Astrophysics of Galaxies
The Far-Ultraviolet Extragalactic Legacy (FUEL) Survey: Hubble Far-UV Images and Catalogs of the Extragalactic Legacy Fields
Aliakbar Kavei, Brian Siana, Harry I. Teplitz et al. (+7 more)
We present far-ultraviolet (FUV) images and catalogs from the Hubble Space
Telescope (HST) Advanced Camera for Surveys/
Solar Blind Channel (ACS/SBC) F150LP (about 1600 Angstrom) of three extragalactic fields: GOODS-S, GOODS-N, and COSMOS. The data comprise 365 orbits of high-resolution imaging of 151 pointings covering an area of 44.7 square arcmin to typical depths of FUV about 28.7 AB (3-sigma, 0.5 arcsec diameter aperture). We provide a new model of the spatially varying dark "glow" created from all 365 orbits of data, and scale and subtract it from all pointings. We provide drizzled image mosaics, weight maps, and exposure time maps matched in coordinates and pixel scale to the Hubble Legacy Fields (HLF) frame, and the original COSMOS tiles.
Galaxy photometry is measured within isophotes defined with existing deep Hubble F606W or F814W optical filters. We detect 1068
galaxies and provide catalogs of all optical detections, including matched IDs to existing 3D-HST and CANDELS catalogs. The
redshift distribution of FUV-detected
galaxies peaks at z about 0.6 and declines to z = 1.2, where the Lyman limit shifts redward of any filter transmission. These data fill the
redshift gap of high-resolution far-UV imaging between z about 0 and z > 1, enabling studies of
star-forming regions,
dust properties, the FUV extragalactic background, and Lyman continuum emission from
galaxies at z > 1.2.
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All authors Aliakbar Kavei, Brian Siana, Harry I. Teplitz, Anahita Alavi, Alberto Dominguez, Simon P. Driver, Alberto Saldana-Lopez, James Colbert, Joel R. Primack, Marco Ajello
Cosmology and Nongalactic Astrophysics
The dark fate of ultra-faint dwarfs: Gravothermal collapse in action
Moritz S. Fischer and Hai-Bo Yu
Ultra-faint
dwarf (UFD)
galaxies are a promising probe for dark matter (DM) physics as they are the most DM-dominated systems known. The Milky Way (MW) hosts many UFDs for which the properties of their DM distribution have been inferred from measurements of their
stellar kinematics. If DM has self-interactions beyond
gravity, the UFD
halos may undergo a gravothermal
evolution, giving rise to a population of
galaxies with more diverse DM density profiles. We investigate DM densities of MW UFDs in self-interacting dark matter (SIDM) models, with an aim of determining the stage of gravothermal
evolution for their
halos. Therefore, we employed idealised high-resolution SIDM N-body simulations targeted to a MW-like system and compared the properties of simulated satellites to those of the observed UFDs. We find that the gravothermal
evolution of SIDM
halos produces diverse DM distributions, aligning with observations of the MW UFDs. Most of the UFDs have high DM densities, indicating that their
halos have passed the period of maximum core expansion and entered the collapse phase, i.e. their central density may increase with time. The depth to which they have evolved into the gravothermal collapse may vary strongly across the satellites. This allows SIDM to account for the diversity in their DM densities. Moreover, the acceleration of the gravothermal
evolution by
tidal stripping can help to explain the diversity of the UFDs, as the ones with smaller pericentre distances require having evolved further into the gravothermal catastrophe. Large SIDM cross-sections of $\sigma / m_\chi \approx$ 80 cm$^2$ g$^{-1}$ at a velocity of $v \approx$ 20 km s$^{-1}$ are plausible, as the
halo densities of MW UFDs are consistent with the gravothermal
evolution predicted in SIDM, with most of them being in the collapse phase.
