Astrophysics of Galaxies
Influence of the resonance ring gravity on the stellar velocity distribution near the OLR of the Galactic bar
A. M. Melnik and E. N. Podzolkova
We constructed the 2D model of the
Galaxy which initially includes an analytical bar, bulge, disk and
halo. The model disk forms the outer elliptical resonance rings R1 and R2 located near the outer Lindblad resonance of the bar (OLR), as well as the inner resonance ring r located near the corotation radius (CR). As the density of
stars in the elliptical rings increased, we introduced additional gravitational perturbations created by the rings. The radial component of gravitational perturbations from the elliptical rings, F_R, at a point with the Galactocentric coordinates (R, theta) was represented as a combination of three
polynomials in powers R/Re or Re/R, where Re is the distance to the midline (middle) of the ring at a given angle theta. The azimuthal component of the disturbances, F_T, was calculated using the force F_R. The difference between the values of the force F_R (F_T) calculated using the numerical differentiation of the potential and using the analytical representation does not exceed 5.7% (1.3%) of the maximum value of the force F_R generated by the elliptical rings. In general, the
gravity of the elliptical rings has little effect on the process of adjustment of epicyclic motions near the OLR of the bar.
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Astrophysics of Galaxies
CAPOS: The bulge Cluster APOgee Survey XII. Abundances for 98 PIGS metal-poor Bulge field giants
Carolina Salgado, Sandro Villanova, Doug Geisler et al. (+1 more)
The inner Milky Way hosts overlapping
stellar populations (bar–bulge, inner thin and thick disks, and
halo), complicating population assignments along the line of sight. A joint chemical–dynamical approach is required to isolate a clean field bulge sample. Metal-poor bulge
stars are valuable as they likely trace the earliest phases of chemical enrichment in the inner
Galaxy. We aim to characterize the alpha-element (Si, Mg) and selected Fe-peak abundances of a dynamically defined sample of bulge field
stars, and to contrast these trends with the inner-
halo tail in the metal-poor regime. We analyze metal-poor candidates from the Pristine Inner
Galaxy Survey observed by the bulge Cluster APOGEE Survey. Using APOGEE/ASPCAP abundances (S/N >= 50), we integrate full 6D orbits in a barred Milky Way potential. Bulge membership is defined via orbital confinement using an apocenter cut and the high-density locus in the (E_J, L_z) plane, with uncertainties estimated using Monte Carlo simulations. We identify 98
stars as bulge members. The
metallicity distribution spans -2.5 <= [Fe/H] <= -0.4, with a median [Fe/H] = -1.71, offset to higher
metallicity than the inner
halo (median [Fe/H] = -1.96). The sample follows a high-alpha sequence with slopes d[Si/Fe]/d[Fe/H] = -0.020(+0.012,-0.051) and d[Mg/Fe]/d[Fe/H] = -0.097(+0.062,-0.133). Fe-peak tracers show [Ni/Fe] ~ 0, while [Mn/Fe] declines with [Fe/H] with a mild upturn at higher
metallicity. We detect no significant [Si/Fe] gradients with R_apo or Z_max (+0.010(+0.018,0.000) and +0.006(+0.022,-0.011) dex kpc^-1, respectively). Results are insensitive to Omega_p, yielding indistinguishable memberships. The chemo-orbital evidence favors an in situ origin within the inner
Galaxy for the metal-poor bulge field, enriched at early times and rearranged by secular bar
evolution, with a minor contribution from
halo stars at the most metal-poor end.
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All authors Carolina Salgado, Sandro Villanova, Doug Geisler, Nicolás Barrera
Cosmology and Nongalactic Astrophysics
Galaxy formation in modified gravity – II. galaxy halo connection and assembly bias
Michael Collier, Sownak Bose and Baojiu Li
Modern surveys such as DESI and Euclid, which collect data for hundreds of millions of
galaxies to map the large-scale structure (LSS) of the Universe, hold the key to determining the cosmological parameters and testing new physics. This ambition, however, is limited by uncertainties in the
galaxy-
halo connection: the link between observed
galaxies and the underlying, unobservable matter field, by accounting for effects such as
galaxy bias and assembly bias (AB). These are particularly poorly-understood for modified
gravity (MG) models, which are popular alternatives to the cosmological constant to explain accelerated expansion. We approach this problem using mock emission line
galaxy (ELG) and luminous red
galaxy (LRG) catalogues in $f(R)$
gravity matching the specifications of ongoing Stage-IV
galaxy surveys, generated from state-of-the-art MG hydrodynamical simulations. While the interplay between MG – especially the chameleon screening mechanism – and
galaxy formation leaves complicated imprints in the
galaxy-
halo connection, a simple physical picture emerges in which
halo and
galaxy formation are enhanced for progressively more massive
haloes over time. We confirm that the basic
galaxy-
halo connection model, the
halo occupation distribution (HOD), in which
galaxy occupation is determined solely by
halo mass, underestimates
galaxy clustering strength in $\Lambda$CDM by $10$–$20\%$ at $z\lesssim1$ when neglecting AB, and demonstrate that MG introduces further complexity. Extending this model with a suitably-chosen environment density as a secondary HOD variable reduces the AB effect in all models to $2$–$3\%$ for $z\lesssim0.5$. This provides a well-motivated starting point for further works on minimising the impact of AB when testing non-standard cosmological models with LSS.
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Cosmology and Nongalactic Astrophysics
Complex yet Hermitian: Gaussian covariance of cross-correlation and multi-tracer power spectra
Federico Montano, Stefano Camera, Emiliano Sefusatti et al. (+1 more)
Accurate modelling of the covariance of clustering observables is essential to fully exploit current and future survey data, which is expected to constrain large-scale clustering signals with unprecedented precision. Computational costs of simulation-based estimates motivate analytical approaches, especially in light of the growing interest towards multi-tracer analyses and parity-odd signatures in two-point statistics, which respectively mitigate
cosmic variance and probe relativistic projection effects on cosmological scales. In this work, we generalise previous theoretical results for the Gaussian covariance of multi-tracer power spectrum measurements, providing a general expression applicable to both real (even-parity) and complex (both even- and odd-parity) power spectra. We focus on a generic weighted
estimator at first, and then showcase how our general formalism applies to Legendre power spectrum multipoles and two-dimensional power spectrum, recovering known limits in appropriate cases. We validate our predictions against Gaussian Monte Carlo simulations and investigate the structure of the covariance
matrix, including the Hermitian properties of its imaginary part.
