Cosmology and Nongalactic Astrophysics
The effect of baryons on the positions and velocities of satellite galaxies in the MTNG simulation
Sergio Contreras, Raul E. Angulo, Sownak Bose et al. (+5 more)
Mock
galaxy catalogues are often constructed from dark-matter-only simulations based on the
galaxy-
halo connection. Although modern mocks can reproduce
galaxy clustering to some extent, the absence of
baryons affects the spatial and kinematic distributions of
galaxies in ways that remain insufficiently quantified. We compare the positions and velocities of satellite
galaxies in the MTNG hydrodynamic simulation with those in its dark-matter-only counterpart, assessing how baryonic effects influence
galaxy clustering and contrasting them with the impact of
galaxy selection, i.e. the dependence of clustering on sample definition. Using merger trees from both runs, we track satellite subhaloes until they become centrals, allowing us to match systems even when their z=0 positions differ. We then compute positional and velocity offsets as functions of
halo mass and distance from the
halo centre, and use these to construct a subhalo catalogue from the dark-matter-only simulation that reproduces the
galaxy distribution in the hydrodynamic run. Satellites in the hydrodynamic simulation lie 3-4% closer to
halo centres than in the dark-matter-only case, with an offset that is nearly constant with
halo mass and increases toward smaller radii. Satellite velocities are also systematically higher in the dark-matter-only run. At scales of 0.1 Mpc/h, these spatial and kinematic differences produce 10-20% variations in clustering amplitude – corresponding to 1-3$\sigma$ assuming DESI-like errors – though the impact decreases at larger scales. These baryonic effects are relevant for cosmological and
lensing analyses and should be accounted for when building high-fidelity mocks. However, they remain smaller than the differences introduced by
galaxy selection, which thus represents the dominant source of uncertainty when constructing mocks based on observable quantities.
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All authors Sergio Contreras, Raul E. Angulo, Sownak Bose, Boryana Hadzhiyska, Lars Hernquist, Francisco Maion, Ruediger Pakmor, Volker Springel
Cosmology and Nongalactic Astrophysics
On distance and velocity estimation in cosmology
Adi Nusser
Scatter in distance indicators introduces two conceptually distinct systematic biases when reconstructing peculiar velocity fields from
redshifts and distances. The first is distance Malmquist bias (dMB) that affects individual distance estimates and can in principle be approximately corrected. The second is velocity Malmquist bias (vMB) that arises when constructing continuous velocity fields from scattered distance measurements: random scatter places
galaxies at noisy spatial positions, introducing spurious velocity gradients that persist even when distances are corrected for dMB. Considering the Tully-Fisher relation as a concrete example, both inverse and forward formulations yield unbiased individual peculiar velocities for
galaxies with the same true distance (the forward relation requires a selection-dependent correction), but neither eliminates vMB when
galaxies are placed at their inferred distances. We develop a modified Wiener filter that properly encodes correlations between directly observed distance $d$ and true distance $r$ through the conditional probability $P(r|d)$, accounting for the distribution of true distances sampled by
galaxies at observed distance $d$. Nonetheless, this modified filter yields suppressed amplitude estimates. Since machine learning autoencoders converge to the Wiener filter for Gaussian fields, they are unlikely to significantly improve velocity field estimation. We therefore argue that optimal reconstruction places
galaxies at their observed
redshifts rather than inferred distances; an approach effective when distance errors exceed $\sigma_v/H_0$, a condition satisfied for most
galaxies in typical surveys beyond the nearby volume.
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Cosmology and Nongalactic Astrophysics
Multimessenger Constraints on Supermassive Dark Stars and Their Black Hole Remnants
Marco Manno, Thomas Schwemberger and Volodymyr Takhistov
Dark matter (DM) annihilation can power the first generation of
stars as long lived dark
stars (DSs) that grow to supermassive scales $M_{\rm DS}\gtrsim 10^{5} M_{\odot}$ and eventually collapse into heavy black holes that could seed the supermassive black holes observed at high
redshifts. We compute the diffuse electromagnetic emission from a cosmological population of such supermassive DSs and their black hole remnants, tracking the entire DS history and including thermal surface radiation, DM annihilation in adiabatically contracted
halos as well as late-time emission from DM overdensity spikes around the resulting black holes. After accounting for
photon attenuation, we find that DS related contributions can exceed the
Fermi-LAT extragalactic $\gamma$-ray background for thermal relic annihilation cross-sections and DM masses below $\sim 1$ TeV. Our results constitute the first population integrated diffuse multimessenger constraints on supermassive DSs as progenitors of early black holes and demonstrate that diffuse
photon and
neutrino backgrounds offer a powerful and complementary avenue for probing the role of DM in the formation of the earliest massive structures.
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Astrophysics of Galaxies
Growth of Aromatic Hydrocarbon Dust Particles in the Extremely Metal-poor Galaxy Sextans A
Elizabeth J. Tarantino, Julia Roman-Duval, Karin M. Sandstrom et al. (+17 more)
The mid-infrared spectrum of
star-forming, high
metallicity galaxies is dominated by emission features from aromatic and aliphatic bonds in small carbonaceous
dust grains, often referred to as polycyclic aromatic hydrocarbons (PAHs). In metal-poor
galaxies, the abundance of PAHs relative to the total
dust sharply declines, but the origin of this deficit is unknown. We present JWST observations that detect and resolve emission from PAHs in the 7%
Solar metallicity galaxy Sextans A, representing the lowest
metallicity detection of PAH emission to date. In contrast to higher
metallicity galaxies, the clumps of PAH emission are compact (0.5-1.5$''$ or 3-10 pc), which explains why PAH emission evaded detection by lower resolution instruments. Ratios between the 3.3, 7.7, and 11.3 $\mu$m PAH features indicate that the PAH grains in Sextans A are small and neutral, with no evidence of significant processing from radiation fields. These results favor inhibited grain growth over enhanced destruction as the origin of the low PAH abundance in Sextans A. The compact clumps of PAH emission are likely active sites of in-situ PAH growth within a dense, well-shielded phase of the interstellar medium. Our results show that PAHs can form and survive in extremely metal-poor environments common early in the
evolution of the Universe.
