Instrumentation and Methods for Astrophysics
BGRem: A background noise remover for astronomical images based on a diffusion model
Rodney Nicolaas, Sascha Caron, Fiorenzo Stoppa et al. (+4 more)
Context: Astronomical imaging aims to maximize signal capture while minimizing noise. Enhancing the signal-to-noise ratio directly on detectors is difficult and expensive, leading to extensive research in advanced post-processing techniques. Aims: Removing background noise from images is a valuable pre-processing step catalog-building tasks. We introduce BGRem, a machine learning (ML) based tool to remove background noise from astronomical images. Methods: BGRem uses a
diffusion-based model with an
attention U-Net as backbone, trained on simulated images for optical and gamma ({\gamma})-ray data from the MeerLICHT and
Fermi-LAT
telescopes. In a supervised manner, BGRem learns to denoise astronomical images over several
diffusion steps. Results: BGRem performance was compared with a widely used tool for cataloging astronomical sources, SourceExtractor (SExtractor). It was shown that the amount of true positive sources using SExtractor increased by about 7% for MeerLICHT data when BGRem was used as a pre-processing step. We also show the generalizability of BGRem by testing it with optical images from different
telescopes and also on simulated {\gamma}-ray data representative of the
Fermi-LAT
telescope. We show that in both cases, BGRem improves the source detection efficiency. Conclusions: BGRem can improve the accuracy in source detection of traditional pixel-based methods by removing complex background noise. Using zero-shot approach, BGRem can generalize well to a wide range of optical images. The successful application of BGRem to simulated {\gamma}-ray images, alongside optical data, demonstrates its adaptability to distinct noise characteristics and observational domains. This cross-wavelength performance highlights its potential as a general-purpose background removal framework for multi-wavelength astronomical surveys.
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All authors Rodney Nicolaas, Sascha Caron, Fiorenzo Stoppa, Saptashwa Bhattacharyya, Roberto Ruiz de Austri, Paul J. Groot, Andrew J. Levan
Astrophysics of Galaxies
Matching JWST UV Luminosity Functions with Refined $\Lambda$CDM Halo Models
Saeed Fakhry, Maryam Shiravand and Antonino Del Popolo
The James Webb Space
Telescope (JWST) has unveiled a population of unexpectedly massive and luminous
galaxies at
redshifts $z \gtrsim 7$, posing a significant challenge to the standard $\Lambda$CDM cosmological paradigm. In this work, we address the tension between early JWST observations of luminous high-
redshift galaxies and predictions of the standard $\Lambda$CDM model by revisiting the physics of dark matter
halo formation. Employing refined
halo mass functions derived by Del Popolo et al. (DP1 and DP2) that incorporate angular momentum, dynamical friction, and
redshift-dependent collapse barriers, we demonstrate a significant enhancement in the abundance of massive
halos at $z \gtrsim 7$ compared to the conventional Sheth-Tormen (ST) formalism. Using a semi-empirical framework linking
halo mass to UV luminosity, we show that the DP2 model reproduces the observed UV luminosity functions from $z = 7$ to $14$ with moderate
star formation efficiencies, whereas the ST model requires implausibly high efficiencies. Our results suggest that the JWST overabundance problem stems not from new physics beyond $\Lambda$CDM, but from oversimplified treatments of gravitational collapse, highlighting the critical role of small-scale dissipative dynamics in early structure formation.
