High Energy Astrophysical Phenomena
The role of accretion efficiency, natal kicks, and angular momentum transport in the formation of the Gaia black holes
Michela Mapelli, Cecilia Sgalletta, Johanna Müller-Horn et al. (+5 more)
Gaia has the potential to deliver several tens of new dormant black holes (BHs) with low-mass
stellar companions (hereafter,
Gaia BHs) in the upcoming fourth data release. Three
Gaia BHs are already known, but their formation pathways remain uncertain. Here, we perform a large parametric study to explore the formation of
Gaia BHs from isolated binary systems with the population-synthesis code SEVN and compare our models with the properties of the three already reported
Gaia BHs. Specifically, we explore the impact of
accretion efficiency, mass transfer stability, natal kicks, angular momentum transport, and core-collapse
supernova prescriptions. We find that models in which stable mass transfer is highly non-conservative and angular momentum is lost as a wind from the donor surface (Jeans mode) maximize the probability of forming dormant systems that match the properties of the observed
Gaia BHs in terms of both orbital period and eccentricity, because such assumptions prevent the initial orbit from shrinking too much when the BH progenitor fills its Roche lobe. If we allow for common-envelope
evolution, we find that models with common-envelope ejection efficiency $\alpha{} < 1$ predict dormant systems with orbital periods that are too short compared to the observed
Gaia BHs. The eccentricity of the observed
Gaia BHs, when combined with information about orbital period and BH mass, favors relatively large natal kicks, similar to those inferred from
Galactic neutron stars. Finally, models in which BH natal kicks are low - e.g. because they are modulated by fallback - result in the formation of a large population of dormant BHs with long orbital periods ($P_{\rm orb}>10^4$ days), which will be tested soon by the fourth
Gaia data release.
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All authors Michela Mapelli, Cecilia Sgalletta, Johanna Müller-Horn, Giuliano Iorio, Stefano Rinaldi, Christian Burt, Daniel Marín Pina, Amedeo Romagnolo
Solar and Stellar Astrophysics
A view of the evolution of a CME and the associated wave-trains at high spatial and temporal resolution
G. Russano, Y. De Leo, F. Frassati et al. (+13 more)
Context. Studying the kinematic and dynamic
evolution of fast eruptive events from the middle to high
solar corona is a primary objective of the Metis coronagraph on
Solar Orbiter. During perihelion, Metis acquires visible light images at a 20s cadence, reaching a spatial resolution of around 2000 km at 0.28 au. This enables capturing coronal mass ejections (CMEs) and transient structures with unprecedented spatial and temporal resolution. Aims. On October 8-9, 2022, an extensive CME was observed by Metis at 0.3 au (resolution: 4.4 $10^{3}$ km/pixel). We aim to exploit this high resolution to resolve multiple substructures within the CME front, revealing
plasma elements with distinct trajectories and speeds to provide a detailed kinematic characterization of the eruption. Methods. A normalization-based running difference
algorithm was applied to enhance the complex morphology. Height-time diagrams were used to estimate propagation speeds and frequency variations. A 3D flux rope reconstruction, combined with multi-spacecraft coronagraphs and disk imagers, enabled tracking the CME from its initiation in the lower corona to approximately 5
solar radii. Joint observations with
Solar Orbiter EUI-FSI provided insights into the eruption's onset, while Metis captured its development into the middle corona. Results. Metis observations resolve the CME's fine structure and internal
plasma motions. The detection of circular, fast-propagating wavefronts (500 km/s, 3 minute period) at the western flank suggests wave excitation and
magnetic reconfiguration processes. Multiple interpretations are proposed for these coronal wave trains, including quasi periodic propagating fast modes, offering new insights into wave generation and energy transport in the
solar corona.
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All authors G. Russano, Y. De Leo, F. Frassati, G. Jerse, V. Andretta, H. Cremades, M. Temmer, S. Mancuso, L. Abbo, A. Burtovoi, F. Landini, M. Pancrazzi, M. Romoli, C. Sasso, R. Susino, M. Uslenghi
High Energy Astrophysical Phenomena
The spectrum of the persistent radio source associated with FRB 20190417A
L. Bruno, D. Pelliciari, G. Bernardi et al. (+3 more)
Persistent
radio sources (PRSs) are (sub-)parsec-scale compact non-thermal continuum sources associated with some repeating fast
radio bursts (FRBs). Their nature is debated, but their properties provide insights into the FRB environment and progenitors. We measure the spectrum of the recently confirmed PRS associated with FRB 20190417A. Spectral features such as the self-absorption and cooling break can be used to constrain the age and size of PRSs and test theoretical models. We present observations made with the 1.26 GHz upgraded
Giant Metrewave
Radio Telescope (uGMRT) and observations from the 6 GHz Karl Jansky Very Large Array (VLA). With complementary archival data and the LOw Frequency ARray Two Meter Sky Survey (LoTSS), we characterise the spectrum of the PRS between 144 MHz and 6 GHz. The spectrum follows a power-law behaviour at gigahertz frequencies. The source is not detected at 144 MHz down to a $2\sigma=170 \; {\rm \mu Jy}$ sensitivity. We modelled the spectrum with a broken power law, obtaining a spectral index $\alpha = 0.20 \pm 0.05$ between 1-6 GHz. We placed a lower limit on the turn-over frequency of $> 370$ MHz ($95\%$ confidence). The flat spectrum and low-frequency turn-over of the target are consistent with the spectral properties predicted for magneto-ionic nebulae, inflated behind the
supernova ejecta by a flaring young magnetar. Considering the multi-zone magnetar wind nebula scenario, we estimate an age of $t< 250$ yr and a radius of $R< 0.4$ pc for the target, which would thus be slightly older than the PRSs associated with FRB 20121102A and FRB 20190520B.
