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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 15 July

Astrophysics of Galaxies

Chemodynamical evidence of the HR 1614 moving group as a bar resonance

Andreas J. Koch-Hansen, Vladislav Gulaev, Dominik H. Plonka et al. (+4 more)

Moving groups (MGs) are ensembles of disk stars that clump in velocity and action space. A multitude of explanations as to their origin has been attempted, from dissolved star clusters to resonances with the Galactic bar, or other non-axisymmetric perturbations. The object of this work, the old HR 1614 group, has in the past already been shown to not be a disrupted cluster in terms of its broad age and metallicity distribution. Thus its stars have more likely been trapped by the Milky Way bar at corotation. Here, we present a new study that aims to chemically and dynamically characterize this group in the context of such a resonance. To this end, we used MIKE/Magellan high-resolution, high signal-to-noise spectra of six member stars of the HR 1614 MG to determine the chemical abundance ratios for 24 elements, several for the first time in those stars. The Fe-abundances of our sample range from +0.13 to +0.38 dex and the majority of abundance ratios is fully in line with those of metal-rich Milky Way disk stars, with few exceptions. In particular, the group's eponym, HR 1614, is enhanced in essentially all abundances and coincides with the higher-[X/Fe] trends of the Milky Way's thick disk. All elements (but S and Ca) show significant intrinsic abundance scatter that argue against this MG having formed in a contained environment such as a dissolved cluster. Isochrone ages, tailored to the measured metallicities support earlier findings of a broad age mix in this group, ranging from 1 Gyr to as old as 8 Gyr. We performed an orbital frequency analysis in a Galactic potential that includes a rotating bar. Indeed, our sample stars fall onto thin resonances on corotation. Hence, our results support the idea that the HR 1614 MG is a resonantly perturbed disk feature, mustering a melange of stars from different parent populations in the inner Galaxy.
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All authors Andreas J. Koch-Hansen, Vladislav Gulaev, Dominik H. Plonka, Camilla Juul Hansen, Andrew McWilliam, Victor P. Debattista, Zdenek Prudil

High Energy Astrophysical Phenomena

Signatures of Black Hole Spin in Horizon-Scale Polarimetry

George N. Wong, Daniel C. M. Palumbo, Zachary Gelles et al. (+1 more)

The angular momentum of a black hole, usually expressed in terms of a dimensionless "spin," both shapes the strong-field spacetime and provides a reservoir of rotational energy that can be exchanged with surrounding plasma. Very long baseline interferometry (VLBI) has now begun to resolve polarized emission on event-horizon scales. We distinguish polarimetric signatures of spin arising primarily from photon propagation in the Kerr spacetime from those mediated by horizon-threading electromagnetic fields and magnetized plasma dynamics. We trace the inference from VLBI correlations through Stokes images and compact summary statistics to constraints on the source and, ultimately, on spin. Within this framework, we review diagnostics linked to horizon regularity and magnetic-field winding, magnetically arrested accretion, electromagnetic energy extraction, jet-base and light-cylinder structure, and horizon and photon-ring polarization. Current Event Horizon Telescope observations constrain magnetic-field geometry, variability, source orientation, magnetic flux state, and aspects of the disk-jet connection more robustly than they constrain spin magnitude or sense. Future observing and modeling programs should prioritize combinations of polarimetric diagnostics with complementary systematics and test whether a common spin-dependent interpretation is supported across independent data products and plausible source models.
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All authors George N. Wong, Daniel C. M. Palumbo, Zachary Gelles, Andrew Chael

Cosmology and Nongalactic Astrophysics

Non-Primordial Contribution to the Cosmic Microwave Background

Akshith Asundi and Vikram Khaire

The cosmic microwave background is interpreted as relic thermal radiation from the epoch of recombination at z~1090. Recent work by Gjergo & Kroupa (GK25) have challenged this assumption proposing that dust-enshrouded starbursts in the progenitors of massive early-type galaxies at z~15-20 contribute to the CMB at the percent level of the present-day CMB energy density. Existing test of this scenario rely on CMB monopole; here we present the first test against the CMB anisotropy power spectrum, which probes the dynamical imprint of the radiation content on the sound horizon and acoustic peaks. We introduce a single parameter $\varepsilon_{\rm CMB}$ that rescales the primordial photon energy density above a redshift (z=17). Constraining the model with the Planck 2018, lensing likelihoods and BAO measurements, we find a percent-level dust contribution to be fully consistent with the data. When we restrict $\varepsilon_{\rm CMB}\leq1$, the data place a 68 (95) per cent lower bound $\varepsilon_{\rm CMB}\gtrsim 0.971$(0.953), permitting a non-primordial contribution of up to ~3 (~5) per cent of the CMB energy density. When sampled with $\varepsilon_{\rm CMB}$ as a free parameter, the data yield a well-resolved posterior with $\varepsilon_{\rm CMB} = 1.0104^{+0.025}_{-0.024}$. The 1.4 per cent contribution conservatively estimated by GK25 lies within the 1$\sigma$ region of both cases, whereas a contribution approaching the full CMB energy density is excluded at 42$\sigma$. Treating z as a free parameter returns a flat posterior across 5<z<50 indicating the anisotropy constrains the dust contribution, but not when it occurs. The standard LCDM parameters are recovered without significant shifts, showing that current CMB precision cosmology has sufficient room to accommodate a dust contribution at the level predicted by GK25 without detectable consequence for parameter inference.
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Cosmology and Nongalactic Astrophysics

The topology of the magnetic field in Abell 2255 out to its virial radius. Results from the LOFAR Galaxy Cluster Ultra-Deep Field

