Solar and Stellar Astrophysics
The Gothard Observatory Synthetic Stellar Photometry Database
József Kovács, Szabolcs Mészáros, Beáta Harmati et al. (+6 more)
Context. In order to determine
stellar luminosities and radii, it is necessary to know the total bolometric fluxes emitted by the
stars, or equivalently the bolometric corrections (BCs) as accurately as possible. Aims. The aim of this paper is to present and describe a new database of synthetic
stellar magnitudes and bolometric corrections for 752 filters from 78 ground- and space-based instruments calculated using the most recent version of the BOSZ synthetic
stellar spectral library. Methods. From the entire grid of the BOSZ theoretical spectra, our synthetic magnitudes in the Vega magnitude system were determined using the corresponding routines of the Python package species. Results. The database spans effective temperatures from 2800 to 16000~K, log g from $-0.5$ to 5.5,
metallicities from $-2.5$ to 0.75, [$\alpha$/M] from $-0.25$ to 0.5, [C/M] from $-0.75$ to 0.5, and reddening up to $A_V$ = 3.1 mag. Using high-resolution (R = 50000) synthetic spectra allowed us to precisely track the effect of abundances on the bolometric corrections and luminosity of
stars. Conclusions. By applying the new bolometric corrections (BCs) to 192\,000 APOGEE
stars we calculated luminosities, and also demonstrated that neglecting carbon can introduce up to $\pm$0.2% errors in luminosity. The new Gothard Observatory Synthetic
Stellar Photometry Database may enable more accurate fundamental parameter determinations for large
stellar samples using a vast amount of past, present, and upcoming surveys, such as
Gaia, LSST, and the Roman Space
Telescope.
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All authors József Kovács, Szabolcs Mészáros, Beáta Harmati, Borbála Cseh, Viola Hegedűs, Gyula M. Szabó, László Szigeti, Blanka Világos, Aliz Derekas
Cosmology and Nongalactic Astrophysics
First measurement of the Hubble constant from gravitational wave-galaxy cross-correlations
Isabela Santiago de Matos, Charles Dalang, Tessa Baker et al. (+3 more)
We measure for the first time the Hubble constant ($H_0$) from the cross-correlation of
galaxies and gravitational waves (GW), by applying the $\textit{Peak Sirens}$ method. This method consists of finding the peak of the 3D angular cross-spectrum $C_{\ell}(z,D_L)$ between the
galaxy redshifts ($z$) and the GW luminosity distances ($D_L$). Using two GW events from the GWTC-3.0 catalog and the GLADE+
galaxy catalog, we make the first detection of the cross-correlation peak at $5.9\sigma$ confidence. This signal comes mostly from the best localized event in the catalog, GW190814, which alone provides a $3.4\sigma$ significance. Adding also the multimessenger event GW170817, but without using its known
redshift, we find $H_0 = 67^{+18}_{-15}$ km s$^{-1}$Mpc$^{-1}$ and the first observational constraint on the GW bias, $b_{\rm gw} < 4.3$ at 95% CI. These measurements set the stage for future novel cosmological constraints with this technique.
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All authors Isabela Santiago de Matos, Charles Dalang, Tessa Baker, Raul Abramo, João Ferri, Miguel Quartin
Solar and Stellar Astrophysics
Photometric and spectroscopic variability of the blue supergiant rho Leo
V.A. Checha, A. Aret, I. Kolka et al. (+12 more)
Context. The post-main-sequence
evolution of massive
stars remains poorly understood, particularly for blue supergiants. These objects play a crucial role in the dynamical and chemical
evolution of
galaxies and exhibit pronounced photometric and spectroscopic variability, often quasi-periodic rather than strictly periodic. Aims. We investigate the variability of the evolved B-type
star rho Leo to determine its physical properties, identify the underlying mechanisms driving its variability, and constrain its evolutionary stage. Methods. We analyse long-term spectroscopic and photometric
datasets obtained from multiple sources, including the TESS and Kepler space missions and observations with the 1.5 m
telescope in Estonia. Period analysis is performed using the Generalized Lomb-Scargle periodogram, Lomb-Scargle pre-whitening, and the Weighted Wavelet Z-Transform. Fundamental
stellar parameters are derived by fitting synthetic line profiles computed with the FastWind code to the HARPS spectrum, while the
stellar rotation inclination is estimated using the ZPEKTR code. Results. The He I 6678.151 A line shows significant radial-velocity and line-profile moment variations. We detect a set of periods and harmonics spanning approximately 0.8 to 35 days. Some periods remain stable over time, whereas others vary between observing seasons. A comparison of spectroscopic and photometric variability, together with phase-curve morphology, allows us to constrain the origin of several signals. In particular, the approximately 11 day period is attributed to
stellar rotation, while the approximately 17 day period is linked to radial pulsations. Conclusions. Although the variability is quasi-periodic, most detected periods persist across multiple seasons. The wide range of timescales suggests that rho Leo is likely evolving along a blue loop following the red supergiant phase.
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All authors V.A. Checha, A. Aret, I. Kolka, T. Liimets, I. Araya, A. Christen, G.F. Avila Marín, R.S. Levenhagen, L. Cidale, T. Eenmäe, G. Hajiyeva, Ü. Kivila, V. Mitrokhina, H. Ramler, T. Verro
Earth and Planetary Astrophysics
JWST NIRSpec finds no clear signs of an atmosphere on TOI-1685 b
Chloe E. Fisher, Matthew J. Hooton, Amélie Gressier et al. (+21 more)
Determining the prevalence of atmospheres on terrestrial
planets is a core objective in exoplanetary science. While M
dwarf systems offer a promising opportunity, conclusive observations of terrestrial atmospheres have remained elusive, with many yielding flat transmission spectra. We observe four transits of the hot terrestrial
planet TOI-1685 b using JWST's NIRSpec G395H instrument. Combining this with the transit from the previously-observed phase curve of the
planet with the same instrument, we perform a detailed analysis to determine the possibility of an atmosphere on TOI-1685 b. From our
retrievals, the
Bayesian evidence favours a simple flat line model, indicating no evidence for an atmosphere on TOI-1685 b, in line with results from the phase curve analysis. Our results show that hydrogen-dominated atmospheres can be confidently ruled out. For heavier, secondary atmospheres we find a lower limit on the mean molecular weight of ~10, at a significance of ~5 sigma. Pure CO2, SO2, H2O, and CH4 atmospheres, or a mixed secondary atmosphere (CO+CO2+SO2) could explain the data (Delta lnZ < 3). However, pure CH4 atmospheres may be physically unlikely, and the pure H2O and CO2 cases require a high-altitude cloud, which could also be interpreted as a thin cloud-free atmosphere. We discuss the theoretical possibility for different types of atmosphere on this
planet, and consider the effects of atmospheric escape and
stellar activity on the system. Though we find that TOI-1685 b is likely a bare rock, this study also highlights the challenges of detecting secondary atmospheres on rocky
planets with JWST.
