Instrumentation and Methods for Astrophysics
Gram-Schmidt correlation bookkeeping for weighted FBET-type frameworks: separating short- and long-range correlation scales in correlated measurements, with an application to radio luminosity functions
Marko Imbrišak and Krešimir Tisanić
Uncertainty quantification for correlated measurements frequently requires a covariance model that mixes several qualitatively different correlation structures: local measurement noise, short-range (e.g. cyclic or seasonal) correlations, and long-range correlations associated with trend, drift, or long-
memory behavior. Weighted and generalized least squares can encode such structure only when the covariance
matrix is known or credibly specified in advance, which in practice it rarely is. We describe a structured correlation bookkeeping construction intended for use inside a weighted FBET-type (wFBET) uncertainty-quantification framework: candidate correlation basis functions associated with distinct lag variables are orthogonalized with a weighted Gram-Schmidt procedure (under an explicitly declared, statistically motivated metric) before they are allowed to enter the covariance or metric construction. This avoids the double counting inherent in naive additive covariance decompositions of the form $\Sigma = \Sigma_{\mathrm{short}} + \Sigma_{\mathrm{long}}$. We
benchmark the construction (in its vectorized form, its operator-valued kernel form, and the finite-rank basis-function realization used by the implementation) on the classic AirPassengers
benchmark dataset, and we apply it to the astrophysical case of
radio luminosity functions measured in
redshift bins. No claim of universal optimality is made; the goal is a transparent and auditable way to organize correlation scales within weighted information-
geometric fitting frameworks.
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Earth and Planetary Astrophysics
The forced orbital planes of the Plutinos and other resonant KBOs
Ian Matheson and Renu Malhotra
The forced plane of non-resonant minor
planets has been understood to be well-estimated by the local Laplace plane given by linear Laplace-Lagrange secular perturbation theory, but there is no extant theory for the forced plane of resonant minor
planets. With improved methodology, we revisit our previous measurement of the mean orbital plane of the observed Plutinos, a group of Kuiper belt objects locked in Neptune's 3:2 mean motion resonance. In the J2000 ecliptic-equinox reference frame, the measured mean plane has an inclination of 1.9 degrees and an ascending node at 46.8 degrees longitude, with a 95% confidence of 2 degrees in the plane position; it is well separated from the local Laplace plane but is indistinguishable from the
solar system's invariable plane. We also show that, at high statistical confidence, the two dynamical subgroups, the doubly resonant Plutinos whose arguments of perihelion librate about +90 and -90 degrees, have different mean planes from each other. Additionally, we measure the mean planes of four other observed resonant groups in the Kuiper belt: the 5:3, 7:4, 2:1, and 5:2. Although these groups have substantial sample sizes (in the range 56-105), their mean planes are presently not statistically distinguishable from their local Laplace plane, Neptune's plane, and the invariable plane. For all five resonant groups, we also report the best-fit von Mises function for their inclinations. These empirical measurements underscore the need for theoretical analysis to understand the spatial dynamics of resonant populations of minor
planets. Such analysis could potentially enable their use for uncovering unmodeled perturbations and/or undiscovered perturbers.
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High Energy Astrophysical Phenomena
Reconstructing Core-Collapse Supernova Gravitational-Wave Signals with Transdimensional Bayesian Inference
Hayden Chapman, Jade Powell, Nir Guttman et al. (+2 more)
Core-collapse
supernovae (CCSNe) are promising future sources of gravitational waves for current and next-generation observatories. Reconstructing CCSN gravitational-wave signals is challenging as they contain
stochastic elements, have multiple complex features, and cover a wide frequency band. The stochasticity of the signal in particular motivates the need for morphology-independent reconstruction techniques which, once observed, will enable us to infer properties of the newly born proto-
neutron star, the rotation, and the unknown CCSN explosion mechanism. In this work, we investigate the reconstruction of gravitational-wave signals from CCSNe using the transdimensional
Bayesian inference framework tBilby. We demonstrate the method using simulated signals in synthetic Advanced LIGO detector noise at a range of signal-to-noise ratios. We reconstruct the signals using two types of wavelets: sine Gaussians and chirplets. We calculate overlaps between injected and reconstructed signals of up to 85%. We find that even when reconstruction overlap values are low, enough of the time-frequency structure of the dominant mode is captured to still make statements about the size of the evolving proto-
neutron star. These capabilities establish tBilby as a powerful tool for gravitational-wave astronomy with burst sources.
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All authors Hayden Chapman, Jade Powell, Nir Guttman, Yi Shuen Christine Lee, Paul D. Lasky
Astrophysics of Galaxies
The Zero-Age Massive Stellar Population of W49A from VLA Observations
M. Juárez-Gama, R. Galván-Madrid, G. Suárez et al. (+14 more)
We use all-configuration VLA data at 3.3 cm with a physical resolution of ~2000 AU to infer the embedded zero-age massive
stellar population of the W49A protocluster, as traced by its compact, ultracompact (UC), and hypercompact (HC) H II regions. Our method consists of visual source identification, the derivation of
stellar ionizing-
photon rates from the observed emission measure, and the further derivation of
stellar masses and luminosities using state-of-the-art
stellar calibrations. Considering the 101 robust detections, maximum-likelihood estimation fitting of the high-mass end (M > 10.9 M_\odot) of the sample yields power-law slopes Gamma >= 2.40 for the logarithmic representation of the
stellar initial mass function (IMF): dN/d(log M) proportional to M^{-Gamma}. The result is robust considering different assumptions for the ionizing
stellar systems. The slopes remain at Gamma >= 1.88 after correction for optical depth effects at 3.3 cm. Therefore, the inferred distribution of
stellar masses presents a clear deficit in the high-mass end as compared to the standard
stellar IMF (Gamma = 1.35). We propose that this is due to a shorter lifetime of the
radio-detected H II regions produced by higher-mass
stars, but evolutionary effects in the mass distribution of
star formation within embedded protoclusters cannot be discarded.