A. Botteon, R. J. van Weeren, Y. Hu et al. (+14 more)

We present the LOFAR Galaxy Cluster Ultra-Deep Field, in which 336 h of LOFAR observations at 120$-$168 MHz have been collected on the nearby ($z=0.080$) cluster Abell 2255. This massive and merging system is known to host spectacular radio emission from both cluster galaxies and the intracluster medium. Previous LOFAR observations revealed pervasive diffuse synchrotron emission extending from the cluster center to its dynamically active outskirts, tracing relativistic electrons propagating in large-scale magnetic fields. In this work, we present a set of new ultra-deep images at the central frequency of 144 MHz based on the 224 h of data with the best quality, which reach a sensitivity of 24 $\mu$Jy beam$^{-1}$ at 7.1" $\times$ 4.3" resolution. These images represent the deepest radio observations of a galaxy cluster obtained to date and provide a glimpse of what should be routinely observed in clusters with SKA-Low in the near future. Using these data, we investigate the topology of the cluster magnetic field out to its virial radius by applying the synchrotron intensity gradient technique. We find that the inferred magnetic field exhibits preferential orientations in distinct regions of the cluster, such as in the radio halo extensions (bridges) and in the relics, suggesting that the dynamics of the cluster formation process is shaping the large-scale magnetic field. This interpretation is supported by the comparison with the magnetic field orientation obtained from cosmological magnetohydrodynamic simulations. This work provides the first indication of a coherent, large-scale magnetic field topology across an entire galaxy cluster, from core to outskirts, and demonstrates the unique power of ultra-deep, low-frequency observations to trace the structure of cluster magnetic fields on megaparsec scales, thereby probing the magnetization of the large-scale structure of the Universe.
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All authors A. Botteon, R. J. van Weeren, Y. Hu, F. Vazza, G. Brunetti, K. Rajpurohit, A. Lazarian, T. W. Shimwell, E. De Rubeis, M. Balboni, A. Bonafede, R. Cassano, G. Di Gennaro, F. Gastaldello, M. J. Hardcastle, A. Ignesti, H. J. A. Röttgering

Solar and Stellar Astrophysics

The Open Cluster Chemical Abundances and Mapping Survey: IX. Measuring the Effects of Stellar Diffusion in the Open Clusters NGC 752 and Ruprecht 147 using APOGEE

Diogo Souto, Taylor Spoo, Peter M. Frinchaboy et al. (+4 more)

A growing understanding of stellar processes that alter surface chemical abundances over time has opened new avenues for using these changes as probes of stellar properties. On the main sequence and near the turnoff, stellar surface abundances are affected by gravitational settling and radiative acceleration, collectively known as atomic diffusion. In this work, we use SDSS/APOGEE DR17/DR19 data to investigate atomic diffusion in the open clusters NGC~752 and Ruprecht~147, thereby constraining how these signatures vary with age. From the analysis of Fe, C, N, Na, Mg, Al, Si, S, K, Ca, Ti, V, Cr, Mn, Co, and Ni, we find significant abundance differences between stars near the turnoff and the cooler main-sequence, where warmer stars are depleted relative to the cooler main-sequence stars at the $\geq1\sigma$ level for all elements available in the analysis. These abundance differences are consistent with the signatures expected from atomic diffusion and are further supported by comparisons with stellar models that include diffusion. By fitting the observed $T_{\rm eff}$–[Fe/H] patterns with MIST isochrones, we obtain best-fit ages of 1.0~Gyr for NGC~752 and 2.5–3.2~Gyr for Ruprecht~147. Carbon is a key diagnostic, as it shows both atomic diffusion and extra-mixing signatures associated with first-dredge-up. For NGC~752, the coolest stars in our sample, which provide the best proxy for the initial cluster composition, yield [Fe/H]$_{\rm CS} = 0.01~\pm~0.02(\pm~0.05)$ dex. For Ruprecht~147, we obtain [Fe/H]$_{\rm CS} = 0.17~\pm~0.00(\pm~0.05)$ dex. Our findings further constrain atomic diffusion models, suggesting that atomic diffusion affects age estimates of stars near the main-sequence turnoff.
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All authors Diogo Souto, Taylor Spoo, Peter M. Frinchaboy, Katia Cunha, Jamie Tayar, Alessa Ibrahim Wiggins, Natalie Myers

Cosmology and Nongalactic Astrophysics

Measuring satellite galaxy subhalo masses in redMaPPer clusters with UNIONS weak lensing data

Roman Akhmetshyn, Jack Elvin-Poole, Michael J. Hudson et al. (+13 more)

In this work, we present the observed galaxy-galaxy lensing signal of satellite galaxies in rich clusters obtained from the Ultraviolet Near-Infrared Optical Northern Survey (UNIONS). Such observations are crucial for understanding dark matter halo physics and interaction dynamics in the cluster environment. Our goal is to investigate the tidal stripping of cluster subhalos. Theoretical predictions, supported by recent studies, suggest that as satellite galaxies fall into clusters, their dark matter halos are stripped and dispersed into the cluster's main halo, while their stellar mass remains relatively intact. A robust method to probe this phenomenon is through statistical measurements of the excess surface mass density of satellite galaxies at different cluster-centric distances. Our results reveal a significant lensing signal, with strong statistical power from the large number of lens-source pairs. A simple model used in the fitting process to constrain subhalo masses effectively reproduces the observed lensing signal at relevant satellite-centric distances. However, it lacks the complexity to accurately fit the excess surface density at larger distances, where the host cluster halo dominates. We measure the subhalo-to-stellar mass ratio as a function of cluster-centric radius and find a strong positive trend. These results confirm tidal stripping or other environmental processes that impact the relative masses of a satellite galaxy's stellar component and its dark matter halo.
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All authors Roman Akhmetshyn, Jack Elvin-Poole, Michael J. Hudson, Isaac Cheng, Thomas de Boer, Sébastien Fabbro, Sam Farrens, Sacha Guerrini, Axel Guinot, Stephen Gwyn, Hendrik Hildebrandt, Martin Kilbinger, Charlie T. Mpetha, Calum Murray, Ludovic Van Waerbeke, Anna Wittje

Cosmology and Nongalactic Astrophysics

Simulation-Based Priors for HI Bias from Halo Occupation Physics

Debanjan Sarkar and Simon Foreman

Full-shape analyses of 21 cm intensity maps with the effective field theory of large-scale structure will require priors on HI bias parameters, and the standard choice of broad uninformative priors can lead to cosmological constraints that are unnecessarily conservative. We present a simulation-based framework that replaces these broad priors with informative priors based on learning the conditional distribution $p(\bm{\theta}_{\rm EFT}\mid\bm{\theta}_{\rm HOD})$ between effective-field-theory-based bias parameters and the parameters of a model for HI clustering in the nonlinear regime. Specifically, we train a conditional normalizing flow on field-level measurements of the lowest-order local bias parameters $(b_1,b_2,b_3)$ and the tidal bias $b_{\mathcal{G}_2}$ by applying a simple HI halo occupation distribution (HOD) to the Hidden Valley simulations. We find that the resulting HOD-to-bias mapping is highly structured, displaying a strong dependence on the power of halo mass in the HOD model. Propagating CHORD-like telescope sensitivity forecasts for the 21 cm power spectrum on nonlinear scales through this mapping produces non-Gaussian, correlated priors on the bias parameters that are substantially tighter than conventional flat priors across $z=1$–$3$, with the improvement most dramatic at high redshift. By repeating our analysis using halo catalogs from the IllustrisTNG simulations, we find non-negligible differences from the Hidden Valley results, indicating that future applications of simulation-based HI priors will need to carefully account for the dependence of these priors on the simulations used to construct them. Our framework provides an initial step toward informative EFT priors for current and forthcoming HI intensity mapping surveys, including CHIME, CHORD, and MeerKLASS.
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Earth and Planetary Astrophysics · Cross-listed from physics.hist-ph