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Cosmology and Nongalactic Astrophysics
Stochastic instantons and the tail of the inflationary density perturbation
Jaime Calderón-Figueroa and David Seery
In the "
stochastic $\delta N$ formalism", the statistics of the inflationary density perturbation are obtained from the first passage distribution of a
stochastic process. We develop a general framework in which to evaluate the rare tail of this distribution, based on an instanton approximation to a path integral representation for the transition probability. We relate our formalism to the Schwinger-Keldysh path integral, by integrating out short wavelength degrees of freedom to produce an influence functional. This provides a principled way to extend the calculation beyond the slow-roll limit, and to models with multiple fields. We argue that our framework has a number of advantages in comparison with existing methods. In particular, it reliably captures the tail behaviour in cases where existing techniques do not apply, including cases where the noise amplitude has strong time dependence. We demonstrate the method by computing the tail probability in a number of scenarios, including a beyond-slow-roll analysis of a linear potential, ultra-slow-roll, and constant-roll inflation. We find close agreement with results already reported in the literature. Finally, we discuss a scenario with exponentially decaying noise amplitude. This is a model for the
stochastic evolution of a fixed comoving volume of spacetime on superhorizon scales. In this case we show that the tail reverts to a Gaussian weight.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Testing black hole metrics with binary black hole inspirals
Zhe Zhao, Swarnim Shashank, Debtroy Das et al. (+1 more)
Gravitational wave astronomy has opened an unprecedented window onto tests of
gravity and fundamental physics in the strong-field regime. In this study, we examine a series of well-motivated deviations from the classical Kerr solution of General Relativity and employ gravitational wave data to place constraints on possible deviations from the Kerr geometry. The method involves calculating the phase of gravitational waves using the effective one-body formalism and then applying the parameterized post-Einsteinian framework to constrain the parameters appearing in these scenarios beyond General Relativity. The effective one-body method, known for its capability to model complex gravitational waveforms, is used to compute the wave phase, and the post-Einsteinian framework allows for a flexible, model-independent approach to parameter estimation. We demonstrate that gravitational wave data provide evidence supporting the Kerr nature of black holes, showing no significant deviations from General Relativity, thereby affirming its validity within the current observational limits. We further assess the potential impact of orbital eccentricity and find that, within observationally allowed ranges, its contribution to the inferred deviations is subdominant. This work bridges theoretical waveform modeling with observational constraints, providing a pathway to test the no-hair
theorem and probe the astrophysical viability of modified black holes.
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All authors Zhe Zhao, Swarnim Shashank, Debtroy Das, Cosimo Bambi
Cosmology and Nongalactic Astrophysics
Neutrinogenic CMB spectral distortions
Shao-Ping Li and Jens Chluba
Extra radiation injection after
neutrino decoupling in the early Universe contributes to the effective number of
neutrino species that can be constrained by the
cosmic microwave background (CMB). However, any effective
neutrino number itself cannot uniquely determine the underlying source. We argue that the degeneracy can be relaxed by CMB spectral distortions, which are caused by energy exchange between the extra radiation and
photons. We consider neutrinogenic CMB spectral distortions, where extra energy is released in the form of
neutrinos but still creates the CMB spectral distortions via electroweak interactions. The synergy between the effective
neutrino number and CMB spectral distortions provides a complementary probe of hidden sectors that dominantly couple to
neutrinos, opening up parameter space that can be targeted by joint CMB anisotropy and spectral distortion experiments.
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Solar and Stellar Astrophysics
Quasi-Periodic Pulsations Driven by Structural Oscillations in a Kink-Unstable Flaring Coronal Loop
James Stewart, Philippa K. Browning and Mykola Gordovskyy
Twisted coronal loops in the
solar atmosphere may become kink-unstable when their
magnetic field lines are sufficiently twisted. This instability can trigger
magnetic reconnection, leading to the emission of electromagnetic radiation, which manifests as a
