Astrophysics of Galaxies · Cross-listed from gr-qc
Dynamics of Relativistic Binaries in Structured and Stochastic Environments: A Lagrange-Fourier-Hansen Framework
Lorenz Zwick, Conor Dyson, Brian C. Seymour et al. (+2 more)
We develop a general framework to characterize non-
vacuum perturbations to relativistic binaries in the gravitational-wave (GW) driven regime, for use in GW parameter estimation studies. The effect of smooth, structured and
stochastic perturbations to the binary's motion is reduced to a resonant spectral projection defined on a rolling averaging window, with weights given by Hansen coefficients. This is combined with practical criteria for identifying and evaluating the corresponding dynamical response to perturbations, starting from either analytical models or numerical simulations of binaries in environments. The result is a set of coupled ODEs for the orbital elements that capture epi-cyclic, apsidal and nodal resonances, consistently incorporate feedback from radiation reaction and can be solved efficiently on a coarse time grid. We demonstrate the practical application of the framework in two representative astrophysical scenarios: a compact binary in a variable
tidal field and an extreme-mass-ratio inspiral in an
accretion disk. We propose the Lagrange-
Fourier-Hansen framework as a unified tool for modeling environmental effects in GW templates for eccentric and precessing binary sources, and particularly for bridging the gap between phenomenological prescriptions and realistic models of binaries in environments.
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All authors Lorenz Zwick, Conor Dyson, Brian C. Seymour, János Takátsy, Johan Samsing
Astrophysics of Galaxies
Discovery of an extremely narrow trail-like feature crossing the Veil Supernova Remnant in deep amateur observations
David Martinez-Delgado, Jan-Niklas Pippert, Miguel A. Perez-Torres et al. (+9 more)
We report the discovery of an extremely narrow and highly collimated gaseous trail-like structure crossing the eastern region of the Veil Nebula (Cygnus Loop). The feature was first identified in deep narrow-band H-alpha images obtained by a small
telescope and was confirmed in more than a dozen publicly available amateur and professional images in the last two decades, rejecting the possibility of being an artifact (e.g., artificial satellite trail). To characterize its structural and luminosity parameters, we applied a model-fitting code originally developed for the analysis of extragalactic
stellar tidal streams. The structure is only detected in H-alpha emission, with no detectable counterpart in [SII] or in visible observations, and shows an almost constant brightness and width along its extension. It exhibits a surface brightness of 22.32+/- 0.13 H-alpha mag arcsec^2. Model fitting yields a median width of 1.63", which corresponds to a physical scale of approximately 1200 UA, assuming it is at the same distance (2400 light-years) as the Veil Nebula remnant. We discuss several potential scenarios for the origin of this feature: a Herbig-Haro-like jet, the trail of a high-velocity object, or a non-radiative shock associated with the
supernova remnant. We rule out the Herbig-Haro scenario, given the absence of a driving
stellar source and the lack of [S II] emission. A high-velocity-object wake cannot yet be excluded, particularly if the driver is a compact remnant, but the absence of an obvious source or bow-shock apex and the extremely small, nearly constant width of the structure make a normal runaway-
star origin unlikely. The current evidence instead favours a Balmer-dominated non-radiative shock associated with the Cygnus Loop, generated as the SNR blast wave encounters a dense material layer or
magnetic structure viewed nearly edge-on.
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All authors David Martinez-Delgado, Jan-Niklas Pippert, Miguel A. Perez-Torres, Malte Busmann, Emilio J. Alfaro, Mark Hanson, Giuseppe Donatiello, Alexander Zaytsev, Claudia Toci, Claus Gossl, Michael Schmidt, Christoph Ries
Astrophysics of Galaxies
The Impact and Environment of Massive Stars and Stellar Clusters
Loren Anderson, Jagadheep D. Pandian, Jyotirmoy Dey et al. (+10 more)
Massive
stars and
stellar clusters shape
galactic evolution through powerful feedback mechanisms including radiation pressure, photoionization,
stellar winds, and
cosmic ray acceleration. However, their impact remains poorly understood due to observational challenges: they are rare, distant on average, and deeply embedded within dense, dusty environments.
Radio observations provide a unique window into these processes, as
radio emission penetrates obscuring material and traces both thermal free-free emission from ionized gas and non-thermal synchrotron emission from shocks and particle acceleration. The Square Kilometre Array (SKA) will revolutionize massive
star studies through unprecedented sensitivity and angular resolution. SKA observations will enable detailed characterization of hierarchical structures within HII regions, measurements of physical conditions through hydrogen, helium, and carbon
radio recombination lines (RRLs), and detection of non-thermal emission from
cosmic ray acceleration in
star-forming regions. SKA will permit systematic measurements of
stellar wind mass-loss rates, studies of photoionized gas kinematics and dynamics, and exploration of photodissociation regions surrounding ultracompact HII regions. Additionally,
magnetic field strengths can be probed through Zeeman effect observations of RRLs. This chapter discusses the current understanding of massive
stars and
stellar clusters and their feedback processes. We highlight how SKA observations will advance our knowledge of massive
star formation,
stellar winds, hierarchical structures in HII regions,
cosmic ray acceleration, and
magnetic field regulation of
star formation - providing crucial insights into feedback mechanisms governing the structure and
evolution of the Milky Way and
galaxies.
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All authors Loren Anderson, Jagadheep D. Pandian, Jyotirmoy Dey, Marco Padovani, Ramlal Unnikrishnan, Annie Zavagno, Grazia Maria Umana, Jakob van den Eijnden, Giovanni Sabatini, Kimberly L. Emig, Alessio Traficante, Álvaro Sánchez-Monge, D. Anish Roshi
Astrophysics of Galaxies · Cross-listed from gr-qc
Determination of the metric of a Schwarzschild black hole surrounded by a halo of dark matter
M. Castillo Alarcón, Leonel Bixano, I. A. Sarmiento-Alvarado et al. (+2 more)
Following the landmark acquisition of the first image of a black hole, systems comprising a black hole enveloped by a dark matter
halo have attracted considerable
attention. This work implements a novel method to analyze the structure of a system composed of a Schwarzschild black hole and a dark matter
halo modeled as an anisotropic fluid, while ensuring that the proposed metric constitutes an exact solution of the Einstein field equations. Numerical results show that the connection between the temporal and radial metric functions preserves an inverse relationship, namely $A(r) \approx 1/B(r)$. Furthermore, we analytically demonstrate that the resulting functions satisfy $A(r)B(r) = 1 + \mathcal{O}(10^{-6})$, in excellent agreement with the numerical findings. In addition, the Einstein equations imply that the variation of the product $A(r)B(r)$ is governed by the factor $\varepsilon_h=\frac{8\pi G\rho_0r_0^2}{c^2}$. Finally, we show that the interior Schwarzschild region and the exterior dark matter
halo can be joined smoothly via a regular Darmois Israel junction, without generating any thin shell
curvature steps. To assess the observational implications of the model, we compare its theoretical predictions for the pericenter precession of the S2
star and the angular size of the shadow of Sgr A*. In both cases, the predicted deviations remain within the observational uncertainties reported by the
GRAVITY Collaboration and the Event Horizon
Telescope (EHT), respectively. These results demonstrate that the proposed black hole dark matter
halo configuration is not only mathematically consistent, but also compatible with current observational constraints.