The orientation of the Amazonian geoglyphs as a clue for their interpretation

Giulio Magli

Amazonian earthworks, also called geoglyphs, are thousands of man-made earthen structures, mostly of geometrical shape, which progressively emerged from the tropical forest due to progressive deforestation. They were probably built between the fifth century BC and the end of the first millennium AD, but archaeological investigation on the culture of their builders is yet at the beginning. Nevertheless, a ceremonial rather than practical function seems likely, at least for those having a very regular shape. In the present paper, simple remote-sensing technique, combined with the methodological approach of modern Archaeoastronomy, are applied to study for the first time their orientation. The analysis takes in consideration virtually all known squared and rectangular structures for a total of 326 earthworks. The results show without doubts a non-random choice for their orientation and a clear interest of their builders for the annual cycle of the Sun.
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Instrumentation and Methods for Astrophysics

Development and characterization of a millimeter-wave cold load prototype

Ruya Cong, Junjie Zhou, Yu Xu et al. (+7 more)

Superconducting transition-edge sensors (TESs) are crucial detectors for cosmic microwave background (CMB) observations and require stable and tunable millimeter-wave cold loads for optical-efficiency calibration. This work presents the design, fabrication, and preliminary characterization of a 4-20 K millimeter-wave cold load prototype intended for integration into the 1 K stage of a dilution refrigerator and subsequent 40/90 GHz CMB TES calibration experiments. Two absorber prototypes based on commercially available CR-110 and a Stycast 2850FT composite were fabricated and studied. Simulation results show that both absorber structures exhibit small predicted steady-state temperature gradients and low normal-incidence reflectance in the target frequency bands. Room-temperature S11 measurements were used only to screen low-reflectance cold load prototype, and the measured results generally agree with the electromagnetic simulations. The measured S11 of the Stycast 2850FT composite is comparable to that of the commercial absorber TK RAM. Additionally, to explore a more readily obtainable alternative absorber material, TIE280-25AB was preliminarily evaluated by measuring its electromagnetic parameters. Based on the measured parameters, the simulated S11 of the TIE280-25AB pyramidal absorber structure is comparable to those of CR-110 and the Stycast 2850FT composite over 33-110 GHz. These results identify CR-110 and the Stycast 2850FT composite as promising absorbers for subsequent cryogenic evaluation. The absolute low-temperature emissivity, effective radiation temperature, and TES calibration performance remain to be established through future cryogenic radiometric and TES based optical-power measurements.
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All authors Ruya Cong, Junjie Zhou, Yu Xu, Xuefeng Lu, Jianrong Cai, Haoxuan Gao, Kang Zhang, Xingyuan Hou, Zhengwei Li, Shaoliang Wang

Astrophysics of Galaxies

Cold Stream Penetration of Virial Shocks: Fragmentation, Coagulation, and Disruption in the Hot Circumgalactic Medium

Zhiyuan Yao, Nir Mandelker and S. Peng Oh

Cold streams penetrating virial shocks of massive halos along cosmic web filaments are expected to fuel galaxy growth at high redshift, yet the physical processes governing their penetration remain uncertain. We investigate cylindrical cold streams penetrating a hot circumgalactic medium (CGM) using idealized three-dimensional simulations. We systematically vary the stream radius, Mach number, and initial stream-to-CGM pressure contrast across three density contrasts, while controlling stream properties after pressure equilibrium is re-established. We identify three evolutionary regimes: coagulation, fragmentation, and disruption, plus a borderline regime in which the stream core marginally survives while detached fragments are disrupted. At modest pressure contrast, survival depends primarily on the competition between velocity shear and radiative cooling. Increasing pressure contrast produces a transient response during pressure restoration, temporarily enhancing or suppressing cold-gas mass and cold-hot interfacial area before evolution converges to a shear-dominated state. At larger pressure contrasts, the oblique shock steepens into a bow shock, and the final outcome is determined by the ratio of post-shock cooling time to virial crossing time. In all survival cases, post-equilibration evolution is well described by turbulent radiative entrainment at the stream-CGM interface: cold-gas mass flux increases while mean streamwise momentum flux remains approximately conserved. Applying these results to a galaxy evolution framework, we find that cold streams are expected to penetrate virial shocks around massive halos at $z>2$, though they may fragment into multiphase structures within the hot CGM at $M_\mathrm{v}\gtrsim2\times10^{12}\,\mathrm{M}_\odot$. Toward lower redshift, bow-shock heating and inefficient post-shock cooling can suppress cold-stream penetration.
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Astrophysics of Galaxies

Investigating anomalous microwave emission near G107.2+5.20 in Ku-band with the Green Bank Telescope

Jordan E. Shroyer, Bradley R. Johnson, Dillon J. Bass et al. (+5 more)