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All authors Chloe E. Fisher, Matthew J. Hooton, Amélie Gressier, Merlin Zgraggen, Meng Tian, Kevin Heng, Natalie H. Allen, Richard D. Chatterjee, Brett M. Morris, Nicholas W. Borsato, Néstor Espinoza, Daniel Kitzmann, Tobias G. Meier, Lars A. Buchhave, Adam J. Burgasser, Brice-Olivier Demory, Mark Fortune, H. Jens Hoeijmakers, Raphael Luque, Erik A. Meier Valdés, João M. Mendonça, Bibiana Prinoth, Alexander D. Rathcke, Jake Taylor
High Energy Astrophysical Phenomena
Prospects on detection of the Fermi Bubbles with CTAO
Francesco Xotta, Nina Bavdaž, Christopher Eckner et al. (+3 more)
In 2010, the
Fermi Gamma-ray Space
Telescope observed two gamma-ray emitting structures, the
Fermi Bubbles (FBs), that extend up to 55{\deg} above and below the
Galactic plane and that seem to emanate from the
Galactic center region. Although the spectrum at latitudes |b| > 10{\deg} has a softening or a cutoff around 100 GeV, the one at the base of the FBs, |b| <10{\deg}, extends up to about 1 TeV without a significant cutoff in the
Fermi LAT data. The mechanism behind the FBs production is currently under debate. More observations of the FBs at different energies are required to improve our understanding of their origin. Recently, H.E.S.S. and HAWC observatory have set upper limits on the FBs. In this work, we assess the sensitivity of the Cherenkov
Telescope Array Observatory (CTAO) using the "alpha configuration" in the South site to detect the FBs and investigate the optimal strategies for their detection at low latitudes. We simulate the observations using the official CTAO science tool gammapy, considering several
benchmark models for the FBs and the interstellar emission and test different observational strategies taking advantage of the proposed CTAO consortium surveys. We use these simulations to estimate the CTAO sensitivity to the FBs.
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All authors Francesco Xotta, Nina Bavdaž, Christopher Eckner, Dmitry Malyshev, Judit Pérez-Romero, Gabrijela Zaharijas
Cosmology and Nongalactic Astrophysics
Beyond Stage IV: Quasar and Galaxy Clustering and the Fundamental Physics of the 2040s
M. Guidi, M. Moresco, H. K. Herrera-Alcantar et al. (+24 more)
Stage IV
galaxy surveys (DESI, 4MOST, MOONS, Euclid) are establishing precision constraints on cosmological parameters through
baryon acoustic oscillations and
redshift-space distortions, yet fundamental questions on
neutrino masses, inflationary physics, and the nature of
gravity remain beyond their reach. We present a science case for next-generation wide-field spectroscopic surveys targeting $1 < z < 6$ with simultaneous observations of thousands of
galaxies,
quasars, and emission-line
galaxies. Such surveys would deliver transformative advances: (i) cosmological constraints on absolute
neutrino masses ($\Sigma m_\nu \lesssim 0.015\,\mathrm{eV}$), three times more stringent than Stage IV, enabling resolution of the
neutrino mass hierarchy; (ii) detection of
primordial non-Gaussianity at the level of $f_{\mathrm{NL}} \sim 1$, probing multi-field inflation; (iii) measurements of structure growth $f\sigma_8(z)$ spanning
cosmic time to constrain dark energy and test gravitational modifications. Achieving these goals requires revolutionary advances in spectroscopic multiplexing ($\mathcal{O}(1000)$ simultaneous spectra), sub-$2\times10^{-4}(1+z)$
redshift precision at scale, and field-level inference techniques exploiting higher-order clustering statistics. We demonstrate that the proposed Wide-field Spectroscopic
Telescope concept provides a technically feasible and scientifically compelling path to unlock the physics of
neutrinos, inflation, and
gravity that will remain inaccessible to Stage IV surveys.
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All authors M. Guidi, M. Moresco, H. K. Herrera-Alcantar, G. Aricò, S. Camera, C. Carbone, A. Cimatti, S. Contarini, P. Dayal, G. Degni, A. Farina, C. Giocoli, V. Iršič, A. Labate, F. Marulli, F. Montano, C. Moretti, L. Moscardini, A. Pisani, A. Pollo, S. J. Rossiter, E. Sarpa, S. Sartori, E. Sefusatti, M. Talia, F. Verdiani, A. Veropalumbo
Cosmology and Nongalactic Astrophysics
Ultralight Dark Matter Constraints from NanoHertz Gravitational Waves
Shreyas Tiruvaskar, Russell Boey, Richard Easther et al. (+1 more)
We investigate the impact of ultralight dark matter (ULDM) on the mergers of supermassive black holes (SMBH) and the resulting
stochastic gravitational wave background. ULDM is based on exceptionally light particles and yields
galactic halos with dense central
solitons. This increases the drag experienced by binary SMBH, decreasing merger times and potentially suppressing gravitational radiation from the binary at low frequencies. We develop semi-analytic models for the decay of SMBH binaries in ULDM
halos and use current
pulsar timing array (PTA) measurements to constrain the ULDM particle mass and its fractional contribution to the dark matter content of the universe. We find a median ULDM particle mass of $7. \times 10^{-22}$ eV and show that scaling relations suggest that the drag remains effective at relatively low ULDM fractions, which are consistent with all other constraints on the model. Consequently, future
pulsar timing measurements will be a sensitive probe of any ULDM contribution to the overall dark matter content of the universe.