solar flare. Previous research has demonstrated that oscillations in microwave emissions, resembling observed quasi-periodic pulsations (QPPs), can be generated by the reconnecting loop. Our aim is to investigate the relationship between the oscillations of the loop and these microwave pulsations. Using 3D magnetohydrodynamical simulations, we examine two models: a straight loop in a uniform-density atmosphere and a curved loop in a gravitationally stratified atmosphere. Using new methodology, we extract the reconnecting loop-top from both models and identify structural oscillations. We then compare these oscillations with the gyrosynchrotron (GS) radiation emitted from the simulations, which is forward-modelled using a radiative transfer code. We find that oscillations in the GS emissions are driven by sausage and kink-mode oscillations. However, the relationship between the oscillation frequencies of the GS emission and the identified loop oscillation modes is complex. The dominant mode in the former may result from interference between sausage-mode and kink-mode oscillations or entirely different mechanisms. Results such as these increase our understanding of the time-dependent behaviour of
solar flares and lay the groundwork for potential diagnostic tools that could be used to determine physical parameters within a flaring loop
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Earth and Planetary Astrophysics
Edge-On Disk Study (EODS) II: HCO$^+$ and CO vertical stratification in the disk surrounding SSTTau042021
C. Foucher, A. Dutrey, V. Piétu et al. (+17 more)
Context. Edge-on disks offer a unique opportunity to directly examine their vertical structure, providing valuable insights into
planet formation processes. We investigate the
dust properties, as well as the CO and HCO$^+$ gas properties, in the edge-on disk surrounding the T Tauri
star 2MASS J04202144+281349 (SSTTau042021). Aims. We estimate the radial and vertical temperature and density profile for the gas and the
dust. Methods. We use ALMA archival data of CO isotopologues and continuum emission at 2, 1.3 and 0.9 mm together with new NOEMA HCO$^+$ 3-2 observations. We retrieve the gas and
dust disk properties using the tomographic method and the DiskFit model. Results. The vertical CO emission appears very extended, partly tracing the H$_2$ wind observed by JWST. C$^{18}$O, $^{13}$CO and HCO$^+$ emission characterize the bulk of the molecular layer. The
dust and gas have a mid-plane temperatures of $\sim 7-11$ K. The temperature of the molecular layer (derived from $^{13}$CO and HCO$^+$) is on the order of 16 K. HCO$^+$ 3-2 being thermalized, we derive a lower limit for the H$_2$ volume density of $\sim 3 \times 10^6$ cm$^{-3}$ at radius 100-200 au between 1 and 2 scale heights. The atmosphere temperature of the CO gas is of the order $\sim$ 31 K at a radius of 100 au. We directly observe CO and HCO$^+$ gas onto the mid-plane beyond the
dust outer radius ($\ge 300$ au). The (gas+
dust) disk mass estimated up to a radius of 300 au is on the order of $4.6 \times 10^{-2} \mathrm{M}_\odot$. Conclusions. Thanks to the favorable disk inclination, we present the first quantitative evidence for vertical molecular stratification with direct observation of CO and HCO$^+$ gas along the mid-plane. We estimate the temperature profile with temperature of 7-11 K near the mid-plane, and 15-20 K in the dense part of the molecular layer up to $\sim$ 35 K above.
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All authors C. Foucher, A. Dutrey, V. Piétu, S. Guilloteau, E. Chapillon, O.Denis-Alpizar, E.Dartois, E. Di Folco, S. Gavino, U. Gorti, Th. Henning, Á. Kóspál, F. Le Petit, L. Majumdar, R. Meshaka, N. T. Phuong, M. Ruaud, D. Semenov, Y.W. Tang, S. Wolf
Instrumentation and Methods for Astrophysics
Interactive High-Performance Visualization for Astronomy and Cosmology
Eva Sciacca, Nicola Tuccari, Umer Arshad et al. (+3 more)
The exponential growth of data in Astrophysics and Cosmology demands scalable computational tools and intuitive interfaces for analysis and visualization. In this work, we present an innovative integration of the VisIVO scientific visualization framework with the InterActive Computing (IAC) service at Cineca, enabling interactive, high-performance visual workflows directly within HPC environments. Through seamless integration into Jupyter-based science gateways, users can now access GPU-enabled compute nodes to perform complex 3D visualizations using VisIVO via custom Python wrappers and preconfigured interactive notebooks. We demonstrate how this infrastructure simplifies access to advanced HPC resources, enhances reproducibility, and accelerates exploratory workflows in astronomical research. Our approach has been validated through a set of representative use cases involving large-scale simulations from the GADGET code, highlighting the effectiveness of this system in visualizing the large-scale structure of the Universe. This work exemplifies how science gateways can bridge domain-specific tools and advanced infrastructures, fostering user-centric, scalable, and reproducible research environments.