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All authors Elizabeth J. Tarantino, Julia Roman-Duval, Karin M. Sandstrom, J.-D. T. Smith, Cory M. Whitcomb, Bruce T. Draine, Martha L. Boyer, Jérémy Chastenet, Ryan Chown, Christopher J. R. Clark, Meriem Elyajouri, Karl D. Gordon, Brandon S. Hensley, Thomas S.-Y. Lai, Christina W. Lindberg, Kristen B. W. McQuinn, Max J. B. Newman, O. Grace Telford, Dries Van De Putte, Benjamin F. Williams
Solar and Stellar Astrophysics
TT Arietis: New approach to the analysis of quasi-periodic oscillations
I. Vega-Manubens, N. Vogt, A. Lopera-Mejía et al. (+2 more)
Context. TT Arietis (TT Ari) is a nova-like cataclysmic variable of the VY Scl subtype with light-curve variations on multiple timescales. In addition to the superhump modulation, quasi-periodic oscillations (QPOs) have been found. Aims. Our aim is to determine the occurrence, strength, and variability of QPOs in TT Ari based on more complete data than in previous works. Methods. The data were obtained during the high state of TT Ari in October 2012 by the MOST space
telescope, covering a total of 361.2 hours of continuous observation. We searched for frequencies over subsets of time using a
Fourier-like power spectrum and then added the frequencies together, forming groups. Results. Our method has revealed QPOs that occur in "frequency groups", which are events with a continuous oscillation of similar, constant or slowly variable frequency. We report a total of 160 frequency groups in the period range between 14 and 53 minutes (27 and 98 days-1), with two peaks in the power spectrum at 18.5 and 33.8 minutes (42.5 and 77.5 days-1). The duration of these frequency groups varies between 0.72 and 7.5 hours (average 2.8 hours) revealing between 3 and 18 complete cycles in the light curve. Most of them show significant frequency variations over the course of their duration. Sometimes two frequency groups occur simultaneously. An analysis with randomised data confirms that
stochastic processes can only explain a fraction of the QPOs found. The occurrence of QPOs appears not to be related to the superhump phase.
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All authors I. Vega-Manubens, N. Vogt, A. Lopera-Mejía, G. Aravena-Rojas, P. A. Rojas Lobos
Astrophysics of Galaxies
The Nature of Nitrogen Enhanced High Redshift Galaxies
Peixin Zhu, James Trussler and Lisa J. Kewley
Recent JWST observations have revealed a population of high-
redshift galaxies ($z\gtrsim5$) exhibiting unexpectedly bright ultraviolet (UV) nitrogen emission lines. The strong N III] and N IV] features imply nitrogen-to-oxygen abundance ratios (N/O) as high as $-0.8 \lesssim \log(\mathrm{N/O}) \lesssim 0.4$ in these low-
metallicity galaxies ($12+\log(\mathrm{O/H}) \lesssim 8.2$), compared to the local value of $\log(\mathrm{N/O})\approx-1.5$. If confirmed, this level of nitrogen enrichment challenges existing models of nucleosynthesis and
galaxy evolution. However, the presence of active
galactic nuclei (AGNs) can affect spectral diagnostics, and previous studies often excluded AGN contamination using photoionization models based on local N/O ratios. In this work, we compare nitrogen-enhanced AGN and H II region models to observed spectra of eight high-
redshift galaxies to constrain their nitrogen abundance, excitation source, gas-phase
metallicity, ionization parameter, and gas pressure, simultaneously. We find seven
galaxies (GHZ9, GS 3073, GN-z9p4, CEERS-1019, GHZ2, GN-z11, and GS-z9-0) are best described by nitrogen-enhanced AGN models, while RXCJ2248-ID is best reproduced by the nitrogen-enhanced H II model. The presence of AGN does not significantly impact ($\lesssim0.1\,$dex) the derived N/O ratio. We also find that equivalent width (EW)-based diagrams are the most robust UV diagnostic diagrams to distinguish AGNs and
star-forming
galaxies for situations where the nitrogen abundance is varying. All nitrogen-enhanced
galaxies have moderate to high gas pressure ($7.0\leq\log (P/k)\leq9.8$) and high ionization parameter ($\log(U)\gtrsim-2.0$), indicating a dense and compact environment. We suggest that super
star clusters containing Wolf-Rayet
stars and massive
stars are the most likely contributors to the elevated nitrogen abundance in these
galaxies.
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Solar and Stellar Astrophysics
Modeling of Rayleigh Scattering and Interstellar Polarization for Evolved Late-Type Stars
R Ignace, C Erba, K DeGennaro et al. (+1 more)
Evolved late-type
stars are frequently identified as photometric and spectroscopic variables, such as Mira-type or semi-regular variable objects. These
stars can also be polarimetrically variable, an indicator of non-spherical geometry for spatially unresolved sources. Departures from
symmetry can arise in a number of ways, such as the presence of a binary companion (e.g., multiple illumination sources for scattered light), brightness variations in the
stellar atmosphere (e.g., large convective
cells), or aspherical circumstellar envelopes (e.g., disks or aspherical
stellar winds). Common polarigenic opacities for cool
stars include Rayleigh scattering and
dust scattering. The classic wavelength dependence of lambda^-4 for Rayleigh single scattering is generally straightforward; however, that signature can be confounded by interstellar polarization (ISP). We explore strategies for interpreting polarimetric observations when the interstellar polarization (ISP) cannot be removed. We introduce a "hybrid" spectrum that includes both Rayleigh polarization for a
stellar contribution and the Serkowski Law for an interstellar contribution. We find the polarization spectral slope can be more shallow than expected from Rayleigh scattering alone. For
stellar variability, shorter wavelengths give higher amplitude changes when Rayleigh scattering dominates the interstellar signal. Quite anomalous slopes can occur over limited wavelength intervals if the
stellar and interstellar position angles differ by 90 deg. Results of the models are discussed in the context of photopolarimetry methods, and an application is considered in terms of variable polarization from the carbon
star, R Scl.