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All authors M. Juárez-Gama, R. Galván-Madrid, G. Suárez, C. G. De Pree, J. J. Tobin, G. Bruzual, A. Ginsburg, J. E. Mendoza-Torres, H. B. Liu, D. Wilner, T. Nony, A. Parra-López, R. Rivera-Soto, A. F. McLeod, N. Cunningham, X. Lu, E. F. Jiménez-Andrade
Earth and Planetary Astrophysics
SMA 200-400 GHz Survey for 10 faint Class II Disks in the Taurus Molecular Cloud
Chia-Ying Chung, Hauyu Baobab Liu, Sean M. Andrews et al. (+3 more)
We have performed Submillimeter Array (SMA) observations of 198.0-407.5 GHz broadband spectra of 10 Class II protoplanetary disks in the Taurus-Auriga region. The 337 GHz flux densities ($F_{\rm 337 GHz}$) of these objects are in the range of 8.2-34 mJy. The median and standard deviation of the 198-358 GHz spectral indices ($\alpha_{198-358}$) of these 10 Class II disks are 1.9 and 0.3, respectively. Compared to the recent, similar SMA survey on another 47 Class II disks that are brighter at (sub)millimeter bands ($F_{\rm 337 GHz}\sim$20-730 mJy), there is no evidence that these newly observed 10 fainter Class II disks have systematically different $\alpha_{198-358}$ values. At $>$230 GHz frequencies, the optical depths of these 10 fainter Class II disks may be as high as those of the brighter sources, which may be $\gtrsim$5. In addition, the low ($<$2.0) values of $\alpha_{198-358}$ in some faint objects may be explained by the effect of
dust self-scattering, with maximum
dust grain size ($a_{\rm max}$) $\sim$ 100 $\mu$m, or by contamination by free-free emission.
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All authors Chia-Ying Chung, Hauyu Baobab Liu, Sean M. Andrews, Mark A. Gurwell, Melvyn Wright, Feng Long
Solar and Stellar Astrophysics
The IACOB project XVIII. Prevalence of short-period binaries among Galactic helium rich O-type stars
C. Martínez-Sebastián, R. Gamen, O. G. Benvenuto et al. (+6 more)
For decades, the origin of helium enrichment in O-type
stars has remained an open question. In this study, we investigate the correlation between surface helium abundance and orbital parameters for a sample of 45 O-type SB1 systems –including Cyg X-1. We find seven He-rich systems, all of which are concentrated at short orbital periods (P$\lesssim 15$ days) and are classified as runaways. In addition, four of them present relatively high eccentricities, while the other three have ellipsoidal variations. We argue that these properties are the result of binary interaction. These findings provide strong observational evidence that binary interaction is the dominant origin of helium enrichment in O-type
stars. This result has important implications for the treatment of chemical mixing and surface abundances in massive-
star evolutionary models, and establishes helium enrichment as a promising observational tracer for identifying post-interaction binary systems.
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All authors C. Martínez-Sebastián, R. Gamen, O. G. Benvenuto, E. A. Saavedra, M. Carretero-Castrillo, M. Contreras, G. Holgado, J. Maíz Apellániz, S. Simón-Díaz
Instrumentation and Methods for Astrophysics
Development of next-generation event-driven x-ray hybrid CMOS detectors
Timothy R. Emeigh, Abraham D. Falcone, Joseph M. Colosimo et al. (+14 more)
The Penn State University High Energy Astrophysics Detector and Instrumentation Lab, in collaboration with Teledyne Imaging Sensors, has developed a next-generation event-driven X-ray hybrid CMOS detector. This detector is an HCD with a 1,024x1,024 array of 21-micron pitch pixels, featuring a comparator in each pixel to enable event-driven readout. While the full frame operation of this detector can reach readout speeds of up to 150 Hz, this event-driven operation allows readout of only those pixels that surpass a user-set charge threshold, enabling effective rates of up to 10 kHz. Here we report on the past detector development efforts at Penn State and describe these new detectors and expected performance improvements.
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All authors Timothy R. Emeigh, Abraham D. Falcone, Joseph M. Colosimo, Kadri M. Nizam, Lukas R. Stone, Md. Arman Hossen, Laurel ONeill, Ian Ashcroft, Kyle Bonene, Brynn Bortree, Zachary E. Catlin, Sierra Deppe, Killian M. Gremling, Gavin Houlihan, Katie McWhirter, David M. Palmer, Abigail A. Raytsis
Instrumentation and Methods for Astrophysics
Proof of concept of the COSMOCal project at the IRAM 30m telescope
S. Savorgnano, L. Bizzarri, A. Ritacco et al. (+25 more)
This work reports on a test campaign conducted at the IRAM 30m
telescope to validate the COSMOCal instrument, a novel concept for absolute calibration of polarization angle, beam properties, and instrumental efficiency. The development is motivated by the stringent calibration requirements of current and next-generation
Cosmic Microwave Background (CMB) experiments, whose goal is the precise measurement of CMB polarization. Such measurements are essential to probe fundamental physics, including the possible imprint of
primordial inflation. The COSMOCal concept is designed as a space-borne calibration reference intended to provide a stable and absolute polarized signal observable simultaneously by multiple large-aperture ground-based observatories. Prior to any space deployment, a terrestrial prototype was developed and characterized in the laboratory, as reported in Ritacco et al. 2024. The results presented here describe the first validation of the system coupled to an
antenna, carried out at the IRAM 30m
telescope in September 2024. This campaign aimed at assessing the performance of the full instrument under realistic observational conditions, including its ability to reconstruct polarization observables and interface with a state-of-the-art millimeter-wave polarimeter.