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All authors L. Bruno, D. Pelliciari, G. Bernardi, M. Pilia, L. Beduzzi, P. Esposito
Earth and Planetary Astrophysics · Cross-listed from gr-qc
Dark matter heating of Planet 9, and its observational implications
Tiberiu Harko
The observed unusual behaviors of the orbits of Trans-Neptunian objects as well as the gravitational anomalies detected by the Optical Gravitational
Lensing Experiment can be explained by assuming the existence of a ninth
planet in the
Solar System, having a mass of the order of $5-10M_{\oplus}$, and located at the distance of 300-1000 AU from the Sun. Since no optical counterpart of
Planet 9 was observed, it is reasonable to assume that it has a very low luminosity. Various proposals on the nature of
Planet 9 have been advanced, including the possibility that it is a black hole, an
axion or a dark matter
star. We propose that dark matter heating of
Planet 9 could generate a thermal
radio flux that could allow its observational detection, even if
Planet 9 is a very dark object. We estimate the dark matter impact parameter, the mass and the kinetic energy deposition rates, as well as the surface temperature of
Planet 9. By adopting a specific model for the time
evolution of the
planet, and assuming a long time capture of dark matter, the surface temperature of
Planet 9, and the spectral features of the emitted radiation are obtained. Our results indicate that dark matter capture may provide an efficient mechanism for the heating of
Planet 9, and also provide a specific observational signature of the
planet. The numerical evaluations depend on the unknown value of the dark matter-ordinary matter interaction cross-section, with the estimates obtained as a function of its ratio and the saturation cross section for dark matter to deposit its entire energy. For a value of this ratio of $10^{-10}$, and for a dark matter density of the order of $1.32\times 10^{-17}$ g/cm$^3$, in a few Gyrs the surface temperature of
Planet 9 can reach values of the order of 200 K, or even higher, with a maximum wavelength of around $\lambda_{max}=1.44\times 10^{-3}$ cm, situated in the infrared domain.
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High Energy Astrophysical Phenomena
Gravitational Gertsenshtein-Zeldovich mechanism for the Association between GW190425 and FRB 20190425A
Shao-Qin Wu, Jing-Rui Zhang, Rong-Gen Cai et al. (+2 more)
The temporal and spatial coincidence between the gravitational wave (GW) event GW190425 and the fast
radio burst (FRB) event FRB 20190425A raises the intriguing possibility of a physical connection between the two. The widely discussed possibility invoking the collapse of a supermassive
neutron star as the merger product suffers the inconsistency between the model prediction and the measured inclination angle of the system. Here, we propose a novel physical mechanism to account for the association. We envisage a magnetar located at about 2.5 light hours away from the binary
neutron star merger site. The kiloherz GWs generated by the merger are converted into kiloherz electromagnetic (EM) radiation via the Gertsenshtein-Zeldovich (GZ) effect near the magnetar. Subsequent inverse Compton scattering off the kilohertz EM waves by relativistic particles generates the observed gigahertz FRB emission. Our calculation reveals that, with appropriate parameter choices, the properties of FRB 20190425A can be reproduced.
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All authors Shao-Qin Wu, Jing-Rui Zhang, Rong-Gen Cai, Bing Zhang, Yun-Long Zhang
Solar and Stellar Astrophysics
Variability classification of TESS targets in LOPS2, the first long-term pointing field of PLATO. Version 1 of the public variability catalogue
Mykyta Kliapets, Pablo Huijse, Jeroen Audenaert et al. (+28 more)
The PLAnetary Transits and Oscillations of
stars (PLATO) mission is expected to launch in January 2027. A total of 8% of its data rate will be dedicated to complementary science targets selected from approved Guest Observer proposals. We seek to provide an open-source catalogue of variable
stars in PLATO's first long-term observing field, LOPS2. We want to use existing observations from the Transiting
Exoplanet Survey Satellite (TESS), which has observed many
stars in LOPS2. We classified 38 million calibrated aperture light curves from the TESS-
Gaia Light Curve pipeline (TGLC, $G\lesssim17$) for 6 million unique sources in LOPS2 with two machine learning frameworks – a deep neural network and a feature-based gradient-boosted decision-tree ensemble. We combined their predictions to create this first version of the LOPS2 variability catalogue, performed manual vetting of a sub-sample classified light curves, and a statistical analysis of the results to validate our methodology and to assess the variability properties and parameters of the
stars in the catalogue. Our classification resulted in the identification of approximately 72% of the light curves having dominant instrument- or pipeline-induced signal, with the remaining 28% representing 3.6 million individual candidate variable
stars, including pulsating, rotating, and eclipsing
stars. Candidate pulsators exhibit varied behaviour in terms of their frequencies, amplitudes, rotation, and fundamental parameters. To ensure purity of the samples, filtering on colour, luminosity, the dominant frequency and its amplitude, and presence of close neighbours is helpful. We provide the first version of our PLATO LOPS2 variability catalogue to the community for further study and scrutiny. It is to date one of the largest catalogues of variable
stars from an automated classification pipeline.
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All authors Mykyta Kliapets, Pablo Huijse, Jeroen Audenaert, Andrew Tkachenko, Marek Skarka, Paul F. X. Gregory, Dominic M. Bowman, Simon J. Murphy, Poojan Agrawal, József M. Benkő, Hannah Brinkman, Nicholas Jannsen, Yoshi Nike Emilia Eschen, Allison Eto, Dario J. Fritzewski, Alex Kemp, Viktor Khalack, Gang Li, Ricardo Ochoa-Armenta, Inês Rolo, Nena Scheller, Rose S. Stanley, Keegan Thomson-Paressant, Emese Plachy, Vincent Vanlaer, Mathijs Vanrespaille, Jasmine Vrancken, Haotian Wang, Yian Xia, George R. Ricker, Conny Aerts
Solar and Stellar Astrophysics
Solar Orbiter observations of solar energetic electron events associated with hard microflares
Diane Mittaine, Andrea Francesco Battaglia, Laura Rodríguez-García et al. (+4 more)
Generally, large
solar flares accelerate electrons to high energies more efficiently than microflares. However, some microflares, known as hard microflares (HMFs), also produce high-energy electrons, as indicated by their flat hard X-ray (HXR) spectra. These events are typically associated with footpoints located in or at the edge of sunspots. The mechanisms behind this efficient acceleration, and their connection to
solar energetic electrons (SEEs), remain unclear. We compare, for the first time, HXR spectra of HMFs with in-situ electron spectra of associated SEEs using
Solar Orbiter STIX and EPD observations. This provides insight into acceleration processes and the transport of high-energy electrons into interplanetary space. We identify eight HMFs observed jointly by
Solar Orbiter and Earth-based instruments that are associated with SEEs, confirmed through timing and
magnetic connectivity analysis. Each event is studied using HXR spectroscopy, SEE velocity-dispersion analysis, and in-situ electron spectral analysis. Seven of eight events show consistent timing between
flare HXR emission and inferred electron injection, as well as good agreement with
magnetic connectivity estimates. The known correlation between HXR
photon and in-situ electron spectral indices extends to HMFs, which occupy the hard end of the distribution, even compared to larger
flares. We conclude that HMFs produce
prompt SEEs with hard spectra, demonstrating efficient electron acceleration without requiring large
flare energy release. Their
magnetic configuration, involving open field lines from the sunspot, suggests they may be an important contributor to filling the heliosphere with energetic particles.