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All authors Shreyas Tiruvaskar, Russell Boey, Richard Easther, Chris Gordon
Astrophysics of Galaxies
Stefania Barsanti, Clotilde Laigle, Nicolas Bouché et al. (+7 more)
By the 2040s, several all-sky surveys will have transformed our view of the large-scale structure. However, one of the major outstanding questions in astrophysics will remain: understanding how
galaxies acquire and evolve their angular momentum and how this connects to the
cosmic web. Measuring the
alignments between
galaxy spins and
cosmic filaments across
cosmic time, and understanding what this reveals about
galaxy evolution, requires surveys that also characterise intrinsic
alignments, i.e. correlations in
galaxy shapes produced by the
cosmic web itself rather than by
lensing. Intrinsic
alignments are a major source of systematic error in weak-
lensing measurements of the fundamental parameters of the Universe. Addressing both questions together will necessitate new types of MOS surveys that combine kinematic information with high-completeness
redshifts down to at least 24-25mag. To achieve our science goals, we require a new generation of wide-field spectroscopic facilities that can obtain
spin-filament
alignment measurements for millions of
galaxies while simultaneously delivering sub-Mpc resolution of the
cosmic web and spatially-resolved kinematics required to map the
spin-filament connection at the level of individual
galaxies within their local
cosmic environment. Such a program would provide a unique legacy survey of
galaxies and
cosmic structures from kiloparsec to megaparsec scales, establishing ESO's leadership in bridging the physics of
galaxy evolution with the systematic-control requirements for Stage-IV cosmological surveys.
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All authors Stefania Barsanti, Clotilde Laigle, Nicolas Bouché, Anna Rita Gallazzi, Mark Sargent, Sabine Thater, Matthew Colless, Scott M. Croom, Edward N. Taylor, Laurence Tresse
Cosmology and Nongalactic Astrophysics
Accurate neural network emulator for primordial light element abundances
Fan Zhang, Hang Diao, Bohua Li et al. (+2 more)
Big-Bang Nucleosynthesis (BBN) predictions of
primordial light-element abundances offer a powerful probe of early-Universe physics. However, high-accuracy numerical BBN calculations have become a major computational bottleneck for large-scale cosmological inferences due to the complex
nuclear network. Here we present BBNet, a fast and accurate deep learning emulator for
primordial abundances. The training data are generated by full numerical calculations using two public BBN codes, PArthENoPE and AlterBBN, modified to accommodate extended cosmologies that include dark radiation and a stiff equation of state. The network employs a residual multi-head architecture to capture convoluted physical relationships. BBNet produces
primordial helium-4 and deuterium abundances with negligible errors in milliseconds per sample, achieving a speed-up of up to $10^4$ times relative to first-principles solvers while remaining unbiased over wide parameter ranges. Therefore, our emulator can supersede traditional simplified numerical prescriptions that compromise accuracy for speed. Based on extensive assessments of its performance, we conclude that BBNet is an optimal solution to the theoretical prediction of
primordial element abundances. It will serve as a reliable tool for precision cosmology and new-physics searches.
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All authors Fan Zhang, Hang Diao, Bohua Li, Joel Meyers, Paul R. Shapiro
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Massive boson stars: Stability and GW emission in head-on mergers
Bo-Xuan Ge
We investigate quartically self-interacting massive
boson stars by constructing
equilibrium sequences and performing dynamical evolutions. The mass curve $M(|\phi_c|)$ along these sequences develops multiple extrema, yet stability changes only at the first maximum; configurations beyond it become highly compact and collapse under numerically induced perturbations, with near-critical models displaying a short-lived double-dive behaviour. Head-on collisions of equal-mass
stars yield three distinct outcomes –
boson star remnants, black hole formation at contact, and collapse of each
star to a black hole prior to contact. The associated gravitational-wave energies reflect a competition between increasing compactness, which enhances the efficiency of gravitational-wave emission, and decreasing
tidal deformability, which suppresses merger asymmetries, and at large self-interaction strengths the collapse-before-contact branch exhibits a pronounced non-monotonic structure. The simulations reported here constitute a substantial catalogue of initial conditions and waveforms, providing a natural basis for constructing surrogate models capable of rapidly predicting gravitational-wave signals across an extended parameter space.
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High Energy Astrophysical Phenomena
Magnetised turbulent plasmas as high-energy particle accelerators
M. Lemoine
This proceedings paper reports on the theoretical modelling of particle acceleration in magnetised turbulent
plasmas. It briefly reviews some recent findings obtained from fully kinetic numerical simulations of large-amplitude, semi to fully relativistic
turbulence. The paper then argues that these findings can be understood within the framework of a “generalised
Fermi” picture of
stochastic acceleration, which it summarises. The dominant contributions to acceleration appear to arise from particle interactions with sharp, dynamic bends of the
magnetic field lines and regions of velocity compression. Interestingly, the acceleration rate is spatially inhomogeneous and its probability distribution follows a broken power law extending up to large values. This makes relativistic, large-amplitude
turbulence an extreme particle accelerator. Some implications for particle transport and the shape of the particle energy spectrum in the presence of radiative losses and over long timescales are also discussed.
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Solar and Stellar Astrophysics
XRISM view of a stellar flare: High-resolution Fe K spectra of HR 1099, an RS CVn-type star
Miki Kurihara, Masahiro Tsujimoto, Michael Loewenstein et al. (+21 more)
A high-resolution X-ray spectroscopic observation was made of the RS CVn-type binary
star HR 1099 using the Resolve instrument onboard XRISM for its calibration purposes. During the $\sim$400 ks
telescope time covering 1.5 binary orbit, a
flare lasting for $\sim$100 ks was observed with a released X-ray radiation energy of $\sim 10^{34}$ erg, making it the first
stellar flare ever observed with an X-ray microcalorimeter spectrometer. The
flare peak count rate is 6.4 times higher than that in quiescence and is distinguished clearly in time thanks to the long
telescope time. Many emission lines were detected in the 1.7–10 keV range both in the
flare and quiescent phases. Using the high spectral resolution of Resolve in the Fe K band (6.5–7.0 keV), we resolved the inner-shell lines of Fe XIX–XXIV as well as the outer-shell lines of Fe XXV–XXVI. These lines have peaks in the contribution functions at different temperatures over a wide range, allowing us to construct the differential emission measure (DEM) distribution over the electron temperature of 1–10 keV (roughly 10–100 MK) based only on Fe lines, thus without an assumption of the elemental abundance. The reconstructed DEM has a bimodal distribution, and only the hotter component increased during the
flare. The elemental abundance was derived based on the DEM distribution thus constructed. A significant abundance increase was observed during the
flare for Ca and Fe, which are some of the elements with the lowest first ionization potential among those analyzed, but not for Si, S, and Ar. This behavior is seen in some
giant solar flares and the present result is a clear example in
stellar flares.