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All authors Federico Montano, Stefano Camera, Emiliano Sefusatti, Mohamed Yousry Elkhashab
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Tachyonic Encore: A universal shift of inflationary observables
Diogo S. Gorgulho, Margherita Putti, Rodrigo Gonzalez Quaglia et al. (+3 more)
We propose a generic, largely inflaton-potential-independent mechanism in which a light
axion spectator, initialized near the hilltop of its potential, reshapes inflationary observables through purely gravitational multi-field dynamics. During inflation the
axion is frozen and the background follows an effectively single-field trajectory. After inflation ends, the
axion rolls, inducing a turn in field space and transient tachyonic phases of the isocurvature mode. The resulting “tachyonic encore” occurs entirely on super-horizon scales. These phases generate a nearly scale-invariant enhancement of the
curvature power spectrum, suppressing the tensor-to-scalar ratio and shifting the scalar tilt to a weighted combination of adiabatic and entropic tilts at horizon crossing. We show that these effects can reconcile otherwise disfavored inflaton potentials with current CMB constraints. The same dynamics predict local non-Gaussianity, $f_{\rm NL}^{\rm loc.}\sim \mathcal{O}(1)$, within reach of upcoming surveys.
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All authors Diogo S. Gorgulho, Margherita Putti, Rodrigo Gonzalez Quaglia, Ema Dimastrogiovanni, Matteo Fasiello, Diederik Roest
Astrophysics of Galaxies
Constraining the Geometry of Galactic Dark Matter with Gaia Data Release 3
Francesco Sylos Labini and Roberto Capuzzo-Dolcetta
We derive both the mid-plane and off-plane rotation curves, $v_c(R,z)$, and the vertical acceleration, $a_z(R,z)$, of the Milky Way (MW) using
Gaia~DR3 data over the ranges of vertical heights $z \in (-2,2)\,$ kpc and galactocentric distances $R \in (8.5,14)$ kpc where the velocity components are determined with high precision, i.e., with an error $< 5\%$. In contrast, the vertical acceleration $a_z(R,z)$ is dominated by model-dependent systematics, with uncertainties of up to $\sim 20\%$. This level of accuracy allows us to place stringent constraints on the geometry of the MW's dark matter (DM) distribution, as the vertical gradients of the gravitational potential attain their maximum within this range of radial and vertical distances corresponding to the characteristic scales of the disk. We find that models including the observed
stellar components together with a spherical DM
halo fail to reproduce both the pronounced variation of $v_c(R,z)$ with height and the observed behavior of $a_z(R,z)$. In particular, spherical
halos with a scale radius of $r_s \sim 15$ kpc contribute negligibly to the off-plane rotation curve and vertical acceleration in the inner disk, leaving these features primarily determined by the
stellar mass distribution. Conversely, models in which DM is confined to a flattened, disk-like configuration predict substantial contributions to both $v_c(R,z)$ and $a_z(R,z)$, resulting in a markedly better agreement with the data. We conclude that disk-like DM distributions are strongly favored over spherical
halo models. Forthcoming
Gaia data releases will enable even more stringent tests of the geometry and distribution of the MW's DM component.
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High Energy Astrophysical Phenomena
Spectral analysis of magnetized advective accretion flows around rotating black holes
Mayank Pathak, Shubhrangshu Ghosh and Banibrata Mukhopadhyay
The spectra of an
accretion disk around black holes are the basic diagnostic tool to enlighten the underlying flows and then black holes.
Accretion flows around black holes, however, are controlled by parameters like the
magnetic field,
spin of the black hole,
accretion rate and temperature of the flow. These quantities affect the (magneto)hydrodynamics of the flow thus consequently lead to variations in the spectrum. We first consider numerical steady state magnetohydrodynamic (MHD) solutions of magnetized
accretion flows around black holes to study the dependence of the spectra on these disk properties. The spectrum exhibits strong dependence on the
spin of the black hole,
accretion rate,
magnetic field and the electron temperature of the flow. Variations in these quantities influence the emission peaks and overall luminosity, which can be a tell-tale sign to extract physics of observed spectra. We further validate our results with general relativistic MHD (GRMHD) simulations using the standard and normal
evolution (SANE) and magnetically arrested disk (MAD) vector potentials. We consider two black hole
spins ($a=0.5$ and $a=0.9375$) to model the
magnetic field configurations and study the resulting spectra by comparing MAD and SANE results. We find a large difference in the bolometric luminosities and the location of the emission peaks between SANE and MAD flows. Certain properties of the spectra, like, the ratio of synchrotron radiation to synchrotron self-Comptonization peaks in SANE and MAD, show drastically distinct features. The overall luminosity combined with such metrics can distinguish the
magnetic field characteristics in astrophysical systems.
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High Energy Astrophysical Phenomena
Implementation of multi-grid Poisson solver in numerical relativity and its application to gravitational collapse of massive star
Kenta Kiuchi and Hirotada Okawa
We develop a new grid-based multi-grid Poisson solver in numerical relativity. We report the performance of the multi-grid Poisson solver in the initial value problems for two-puncture black holes, a static spherical
neutron star, a uniformly rotating
neutron star in
equilibrium, and a gravitationally collapsing massive
star. As a demonstration, we conduct a numerical-relativity
neutrino-radiation-transfer hydrodynamics simulation of the gravitational collapse of the $9M_\odot$ massive
star in Ref.~\cite{Aguilera-Dena:2020mfh} up to the core bounce. During the simulation, we employ the constraint-preserving regird prescription with the newly developed multi-grid Poisson solver to improve the resolution. It shows that the baryonic mass, the Arnowit-Deser-Misner (ADM) mass, and the ADM-like angular momentum are, respectively, preserved with $O(10^{-3})\%$ and $O(10^{-2})$–$O(10^{-1})$% accuracy.