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All authors Diane Mittaine, Andrea Francesco Battaglia, Laura Rodríguez-García, Nils Janitzek, Raúl Gómez-Herrero, Francisco Espinosa Lara, Louise Harra
Earth and Planetary Astrophysics
Constraining Electron-Impact Ionization of O$_2$ Through UV Aurora Observations at Ganymede
Stefan Duling, Joachim Saur, Darrell Strobel et al. (+3 more)
While photoionization rates of Ganymede's O$_2$ dominated atmosphere are well constrained, the contribution of electron-impact ionization is rather uncertain. Previous quantitative estimates have relied on assumptions about densities and energy distributions of precipitating electrons, or on rare spacecraft measurements that cannot be unambiguously mapped to the regions of ionization. In this study, we present a novel approach to quantify electron-impact ionization rates directly through OI 1356 Å emission brightness observations. The analysis of measured cross sections reveals that the ionization-to-excitation ratio is limited to 10-60 over all electron energies, reducing the uncertainty of estimating ionization rates to a factor less than 6. We apply this method to Juno UVS observations of Ganymede's aurora. We find that the OI 1356 Å brightness of the auroral ovals is well described by 3-5{\deg} latitude wide Gaussian distributions centered on the open-closed field line boundary, with an average peak of 120 R. The average brightness outside the ovals in the polar and equatorial background regions is ~8 R. From these observations, we derive a global map of electron-impact ionization rates, which are at least an order of magnitude higher than photoionization rates. The estimated total global ionization rate is 1.3-7.6$\times$10$^{26}$ s$^{-1}$, with average column rates of ~5$\times$10$^{9}$ cm$^{-2}$s$^{-1}$ in the ovals and ~3$\times$10$^{8}$ cm$^{-2}$s$^{-1}$ in the background regions. Comparison of
radio occultation measurements with predicted electron densities indicates that transport processes are the dominant loss mechanism in Ganymede's ionosphere. The rate of ionospheric
outflow of O$_2^+$ is 0.1-2$\times$10$^{26}$ s$^{-1}$ or 0.5-11 kg s$^{-1}$, indicating 0.03-0.5 cm Myr$^{-1}$ erosion of Ganymede's surface ice.
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All authors Stefan Duling, Joachim Saur, Darrell Strobel, Philippa Molyneux, Jamey R. Szalay, Thomas K. Greathouse
Earth and Planetary Astrophysics
A Search for Hydroacoustic Signals from Bolides
P. Brown, L. McFadden, D. McCormack et al. (+2 more)
Here we present a survey aimed at detecting hydroacoustic signals from fireballs using the six hydrophone stations operated as part of the Comprehensive Test Ban Treaty Organisation (CTBTO) International Monitoring System. We identified 30 fireballs where propagation paths to stations exist. These included high energy fireballs (E $\geq$ 5 kT), those which occurred over favorable locations for coupling into the deep ocean as well as a selection of bolides close to CTBTO hydrophone stations. The largest of these impactors were $>$ 5 meters in diameter. From theoretical and empirical considerations we show that direct hydroacoustic shock transmission is the most likely source mechanism, though large meteorites impacting the ocean surface from a fireball might be detectable in extreme cases. We find one possible instance of a fireball occurring on Sep 2, 2003 off the coast of Alaska, where a linked hydroacoustic signal with the expected timing and backazimuth is detected. However, given the size of our survey and the random background rate of signals, this detection is statistically weak. We conclude that hydroacoustic detection in the SOFAR channel of fireballs is very rare. Using our chosen set of signal processing parameters, assuming direct path H-phase signals, adopting a signal celerity range of 1.42-1.55 km/s we find no unambigous detections in 53 station-fireball pairs. Based on SOFAR-equivalent yields derived assuming the minimum detectable amplitude signal family association is representative of the noise background in our survey we estimate a conditional upper limit for fireball coupling efficiency of order 10$^{-10}$. A single well recorded airplane impact provides an empirical estimate for the energy coupling of surface ocean impacts to the SOFAR channel of 10$^{-4}$ for high velocity surface impacts.
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All authors P. Brown, L. McFadden, D. McCormack, M. Adams, D. Vida
Cosmology and Nongalactic Astrophysics
Illuminating the Local Universe: Large-Scale Structure from ZTF Type Ia Supernovae
Antoine Gilles Lordet, Ariel Goobar, Jens Jasche et al. (+12 more)
Within the volume-limited subsample at $z<0.06$ of the Zwicky Transient Facility (ZTF) DR2 sample, we confirm a statistically significant excess of Type Ia
supernovae (SNe Ia) around $z \simeq 0.02-0.04$, previously reported but not explained by survey selection effects. Forward simulations assuming a uniform volumetric SN Ia rate and realistic ZTF detection efficiencies fail to reproduce the feature, rejecting this hypothesis at a $12.2\sigma$ level for the volume-limited sample. We further detect excesses in the rates compared to our survey simulations at $z \simeq 0.08$ and $0.14$, increasing the significance to $14\sigma$ when extending the
redshift range up to $0.12$. To investigate the origin of these inhomogeneities, we compare the observed SN Ia distribution to constrained reconstructions of the local matter density field from the Manticore project, based on
Bayesian forward modelling of the 2M++
galaxy catalogue. While SN overdensities are spatially associated with prominent nearby structures such as the Perseus, Coma, and Hercules superclusters, the amplitude of the SN excesses significantly exceeds that expected from local matter overdensities alone. By reconstructing a
redshift-dependent volumetric SN Ia rate, we find that local enhancements can reach factors of three to eight within specific clusters, while the sample-averaged rate remains consistent with previous low-
redshift measurements. These results indicate that the SN Ia rate is not a linear tracer of the underlying matter density and suggest a strong environmental dependence in dense structures. We discuss possible physical origins and highlight the implications for low-
redshift SN cosmology, including correlated peculiar velocities and additional covariance beyond standard linear corrections.