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All authors Miki Kurihara, Masahiro Tsujimoto, Michael Loewenstein, Yoshitomo Maeda, Marc Audard, Ehud Behar, Megan E. Eckart, Adam Foster, Liyi Gu, Matteo Guainazzi, Kenji Hamaguchi, Natalie Hell, Shun Inoue, Yukiko Ishihara, Satoru Katsuda, Caroline A. Kilbourne, Maurice A. Leutenegger, Eric D. Miller, Nagisa Nagashima, Frederick Scott Porter, Makoto Sawada, Yohko Tsuboi, Vinay L. Kashyap, David H. Brooks
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Multiple mountains on a pulsar: implications for gravitational waves and the spin-down rate
Paritosh Verma and Sudip Bhattacharyya
A
pulsar, i.e., a spinning
neutron star, with a deformation could emit gravitational waves continuously. Such continuous waves, which have not been detected yet, will be very useful to study gravitational physics and to probe the extreme physics of
neutron stars. While typically such waves from a
pulsar are estimated considering an overall
stellar ellipticity, there can be multiple irregularities or mountains in the
stellar crust that the
gravity of the
star cannot smooth. In this paper, we consider this realistic situation and compute the strain, power, torque and the
pulsar spin-down rate due to multiple mountains supported by the
stellar crust. Here, we consider astronomically motivated mountain distributions and use the Brans-Dicke theory of
gravity which has three polarization states: two tensors dominated by the time-varying quadrupole moment and one scalar dominated by the time-varying dipole moment. We also give the limiting results for general relativity.
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Earth and Planetary Astrophysics
Characterising injection signatures in Jupiter's ultraviolet aurora using Juno observations
Linus Head, Denis Grodent, Bertrand Bonfond et al. (+12 more)
Discrete features in Jupiter's ultraviolet aurora have been interpreted as signatures of
plasma injections in the middle magnetosphere. There exists some ambiguity whether magnetodisc scattering or high-latitude Alfvenic acceleration best describes the observed properties of these injection signatures, and also to what extent arcs in the outer emission are related to injections. Many injection signatures are the result of the
evolution of dawn storms; there is, however, limited evidence that non-dawn-storm injection signatures are sometimes present in the aurora. We use automatic detection of these discrete features, alongside data from Juno-UVS and in-situ measurements by other Juno instruments, to show that scattering likely accounts for most of the electron precipitation associated with injection signatures. Additionally, there is evidence that injection signatures can be classified into two types: dawn-storm and non-dawn-storm. Arc-like features in the outer emission show very similar properties to traditional blob-like injection signatures and may consist of sequences of injection signatures that have broadened into an arc via energy-dependent electron drift.
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All authors Linus Head, Denis Grodent, Bertrand Bonfond, Alessandro Moirano, Guillaume Sicorello, Julie Vinesse, Alyssa Mouton, Maïté Dumont, Thomas Greathouse, Vincent Hue, Ali Sulaiman, Barry Mauk, Zhonghua Yao, Ruilong Guo, Jinyan Zhao
Instrumentation and Methods for Astrophysics
Expanding stellar horizons with polarized light
J. Vandersnickt, R. Ochoa Armenta, V. Vanlaer et al. (+16 more)
The polarization of light is a critically under-utilized, rich source of information in astronomy. For
stars in particular, surface magnetism polarization that can be detected and measured with spectro-polarimetry. Many questions about these surface fields remain unanswered due to a lack of dedicated instruments capable of probing weak and strong surface
magnetic fields for the entire mass range of
stars, from M-
dwarfs (and even substellar objects) to massive O-type
stars at different evolutionary stages and
metallicities. These questions range from the origin of these fields to their true incidence rate throughout the
stellar population and the dependence on
metallicity.
Magnetic fields, although currently often excluded from
stellar evolution models, play an important role in
stellar evolution. Connecting the surface fields to internal fields through asteroseismology will instigate a new era of understanding
stellar evolution and the transport of angular momentum and chemical elements throughout
stellar interiors, also impacting our understanding of
star-
planet interactions and
stellar remnants. Polarimetry is also an under-utilized tool to observationally constrain the mode identification of nonradial oscillations, which lies at the basis of accurate asteroseismic parameter estimation at percentage-level for
stellar radii, masses, ages, internal rotation, and
magnetic field strengths. Combining strong constraints on mode identification and surface
magnetic properties through the acquisition of time-resolved, high-resolution and high-signal-to-noise (S/N) spectro-polarimetry and spectroscopy promises to bring leaps forward in our understanding of
stellar structure, particularly when combined with long-term space photometric data from past, current, and future missions.
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All authors J. Vandersnickt, R. Ochoa Armenta, V. Vanlaer, A. David-Uraz, C. Aerts, S. B. Das, J.-C. Bouret, D. M. Bowman, L. Bugnet, V. Khalack, J. Labadie-Bartz, S. Mathis, Y. Nazé, C. Neiner, P. Petit, V. Petit, K. Thomson-Paressant, T. Van Doorsselaere, M. Vanrespaille
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Strong lensing cosmography using binary-black-hole mergers: Prospects for the near future
Koustav N. Maity, Souvik Jana, Tejaswi Venumadhav et al. (+2 more)
A small fraction of gravitational-wave (GW) signals from binary black holes (BBHs) will be gravitationally lensed by intervening
galaxies and
galaxy clusters. Strong
lensing will produce multiple identical copies of the GW signal arriving at different times. Jana et al.~\cite{Jana_2023} recently proposed a method to constrain cosmological parameters using strongly lensed GW events detected by next-generation (XG) detectors. The idea is that the number of strongly lensed GW events and the distribution of their
lensing time delays encode imprints of the cosmological parameters. From the observed number of lensed GW events (tens of thousands) and their time delay distribution, this method can provide a new probe of cosmology, obtaining information at intermediate
redshifts. In this work, we explore the possibility of doing
lensing cosmography using upcoming observations of the upgraded LIGO-Virgo-KAGRA (LVK) network. This requires incorporating the detector network selection effects in the analysis, which was neglected earlier. We expect dozens of lensed GW events to be detected by upgraded LVK detectors, potentially enabling modest constraints on cosmological parameters. Even with relatively modest numbers of lensed detections, we demonstrate the potential of
lensing cosmography. For XG detectors, our revised forecasts are consistent with the earlier forecasts that neglected the selection effects.