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Astrophysics of Galaxies
DESI as sparse Integral Field Spectrograph I: Spatially resolved chemical enrichment in star-forming galaxies at $z\leq0.1$
Vibhore Negi, Ravi Joshi, B. Vishnupriya et al. (+8 more)
We present a spatially resolved chemical abundance analysis of 2291
star-forming
galaxies at $z \leq 0.1$, spanning nearly four orders of magnitude in
stellar mass ($8 \le \rm log (M_{\star}/M_{\odot}) \le 11.5$), by exploiting the multi-fibre spectra from the Dark Energy Spectroscopic Instrument (DESI) as a sparse integral field spectrograph. In the inner regions ($<2R_e$), the radial gas-phase
metallicity profiles show an outward-declining trend for massive
galaxies, with the steepest gradient ($\nabla_{log(O/H)}$) $\sim-0.08$ dex/R$_{e}$, whereas low-mass
dwarf galaxies exhibit nearly flat profiles ($\nabla_{log(O/H)}\sim-0.02$ dex/R$_{e}$). The large galactocentric radii ($\sim$5 R$_{e}$) probed in this study, reveal flat
metallicity profiles near the disk-
halo interface. Strikingly, these flat
metallicity values are consistent across a wide
stellar mass range, likely reflecting the influence of low SFR and metal poor inflows in the outer regions. The
metallicity gradient -
stellar mass relation exhibits a turnover at $\log(M_\star/M_\odot) \sim 10.5$, beyond which gradients become shallower, possibly driven by the chemical
equilibrium in the inner disk of massive
galaxies and/or dilution from
cosmic gas
accretion. At fixed
stellar mass, a strong size dependence is observed, where compact
galaxies show flatter gradients and higher central enrichment than their extended counterparts. The abundance gradients are further linked with the
stellar age distribution within the
galactic disk, where
galaxies with younger outskirts show steeper gradients than the ones with older outskirts, consistent with ongoing inside-out disc growth sustaining centrally concentrated chemical enrichment. These results underscore the interplay of
star formation efficiency,
stellar feedback, and metal-poor gas
accretion in governing the radial chemical structure in
galaxies.
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All authors Vibhore Negi, Ravi Joshi, B. Vishnupriya, Xue-Bing Wu, Hassen M. Yesuf, Luis C. Ho, Ayan Acharyya, Ramya Sethuram, Abhijeet Anand, Michele Fumagalli, Celine Peroux
Astrophysics of Galaxies
Getting to know the Stellar Clusters in NGC 1569: Bayesian inference of stellar cluster properties in a dwarf starburst galaxy
Bjarki Björgvinsson, Anna F. McLeod, Bronwyn Reichardt Chu et al. (+3 more)
We present a
Bayesian analysis of
star clusters in the
dwarf starburst
galaxy NGC 1569 based on high-resolution Hubble Space
Telescope imaging combined with integral-field spectroscopy from the Keck
Cosmic Web Imager, obtained as part of the DUVET survey. For each cluster identified, we infer posterior probability distributions for mass and age using a forward modelling method that properly accounts for uncertainties due to
stochastic sampling of the IMF. We investigate how the inferred properties depend on photometric coverage by repeating the analysis with different filter combinations, including mock extensions to the ultraviolet and near-infrared that emulate the addition of HST UV bands and James Webb Space
Telescope imaging. We find that, while inclusion of these wavelength regimes further breaks age and mass degeneracies, the currently available data yields reasonably strong constraints on cluster parameters. We compare inferred cluster properties to the conditions of the local interstellar medium, and find evidence for multiple interesting correlations. The truncation mass of the cluster mass function varies with galactocentric distance, particularly moving off the disk, consistent with a dependence on the density of the interstellar medium. Cluster mass positively correlates with
metallicity, suggesting that massive clusters preferentially form in pre-enriched gas, and the ionisation state of the gas, reflecting the increased prevalence of high-mass
stars in high-mass clusters. These results demonstrate the power of
Bayesian, initial mass function-aware modelling for resolving cluster populations in nearby starburst
dwarfs and provide new insight into how cluster formation and feedback respond to local
galactic conditions.
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All authors Bjarki Björgvinsson, Anna F. McLeod, Bronwyn Reichardt Chu, Magdalena J. Hamel-Bravo, Deanne B. Fisher, Mark R. Krumholz
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Directional dark matter signatures of the Large Magellanic Cloud
Javier Reynoso-Cordova, Nassim Bozorgnia and Marie-Cécile Piro
The Large Magellanic Cloud (LMC), the most massive satellite of the Milky Way (MW), can significantly perturb the local dark matter (DM) distribution. We study its impact on directional DM detection using the Auriga cosmological simulations of a MW analogue hosting an LMC analogue. We find that the LMC induces strong anisotropies in directional
recoil signals, driven primarily by the non-zero mean azimuthal velocity of the local DM distribution. The characteristic ring-like feature predicted in the Standard
Halo Model (SHM) for heavy DM and low
recoil energies is strongly distorted, producing an asymmetric
recoil pattern concentrated at preferred azimuthal angles. Differences between
recoil maps for the MW-LMC analogue and the SHM reach up to $\sim80\%$ near the signal maximum. These distortions significantly enhance directional discovery prospects, reducing the number of events required to reject isotropy by nearly a factor of five for a 100 GeV DM particle in a near-future CYGNUS-like experiment, and by even larger factors for heavier DM. Our results highlight the importance of the LMC for interpreting and optimizing future directional DM searches.