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All authors R Ignace, C Erba, K DeGennaro, G Henson
Instrumentation and Methods for Astrophysics
Large Language Models for Limited Noisy Data: A Gravitational Wave Identification Study
Yixuan Li, Yuhao Lu, Yang Liu et al. (+7 more)
This work investigates whether large
language models (LLMs) offer advantages over traditional neural networks for astronomical data processing, in regimes with non-Gaussian, non-stationary noise and limited labeled samples. Gravitational wave observations provide an suitable test case, using only 90 LIGO events, finetuned LLMs achieve 97.4% accuracy for identifying signals. Further experiments show that, in contrast to traditional networks that rely on large simulated
datasets, additional simulated samples do not improve LLM performance, while scaling studies reveal predictable gains with increasing model size and
dataset size. These results indicate that LLMs can extract discriminative structure directly from observational data and provide an efficient assessment for gravitational wave identification. The same strategy may extend to other astronomical domains with similar noise properties, such as
radio or
pulsar observations.
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All authors Yixuan Li, Yuhao Lu, Yang Liu, Liang Li, R. Ruffini, Di Li, Rong-Gen Cai, Xiaoyan Zhu, Wenbin Lin, Yu Wang
Cosmology and Nongalactic Astrophysics
Freeze-out and spectral running of primordial gravitational waves in viscous cosmology
Giuseppe Fanizza, Eliseo Pavone and Luigi Tedesco
We investigate the impact of shear viscosity on the propagation of
primordial gravitational waves (pGW) after inflation. Without assuming a specific inflationary scenario we focus on the
evolution of pGWs after they re-enter the horizon during a cosmological epoch characterized by the presence of shear viscosity. We show that shear viscosity introduces an additional damping term in the tensor equation, modifying both the transfer function and the energy density power spectrum. For a constant shear viscosity-to-Hubble ratio the transfer function acquires an extra red tilt, while a time-dependent viscosity leads to a running spectral index $\Omega_\text{GW}\sim k^{n_\text{eff}(k)}$ controlled by the time
evolution of the mean free path of the viscous fluid. Our analysis provides a general framework to analytically quantify how shear viscosity can alter the
primordial gravitational wave background in standard and non-standard post-inflationary scenarios. As a case study we evaluate the effect of viscosity of the electron-
photon-
baryon plasma, on both the transfer function and the normalized energy density, finding a $k$-dependent blue tilt due to gravitational wave freeze-out from the viscous phase. This effect corresponds to a fractional difference of order $10^{-3}$.
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High Energy Astrophysical Phenomena
Hydrogen-Rich to Stripped-Envelope:Observational Continuity and Biases in CCSNe
Anjasha Gangopadhyay and Priscila J. Pessi
Although historically classified into discrete subclasses, there is growing evidence that indicates that core-collapse
supernovae (CCSNe) categories often overlap, reflecting continuous variations in progenitor structure, mass-loss history, and circumstellar environments rather than strictly distinct channels. In this review, we explore the proposed continua that link hydrogen-rich Type II SNe to stripped-envelope explosions (IIb-Ib-Ic), and that extend further into interaction-dominated and superluminous events. We discuss the physical processes-
stellar winds, binary interaction, eruptive outbursts, and circumstellar interaction-that may produce graded outcomes across classes, while highlighting where observational evidence supports or challenges smooth transitions. We propose that CCSNe are better viewed as a multidimensional continuum of explosion outcomes, where traditional subclasses act as reference points rather than strict boundaries. Future progress will rely on large, homogeneous
datasets and advanced modeling to disentangle true evolutionary sequences from apparent overlaps, ultimately connecting progenitor pathways to the observed diversity of explosions
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Astrophysics of Galaxies
The Nuclear Star Cluster of M 74: a fossil record of the very early stages of a star-forming galaxy
Francesca Pinna, Nils Hoyer, Jairo Méndez Abreu et al. (+13 more)
Nuclear star clusters (NSC) are dense and compact
stellar systems, of sizes of few parsecs, located at
galactic centers. Their properties and formation mechanisms seem to be tightly linked to the
evolution of the host
galaxy, with potentially different formation channels for late- and early-type
galaxies (respectively, LTGs and ETGs). While most observations target ETGs, here we focus on the NSC in M~74 (NGC~628), a relatively massive, gas-rich and
star-forming spiral
galaxy, part of the PHANGS survey. We analyzed the central arcmin of the PHANGS-MUSE mosaic, in which the NSC is not spatially resolved. We analyzed the NSC
stellar populations in a point spread function (PSF) aperture, and compared it to the host
galaxy. Within the PSF size, the NSC is contaminated by the host-
galaxy light. We performed a two-dimensional spectro-photometric decomposition of the MUSE cube, employing a modified version of the C2D code, to disentangle the NSC from its host. This method provided different data cubes for the NSC and the host
galaxy, allowing for both their comparison in a PSF aperture, and the spatially resolved analysis of the host. Our results show a very old and metal-poor NSC, in contrast to the surrounding regions. While similar properties were found in NSCs hosted by
galaxies of different masses and/or morphological types from M~74, they are somewhat unexpected for a relatively massive
star-forming spiral
galaxy. The spatially resolved
stellar populations of the host
galaxy display much younger (light-weighted) ages and higher
metallicities, especially in the central region (${\sim}500$~pc) surrounding the NSC. This suggests that this NSC formed a long time ago, and evolved passively until today, without any further growth. No significant amounts of gas would have reached the very central region in the last 8~Gyr.