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All authors S. Savorgnano, L. Bizzarri, A. Ritacco, J. Aumont, F. Boulanger, A. Catalano, F. Cuttaia, A. Denis, F.-X. Désert, D. González Ovejero, S. Leclercq, J.-F. Macías-Pérez, B. Maffei, M. Migliaccio, L. Montier, P. Morfin, L. Mousset, M. Murgia, F. Nati, P. Ortu, M. Pérault, G. Pisano, T. Pisanu, N. Ponthieu, L. Terenzi, J. Treuttel, L. Vacher, M. Zannoni
Instrumentation and Methods for Astrophysics
Graph reconstruction from random-walk co-visitation: Geometric, empirical, and controlled networks
Marko Imbrišak and Krešimir Tisanić
Reconstructing an unknown graph from the trajectory of a random walk arises both for spatial correlation networks in astrophysics and for connectivity inference in network science. We present a reconstruction pipeline whose observable is the random-walk co-visitation
matrix, whose model is a pairwise edge-weight basis, and whose fitter is a frame-balanced Levenberg-Marquardt (fbLM) scheme with per-node group weights and a self-calibrated edge readout. Unlike the marginal occupation, the co-visitation retains the ordered pair before the row sum is taken, and the pairwise basis can represent structure that an additive node-potential model cannot; neither change suffices alone. We apply the pipeline to an email communication subgraph, to Delaunay and Voronoi networks built from a COSMOS sky catalogue, and to two controlled 12-vertex test graphs, one unicyclic and one a tree, under both analytic-noise and finite-walk regimes. Reconstructions are scored against the ground-truth adjacency, which enters nowhere in the fit, by true/false positives and the Matthews correlation coefficient (MCC). All test-beds are reconstructed with high fidelity at full graph size: on finite-walk data we recover the COSMOS Delaunay and Voronoi graphs at MCC above 0.98 up to their full extent, N=119 and N=223, the whole graph rather than a cut-out of it, and the empirical email-Eu-core graph at N=240 (417 edges). On the full Delaunay graph a graphical-lasso reference returns MCC 0.540 against 0.988 for fbLM. Each reconstructed edge carries a Fisher-propagated uncertainty, and the residual misses are almost entirely confined to edges the walk never traverses. In the finite-walk regime the limiting factor is therefore walk coverage rather than the fit: essentially every edge the walk visits is recovered, so reconstructibility is governed by the sampling of the graph rather than by the
estimator.
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Instrumentation and Methods for Astrophysics
Information Geometry meets Functional ANOVA: An Exact Fisher-Information Decomposition, with an Application to Radio Luminosity Functions
Marko Imbrišak and Krešimir Tisanić
Information geometry represents a fitted model as a
manifold whose metric is the Fisher information. We show that, for a nonlinear regression model, this metric decomposes exactly across the Hoeffding-Sobol' (functional ANOVA) channels of its
covariates. Treating the score contributions of main effects and interactions as vectors in a
Hilbert space, their Gram
matrix reproduces the (Gauss-Newton) Fisher information metric exactly, and this identity extends to an exact, additive decomposition of the Fisher information
matrix into main-effect, interaction, and cross-channel terms: a Sobol'-type accounting for parameter information rather than output variance, and equivalently a channel-resolved pullback of the ambient Fisher metric along the model
embedding. We give the exact decomposition
theorem with a short proof (deriving both the centered and uncentered Fisher information), define information-theoretic analogues of Sobol' indices, characterize the sign and finite-sample behaviour of the cross-channel terms, and describe two practical
estimators. As an astrophysical application we decompose the parameter information of a combined 1.4 GHz
radio luminosity-function model spanning active
galactic nuclei (AGN) and
star-forming
galaxies (SFG), fit to 6dFGS-NVSS and VLA-COSMOS 3 GHz data: the decomposition localizes where in luminosity each population and survey constrains the fit, and exposes the compensating ("sloppy") channel combinations near the luminosity-function turnover. A plant CO2-uptake experiment serves as a small, fully categorical companion example.
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Instrumentation and Methods for Astrophysics
Comparing the contrast performance of two IFU technologies for exoplanet direct imaging with ELT-PCS
Ryan Griffiths, Siddharth Maharana and Matthias Tecza
A key science goal for the Planetary Camera and Spectrograph (ELT-PCS) instrument is to image rocky
exoplanets in reflected light around nearby M- and K-
dwarfs. These observations will require a contrast of 10^(-9) at 100 mas angular separation, and 10^(-8) at 10 mas. To achieve such an extreme performance, every instrument design choice must be carefully evaluated. For ELT-PCS's science instruments, perhaps the most critical design choice is which integral field unit (IFU) technology to use. To this end, we have developed a modular, lab-based integral field spectrograph test bench with which to compare the performance of two popular IFU technologies: image slicers and lenslet arrays. The test bench implements a Lyot coronagraph and a spatial light modulator to simulate a high-contrast imaging system, which feeds each IFU with a diffraction-limited PSF image. Each IFU is coupled to the spectrograph, which achieves R ~ 3000 with the image slicer and R ~ 100 with the lenslet array. The calibration and data reduction for each IFU design are described and the initial results of a contrast comparison are presented. The lenslet array achieves a deeper contrast at angular separations of less than 6 lambda/D. The image slicer, however, gains more at small separations from applying spectral deconvolution, with a 3.4x greater gain at 4 lambda/D. Spectral deconvolution further yields a contrast curve close to the detector noise floor. Further work will focus on carrying out a fully-controlled characterisation of the lenslet array IFU and a more comprehensive study into the effects of adaptive optics residuals on the contrast.
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Solar and Stellar Astrophysics
Revisiting BV & BW Draconis: Detailed Study of Intriguing Multiple System
J. J. Tokarek, W. Dimitrov, M. Polińska et al. (+6 more)
The BV & BW Draconis system is a unique coplanar system of two eclipsing contact binaries. The main objective of this study is to develop a model based on new observations. The only model of the system was obtained 40 years ago. New photometric and spectroscopic data have been collected. Brightness measurements were performed using the differential aperture photometry method, while radial velocity measurements were performed using the cross-correlation method. The resulting curves were analyzed using the Wilson-Devinney method. The resulting model is similar to the one obtained previously; however, the masses of the four components are higher, and the differences are outside the margin of error. In the case of BW Dra, the photometric data indicate the presence of a spot on the
star's surface. Based on our spectroscopic and photometric data, the latest measurements of eclipse times have been obtained. These results, together with other new measurements, confirm previous findings: both pairs exhibit eclipse time variability. In the case of BV Dra, the
parabolic and sinusoidal trends were confirmed and refined. For the second pair, BW Dra, a change in behavior was observed that may be related to a change in period.
