 926~pc (CB188). Weighted-mean values agree within $8.0\%$, supporting the internal consistency of the method and interquartile-range-based uncertainties span 3-9% across the sample. Independent validation with Bayestar19 3D
dust maps supports the CB4 and CB188 results. These refined distances provide an improved basis for future determinations of cloud masses, densities, and
star-formation efficiencies, including the first robust measurement for CB56 and a revised upward distance for CB188.
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Astrophysics of Galaxies
Gravitationally Lensed View of DSFG-1 in PLCK G165.7+67.0: Strong Dust Emission and Spatially Resolved Stellar Population Analysis with JWST and SMA
Zhiyu Yan, Daizhong Liu, Y.Sophia Dai et al. (+7 more)
We present a detailed
stellar population analysis of the strongly lensed dusty
star-forming
galaxy (DSFG) PLCK G165.7+67.0 DSFG-1 at $z = 2.236$, combining JWST NIRCam imaging with new Submillimeter Array (SMA) observations. This source is multiply imaged into two lensed components: image 1a, with a moderate magnification factor of $\mu \sim 5$, and image 1bc, with an extreme magnification factor of $\mu \sim 40$. The new SMA observations detect significant
dust continuum emission at 225GHz and 273GHz, with combined flux densities of $S_{\rm cont}=(1.19\pm0.38)$ mJy in image 1a and $S_{\rm cont}=(10.02\pm0.85)$ mJy in image 1bc, indicating active
star formation at sub-kpc scale. Based on the integrated SED modeling, DSFG-1 exhibits a
lensing amplification-corrected
stellar mass of $M_{\star} = (1.2 \pm 0.4) \times 10^{10} M_{\odot}$, and a
star-formation rate (SFR) of $(103 \pm 14) M_{\odot}\,\mathrm{yr^{-1}}$, similar to previous $H\alpha$-based results, placing it four times above the
star-forming main sequence at this
redshift. Its location on the size-mass plane and its morphological properties suggest that the system occupies a transitional phase between
star-forming late-type
galaxies and compact early-type systems. Together with its elevated
star-formation activity, this is consistent with a rapidly evolving
galaxy observed during
Cosmic Noon. We further investigate the spatially resolved
stellar population properties, and found significant spatial variations in
stellar age and
dust attenuation. These results point to a non-uniform
star-formation history and highlight the complex interplay between
dust geometry,
stellar growth, and gravitational
lensing, consistent with a merger scenario.
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All authors Zhiyu Yan, Daizhong Liu, Y.Sophia Dai, Patrick S. Kamieneski, Pierre Cox, Brenda L. Frye, Qinghua Tan, Fengwei Xu, Yixiao Liu, Ke Wang
Earth and Planetary Astrophysics
Oxygen isotope fractionation in the Martian atmosphere induced by CO$_2$ photolysis and O$_3$ formation
Tatsuya Yoshida, Shohei Aoki, Hiromu Nakagawa et al. (+8 more)
The enrichment of heavy isotopes of volatile elements in the Martian atmosphere indicates that Mars lost a large portion of its atmosphere through escape to space. Recent atmospheric measurements by ExoMars Trace Gas Orbiter (TGO) have suggested that the vertical profiles of oxygen isotopic compositions are influenced by chemical reactions involving isotopic fractionation. However, their quantitative impacts have not yet been fully evaluated. In this study, we develop a 1D photochemical model that incorporates oxygen isotopic fractionation associated with CO$_2$ photolysis and O$_3$ formation to investigate the vertical profiles of oxygen isotopic compositions. Our calculations show that CO is depleted in heavy oxygen isotopes relative to CO$_2$, reaching $\delta ^{18}$O $\sim -25$ per mil and $\delta ^{17}$O $\sim -15$ per mil, primarily due to isotopic fractionation during CO$_2$ photolysis. The vertical profiles of oxygen and carbon isotopic compositions are in good agreement between our model and the TGO measurements. O$_3$ is strongly enriched in $^{18}$O and $^{17}$O, reaching $\delta ^{18}$O $\sim 100$ per mil and $\delta ^{17}$O $\sim 50$ per mil as a consequence of the isotopic fractionation during its formation, whereas atomic oxygen is highly depleted in the heavy oxygen isotopes with $\delta ^{18}$O $\lesssim -100$ per mil and $\delta ^{17}$O $\lesssim -50$ per mil so as to compensate for their enrichment in O$_3$. These chemical fractionation processes can deplete the heavy oxygen isotopes in species that escape from the upper atmosphere, and thereby enhance the isotopic fractionation associated with oxygen escape to space. Such fractionated isotopic compositions of escaping oxygen may be detectable by the Martian Moons eXploration (MMX) mission.