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Astrophysics of Galaxies
Low-resolution spectroscopic characterisation of five poorly known Galactic stellar clusters
E. Ceccarelli, M. Bellazzini, D. Massari et al. (+4 more)
Stellar clusters preserve crucial information on the formation and evolutionary processes that shaped the Milky Way (MW) as we see it today. However, several MW clusters still lack sufficient data to constrain their
metallicity, ages, and, in some cases, even their basic kinematic properties. We present low-resolution MODS at LBT spectroscopy for five such systems (i.e. Koposov 1, Koposov 2, Muñoz 1, Pfleiderer 2, and RLGC2) from which we derive systemic heliocentric radial velocities ($V_{\rm sys}$) with typical uncertainties of $\le 10$ km/s, and
metallicities based on the equivalent widths of the infrared Ca II triplet measured in red
giant branch members. For Pfleiderer 2 and RLGC2, we provide the first spectroscopic determinations of their systemic velocities and
metallicities, finding $V_{\rm sys}= 6 \pm 5$ km/s and $-313 \pm 6$ km/s, and $\mathrm{[Fe/H]}= -0.75 \pm 0.09$ dex and $-2.33 \pm 0.13$ dex, respectively. For the other three clusters, we find results that are consistent with the existing literature. Thanks to our new spectroscopic measurements, we were able to perform an orbital analysis to investigate their origin. We find that Pfleiderer 2 likely formed within the MW, RLGC2 is dynamically associated to the
Gaia-Sausage-Enceladus
accretion event, and Koposov 1 was likely stripped from the Sagittarius
dwarf spheroidal while Muñoz 1 is only tentatively associated with the latter system. In the end, Koposov 2 at high orbital energy does not show a clear association with any known progenitor system.
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All authors E. Ceccarelli, M. Bellazzini, D. Massari, A. Mucciarelli, M. De Leo, M. Libralato, E. Dodd
Astrophysics of Galaxies
Massimiliano Parente, Francesco Salvestrini, Gian Luigi Granato et al. (+7 more)
Observations of the rest-frame far-infrared (far-IR) emission of
galaxies suggest a mild increase of
dust temperature $T_{\rm dust}$ with
redshift, although constraining $T_{\rm dust}$ in high-
redshift systems remains challenging due to limited sampling of the far-IR spectral energy distribution (SED). We present and discuss the
redshift evolution of $T_{\rm dust}$ predicted by a cosmological
galaxy evolution simulation with
dust treatment, and interpret its dependence on other
galaxy physical properties. We use a semi-analytic model of
galaxy formation that includes an explicit treatment of
dust, post-processed with radiative transfer.
Dust temperatures are derived by applying modified blackbody SED fitting to the simulated
galaxies, mirroring the methodology adopted in most observational studies. The
dust temperature of simulated
galaxies increases with
redshift, in broad agreement with observational results. A feature-importance analysis reveals that the
star formation rate surface density $\Sigma_{\rm SFR}$ and the
dust-to-gas ratio (DTG) are the main drivers of
dust temperature, tracing the intensity of the interstellar radiation field and the optical depth of warm molecular clouds, respectively.
Galaxies with higher
star formation rate surface density and lower DTGs – common conditions at high$-z$ – are associated with warmer
dust. We provide a simple relation to estimate DTG from $\Sigma_{\rm SFR}$, $T_{\rm dust}$, and
redshift. Variations in
dust grain size and chemical composition have a negligible impact on $T_{\rm dust}$. Our results are particularly relevant to the study of
dust properties with observations of high-z
galaxies, where far-IR
dust emission is not fully sampled.