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All authors Eva Sciacca, Nicola Tuccari, Umer Arshad, Fabio Pitari, Giuseppa Muscianisi, Emiliano Tramontana
Instrumentation and Methods for Astrophysics
Introducing The SHell misAlignment Detection for straylight Estimation (SHADE) algorithm: the case of XMM-Newton
S.Piscitelli, G. Ponti, M. Civitani et al. (+1 more)
When performing X-ray observations with a Wolter-I
telescope, the presence of bright off-axis sources can introduce unfocused rays, known as straylight, which contaminate the detector and compromise the scientific analysis. Among the different components of straylight, single reflections off the hyperboloid section of the mirror shells often produce arc-like patterns on the detector. These arcs depend not only on the off-axis angle of the source but also on the geometrical
alignment of the individual shells. In this paper, we introduce the SHell misAlignment Detection for straylight Estimation (SHADE)
algorithm, a novel and flexible tool designed to infer the misalignment parameters of individual shells, reproduce the geometry of straylight arcs and predict its pattern on the detector. SHADE allows us to model each shell displacement with two parameters: $(\gamma,\xi)$ that represents the tilt amplitude and direction. While the
algorithm is general and applicable to any Wolter-like
telescope, we demonstrate its effectiveness using a set of XMM-Newton observations of the low-mass X-ray binary GX5-1. As a proof of concept, we recover the best-fit misalignment parameters for a selected shell, obtaining $\gamma = 21.9''^{+10.3}_{-9.02}$ and $\xi = 5.88^{+1.02}_{-0.97}$ rad. SHADE represents a new approach to diagnosing mirror misalignments from straylight patterns and can support both pre and post-launch calibration efforts and future
telescope designs.
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All authors S.Piscitelli, G. Ponti, M. Civitani, D. Spiga
High Energy Astrophysical Phenomena
Combining the second data release of the European Pulsar Timing Array with low-frequency pulsar data
F. Iraci, A. Chalumeau, C. Tiburzi et al. (+46 more)
Low-frequency
radio data improve the sensitivity of
pulsar timing arrays (PTAs) to propagation effects such as dispersion measure (DM) variations, enabling better noise characterization essential for detecting the
stochastic gravitational wave background (GWB). We combined LOFAR (100-200 MHz) and NenuFAR (30-90 MHz) observations with the recent European and Indian PTA release (DR2new+) into a new
dataset, DR2low, spanning ~11 years for 12
pulsars. DR2low allows updated noise models, increasing PTA sensitivity to the GWB. Using Libstempo and Enterprise, we applied standard noise models including red noise (RN) and time-variable DM (DMv) as power laws, and performed
Bayesian model selection over RN, DMv, and an additional chromatic noise term (CN4). Compared to DR2new+, DR2low improves DM constraints and separates DM and RN contributions. We found that the RN is required in the final model for 10 out of 12
pulsars, compared to only 5 in the DR2new+
dataset. The improved sensitivity to
plasma effects provided by DR2low also favors the identification of significant CN4 in eight
pulsars, while none showed such evidence in DR2new+. The analysis also reveals unmodelled
solar wind effects, particularly near
solar conjunction, with residual delays absorbed into the DM component, highlighting the importance of accurately modelling the
solar wind in PTA
datasets.
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All authors F. Iraci, A. Chalumeau, C. Tiburzi, J. P. W. Verbiest, A. Possenti, S. C. Susarla, M. A. Krishnakumar, G. M. Shaifullah, J. Antoniadis, M. Bagchi, C. Bassa, R. N. Caballero, B. Cecconi, S. Chen, S. Chowdhury, B. Ciardi, I. Cognard, S. Corbel, S. Desai, D. Deb, J. Girard, A. Golden, J-M. Grießmeier, L. Guillemot, M. Hoeft, H. Hu, F. Jankowski, G. Janssen, B. C. Joshi, S. Kala, E. Keane, K. Nobelson, A. Konovalenko, I. Kravtsov, M. Kramer, K. Liu, A. Parthasarathy, P. Rana, D. Schwarz, J. Singha, A. Srivastava, K. Takahashi, P. Tarafdar, G. Theureau, O. Ulyanov, C. Vocks, J. Wang, V. Zakharenko, P. Zarka
High Energy Astrophysical Phenomena
The Role of Acoustic Instability in Cosmic-Ray Self-Confinement
Antonio Capanema, Pasquale Blasi and Emanuele Sobacchi
Over the past decades, there has been growing observational and theoretical evidence that
cosmic-ray-induced instabilities play an important role in both acceleration and transport of
cosmic rays (CRs). For instance, the efficient acceleration of charged particles at
supernova remnant shocks requires rapidly growing instabilities, so much so that none of the proposed processes seem sufficient to warrant acceleration to PeV energies. In this work, we investigate whether an acoustic instability triggered by the presence of a CR pressure gradient can lead to significant self-confinement of charged particles in the vicinity of shocks. We validate the expected growth rates and obtain the scale and energy of
magnetic field perturbations induced by such system using magnetohydrodynamical simulations. Our results suggest a strong suppression of the
diffusion coefficient for particles with Larmor radius around a thousandth of the precursor scale length.