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All authors Tatsuya Yoshida, Shohei Aoki, Hiromu Nakagawa, Naoki Terada, Juan Alday, Akinori Hasebe, Yuki Nakamura, Shungo Koyama, Shotaro Sakai, Ryoya Sakata, Ann Carine Vandaele
Instrumentation and Methods for Astrophysics
Synthesis imaging with a lunar orbit array: III. Augmented lagrangian Multiplier Imaging using Gradient descent Optimization (AMIGO)
Meng Zhou, Furen Deng, Yidong Xu et al. (+1 more)
Ground-based
radio observations below 30 MHz are severely limited by ionospheric interference and
radio frequency interference (RFI) from Earth. A lunar-orbiting
radio interferometer mission, the Discovering the Sky at the Longest wavelength (DSL, also known by its Chinese name “Hongmeng”), has been proposed to overcome these obstacles. However, for such a mission, there are new challenges, such as the nearly all-sky field of view and dynamic 3D baselines, which require a huge computational cost for interferometric image reconstruction. In this work, we present AMIGO (Augmented lagrangian Multiplier Imaging using Gradient descent Optimization), a novel imaging
algorithm tailored to lunar-orbiting arrays like DSL, combining the Mini-Batch Gradient Descent (MBGD) method with the Augmented Lagrangian Multiplier (ALM) technique. MBGD reduces the computational complexity and
memory cost, enabling efficient handling of large
datasets. ALM flexibly incorporates physical priors like non-negative sky temperature and prior angular power spectrum into the imaging
algorithm, with adjustable stopping criteria to quantitatively control prior strength. We validate AMIGO using mock visibility data generated under realistic DSL orbit configurations. Reconstructed sky maps at various frequencies and spatial resolutions show that this approach provides a computationally feasible framework for all-sky imaging with a lunar-orbiting array.
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All authors Meng Zhou, Furen Deng, Yidong Xu, Xuelei Chen
Instrumentation and Methods for Astrophysics
Fast(er)PM and Moving Mesh: JAX-native Geometric Multigrid Methods
Benjamin Horowitz
Efficient, differentiable Poisson solvers are a key component of modern particle–mesh simulations and field-level inference pipelines. FFT-based solvers are extremely effective on fixed Cartesian meshes, but they impose global all-to-all communication and rely on
symmetries that are lost in adaptive or non-Cartesian coordinates. In this work, we present a JAX-native
geometric multigrid framework for particle–mesh
gravity and argue that multigrid plays two complementary roles: on fixed meshes it can be a competitive, communication-avoiding alternative to FFTs, while on moving meshes it becomes the enabling solver. For static FastPM
evolution, warm-started Chebyshev multigrid acts as a defect-correction method, exploiting temporal coherence between time steps to reduce the number of V-cycles required for field-level accuracy. At large mesh sizes this reduces
memory pressure and yields comparable or faster wall-clock performance than distributed FFTs, with up to a factor of two reduction in total GPU time at fixed final mesh size. We then embed the same solver in a differentiable moving-mesh particle–mesh method, where adaptive coordinate deformation produces a variable-coefficient curvilinear Poisson equation that cannot be solved by ordinary FFT diagonalization. The resulting method concentrates force resolution in nonlinear structures while retaining a regular, JAX-compilable, automatically differentiable array workflow. These results suggest
geometric multigrid can be a practical bridge between fast fixed-grid PM methods and differentiable adaptive-force cosmological simulations.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
A Space Mission to Earth's Nearest Black Hole: Reality or Science Fiction?
Cosimo Bambi
Black holes are the sources of the strongest gravitational fields in the present-day Universe, offering unparalleled opportunities to test Einstein's theory of General Relativity in the strong-field regime. In this talk, I will examine the prospect of sending small spacecraft on an interstellar mission to the nearest black hole. While highly speculative and fraught with technical challenges, such an endeavor is not entirely beyond the realm of possibility. Although the necessary technology does not yet exist, it may become available within the next 20 to 30 years. The mission itself could span 80 to 100 years, yet the scientific return would be profound and potentially unattainable through other means.
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Solar and Stellar Astrophysics
Magnetic field configuration favoring X-class solar flares: violation of Joy's and Hale's laws
S. Liu, J.T. Su, M. Zhang et al. (+1 more)
We investigate the statistical relationship between
magnetic tilt angle and X-class
flare productivity using 39
flare-productive active regions that produced 64 X-class
flares. By classifying global
magnetic tilt properties into four quadrants based on compliance with Hale's and Joy's laws, we identify their distinctive
flare productivity characteristics. The Green quadrant (following both laws) contains 18 active regions producing 24 X-class
flares, while the Yellow quadrant (following Hale's law but violating Joy's law) shows significantly enhanced productivity with 18 active regions producing 36 X-class
flares. The Black quadrant (violating both laws), though containing only 3 active regions, produces 4 X-class
flares. More importantly,
flares in both the Yellow and Black quadrants exhibit systematically higher
flare classes compared to those in the Green quadrant. Our statistical analysis demonstrates that violation of Hale's or Joy's law at the global scale are strongly associated with increased
flare occurrence and
flare intensity. Furthermore, examination of globally normal (Green quadrant) regions reveals that localized tilt anomalies are universally present and also contribute to X-class
flare production. These results establish that abnormal
magnetic tilt configurations - whether occurring at the global or local scale - are key indicators of major
flare activity.