Anomalous microwave emission (AME) is 30 GHz-peaking continuum emission thought to arise from spinning dust grains. Observations suggest that the local environment shapes the AME spectral energy distribution (SED), so building a spatially resolved sample of AME regions is a key step towards understanding its emission mechanism. Using the Green Bank Telescope Ku-band receiver, we obtained a ~1 arcmin resolution map of radius 1.25 deg centered on G107.2+5.20. Our first objective was to constrain the low-frequency side of the AME SED with 13 GHz data. Using matched-resolution aperture photometry, we measure the SED from 408 MHz-3 THz and fit two emission models: one including spinning dust, the other optically thick free-free emission. We find that the spinning dust model is superior, with an amplitude of $14.1\pm1.1$ Jy and a peak frequency of $27\pm2$ GHz. Our second objective was to spatially locate excess 13 GHz emission consistent with spinning dust. We compare our Ku-band map to multi-wavelength gas and dust tracers at ~4 arcmin resolution. We observe two sources of 13 GHz excess at 3$\sigma$ significance consistent with spinning dust emission, though potential contributions from optically thick free-free emission remain ambiguous. “Region A” (G106.95+5.19) is spatially coincident with peak dust radiance. “Region B” (G107.08+4.90) is spatially coincident with peak PAH abundance. If regions A and B are indeed sources of spinning dust emission, they are a resolved example of how AME-dust correlation varies with environment.
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All authors Jordan E. Shroyer, Bradley R. Johnson, Dillon J. Bass, Anna Dignan, Stuart E. Harper, Brian S. Mason, Andrey Moore, Eric J. Murphy

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

Entropy release from Minkowski breaking in regular Schwarzschild black holes

Francisco S. N. Lobo and Manuel E. Rodrigues

The classical formation of a Schwarzschild black hole from a regular, non-singular configuration has recently been shown to be impossible within general relativity: the geometry inevitably develops a discontinuity at the origin, a phenomenon termed Minkowski breaking by Ovalle, Casadio, and Kamenshchik [PRD 113 (2026), 064042]. This obstruction signals that the transition to the Schwarzschild point mass must be a discrete, quantum event. We uncover the thermodynamic footprint of this transition. Using the explicit family of regular Schwarzschild black holes with a de Sitter core, we show that the inner Killing horizon carries a formal Bekenstein-Hawking entropy $S_{\rm inner} = A_{\rm inner}/4$ that is absent in the singular Schwarzschild state. This entropy is hidden from external observers in equilibrium but, assuming the generalized second law, must be released when the inner horizon disappears. As the collapse parameter $n$ decreases, the inner horizon shrinks and its entropy is gradually released during classical evolution, until the horizon finally vanishes at $n=0$ with the Minkowski breaking. The surface gravity diverges as $n\to0^+$, with the semiclassical description breaking down at $n \sim 1/\ln(h/\ell_P)$; the final disappearance is therefore a deep quantum process. For the $n=3$ regular black hole, the stored entropy is approximately $59\%$ of $A/4$; in the semiclassical limit $n\gg1$, it approaches the full $A/4$. The integer nature of $n$ implies a quantized entropy spectrum, with the Schwarzschild black hole as the ground state within the OCK family. We discuss how the classical mass-inflation instability may be circumvented by the quantum disappearance of the Cauchy horizon, and clarify the continuous vs. discrete nature of the collapse.
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Astrophysics of Galaxies

Magnesium isotope ratios in Milky Way and dwarf galaxy stars

M. McKenzie, S. Monty, D. Yong et al. (+8 more)

Under the assumption of hierarchical galaxy formation, dwarf galaxies are the closest existing analogues to the high-redshift protogalaxies that merged to form the Milky Way. These low-mass systems serve as unique laboratories for studying nucleosynthetic channels, given that the chemical compositions of their stars play a pivotal role in constraining their chemical enrichment history. To date, stellar abundances in dwarf galaxies have focused almost exclusively on elemental abundance ratios. While important, elemental abundances omit critical information about the isotopic composition. Here, we compute the Mg isotopic ratios of six accreted dwarf galaxy stars (low-alpha) and seven Milky Way stars (high-alpha) using a set of high-resolution (65000 < R < 160000) and high signal-to-noise ratio (S/N > 250) optical spectra. We show, for the first time, that at a given [Fe/H], stars born in a dwarf galaxy differ in their Mg isotopic ratios from stars born in the Milky Way. However, when comparing isotopic ratios at a given [Mg/H] rather than [Fe/H], a powerful diagnostic emerges that suggests nucleosynthesis processes are consistent across different stellar environments. This universality of Mg isotopic abundances provides additional dimensionality for chemical evolution models and helps to constrain massive-star nucleosynthesis across cosmic time.
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All authors M. McKenzie, S. Monty, D. Yong, C. Kobayashi, A. I. Karakas, P. E. Nissen, J. E. Norris, A. Rains, A. Mura-Guzmán, E. X. Wang, S. Martell

Astrophysics of Galaxies

The complex stellar system M 22: constraining the chemical enrichment from AGB stars using magnesium isotope ratios

M. McKenzie, D. Yong, A. I. Karakas et al. (+8 more)

The complex star cluster M 22 (NGC 6656) provides a unique opportunity for studying slow neutron-capture (s-process) nucleosynthesis at low metallicity due to its two stellar groups with distinct iron-peak and neutron-capture element abundances. Previous studies attribute these abundance differences to pollution from 3-6 solar-mass asymptotic giant branch (AGB) stars, which produce significant quantities of the neutron-rich Mg isotopes 25Mg and 26Mg. We report the first-ever measurements of Mg isotopic abundance ratios at [Fe/H] approximately -2 in a globular-cluster-like system using very high-resolution and high signal-to-noise spectra (R = 110000, S/N = 300 per pixel at 514 nm) from the VLT/UVES spectrograph for six stars, three in each s-process group. Despite the presence of star-to-star variations in 24Mg, 25Mg, and 26Mg, we find no correlation with heavy-element abundances, implying that the nucleosynthetic source of s-process enrichment must not influence Mg isotope ratios. Instead, a key result of this work is that we identify correlations between 26Mg/24Mg and some light elements. Using a custom suite of AGB nucleosynthesis yields tailored to the metallicity of M 22, we find that low-mass AGB stars of approximately 1-3 solar masses are capable of reproducing the observed s-process abundances of M 22 and that the absence of any difference in Mg isotope ratios between the two s-process groups precludes AGBs with masses above approximately 3 solar masses. This places tighter constraints on possible formation scenarios and suggests an age difference of at least approximately 280-480 Myr between the two populations that is independent of isochrone fitting.
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All authors M. McKenzie, D. Yong, A. I. Karakas, E. Wang, S. Monty, A. F. Marino, A. P. Milone, T. Nordlander, A. Mura-Guzmán, S. Martell, M. Carlos

Astrophysics of Galaxies

The complex stellar system M 22: confirming abundance variations with high precision differential measurements