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All authors Francesca Pinna, Nils Hoyer, Jairo Méndez Abreu, Adriana de Lorenzo Cáceres Rodriguez, Nadine Neumayer, Médéric Boquien, Salvador Cardona Barrero, Daniel A. Dale, Ivan S. Gerasimov, Kathryn Grasha, Ralf S. Klessen, Carlos Marrero de la Rosa, Miguel Querejeta, Thomas G. Williams, Smita Mathur, Eva Schinnerer
Astrophysics of Galaxies
Separating halo and disk stars in galaxies with Fuzzy Set Theory
Amit Mondal and Biswajit Pandey
Disk and
halo stars are generally classified using several conventional methods, such as the Toomre diagram, sharp cuts in
metallicity ([Fe/H]), vertical distance ($\left|Z\right|$) from the
Galactic plane, or thresholds on the orbital circularity parameter ($\epsilon$). However, all these methods rely on hard selection cuts, which either contaminate samples when relaxed or exclude genuine members when applied too strictly, leading to uncertain and biased classifications. We develop a flexible and reliable approach to classify disk and
halo stars in
galaxies by applying fuzzy set theory, which can overcome the limitations of traditional hard-cut selection methods. As a case study, we analyze one of the Milky Way/M31-like
galaxies in the TNG50 catalogue. We consider multiple
stellar properties as fuzzy variables and characterize their variations between disk and
halo stars to construct the respective membership functions. These functions are then combined to assign each
star a membership degree corresponding to its
galactic component. Our fuzzy set approach provides a more realistic distinction between the disk and the
halo stars. This method effectively reduces contamination and recovers genuine members that are often excluded by rigid selection criteria. The fuzzy set theory framework offers a robust alternative to conventional hard-cut methods, enabling more accurate and physically meaningful separation of
stellar populations in
galaxies.
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Earth and Planetary Astrophysics
Further constraints on Jupiter's primordial structure
Henrik Knierim, Konstantin Batygin, Ravit Helled et al. (+2 more)
The
primordial structure of Jupiter remains uncertain, yet it holds vital clues on the
planet's formation and early
evolution. Recent work used dynamical constraints from Jupiter's inner moons to determine its
primordial state, thereby providing a novel, formation-era anchor point for interior modeling. Building on this approach, we combine these dynamical constraints with thermal
evolution simulations to investigate which
primordial structures are consistent with present-day Jupiter. We present 4,250 evolutionary models of the planetary structure, including compositional mixing and helium phase separation, spanning a broad range of initial
entropies and composition profiles. We find that Jupiter's present-day structure is best explained by a warm ($4.98_{-2.57}^{+3.00}\, \mathrm{k_B\, m_u^{-1}}$), metal-rich dilute core inherited from formation. To simultaneously satisfy constraints on Jupiter's
primordial spin, however, its envelope must have been significantly warmer ($9.32_{-0.58}^{+0.48}\, \mathrm{k_B\, m_u^{-1}}$) at the time of disk dispersal. We determine Jupiter's
primordial radius to be $1.89_{-0.49}^{+0.40}\, \mathrm{R_J}$. These results provide new constraints on Jupiter's formation, suggesting that most heavy elements were accreted early during runaway gas
accretion, and placing bounds on the energy dissipated during the
accretion shock.
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All authors Henrik Knierim, Konstantin Batygin, Ravit Helled, Luca Morf, Fred C. Adams
Cosmology and Nongalactic Astrophysics
Primary gravitational waves at high frequencies I: Origin of suppression in the power spectrum
Alipriyo Hoory, Jerome Martin, Arnab Paul et al. (+1 more)
[Abridged] The primary gravitational waves (PGWs) are generated in the early universe from the
quantum vacuum during inflation. In slow roll inflation, the power spectrum (PS) of PGWs over large scales, which leave the Hubble radius during inflation, is nearly scale-invariant. However, over very small scales, which never leave the Hubble radius, the PS of PGWs behaves as k^2, where k denotes the wave number. We examine the PS of PGWs at such high wave numbers or frequencies when the PGWs are evolved post-inflation, through the epochs of radiation and matter domination. Firstly, we argue that the PS has to be regularized in order to truncate the unphysical k^2 rise at high frequencies. Assuming instantaneous transitions from inflation to the epochs of radiation and matter domination, we carry out the method of adiabatic regularization to arrive at the PS of PGWs over a wide range of frequencies. We show that the process of regularization truncates the k^2 rise and the PS of PGWs oscillates with a fixed amplitude about a vanishing mean value over small scales or, equivalently, at high frequencies. Secondly, we smooth the transition from inflation to radiation domination (to be precise, we smooth the 'effective potential' governing the equation of motion of PGWs) and examine the impact of the smoothing on the regularized PS of PGWs. With the help of a linear smoothing function, we explicitly show that the smoother transition leads to a power-law suppression in the amplitude of the oscillations (about the zero mean value) of the regularized PS of PGWs over small scales that never leave the Hubble radius during inflation. Our analysis indicates that, when transitions are involved, regularization as well as smooth transitions seem essential to ensure that the correlation functions of the PGWs in real space are well behaved. We discuss the directions in which our results need to be extended.
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All authors Alipriyo Hoory, Jerome Martin, Arnab Paul, L. Sriramkumar
High Energy Astrophysical Phenomena
Line Polarization of Si II $\lambda$6355 Å\ in Type Ia Supernovae: A New Statistical Approach to Probe the Explosion Physics and Diversity
Aleksandar Cikota, Peter Hoeflich, Dietrich Baade et al. (+6 more)
Spectropolarimetry provides a unique probe of ejecta asphericities, offering direct insights into the underlying explosion physics of Type Ia
supernovae (SNe Ia). We analyze the statistical properties of pre-maximum spectropolarimetric data for 24 SNe Ia observed with VLT/FORS, focusing on the Si II $\lambda$6355 Åline. Previous studies have revealed a correlation between the peak Si II polarization degree and the expansion velocity. Here, we combine these observations with multi-dimensional non-LTE radiative transfer simulations. We consider two asphericity classes: (i) lopsided abundance distributions produced by off-center delayed-detonation transitions in near-$M_{Ch}$ white
dwarfs or, for example, WD collisions (Class I), and (ii) global, axisymmetric density asphericities such as those arising from explosions of rapidly rotating WDs or mergers (Class II). Our model grid spans normal to subluminous SNe Ia and successfully reproduces the observed Si II velocity-polarization trend, with higher velocities associated with stronger asphericities. Consistent with observations, transitional SNe Ia and the faint end of the normal SNe Ia population show the highest Si II polarization and are best explained by Class I scenarios. In contrast, subluminous SNe Ia are dominated by Class II asphericities, characterized by lower Si II polarization but significant continuum polarization. The observed distribution of Si II polarization depends on both the observer's viewing angle $\theta$ and the intrinsic asphericity. Statistical analysis of these spectropolarimetric snapshots enables the separation of Class I and Class II contributions and highlights the intrinsic diversity among SNe Ia. Our results imply viewing-angle-dependent luminosities in our local sample, which may have implications when using high-
redshift SNe Ia as evidence for the need of non-standard cosmology.