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All authors S. Liu, J.T. Su, M. Zhang, J.X. Wang
Solar and Stellar Astrophysics
What Causes the Asymmetry of Conjugate Hard X-Ray Footpoints in Solar Flares?
Mirabbos Mirkamalov, Rui Liu, Runbin Luo et al. (+1 more)
Hard X-ray (HXR) emission in
solar flares critically diagnoses nonthermal electron acceleration, transport, and precipitation. Observations commonly show asymmetric HXR
photon fluxes between paired footpoints, whose physical origin remains debated, as the conventional
magnetic mirroring mechanism often fails to explain the observed asymmetry. Here we performed rigorous statistical tests on the association between photospheric
magnetic parameters within the HXR footpoint regions and the asymmetry of HXR production. We analyzed 103 time intervals taken from around the peaks of HXR bursts in 67 M- and X-class
flares with a clear double-ribbon morphology observed by both the Ramaty High Energy
Solar Spectroscopic Imager and the
Solar Dynamics Observatory. We found that conjugate HXR footpoint sources are asymmetric in
photon fluxes, maximum intensities, and sizes, but rather symmetric in mean intensities. The
photon flux ratio of the stronger over weaker footpoint source shows a strong linear correlation with the size ratio and a nonlinear correlation with the maximum intensity ratio. The asymmetry of
magnetic field strength and flux at the conjugate footpoints shows a positive correlation with the HXR asymmetry, contrary to what
magnetic mirroring effects predict. Importantly, the asymmetry of unsigned photospheric vertical electric current (PVEC) exhibits a strong positive correlation with the HXR footpoint asymmetry. PVEC at HXR footpoints most likely maps the footprints of coronal current layers where flaring reconnections occur. This tight linkage suggests that the electric-current-associated physical processes, including reconnection-induced electric fields and current-driven micro-
turbulence, are at work to modulate the production and precipitation of nonthermal electrons.
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All authors Mirabbos Mirkamalov, Rui Liu, Runbin Luo, Arun Kumar Awasthi
Cosmology and Nongalactic Astrophysics
Constraints on Annihilating Dark Matter from Gamma-Ray Background-Galaxy Shape Correlations: Model-independent Null Results and Moderate Template-based Signals
Masato Shirasaki, Deheng Song, Oscar Macias et al. (+2 more)
We revisit the cross-correlation between the unresolved $\gamma$-ray background and
galaxy shapes to constrain the annihilation cross section of particle dark matter. Our analysis uses $\gamma$-ray
photons from 14 years of observations with the
Fermi Large Area
Telescope (LAT), together with
galaxy shape catalogs from the Dark Energy Survey Year 3 (DES Y3) and the Dark Energy Camera All Data Everywhere (DECADE) project, enabling us to probe cosmological large-scale signals over a common sky area of $\sim 12{,}000\,\mathrm{deg}^2$ shared by the $\gamma$-ray and
galaxy data sets. In order to better access signals from large-scale structure, we employ a
Fourier-space
estimator for the cross-correlation in contrast to the previous DES Y3 analysis. We find that our measurements are consistent with a null detection in a model-independent $\chi^2$ test, while template-based analyses yield signals at the $\sim 3\sigma$ level. Our null results exclude an enhanced annihilation cross section for wino-like dark matter with a mass of $2-3$ TeV under a modest substructure boost factor of $\sim 30$ in Milky Way-sized
halos. For larger boost factors of $\sim 100$, the constraints become significantly stronger and exclude the canonical thermal annihilation cross section $\langle \sigma v \rangle = 3 \times 10^{-26}\,\mathrm{cm}^3/\mathrm{s}$ for a $7-40$ GeV dark matter particle annihilating into $b\bar{b}$ or $\tau^{+}\tau^{-}$. The template-based analysis favors a power-law $\gamma$-ray energy dependence of the cross-correlation, but also indicates deviations from that expected based on the mean intensity of the unresolved $\gamma$-ray background around 100 GeV. We further consider decaying dark matter scenarios and derive $2\sigma$ lower limits on the particle lifetime of $\sim 10^{26}-10^{27}\,\mathrm{s}$, depending on the decay channel.
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All authors Masato Shirasaki, Deheng Song, Oscar Macias, Shunsaku Horiuchi, Naoki Yoshida