M. McKenzie, D. Yong, A. F. Marino et al. (+8 more)

M 22 (NGC 6656) is a chemically complex globular cluster-like system reported to harbour heavy element abundance variations. However, the extent of these variations and the origin of this cluster is still debated. In this work, we investigate the chemical inhomogeneity of M 22 using differential line-by-line analysis of high-quality (R = 110,000, S/N = 300 per pixel at 514 nm) VLT/UVES spectra of six carefully chosen red giant branch stars. By achieving abundance uncertainties as low as ~0.01 dex (~2 per cent), this high-precision data validates the results of previous studies and reveals variations in Fe, Na, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, Zn, Y, Zr, La, Ce, Nd, Sm and Eu. Additionally, we can confirm that the cluster hosts two stellar populations with a spread of at least 0.24 dex in [Fe/H] and an average s-process abundance spread of 0.65 dex. In addition to global variations across the cluster, we also find non-negligible variations within each of the two populations, with the more metal-poor population hosting larger spreads in elements heavier than Fe than the metal-rich. We address previous works which do not identify anomalous abundances and relate our findings to our current dynamical understanding of the cluster. Given our results, we suggest that M 22 is either a nuclear star cluster, the product of two merged clusters, or an original building block of the Milky Way.
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All authors M. McKenzie, D. Yong, A. F. Marino, S. Monty, E. Wang, A. I. Karakas, A. P. Milone, M. V. Legnardi, I. U. Roederer, S. Martell, D. Horta

Instrumentation and Methods for Astrophysics

Update on the Magellan InfraRed Multi-Object Spectrograph (MIRMOS)

Maren Cosens, Nicholas P. Konidaris II, Gwen C. Rudie et al. (+21 more)

The Magellan InfraRed Multi-Object Spectrograph (MIRMOS) will be a next generation multi-object (MOS) and integral field spectrograph (IFS) for the 6.5m Magellan telescopes at Las Campanas Observatory in Chile. MIRMOS will perform R~3700 spectroscopy over a simultaneous wavelength range of 0.886-2.404um (Y, J, H, and K bands) in addition to imaging over the range of 0.7-0.886um. Target selection in the MOS mode is achieved through a cryogenic mechanism capable of making up to 92 slits over a 13'x3' field of view (FoV). This mechanism can be reconfigured in real time to adjust slit widths for seeing conditions, change to a different mask, or form a long slit. The IFS mode of operation for MIRMOS will be achieved via an image slicer style integral field unit (IFU) which will provide an ~18"x26" FoV made up of 0.84"x26" slices. MIRMOS's design will allow it to address a wide range of science cases from performing spectroscopy of high-redshift galaxies as well as high signal-to-noise transmission spectroscopy of exoplanet atmospheres with the MOS/long slit mode, while also having the largest FoV IFS operating on a large telescope at these wavelengths. We will describe here the design of the MIRMOS instrument – now at the end of the preliminary design phase.
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All authors Maren Cosens, Nicholas P. Konidaris II, Gwen C. Rudie, Andrew B. Newman, Leon Aslan, Robert Barkhouser, Christoph Birk, Julia Brady, Mathias Gumy, Tyson Hare, Stephen C. Hope, Charlie Hull, Karim Kaismoune, Daniel D. Kelson, Gerrad Killion, Alicia Lanz, Jocob McCloskey, Solange V. Ramirez, Cyril Rupf, William Schoenell, Patricio Schurter, Stephen A. Smee, Peter Spanoudakis, Jason E. Williams

Instrumentation and Methods for Astrophysics

Update on the slicer IFU for the Magellan InfraRed Multi-Object Spectrograph (MIRMOS)

Maren Cosens, Patricio Schurter, Nicholas P. Konidaris et al. (+18 more)

The Magellan InfraRed Multi-Object Spectrograph (MIRMOS) is a planned next generation multi-object and integral field spectrograph for the 6.5m Magellan telescopes at Las Campanas Observatory in Chile. MIRMOS will perform $\rm R\sim3700$ spectroscopy over a simultaneous wavelength range of 0.886 - 2.404um (Y, J, H, K bands) in addition to imaging over the range of 0.7 - 0.886um. The integral field mode of operation for MIRMOS will be achieved via an image slicer style integral field unit (IFU) located on a linear stage to facilitate movement into the beam during use or storage while operating in multi-object mode. The IFU will provide an $\rm\sim18''\times26''$ field of view (FoV) made up of $\rm0.84''\times26''$ slices. This will be the largest FoV IFS operating at these wavelengths from either the ground or space, making MIRMOS an ideal instrument for a wide range of science cases including studying the high redshift circumgalactic medium and emission line tracers from ionized and molecular gas in nearby galaxies. We present here an update on the IFU design from our 2024 proceeding. Previously we utilized a re-imaging style slicer which required freeform pupil mirrors in order to achieve the required image quality while obeying significant packaging constraints near the instrument focal surface. In order to reduce the manufacturing cost and decouple the IFU from the configurable slit unit used in multi-object mode, we have moved the IFU deeper into the instrument, allowing for a switch to a virtual style IFU. This now requires a re-imaging doublet before the slicer mirrors, but removes the need for any freeform surfaces. We present here the optical design and predicted performance of the new MIRMOS IFU along with a conceptual design for the opto-mechanical system which will move the IFU between its active and stored positions.
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All authors Maren Cosens, Patricio Schurter, Nicholas P. Konidaris, Gwen C. Rudie, Andrew B. Newman, Leon Aslan, Robert Barkhouser, Christoph Birk, Julia Brady, Tyson Hare, Stephen C. Hope, Charlie Hull, Karim Kaismoune, Daniel D. Kelson, Gerrad Killion, Alicia Lanz, Jacob McCloskey, Solange V. Ramirez, William Schoenell, Stephen A. Smee, Jason E. Williams

Solar and Stellar Astrophysics

Observational Evidence for Counter-helicity Magnetic Reconnection in a Solar Eruption

Jinrui Chang, Yi Bi, Bo Yang et al. (+3 more)