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All authors J. J. Tokarek, W. Dimitrov, M. Polińska, M. K. Kamińska, K. Kamiński, P. Koleńczuk, J. Pietrucha, Sz. Ptak, M. Witczak
Instrumentation and Methods for Astrophysics
Comparative analysis of fiber Bragg grating filter losses inscribed by continuous wave UV and femtosecond-IR lasers for astrophotonics
Aashia Rahman, Ria G. Krämer, Abani Shankar Nayak et al. (+8 more)
Fiber Bragg grating (FBG) filters have been demonstrated as promising components in astrophotonic instrumentation for near-infrared ground-based observations. Given the
photon-starved nature of astronomical applications, it is critical to minimize insertion losses across astrophotonic components. In addition to the insertion loss (IL) introduced by specialty fibers and inscription techniques, FBGs exhibit cladding mode (CM) losses. In this work, we studied the loss characteristics of five filter lines in three photosensitive fibers, i.e., a low-numerical-aperture (NA) fiber, a high-NA bend-insensitive fiber, and a cladding-mode-suppressed (CMS) fiber, and in a non-photosensitive fiber, SMF-28. The filters were inscribed using two phase mask-based illumination methods: a continuous wave ultraviolet (UV)
laser with a complex phase mask allowing for multi-channel filters, and a femtosecond infrared (fs-IR)
laser with phase mask integrated shaping apertures for spectral profile control. Our results show that UV-inscribed gratings in high-NA bend-insensitive fiber yield the lowest CM losses ($\approx$ 0.5 dB) among photosensitive fibers, but exhibit the highest IL (4.6 dB), and FBGs in non-photosensitive SMF-28 fiber, inscribed with fs-IR, achieve the lowest IL (< 0.05 dB) with a comparatively higher CM loss (0.93 dB). To reduce the high IL in high-NA fiber, we explored tapering and bridging methods and report that bridging reduces IL by $\sim$ 3 dB. We show that both filter platforms remain viable for integration into an astrophotonic system, with IL below 1 dB. Finally, we propose a compact bridge-fiber scheme with the potential to further reduce IL to below 0.5 dB while reducing the number of bridging fibers and, consequently, the number of splice junctions by 50%.
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All authors Aashia Rahman, Ria G. Krämer, Abani Shankar Nayak, Julius Göhring, Piyamas Choochalerm, Anna Maria Weiß, Samuel L. Döpfner, Tim Schleifer, Kalaga Madhav, Martin M. Roth, Stefan Nolte
Solar and Stellar Astrophysics
Edson Otoniel, Jonathan A. Rebouças, M. C. Araújo et al. (+1 more)
We construct an effective Tolman Oppenheimer Volkoff system for cold carbon white
dwarfs using the areal radius form of a
polymer metric sector motivated by loop
quantum gravity. The two asymptotic mass parameters of the geometry are retained in the
stellar prescription through $M_B\rightarrow m(R)$ and $M_W=\eta m(R)$, while the
polymer amplitude is controlled by $A_\lambda$. The matter sector is kept fixed and is described by the Chandrasekhar equation of state and by the same carbon model with the Coulomb
lattice correction. The resulting equations recover the general relativistic TOV system and the symmetric
polymer limit. For the undeformed sequences we obtain $M_{\max}=1.4166\,M_\odot$ for the Chandrasekhar model and $M_{\max}=1.3850\,M_\odot$ when the
lattice correction is included. Turning on $A_\lambda$ shifts the massive part of the
equilibrium sequence upward without stiffening the equation of state, reaching $M_{\max}=1.7125\,M_\odot$ and $1.6907\,M_\odot$ at $A_\lambda=100$ for the two matter models. These configurations remain within the matter domain imposed by the inverse beta decay boundary used in the scan. The asymmetric ratio $\eta=M_W/M_B$ changes the metric function near the
polymer transition region, but its effect on white
dwarf observables is small: across the selected configurations, $M_{\max}$ changes by less than $0.1\%$ and the corresponding radius by less than $0.33\%$. The calculation therefore identifies $A_\lambda$ as the parameter controlling the super Chandrasekhar displacement of the mass radius relation, while $\eta$ acts mainly as a
geometric asymmetry parameter in the low compactness regime probed by white
dwarfs.
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All authors Edson Otoniel, Jonathan A. Rebouças, M. C. Araújo, J. Furtado
Astrophysics of Galaxies
Scylla: Observational Evidence for an Order of Magnitude in Dust Mass Opacity Evolution with ISM Density in the Large Magellanic Cloud
Christina W. Lindberg, Christopher J. R. Clark, Claire E. Murray et al. (+11 more)
The emissivity of
dust is known to vary greatly with radiative environment, density, grain chemistry, and geometry. Discrepancies between
dust mass surface densities derived from far-infrared (FIR) emission and visible extinction persist across and within
galaxies in the local Universe. Here, we use new extinction and emission measurements towards the LMC to show that this discrepancy is driven by the
dust mass opacity evolving with the intrinsic density of the ISM, and that the ratio between FIR and optical
dust mass opacity varies with gas surface density. These new findings imply that the
dust mass opacity in the FIR could increase by nearly an order of magnitude (e.g., $\kappa_{160} = 0.3 - 6\ m^2\ kg^{-2}$) across over an order of magnitude of total hydrogen surface density $(\Sigma_H = 4 - 100 M_{\odot}\ pc^{-2})$, corroborating previous theoretical models for
dust mass opacity
evolution in the FIR, and providing new implications for emission-based
dust mass estimates.