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Solar and Stellar Astrophysics
TESS detection of periodic brightness variations during the rise of classical nova PGIR22akgylf
Kirill V. Sokolovsky, Elias Aydi, Konstantin Malanchev et al. (+14 more)
Classical novae are transient events powered by thermonuclear burning in a layer of hydrogen-rich material accreted by a white
dwarf from its binary companion. Most classical novae reach optical maximum within ~1 d, but a rare few rise far more slowly. We probe the envelope structure and ejection mechanism of the slowly-rising nova PGIR22akgylf with TESS photometry spanning 3 to 16 d after the nova discovery, supplemented by ground-based observations that cover its full ~133 d ascent to maximum. We detect a 0.1802 +/-0.0012 d periodic brightness modulation with a peak-to-peak amplitude of ~0.02 mag, identified with PGIR22akgylf via temporal and spatial coincidence. The period is stable over the two weeks of TESS coverage, suggesting an orbital origin. Whether this period corresponds to the full or half orbital period, it implies a
dwarf donor companion. At the time of the TESS observations the nova was >~6 mag above quiescence (but still 4 mag below peak), so its light should be dominated by the expanding photosphere. We interpret the periodic signal as arising from the binary orbital motion distorting the nova envelope while its size remains comparable to the binary separation. This interpretation points to common-envelope interaction as a contributor to shell ejection in PGIR22akgylf and demonstrates that the slow-rise phenomenon is not exclusive to thermonuclear eruptions in symbiotic binaries, where the large orbital separation of the
giant companion inhibits such interaction.
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All authors Kirill V. Sokolovsky, Elias Aydi, Konstantin Malanchev, Koji Mukai, Jennifer L. Sokoloski, Laura Chomiuk, Peter Allen Craig, Rebekah A. Hounsell, Justin D. Linford, Isabella Molina, Montana N. Williams, Kishalay De, Mansi M. Kasliwal, Nicholas Earley, David J. Lane, Filipp D. Romanov, Richard Schmidt
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Gotta light? Illuminating AGN disks with LISA EMRIs
Federico Fantoccoli, Francisco Duque and Jonathan Gair
We study the ability of the upcoming
Laser Interferometer Space
Antenna (LISA) to constrain gas torques acting on extreme-mass-ratio inspirals (EMRIs) when these are embedded in
accretion disks, using recently developed relativistic models for the binary-disk interaction. Using a fully
Bayesian setup, we find that, contrary to previous forecasts based on Newtonian results, these observations can provide simultaneous estimates of the disk surface density and the
accretion rate (or, equivalently, its total luminosity) without the need for an electromagnetic counterpart. Our analysis also indicates that simpler measurement constraints based on the linear-signal (Fisher
matrix) approximation are not valid for these systems. For typical EMRI observations, the torque amplitude can be constrained to within ~10%, strengthening the prospect of probing
accretion physics at (sub)microparsec scales, deep in the strong-field
gravity regime and complementing electromagnetic observations. This also strengthens LISA's ability to help answering questions such as how massive black holes grow and coevolve with their host
galaxies and, by helping to identify the EMRI's host
galaxy through cross-correlation with AGN catalogues, to improve the use of these sources as (dark) sirens for cosmology.
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Earth and Planetary Astrophysics
An early look at how gas giants shape small planet bulk compositions
Joseph Y. Tang, Marta L. Bryan and Eve J. Lee
Gas
giants may shape the reservoir of solids and gas in the inner disk in which the small
planets assemble. To test this possibility, we collect a sample of 43 exoplanetary systems containing 68 inner small
planets (ISP) with both measured masses (1-20 M$_{\oplus}$) and radii (1-4 R$_{\oplus}$). After correcting for heterogeneous individual system sensitivities to distant gas
giants, we calculate the gas
giant occurrence rate in ISP systems P(GG$|$ISP) as a function of inner small
planet density, envelope mass fraction (EMF), and core mass. While we find no significant difference between P(GG$|$ISP) given high/low small
planet density, EMF, or core mass, we see hints of a trend when only looking at the metal-rich systems. Despite the substantial limitations due to small sample sizes, we find that gas
giants in metal-rich systems are preferentially found with lower density
planets with similar core masses. We find consistent hints of trends using larger samples of inner
planets with measured radii divided across the radius valley or with measured masses divided across 10 $M_\oplus$. Our result is consistent with more metal-enriched disks catalyzing rapid core assembly and kickstarting the gas
accretion early, while the muted difference in the outer
giant occurrence rate with respect to core mass may indicate contamination by post-formation photoevaporation.
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Astrophysics of Galaxies
Dark and Luminous Matter in the Coma Cluster: Probing Galaxy Cluster Assembly Through Filaments with Weak Lensing and Multiwavelength Observations
K. HyeongHan, K. Finner, M. James Jee et al. (+11 more)
The Coma cluster (Abell 1656; $z=0.023$) is a nearby rich
galaxy cluster and a key laboratory for studying cluster assembly in the
Cosmic Web. We characterize its projected dark matter distribution and connection to
galaxies, the intracluster medium, and reported intracluster filaments (ICFs) with wide-field ($\sim$12-deg$^2$) Subaru/Hyper Suprime-Cam weak-
lensing (WL) analysis. We reconstruct the two-dimensional mass distribution, fit Navarro-Frenk-White (NFW) models, derive an aperture mass densitometry profile, and compare the WL signal with optical spectroscopy, eROSITA X-ray observations,
radio data, and gas fraction diagnostics. A single-
halo NFW fit yields $M_{200\mathrm{c}}=8.2\pm0.7\times10^{14}~M_{\odot}$. The aperture mass profile agrees with the best-fit NFW model and the X-ray hydrostatic mass at $R\gtrsim20'$ ($\sim$560 kpc), suggesting little merger-induced bias in the global WL mass, while the inner region shows substantial hydrostatic bias. A two-
halo NFW fit centered on NGC 4874 and NGC 4839 gives masses of $7.8\pm0.6$ and $0.9\pm0.2\times10^{14}~M_{\odot}$, implying a $\sim$1:8 minor merger. The gas mass fraction suggests that the system is returning from first apocenter. We find a positive spatial correlation between the WL signal and X-ray surface brightness, strongest along the ICF directions ($110^{\circ}$ and $340^{\circ}$), where shear-selected subhalos are predominantly detected. The Coma $r$-band mass-to-light ratio is radially constant with $\langle M/L_r\rangle\simeq250\pm66~M_{\odot}/L_{\odot}$ within $R_{200\mathrm{c}}$, whereas the northern and western ICFs show higher values of $\sim1000~M_{\odot}/L_{\odot}$, suggesting stronger dark matter dominance. These results show that joint WL and multiwavelength analyses can effectively probe cluster assembly and the dark matter content of ICFs.