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All authors Antoine Gilles Lordet, Ariel Goobar, Jens Jasche, Stuart McAlpine, Jesper Sollerman, Young-Lo Kim, Mickael Rigault, Madeleine Ginolin, Umut Burgaz, Eric C. Bellm, Matthew J. Graham, Joahan Castaneda Jaimes, Frank J. Masci, Josiah Purdum, Reed Riddle
Solar and Stellar Astrophysics
Self-Lensing Signals in Binary Systems Containing White Dwarfs with Neutron star or Stellar-mass Black hole Companions
Sedighe Sajadian and Man Ho Chan
Light curves from binary systems containing white
dwarfs with
neutron star or
stellar-mass black hole companions (WD+NS and WD+BH) with edge-on orbital planes potentially show self-
lensing/eclipsing signals. Here, we evaluate the properties and detectability of these signals in the NASA's Transiting
Exoplanet Survey Satellite (TESS), and the Nancy Grace Roman Space
Telescope (Roman) observations. WD+NS systems with orbital periods $T\lesssim25~$days mostly have considerable finite-source sizes with the normalized source radii $\rho_{\star}\gtrsim1$. WD+BH systems with $T\gtrsim3$ days have $\rho_{\star}\lesssim1$, and $\rho_{\star}\sim0.01$ for BHs with a few tens
solar-mass. Our analytical calculations show the probabilities of occurring self-
lensing signals in WD+NS and WD+BH systems are $\sim10^{-3},~10^{-2}$, and maximize for systems with low-mass WDs revolving massive NSs/BHs. We simulate their light curves and generate synthetic data for them by applying the observing protocols of these two satellites. We assume self-
lensing signals are detectable if (i) $1\leq T\leq T_{\rm{obs}}$ (where $T_{\rm{obs}}=62~\rm{and}~27.4$ days are the Roman and TESS continuous observing windows), (ii) $\rm{SNR}\ge3,~6$, their signals are (iii) deeper than twice the photometric error, and (iv) covered by at least one datum. Systems with detectable self-
lensing signals in the TESS and Roman observations on average have small inclination angles $i\lesssim0.2^{\circ}$, with the orbital periods $\sim6,~19~$days, and their signals last $\sim[6,~30]~\rm{minutes}$. The TESS and Roman efficiencies for detecting these signals are $\sim2-6\times10^{-4}$ and $\sim2-12\times10^{-10}$. Although detecting these self-
lensing signals by Roman is impossible, the TESS
telescope potentially manifests at least one self-
lensing signal due to these binary systems, if $8\%,~\rm{and}~3\%$ of WDs have NS and BH companions.
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Solar and Stellar Astrophysics
The undetectable fraction of core-collapse supernovae in luminous infrared galaxies – II. GSAOI/GeMS dataset
I. Mäntynen, E. Kankare, S. Mattila et al. (+7 more)
Core-collapse
supernovae (CCSNe) in luminous infrared
galaxies (LIRGs) can have extreme line-of-sight host
galaxy dust extinctions, which leads to a large fraction of the events remaining undetected by optical and infrared surveys. This population of undetected CCSNe is important to constrain in order to determine the
cosmic CCSN rates. Our aim is to confirm and refine our estimates for the undetectable fraction of CCSNe in LIRGs in the local Universe. Our study is based on the near-infrared K-band multi-epoch SUNBIRD survey monitoring
dataset of a sample of nine LIRGs using the Gemini-South
telescope with the multi-conjugate GSAOI/GeMS
laser guide
star adaptive optics system. We determined the limiting magnitudes for CCSN detection for each epoch in our
dataset with artificial
supernova injection and image subtraction methods. Subsequently, we used a Monte Carlo method to determine the combined effects of limiting magnitudes, survey cadence, CCSN subtype distribution, and their light curve
evolution diversity. The intrinsic CCSN rates of the sample
galaxies were estimated based on detailed modelling of their spectral energy distribution. Finally, we combined the resulting CCSN detection probabilities with the intrinsic CCSN rates for the
dataset, and compared that against the real CCSN detections over the survey period. Based on our GSAOI/GeMS
dataset, assuming optical or near-infrared example surveys with capabilities to detect CCSNe in local LIRGs with host extinctions of $A_V =$ 3 or 16 mag, respectively, the resulting total undetectable fractions are $86.0^{+4.7}_{-5.9}$ % and $53.6^{+15.6}_{-19.6}$ %. When folding in the results from our previous near-infrared adaptive optics assisted LIRG monitoring
dataset, the corresponding total undetectable fractions are $88.3^{+2.6}_{-3.2}$ % and $61.4^{+8.5}_{-10.6}$ %, respectively.
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All authors I. Mäntynen, E. Kankare, S. Mattila, A. Efstathiou, S. D. Ryder, E. Kool, K. Matilainen, T. M. Reynolds, C. Vassallo, P. Väisänen
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Graviton Production from Inflaton Condensate: Boltzmann vs Bogoliubov
Chenhuan Wang, Yong Xu and Wenbin Zhao
We study graviton production from an oscillating inflaton condensate during reheating by systematically comparing Boltzmann and Bogoliubov descriptions for inflaton potentials of the form $V(\phi)\propto\phi^n$ around the minimum. The Bogoliubov framework provides a unified description of graviton production, capturing both perturbative and non-perturbative effects across short and long wavelengths, whereas the Boltzmann approach is restricted to perturbative production at short wavelengths. For the quadratic case ($n=2$), we find that the two approaches yield identical graviton spectra at short wavelengths, indicating that the Boltzmann treatments fully captures perturbative gravitational production in this regime. For steeper potentials ($n>2$), however, we identify a sizable contribution arising from the non-adiabatic transition between inflation and reheating. This component is naturally incorporated in the Bogoliubov formalism but absent in the Boltzmann description, and we show that it is important over a broad range of momenta. We derive analytic approximations within both frameworks that clarify the physical origin and scaling behavior of the spectrum. Our results delineate the regime of validity of Boltzmann approaches and show that, for steeper inflaton potentials, graviton production is governed by non-adiabatic transition dynamics for which the Bogoliubov formalism provides the most appropriate description.
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Solar and Stellar Astrophysics
Phlegethon: a fully compressible magnetohydrodynamic code for simulations in stellar astrophysics
G. Leidi, A. Holas, K. Vitovsky et al. (+12 more)
We present PHLEGETHON, a fully compressible, Eulerian magnetohydrodynamic (MHD) code designed for multidimensional simulations in
stellar astrophysics. The code uses a time-explicit, second-order, finite-volume method optimized to model a wide range of dynamical processes in
stars, from very low-Mach-number turbulent convection in the cores of massive
stars to supersonic flows in subsurface convection zones. PHLEGETHON employs low-dissipation Riemann solvers and a well-balanced method to accurately capture slow flows arising from strongly stratified media. The induction equation is solved using a staggered constrained-transport method to ensure divergence-free
evolution of the
magnetic field. The MHD equations are coupled to arbitrary
nuclear reaction networks solved in a time-implicit approach, together with super-time-stepping for efficient treatment of thermal
diffusion. Equations of state appropriate for
stellar plasmas are available, accounting for partial ionization, electron degeneracy, and electron-positron pair production. The code is implemented in a compact and user-friendly manner, and it scales to tens of thousands of CPU cores using MPI-based domain decomposition. We perform several verification tests to demonstrate the accuracy and versatility of the code, and present simulations of magnetoconvection in a core-collapse
supernova progenitor
star. The rich variety of physical effects and numerical methods implemented in PHLEGETHON enables the code to model diverse multidimensional processes that play a crucial role in
stellar-interior dynamics, such as reactive convection, convective boundary mixing, internal-wave excitation, and
magnetic-field amplification mechanisms. Within a single framework, these phenomena can be investigated across a wide range of
stellar evolutionary stages, from main-sequence
stars to
supernova progenitors. PHLEGETHON is publicly accessible online.