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All authors Aleksandar Cikota, Peter Hoeflich, Dietrich Baade, Ferdinando Patat, Lifan Wang, J. Craig Wheeler, Yi Yang, Elham Fereidouni, Divya Mishra
Earth and Planetary Astrophysics
Capture into Apsidal Resonance and the Decimation of Planets around In-spiraling Binaries
Mohammad Farhat and Jihad Touma
Transiting circumbinary
planets (CBPs) are conspicuously rare, and entirely absent around
stellar binaries with periods $\leq 7$ days. Here, we exploit a secular resonance to stimulate the orbit of a CBP into strong, disruptive interactions with the host binary. The process requires no tertiary companion and is triggered when the general-relativistic precession of a tightening binary matches the Newtonian precession it induces in its companion
planet. Adiabatic capture in this resonance sees the binary draining angular momentum from the CBP's orbit which grows steadily in eccentricity until destabilization, and eventual ejection or engulfment. We map this resonance in phase space, then investigate the dynamical outcomes of encounter in the course of tidally shrinking binaries. With the help of orbit averaged simulations of a suite of systems, we find that, around tightening binaries: eight out of ten CBPs encounter and are captured in the resonance; three out of four are `destroyed'; and survivors lurk on remote, low-transit-probability orbits. This suggests that the very process which forms tight binaries effectively clears the region where transiting CBPs could reside.
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High Energy Astrophysical Phenomena
The first 10years of the HAWC Gamma-Ray Observatory: science results
Anna Lia Longinotti and HAWC Collaboration
The High-Altitude Water Cherenkov (HAWC) Observatory, located on the slopes of the Sierra Negra volcano in Mexico, began operations in March 2015. Over the past decade, HAWC has enabled the exploration of a broad range of topics in high-energy astrophysics and particle physics, resulting in more than 90 peer-reviewed publications. These studies have significantly advanced our understanding of several previously unexplored and poorly understood phenomena in the TeV energy regime. The present work provides an overview of the key scientific contributions of HAWC during its first ten years of operation.
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Solar and Stellar Astrophysics
X TrA through the eyes of MATISSE: More evidence of clumpy molecular layers around C-type asymptotic giant branch stars
V. Răstău, C. Paladini, J. Drevon et al. (+22 more)
Aims. The goal of this study is to further the understanding of the wind formation mechanism in asymptotic
giant branch (AGB)
stars through the analysis of the close environment (within a few
stellar radii) of the carbon
star X TrA. Methods. X TrA was observed for the first time with the Mid-Infrared SpectroScopic Experiment instrument (MATISSE) in the L and N bands in low spectral resolution mode (R=30), and its close surroundings were mapped in specific wavelength ranges corresponding to specific molecules ($C_2H_2$ and HCN, at 3.1 and 3.8 $\mu$m) and
dust (amorphous carbon and, for example, Sic at 11.3 $\mu$m), via image reconstruction techniques. Results. The angular diameter of the
star ranges from 10 mas in the L band pseudo-continuum (3.5 $\mu$m) to 20 mas at 3.1 and 11.3 $\mu$m. The reconstructed images show some mild elongated features (along the east-west direction) and asymmetric protrusions, which are most evident around 3.1 $\mu$m. Imaging results highlight the clumpy nature of the circumstellar environment, starting from the photospheric region up to more distant layers. Conclusions. The angular diameters found for X TrA in the image data are in agreement with previous photospheric diameter estimates (following VLTI/MIDI 8-13 $\mu$m observations), and their wavelength dependence is similar to values found for other carbon
stars observed with MATISSE (R Scl and V Hya). The 3.1 $\mu$m images presented here show highly asymmetric features, another case of a C-rich
star with irregular morphologies close to the
stellar disk; this supports the notion that the $C_2H_2+HCN$ abundance distribution usually originates from a clumpy layer around carbon
stars.
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All authors V. Răstău, C. Paladini, J. Drevon, J. Hron, F. Kerschbaum, M. Wittkowski, J.P. Fonfria, M. Montargès, T. Khouri, W. Vlemmings, H. Olofsson, K. Ohnaka, J. Alonso-Hernandez, C. Sánchez Contreras, L. Velilla-Prieto, W.C. Danchi, G. Rau, F. Lykou, J. Sanchez-Bermudez, B. Lopez, S. Höfner, B. Aringer, L. Planquart, P. Cruzalèbes, G. Weigelt
Earth and Planetary Astrophysics
Predictions of the LSST Solar System Yield: Neptune Trojans
Joseph Murtagh, Megan E. Schwamb, Pedro H. Bernardinelli et al. (+15 more)
The NSF-DOE Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST), beginning full operations in late 2025, will dramatically transform
solar system science by vastly expanding discoveries and providing detailed characterization opportunities across all small body populations. This includes the co-orbiting 1:1 resonant Neptune Trojans, which are thought to be dynamically hot captures from the protoplanetary disk. Using the survey simulator $\texttt{Sorcha}$, combined with the latest LSST cadence simulations, we present the very first predictions for the Neptune Trojan yield within the LSST. We forecast a model-dependent median number of $\sim130-300$ discovered Neptune Trojans, and infer a notable 2:1 detection bias toward the recently emerged L5 cloud near the
galactic plane versus the L4 cloud, reflecting the lower-cadence coverage in the Northern Ecliptic Spur region that suppresses L4 detections. The additionally simulated Science Validation survey will offer the very first early insights into this understudied cloud. Around 60% of detected main survey Neptune Trojans will meet stringent color light curve quality criteria, increasing the sample size more than fourfold compared to existing
datasets. This enhanced sample will enable robust statistical analyses of Neptune Trojan color and size distributions, crucial for understanding their origins and relationship to the broader trans-Neptunian population. These comprehensive color measurements represent a major step forward in characterizing the Neptune Trojan population and will facilitate future targeted spectroscopic observations.