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Astrophysics of Galaxies
Theoretical Modelling of Early Massive Black Holes
Marta Volonteri
These notes review theoretical models of massive black hole formation, growth and observables. They start with a brief summary of basic properties of massive black hole properties. The current view on massive black holes and active
galactic nuclei at high
redshift is then summarized, highlighting the JWST “revolution” and the questions raised by the recent observations. The notes then touch on massive black hole formation and growth mechanisms, emphasizing the processes at play at early
cosmic times. Then techniques for modeling the
cosmic massive black hole
evolution, are reviewed with an emphasis on cosmological simulations, before approaching how observables are derived from models. They conclude with a section reflecting on the main questions on the JWST-discovered population in light of the material presented in the earlier sections.
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Solar and Stellar Astrophysics
A type II solar radio burst without a coronal mass ejection association
Anshu Kumari and Nat Gopalswamy
Type II
solar radio bursts are commonly associated with shocks generated by coronal mass ejections (CMEs), where
plasma waves are excited by magnetohydrodynamic (MHD) processes and converted into
radio waves at the local
plasma frequency or its harmonics. However, there are instances where type II bursts occur in the absence of whitelight CMEs. We analysed one such metric type II
radio burst observed on November 2, 2023, characterized by split band features and fundamental-harmonic lanes. Notably, no CME was detected with space-based coronagraphs during this event. However, an intense M1.6 class
flare was observed just before the type II burst and an extreme ultraviolet (EUV) disturbance was observed expanding into surrounding regions. The absence of any whitelight CME seen in any coronagraph field of view even though the EUV shock had a moderate speed of $\approx500~km/s$, which was close to the shock speed derived from
radio observations, %indicates that the shock in the inner corona was most-likely produced by the very intense
solar flare and the type II was associated with the EUV disturbance seen in the lower corona. These observations indicate that the shock in the inner corona was most-likely driven by the EUV ejecta seen in the lower corona, but the ejecta did not survive as a CME in the coronagraph field of view.
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High Energy Astrophysical Phenomena
Relativistic hydrodynamics simulations of supernova explosions within extragalactic jets
B. Longo, M. Perucho, V. Bosch-Ramon et al. (+2 more)
Jets in active
galactic nuclei have to cross significant distances within their host
galaxies, meeting large numbers of
stars of different masses and
evolution stages in their paths. Given enough time,
supernova explosions within the jet will eventually happen, and may have a strong impact on its dynamics, potentially triggering powerful non-thermal activity. We carried out a detailed numerical study to explore the dynamics of the interaction between the ejecta of a
supernova explosion and a relativistic extragalactic jet. By means of relativistic hydrodynamics simulations using the code RATPENAT, we simulated the jet-ejecta interaction in two different geometries or scenarios: a two-dimensional, axisymmetric simulation, and a three-dimensional one, which includes the orbital velocity of the exploding
star. Although initially filling a region much smaller than the jet radius, the ejecta expands and eventually covers most of the jet cross section. The expansion is enhanced as more energy from the jet is converted into kinetic and internal energy of the ejecta, which also favors the ejecta disruption, all this occurring on timescales ~ 10^4 yr. Although a complete numerical convergence of the results is unattainable given the subsonic, turbulent nature of the interaction region, the simulations are consistent in their description of the gross morphological and dynamical properties of the interaction process. At the end of the simulations, the
supernova ejecta has already partially mixed with the relativistic jet. The results also suggest that the jet-ejecta interaction may be a non-negligible non-thermal emitter. Moreover, due to efficient mixing, the interaction region can be a potential source of ultra-high-energy
cosmic rays of heavy composition.