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All authors K. HyeongHan, K. Finner, M. James Jee, W. Lee, Y. Jiménez-Teja, S. Cha, W. Kang, H. S. Hwang, H. Cho, E. Churazov, I. Khabibullin, N. Lyskova, R. Sunyaev, A. M. Bykov
Cosmology and Nongalactic Astrophysics
Magnetic fields at the dawn of structure formation I. The CARLA J1510+5958 proto-cluster
A. Pagliotta, A. Bonafede, C. Stuardi et al. (+4 more)
Magnetic fields are a fundamental ingredient of the Universe, influencing the formation and
evolution of
cosmic structures. While
magnetic fields in local
galaxy clusters have been studied, their origin, amplification, and strength at high
redshift are poorly understood. Proto-clusters represent the early stages of
galaxy cluster formation, ideal for investigating the early magnetisation of the intra-cluster medium (ICM). We present a study of CARLA J1510+5958 proto-cluster at z = 1.72, observed with the JVLA in the L-band (1-2 GHz). We aim to investigate the
magnetic field strength and structure in the proto-ICM and the role of AGN in magnetising the environment during early cluster formation. We analyse Faraday rotation on the polarised emission from the central
radio-loud AGN using the Rotation Measure (RM) synthesis and QU fitting technique. We further interpret the observations with 3D simulations of gas density and turbulent
magnetic fields, varying AGN orientation and path length. The two AGN lobes show different polarisation properties. The Western lobe exhibits a uniform RM (average $-115 \pm 32\text{ rad m}^{-2}$, dispersion $36 \pm 11\text{ rad m}^{-2}$), indicating a locally ordered
magnetic field likely compressed by the lobe, while the Eastern lobe is depolarised. Although the asymmetry indicates a turbulent, magnetised medium, simulations rule out a purely isotropic random field for the Western lobe RM distribution. The QU fitting further suggests an internal Faraday component, interpreted as magnetised relativistic
plasma from the lobe mixed with the surrounding gas, indicating possible magnetisation of the ambient medium by the AGN. From this asymmetry, we constrain the average physical
magnetic field in the proto-ICM to a lower limit of 0.4 $\mu$G. These results confirm a magnetised proto-ICM at z = 1.72, proving early field amplification during cluster assembly.
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All authors A. Pagliotta, A. Bonafede, C. Stuardi, C. J. Riseley, D. Vallés-Pérez, P. Tozzi, L. Di Mascolo
Cosmology and Nongalactic Astrophysics
Dark Matter with a Drag at Low Redshift
Martin Schmaltz and Eashwar N. Sivarajan
Recent analyses of $f\sigma_8$ and weak-
lensing data indicate that the linear growth rate at $z\lesssim 1$ may be lower than predicted by $\Lambda$CDM. This motivates models of dark matter in which large scale structure growth slows relative to $\Lambda$CDM at late times. We construct particle models in which dark matter experiences a drag with dark radiation that grows at late times, unlike conventional DM–DR interactions, which fade as the universe expands. A key ingredient is that the radiation interacting with the dark matter is produced at late times from dark matter decay. An explicit model, interacting Decaying Cold Dark Matter (iDCDM), adds two parameters beyond $\Lambda$CDM while leaving the background, BBN, and primary CMB intact. But it predicts a step-shaped suppression of the linear growth rate $f(k,z)$, a distinctive target for DESI, Euclid, and Rubin. Confronted with current data, iDCDM shows a modest preference over $\Lambda$CDM, driven by $f\sigma_8$, with $\Delta\chi^2$ between $-2.7$ and $-7.6$ depending on the assumed scaling of the drag with
redshift and on
neutrino masses. The decisive test will come from upcoming $k$- and $z$-resolved growth measurements.
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Cosmology and Nongalactic Astrophysics
Observing Cosmic Reheating with the expanded Simons Observatory
Lei Ming and Marco Drewes
The Simons Observatory will be extended by three Small Aperture
Telescopes by 2027, increasing the total number of these instruments to six. We study the prospects for probing the reheating temperature and the inflaton coupling with this configuration, assuming a discovery of
primordial gravitational waves in
benchmark scenarios with a tensor-to-scalar ratio r=0.0036 or r=0.01. In popular plateau models of inflation, such an observation would fix the scale of inflation and enable determination of the order of magnitude of the reheating temperature and the inflaton interactions. For QCD-driven Warm Inflation the reheating temperature and inflaton coupling to
gluons could, under optimistic assumptions, be measured with a precision of a few percent. Such a measurement would imply a clear prediction for complementary inflaton searches in
axion experiments, paving the way toward probing the mechanism responsible for the initial conditions of the hot Big Bang in the laboratory.