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All authors Koustav N. Maity, Souvik Jana, Tejaswi Venumadhav, Ankur Barsode, Parameswaran Ajith
High Energy Astrophysical Phenomena
Time Evolution of Optical Darkness in GRB Afterglow: The Case of GRB 240825A
Rui-Zhi Li, Jirong Mao, Yuan-Pei Yang et al. (+4 more)
Long-duration gamma-ray bursts (GRBs) are believed to occur in
star-forming regions. The multiwavelength follow-up observations of the early afterglow of GRB 240825A provided insights into the
evolution of the optical-to-X-ray spectral feature of the afterglow. We comprehensively investigate the
evolution of X-ray spectral properties through time-resolved spectral analysis and calculate optical darkness ($\beta_\mathrm{OX}$) to reveal the physical properties of the afterglow. The X-ray-to-optical SEDs of afterglow in different time intervals are fitted to derive the extinction curves. The $\beta_\mathrm{OX}$ exhibits a trend of decreasing and then increasing, reaching its minimum value at $\sim1000\mathrm{\,s}$ post-trigger. However, at 11 hours post-trigger, $\beta_\mathrm{OX}$ does not meet the criteria for an optically dark burst. The extinction curves in different time intervals indicate that GRB 240825A occurred in a
dust-obscured environment.
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All authors Rui-Zhi Li, Jirong Mao, Yuan-Pei Yang, Bo-Ting Wang, Fei-Fan Song, Yu-Xin Xin, Jin-Ming Bai
Solar and Stellar Astrophysics
Discussion on the vanishment of solar atmospheric structures during magnetic reconnection
Jun Zhang, Tao Ding and Yulei Wang
In
solar atmosphere,
magnetic reconnection alters the topological connectivity, and
magnetic energy is released. However, the length change of the reconnecting structures has rarely been reported. To identify the
evolution of the topological structures, we search for reconnection events which should satisfy 3 criteria. (1) Each event displays an explicit X-type configuration, and the configuration consists of two sets of independent atmospheric structures, (2) the reconnection process is clearly observed, and (3) the topological connectivity of the structures can be tracked from at least 5 minutes prior to the occurrence of
magnetic reconnection to 5 minutes after the reconnection. In this work, 3 events are selected and studied. During the reconnection moment, the total length of the two topological structures in each event shortens suddenly, and the decrements for events 1–3 are 47 Mm, 3.7 Mm, and 8.2 Mm, respectively, implying that partial structures vanish observationally during
magnetic reconnection process. Several possibilities about the vanishment, e.g. the shrinkage of the reconnecting structures due to
magnetic tension, the bizarre change in the third dimension, and
magnetic field annihilation, have been discussed.
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Solar and Stellar Astrophysics
Thermal properties of interplanetary coronal mass ejections at 1 AU and their connection to geoeffectiveness across solar cycles 23-25
Soumyaranjan Khuntia and Wageesh Mishra
Interplanetary coronal mass ejections (ICMEs) are major drivers of heliospheric variability and can produce prolonged disturbances near Earth. Understanding their thermodynamic
evolution is crucial for assessing their heat budget and exploring how thermal states relate to their
plasma dynamics and geoeffectiveness. We conduct a comprehensive statistical analysis of
magnetic ejecta (MEs) over
Solar Cycles 23, 24, and the ascending phase of 25. Leveraging a polytropic framework, we characterized the thermal state of ME based on the event-wise median
proton polytropic index (Gamma_p) from in-situ measurements at 1 AU. We find that MEs are thermodynamically active and rarely evolve adiabatically or isothermally. Notably, a significant fraction (45%) of MEs exhibit a heating state. Heating MEs dominate near
solar maxima and exhibit strong
solar-cycle modulation in Gamma_p,
proton temperature, and expansion speed, indicating active in-transit heating processes. Whereas, Cooling MEs show a nearly constant Gamma_p = 2 across cycles, suggesting enhanced cooling beyond adiabatic expectations and possible thermal energy retention from eruption to 1 AU. Notably, the median Gamma_p value increases from 1.49 (SC23) to 1.88 (SC24), indicating a shift to cooling-dominated states over successive cycles. High-impact ICMEs, predominantly Heating MEs (Gamma_p = 0.59), often manifest as
magnetic clouds with enhanced
magnetic fields, low
plasma beta, pronounced sheath compression, elevated expansion, and post-ICME high-speed flows, making them the most geoeffective drivers of strong geomagnetic storms. These results establish Gamma_p as a useful diagnostic of ICME thermal states, though meaningful assessment of geoeffectiveness requires combined consideration of thermal,
plasma, and
magnetic field properties.
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Astrophysics of Galaxies
Robustness Analysis of USmorph: I. Generalization Efficiency of Unsupervised Strategies and Supervised Learning in Galaxy Morphological Classification
Shiwei Zhu, Guanwen Fang, Yao Dai et al. (+5 more)
We conduct a systematic robustness analysis of the hybrid machine learning framework USmorph, which integrates unsupervised and supervised learning for
galaxy morphological classification. Although USmorph has already been applied to nearly 100,000 $I$-band
galaxy images in the COSMOS field ($0.2 < z < 1.2$, $I_{\mathrm{mag}} < 25$), the stability of its core modules has not been quantitatively assessed. Our tests show that the convolutional autoencoder (CAE) achieves the best performance in preserving structural information when adopting an intermediate network depth, $5\times5$ convolutional kernels, and a 40-dimensional latent representation. The adaptive polar coordinate transform (APCT) effectively enhances rotational invariance and improves the robustness of downstream tasks. In the unsupervised stage, a bagging clustering number of $K=50$ provides the optimal trade-off between classification granularity and labeling efficiency. For supervised learning, we employ GoogLeNet, which exhibits stable performance without overfitting. We validate the reliability of the final classifications through two independent tests: (1) the t-distributed
stochastic neighbor
embedding (t-SNE) visualization reveals clear clustering boundaries in the low-dimensional space; and (2) the morphological classifications are consistent with theoretical expectations of
galaxy evolution, with both true and false positives showing unbiased distributions in the parameter space. These results demonstrate the strong robustness of the USmorph
algorithm, providing guidance for its future application to the China Space Station
Telescope (CSST) mission.