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All authors M. Castillo Alarcón, Leonel Bixano, I. A. Sarmiento-Alvarado, Claudio Salas-Pérez, Tonatiuh Matos
Astrophysics of Galaxies
Self-interacting dark matter promotes bar formation in disk galaxies
Shashank Dattathri, Frank C. van den Bosch, HanYuan Zhang et al. (+4 more)
Despite its remarkable success on large scales, the standard $\Lambda$CDM paradigm faces persistent small-scale challenges that have motivated alternative models for the dark sector. Self-interacting dark matter (SIDM) offers a compelling possibility, in which dark matter particles can scatter off each other.
Stellar bars are a ubiquitous feature of disk
galaxies across
cosmic time. Bars are dynamically coupled to their host
galaxy's dark matter
halo, and therefore their properties provide a powerful probe of the nature and distribution of dark matter. In this paper, we use idealized, high-resolution $N$-body simulations and analytic calculations based on kinetic theory to study bar formation and
evolution in disk
galaxies embedded in SIDM
halos. We find that compared with collisionless CDM, SIDM produces bars that form earlier and grow to larger amplitudes, even for modest self-interaction cross sections. In several cases, disks that remain stable in CDM, including kinematically hot and dark-matter-dominated disks, develop strong bars in SIDM. This accelerated bar growth occurs because self-interactions broaden the bar-
halo resonances and enhance angular momentum transfer from the
stellar disk to the
halo. We explicitly show that this phenomenon is not related to core formation in SIDM
halos. At late times, gravothermal core collapse can raise the central dark matter density enough to weaken or dissolve the bar. These results suggest that the abundance, strength, and
redshift evolution of barred
galaxies offer a promising observational route to constraining dark matter self-interactions, particularly in light of the growing sample of high-
redshift bars revealed by JWST.
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All authors Shashank Dattathri, Frank C. van den Bosch, HanYuan Zhang, Martin D. Weinberg, Eugene Vasiliev, Priyamvada Natarajan, Vasily Belokurov
Astrophysics of Galaxies
The Bright Future of the Dark and Dim Universe
N. Deg, Alejandro Benitez-Llambay, Elizabeth A. K. Adams et al. (+5 more)
This chapter investigates the low-mass frontier of
galaxy formation through two complementary populations: the starless Reionization-Limited HI Clouds (RELHICs) that trace the “dark” Universe, and the faint, gas-rich
galaxies that define the “dim” Universe. RELHICs offer pristine laboratories for probing the distribution of DM on sub-
galactic scales, providing a direct test of the Lambda Cold Dark Matter ($\Lambda$CDM) model predictions. The dim Universe provides statistical constraints on cosmology,
galaxy formation and
evolution, as well as baryoninc physics through key observables including the low-mass end of the neutral-hydrogen mass function (HIMF), the neutral-hydrogen velocity function (HIVF), and the low-mass end of the baryonic Tully-Fisher relation (bTFR). This chapter outlines core science questions that can be tackled leveraging
radio observations of both the dark and dim Universe. Additionally, it outlines strategies to identify RELHICs amid
tidal or pressure-confined contaminants, while providing observational predictions for the dim Universe. The Square Kilometre Array (SKA) in its mid-frequency Array Assembly 4 (AA4) configuration will, for the first time, resolve the internal gas structure of nearby RELHICs and build deep, wide-area
datasets that definitively constrain the HIMF, HIVF, and bTFR down to masses of $10^{6}~\msol$ – offering a complete observational framework to test the $\Lambda$CDM paradigm and the baryonic processes that shape the faint end of
galaxy formation.
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All authors N. Deg, Alejandro Benitez-Llambay, Elizabeth A. K. Adams, N. Chamba, V. Kilborn, Filippo M. Maccagni, T. O'Beirne, K. Spekkens
Earth and Planetary Astrophysics
From Young to Older Disks: JWST/MIRI Evidence for Fading Molecular Emission and Hints for Elevated C/O in Upper Scorpius
Chengyan Xie, Ilaria Pascucci, Feng Long et al. (+23 more)
We present JWST/MIRI spectroscopy of 14 disks in the older (~5-10 Myr) Upper Scorpius (USco) association and use slab of gas in local thermal
equilibrium to infer basic gas properties. We find that half of these disks are molecular rich, with detections of H$_2$O, CO$_2$, HCN, C$_2$H$_2$, and H$_2$, while the other half are molecular poor, showing no molecular emission other than H$_2$. We further combine this sample with 10 other USco disks from the AGE-PRO program and compare the combined older sample to young (~1-3 Myr) JDISCS Cycle~1 systems, which are analyzed in a similar manner. We find that USco disks have lower detection rates of major molecular species but a significantly higher detection rate of rarer C-bearing molecules such as C$_4$H$_2$. At a given
accretion luminosity, molecular line luminosities are systematically lower in USco than in young disks, and the scaling relations with
accretion luminosity differ between the two populations. Moreover, we find that about half of the older disks, preferentially the millimeter faint, and likely more compact disks, have observable mass ratios of C- to O-bearing molecules that are higher than the maximum values in the young sample. These results point to reduced inner-disk molecular gas masses, cooler emitting layers, and higher inner gas C/O ratios in older disks, the latter being consistent with pebble drift. Taken together, our findings provide evidence for chemical
evolution of inner disk gas from young to older systems, with important implications for the
accretion of
primordial planetary atmospheres.