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All authors Massimiliano Parente, Francesco Salvestrini, Gian Luigi Granato, Desika Narayanan, Roberta Tripodi, Simone Bianchi, Manuela Bischetti, Chiara Feruglio, Fabrizio Fiore, Laura Silva
Astrophysics of Galaxies
When self-similarity meets mass spectrum and anisotropy
Václav Pavlík
Self-similar
evolution is widely used in the theory of collisional
stellar dynamics, but its applicability to systems with multiple
stellar masses is not well established. We investigate the structural stability of self-similar
evolution in multi-mass
star clusters and assess the roles of mass segregation and velocity anisotropy. Using a gaseous-model approximation, we develop a theoretical framework to describe the response of a self-similar background to mass-dependent perturbations with isotropic and anisotropic velocity distributions. We show analytically that mass-dependent relaxation leads to a separation of characteristic similarity scales and renders the single-scale solution structurally unstable. In the presence of velocity anisotropy, this similarity-breaking instability splits into distinct radial and tangential modes whose growth rates are modified in a direction-dependent manner. Radial anisotropy reduces the instability through enhanced radial kinetic support, whereas tangential anisotropy increases the effective growth rates and enables faster central
evolution. In systems with a mass spectrum, this instability drives mass segregation and the emergence of a multi-scale, near-homologous
evolution. Together, these results place self-similar
evolution in a consistent theoretical context for collisional
star clusters with multiple
stellar masses and anisotropic velocity distributions.
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Astrophysics of Galaxies
The erasure of Galactic bar resonances by dark matter subhaloes
Elliot Y. Davies, Adam M. Dillamore, Vasily Belokurov et al. (+1 more)
In the context of increasing appreciation for the coupling between the
Galactic bar and the
halo, we introduce a new framework using
stars trapped in resonance with the bar to probe the
Galactic dark matter subhalo population. Since resonant
stars occupy a finite width in action space, perturbations from subhaloes can shift a
star's actions beyond this width, causing them to circulate out of resonance. Physically, the dark substructure in the Milky Way may dissolve, puff-up, or re-order the resonance features in the
stellar halo. To explore the utility of this framework, we treat individual encounters in the impulse approximation and model their cumulative effect as
diffusion in the relevant action. The resulting
diffusion coefficient allows us to link the survival of resonant populations to the subhalo mass function, whose properties depend on the particle nature of dark matter. Test particle integration validates the impulse treatment for low-mass subhaloes and quantifies its regime of applicability. For a Milky Way-like bar, we find individual subhaloes with $M<10^7$ M$_{\odot}$ have negligible impact on
stars in co-rotation resonance, where as the full cold dark matter (CDM) population could erase the resonance over the bar's lifetime. The persistence of resonances therefore implies a suppression of the local subhalo density to less than 1/3 of CDM expectations, consistent with
tidal disruptions and previous literature. The narrow widths of higher-order resonances will increase the constraining power of this framework, and therefore motivates searches for bar-resonant
halo features in observational data.
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All authors Elliot Y. Davies, Adam M. Dillamore, Vasily Belokurov, Lina Necib
Earth and Planetary Astrophysics
NASA's Pandora SmallSat Mission: Simulated Modeling and Retrieval of Near-Infrared Exoplanet Transmission Spectra
Yoav Rotman, Peter McGill, Luis Welbanks et al. (+22 more)
Pandora is a SmallSat mission dedicated to understanding
exoplanets and their host
stars by disentangling the impact of
stellar heterogeneity on
exoplanet transmission spectra. Selected as a NASA Astrophysics Pioneers mission in 2021, Pandora will provide simultaneous long-term visible photometric monitoring (0.4–0.7 $\mu$m) and low-resolution near-infrared (NIR) spectroscopy (0.9–1.6 $\mu$m) of transiting systems for the purposes of monitoring host
star variability and characterizing exoplanetary atmospheres. Pandora's year-long
prime mission from 2026 to 2027 coincides with the middle of a decade defined by targeted efforts for atmospheric characterization of
exoplanets, offering a key opportunity to leverage this new resource to maximize science with JWST and other observatories. Here we investigate Pandora's anticipated performance for the general
exoplanet population accessible to transit spectroscopy, from hot Jupiters to temperate sub-Neptunes. By modeling the atmospheres of five test cases broadly consistent with the bulk properties of HD~209458~b, HD~189733~b, WASP-80~b, HAT-P-18~b, and K2-18~b, we find that Pandora may provide abundance constraints as precise as $\sim$1.0\,dex for main atmospheric absorbers such as H$_2$O and CH$_4$. Then, we explore the synergies between Pandora and JWST. Our results suggest that targets with JWST data in the near-infrared can benefit from the addition of Pandora observations and result in more reliable abundance estimates than with JWST data alone. Moreover, Pandora can serve the community by providing precursory observations of targets of interest for JWST atmospheric characterization. We conclude by outlining strategies for the use of Pandora as a standalone observatory and in synergy with JWST.