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All authors G. Leidi, A. Holas, K. Vitovsky, F. Rizzuti, A. Roy, J. Reichert, K. Bayer, D. Gagnier, R. Andrassy, P. Christians, P. V. F. Edelmann, V. Varma, R. Hirschi, P. S.-H. Cheung, F. K. Röpke
Astrophysics of Galaxies
Dark Matter's influence on Evolution of MBHB in Dwarf Galaxies: A Case Study of Leo I dSph
Muhammad Junaid
In this study, we investigate the dynamical
evolution of a massive binary black hole (MBHB) in the Leo I
dwarf spheroidal
galaxy model and examine how dark matter along with
stellar matter's gravitational interactions influence its long-term behavior. Using high-resolution direct N-body simulations, we follow the orbital
evolution of the binary within a realistic model of the Leo I
stellar and dark matter distribution. We found that the binary separation decreases from an initial 300-parsec orbit to roughly 1 parsec over a period of about 2 Gyr, primarily driven by dynamical friction and
stellar hardening. The orbital
evolution then stalls at this scale, illustrating the well-known final parsec problem. During this phase, the binary also develops increasing orbital eccentricity and produces a modest redistribution of the inner mass profiles in some cases. We then further estimate the final stage of the system's
evolution using gravitational-wave emission models and find that the binary is unlikely to merge within a Hubble time. The prolonged dynamical friction phase appears to be related to the low
stellar and dark matter densities in Leo I. These results suggest that massive binary black holes in
dwarf spheroidal
galaxies such as Leo I will not contribute to the gravitational-waves detectable from LISA even if dark matter is considered.
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Astrophysics of Galaxies
Metal enrichment in the galaxy group IC 1262
Satish S. Sonkamble, Dharam V. Lal, S. Ilani Loubser et al. (+1 more)
We present a new metal enrichment analysis of a unique
galaxy group IC 1262 using archival Chandra and GMRT observations, focusing on metal transport via
radio jet, sloshing cold fronts, and shock front. This group shows two sloshing cold fronts along the east and north-west direction which is nearly orthogonal to the north - south orientated
radio jet. We report discontinuities in the
metallicity at the location of previously detected cold fronts, a more prominent one towards the eastern direction. In addition, the gas inside the cold fronts is 45$\pm$8 per cent more enriched than the gas outside the cold front, suggesting the role of sloshing in transporting metals through the IGrM. We also confirm the presence of a previously reported shock front with higher significance and with greater details. Across this shock, we detect a significant
metallicity drop from 0.45$\pm$0.05 $Z_{\odot}$ to 0.22$\pm$0.04 $Z_{\odot}$, located at a projected distance of 78$\pm$2 kpc in the southern direction. The shock could potentially account for the region of gas enrichment seen in the abundance map and profile, which could be the result of a non-Maxwellian electron distribution in its vicinity. This should be considered a contributing factor rather than the sole cause of the observed discontinuity in the abundance. Furthermore, our spectral analysis reveals two temperature X-ray gas preferentially aligned with the
radio-jet axis, indicating a possible influence of
radio AGN activity on the surrounding gas.
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All authors Satish S. Sonkamble, Dharam V. Lal, S. Ilani Loubser, Mahadev B. Pandge
Solar and Stellar Astrophysics
Kelvin waves over a differentially rotating spherical shell
T. Boismard and M. Rieutord
Context. Be
stars are presently viewed as B-type
stars surrounded by a disc fueled by the
star itself during episodicexcretion events. The origin of these events are poorly understood.Aims. This article aims to determine whether or not surface equatorial Kelvin waves can be unstable and therefore canplay a role in the triggering of the Be phenomenon.Methods. We first derive an analytical expression for gravito-inertial modes in the shallow-water framework. Then, weinvestigate numerically the
evolution of equatorial Kelvin modes as system parameters vary. The study is extended tothick-layer configurations with a constant density fluid. We then analyze the stability of these modes under differentialrotation and viscous effects.Results. We show that equatorial Kelvin waves still exist in a spherical shell of finite thickness, but that their equatorialconfinement is weaker. At low azimuthal wavenumbers, Kelvin waves are in the inertial waves frequency band and thusget specificities of inertial waves like shear layers associated with singularities of the Poincaré equation. These shearlayers are new dissipative structures for Kelvin waves. When a radial (shellular) differential rotation is imposed, we showthat equatorial Kelvin waves can be destabilised provided that differential rotation and viscosity are in an appropriaterange. The non-monotonic behaviour of the growth rate of the instability is traced back to the rise of a critical layerwhere the fluid azimuthal velocity equals the phase speed of the surface waves.Conclusions. This study provides new insights into the behavior of equatorial Kelvin waves in astrophysics, particularlyin rapidly rotating
stars. The results reinforce the idea that gravito-inertial waves, and more specifically the equatorialKelvin waves, can be unstable and thus be key parts in the mechanisms leading to the Be phenomenon.
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Solar and Stellar Astrophysics
Unveiling Dominant Toroidal Magnetic Fields in a Protostellar Outflow
Tao-Chung Ching, Zhi-Yun Li, Qizhou Zhang et al. (+6 more)
Magnetic fields play a fundamental role in the formation of protostellar winds. In the magneto-centrifugal models, poloidal
magnetic fields launch winds from
accretion disks, and fast-rotating gas twists the fields into toroidal geometry that collimates and accelerates winds through
magnetic hoop stress. However, toroidal fields in protostellar winds remain observationally unresolved. Here we report polarization observations of carbon monoxide emission toward the NGC1333 IRAS 4A protostellar
outflow. The inferred
magnetic fields are perpendicular to the
outflow axis and aligned with the rotational structure of the
outflow, indicating toroidal fields with strengths of a few milligauss, sufficient to collimate and accelerate the
outflow at several hundred astronomical units from the protostar. A linear correlation is found between the curl of plane-of-the-sky
magnetic field and the line-of-sight electric current density. Our analysis provides better constraints on ion-electron drift velocity in protostellar
outflows and supports rotating
outflows driven by the magneto-centrifugal mechanism.