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All authors Chengyan Xie, Ilaria Pascucci, Feng Long, Uma Gorti, Andrea Banzatti, Richard Booth, Klaus Pontoppidan, Tamara Molyarova, John Carpenter, Min Fang, Yao Liu, Eshan Raul, Ke Zhang, Steve Ertel, Jordan Stone, Aaron Empey, Carlo F. Manara, Paola Pinilla, Colette Salyk, Benoit Tabone, Miguel Vioque, Lucas Cieza, Giovanni Rosotti, James Miley, Geoffrey A. Blake, Abygail Waggoner
Earth and Planetary Astrophysics
Chemical Divergence and Water Depletion: Gas Properties of Evolved Upper Scorpius Disks Revealed by JWST/MIRI
Eshan Raul, Ke Zhang, Abygail Waggoner et al. (+25 more)
Tracing the chemical
evolution of protoplanetary disks over time requires observations of disks at different ages. However, most JWST/MIRI surveys published to date have targeted younger ($\sim$1-3 Myr) rather than older systems. We present the results of a JWST/MIRI MRS survey of the inner regions of 10 protoplanetary disks (ages $\sim$2-6 Myr, spectral types M0-M4.5) in the Upper Scorpius region previously characterized by the ALMA AGE-PRO large program. Using MCMC slab modeling, we fit to a wide variety of detected molecules, including H$_2$O, CO, C$_2$H$_2$, $^{13}$CCH$_2$, HCN, HC$_3$N, CO$_2$, $^{13}$CO$_2$, C$_2$H$_6$, C$_4$H$_2$, and OH, as well as C$_6$H$_6$, CH$_3$, and H$_2$ visually. We classify each disk along two independent axes-a Water Classification based on H$_2$O line luminosity (Water-Rich, Water-Poor, or Water-Absent) and a Chemotype based on the dominant non-water chemistry (Organic-Rich, CO$_2$-Dominated, or Molecule-Absent)-and find an unexpectedly high diversity of distinct chemical compositions within our population. We leverage the heterogeneity of detected molecules in our sample to present new characteristic "diagnostic" wavelength regions for most species. We find that carbon-based molecules consistently exhibit markedly lower excitation temperatures ($\lesssim$300 K) compared to younger ($\sim$1-3 Myr)
star-forming regions ($\sim$600-1000 K), hinting at relatively colder molecular reservoirs. We also determine that Upper Scorpius disks show systematically lower water luminosities by factors of 10-1000. In particular, disks with strong carbon-based molecular features but no observed H$_2$O defy expectations of an inner-disk
dust cavity or a low ($\lesssim3$) $R_{\rm gas}/R_{\rm dust}$ ratio, instead suggesting that the presence of a strong outer-disk
dust trap largely controls the chemical outcome of the terrestrial
planet-forming region.
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All authors Eshan Raul, Ke Zhang, Abygail Waggoner, Chengyan Xie, Nicholas Tallon, Andrea Banzatti, Colette Salyk, Klaus Pontoppidan, Ilaria Pascucci, Nicole Arulanantham, Miguel Vioque, Aaron Empey, Carlo Manara, Geoffrey A. Blake, Paola Pinilla, Feng Long, Jinghuai Yao, Jayatee Kanwar, Naman S. Bajaj, María José Colmenares, Till Kaeufer, Benoit Tabone, Edwin Bergin, Lucas A. Cieza, Mayank Narang, James Miley, Sebastiaan Krijt, Giovanni Rosotti
Astrophysics of Galaxies
JWST Reveals Compact Nuclear Starbursts Masquerading as AGNs in Metal-Poor Dwarfs: Where Are the Accreting Intermediate-Mass Black Holes?
William Matzko, Shobita Satyapal, Jeffrey D. Mckaig et al. (+18 more)
We present JWST/NIRSpec spectroscopy of the low-mass, metal-poor
galaxy SDSS~J160135.95+311353.7 (J1601), selected for its extreme mid-infrared colors and compact
nuclear emission, placing it within widely used WISE color diagnostics for active
galactic nuclei (AGNs). Despite this selection, we find no evidence for coronal lines, X-ray emission, or variability typically associated with
accretion activity. We compare J1601 to SDSS~J120122.30+021108.3 (J1201), a similar but lower-mass, more metal-poor system studied previously (Doan, 2025). Both
galaxies host compact
nuclear starbursts but differ in their
stellar populations and
dust properties: J1601 shows CO bandhead absorption indicative of red supergiants, weak
nuclear Wolf–Rayet features, and a circumnuclear PAH ring, consistent with a more developed recent starburst, while J1201 is more
dust-enshrouded and chemically primitive. Despite these differences, neither system shows evidence for AGN activity, indicating that the absence of
accretion is not simply due to evolutionary timing. Photoionization models show that the weakness of high-ionization emission cannot be explained by low
metallicity alone, implying a genuine deficit of hard ionizing
photons. Crucially, the red mid-infrared colors in both systems originate from compact, unresolved
nuclear emission confined to the
nuclear star cluster. These results demonstrate that compact
nuclear starbursts can mimic AGN-like mid-infrared colors without
accretion, and that commonly used AGN diagnostics may not uniquely identify accreting black holes in metal-poor
dwarf galaxies. Our findings suggest that such systems may not provide the conditions required for efficient black hole growth and/or may lie near or below the regime where black hole seeds can form.
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All authors William Matzko, Shobita Satyapal, Jeffrey D. Mckaig, Sara Doan, Michael McDonald, Archana Aravindan, Gabriela Canalizo, Jenna M. Cann, Nicholas P. Abel, Omkar Bait, Laura Blecha, Torsten Böker, Thomas Bohn, Jacqueline Fischer, Stephanie LaMassa, Suzanne C. Madden, Mallory Molina, Barry Rothberg, D. Schaerer, Anil Seth, Remington O. Sexton.
High Energy Astrophysical Phenomena
Modelling Dissipative Dynamics of r-mode Instability in Hybrid Stars
Khushbu Zala and Sreemoyee Sarkar
Compact
star cores reach extreme densities and may contain exotic dense-matter phases. Information about the exotic interiors of rapidly rotating
pulsars can be inferred from r-mode oscillations, whose stability is governed by viscous dissipation. In this work, we model a compact
star containing a possible mixed phase of hadronic and
quark matter and employ a hybrid statistical framework based on
Bayesian inference to infer the dissipation time scales associated with the hybrid phase. Using low-mass X-ray binaries (LMXB) timing observations together with mass-radius constraints from the
Neutron Star Interior Composition Explorer (NICER) mission, we estimate the shear and bulk viscosity contributions to r-mode damping for a hybrid
star of two layers. Our inference yields shear and bulk viscous dissipation time scales of $\tau_s=(4.99^{+0.49}_{-0.52}) \times 10^8 T^{\frac{5}{3}}$s and $\tau_B=(2.150^{+1.23}_{-0.60}) \times 10^{19} (T^4 10^{-12}+T^2 10^{-6})^{-1}\Omega^{-2}$s respectively. The timescales thus obtained can be implemented to obtain the minima of the
star's rotation frequency at $\Omega=451.87$ Hz at temperature $T=0.259$ MeV for a hybrid
star of mass $1.5$ $M_{\odot}$ and $\Omega=517.47$ Hz at $T=0.234$ MeV for $M=1.75 M_{\odot}$. We find that the instability window obtained through the inference framework effectively explains the observed stability of millisecond
pulsars in both the
radio and LMXB populations, particularly for XTE J0929-314 and XTE J1807-294, J0437-4715, J2124-3358, respectively. These results demonstrate that
Bayesian inference combined with r-mode phenomenology provides a powerful and observationally consistent framework for constraining the transport properties of dense hybrid matter.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
The crust of dark-matter admixed neutron stars: bulk properties and torsional oscillations
Jiayi Zhang and Hector O. Silva
We study how dark matter (DM) impacts the crust and the spectrum of torsional crust oscillations of dark-matter-admixed
neutron stars (DANSs). We construct two-fluid
equilibrium solutions wherein baryonic and DM interact gravitationally only, adopting a unified