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All authors Shiwei Zhu, Guanwen Fang, Yao Dai, Chichun Zhou, Yirui Zheng, Jie Song, Shiying Lu, Xu Kong
Astrophysics of Galaxies
An updated efficient galaxy morphology classification model based on ConvNeXt encoding with UMAP dimensionality reduction
Guanwen Fang, Shiwei Zhu, Jun Xu et al. (+5 more)
We present an enhanced unsupervised machine learning (UML) module within our previous USmorph classification framework featuring two components: (1) hierarchical feature extraction via a pre-trained ConvNeXt convolutional neural network (CNN) with transfer learning, and (2) nonlinear
manifold learning using Uniform
Manifold Approximation and Projection (UMAP) for
topology-aware dimensionality reduction. This dual-stage design enables efficient knowledge transfer from large-scale visual
datasets while preserving morphological pattern geometry through UMAP's neighborhood preservation. We apply the upgraded UML on I-band images of 99,806 COSMOS
galaxies at
redshift $0.2<z<1.2$ (to ensure rest-frame optical morphology) with $I_{\mathrm{mag}}<25$. The predefined cluster number is optimized to 20 (reduced from 50 in the original framework), achieving significant computational savings. The 20 algorithmically identified clusters are merged into five physical morphology types. About 51% of
galaxies (50,056) were successfully classified. To assess classification effectiveness, we tested morphological parameters for massive
galaxies with $M_{*}>10^{9}~M_{\odot}$. Our classification results align well with
galaxy evolution theory. This improved
algorithm significantly enhances
galaxy morphology classification efficiency, making it suitable for large-scale sky surveys such as those planned with the China Space Station
Telescope (CSST).
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All authors Guanwen Fang, Shiwei Zhu, Jun Xu, Shiying Lu, Chichun Zhou, Yao Dai, Zesen Lin, Xu Kong
Earth and Planetary Astrophysics
Modeling of Collisional Outcomes Based on Impact Simulations of Mars-sized Bodies
Hiroshi Kobayashi, Hidekazu Tanaka, Yukihiko Hasegawa et al. (+1 more)
We investigate the outcomes of collisions between Mars-sized bodies through smooth particle hydrodynamics (SPH) simulations, focusing on the transitions among “merging”, “hit-and-run”, and catastrophic disruption. By systematically varying impact velocity, angle, and mass ratio, we characterize the dependence of collision outcomes on
geometric and energetic parameters. A new analytic model is developed using characteristic energies – particularly the energy deposited in overlapping regions of the colliding bodies – to accurately describe the mass of the largest and second-largest remnants. The model successfully reproduces simulation results across a broad range of impact conditions and improves on previous models by better capturing the transitions between “merging”, “hit-and-run”, and disruption. We also derive outcome formulas averaged over impact-parameter-weighted angular distributions, enabling more realistic applications to integrated modeling of
planet formation. The model further shows consistency with outcomes from
dust aggregate collision simulations, highlighting its utility for modeling collisional processes not only for large planetesimals but also for smaller bodies.
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All authors Hiroshi Kobayashi, Hidekazu Tanaka, Yukihiko Hasegawa, Shu-ichiro Inutsuka
Astrophysics of Galaxies
Dual-coding contrastive learning based on ConvNeXt and ViT models for morphological classification of galaxies in COSMOS-Web
Shiwei Zhu, Guanwen Fang, Chichun Zhou et al. (+4 more)
In our previous works, we proposed a machine learning framework named USmorph for efficiently classifying
galaxy morphology. In this study, we propose a self-supervised method called contrastive learning to upgrade the unsupervised machine learning (UML) part of the USmorph framework, aiming to improve the efficiency of feature extraction in this step. The upgraded UML method primarily consists of the following three aspects. (1) We employ a Convolutional Autoencoder to denoise
galaxy images and the Adaptive Polar Coordinate Transformation to enhance the model's rotational invariance. (2) A pre-trained dual-encoder convolutional neural network based on ConvNeXt and ViT is used to encode the image data, while contrastive learning is then applied to reduce the dimension of the features. (3) We adopt a Bagging-based clustering model to cluster
galaxies with similar features into distinct groups. By carefully dividing the
redshift bins, we apply this model to the rest-frame optical images of
galaxies in the COSMOS-Web field within the
redshift range of $0.5 < z < 6.0$. Compared to the previous
algorithm, the improved UML method successfully classifies 73%
galaxies. Using the GoogleNet
algorithm, we classify the morphology of the remaining 27%
galaxies. To validate the reliability of our updated
algorithm, we compared our classification results with other
galaxy morphological parameters and found a good consistency with
galaxy evolution. Benefiting from its higher efficiency, this updated
algorithm is well-suited for application in future China Space Station
Telescope missions.
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All authors Shiwei Zhu, Guanwen Fang, Chichun Zhou, Jie Song, Zesen Lin, Yao Dai, Xu Kong
Astrophysics of Galaxies
Stellar Morphology of Optically Dark or Faint Galaxies at $z>3$ with JWST
Arpita Ganguly, Mengyuan Xiao, Pascal A. Oesch et al. (+11 more)
JWST offers an unprecedented view of optically dark or faint
galaxies (OFGs), previously missed by HST. They are likely massive, heavily
dust-obscured
star-forming
galaxies (SFGs) that substantially contribute to the
cosmic SFR density at $z>$3. To identify drivers of their high
dust attenuation and their role in early universe
galaxy evolution, we analyse the
stellar morphology of 65 OFGs (from 1892 SFGs at 3$<z<$4) using NIRCam/F444W imaging from the PRIMER and CEERS fields. We study correlations between
dust attenuation ($A_v$) and
galaxy properties, like
stellar mass, size, and orientation, and compare scaling relations between OFGs and typical SFGs. We find that OFGs are ~8-9 times more massive and ~4 times more
dust attenuated than the parent sample. Structurally, OFGs resemble parent SFGs in median $R_e$ and median $\Sigma_{R_e}$ but may be slightly rounder on average. While $A_v$ strongly correlates with
stellar mass, it does not show significant dependence on
stellar mass-normalised effective radius and
stellar mass surface density, Sérsic index, axis ratio, or SFR surface density. The mass-size and mass-surface density relations place OFGs as a higher-mass extension of SFGs, with no concrete proof of evolutionary differences between them. This suggests that OFGs are heavily
dust-obscured primarily due to their high
stellar masses, which facilitates
dust production and retention, with older
stellar populations likely contributing as well. Although some OFGs exhibit high $\Sigma_\mathrm{{R_e}}$ and occupy regions of the mass-size plane similar to quiescent
galaxies, the overall sample is not representative of this. Their current structures resemble typical SFGs, with no concrete signs of rapid compaction. Diversity in their physical properties shows that OFGs span a range of evolutionary states with few showing reduced
star formation, while most remain actively
star-forming.