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All authors Joseph Murtagh, Megan E. Schwamb, Pedro H. Bernardinelli, Hsing Wen Lin, Jacob A. Kurlander, Stephanie R. Merritt, Samuel Cornwall, Mario Jurić, Grigori Fedorets, Matthew J. Holman, Siegfried Eggl, R. Lynne Jones, Peter Yoachim, Joachim Moeyens, Jeremy Kubica, Drew Oldag, Maxine West, Colin Orion Chandler
Instrumentation and Methods for Astrophysics · Cross-listed from physics.hist-ph
Comparing land- and skyscapes in the three main manorial-conquered lands of the Canary Islands
Maria Florencia Muratore, Alejandro Gangui, Juan Antonio Belmonte et al. (+1 more)
This work is a study of the relationship between astronomy and landscape focused on the orientation of Christian churches of the three main Manorial (Señorío) Islands of the Canary archipelago (Spain): Lanzarote, La Gomera and Fuerteventura. As a background, we have the information provided by the texts of early Christian writers, which imposed that churches should be oriented towards the east [..]. The fieldwork that supports our comparative study is based on the measurement of the precise location coordinates, axis' azimuth and angular height of the horizon for most of the churches of the three islands, which amounts to about 120 sets of measurements. For the study of the sample, we have employed various analyses, both statistical, as well as calendric and orographic. Our results show that on all the islands, the pattern of double orientations is repeated, which contemplates the canonical tradition of orienting the altars of churches within the
solar range (pointing either eastward or westward). Very few cases also occur where it is possible to identify constructions whose orientation follows solstitial patterns, perhaps as imitation of aboriginal worship. But this double pattern also includes a high proportion of churches with orientations far from this range. An example is Lanzarote and Fuerteventura, both islands subjected to the same flow of the prevailing trade winds in the region, but each with its own characteristics. Another example is given by the particular orography of deep ravines of La Gomera, which determines the orientation of the temples located in those geographical accidents. In this paper we show how the combination of elements of the land- and skyscape can, with a high degree of probability, offer a satisfactory explanation to the particular orientation of these insular centres of worship, which were built during the first decades after the European conquest.
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All authors Maria Florencia Muratore, Alejandro Gangui, Juan Antonio Belmonte, Carmelo Cabrera
High Energy Astrophysical Phenomena
The anisotropy and magnetic field structure of neutron stars through gravitational wave
Zhao-Wei Du and Xi-Long Fan
We investigate how gravitational wave (GW) observations can probe the internal physics of
neutron stars by extending the Tolman-Oppenheimer-Volkoff framework to include pressure anisotropy and internal
magnetic fields. Two representative
magnetic field configurations, radial orientation dominated (RO) and transverse orientation dominated (TO), are implemented with strength and decay prescriptions. We found that both anisotropy and
magnetic fields increase the maximum supported mass and modify the
tidal deformability $\Lambda$, thereby imprinting measurable signatures on GW signals. For the equal mass binary ($1.2M_\odot$-$1.2M_\odot$), anisotropy
neutron star with RO
magnetic field yield more compact
stars and a larger shift in $\Lambda$, allowing discrimination at signal-to-noise ratios (SNRs) as low as $\sim18$ using the O4 power spectra density. TO fields produce weaker effects and require substantially higher SNRs for detection. In conclusion, we conclude that gravitational waves are capable of probing the internal structure of
neutron stars.
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Cosmology and Nongalactic Astrophysics
The Cosmological Dipole in Tilted Anisotropic Universes
Alicia Martín, Constantinos Skordis, Deaglan J. Bartlett et al. (+3 more)
There is tentative evidence for a mismatch between the rest frames of matter and the
cosmic microwave background, the "
quasar dipole anomaly". We consider such a dipole in tilted anisotropic models, for a range of scenarios and sources: spatial
curvature,
cosmic heat flux, large scale electromagnetic fields and a Khronon field. Crucially, we determine the ancillary effects on other cosmological observables in each of these models and we show that, apart from the case of the Khronon field, it is unlikely that one can obtain a dipole with the amplitude that is being observed unless one considers additional exotica.
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All authors Alicia Martín, Constantinos Skordis, Deaglan J. Bartlett, Harry Desmond, Pedro G. Ferreira, Tariq Yasin
Earth and Planetary Astrophysics · Cross-listed from math.DS
Bifurcations of highly inclined near halo orbits using Moser regularization
Chankyu Joung, Dayung Koh and Otto van Koert
We study the bifurcation structure of highly inclined near
halo orbits with close approaches to the light primary, in the circular restricted three-body problem (CR3BP). Using a
Hamiltonian formulation together with Moser regularization, we develop a numerical framework for the continuation of periodic orbits and the computation of their Floquet multipliers which remains effective near collision. We describe vertical collision orbits and families emerging from its pitchfork, period-doubling, and period-tripling bifurcations in the limiting Hill's problem, including the
halo and butterfly families. We continue these into the CR3BP using a perturbative framework via a
symplectic scaling, and construct bifurcation graphs for representative systems (Saturn-Enceladus, Earth-Moon, Copenhagen) to identify common dynamical features. Conley-Zehnder indices are computed to classify the resulting families. Together, these results provide a coherent global picture of polar orbit architecture near the light primary, offering groundwork for future mission design, such as Enceladus plume sampling missions.