nuclear equation of state for the former and a fermionic equation of state with repulsive self-interaction for the latter. At fixed total gravitational mass and DM mass fraction, we find that DM reduces the crust thickness in comparison to pure baryonic-matter
neutron stars (NSs). The thinning of the crust is negligible when most of the DM distribution extends beyond the
star's baryonic surface. However, the crust thickness can decrease by as much as 12% when the DM distribution is within the
star's baryonic surface, i.e., when the
star has a "dark core." We support these results by deriving approximate analytical formulas for the crust thickness that agree with our numerical calculations at the sub-percent level in best case scenarios. Next, we derive the equation that describes crustal torsional modes of DANSs in the relativistic Cowling approximation. We find that the oscillation frequencies are in general higher than those of a comparable pure baryonic-matter NS, with the largest frequency shifts happening in the same parameter space where the crust thickness decreases the most. Moreover, we study the degeneracy between DM and baryonic-crustal microphysics effects on these modes. As an example, we study electron screening, which softens the crust's shear modulus, thus decreasing the frequencies. We find that the degeneracy between the competing effects of DM and electron screening can be broken in some regions of the parameter space we explored. Should they be measured, our results suggest that torsional oscillations could be used to infer the existence of a DM core within massive NSs. (Abridged)
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Earth and Planetary Astrophysics
The Dynamical Origin of Millimetre-Sized Sporadic Meteoroids
Tam Do, Peter Brown and Petr Pokorný
Determining the relative contributions of cometary and asteroidal sources to the sporadic meteoroid population remains a longstanding challenge, particularly because commonly used orbit-based classification criteria have not been rigorously validated for meteoroids. We evaluate the efficacy of several established orbit-based criteria for meteoroid classification. These include the Whipple $K$-criterion, Kresák $Pe$-criterion, the Tisserand invariant with respect to Jupiter (T$_J$), and a recent classification based on aphelion distance proposed by Borovička. Our validations suggest that $K$ and $Pe$ are most reliable at recovering whether a meteoroid was released from a cometary or asteroidal parent. We applied these criteria to a suite of 386 observed millimetre-sized meteoroids to try to constrain their original source populations. Our analysis used the observed orbit co-variances to backward integrate a suite of clones for each meteoroid to statistically evaluate their dynamical origin. We find that if meteoroids are released in the last ~150-200 kyr, there is a dividing velocity of below 17 km/s where meteoroids in the millimetre to centimetre size range impacting Earth are predominantly asteroidal in origin, independent of the orbital criteria used. Above 17 km/s, the fraction of dynamically cometary meteoroids increases, although a definitively cometary dominated population does not arise until velocities of 27 km/s or higher. For ages older than 200 kyr, lower velocity meteoroids at Earth in the mm-sized range may be a mix of either cometary or asteroidal.
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Instrumentation and Methods for Astrophysics · Cross-listed from cs.DL
A&A community survey on the future of scientific publishing: Credibility over speed, fairness over profit, human judgment over automation
João Alves, Arūnas Kučinskas, Charlotte Van Rooyen et al. (+7 more)
(Abridged) Scientific publishing is undergoing major change, driven by a shift toward open access (OA), the rise of artificial intelligence (AI), and growing demands for transparency, reproducibility, and equity. At the same time, rapid growth in article output strains editors and reviewers and means that metrics and speed can eclipse quality and rigor. To better understand how the community is responding, Astronomy & Astrophysics (A&A) commissioned the {A&A Survey on Trends and Challenges in Scientific Publishing}, which documents community opinion on journal choice, peer review, OA, research evaluation, and the role of AI, with the goal of informing future editorial policies and the wider conversation on sustainable, ethical, and equitable scientific communication. Distributed online in May 2025 to \SI{28787} A&A authors and co-authors, the survey drew \SI{2944} responses from 69 countries by its closing date. The responses were clear. Journal quality and reputation are the most decisive factors in deciding where to publish, followed by cost. The principal worry about peer review is reviewer expertise and
fairness rather than speed. Citation counts are still an important consideration, but many respondents want broader, more qualitative measures of impact. The majority prefers public or institutional funding for OA, and views on AI are polarized, with widespread acceptance of administrative and
language assistance but firm opposition to autonomous decision-making or content generation. Integrity, credibility, and
fairness are common themes in every section of the responses. Overall, the survey portrays an engaged community that values quality over speed,
fairness over profit, and human oversight over automation, providing A&A with clear insight into community preference and a solid framework for shaping future policies on OA, peer review, and the responsible integration of AI.
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All authors João Alves, Arūnas Kučinskas, Charlotte Van Rooyen, Marc Audard, Pierre-Alain Duc, David Elbaz, Thierry Forveille, Laszlo L. Kiss, Tiago Pereira, Eva Villaver
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Collider Probes of Dark Energy Microphysics
Chaitanya Bashyam, Alfredo Gurrola, Andres Florez et al. (+1 more)
The physical origin of dark energy remains one of the most profound open questions in modern physics. Although cosmological observations tightly constrain the equation of state parameter $w$, this information alone does not reveal the underlying microphysics, as many distinct theoretical models can reproduce the same expansion history. A key discriminator among these models is the sound speed of dark energy perturbations, yet this quantity remains largely unconstrained by current astrophysical observations. In this work, we propose a fundamentally new approach: using
collider measurements of beyond-the-Standard-Model (BSM) mediator resonances as a probe of dark energy microphysics. We construct a unified effective-field-theory framework in which a dynamical dark energy scalar is coupled, through
symmetry-motivated derivative interactions, to a pseudoscalar mediator in the 2HDM+$a$ model. These interactions naturally induce invisible decays and modify the propagation of the BSM mediator in a dark energy background, leading to measurable distortions of resonance properties at
colliders such as the LHC. We show that the decay widths, branching ratios, and kinematic structure of the mediator resonance become sensitive to the propagation properties of dark energy fluctuations, in particular the sound speed. As a result,
collider observables provide a direct and complementary handle on dark energy microphysics, with the potential to distinguish between models that are otherwise indistinguishable through cosmology alone. Our results establish a new paradigm in which high-energy
collider experiments can probe the physics of
cosmic acceleration, revealing a connection between the smallest and largest scales in nature and opening a novel experimental pathway to uncover the fundamental origin of dark energy.