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All authors Arpita Ganguly, Mengyuan Xiao, Pascal A. Oesch, Miroslava Dessauges-Zavadsky, Andrea Weibel, Natalie Allen, Longji Bing, Sarah Bosman, Gabriel Brammer, David Elbaz, Emanuele Daddi, Benjamin Magnelli, Tim B. Miller, Maxime Tarrasse
Instrumentation and Methods for Astrophysics
The use of astronomical data for satellite tracking
Rositsa Miteva, Nikola Antonov and Adrian Sonka
The study explored the usage of astronomical observations for the identification and tracking of artificial satellites. Spacecraft streaks on astronomical images are a growing issue for the astronomical community. The increasing number of satellites in the future will only worsen the situation for ground-based optical and
radio observations of
cosmic objects. In addition, the spacecraft passages often lead to the discarding of the obtained data. In this analysis, we propose an estimation of the usefulness of dedicated astronomical observation for spacecraft monitoring, identification, and deduction of orbital parameters. We use astronomical data from the Astronomical Observatory Meshtitsa (Bulgaria) and the https://www.tycho-tracker.com/ software for the streak analysis. The results are compared with well-known satellite databases, such as https://celestrak.org/. The findings are discussed in the framework of space weather research.
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Earth and Planetary Astrophysics
ALMA Band 7 Observations of Water Lines in the Protoplanetary Disk of V883 Ori
Hiroto Nakasone, Shota Notsu, Tomohiro C. Yoshida et al. (+8 more)
The FU Orionis
star V883 Ori provides a unique opportunity to probe the water snowline in a protoplanetary disk. During an
accretion burst, the enhanced
stellar luminosity heats the disk, sublimating ices and bringing volatile species into the gas-phase. The water snowline, located at $\sim$80 au in the midplane, represents a key boundary for
dust growth and volatile delivery to forming
planets. We present Atacama Large Millimeter/submillimeter Array Band 7 observations of V883 Ori that detect two targeted water isotopologue transitions: para-H$_2$$^{18}$O $5_{1,5}$-$4_{2,2}$ at 322 GHz and HDO $3_{3,1}$-$4_{2,2}$ at 335 GHz. After correcting for Keplerian rotation, we detect HDO and H$_2$$^{18}$O at 23.6$\sigma$ and 9.3$\sigma$, respectively. Rotational-diagram analysis using a Markov Chain Monte Carlo approach yields $T_\mathrm{rot}=116.89\pm12.81$ K and $N=(4.90\pm1.69)\times10^{15}\,\mathrm{cm}^{-2}$ for H$_2$$^{18}$O, and $T_\mathrm{rot}=87.46\pm4.95$ K and $N=(4.47\pm0.62)\times10^{15}\,\mathrm{cm}^{-2}$ for HDO. These results imply water vapor abundances of $N_{\mathrm{H_2O}}/N_{\mathrm{H_2}}\sim3\times10^{-7}$-$5\times10^{-6}$ and an HDO/H$_2$O ratio of $(0.4$-$2.0)\times10^{-3}$ just inside the water snowline, broadly consistent with inheritance from protostellar envelopes. The HDO line in Band 7 is significantly weaker than predicted from Band 6 extrapolation, showing only $\sim$26% of the expected strength. This attenuation can be explained by a more compact, hotter emitting region with an effective radius of $\sim$53 au and/or frequency-dependent
dust absorption that enlarges the apparent inner cavity at higher frequency. Our results highlight both the diagnostic power of water isotopologue lines and the need for higher angular resolution observations to resolve the water snowline and test these scenarios.
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All authors Hiroto Nakasone, Shota Notsu, Tomohiro C. Yoshida, Hideko Nomura, Takashi Tsukagoshi, Tomoya Hirota, Mitsuhiko Honda, Eiji Akiyama, Alice S. Booth, Jeong-Eun Lee, Seokho Lee
Solar and Stellar Astrophysics
The Centennial Evolution of Solar Chromospheric Rotation
N. B. Xiang, X. H. Zhao, L. H. Deng et al. (+3 more)
Rotation is a prominent feature of the Sun, and it plays a crucial role in the generation and dynamic
evolution of
solar magnetic fields. The daily composite time series of Ca II K plage areas from 1907 February 1 to 2023 December 31 is used to analyze its periodicity and examine the temporal variation of its rotation period lengths (RPLs) using continuous wavelet transform. Wavelet analysis reveals that over a time span of more than a century, chromospheric rotation exhibits a dominant synodic period of approximately 26.62 days, with complex temporal variations. The long-term trend of chromospheric rotation is well-characterized by a statistically significant quadratic
polynomial, showing a gradual deceleration from
solar cycles 15 to 19, followed by a gradual acceleration from cycles 19 to 24. The RPLs exhibit a negative correlation between the rotation rate of the chromosphere and
solar magnetic activity. Their behavior follows a distinct pattern within a Schwabe cycle: the rotation period progressively lengthens during the initial approximately 3 years, then maintains a relatively long value from year 3 to approximately 7.5, and finally shortens during the declining phase, returning to a minimum near the subsequent
solar minimum. The variations of chromospheric RPLs show significant periods of 3.2, 5.7, 7.7, 10.3, and 12.3 years, with cross-correlation analysis pointing to a complex relationship with
solar activity. The possible mechanisms for the temporal variation of the chromospheric rotation are discussed.