Magnetic reconnection between coronal magnetic systems carrying opposite self-helicity may play a role in solar eruptions, but observational evidence remains limited. We investigate an M7.0 flare in NOAA Active Region 13615 on 2024 March 28 using multiwavelength observations and nonlinear force-free field extrapolations. The reconstructed coronal field reveals a low-lying positive-helicity core field beneath an overlying magnetic system of opposite sign. During the eruption, the footpoint connectivity of these two magnetic systems changes markedly: field lines rooted in the western footpoint region change from positive to negative helicity, and the positive-helicity domain is substantially reduced. These changes are accompanied by a remote chromospheric brightening, intermittent EUV stripe-like brightenings extending from the source region toward the remote chromospheric brightening, the subsequent formation of large-scale coronal loops, and a weak outer hard X-ray source located at a footpoint of the core field. Together, these results suggest that the eruption was closely associated with reconnection between the core field and the overlying counter-helicity system, providing observational evidence that counter-helicity reconnection can contribute to the destabilization of eruptive solar magnetic fields.
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All authors Jinrui Chang, Yi Bi, Bo Yang, Junchao Hong, Jiayan Yang, Qingmei Wang

Cosmology and Nongalactic Astrophysics

Supermagnified Stars in Lensing Clusters and Small-Scale Structure in the Dark Matter

Gabriel Torralba and Jordi Miralda-Escudé

Supermagnified stars, discovered by HST and JWST in lensing clusters of galaxies, are luminous stars in source galaxies lying near lensing caustics that are magnified by large factors ($\sim 1000$), making them detectable at cosmological distances. Intracluster stars in the lens modify the large-scale caustic into a corrugated network of micro-caustics, causing frequent microlensing events of the supermagnified stars. The frequency and lightcurves of these micro-caustic crossings are extremely sensitive to any small-scale, low amplitude surface density fluctations in the lensing cluster, making them a unique probe to dark matter minihalos or any small-scale irregularities. Furthermore, the disks of supermagnified stars can be resolved (at cosmological distances!) from photometric monitoring of micro-caustic crossing events, exploiting the limb darkening effect. Examples are shown of model lightcurves to fit the Kelly et al. (2018) observations of the first supermagnified star discovered. The unique sensitivity and angular resolution of the Habitable Worlds Observatory enables photometry of microlensing events of supermagnified stars sensitive to small-scale structure different from intracluster stars, a probe to the nature of dark matter that is not accessible to other observations at present.
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Instrumentation and Methods for Astrophysics

phoptic – a Python package for reducing astronomical images

Zackery A. Irving, Noel Castro Segura, Diego Altamirano et al. (+6 more)

Publicly-available photometry pipelines make astronomical data reduction accessible to non-experts, reduce the margin for human error, and enable reproducible reduction. In many cases, bespoke reduction software is written on a per-instrument basis; this results in rigid pipelines that cannot be straightforwardly applied to data from other instruments. To alleviate this problem, we present phoptic, an open source photometry pipeline written in Python. phoptic began as a dedicated pipeline for the the OPtical TIming CAMera (OPTICAM), a triple-camera system mounted on the 2.1~m telescope at the Observatorio Astronomico Nacional in San Pedro Martir, Mexico. However, phoptic now serves as a generic photometry pipeline with a simple interface to reduce data from other instruments. At its core, phoptic leverages the astropy Python package, and affiliated packages thereof, to provide a flexible, modern, and interoperable reduction pipeline. In particular, phoptic uses photutils for background estimation, source detection, and performing aperture photometry. Additionally, phoptic implements optimal photometry, improving the signal-to-noise ratio over aperture photometry by up to $\sim 10$ per cent. We describe phoptic's functionality, discuss its default behaviour, and demonstrate its flexible interface by reducing data from the HiPERCAM, MEXMAN, OPTICAM, and ULTRACAM instruments. We also review the performance of phoptic, and show that it is highly scalable on multi-core CPUs.
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All authors Zackery A. Irving, Noel Castro Segura, Diego Altamirano, Federico Vincentelli, Angel Castro, Romina P. Petrucci, Raul Michel, Adam B. Hill, Juan V. Hernandez Santisteban

Solar and Stellar Astrophysics

The potential broader complex linked to the key Cepheid SV Vul

Daniel Majaess, Ignacio Negueruela, Leonid N. Berdnikov et al. (+10 more)

A new distance was established to the Cepheid SV Vul ($P\simeq45^{d}$) and its host cluster Alicante 13, and is tied in part to deeper UKIDSS-DR6 photometry and Gaia DR3 observations ($d=2.30\pm0.13$ kpc). SV Vul and Alicante 13 possibly belong to a broader coeval stellar complex, which could include Liu-Pang 1738. The clusters and Cepheid share comparable astrometry (e.g., $\sigma_\pi\simeq0.02$ mas, $\sigma_{\mu_\delta}\simeq0.06$ mas yr$^{-1}$), and similar cluster turnoffs (ages) exist as indicated by ultraviolet UVEX color-color analyses, Gaia XP spectroscopically differentially dereddened color-magnitude diagrams, and Padova isochrones. Yet SV Vul may be comparatively overluminous. Robust radial velocities for both clusters could substantiate certain hypotheses.
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All authors Daniel Majaess, Ignacio Negueruela, Leonid N. Berdnikov, Charles J. Bonatto, David G. Turner, Dante Minniti, Vittorio F. Braga, Giovanni Carraro, Igor Usenko, Giuseppe Bono, Matias Gomez, Roberto K. Saito, Maria G. Navarro

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

Dark matter environments and safeguards for spacetime inference from horizon scale interferometry

Mohsen Fathi

Horizon scale interferometry can test a black hole spacetime only when the data, source model, and numerical response are reliable. We study this requirement with the public 2017 M87* closure data, a frozen semi analytic emission model, explicit dark matter controls, and a rotating tidal charge deformation. We normalize NFW and Einasto halos, an adiabatic spike, a capture suppressed spike, and a heated crest for M87*. Even the intentionally optimistic rendered case, $M_{\rm DM}(<10M)/M_{\rm BH}=7.33\times10^{-5}$, changes the normalized image and visibility by only about $2.65\times10^{-6}$ and $4.9\times10^{-7}$. We then build an independent closure phase and log closure amplitude likelihood with covariance and three fixed high/low band correlation cases. Synthetic Kerr tests recover the expected statistic, coverage, and false positive rate. The real data give $\chi^2/N=1.7583$, $1.7206$, and $1.6873$, above the global adequacy limit of $1.5$; the worst band gives $2.0216$. Removing the most influential scan still leaves $\chi^2/N=1.6472$. If tidal charge is allowed anyway, the residual projects strongly onto it, but the preferred direction changes sign between image resolutions. Direct libraries at $N=192$, 224, and 256 also fail the differential response convergence tests. At a smoothing width of $0.5M$, the Kerr image changes by about $0.45\%$ between $N=192$ and 224, while the tidal charge response changes by about $49\%$. We therefore report no posterior or bound. Spacetime inference should remain closed until the adopted data and covariance are validated, the undeformed source passes an absolute adequacy test, and the differential metric response converges independently of the image.
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High Energy Astrophysical Phenomena