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All authors Chaitanya Bashyam, Alfredo Gurrola, Andres Florez, Cristian Rodriguez
Cosmology and Nongalactic Astrophysics
Simulation-Based Inference for Cluster Cosmology with Set-Based Neural Network Architectures
S. Zelmer, E. Bulbul, K. Lehman et al. (+18 more)
The unprecedented statistical power of
galaxy cluster catalogs from the SRG (Spectrum Roentgen Gamma)/eROSITA All-Sky Survey provides a unique opportunity to place stringent constraints on cosmological models through measurements of structure growth. Fully exploiting the potential of these large X-ray-selected cluster samples, however, requires robust statistical frameworks that accurately connect observable quantities to the underlying cosmological parameters. We develop and implement a simulation-based inference (SBI) framework for cosmological parameter estimation using a realistic mock-generation pipeline calibrated on eRASS1 simulations. Synthetic
galaxy cluster catalogs are propagated through the survey selection function to produce mock eRASS1 observations that reproduce the data's statistical properties. At the core of the method lies a set-based neural network (GNN on sets) that encodes information from individual clusters and is coupled to a masked autoregressive flow for flexible posterior density estimation. This approach enables the use of the full cluster-level information content without compressing the observables into binned summary statistics. Our framework recovers the input cosmologies within the inferred uncertainties, and passes calibration tests, demonstrating robustness in the presence of realistic survey effects. We obtain mock constraints of 11.5% on $\Omega_m$ and 4.4% on $\sigma_8$ averaged over a suite of simulated cluster catalogs matching the effective sample size of the data set (3,259 clusters). We achieve a precision comparable to that obtained with traditional MCMC analyses based on substantially larger cluster samples. The framework is readily extensible to more complex forward models and additional observables. This work highlights the potential of SBI methods for next-generation large-scale structure analyses with forthcoming X-ray cluster surveys.
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All authors S. Zelmer, E. Bulbul, K. Lehman, S. Krippendorf, E. Artis, S. Grandis, N. Clerc, Z. Ding, L. Fiorino, V. Ghirardini, M. Kluge, N. Malavasi, A. Merloni, T. Mistele, K. Nandra, M. E. Ramos-Ceja, J. S. Sanders, F. Pacaud, A. von der Linden, J. Weller, X. Zhang
Cosmology and Nongalactic Astrophysics
Three-form dark energy: constraints and multi-probe comparison with $\Lambda$CDM
Mariam Bouhmadi-López, Hsu-Wen Chiang, Carlos G. Boiza et al. (+3 more)
Three-form fields provide a theoretically well-motivated framework for dark energy, arising in higher-dimensional theories and exhibiting a rich cosmological phenomenology. We investigate a minimally coupled three-form dark energy model with a Gaussian potential and constrain it using current cosmological observations, including CMB shift parameters, DESI DR2
baryon acoustic oscillation measurements, Pantheon+
supernovae with and without SH0ES calibration,
cosmic chronometers, and gamma-ray bursts. Parameter estimation is performed within a
Bayesian Markov-chain Monte Carlo framework, while model comparison relies on several information criteria and the
Bayesian evidence, as well as tension statistics. We find that the three-form model provides a viable and competitive description of the expansion history of the Universe. It is mildly preferred over $\Lambda$CDM for the combination of early and late-time
datasets that are heavily tensioned (CMB+BAO and Pantheon+SH0ES). This preference decreases to neutrality for the other, less tensioned combination of early and late-time data, while for individual early-time or late-time
datasets analysed separately, the information criteria are neutral or favour $\Lambda$CDM. This suggests that the additional degrees of freedom of the three-form field may help accommodate cosmological observations of different origins within a common framework. The reconstructed dark energy dynamics exhibit a characteristic phantom phase at intermediate
redshifts while approaching a cosmological-constant-like behaviour at early and late times, providing a distinctive observational signature. Although the model does not significantly alleviate the Hubble tension despite allowing higher values of $H_0$, it remains consistent with current observations and offers a well-motivated alternative to $\Lambda$CDM whose predictions can be tested by future cosmological surveys.
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All authors Mariam Bouhmadi-López, Hsu-Wen Chiang, Carlos G. Boiza, Javier Ortega del Río, Thomas J. Broadhurst, Pisin Chen
High Energy Astrophysical Phenomena
Parsec-scale polarimetry and kinematics of a spine-sheath jet in the neutrino-blazar TXS 0506+056
F. Eppel, P. Benke, C. Degli Agosti et al. (+10 more)
In 2017, the blazar TXS 0506+056 showed a remarkable gamma-ray outburst simultaneously with a high-energy
neutrino detection by IceCube from the same sky region. The significance of this association was found to be on the order of 3 sigma thus providing a strong link between the
neutrino emission and the blazar
flare. The high-energy
flare in TXS 0506+056 was followed by a delayed
radio flare, peaking in $\sim2020$ in the aftermath of the
neutrino event. We investigate the parsec-scale jet structure and dynamics of TXS 0506+056 using 15 GHz full-polarization VLBI observations obtained between 2009 and 2025 with the Very Long Baseline Array. Our kinematic analysis reveals moderate superluminal jet speeds of $\sim(1-2)$c and two quasi-stationary components. A new jet component with comparable speed was ejected contemporaneously with the 2017 IceCube
neutrino event. The stacked polarization map is consistent with a stratified spine-sheath jet structure: an inner spine with EVPA aligned with the jet, surrounded by a sheath layer with perpendicular EVPA. Variability in total intensity and polarization further indicates interaction between these layers, particularly evident in characteristic linear polarization
flares, associated with EVPA rotations of the quasi-stationary components. The multi-layered jet configuration is consistent with previous studies that were able to explain the
neutrino emission in this TXS 0506+056 through a spine-sheath jet structure. We suggest that TXS 0506+056 represents an archetypal case and that similar polarization signatures and
geometric light curve
flares may be present in other
neutrino-emitting sources, potentially offering a solution to the Doppler-crisis phenomenon observed in TeV-emitting blazars.
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All authors F. Eppel, P. Benke, C. Degli Agosti, J. L. Gómez, D. C. Homan, M. Kadler, Y. Y. Kovalev, M. L. Lister, V. A. Makeev, A. V. Plavin, A. B. Pushkarev, E. Ros, T. Savolainen
High Energy Astrophysical Phenomena
Gamma-ray Bursts in the Radio Sky: the Role of the SKA-VLBI
Stefano Giarratana, Om Sharan Salafia, Xue-Feng Wu et al. (+6 more)
Radio observations of $\gamma$-ray bursts (GRBs) employing the very long baseline interferometry (VLBI) technique provide us with fundamental information on the dynamics and the geometry of the GRB blast wave. With its high angular resolution ($\sim$milli-arcsecond), VLBI allows us to measure the apparent superluminal expansion, to characterise the structure of the jet and to constrain the viewing angle and jet opening angle. While this information is crucial to understand these transient events, such studies have been possible only for three GRBs to date, owing to both the poor sensitivity of current
radio facilities and the paucity of close and bright GRBs. In this chapter, we estimate the impact that the SKA-Mid will have on these studies, when included in a VLBI network. We performed a series of dedicated simulations of VLBI observations of GRBs, considering five VLBI networks and the SKA-Mid, both in its AA* and AA4 configurations. We show that including the SKA-Mid in a global-VLBI experiment will: (i) allow us to measure the size and the expansion of a GRB up to a
redshift $z\simeq 0.25$ (at a confidence level of $3\sigma$); (ii) constrain the size $\gtrsim$2 times better than the current global-VLBI array; (iii) improve the localisation precision in Declination from 4 to 30 times; (iv) detect the apparent proper motion of GRBs seen slightly off-axis with a confidence level 3 times better than current VLBI networks. Ultimately, the SKA-Mid will open a new window on a portion of the GRB population that has been inaccessible so far.