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All authors Christina W. Lindberg, Christopher J. R. Clark, Claire E. Murray, Julia Roman-Duval, Caroline Bot, Yumi Choi, Roger E. Cohen, Steven R. Goldman, Karl D. Gordon, Kristen B. W. McQuinn, Elizabeth Tarantino, Benjamin F. Williams, Petia Yanchulova Merica-Jones, Catherine Zucker
High Energy Astrophysical Phenomena
AT2025agpz in Rubin commissioning data: distinguishing a luminous interacting supernova from nuclear transients in compact galaxies
C. R. Angus, M. Quilt, H. F. Stevance et al. (+37 more)
The Vera C. Rubin Observatory's Legacy Survey of Space and Time will discover unprecedented numbers of rare, long-lived optical transients, many of which will be too faint or too numerous for comprehensive spectroscopic follow-up. Characterising objects that span the boundaries between established transient classes is therefore essential for improving photometric classification. We present AT2025agpz, a luminous transient at $z=0.147$, discovered around peak by ATLAS but extensively monitored during Rubin commissioning observations of the Euclid Deep Field South. The transient is coincident with the
nucleus of a faint
dwarf galaxy, exhibits a rest-frame rise time of $77.9\pm1.3$ d, and reaches a peak bolometric luminosity of $6.3\times10^{43}$ erg s$^{-1}$. The exceptional depth and cadence of the Rubin commissioning data, combined with complementary DECam imaging, tightly constrain the explosion epoch and yield an early-time power-law rise of $n=3.33^{+0.33}_{-0.28}$. Follow-up spectroscopy reveals remarkably slow spectral
evolution dominated by narrow Balmer emission, while high-resolution X-shooter observations resolve broad electron-scattering wings and multiple H$\alpha$ emission components characteristic of interaction-powered
supernovae. Spectral energy distribution modelling indicates a low-mass, moderately
star-forming host
galaxy. Although AT2025agpz occupies observational parameter space shared by the recently identified Ambiguous
Nuclear Transient population, its colour
evolution, host environment, and emission-line morphology favour an interaction-powered luminous
supernova. More broadly, this event highlights the growing observational overlap between luminous interacting
supernovae and
nuclear transients, illustrating both the challenges and opportunities for transient classification in the Rubin era.
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All authors C. R. Angus, M. Quilt, H. F. Stevance, M. Nicholl, S. J. Smartt, P. Wiseman, A. Möller, C. T. Murphey, P. J. Pessi, K. Auchettl, M. Dennefeld, M. Dominik, C. Frohmaier, P. Francis, M. Gromadzki, A. Lawrence, G. Leloudas, C. Lidman, D. Magill, I. Mandel, B. Martin, S. Mattila, G. Narayan, F. Onori, S. R. Oates, H. M. L. Perkins, L. Rauf, A. Rest, S. Romagnoli, R. Roy, S. Schulze, X. Sheng, K. W. Smith, K. de Soto, P. M. Veres, M. E. Verrico, A. Wasserman, R. Williams, Ł. Wyrzykowski, D. R. Young
Astrophysics of Galaxies
Expanding stellar associations as Galactic accelerometers
Till Sawala and Núria Miret Roig
The gravitational potential of the Milky Way is fundamental for understanding the
evolution of our
Galaxy and the nature of dark matter. We introduce a new method to constrain the
Galactic potential using expanding young
stellar associations. We exploit the physical constraint that these
stars share a common, compact origin to reconstruct their most likely orbits and infer the gravitational potential in which they have evolved. We define the size of an association using the trace and determinant of its position covariance
matrix. By integrating synthetic associations backward in different trial potentials, we show how the true potential can be identified as the one that minimises these metrics. We demonstrate that, while current observational errors are still too large, upcoming observations will allow us to distinguish between different potentials. Our results suggest that with
Gaia DR4 astrometry and radial velocity errors below 0.2 km/s, the
halo mass can be constrained with a precision of 0.6 trillion
solar masses and the concentration with a precision of < 0.8 using a single association, albeit with significant degeneracies. In addition, we show that the inferred dynamical traceback age is sensitive to the gravitational potential, suggesting that independent age information can help break existing degeneracies, but also that traceback-age estimates are not independent of the assumed potential. Expanding
stellar associations carry information about the gravitational potential in which they have evolved. With the arrival of next-generation astrometry and high-precision radial velocities, they will provide a complementary tool for constraining the
Galactic potential.
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Cosmology and Nongalactic Astrophysics
3-form dark energy and cosmic birefringence
Kohei Kamada and Tucker Manton
3-forms are interesting fields to study in the cosmological context for numerous reasons, such as being candidates for explaining inflation and dark energy. The background
evolution of a 3-form field is similar to but distinguishable from a scalar field in an expanding universe, and its tensorial structure allows for unique couplings that cannot be experienced by canonical scalars. In this work, we explore the possibility that 3-form dark energy can explain
cosmic birefringence. We consider two EFT-inspired couplings between the 3-form and the
photon, and compute the birefringence angle $\beta$. We find that a dimension-6 gauge-invariant operator necessitates an extremely large coupling to explain $\beta\sim0.3^\circ$, the value suggested by observations of recent
cosmic microwave background radiation. Conversely, a dimension-4 operator can accommodate $\beta\sim0.3^\circ$ at the expense exciting the longitudinal mode of the
photon. Interestingly, demanding a self-consistent decoupling limit implies the
photon mass lies within a few orders of magnitude of $H_0$. We also derive `universal' profiles for $\beta(z)$, finding the $\beta$ from the dimension-4 operator is insensitive to the form of the 3-form potential but is sensitive to the initial conditions. Contrarily, the dimension-6 operator is highly sensitive to the form of the potential. We finally compare the universal profiles to that of
axion-like particle (ALP) dark energy and an ultralight massive 3-form, the latter obtained from numerically integrated cosmological histories consistent with $\Lambda$CDM up to low
redshift. Our results show that birefringence from 3-form dark energy can both mimic that from an ALP or be distinguishable, depending on the field configuration in the early universe.