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High Energy Astrophysical Phenomena
Black Hole Polarimetry: Universal Polarization of Synchrotron Radiation at the Horizon
Andrew Chael, Alexandru Lupsasca, George N. Wong et al. (+2 more)
Polarized images of a black hole encode the direction of electromagnetic energy flow near its event horizon. Measuring polarization from near-horizon emission can help determine whether this energy flow is powered by the accreting
plasma or the black hole
spin. Here we consider the linear polarization of synchrotron radiation emitted from the base of horizon-threading field lines in a time-stationary, axisymmetric, and degenerate Kerr magnetosphere with nonzero poloidal current. We show that the observed polarization pattern displays universal behavior: it is completely determined by the black hole
spin and observer inclination and is independent of the
magnetic field geometry. We derive a simple analytic formula for this
spin-dependent horizon polarization pattern. We find that this predicted pattern is also approached in time-averaged images from General Relativistic Magnetohydrodynamic simulations. Future observations with Very-Long-Baseline Interferometry at microarcsecond resolution could detect the trend of polarization toward the unique horizon value in M87*. Such observations may enable new measurements of black hole
spin and provide evidence that
magnetic field lines thread the horizon, a necessary condition for
spin-energy extraction via the Blandford–Znajek process.
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All authors Andrew Chael, Alexandru Lupsasca, George N. Wong, Zachary Gelles, Eliot Quataert
Astrophysics of Galaxies
The Hubble Missing Globular Clusters Survey IV. Ultra-faint compact satellites of the Milky Way. The case of Koposov 2
M. Bellazzini, R. Pascale, E. Dodd et al. (+16 more)
In the last decades a number of extremely faint and compact
Galactic satellites (Ultra Faint Compact Satellites; UFCS) have been discovered by large panoramic surveys. Their nature is uncertain due to their location in the overlapping
dwarf galaxy-
star cluster region of the $M_V-R_h$ plane and their faintness and distance. Here we show how the deep HST photometry from the Missing Globular Clusters Survey (MGCS), combined with spectroscopic
metallicities, provides new insight into the nature of these satellites through accurate distance and age estimates. We consider the case of Koposov 2, currently the most metal-poor bound
star cluster known in the Milky Way or an extreme case of Ultra Faint
Dwarf galaxy. By performing a spectroscopically-informed
bayesian isochrone fit on the MGCS data we find $(m-M)_0=16.85\pm0.06$ ($D=23.4\pm0.6$ kpc) and age=$13.7^{+0.9}_{-1.3}$ Gyr, showing that, contrary to previous age estimates, Koposov 2 is as old as the oldest
Galactic globular clusters. The luminosity function, corrected for incompleteness, is well reproduced by a model with the same age and
metallicity and a slope of the mass function $x=-0.35$, suggesting a significant depletion of faint
stars. We model the surface
stellar density field, deriving new robust estimates of the half-light radius ($R_h=0.39^{+0.06}_{-0.04}$ arcsec, corresponding to $R_h=2.7^{+0.4}_{-0.3}$ pc), of the absolute integrated magnitude ($M_V=-0.95\pm0.22$) and of the
stellar mass $M_\star=371.8\pm41.6M_{\odot}$), showing that Koposov 2 is much more compact than confirmed
dwarf galaxies of similar
stellar mass. The new evidence significantly support the hypothesis that Koposov 2 is a
star cluster that may have lost a large fraction of its mass. Finally we show that most UFCS lie in the same locus of the $M_\star-R_h$ plane as
Galactic open clusters, hinting to a possible additional channel for their formation.
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All authors M. Bellazzini, R. Pascale, E. Dodd, E. Ceccarelli, D. Massari, M. Libralato, S. Cassisi, M. De Leo, A. Della Croce, E. Vesperini, A. Mucciarelli, E. Dalessandro, M. Salaris, F. Aguado-Agelet, A. Bellini, F.R. Ferraro, B. Lanzoni, M. Monelli, S. Saracino
Astrophysics of Galaxies
Bar-induced migration of $\omega$ Centauri away from Gaia Sausage-Enceladus
Adam M. Dillamore, Hanyuan Zhang and Vasily Belokurov
The globular cluster $\omega$ Cen has been suggested to have originated in the
Gaia Sausage-Enceladus (GSE) merger event, possibly as its
nuclear star cluster. However, the present-day orbits of $\omega$ Cen and the GSE debris are very different. We investigate the scenario in which $\omega$ Cen originated in the GSE and migrated to its current position due to perturbations from the
Galactic bar. The [$\alpha$/M] distributions of
stars located between the GSE debris and $\omega$ Cen in $(L_z,E)$ space tentatively support this scenario, but are not conclusive. We run simulations of the GSE debris and $\omega$ Cen in a realistic Milky Way potential with a decelerating bar at various present-day pattern speeds. We find that $\omega$ Cen can indeed be traced back to the phase space region occupied by the GSE debris. However, this would likely require a pattern speed of $\Omega_\mathrm{b}\lesssim26$ km s$^{-1}$ kpc$^{-1}$, which is much lower than most recent estimates. We conclude that a GSE origin for $\omega$ Cen is dynamically and chemically plausible, but only with a re-evaluation of the current consensus on the bar's pattern speed.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Localization of Chiral Electromagnetic Waves on Thick Axion Domain Walls
Nemanja Kaloper
We analyze Maxwell theory coupled to an
axion domain wall as a spectral boundary value problem. We find that a finite-width
axion domain wall generically supports a localized normalizable
chiral electromagnetic mode with linear, gapless dispersion. This mode arises from helicity-dependent coupling sourced by the
axion gradient: one polarization experiences an effective attractive potential and forms a bound state, while the opposite polarization is repelled. The existence of this
chiral surface
photon is robust over a wide regime of wall structures and
axion masses. Our result shows that
axion domain walls generically support a localized
chiral photon that has been missed in previous analyses.
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Astrophysics of Galaxies
Unification models of Active Galactic Nuclei
Claudio Ricci
This chapter presents an overview of the unification models for Active
Galactic Nuclei (AGN), focusing on the physical structures, classification schemes, and evolutionary processes that characterize accreting supermassive black holes. We introduce the fundamental components of AGN, including the supermassive black hole,
accretion disk, jets,
outflows, broad-line and narrow-line regions, polar
dust and the dusty anisotropic obscurer. The traditional orientation-based unification model is reviewed, with a focus on the role of the covering factor of the obscuring material in shaping observed properties. We introduce the radiation-regulated unification model, which accounts for the influence of radiative feedback on the
nuclear environment of SMBHs. We also examine the evolutionary aspects of AGN unification, including the impact of
galaxy mergers, host
galaxy properties, and
redshift-dependent trends. Finally, we discuss changing-look AGN, which challenge conventional unification frameworks by exhibiting dramatic spectral variability.