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All authors Stefano Giarratana, Om Sharan Salafia, Xue-Feng Wu, Jin-Jun Geng, Tao An, Benito Marcote, Marcello Giroletti, Giancarlo Ghirlanda, Tiziana Venturi
Instrumentation and Methods for Astrophysics
The Hidden Geometry of Astrophysical Spectra: Path-Signatures of Line Profiles
Rafael S. de Souza and Severin Bunk
The morphology of a spectral-line profile contains information beyond scalar summaries of line strength, centroid, width, global asymmetry, or diagnostic line ratios. Broad wings, shoulders, double peaks, secondary components, and composite emission–absorption structures encode how flux is ordered across wavelength but can remain indistinguishable under conventional summaries. We introduce an interpretable
geometric representation of line profiles inspired by rough path theory. Each wavelength-sampled profile is mapped to a common systemic rest-frame velocity grid and treated as a trajectory in velocity–flux space, traversed from blue to red. From this path, we define a compact set of low-order descriptors measuring signed velocity–flux area, blue–red imbalance localization, higher-order shape complexity, and emission–absorption ordering. Using synthetic profiles, we show that these descriptors separate morphologies with similar full width at half maximum (FWHM), non-parametric velocity width ($W_{80}$), and low-order moment summaries. We then apply the method to MaNGA integral-field spectroscopy by computing H$\alpha$ descriptors in individual spaxels and clustering them in a low-dimensional feature space. The resulting classes form spatially coherent regions of similar ordered line morphology. Although no external velocity field is supplied to the clustering, stacked spectra within these regions recover coherent large-scale centroid-velocity patterns broadly consistent with the MaNGA reference velocity fields. We release a minimalist MIT-licensed package ${\it spectropath}$, available at \href{https://rafaelsdesouza.com.br/spectropath/}{the project website}.
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High Energy Astrophysical Phenomena
A hidden ultra-relativistic spine in the jet of a neutrino-associated blazar
Y. Y. Kovalev, F. Eppel, D. C. Homan et al. (+16 more)
Supermassive black holes launch powerful jets of
plasma that can accelerate particles to extreme energies, but the physical conditions required to produce high-energy
neutrinos remain unknown. In the blazar TXS 0506+056, the first source individually linked to a high-energy
neutrino,
radio images had seemed to reveal a jet too slow to sustain the extreme conditions required for
neutrino production. Here we resolve this tension using long-term
radio monitoring, particularly Very Long Baseline Interferometry (VLBI) imaging. We uncover a disturbance in emission propagating with an apparent speed of 21+-1 times the speed of light, that is masked by slower,
radio-bright features that dominated earlier analyses. We interpret this as the signature of a stratified jet: an ultra-relativistic spine with Lorentz factor Gamma>20 embedded within a slower outer sheath. As the disturbance travels along the spine, it progressively illuminates the sheath, producing the delayed
radio flare and naturally accounting for the years-long offset between
neutrino and
radio emission. The same pattern recurs in a second
neutrino-associated event, pointing to a repeatable multi-messenger engine. These findings challenge the standard interpretation of VLBI jet speeds and establish a concrete, testable framework connecting structured jets to the sources of the Universe's highest-energy
neutrinos.
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All authors Y. Y. Kovalev, F. Eppel, D. C. Homan, A. V. Plavin, P. Benke, A. K. Erkenov, J. L. Gomez, M. Kadler, K. I. Kellermann, P. I. Kivokurtseva, Yu. A. Kovalev, M. L. Lister, V. A. Makeev, A. V. Popkov, A. B. Pushkarev, E. Ros, T. Savolainen, Yu. V. Sotnikova, S. V. Troitsky
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Massive scalar fields in eccentric regime: Detectability and constraints from LISA observations of extreme mass-ratio inspirals
Tieguang Zi, Shailesh Kumar, Genliang Li et al. (+3 more)
Extreme mass-ratio inspirals (EMRIs) are among the most promising sources for future space-based gravitational wave (GW) observatories and provide sensitive probes of additional fundamental fields in the strong-
gravity regime. In the present work, we investigate eccentric equatorial EMRIs around Kerr black holes in the presence of a massive scalar field. We assume that the inspiralling object carries a scalar charge, therefore, emits scalar radiation in addition to GWs. By solving the massive scalar perturbation equation in the frequency domain, we compute the relativistic scalar energy fluxes at the event horizon and at infinity and incorporate them into an adiabatic inspiral model. We investigate the impact of the scalar charge and scalar field mass on the orbital
evolution and gravitational waveforms by analysing the accumulated phase differences and waveform mismatches relative to both general relativity (GR) and the massless scalar limit. Our results show that the massive scalar radiation can produce significant GW dephasing, with the effect becoming increasingly pronounced for more eccentric orbits. In addition, the scalar flux is suppressed for larger scalar field masses as fewer scalar harmonics satisfy the propagation condition at infinity. Finally, using both Fisher-information-
matrix forecasts and
Bayesian parameter estimation, we assess the capability of the
Laser Interferometer Space
Antenna to constrain the scalar charge and scalar field mass. The two inference approaches gives consistent constraints, demonstrating that eccentric EMRIs provide a promising avenue for probing massive scalar fields and scalar-tensor extensions of
gravity in the strong-field regime.
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All authors Tieguang Zi, Shailesh Kumar, Genliang Li, Jun-Kun Zhao, Bao-Min Gu, Fu-Wen Shu
Astrophysics of Galaxies
SEEDZ: Rapid Galaxy Assembly as a Pathway to Supermassive Stars, Dense Stellar Environments and Massive Black Hole Seeds
Lewis R. Prole, John A. Regan, Daxal Mehta et al. (+14 more)
We investigate the assembly history of early
galaxies in the SEEDZ hydrodynamic simulations, to investigate the high inflow rates believed to be required for the formation of supermassive
stars (SMSs), dense
stellar clusters and subsequently heavy seed black holes. Using a heavy seed formation criteria of $>$1 M$_\odot$ yr$^{-1}$ flowing into 10 pc regions, we find that heavy seeds form in
halos that grow rapidly compared to those
halos that never meet the criteria.