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All authors Tao-Chung Ching, Zhi-Yun Li, Qizhou Zhang, Josep Miquel Girart, Shih-Ping Lai, Chin-Fei Lee, Di Li, Ramprasad Rao, Emmanuel Momjian
Cosmology and Nongalactic Astrophysics
Impact of the SNe Ia Magnitude Transition at 20 Mpc on Cosmological Parameter Estimation
Leandros Perivolaropoulos and Chrisostomos-Panagiotis Stamou
We investigate the impact of a late-time transition in the standardized absolute magnitude $M$ on the best-fit values of cosmological parameters using the Pantheon+
dataset. Extending previous analyses which focused on flat $\Lambda$CDM, we examine this transition within flat $\Lambda$CDM, wCDM, and CPL cosmologies, as well as a model-independent cosmographic expansion, employing both frequentist ($\chi^2$ minimization with AIC/BIC) and
Bayesian (MCMC and Nested Sampling) inference frameworks. We confirm that the data consistently favor a step in absolute magnitude of $\Delta M \simeq 0.19~\mathrm{mag}$ at a characteristic distance of $d_{\mathrm{crit}} \approx 20~\mathrm{Mpc}$. The inclusion of this transition leads to a statistically significant improvement in the quality of fit and has a distinct impact on parameter estimation: it induces a systematic increase in the inferred Hubble constant of approximately $2\%$ across all tested models. In contrast, we find that the dynamical parameters governing the background expansion, including the matter density $\Omega_m$ and the dark energy equation of state ($w_0, w_a$), remain stable and largely unaffected. These results indicate that the $20~\mathrm{Mpc}$ feature acts primarily as a low-
redshift calibration shift rather than a modification of the late-time expansion history.
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Cosmology and Nongalactic Astrophysics
Primordial Black Holes Formation Beyond the Standard Cosmic QCD Transition
Maël Gonin, Oleksii Ivanytskyi, David Blaschke et al. (+1 more)
We review the role of
primordial black holes (PBHs) for illuminating the dark ages of the cosmological
evolution and as dark matter (DM) candidates. We elucidate the role of phase transitions for
primordial black hole formation in the early Universe and focus our
attention on the cosmological QCD phase transition within a recent microscopical model. We explore the impact of physics beyond the Standard Model (SM) on the
cosmic equation of state and the probability distribution for the formation of PBHs which serve as candidates for DM and contribute to present-day binary black-hole merger events.
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All authors Maël Gonin, Oleksii Ivanytskyi, David Blaschke, Günther Hasinger
Astrophysics of Galaxies
Deriving volume density profiles of filaments from observed surface densities
Alexander Men'shchikov and Guo-Yin Zhang
Accurate characterization of filamentary structures in
star-forming clouds is essential for understanding
star formation. Traditional methods fit observed surface density profiles $\Sigma(r)$ with slope $\gamma$ and width $H$ using the Plummer function, assuming $\beta=\gamma+1$ and $h\approx H$ for the volume density slope and width. These assumptions break down for shallow profiles, with the slope and width relations deviating progressively more for compact and extended filaments, respectively. We present a new fitting method that explicitly accounts for finite cylindrical geometry and establishes self-consistent empirical relationships between the parameters of $\Sigma(r)$ and those of the volume density profile $\rho(r)$ with slope $\beta$ and width $h$. The method was validated on model profiles and applied to selected filaments in the California molecular cloud. The slope difference $\delta\equiv\beta-\gamma$ falls below unity for shallow ($\beta\lesssim 2$) and compact profiles; $h$ and $H$ can differ by over an order of magnitude for extended filaments with shallow slopes. Accurate parameter recovery requires high resolvedness $R\equiv H/O\gtrsim 10$ (where $O$ is the beam width); at lower resolvedness, slopes are severely overestimated and filaments remain unresolved even when $H\gg O$. The traditional Plummer function yields systematically overestimated slopes. Accurate deconvolution requires a priori knowledge of the true parameters, creating a fundamental circular problem whose only robust solution is obtaining sufficiently high angular resolution. Current far-infrared observations typically lack sufficient resolution, and some previously reported filament properties may require reinterpretation.
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Astrophysics of Galaxies
M1-92: AGB interruption and isotopic ratio paradox. Chemistry and morpho-kinematics from improved shapemol modelling
E. Masa, J. Alcolea, M. Santander-García et al. (+5 more)
The shaping of planetary nebulae on their
evolution from asymptotic
giant branch circumstellar envelopes to their final, most often axisymmetrical, form is still a process with many unknown details. The key to understanding the whole shaping process is the study of the transition objects called pre-planetary nebulae (pPNe). In this context, modelling tools must be kept to the standard of
radio telescope capabilities, so we can make the most of the data they collect. In this work we first present the newest update of the SHAPE and SHAPEMOL modelling tools, adding ten new molecular species to be reproduced together with other general improvements. Later, we put this new update into practice to study M1-92, a pPN with a rich chemistry that can provide valuable information on its origin and shaping. We created a 3D morpho-kinematical model of the nebula in SHAPE that is able to reproduce 23 line profiles from the IRAM 30m
telescope and HIFI/HSO and five maps from IRAM NOEMA. The observational
dataset is reproduced simultaneously under the same physical conditions, adjusting only the relative abundance of the different species. We obtained a full description of the nebula's physical and chemical properties, and we provide the total estimates for mass (0.79 $M_\odot$), linear momentum (4.10$\times10^{39}$ g cm s$^{-1}$), and kinetic energy (6.48$\times10^{45}$ erg) as well as their detailed distribution across the nebula. We also analysed the isotopic ratios, finding robust discrepancies (values of 10 versus 30) in the $^{12}$C/$^{13}$C ratio across structures depending on their age.
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All authors E. Masa, J. Alcolea, M. Santander-García, V. Bujarrabal, C. Sánchez Contreras, A. Castro-Carrizo, W. Steffen, N. Koning
Solar and Stellar Astrophysics
Evidence for a bloated massive protostar in IRAS20126+4104
Riccardo Cesaroni
Variability is a well known phenomenon in low-mass young
stellar objects, but in recent years the monitoring of methanol masers and infrared continuum emission has permitted the detection of both burst-like episodes and periodic variations also in high-mass (proto)
stars. Multi-epoch studies on large samples of these objects have become possible thanks to the NEOWISE database, which surveyed the sky in the mid-IR for about a decade. Our goal is to analyse the mid-IR emission from the well studied massive protostar IRAS20126+4104 and confirm the hypothesis that such emission is periodic, as proposed in previous studies. We take advantage of the NEOWISE, ALLWISE, and Spitzer databases to obtain 24 images of the 3.4 $\mu$m emission from IRAS20126+4104 spanning 19 years, with $\sim$6 months sampling over a decade. With these data we create a light curve for each lobe of the bipolar nebulosity/
outflow associated with the protostar. Our results confirm that the IR emission from IRAS20126+4104 varies regularly with a period of $\sim$6.8 yr. The period is the same for both lobes, but their emissions are anticorrelated with a phase difference of $\sim$2.5 yr. The variation is consistent with that found in previous studies for the 6 GHz CH$_3$OH masers and the near-IR emission from the lobes. After discussing four possible “clocks” that could determine the observed periodicity, we rule out all but a model involving rotation of the
star with a spot obscuring $\sim$20% of the
stellar surface. The long rotation period implies that the 12 $M_\odot$ protostar is bloated, with a radius of $\sim$200 $R_\odot$.