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Astrophysics of Galaxies
Tracing the Cosmic Evolution of the Cool Circumgalactic Medium of Luminous Red Galaxies with DESI Year 1 Data
Yu-Ling Chang, Ting-Wen Lan, J. Xavier Prochaska et al. (+44 more)
We investigate the properties of the cool circumgalactic medium (CGM) of massive
galaxies and their
cosmic evolution. By using the year 1
dataset of luminous red
galaxies (LRGs) and QSOs from the Dark Energy Spectroscopic Instrument survey, we construct a sample of approximately 800,000
galaxy-
quasar pairs and measure the radial distribution and kinematics of the cool gas traced by Mg II absorption lines as a function of
galaxy properties from
redshift 0.4 to
redshift 1.2. Our results show that the covering fraction of the cool gas around LRGs increases with
redshift, following a trend similar to the global
evolution of
galaxy star formation rate. At small radii (< 0.3rvir), the covering fraction anti-correlates with
stellar mass, suggesting that mass-dependent processes suppress the cool gas content in the inner region. In addition, we measure the gas dispersion by modeling the velocity distribution of absorbers with a narrow and a broad components – sigma_n ~ 160 and sigma_b ~ 380 km/s – and quantify their relative contributions. The results show that the broad component becomes more prominent in the outer region, and its relative importance in the central region grows with increasing
stellar mass. Finally, we discuss possible origins of the cool gas around massive
galaxies, including the contribution of satellite
galaxies and the precipitation scenario.
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All authors Yu-Ling Chang, Ting-Wen Lan, J. Xavier Prochaska, Malgorzata Siudek, J. Aguilar, S. Ahlen, A. Anand, D. Bianchi, D. Brooks, F. J. Castander, T. Claybaugh, A. de la Macorra, P. Doel, S. Ferraro, A. Font-Ribera, J. E. Forero-Romero, E. Gaztanaga, S. Gontcho A Gontcho, G. Gutierrez, J. Guy, K. Honscheid, R. Joyce, S. Juneau, A. Kremin, O. Lahav, C. Lamman, M. Landriau, L. Le Guillou, M. E. Levi, M. Manera, A. Meisner, R. Miquel, S. Nadathur, J. A. Newman, W. J. Percival, C. Poppett, F. Prada, I. Perez-Rafols, G. Rossi, E. Sanchez, D. Schlegel, M. Schubnell, D. Sprayberry, G. Tarle, B. A. Weaver, R. Zhou, H. Zou
Solar and Stellar Astrophysics
Magnetic activity on the young Sun: a case study of EK Draconis
A. Görgei, L. Kriskovics, K. Vida et al. (+8 more)
Context. Young,
solar analogue
stars provide key insights into the early stages of
stellar evolution, particularly in terms of
magnetic activity and rotation. Their rapid rotation, high flaring rate, and enhanced surface activity make them ideal laboratories for testing
stellar models or even the
solar dynamo. Aims. Using long-term photometric data, we investigated the cyclic behaviour of EK Dra over the last century. We analyze its short-term activity based on 13 Transiting
Exoplanet Survey Satellite (TESS) sectors. Applying Doppler imaging on high-resolution spectral data we investigate short and long-term spot
evolution and surface differential rotation. Methods. We use Short-term
Fourier-transform on a 120 years long archival photometric data in order to search for activity cycles. The short-term space photometry data is fitted with an analytic three-spot model, and we hand-select
flares from it to analyze their phase and frequency distribution. Spectral synthesis is used to determine the astrophysical parameters of EK Dra. Using the iMap multi-line Doppler imaging code, we reconstruct 13 Doppler images. Differential rotation is derived by cross-correlating consecutive Doppler maps. Results. Long-term photometric data reveal a 10.7-12.1 year cycle that was persistently present for 120 years. In the more recent half of the light curve a 7.3-8.2 years-long signal is also visible. The distribution of the 142
flares in the TESS data shows no correlation with the rotational phase or with the spotted longitudes. The reconstructed Doppler images show a surface that varies from rotation to rotation, putting the lower limit of the spot lifetime between 10-15 days. Based on the cross-correlation of the Doppler maps, EK Dra has a
solar-type differential rotation with a surface shear parameter of $\alpha_{DR} = 0.030 \pm 0.008$.
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All authors A. Görgei, L. Kriskovics, K. Vida, B. Seli, K. Oláh, P. Sági, A. Bódi, S.P. Järvinen, K.G. Strassmeier, A. Pál, Zs. Kővári
Cosmology and Nongalactic Astrophysics
The impact of our peculiar motion on primordial non-Gaussianity measurements using the LIGER4GAL framework
Bartolomeo Bottazzi Baldi, Mohamed Yousry Elkhashab, Daniele Bertacca et al. (+1 more)
Current and forthcoming
galaxy surveys will map the observable Universe with unprecedented depth, sky coverage, and precision. These maps are affected by relativistic
redshift-space distortions (RSDs), which become increasingly relevant on ultra-large scales. Accurate modelling of these relativistic RSDs is essential to avoid systematic biases in key cosmological measurements, such as
primordial non-Gaussianity (PNG). To address this, we introduce an updated implementation of the LIGER method, LIGER4GAL, which incorporates all linear-order relativistic RSDs directly at the tracer level of high-resolution N-body simulations. We demonstrate that LIGER4GAL improves upon previous iterations of the LIGER method by reproducing the expected non-linear clustering while maintaining accuracy for relativistic RSDs on large scales. We use the updated code to generate a DESI-like sample of luminous red
galaxies from the Huge MultiDark Planck simulation. By measuring the power spectrum multipoles of this sample with and without the imprint of relativistic RSDs, we assess the impact of relativistic effects on measurements of the local PNG signal ($f_\mathrm{nl}$). We find that the omission of the”finger-of-the-observer” (sourced by the peculiar velocity of the observer) effect in the power spectrum modelling can bias measurements of $f_{\rm nl}$ by more than $1$ ($0.25$) $ \sigma_{f_{\rm nl}}$ in 40% (80%) of the possible realizations of the universe if scales down to $k_\mathrm{min} = 0.0015\,h/\mathrm{Mpc}$ are included.