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All authors B. Longo, M. Perucho, V. Bosch-Ramon, J.M. Martí, G. Fichet de Clairfontaine
Solar and Stellar Astrophysics
Ten new, ultracompact triply eclipsing triple star systems
T. Borkovits, S. A. Rappaport, T. Mitnyan et al. (+15 more)
We have identified more than a hundred close triply eclipsing hierarchical triple
star systems from data taken with the space
telescope TESS. Many of them have outer periods less than or, close to 100 days, hence, we call them `ultracompact hierarchical triples'. These systems are noteworthy in that we can potentially determine their dynamical and astrophysical parameters with a high precision, in many cases even without radial velocity data. In the present paper we report the comprehensive study of ten new ultracompact triply eclipsing triple
star systems, located in the northern ecliptic hemisphere, taken from this larger sample: TICs 198581208, 265274458, 283846096, 337993842, 351404069, 378270875, 403792414, 403916758, 405789362, 461500036. Most of the data for this study come from TESS observations, but we obtained supplemental ground-based photometric measurements for two of the systems. The eclipse timing variation curves extracted from the TESS and the ground-based follow up data, the photometric light curves, and the spectral energy distribution are combined in a complex photodynamical analysis to yield the
stellar and orbital parameters of all ten systems. The outer periods are in the range of 46.8-101.4 days. We found third-body forced, rapid apsidal motion in four systems. Moreover, TIC 403916758 was found to be a double twin triple (i.e. both the inner and the outer mass ratios are close to unity). All of the systems are substantially flat, with mutual inclination angles of $<5^o$. Finally, we have taken the results for the ten systems in the present paper, and combined them with the system parameters for more than 30 other compact triples that we have reported on in previous work, in order to examine some of the global properties of these systems on a statistical basis.
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All authors T. Borkovits, S. A. Rappaport, T. Mitnyan, R. Gagliano, T. Jacobs, B. Powell, V. Kostov, M. Omohundro, M. H. Kristiansen, I. Terentev, H.M. Schwengeler, D. LaCourse, Z. Garai, T. Pribulla, I. B. Bíró, I. Csányi, Z. Dencs, A. Pál
High Energy Astrophysical Phenomena
Finding Supermassive Black Hole Binary Mergers in Pulsar Timing Array Data
Sharon Mary Tomson, Boris Goncharov and Rutger van Haasteren
Galaxy observations suggest that mergers of supermassive black hole binaries (SMBHBs) are rare events, with rates of order one per decade across the observable Universe. We present a framework to search for merging SMBHBs in
pulsar timing array (PTA) data using a physically complete waveform model including inspiral, merger, ringdown, and gravitational-wave
memory. This enables a unified treatment of continuous emission and the non-oscillatory
memory signal. Using simulated PTA
datasets, we demonstrate parameter estimation for representative systems with chirp masses of $10^8$ and $10^{10}~M_\odot$ at distances of $3$ Mpc to $100$ Mpc respectively. For sufficiently strong signals, we recover binaries with log Bayes factors >10 and constrain chirp mass and luminosity distance, subject to their characteristic degeneracy. Sky localization uncertainties of a few degrees could potentially enable electromagnetic follow-up and multi-messenger observations of SMBHB mergers. We further demonstrate that commonly used
memory burst approximations lead to biased strain amplitudes and inferred source parameters when compared to the full SMBHB waveform, even when optimally tuned. These results establish a pathway for searching for SMBHB mergers with PTAs using complete waveform models.