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All authors N. B. Xiang, X. H. Zhao, L. H. Deng, F. Y. Li, M. Wan, S. Y. Qi
Astrophysics of Galaxies
Dark matter in ALFALFA galaxies: Investigating galaxy-halo connection
Meng Yang, Ling Zhu, Niankun Yu et al. (+4 more)
This paper aims to investigate the
galaxy-
halo connection using a large sample of individual
galaxies with $\mathrm{H\,I}$ integrated spectra. We determine their dark matter content by applying a dynamical method based on $\mathrm{H\,I}$ line widths measured with the curve-of-growth technique, together with inclination corrections inferred from optical images. We build a sample of 2453 gas-rich predominantly late-type
galaxies spanning a
stellar mass range of $10^{8.7}M_\odot$ to $10^{11.4}M_\odot$ by matching them one-to-one with their counterparts from the ALFALFA survey and the TNG100 simulation, ensuring a direct match of
stellar mass and $\mathrm{H\,I}$ radius. We generate mock images and mock $\mathrm{H\,I}$ integrated spectra for TNG100
galaxies, and apply the same dynamical method to both ALFALFA and TNG100 mock
galaxies to infer their dark matter masses. Across all
stellar mass bins, ALFALFA
galaxies exhibit lower median dark matter masses than the mock TNG100 simulation results. In each bin, this offset is driven by a tail of
galaxies with comparatively low dark matter content, which becomes more prominent toward higher
stellar masses. In the highest mass bin ($M_* > 10^{11} M_\odot$), late-type ALFALFA
galaxies show a median dark matter mass that is 23% lower than that of their counterparts in the TNG100 dark-matter-only simulation, with 32% of ALFALFA
galaxies having $M_\mathrm{DM}(<R_\mathrm{HI})<10^{11.5} M_\odot$, compared to 17% in the mock TNG100 sample. These results suggest that a larger fraction of massive late-type
galaxies reside in relatively less massive dark matter
haloes than predicted by the TNG100 simulation.
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All authors Meng Yang, Ling Zhu, Niankun Yu, Yu Lei, Runsheng Cai, Jie Wang, Zheng Zheng
High Energy Astrophysical Phenomena
A Comprehensive Interpretation of Fermi-LAT Pulsars: Fundamental-Plane Death Border, Visibility Thresholds, and GeV-TeV Unification
Constantinos Kalapotharakos, Zorawar Wadiasingh, Alice K. Harding et al. (+2 more)
We present a framework that links equatorial-current-sheet (ECS) physics to catalog-level, phase-averaged gamma-ray
pulsar properties. Guided by analytic scalings and particle-in-
cell (PIC) simulations, we show that the
pulsar “Fundamental Plane” (relating gamma-ray luminosity, spectral cutoff energy,
spin-down power $\dot{\cal{E}}$, and surface
magnetic field) is bounded by two regimes: a radiation-reaction-limited branch and a potential-drop-limited branch. Their intersection defines a transition in $\dot{\cal{E}}$ that maps to a gamma-ray visibility threshold on the $P-\dot{P}$ diagram, above which detectability is set by distance and beaming, and below which both cutoff energy and efficiency decline rapidly. Placing ATNF
pulsars and McGill magnetars onto these planes reproduces the observed
Fermi occupancy, with millisecond
pulsars (MSPs) on the observable side, young
pulsars (YPs) straddling the threshold, and magnetars clustering at or just below it. At higher $\dot{\cal{E}}$, both MSPs and YPs depart from the maximal radiation-reaction-limited envelope at similar cutoff energies, suggesting that enhanced pair creation screens the accelerating electric field in the ECS. We interpret this behavior with a compactness-based criterion for optically thin $\gamma\gamma$ pair feedback in or near the ECS and briefly note an extension to $\gamma\gamma\rightarrow\mu^\pm$ that could yield pulsed multi-TeV
neutrinos in the most energetic systems. The framework predicts a MeV-bright, GeV-faint corridor below
Fermi sensitivity, a target for next-generation MeV missions. Finally, motivated by the recent HESSII detection of pulsed multi-TeV emission from Vela, we use PIC particle distributions with a seed-
photon model to reproduce a multi-TeV inverse-Compton component alongside the GeV
curvature emission, supporting a unified ECS-based GeV-TeV origin.
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All authors Constantinos Kalapotharakos, Zorawar Wadiasingh, Alice K. Harding, Demosthenes Kazanas, Dimitrios Skiathas
Astrophysics of Galaxies
A global view on star formation: The GLOSTAR Galactic plane survey XII. Effelsberg's continuum view and data release
Y. Gong, W. Reich, M. R. Rugel et al. (+24 more)
Extended
radio continuum emission and its linear polarization play a key role in probing large-scale structures of synchrotron and free-free emission in the Milky Way. Despite the existence of many
radio continuum surveys, sensitive and high-angular-resolution single-dish surveys of extended
radio continuum emission remain scarce. As part of the GLObal view of
STAR formation (GLOSTAR) survey, we will also crucially complement the existing data from the Karl G. Jansky Very Large Array (VLA) by addressing the missing zero-spacing gap. Within the framework of the GLOSTAR
Galactic plane survey, we performed large-scale
radio continuum imaging observations toward the
Galactic plane in the range $-2^{\circ}< \ell <60^{\circ}$ and $|b|<1.1^{\circ}$, as well as the Cygnus X region with the Effelsberg 100-m
radio telescope. We present the Effelsberg continuum survey at 4.89GHz and 6.82GHz including linear polarization with angular resolutions of 145$^{\prime\prime}$ and 106$^{\prime\prime}$, respectively. The survey has been corrected for missing large-scale emission using available low-angular-resolution surveys. Comparison with previous single-dish surveys indicates that our continuum survey represents the highest-quality single-dish data collected to date at this frequency. More than 90% of the flux density missed by the VLA D-array data is effectively recovered by the Effelsberg continuum survey. The improved sensitivity and angular resolution of our survey enable reliable mapping of
Galactic magnetic field structures, with polarization data that are less affected by depolarization than in previous surveys. The GLOSTAR single-dish continuum data will be released publicly, offering a valuable resource for studying extended objects including HII regions,
supernova remnants, diffuse interstellar medium, and
Galactic structure. (Abridged)
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All authors Y. Gong, W. Reich, M. R. Rugel, K. M. Menten, A. Brunthaler, F. Wyrowski, P. Müller, S. A. Dzib, J. S. Urquhart, A. Y. Yang, R. Dokara, G. N. Ortiz-León, B. Winkel, A. Kraus, S. P. Sathyanarayanan, W.-J. Kim, H. Beuther, J. D. Pandian, A. Cheema, S. Khan, V. S. Veena, N. Roy, C. Carrasco-Gonzalez, W. Cotton, T. Csengeri, S.-N. X. Medina, H. Nguyen