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All authors Bartolomeo Bottazzi Baldi, Mohamed Yousry Elkhashab, Daniele Bertacca, Cristiano Porciani
Astrophysics of Galaxies · Cross-listed from gr-qc
Approximations and modifications of celestial dynamics tested on the three-body system
Søren Toxvaerd
Large-scale simulations of celestial systems are based on approximations or modifications of classical dynamics. The approximations are with “particle-mesh” (PM) substitutions of the attractions from objects far away, or one modify the Newtonian accelerations (MOND) or the gravities (MOGA). The PM approximation and MOND modification of classical dynamics break the invariances of classical dynamics. The simple three-body system (TBS) is the simplest system to test the approximations and modifications of celestial dynamics, and it is easy to implement on a computer. Simulations of the TBS show that the PM approximation and MOND destabilize TBS. In contrast, the MOGA modification of
gravity by replacing Newton's inverse square attraction with an inverse attraction for far-away interactions stabilizes the system. The PM approximation and the MOND modification of classical dynamics do not preserve the momentum and angular momentum of a conservative system exactly, and PM does not obey Newton's third law. Although the errors and shortcomings of these PM approximations and MOND modifications are small, they cause the instability of the regular dynamics.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
A strategy for optimal material identification in solar dark photon absorption
Theresa M. Backes, Riccardo Catena and Michael Krämer
Dark
photons with masses in the 1-100 eV range can be produced in the Sun and subsequently absorbed in terrestrial detectors, offering a promising avenue for probing hidden-sector physics beyond the Standard Model. In this work, we develop a theoretically grounded strategy to identify optimal detector materials for
solar dark
photon absorption. Our strategy builds on a material-independent upper limit on the absorption rate, which we derive from Kramers-Kronig relations applied separately to the longitudinal and transverse dark
photon modes. We show how the optimal material properties depend on the dark
photon mass relative to the detector's
plasma frequency, identifying the conditions under which a detector can saturate the theoretical upper limit. We then assess the performance of commonly used detector materials in light of these criteria and comment on the prospects of metamaterials featuring tunable
plasma frequencies. Our results provide a general and model-independent framework to effectively guide the design of next-generation experiments targeting
solar dark
photons.
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Instrumentation and Methods for Astrophysics
Gamma-ray astronomy from the ground – future perspectives
Jim Hinton
I provide a personal perspective on the future of the field of ground-based gamma-ray astronomy, on the occasion of the 2024 Gamma conference in Milan. I discuss some of the scientific motivations for new instrumentation and the major new projects that are in development or already under construction, together with emerging concepts for instrumentation in the farther future. I stress the strong complementarity of the ground-level particle detector arrays, with their wide-field capabilities, and the more precise Cherenkov
telescope arrays. The key science topics for the next decades require both approaches and both are developing rapidly towards major performance advances and full sky coverage. I will briefly outline the status and roles of the projects CTAO and SWGO which will dominate the next decade. Beyond these projects are several developments which might boost performance at both ends of the ground-based gamma-ray energy range, including the plenoscope approach at low energies and diverse approaches to ultra-high-energy gamma-ray astronomy; from lake-based instruments to arrays of very small Cherenkov
telescopes. I will again briefly review these activities and how they may contribute long term.
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High Energy Astrophysical Phenomena
The broad-lined type Ic supernova 2020lao experienced an energetic explosion with no central-engine signatures
M. D. Stritzinger, T. J. Moriya, S. Bose et al. (+18 more)
We present infant-phase observations of the SN Ic-BL 2020lao, including optical spectroscopy beginning 48 hrs after explosion. The explosion time was constrained by power-law fits to the rising TESS and ZTF light curves, with the first ZTF detection occurring 27 hrs after explosion. The optical light curves show a rapid rise lasting 8.8 days and a peak luminosity typical of SNe Ic-BL (Mr=-18.5 mag). Unlike some engine-driven SN Ic-BL events, the light curve of SN 2020lao shows no evidence of an optical afterglow or excess emission, and the absence of shock-cooling in the TESS and ZTF data constrains the progenitor to a Wolf-Rayet-like
star with radius less than a few times the
solar radius, ruling out any extended envelope. The spectra resemble those of the X-ray-flash-associated SN 2006aj but with higher expansion velocities. From Arnett-type fits to the bolometric light curve and measured FeII velocities, we infer a Ni mass of 0.2
solar masses, an ejecta mass of 3.2
solar masses, and a kinetic energy of about 23x10^51 erg, corresponding to a specific kinetic energy of 7x10^51 erg per
solar mass. Spectral synthesis modeling broadly reproduces the photospheric spectra of SN 2020lao and suggests a specific kinetic energy of 5x10^51 erg per
solar mass. SN 2020lao and SN 2006aj synthesized comparable amounts of Ni, yet SN 2020lao exhibits specific kinetic energy values 5-10 times larger. VLA and Swift/XRT non-detections reveal no afterglow emission, allowing limits on relativistic ejecta and dense circumstellar material. Given that SN 2020lao reaches a specific kinetic energy typical of engine-driven SNe Ic-BL, the lack of an optical excess with the non-detections in the
radio and X-ray bands suggests that if a relativistic jet was launched, it was either viewed far off axis or choked before breakout. If there was no relativistic jet, SN 2020lao would be an extreme nonrelativistic SN Ic-BL.
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All authors M. D. Stritzinger, T. J. Moriya, S. Bose, P. A. Mazzali, P. Lundqvist, E. Karamehmetoglu, L. S. Arndt, C. Ashall, L. Galbany, W. B. Hoogendam, E. Baron, J. M. DerKacy, N. Elias-Rosa, E. Y. Hsiao, P. Höflich, E. Pian, E. A. M. Jensen, S. Moran, A. Pastorello, M. Shahbandeh, G. Valerin