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Astrophysics of Galaxies
Suzaku observations of outskirts of nearby clusters and groups: I. electron density and gas fraction to the virial radius
Kyoko Matsushita, Marie Kondo, Kosuke Sato et al. (+3 more)
We present an analysis of Suzaku observations of 14 nearby
galaxy clusters and groups (z < 0.06), extending radial coverage out to the virial radius (approximately r200). The sample spans a wide mass range, from M500 about 2x10^13 to 7x10^14
solar masses, and includes well-studied systems such as Coma, Perseus, and Virgo. We carefully modeled all background components, including the soft X-ray foregrounds (the Local Hot Bubble, Milky Way
Halo, and super-virial temperature components), the
cosmic X-ray background, and the non-X-ray background, and assessed their effects on the derived properties of the intracluster medium (ICM). We constructed radial profiles of emission measure, electron density, and temperature. Temperatures decrease smoothly with radius, typically dropping to about one-third to half of their peak values near r200. For relaxed clusters, the emission measure profiles outside the core regions are well described by a beta model with beta around 0.6-0.7, while groups show slightly flatter slopes of beta around 0.4-0.65. Beyond r2500, electron density profiles follow a power-law decline with a slope close to 2. At r500 and r200, the electron density and the gas mass fraction show a tight correlation with the system mass, except for three clusters with bright subclusters. In massive clusters, the gas fraction increases with radius and approaches the
cosmic baryon fraction near r200. In contrast, lower-mass systems exhibit gas fractions of around 0.1 at r200. The observed mass dependence of gas fractions suggests that feedback and related processes play an increasingly important role toward the group scale, shaping the connection between
baryons and dark matter
halos.
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All authors Kyoko Matsushita, Marie Kondo, Kosuke Sato, Toru Sasaki, Nobuhiro Okabe, Kotaro Fukushima
Astrophysics of Galaxies
Probing dust torus radius–luminosity relation: An WISE view
Ashutosh Tomar, Suvendu Rakshit, Amit Kumar Mandal et al. (+1 more)
We present measurements of the dusty
torus sizes of 51 active
galactic nuclei (AGNs) with a
redshift of $z<$ 0.8. Our analysis utilizes about 16 years of optical photometric data of 146 AGNs from various time-domain surveys, including ASAS-SN, CRTS, and ZTF, along with 14 years of infrared data in the $W$1 ($\sim$ 3.4 $\mu$m) and $W$2 ($\sim$ 4.6 $\mu$m) bands obtained from the Wide-Field Infrared Survey Explorer (WISE). The estimated
dust torus size ranges from 1000 to 3000 days, using both the cross-correlation analysis and lightcurve modeling through `MICA'. The measured lag has been corrected by $(1+z)^{-0.37}$, to account for cosmological time dilation and the
torus temperature-gradient scaling. We conduct a linear regression analysis for both the $W$1 and $W$2 bands to examine the radius–luminosity ($R$–$L_{BOL}$) relationship under two conditions: one where the slope is fixed at 0.5 and one where it is allowed to vary. For the fixed slope of 0.5, we find the ratio of R$_{\mathrm{BLR}}$: R$_{W1}$: R$_{W2}$ to be 1: 9: 12, indicating that the
torus lies outside the BLR and that its size increases with wavelength. Furthermore, we determine the relationship between
torus size and L$_{BOL}$, yielding best-fit slopes of $0.413\pm0.047$ for the $W$1 band and $0.397\pm0.058$ for the $W$2 band. Both slopes are shallower than predicted by the
dust radiation
equilibrium model. Furthermore, our findings indicate that the
torus size systematically decreases as the Eddington ratio increases, a trend that can be explained by the self-shadowing effects of slim disks.
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All authors Ashutosh Tomar, Suvendu Rakshit, Amit Kumar Mandal, Shivangi Pandey
Astrophysics of Galaxies
High energy gamma-ray sources in the VVV survey - III. Spectroscopic confirmation of an AGN at low Galactic latitudes
Eduardo O. Schmidt, Laura D. Baravalle, Ana Pichel et al. (+9 more)
We aim to spectroscopically confirm the nature of VVV-J181258.71-314346.7, a candidate counterpart to the unassociated gamma-ray source 4FGLJ1812.8-3144. This object was selected based on its near-infrared photometric properties and moderate variability, as part of a broader effort to identify active
galactic nuclei (AGN) behind the
Galactic bulge and disc. We obtained near-infrared spectra using the Flamingos-2 instrument at Gemini South, covering the $1.1 $–$ 1.8~\mu$m range with a spectral resolution of $R \sim 1200$. Standard data reduction procedures were applied, including telluric correction and wavelength calibration. The analysis focused on the identification of emission lines and the estimation of the
redshift using cross-correlation techniques and spectral template fitting. Despite a relatively low signal-to-noise ratio, the spectrum reveals the presence of Pa$\beta$ and Fe\,ii emission lines. The measured
redshift is $z = 0.206 \pm 0.001$, which confirms the extragalactic nature of the source. The spectral features such as line ratios and full width at half maximum are consistent with those typically observed in type-1 AGNs, particularly Seyfert 1
galaxies. This study demonstrates the ability of near-infrared spectroscopy to reveal AGNs that are obscured by highly extincted and crowded
galactic fields. The confirmation of an AGN at low
Galactic latitude ($b\sim -6.5${\deg}) shows that near-IR surveys like VVV can successfully penetrate the zone of avoidance. Extending this approach to additional candidates is crucial for improving the census of AGNs hidden behind the Milky Way, as well as for constraining the population of unassociated gamma-ray sources in these troublesome regions.