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Cosmology and Nongalactic Astrophysics
Summary statistic for pulsar timing arrays
Gabriela Sato-Polito, Matias Zaldarriaga and Barak Zackay
The timing residuals produced by gravitational-wave signals can be described as an incoherent (
pulsar term) contribution and a coherent (Earth term) map on the sky, which PTAs measure at the locations of the timed
pulsars. The observed Earth term map and the variance induced by the
pulsar term contain all of the information about any GW signal available to a PTA (assuming
pulsar distances are unknown). Furthermore, any type of signal produces on average the same angular correlation function, the Hellings and Downs curve, which decays steeply with multipole as $C_\ell \propto 1/[(\ell+2)(\ell+1)\ell(\ell-1)]$. This suggests that the signal is inherently low-dimensional and therefore only a small number of parameters are needed to fully characterize it. We present an expression for the PTA likelihood that makes the dependence on the Earth term map and
pulsar term variance explicit, and show that only a few spherical harmonic coefficients are needed to capture most of the information about the signal. To quantify this in a realistic setting, we compute the Fisher
matrix of the amplitude of a
stochastic background or a deterministic point source assuming the noise properties and sky locations of the
pulsars in the NANOGrav 15yr
dataset. We find that $\ell_{\rm max}=2$ of the Earth term map and the monopole of the
pulsar term variance retain $\sim 95\%$ of the information about the signal. For a point source, including the dipole of the
pulsar term variance is important to achieve a similar fraction.
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Earth and Planetary Astrophysics
Size Constraints for the Pre-atmospheric Parent Bodies of Ordinary Chondrites
Juan A. Sanchez, David C. Cantillo, Adam Battle et al. (+7 more)
The study of S-complex near-Earth objects (NEOs), the parent bodies of ordinary chondrites, has shown that they are dominated by asteroids with LL chondrite-like compositions. This is surprising because among the three subtypes of ordinary chondrites (H, L, and LL), LL chondrites are the least common, representing only 10% of all ordinary chondrite falls. This discrepancy has been attributed to the size of the NEOs studied, which are likely too large to be the immediate precursors of the meteorites that fall on Earth. To test this hypothesis, we obtained near-infrared spectra (0.7-2.5 $\mu$m) of a group of objects with absolute magnitudes 20.0 $\leq$ $H$ $\leq$ 29.2 (sizes $\sim$4-343 m). The sample was divided into subgroups based on their $H$ value, and the composition of the asteroids was determined. We found that the dominance of LL chondrite-like objects disappears at sizes of $\sim$31-49 m. At this size range, asteroids with L chondrite-like compositions become dominant, matching the fraction of L chondrite meteorite falls. In contrast, the fraction of H chondrite-like NEOs was found to be much lower than the proportion of H chondrite falls, even among the smallest objects. We determined an upper size limit of $\sim$18 m for the parent bodies of these meteorites. The same upper limit was established for the pre-atmospheric parent bodies of LL chondrites. These results constitute the first observational evidence for a size dependence in the composition of S-complex NEOs.
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All authors Juan A. Sanchez, David C. Cantillo, Adam Battle, Miren Miranda, Benjamin N. L. Sharkey, Tanner S. Campbell, Rogerio Deienno, William F. Bottke, David Nesvorný, Vishnu Reddy
Astrophysics of Galaxies
Variations in the 3.3 ${\mu}$m Polycyclic Aromatic Hydrocarbon Feature Across Nearby Galaxies Driven by Metallicity and Radiation Field Spectrum
Hannah B. Koziol, Karin Sandstrom, Dalya Baron et al. (+29 more)
We use JWST NIRCam imaging to investigate the 3.3 ${\mu}$m polycyclic aromatic hydrocarbon (PAH) feature in nearby
galaxies. NIRCam observations of the 3.3 ${\mu}$m feature are emerging as a powerful tool for studying the structure of the interstellar medium (ISM) and the conditions of the
dust at ~0".1 resolution. These maps require accurate subtraction of the underlying continuum emission. We present an empirical method to isolate the PAH-correlated emission in the F335M filter using the F300M and F360M filters for continuum subtraction. We find that the slope of the F335M/F300M versus F360M/F300M colors for PAH-correlated emission shows a dependence on local ISM properties, with the strongest dependence on specific
star formation rate. Weaker emission features captured by these bands appear suppressed relative to the main 3.3 ${\mu}$m feature in regions of active
star formation. We find trends in the 3.3/7.7 and 3.3/11.3 ${\mu}$m ratios that suggest changes in PAH size, charge, and heating by a varying radiation field spectrum. We find decreases in both band ratios with increasing
metallicity, which we attribute to a shift to smaller PAH populations at low
metallicity. Comparison to optical ionized gas line ratios and
dust models show that variations in the interstellar radiation field spectrum influence the PAH feature ratios. This analysis supports inhibited growth formation scenarios for the observed PAH band ratio trends with
metallicity and emphasizes the importance of considering the local radiation field characteristics and gas-phase
metallicity when using these band ratios as PAH property diagnostics.
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All authors Hannah B. Koziol, Karin Sandstrom, Dalya Baron, Adam K. Leroy, Jérémy Chastenet, Ryan Chown, Daniel A. Dale, Oleg V. Egorov, Lindsey Hands, Mansi Padave, Debosmita Pathak, Erik Rosolowsky, Jessica Sutter, Tony D. Weinbeck, Thomas G. Williams, Alberto Bolatto, Médéric Boquien, Yixian Cao, Enrico Congiu, Simon C. O. Glover, Hwihyun Kim, Ralf S. Klessen, Kirsten L. Larson, Justus Neumann, Elias K. Oakes, Hsi-An Pan, Ismael Pessa, Sumit K. Sarbadhicary, Benjamin W. Stadel, Jiayi Sun, David A. Thilker, Leonardo Úbeda
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Novel Signatures of Matter-Induced Dark Matter Decay in Large-Volume Neutrino Telescopes
Hooman Davoudiasl, Dan Hooper and Samyak Jain
Large-volume
neutrino telescopes offer a unique opportunity to search for decaying dark matter through events containing a pair of energetic, highly non-collimated
muon tracks emerging from a common vertex. Such events would have negligible Standard Model backgrounds and would constitute a striking signature of new physics. Conventional dark matter annihilation or decay, however, is too strongly constrained to produce an observable rate of such events. We therefore consider scenarios in which an excited dark matter state is extremely long-lived in
vacuum but decays much more rapidly in the presence of ordinary matter. We present two realizations of this mechanism. In the first, a long-range scalar field sourced by ordinary matter modifies the dark-sector mass spectrum, kinematically opening the decay $\chi_2 \rightarrow \chi_1 Z'$ near the Earth while leaving it forbidden in
vacuum. In the second, the scalar background induces kinetic mixing between a heavy $Z'$ and the
photon, greatly enhancing the three-body decay $\chi_2\to\chi_1\mu^+\mu^-$ in matter-rich environments. We calculate the resulting distributions of
muon energies and opening angles and show that viable regions of parameter space can yield observable event rates in IceCube, KM3NeT, and other large-volume
neutrino telescopes while remaining consistent with existing constraints. We also briefly consider the sensitivity of IceCube to multi-
muon events produced by the decays of cosmologically long-lived charged particles with masses $\gtrsim 1$ TeV.