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Astrophysics of Galaxies
The nature of `little blue dots'
Albert Sneppen, Darach Watson, James H. Matthews et al. (+1 more)
Previous Sirocco radiative-transfer models of gas-cocooned AGN predicted lower-column counterparts to little red dots (LRDs): compact, X-ray-weak sources with bluer continuum slopes and Balmer jumps rather than Balmer breaks. The recently identified population of little blue dots (LBDs) closely resembles this predicted phase. Here we explore these lower-column-density cocoons in which nebular recombination emission remains visible while strong Balmer-continuum absorption is avoided. We find that a sequence of increasing column density connects more classical AGN spectra, Balmer-jump LBD-like spectra at $N_{\rm H}\!\sim\!{\rm few}\times10^{24}\,\mathrm{cm^{-2}}$, and Balmer-break LRD-like spectra at higher columns. Along this sequence, electron scattering produces exponential line wings and suppresses X-ray emission before strong Balmer absorption features emerge. The models predict that LBDs should share X-ray weakness and exponential line wings with LRDs, while being distinguished by Balmer jumps in emission, weak or absent absorption features, potential He II $\lambda$4686 emission, lower H$\alpha$ luminosities and narrower H$\alpha$ lines. We compare with spectra of eight LBDs and find that significant Balmer-jump signatures are common. We therefore suggest that LBDs are lower-column analogues of LRDs within a common gas-cocooned AGN sequence.
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All authors Albert Sneppen, Darach Watson, James H. Matthews, Georgios Nikopoulos
Instrumentation and Methods for Astrophysics
Artifact-Conditioned Interval Diagnostics for Flow-Matching Neural Posterior Estimation in a Controlled Gravitational-Wave Benchmark
Zhi Luo and Qi-Qin Jing
Calibration checks for neural posterior
estimators in gravitational-wave inference should remain interpretable when observations contain data-quality artifacts. We study marginal interval calibration in a controlled frequency-domain binary-black-hole
benchmark with synthetic glitches, frequency masks, and power spectral density (PSD) mismatch. The posterior sampler is a support-aware flow-matching posterior
estimator (FMPE) with a circular representation of coalescence phase. We compare raw marginal credible intervals with global rescaling, oracle artifact-stratified rescaling, hard predicted-label rescaling, and soft learned artifact-aware interval rescaling (LAIR). In the 1024-bin evaluation, a single global scale fitted on mixed calibration data transfers poorly to frequency-mask cases, giving a mean absolute 90% marginal coverage error (MA90CE) of 0.1195. Soft LAIR lowers the corresponding error to 0.0672, although it is not uniformly better than the raw FMPE intervals. A 40-split LAIR evaluation and a six-checkpoint FMPE training-seed study show that the frequency-mask behavior is not a single-split artifact. The classifier recognizes frequency masks and PSD mismatch reliably, while glitch recall remains low. Waveform-resolution tests, PyCBC/LAL TaylorF2 backend checks, prior and Gaussian baselines, and controlled-likelihood reference-posterior probes indicate that marginal coverage must be read together with posterior width, geometry, and likelihood-based diagnostics. These results support using LAIR as an artifact-structured interval diagnostic, not as a substitute for posterior validation.
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Earth and Planetary Astrophysics
Multifractal Signatures of Hamiltonian Chaos in Hyperion's Rotational Dynamics
S. Jaroszewicz, N. Mendez, Maria P. Beccar-Varela et al. (+1 more)
The chaotic rotation of Saturn's moon Hyperion is a paradigmatic example of
Hamiltonian chaos in a natural system. Although its tumbling motion is well established theoretically, identifying a robust observational signature of chaos from sparse and noisy astronomical time series remains a major challenge, making phase-space reconstruction techniques impractical under realistic conditions. In this work, we show that multifractal detrended fluctuation analysis (MFDFA) provides an effective alternative for detecting chaotic dynamics directly from photometric observations. Using historical ground-based light curves and synthetic
datasets, we demonstrate that the intermittency associated with chaotic tumbling produces a broad multifractal singularity spectrum. While multifractality is a known feature of
Hamiltonian chaos, we show that it can serve as a practical observational diagnostic when traditional chaos indicators fail because of sparse sampling. In particular, the multifractal spectrum remains detectable after realistic observational filtering and distinguishes chaotic tumbling from aliased regular rotation. By contrast, regular resonant rotation exhibits a significantly narrower spectrum, approaching the monofractal behavior expected for uncorrelated noise. For the observational data, we measure a broad spectral width consistent with the synthetic chaotic model, statistically distinct from surrogate
datasets, and robust against finite time-series length. These results establish multifractal scaling as a viable observational signature of
Hamiltonian chaos in sparse astronomical
datasets, bridging nonlinear dynamics and planetary photometry.
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All authors S. Jaroszewicz, N. Mendez, Maria P. Beccar-Varela, Maria Cristina Mariani
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
When direct detection constrains reheating temperature: freeze-in with stronger couplings and inflaton-seeded freeze-in
Xavier Bertou, Olivier Deligny, Mathieu Gross et al. (+2 more)
Recent results from the DAMIC-M and PandaX collaborations have excluded the standard freeze-in production of dark matter for masses in the range $3~\mathrm{MeV} \lesssim m_\chi \lesssim 1~\mathrm{GeV}$ in the context of extensions of the Standard Model featuring an additional ultra-light $U(1)_{\rm X}$ gauge
boson. In this work, we analyze the constraints induced by DAMIC-M and PandaX results on the reheating temperature in freeze-in models at stronger coupling, or when a non-thermal source (such as inflaton decay) comes into play. We identify viable scenarios in which the DM relic abundance is correctly reproduced while evading current experimental bounds on the electron-scattering cross section, $\overline{\sigma}_\mathrm{e}$. In particular, we show that for reheating temperatures below the electroweak scale, Boltzmann suppressed production can be compensated by stronger couplings, bringing freeze-in scenarios within present experimental reach. Finally, we study a hybrid scenario in which a small branching ratio of inflaton decay seeds a nonzero initial dark-matter abundance. We show that such contributions can significantly modify freeze-in predictions across broad regions of parameter space, offering an additional pathway for probing extremely feeble interactions.