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All authors Eduardo O. Schmidt, Laura D. Baravalle, Ana Pichel, Damián Mast, María Victoria Alonso, Jorge Díaz Tello, Luciano H. García, Valentin D. Ivanov, Dante Minniti, Nicola Masetti, Laura G. Donoso, Rodrigo Zelada Bacigalupo
Astrophysics of Galaxies
Analysis of Galaxies at the Extremes: Failed Galaxy Progenitors in the MAGNETICUM Simulations
Jonah S. Gannon, Lucas C. Kimmig, Duncan A. Forbes et al. (+5 more)
There is increasing observational evidence for a failed
galaxy formation pathway for some ultradiffuse
galaxies (UDGs) at low
redshift however they currently lack simulated counterparts. We attempt to identify dark matter
halos at high
redshift within the MAGNETICUM cosmological simulations that could plausibly be their progenitors. We build a toy model of passive
galaxy evolution within the
stellar mass-
halo mass relation to trace z = 0 observations of UDGs back to their z = 2 locations. We identify a population of 443
galaxies that match these parameter space positions within the simulation. We build two comparison samples within the simulation that follow the
stellar mass-
halo mass relationship at z = 2, one of which is
stellar mass matched (with varying smaller
halo masses) and the other is
halo mass matched (with varying larger
stellar masses) to our sample. We identify that our failed
galaxy progenitor candidates have 1) flatter, cored dark matter
halos; 2) more extended
stellar bodies; 3) a larger fraction of their gas in the outskirts of their
halos; 4) lower
metallicities and 5) higher
star formation rates than the control samples. Findings 1) and 2) are similar to low
redshift observations of UDGs. Finding 3) will aid the removal of gas and permanent quenching of
star formation which is a requirement of the failed
galaxy formation scenario. The low
metallicities of finding 4) match those observed in low
redshift failed
galaxy UDGs. Comparing the high
star formation rates of finding 5) to recent JWST observations suggests that a starburst would naturally explain the high globular cluster richness of the UDGs. Many of the properties we find for these failed
galaxy progenitors can be explained by an assembly bias of their dark matter
halo to later formation times. We conclude by proposing that the fraction of failed
galaxy UDGs is expected to increase with environmental density.
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All authors Jonah S. Gannon, Lucas C. Kimmig, Duncan A. Forbes, Jean P. Brodie, Lucas M. Valenzuela, Rhea-Silvia Remus, Joel L. Pfeffer, Klaus Dolag
High Energy Astrophysical Phenomena
Latest view of CTA 1 with VERITAS
Alisha Chromey
CTA 1 is a shell-type
supernova remnant (SNR) with a central
pulsar wind nebula (PWN), visible at very-high-energy (VHE) from 50 GeV to 100 TeV from a moderately extended emission region. While general consensus concludes the VHE emission originates from relativistic
leptons accelerated by the PWN and undergoing inverse Compton scattering, questions remain about electron escape and propagation, as well as the evolutionary stage of this particular PWN. CTA 1 is on the cusp of middle age (~13 kyr) and spatially resolvable at energies visible to imaging atmospheric Cherenkov
telescopes (IACTs), such as the Very Energetic Radiation Imaging
Telescope Array System (VERITAS) (PSF < 0.1 deg). Therefore, this remnant is an excellent candidate to study
lepton propagation and escape between different PWN evolutionary stages. Since the initial VERITAS publication on CTA 1 in 2013, VERITAS has performed new observations, adding to a total exposure of about 120 hours. We have analyzed the entire VERITAS CTA 1
dataset to date and report results.
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