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High Energy Astrophysical Phenomena
POLARIS: A Sparse Radial Neutrino Telescope Design for the Pacific Ocean
Karolin Hymon, Alexander Chen, Meng-Xue Tsai et al. (+3 more)
The cubic-kilometer
neutrino telescopes have opened
neutrino astronomy as an observational discipline. The recent detection of KM3-230213A, the highest-energy
neutrino ever observed at ~220 PeV, as a near-horizontal
muon track underscores that the ultra-high-energy frontier is accessed through horizontal directions where the Earth's opacity above ~100 TeV confines the observable sky to a narrow band around and above the horizon. Yet extending general-purpose detector architectures into this regime requires disproportionate increases in instrumentation, cost, and logistical complexity. A compelling alternative is to deploy specialized detectors that target this natural geometry. POLARIS (Pacific Ocean Large Area Radial Instrumented Sparse array) is a sparse planar deep-water Cherenkov array optimized for
neutrino-induced
muon tracks from horizontal directions in the multi-TeV to PeV regime. By rotating the conventional vertical string layout into a radial planar configuration, the detector presents maximal cross-section to horizontal tracks while naturally suppressing the down-going atmospheric background. With only 1100 optical modules, the five-arm design reaches point source and diffuse flux sensitivities at PeV energies competitive with detectors deploying several times more instrumentation. As a dedicated $\nu_\mu$ track detector, POLARIS provides the
muon-
flavor channel that tau-optimized experiments such as TAMBO and Trinity do not cover, enabling full
flavor composition measurements from astrophysical sources. Using the Prometheus simulation framework, this study demonstrates that targeted sparse geometries can open new discovery space at the high-energy frontier at a fraction of the cost of general-purpose arrays.
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All authors Karolin Hymon, Alexander Chen, Meng-Xue Tsai, Wan-Ting Hseu, Tzu-Hsuan Su, Anatoli Fedynitch
High Energy Astrophysical Phenomena
Acoustic instability at shock-wave precursors
Antonio Capanema, Pasquale Blasi and Emanuele Sobacchi
Magnetic field amplification is an integral part of the process of particle acceleration at non-relativistic shocks. It is necessary to reach the maximum energies required by observations, especially in
supernova remnants, thought to be sources of the bulk of
Galactic cosmic rays. Such amplification can be caused by the acoustic instability that develops when small density perturbations interact with the
cosmic-ray pressure gradient in the upstream of a
cosmic-ray-modified shock. The vorticity induced by the nonlinear development of the instability may lead to
turbulence, which amplifies the pre-existing
magnetic fields. To study this phenomenon, we use the PLUTO code to carry out 2D (and some 3D) magnetohydrodynamical simulations of the
evolution of small density perturbations in the presence of an assigned
cosmic-ray pressure gradient. Adopting more realistic values of Mach number and
cosmic-ray acceleration efficiency than previously assumed in the literature, we show that the acoustic instability can transform small density perturbations into large nonlinear structures while the fluid crosses the precursor region of a
cosmic-ray-modified shock. We study the power spectrum of turbulent
magnetic fluctuations that may be important to scatter particles. We comment on the possible constructive interference between acoustic and non-resonant streaming instabilities. We discuss limitations of previous and current numerical investigations in accessing spatial scales where
turbulence is expected to turn nonlinear, and outline perspectives for future investigations.
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High Energy Astrophysical Phenomena
Interaction-powered Type Ibn Supernovae as a Transient PeVatron Candidate: The Case of SN 2023uqf
Ryo Sawada, Yusuke Inoue and Yosuke Ashida
We investigate whether the Type Ibn
supernova SN 2023uqf, reported close in time and direction to the $\sim$442 TeV IceCube alert IC-231004A, is physically consistent with a shock–circumstellar medium (CSM) interaction scenario. One-dimensional radiation-hydrodynamics calculations with STELLA reproduce the ZTF optical light curves with a dense helium-rich CSM following $\rho_\mathrm{CSM} \propto r^{-3}$ and a CSM density parameter $D'\approx 50$. Using the shock
evolution and CSM conditions obtained from the optical-fit RHD model, we model time-dependent
cosmic-ray acceleration and hadronic
neutrino production during the interaction phase. In our fiducial model, the inferred shock and CSM properties open a short-lived window in which multi-PeV
hadron acceleration and efficient hadronic interactions can coexist. Additional loss-limited effects could reduce the high-energy cutoff, but the model provides a useful optical-to-
neutrino consistency test for a transient PeVatron-like phase. After folding the predicted
neutrino emission through the IceCube effective area, we obtain an expected number of $\sim10^{-5}-10^{-4}$ track-like events at $d = 723$ Mpc, depending on the alert selection. In the low-count regime, the model predicts a detection-time weighting for a rare event, and the detection time of IC-231004A falls within the high-weight interval while its energy scale is compatible with the modeled spectrum. Although a single event cannot establish a definitive association, our results show that the optically inferred environment of SN 2023uqf can satisfy the basic timing and energy requirements for a transient PeVatron-like phase in the fiducial model and illustrate how interaction-powered Type Ibn
supernovae can be tested as high-energy
neutrino sources.
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Solar and Stellar Astrophysics
Multiwavelength Study of Blue Straggler Stars in Tombaugh 2: Evidence for Binary Mass Transfer and Constraints on Cluster Dynamical State
D. Bisht, Ing-Guey Jiang, K. Belwal et al. (+7 more)
We present a focused multiwavelength study of blue straggler
stars (BSSs) in the intermediate-age open cluster Tombaugh 2, located in the outer
Galactic disk, to constrain the dominant formation pathways of BSSs in a low-density environment. Cluster members are identified using
Gaia DR3 astrometry through a Gaussian Mixture Model, yielding a clean sample of high-probability members. Color-magnitude diagram analysis indicates an age of 1.74 Gyr. The radial surface density profile is well described by a King model, indicating a centrally concentrated overall structure, while the cluster exhibits only weak or no clear evidence of mass segregation among its
stellar populations. We identify 26 BSS candidates and 2 YSS candidates. Spectral energy distributions constructed from ultraviolet, optical, and infrared photometry reveal that 9 BSSs (32%) exhibit significant ultraviolet excess, indicating an additional hot component. Binary SED decomposition identifies stripped companions with effective temperatures Teff $\sim$ (1.5-8) $\times$ 10$^4$ K and radii R $\sim$ 0.04-0.28 R_$\odot$, consistent with proto-white
dwarfs, extremely low-mass pre-helium white
dwarfs, and young hot remnants formed through recent mass transfer. A slight central concentration of BSSs, together with stripped companions, suggests that binary mass transfer is an important formation channel, with no evidence for merger-driven formation. Multi-epoch VLT/FLAMES spectroscopy reveals radial-velocity variability in several systems, providing independent evidence for binarity. Our results highlight that optical-infrared photometric analyses alone may fail to detect hot compact companions, while spectroscopy and ultraviolet observations provide complementary constraints, with ultraviolet data offering a direct probe of such companions in intermediate-age open clusters.