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Astrophysics of Galaxies
Emission line formation in scattering dominated media: implications for LRDs
Elisha Modelevsky, Omri Nitzan, Re'em Sari et al. (+1 more)
Recent JWST observations of “Little Red Dots” (LRDs) reveal broad and prominent Balmer emission lines. We present a theoretical framework for intrinsic emission line formation and broadening within static, optically thick, scattering-dominated gas envelopes with thermal populations. Using random-walk and
diffusion approximations, we derive analytical line profiles for lines forming intrinsically within the scattering medium. We demonstrate that a geometrically thin planar photosphere produces a shallow line profile characterized by a logarithmic plateau and a $v^{-1}$ wing. A radially extended photosphere yields a broken power-law spectrum transitioning from $v^{-\alpha}$ to $v^{-(\alpha+1)}$, with $0 < \alpha < 1$. This is in contrast to a scattering medium external to the line-forming region, which produces an exponential line profile. We show that this broken power-law model can fit the $\mathrm{H}\alpha$ line profiles observed in LRDs. Higher quality spectra may be able to distinguish between intrinsic and extrinsic models for the line broadening in LRDs. In our LTE models, the high contrast between the $\mathrm{H}\alpha$ and continuum flux cannot be explained. Quantitative comparison to LRD spectra requires expanding our models to non-LTE situations.
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All authors Elisha Modelevsky, Omri Nitzan, Re'em Sari, Eliot Quataert
Astrophysics of Galaxies
On the Origin of the Ly$\alpha$ Damping Wing in Galaxies at $8\le z \le 10$: Explorations using the NINJA Simulations
Sukanya Mallik, Raghunathan Srianand and Nishikanta Khandai
Ly$\alpha$ damping wing measurements of
galaxies at $7\leq z\leq14$ with the JWST provide a powerful probe of the Epoch of Reionization. We combine the large-scale cosmological hydrodynamical NINJA simulations with an idealized ionized-bubble model at z=8 and 10 to quantify the contributions of the intergalactic medium (IGM), circumgalactic medium (CGM), and interstellar medium (ISM) to the observed Ly$\alpha$ damping wing. We generate mock Ly$\alpha$ absorption spectra, and consider three idealized scenarios: (i)
galaxies embedded in a uniformly ionized IGM, (ii)
galaxies surrounded by HII regions with radii of 0-400 pkpc, and (iii) the same models including Ly$\alpha$ absorption from partially ionized gas within the virial radius. We explore IGM neutral fractions ($x_{\rm HI}$) of 0.1, 0.8, and 1.0, and compare the distribution of inferred HI column densities (NHI) with observations to constrain the sizes of HII regions and $x_{\rm HI}$ of the IGM and gas in and around
galaxies.
Galaxies are surrounded by over-dense gas extending to $\sim$60-100 pkpc, with its extent increasing with
halo mass and showing little
evolution between z=8 and 10. The inferred NHI also increases with
halo and
stellar mass. While the observed incidence of damped Ly$\alpha$ absorption and the median NHI can be reproduced by different combinations of $x_{\rm HI}$ of the IGM and HII region size, models with a uniformly ionized IGM or HII regions larger than $\sim50$ pkpc fail to reproduce the strongest absorbers (NHI>$10^{22}cm^{-2}$). Including partially ionized gas within the virial radius substantially increases the incidence of these absorbers, although the predicted values remain below the observations, suggesting an additional contribution from unresolved gas in
stellar birth clouds. The strongest damped Ly$\alpha$ absorbers therefore provide a unique probe of the ionization state of the ISM, CGM, and IGM.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Axion-driven spontaneous leptogenesis, precisely
Konstantin Kuckenberg, Martin A. Mojahed, Kai Schmitz et al. (+1 more)
We revisit a minimal scenario for spontaneous leptogenesis where the asymmetry generation is driven by a heavy
axion-like field evolving via standard misalignment. We focus on the simplest framework in which
lepton number violation originates from the dimension-five Weinberg operator and contributions from standard thermal leptogenesis become negligible. The asymmetry is computed by solving a set of transport equations, which incorporate fully
flavor-dependent interaction rates for the Weinberg operator that are presented here for the first time. We also derive a simple algebraic master formula for the generated $B\!-\!L$ asymmetry, valid for arbitrary
axion velocities and classically shift-symmetric couplings to the Standard Model, that reproduces the $B\!-\!L$-production dynamics of the full set of transport equations in controlled parameter regions. Along the way, we quantify the importance of low-scale
neutrino masses and the two mass orderings on the final prediction for the generated asymmetry. Finally, we assess the cosmological viability of different
axion couplings by accounting for
entropy dilution from late-time
axion decays and imposing constraints from baryonic isocurvature perturbations. We demonstrate that explaining the
baryon asymmetry via standard Majoron misalignment is under severe tension due to dilution from late-time decays. In contrast,
axions coupled to strong or weak sphalerons can successfully produce the observed asymmetry for decay constants near the energy scale of grand unification and
axion oscillation temperatures $T_{\text{osc}} \gtrsim 10^{11\cdots12}$ GeV, provided a cosmological history featuring high-scale inflation and efficient reheating.