Halos with growth rates of $\gtrsim$1 M$_\odot$ yr$^{-1}$ at their virial radius (scales of a few hundred pc) are able to sustain a flow rate of 0.1 M$_\odot$ yr$^{-1}$ into the inner 1 pc of the
halo, maintaining higher density environments within the central 10 - 100~pc. These
halos continue to grow rapidly after their initial collapse, typically forming heavy seeds $\sim$100 Myr after forming their first
stars and
stellar mass black holes. By $z=10$, most heavy seeds form in regions of near-
solar metallicity, although a minority of heavy seeds do continue to form in low
metallicity (10$^{-2}$ Z$_\odot$) regions. Under the assumption that a SMS forms as the progenitor to a heavy seed if it forms in a region of low (10$^{-2}$ Z$_\odot$)
metallicity, and can sustain high
accretion rates above 0.02 M$_\odot$ yr$^{-1}$ throughout the SMS lifetime of 2 Myr, we find a number density of SMSs of 0.1 cMpc$^{-3}$, meaning that only a fraction of 10$^{-4}$ of these SMSs would need to be visible to JWST to account for the observed population of Little Red Dot
galaxies.
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All authors Lewis R. Prole, John A. Regan, Daxal Mehta, Devesh Nandal, Rüdiger Pakmor, Ricarda S. Beckmann, Michael Tremmel, Martin G. Haehnelt, Simon C.O. Glover, Ralf S. Klessen, John H. Wise, Sophie Koudmani, Martin A. Bourne, Debora Sijacki, John Brennan, Pelle van de Bor, Paul C. Clark
Astrophysics of Galaxies
Too shy to spin? Cosmic wallflowers as proto-globular clusters
Floor van Donkelaar, Lucio Mayer and Pedro R. Capelo
We investigate the rotational properties of
star-forming clusters at $z \sim 7.6$ in the high-resolution simulation MassiveBlackPS, focusing on two formation channels: clusters forming in
galactic discs via gravitational instability and isolated circumgalactic systems, referred to as
cosmic wallflowers, born out of
cosmic filaments. Using
stellar kinematics, we compare their rotational velocities, $v_{\rm rot}$, and rotational support, $v/\sigma$, to study whether formation environment leaves a clear dynamical imprint. We find a clear separation, wherein
cosmic wallflowers systematically have lower rotational velocities and span a wide range in $v/\sigma$, whereas the identified disc clusters are strongly rotation-dominated and extend to higher $v_{\rm rot}$. When combined with
stellar surface densities, a subset of the low-$v_{\rm rot}$
cosmic wallflowers lie surprisingly close to the observed globular cluster population in the Milky Way, whereas disc clusters remain offset. Within the
cosmic wallflower population, we identify two regimes: lower-density, weakly rotating systems that overlap with these globular cluster properties, and denser, more rotationally supported systems that likely follow a different evolutionary pathway, possibly linking them to the origin of massive black hole seeds at high
redshift. We further find that the gas content correlates with this behaviour, with gas-rich
cosmic wallflowers preferentially occupying this low-rotation regime. This all suggests that environment and baryonic content together play a key role in setting the initial dynamical state and possible fate of clusters. In particular, weakly rotating, gas-rich
cosmic wallflowers emerge as natural proto-globular cluster candidates, potentially evolving towards present-day systems through angular momentum loss and dynamical heating.
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High Energy Astrophysical Phenomena
Impact of neutrino-electron scattering and an improved treatment of pair processes on binary neutron star mergers
Francois Foucart, Samantha Rath, Rowan Davidson et al. (+5 more)
Multimessenger observations of
neutron star mergers are unique opportunities to constrain the properties of dense matter and the production site of heavy
nuclei. To leverage these observations, we require reliable models of the electromagnetic signals powered by mergers. An important limitation to our ability to develop such models is the use of approximate
neutrino physics in simulations. Here, we present simulations using an improved version of our Monte Carlo transport
algorithm specifically designed to allow for more advanced on-the-fly calculations of reaction rates that use the simulated energy distribution of
neutrinos, including in blocking factors, while still relying on approximations for the angular distribution of
neutrinos. We use these new methods to include in simulations inelastic scattering of
neutrinos on electrons, and to improve our treatment of
neutrino-antineutrino pair annihilation. We find that, without increasing the cost of simulations, we can marginally get to the point when the addition of a single packet represents a change $\Delta f_\nu<1$ in the angle-integrated distribution function, at the cost of increased shot noise in the coupling to the fluid. With inelastic scattering and a better treatment of pair processes, we find a reduction in the average energy and total luminosity of heavy-
lepton neutrinos, and an increase in the amount of mass ejected – here by $50\%$, although on a relatively low amount of total ejected mass $<0.005M_\odot$. In a separate set of simulations varying the total mass of the binary away from its
prompt collapse threshold, we find rapid variations in the amount of ejected matter and in the geometry and composition of the
outflows with the total mass of the system. Finally, we use the simulations with our more advanced transport scheme to study in more detail the energy spectrum of
neutrinos across the merger remnant.
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All authors Francois Foucart, Samantha Rath, Rowan Davidson, Patrick Chi-Kit Cheong, Matthew D. Duez, Lawrence Kidder, Harald Pfeiffer, Mark Scheel
Astrophysics of Galaxies
Analytical and fitting formulae for solutions to Lyman-alpha radiative transfer equations: the effects of geometry, recoil, and velocity gradients
Pengfei Li and Zheng Zheng
Lyman-alpha (Ly$\alpha$) radiative transfer (RT) is important in many astrophysical environments and governed by multiple physical processes. In this paper, we provide analytical formulae/procedures for the solutions to Ly$\alpha$ RT equations under three simple geometrical
symmetries and investigate the effects of atomic
recoil and gas bulk motion. We first study Ly$\alpha$ spectra by solving Ly$\alpha$ RT equations for a static, uniform gas cloud under cylindrical geometry. The solution is verified through Ly$\alpha$ Monte Carlo RT simulations, and compared to those under slab and spherical geometries in literature. Second, to characterise the
recoil effect, we empirically modify
recoil-free Ly$\alpha$ spectra. The method is motivated by Ly$\alpha$ RT equations with
recoil and justified by simulations. Finally, we account for constant velocity gradients in Ly$\alpha$ RT equations and obtain series solutions for Ly$\alpha$ spectra. The solutions demonstrate good agreement to Ly$\alpha$ spectra from simulations for small velocity gradients (i.e. edge velocity $v_{\rm E}$ of a cloud being comparable to the thermal velocity $b$) but become less accurate for large ones. To characterise Ly$\alpha$ spectra under large velocity gradients, we empirically extend the functional form of solutions and constrain them from fitting simulated Ly$\alpha$ spectra. The resulting fitting formulae show significant improvement for large velocity gradients ($v_{\rm E}/b \sim 100$) under large optical depths. The analytical study of Ly$\alpha$ spectra in this work completes the set of solutions under simple geometries, provides physical insights for Ly$\alpha$ RT under
recoil and velocity gradient, and develops analytical tools for theoretical studies that require inputs from Ly$\alpha$ RT.