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All authors D. Bisht, Ing-Guey Jiang, K. Belwal, D. C. C{\i}nar, Arvind K. Dattatrey, Geeta Rangwal, A. Raj, Shraddha Biswas, Mohit Singh Bisht, Alok Durgapal
Solar and Stellar Astrophysics
The $\mu$ Herculis system solved after nearly three centuries
Marcus L. Marcussen, Mikkel N. Lund, Frank Grundahl et al. (+11 more)
$\mu$ Herculis is a bright, nearby quadruple system. Its brightest member, $\mu$ Her Aa, displays
solar-like oscillations, establishing the system as a crucial
benchmark for asteroseismology, provided that its mass can be determined independently of
stellar models. We aim to resolve the full hierarchical architecture of the system and determine precise, model-independent dynamical masses for all four components (Aa, Ab, B, and C), along with a consistent astrometric solution for the system's centre of mass. We performed a joint fit of radial velocities, relative astrometry and absolute astrometry from Hipparcos,
Gaia DR3, and ground-based catalogues, spanning nearly three centuries. Our forward-modelling framework simultaneously constrains the Keplerian orbits of the inner Aa–Ab and B–C subsystems, the wide A–BC orbit, and the sky motion and parallax of the total centre of mass. Leveraging several complementary
datasets and the decisive 2023 periastron passage of the Aa–Ab pair, we precisely determine all orbital parameters and obtain sub-percent precision on the component masses: $M_{\rm Aa} = 1.134 \pm 0.007\,M_{\odot}$, $M_{\rm Ab} = 0.2286 \pm 0.0006\,M_{\odot}$, $M_{\rm C} = 0.445 \pm 0.005\,M_{\odot}$, and $M_{\rm B} = 0.417 \pm 0.005\,M_{\odot}$. We derive a system parallax of $\varpi_{\rm CM} = 120.069 \pm 0.089\,\mathrm{mas}$ that reconciles and improves upon the individual Hipparcos and
Gaia DR3 values.
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All authors Marcus L. Marcussen, Mikkel N. Lund, Frank Grundahl, Daniel Huber, Emil Knudstrup, Adam L. Kraus, Christoph Baranec, Pere L. Pallé, Trent J. Dupuy, Guillaume Huber, James Ou, Zach Werber, Ruihan Zhang, Reed Riddle
High Energy Astrophysical Phenomena
Accretion-Mode Transition: The Driver Behind Spectral Changes in Changing-Look AGNs
Pengyuan Han, Huaiyuan Lu, Bing Lyu et al. (+2 more)
The physical origin of optical changing-look AGNs (CLAGNs), characterized by the appearance or disappearance of broad emission lines, is thought to be mainly driven by the variation of the black-hole (BH)
accretion rate. In this work, we explore this issue based on a sample of {224} CLAGNs with UV-to-optical continua, where the UV radiation is more sensitive to the
accretion state near the BH horizon. We find that the luminosity correlation of $L_{3000}$–$L_{5100}$ at 3000$\rm \AA$ and 5100$\rm \AA$ becomes steeper at low luminosities (e.g., $L_{3000}\lesssim10^{44}\rm erg/s$), where the sources with high luminosities are roughly consistent with the prediction of a standard
accretion disk. At lower luminosities, the observations are more consistent with the prediction of a truncated disk. The whole sample has a median bolometric Eddington ratio of $\sim$2.2%, which is consistent with the critical value for state transition in X-ray binaries. Such transitions can significantly alter the UV-to-optical continuum, largely due to variations in the truncation radius, even when the change in the overall
accretion rate is minimal. The deficit of ionization
photons resulting from an increase in the truncation radius will lead to the weakening or disappearance of broad lines, which triggers the AGN changing-look.
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All authors Pengyuan Han, Huaiyuan Lu, Bing Lyu, Jiancheng Wu, Qingwen Wu
Astrophysics of Galaxies
Enhancing Ly{\alpha} Emitter Identification in HETDEX with a Convolutional Neural Network
Shiro Mukae, Erin Mentuch Cooper, Karl Gebhardt et al. (+9 more)
We present a deep learning framework to enhance the identification of Ly$\alpha$ emitters (LAEs) in the Hobby-Eberly
Telescope Dark Energy Experiment (HETDEX), an untargeted spectroscopic survey of LAEs at $1.9 < z < 3.5$ without imaging pre-selection. We primarily address the low signal-to-noise ratio (S/N) regime ($4.8 \leq \mathrm{S/N} \leq 5.5$), where LAE candidates suffer from substantial noise contamination. To distinguish LAE candidates from artifacts and sky residuals, we employ a convolutional neural network (CNN) trained on two-dimensional spectral images of single emission lines. The training sample is constructed from the HETDEX COSMOS catalog, with external validation from ancillary observations and our participatory science project, Dark Energy Explorers. For small-format, low-resolution spectroscopic data, the model achieves a balanced accuracy, precision, and recall of $94.1\%$, $97.5\%$, and $97.5\%$, respectively, in the high-S/N regime ($\mathrm{S/N}>5.5$), and $85.1\%$, $78.2\%$, and $84.4\%$ in the low-S/N regime. Using HETDEX LAEs independently identified by DESI spectroscopy, the model recovers $99\%$ and $93\%$ of the high- and low-S/N LAEs, respectively. Visual attribution indicates that the CNN attends to smooth, spatially extended central emission in true positives and to irregular or noisy features in true negatives. Applied to the full HETDEX catalog, the CNN enables an S/N threshold down to 4.8 by suppressing spurious spikes across $z\sim 1.9$–$2.5$ in the
redshift distribution. Our approach facilitates HETDEX cosmological analyses by mitigating false positives in
galaxy clustering and highlights the value of domain-specific deep learning for refining low-S/N spectroscopic identification in untargeted surveys.
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All authors Shiro Mukae, Erin Mentuch Cooper, Karl Gebhardt, Dustin Davis, Lindsay R. House, Mahdi Qezlou, Julian B. Muñoz, Shun Saito, Daniel J. Farrow, Caryl Gronwall, Donald P. Schneider, Eric Gawiser