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All authors Xavier Bertou, Olivier Deligny, Mathieu Gross, Yann Mambrini, Issam-Eddine Mellouki
Cosmology and Nongalactic Astrophysics
Bounding the Effect of HOD Assumptions on Small-Scale Clustering Constraints
Nick Magnelli, Zachery Brown and Lado Samushia
Small-scale
galaxy clustering is expected to contain substantial cosmological information, but the extent to which this information constrains
halo-based cosmologies independent of an assumed
galaxy–
halo connection remains unclear. We quantify this dependence using LRG-like mock
galaxy catalogs built from 81 cosmologies in the {\tt AbacusSummit} suite. We analyze two-point correlation function multipoles on scales ranging from $5$–$80$ Mpc/$h$ and compare two limiting treatments, the \enquote{floor} and \enquote{ceiling}, of the standard five-parameter HOD model. In the conservative floor case, we impose only broad initial HOD bounds and profile over HOD parameters to determine the minimum constraining power available; we accomplish this with HODmin, a two-stage global optimization
algorithm written for minimizing $\chi^2$ in HOD space. In the optimistic ceiling case, we assume the HOD parameters are known exactly. We find a significant difference between the floor and ceiling when comparing against the same Planck $\Lambda$CDM mock data vector with identical modeling assumptions: for the floor, $25\%$ of the discrete {\tt AbacusSummit} cosmologies tested are excluded at $3\sigma$, whereas for the ceiling, $\sim81\%$ are excluded. Many cosmologies agree well with data in the floor, and yet in the ceiling are excluded by multiple orders of magnitude in $\chi^2$. We therefore observe the strength of small-scale clustering constraints depends heavily on the amount of prior HOD information assumed. We compare the sensitivity of this effect to various choices like scale cut, angle cut, multipole inclusion, mock phase, and mock HOD model. Our wide floor–ceiling bracket indicates that informative
galaxy–
halo priors are necessary for extracting strong small-scale clustering constraints.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Collective neutrino oscillations: Many-body non-forward effects and non-classicality
Julien Froustey, Ermal Rrapaj, Yuhao Liu et al. (+3 more)
Neutrino evolution in dense astrophysical environments is typically described either within a
quantum kinetic framework, which neglects the build-up of multi-body correlations, or through simplified many-body calculations that allow significant
entanglement to develop. In this work, we compare these two approaches in a simple
neutrino-gas configuration, with particular emphasis on the role of non-forward scattering processes. These effects are incorporated either through a collision term in the kinetic description, or by considering the full
neutrino-
neutrino many-body
Hamiltonian. We highlight differences between the two descriptions in both their characteristic timescales and asymptotic behavior. Motivated by the natural suitability of
quantum computing for many-body calculations, we further investigate the non-classicality of
neutrino evolution, discussing Trotter error scaling, along with the associated costs of constructing
quantum circuits in terms of entangling gates and non-Clifford gates. We find that the resources needed for
neutrino many-body
evolution are on the low end of typical high-energy physics problems and on the mid to high end with respect to
quantum chemistry problems. For the full
Hamiltonian, resource requirements increase relative to the truncated version. We emphasize the importance of efficient
fermion-to-
qubit encodings, which are essential for reducing the substantial computational resources required for such simulations.
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All authors Julien Froustey, Ermal Rrapaj, Yuhao Liu, Gushu Li, Costin Iancu, Vincenzo Cirigliano
Earth and Planetary Astrophysics
The carbon isotope ratio of \beta\ Pic b with high-resolution spectroscopy
D. González Picos, I.A.G. Snellen, R. Landman et al. (+6 more)
Isotopic ratios trace the formation and
evolution of
planets and link their atmospheres to the chemistry of their natal protoplanetary discs. We measure $^{12}\mathrm{C}/^{13}\mathrm{C} = 58^{+18}_{-15}$ in the atmosphere of the young super-Jupiter $\beta$ Pic b from 11 nights of CRIRES+ K-band spectroscopy ($\mathcal{R} \approx 100{,}000$) at the Very Large
Telescope (VLT). We detect both $^{12}\mathrm{CO}$ and $^{13}\mathrm{CO}$ and constrain $^{12}\mathrm{C}/^{13}\mathrm{C}$ with a
Bayesian retrieval jointly fitted with near-infrared photometry. The inferred $^{12}\mathrm{C}/^{13}\mathrm{C}$ is consistent with the present-day interstellar medium (ISM), is below the
solar value, and is comparable to measurements in other young super-Jupiters. We also retrieve $T_{\rm eff} = 1629^{+30}_{-28}\,\mathrm{K}$, near-
solar to mildly super-
solar metallicity ([M/H]$ = 0.20^{+0.16}_{-0.12}$), a
solar-like carbon-to-oxygen ratio (C/O$ = 0.52 \pm 0.03$), and tentative evidence for thick clouds. We analyse each night independently and combine the results of the six epochs with the highest signal-to-noise ratio (S/N), propagating night-to-night scatter into the final uncertainties. This provides an isotopic
benchmark for a directly imaged
planet interior to the CO snow line.
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All authors D. González Picos, I.A.G. Snellen, R. Landman, S. de Regt, N. Grasser, J. L. Birkby, T. Stolker, I. Koutalios, M.A. Kenworthy