The Origin of Multi-TeV Gamma-rays in LHAASO J0341+5258 via Cosmic Ray Illumination of Molecular Clouds

Abhijit Roy, Alan Sunny, Martina Cardillo et al. (+2 more)

We investigate the origin of the ultra-high-energy $\gamma$-ray emission detected by the Large High Altitude Air Shower Observatory (LHAASO) from the source LHAASO J0341+5258, which has not yet been associated with any known astrophysical object within the detector's field of view. The observed UHE emission is modelled within two independent frameworks: initially with a time-dependent, source-independent hadronic scenario implemented with the numerical package GAMERA, where particles propagate through the interstellar medium and subsequently interact with the molecular gas observed in the region and finally with an analytical description of the interaction between the accelerated cosmic-ray population from a supernova remnant (SNR) and the molecular gas around it. The relevant parameter space for the hypothetical past SNR is explored using the observed TeV $\gamma$-rays. We show that, for physically plausible source-cloud separations and propagation timescales, GAMERA provides a first-order approximation to the spectral modifications induced by particle transport and yields an adequate fit to the ultra-high-energy $\gamma$-ray data. Within the framework of our analytical approach, we demonstrated that the observed GeV emission can plausibly originate from the SNR itself, while the TeV emission detected by LHAASO can be consistently interpreted as arising from particles that have escaped from the SNR and are illuminating nearby molecular clouds. We invoke a spatio-temporally evolved SNR-molecular cloud interaction scenario to account self-consistently for the entire $\gamma$-ray spectrum from GeV to TeV energies. Despite the remaining uncertainty regarding the nature of the acceleration source, we conclude that the TeV emission detected by LHAASO can be consistently interpreted within the framework of an illumination scenario.
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All authors Abhijit Roy, Alan Sunny, Martina Cardillo, Jagdish C. Joshi, Ritabrata Sarkar

Cosmology and Nongalactic Astrophysics

A Universal Relation Between Primordial Density-Potential Cross-correlation Coefficient and Spin Factor Distribution

Jun-Sung Moon, Jounghun Lee and Juhan Kim

Recent studies have revealed that the key properties of visible galaxies like their optical sizes, stellar ages, star formation rates and morphologies are closely linked with the angular momenta of their host dark matter halos. According to the linear tidal torque theory, the halo angular momentum, as a conserved quantity, is directly proportional to the primordial spin factor, $\tau$, defined as the degree of misalignment between the principal axes of the initial density and potential Hessian matrices, which were found by numerical experiments to follow a Gamma distribution, fully characterized by its mean and variance. In this study, we heuristically develop an analytic expression for the mean and variance of $\tau$ in terms of the initial density-potential cross-correlation coefficient, $q$. Analyzing a dataset from the Multiverse simulations performed for both of the flat $\Lambda$CDM and $w$CDM cosmologies, we prove that this analytic expression is universally valid in describing how the mean and variance of $\tau$ change with $q$, regardless of the smoothing scales for both of the cosmologies. Given the prior finding that the $\tau$-distribution can be reconstructed from the observable galaxy size distribution, this universal analytic expression may allow us to determine $q$ from the same observable via the mean and variance of $\tau$. We discuss a possibility of constraining the early universe physics from the reconstructed $q$ via our heuristic model, without suffering from cosmological degeneracies.
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Astrophysics of Galaxies

Even central galaxies feel their environment: cosmic siphoning of cool gas accretion

Ke Xu and Tao Wang

Identifying the key processes regulating cool gas accretion in galaxies is essential for understanding the baryon cycle within galactic ecosystems. Recent studies indicate that the most fundamental internal process is likely the competition between halos and central black holes. This is revealed through a universal relation between increasing black hole masses and decreasing cool gas fraction ($\mu_{\rm HI} \equiv M_{\rm HI}/M_{\star} \propto M_{\rm BH}^{-0.6}$). Here we further explore the primary external effects on cool gas accretion in central galaxies. We find that galaxies deviating significantly from the $\mu_{\rm HI}-M_{\rm BH}$ relation are overwhelmingly isolated central galaxies without substantial satellites. These isolated, gas-poor centrals exhibit systematically higher black-hole-to-stellar-mass ratios and more prominent bulges, suggesting a greater susceptibility to AGN feedback. At larger scales, they are preferentially located near massive neighboring halos. We interpret these as evidence of "cosmic siphoning” – a multi-scale, gravity-driven process in which cool gas is channeled into deeper potential wells. On inter-halo scales, it manifests as competitive accretion: massive dark matter halos intercept cold filamentary streams, starving neighboring low-mass halos and quenching their star formation. On sub-halo scales, an analogous siphoning operates within groups and clusters, where the central galaxy systematically drains gas from its satellites through tidal interactions and accretion of satellite circumgalactic medium. This multi-scale mechanism – from inter-halo competition to central-satellite interplay – naturally drives the observed differences in the cool gas fractions between isolated and group centrals, or among the isolated, between those with and without a massive neighboring halo, and embodies a cosmic "rich-get-richer" paradigm.
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Instrumentation and Methods for Astrophysics · Cross-listed from cs.CV

PlumeQuant: Uncertainty-aware consistency assessment of methane plume masks and emission-rate estimates

Parisa Masnadi Khiabani, Wolfgang Jentner, Alireza Rangrazjeddi et al. (+4 more)