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All authors Konstantin Kuckenberg, Martin A. Mojahed, Kai Schmitz, Hidenaga Watanabe
Solar and Stellar Astrophysics
A Galactic intermediate-mass stripped star with a Wolf-Rayet-like wind
Johanna Müller-Horn, Kareem El-Badry, Andreas A. C. Sander et al. (+17 more)
Binary interaction in massive
stars is expected to produce a large population of intermediate-mass ($2$-$8$ M$_\odot$) envelope-stripped
stars, yet such objects have remained elusive in the Milky Way. We report the identification of an unambiguous
Galactic example in a short-period ($P=5.94$ d), double-lined spectroscopic binary, discovered in the SDSS-V Milky Way Mapper survey. The system consists of a rapidly rotating O-type
star and a hotter, lower-mass companion, which shows He II and N IV emission lines with large radial velocity variations, revealing its binary nature. Combined orbital constraints and joint spectroscopic and photometric modelling show that the companion is a hot ($T_\ast \approx 60$ kK), helium-rich
star with a mass of $3.2$-$5.8$ M$_\odot$, placing it squarely in the intermediate-mass regime and below values typically inferred for classical Wolf-Rayet (WR)
stars. The system's short period, negligible eccentricity, and rapidly rotating O-
star point to a post-interaction configuration following efficient mass transfer and
spin-up of the accretor. Comparison with binary
evolution models suggests that the stripped
star is observed in a brief inflated phase following mass transfer, which increases its optical flux contribution and facilitates its detection. The inferred mass-loss rate $\log \dot{M} = -6.3 \pm 0.1$ is in line with mass-loss rates observed for classical WR
stars in the Milky Way and exceeds those measured for intermediate-mass stripped
stars in the Magellanic Clouds, with the caveat that our target selection is biased towards systems with stronger emission features. As an unambiguous and well-characterised intermediate-mass stripped
star, this system provides a key
benchmark for models of binary
evolution at
solar metallicity, stripped-envelope
supernova progenitors, and the formation of compact-object binaries.
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All authors Johanna Müller-Horn, Kareem El-Badry, Andreas A. C. Sander, Hans-Walter Rix, Lisa Blomberg, J. J. Hermes, Pranav Nagarajan, Sahar Shahaf, Harim Jin, Dominick M. Rowan, Debasish Dutta, José G. Fernández-Trincado, Ylva Götberg, Ilya Ilyin, Tom Maccarone, José Eduardo Méndez Delgado, Guy S. Stringfellow, Andrew Tkachenko, Jaime I. Villaseñor, Eleonora Zari
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
The glow of eternal black holes
Vladimir Strokov
We compute the optical appearance of a maximally extended (eternal) Schwarzschild black hole surrounded by a geometrically thin
accretion disk. Unlike astrophysical black holes formed by gravitational collapse, the eternal solution contains a white hole (WH) region connected to a past singularity. Following Markov's hypothesis of a limiting density of matter, we replace the past singularity with a spacelike "surface of last scattering" at $r=r_{\rm m}$ and assume that it emits black-body radiation with temperature $T$. Past-directed rays that cross the past horizon terminate on this surface, resulting in a bright spot at the center of the shadow of an eternal black hole. The radial profile of the spot is set by the gravitational frequency shift, with a blueshifted center when the spacelike surface is sufficiently close to the singularity. We use ray tracing to generate an image of the disk and the spot, and we derive a closed-form interferometric signature of the spot. Its visibility is a pure exponential in the baseline length, in contrast to the power-law envelopes of the disk and the
photon ring. We constrain the product $r_{\rm m} T$ from the observed 230 GHz fluxes of M87* and Sgr A*. We also consider a Planck-
star scenario in which the value of $r_{\rm m}$ is determined on dimensional grounds, and show that it is out of reach of any current or planned facilities. Nevertheless, the darkness of the observed shadows remains a test of whether these black holes are eternal.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Baryogenesis via the CKM Matrix with Minimal Flavor Violation
Innes Bigaran, Gordan Krnjaic, Kevin Langhoff et al. (+1 more)
It is often claimed Standard Model CP violation is insufficient for baryogenesis. We present a counterexample using minimal
flavor violation (MFV) in which all CP-violating effects arise from the Cabibbo-Kobayashi-Maskawa (CKM)
matrix. Our scenario involves a leptoquark field with MFV-preserving interactions whose decays to Standard Model particles yield the observed
baryon asymmetry in the early universe. Unlike previous efforts to realize baryogenesis through the CP violation of the CKM
matrix, our scenario does not require any time-variation of model parameters.
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All authors Innes Bigaran, Gordan Krnjaic, Kevin Langhoff, Huangyu Xiao
Astrophysics of Galaxies
Where did all the Little Red Dots go? The abundance of LRD analogues among objects with broad lines at $z < 0.35$
Lasse Seyberlich and Sarah E. I. Bosman
One of the most puzzling discoveries since the launch of the James Webb Space
Telescope is a numerous population of sources at high
redshift nicknamed “Little Red Dots” (LRDs). Characterized by broad Balmer emission lines, compact morphologies and v-shaped spectral energy distributions (SEDs) in the rest-frame optical, the nature of LRDs remains elusive. A major challenge is the high
redshift nature of LRDs, which makes observations very expensive and difficult. Finding local LRD analogues is a crucial step in unravelling the physical processes giving rise to LRDs, as cheaper observations with many facilities would become available. In this paper, we conduct a search for local LRD analogues by starting from an unbiased parent catalogue of all SDSS objects with broad H$\alpha$ or H$\beta$ emission lines (both
galaxies and
quasars) at $0 < z < 0.35$, complemented by archival photometry and spectroscopy. We find that among broad-line objects, $19\%$ show a v-shaped SED. We then select objects whose SED is well described by a modified black body (MBB), and identify nine local LRD analogues, corresponding to $0.08\%$ of all objects with broad lines. Among only objects which match the typical continuum and emission line luminosities of LRDs, $5\%$ display a v-shape and $0.37\%$ display a MBB-like SED. We recover one previously-identified local LRD analogue (the so-called “Egg”), validating our methodology. Among the other eight analogues, one (J0302$-$0101) shows all the hallmarks of an LRD despite being visibly embedded in the core of a
galaxy; another object is ambiguous, and the remaining six may have alternative explanations for their peculiar SEDs. Our study highlights that LRDs are extremely rare at $z < 0.35$; we find very few objects with broad lines which have LRD-like SEDs, even without attempting to match the compactness of LRDs.
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