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Earth and Planetary Astrophysics
Revisiting the picture of circumbinary disc truncation
Enrico Ragusa, Elliot Lynch, Guillaume Laibe et al. (+1 more)
Circumbinary discs are observed to develop central cavities carved by the gravitational influence of the binary. Analytical estimates of cavity sizes predict truncation at $\sim 2 \textrm{--} 3$ binary separations, depending on the binary properties. However, numerical studies show only qualitative agreement with these predictions: cavity sizes often evolve on long timescales and can exceed substantially the analytically predicted values. In this work, we revise this paradigm, suggesting that
tidal truncation in circumbinary discs responds to additional dynamical parameters that have so far been neglected. We analyse a suite of 80 numerical simulations of circumbinary discs to re-examine the physical mechanism responsible for cavity truncation and to provide a prescription for the cavity size independent of the state of
evolution of the system. We find that truncation depends not only on the binary parameters $a_{\rm bin}$, $e_{\rm bin}$, and mass ratio $q$, but also on the instantaneous cavity eccentricity $e_{\rm cav}$ and the relative apsidal orientation $\varpi_{\rm bin}-\varpi_{\rm cav}$. These quantities jointly determine the pericentre of the innermost stable disc orbit $R_{\rm p}$, in a way that shares some similarities with orbital stability in the restricted three body problem. Hydrodynamical effects introduce secondary corrections, with the disc scale height $H$ and viscosity $\alpha$ mildly shifting the cavity edge relative to the purely gravitational prediction. We introduce a semi-analytical prescription that captures these dependences for $R_{\rm p}$ and cavity semi-major axis $a_{\rm cav}$. We conclude that cavity truncation for binaries with mass ratios $q>0.05$ is a process where the instantaneous orbital properties of the disc ($e_{\rm cav}$, $\varpi_{\rm cav}$) play a fundamental role and should be taken into account to accurately evaluate the truncation efficiency.
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All authors Enrico Ragusa, Elliot Lynch, Guillaume Laibe, Richard Alexander
Cosmology and Nongalactic Astrophysics
Unveiling the Microhertz Gravitational-Wave Sky with the Square Kilometre Array Observatory
Alexander C. Jenkins, Diego Blas and Joshua W. Foster
The gravitational-wave sky is expected to contain a rich variety of sources across a very broad range of frequencies. Much like in electromagnetic astronomy, exploring new gravitational-wave frequency bands therefore has the potential to unlock powerful new insights into the Universe. In this chapter, we investigate the prospects for using high-precision timing of binary millisecond
pulsars with the Square Kilometre Array Observatory (SKAO) to search for gravitational waves in the microhertz ($\mu$Hz) frequency band by targeting resonant gravitational-wave perturbations to the orbits of these binaries. Using only a handful of known systems, we show that SKAO observations can achieve unprecedented sensitivity to microhertz gravitational waves, with the potential to detect inspiralling massive black hole binaries in this band. These searches are complementary to conventional
pulsar timing array analyses, adding a new dimension to the gravitational-wave science achievable with the SKAO.
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High Energy Astrophysical Phenomena
Discriminating blazar emission models with high-energy polarimetry: Multi-band predictions and detectability
Sara Capecchiacci, Ioannis Liodakis, Haocheng Zhang et al. (+2 more)
Polarimetric properties of blazars provide key constraints on the acceleration mechanisms powering their relativistic jets, the high-energy emission processes involved, and the composition of the jet itself. We present a multi-band polarimetric study spanning from soft X-rays to gamma-ray energies, considering several bands for current and future missions (0.275 keV, 2-8 keV, 0.5-10 keV, 6-35 keV, 0.2-5 MeV, and 1-100 GeV). Our sample is drawn from the RoboPol monitoring programme, a statistically complete gamma-ray sample including low-, intermediate-, and high-synchrotron-peaked blazars. Using spectral energy distribution fitting performed with the Bjet_MCMC tool, we give predictions on the flux expected for each source in the selected energy bands. We model the polarimetric signatures under three competing emission scenarios: leptonic, hadronic, and hybrid. The detectability of each source was assessed by accounting for the instruments' minimum detectable polarisation (MDP) and by computing the probability of the detection in a blind survey. We show that simultaneous multi-wavelength observations can effectively discriminate between competing emission models due to the difference in the expected polarisation degree. Finally, we derive sensitivity requirements for future gamma-ray polarimetric missions aimed at increasing the number of detectable sources.
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All authors Sara Capecchiacci, Ioannis Liodakis, Haocheng Zhang, Michela Negro, Jorge Otero-Santos
Instrumentation and Methods for Astrophysics
The Karl G. Jansky Very Large Array Sky Survey (VLASS). Data Products
Amy Kimball, Mark Lacy, Juergen Ott et al. (+5 more)
The VLA Sky Survey (VLASS) is a
radio continuum survey of the entire sky visible to the VLA (dec > -40deg) at ~2.5 arcsecond resolution over 2-4 GHz with full polarization. Data processing and quality assurance have proven challenging due to limited computing and staff resources, and require innovative approaches. Although "Quick Look" images in Stokes I continuum were produced within a few weeks of observation, high accuracy images that utilize the full potential of the
dataset are computationally intensive and take much longer to produce. Half of the sky will need correction for w-terms to account for sky
curvature, increasing the computational cost per image by ~100x. This problem will be tackled using GPUs and High-Throughput Computing (HTC) centers. Quality assurance of the tens of thousands of individual images has used a mix of algorithmic and machine learning techniques to automatically identify common artifacts and anomalies in the data. Archiving and dissemination of VLASS data products also pose a significant challenge.
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All authors Amy Kimball, Mark Lacy, Juergen Ott, John Tobin, Tierra Candelaria, Sergio Garza, Drew Medlin, Steven T. Myers
Astrophysics of Galaxies
3D Magnetic Field Vectors in Space: Bubbles, Clouds, and Filaments
Mehrnoosh Tahani, Anna Ordog, Jennifer West et al. (+3 more)
Magnetic fields play important roles in the
star-formation process across different spatial scales. The interplay between
magnetic field strength (a key component of the interstellar medium's energy budget) and field orientation relative to density structures impacts how interstellar material evolves toward
star formation. To understand
galactic evolution toward
stars,
planets, and ultimately life, we need to map three-dimensional (3D)
magnetic field vectors in 3D space. However, determining full vector information remains challenging due to projection effects and the complex relationship between observable tracers and field geometry. We outline the observational techniques that can be used to probe the 3D
magnetic field structures of objects such as
supernova remnants (SNR), superbubbles, HII regions, and HI filaments in the diffuse interstellar medium (ISM), and objects in the dense ISM such as molecular clouds, filaments, and cores. The main SKA-specific observational techniques include synchrotron emission and Faraday rotation of both compact sources and the diffuse emission. We discuss how SKA AA4 will allow implementation of the techniques we describe, leveraging the vastly improved sensitivity, resolution and uv-coverage compared to existing
datasets. This will enhance our ability to reconstruct 3D
magnetic field vectors, advancing our understanding of
magnetic fields in
Galactic evolution and
star formation.
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All authors Mehrnoosh Tahani, Anna Ordog, Jennifer West, Georgia V. Panopoulou, Hiroko Shinnaga, Marijke Haverkorn