Imaging spectrometers increasingly distribute source-resolved methane plume products in which the plume mask, integrated mass enhancement (IME), plume length, emission rate, and uncertainty are physically and algorithmically linked. Using 63 EMIT-derived Carbon Mapper plume records from 27 scenes, we show that these published scalar quantities do not uniquely constrain the plume boundary: substantially different yet plausible masks reproduce the same IME, plume length, and emission rate. Genetic-algorithm (GA) ensembles conditioned on the published IME and plume length make this equifinality explicit: the high-confidence core selected by nearly all target-consistent masks covers a median of 13% of the plausible footprint envelope, and ambiguity is largest for weak, low-overlap plumes. The diagnostics come from PlumeQuant, which recomputes IME, plume length, emission rate, and five-term uncertainty from distributed product components under stated conventions and evaluates four mask representations: the distributed reference mask, a transparent Carbon Mapper-informed analogue (CM-like), the GA ensemble, and optional expert edits. The CM-like mask is generated per plume without access to the reference mask or published quantities, with settings fixed once on a scene-disjoint 44-plume development split. It reproduced published IME with +0.72% median difference and emission rate with +0.16% (6.98% mean absolute), reached 0.843 median intersection-over-union against the reference masks, and matched the published uncertainty scale (median ratio 1.01). Holdout mean absolute errors were 7.6% (IME), 9.5% (length), and 6.1% (rate). These are product-level consistency diagnostics, not independent validation. They flag weak, offset, or ambiguous plumes for expert review.
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All authors Parisa Masnadi Khiabani, Wolfgang Jentner, Alireza Rangrazjeddi, Michael C. Wimberly, Binbin Weng, David Ebert, Charles Nicholson

Astrophysics of Galaxies

The dynamical environment of the high-mass star-forming region G28.288$-$0.364

Jyotirmoy Dey, Devendra K. Ojha and Jagadheep D. Pandian

Massive stars form within deeply embedded dust cores, and the development of hypercompact and ultracompact H II regions characterizes their early evolution. Identifying and analyzing such regions is essential for understanding the physical processes that govern massive star formation and the transitions between early evolutionary stages. In this article, we investigate the physical and kinematic properties of the massive star-forming region G28.288$-$0.364 to constrain the evolutionary stages of embedded H II regions and the surrounding cores. We analyze multiwavelength observations, including uGMRT radio continuum data; archival continuum and radio recombination line data from the GLOSTAR-D survey; high-angular-resolution ALMA Band 3 radio recombination line and 1.36-mm dust continuum data from the ALMAGAL survey; and complementary molecular line tracers. We derive spectral indices, measure linewidths and velocities of the radio recombination line emission, identify compact dust cores using dendrogram analysis, and estimate their physical properties. The radio continuum emission exhibits a positive spectral index, consistent with partially optically thick free-free emission. High-resolution observations resolve the ionized gas into two distinct components with physical sizes of $\sim$ 0.06 pc, and their RRL linewidths ($\sim$ 37 and 32 km s$^{-1}$, respectively) indicate that one component is in a transitional stage between hypercompact and ultracompact H II regions, while the other is more evolved. The 1.36-mm dust continuum data reveal five dust cores with surface densities consistent with the theoretical threshold for massive star formation. In summary, these results highlight the complex and sequential nature of massive star formation in clustered environments and demonstrate the importance of high angular resolution observations for resolving the early evolution of massive stars.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th

NNStar: An end-to-end AI agent for nuclear matter and neutron star physics

Yao Ma, Yong-Liang Ma and Jia-Ying Xiong

Constraining the equation of state of dense matter requires confronting effective models with massive data that spans many orders of magnitude in scale, from sub-saturation nuclear matter properties to the masses, radii, and tidal deformabilities of neutron stars. Exploring the high-dimensional coupling space of such a model and fine tuning it against all of these constraints is a labor- and time-intensive task. We present NNStar, an end-to-end artificial-intelligence agent that automates this workflow. Rather than a bespoke application, NNStar is delivered as a portable skill for an open large-language-model (LLM) agent platform – a self-describing module that pairs worked usage conventions with symbolic and numerical physics engines that (i) build a relativistic mean-field model directly from a Lagrangian, (ii) solve the mean-field equations of motion and evaluate the saturation properties, (iii) construct the $\beta$-equilibrium equation of state, splice it to a crust, and integrate the Tolman–Oppenheimer–Volkoff equations, and (iv) score the resulting predictions through a Bayesian joint analysis against nuclear matter and astrophysical observations. The agent can read a model, fit its parameters, and report the full set of nuclear matter and neutron star observables without human intervention. NNStar therefore provides a new, AI-driven framework for analyzing nuclear matter and neutron-star observations.
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Solar and Stellar Astrophysics

Long-Baseline VLF Observations of Solar Flares from Antarctica

Kamen Kozarev, Peter Petkov, Ivaylo Nachev et al. (+4 more)

We present long-baseline Very Low Frequency (VLF) observations of solar flare-induced ionospheric disturbances obtained at the Bulgarian Polar Astronomical Observatory (St. Kliment Ohridski Base) on Livingston island, Antarctica. Using continuous VLF transmissions at 21.4 kHz (NPM, Hawaii) and 24.0 kHz (NAA, Maine), propagating over trans-hemispheric paths exceeding 11 000 km, we analyze observations of solar flares during the period 24 January-8 February 2025. After removing the strong diurnal signal via superposed epoch analysis, we analyse the flare-related perturbations in VLF amplitude and their correlation with GOES soft X-ray flux for 250 flares of C and M class. The long propagation paths provide enhanced sensitivity to flare-driven changes in D-region ionization. The observations reveal clear, frequency-dependent responses and measurable time delays between X-ray peaks and VLF extrema. These delays, including cases of near-zero or negative correlation lag for stronger events, are consistent with a possible role for flare spectral characteristics and D-region recombination processes, although alternative explanations related to waveguide propagation and signal-profile differences cannot presently be excluded. Our results demonstrate the scientific value of long-baseline Antarctic VLF observations for detecting and timing GOES-class flares, while also highlighting key limitations, such as background variability and path-dependent propagation effects, which must be quantified for reliable VLF-based flare monitoring.
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All authors Kamen Kozarev, Peter Petkov, Ivaylo Nachev, Veselka Radeva, Momchil Dechev, Galin Borisov, Anton Atanasov

Cosmology and Nongalactic Astrophysics

Testing string theory with combined cosmological probes: a case study for dark matter gravitons

Alkistis Pourtsidou

The string theory Swampland programme has resulted in distinct scenarios for the particle nature of dark matter. In this research note, I use combined cosmological probes to constrain the Dark Dimension scenario, which predicts that dark matter consists of decaying massive gravitons characterised by a time-dependent kick velocity. I first provide updated constraints using a combination of CMB and BAO data. I then produce forecasts for a Stage-IV tomographic survey, and outline strategies for predicting the model's behaviour on nonlinear scales. The results demonstrate the potential of surveys like Euclid and LSST to confirm or rule out string theory models of the dark sector.
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