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All authors Yoav Rotman, Peter McGill, Luis Welbanks, Benjamin V. Rackham, Aishwarya Iyer, Daniel Apai, Michael R. Line, Elisa V. Quintana, Jessie L. Dotson, Knicole D. Colon, Thomas Barclay, Christina Hedges, Jason F. Rowe, Emily A. Gilbert, Brett M. Morris, Jessie L. Christiansen, Trevor O. Foote, Aylin Garcia Soto, Thomas P. Greene, Kelsey Hoffman, Benjamin J. Hord, Aurora Y. Kesseli, Veselin B. Kostov, Megan Weiner Mansfield, Lindsey S. Wiser
Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det
Experiments towards a neutron target for measurements in inverse kinematics
S.F. Dellmann, C.M. Harrington, O.R. Cantrell et al. (+28 more)
Neutron-induced reactions play an important role in fundamental
nuclear physics,
nuclear astrophysics, and applications. In the case of reactions on rare isotopes, there are limited options for direct experimental measurements. The
Neutron Target Demonstrator project at Los Alamos National Laboratory seeks to test the feasibility of moderating spallation
neutrons within a 1~m$^3$ graphite cube to create a standing
neutron target for
neutron-induced reaction measurements in inverse kinematics. This paper presents the results of experimental
neutron flux distribution tests using
neutron sources (ranging from 1~keV to 50~MeV) created by accelerators at the University of Notre Dame and Texas A&M University. Measurements were made with both the full graphite cube as well as a ”half cube” setup in which half of the graphite cube was removed. The measured distributions agree with simulated distributions in the case of the full cube moderator, although there remain discrepancies in certain cases for the half cube moderator. The results shown here will provide useful information for an upcoming experimental campaign to test the
neutron target proof-of-principle.
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All authors S.F. Dellmann, C.M. Harrington, O.R. Cantrell, A.L. Cooper, A. Couture, D.V. Gorelov, I. Knapová, S.M. Mosby, R. Reifarth, A. Alvarez, A. Aprahamian, J. Butz, I.J. Bos, M.T. Febbraro, T. Hankins, B.M. Harvey, T. Heftrich, M. Le, J.J. Manfredi, A.B. McIntosh, K.V. Manukyan, M. Matney, S. Regener, D. Robertson, A. Simon, D. Sokolovic, E. Stech, G. Tabacaru, W. Tan, M. Wiescher, S. Yennello
Cosmology and Nongalactic Astrophysics
Post-inflationary axion constraints from the Lyman-$\alpha$ forest
Olga Garcia-Gallego, Vid Iršič, Matteo Viel et al. (+2 more)
Among the most compelling cold dark matter candidates, the
axion has recently been subject to a wide range of astrophysical studies aiming to constraints its properties. We present updated bounds on the isocurvature fraction, $f_{\rm{iso}}$, which parameterizes the contribution of isocurvature perturbations induced by post-inflationary produced
axion-like particles (ALPs) to the ordinary power spectrum. We use new simulations based on the Sherwood-Relics suite to fit high-resolution Lyman-$\alpha$ forest flux power spectrum data. With the published noise model of the Lyman-$\alpha$ forest data, we find a tentative detection of $f_{\rm{iso}}$ = ${0.0064^{+0.0012}_{-0.0014}}$ (68% C.L), after accounting for the degenerate effect of IGM thermal
evolution. With a more conservative modelling of the residual noise in the data, the upper bound is weakened to $f_{\rm{iso}}< 0.0084$ (95% C.L), which translates into an ALP temperature-independent mass $m_a > 1.73 \times 10^{-18}$eV. Our constraints are stronger than bounds derived from large-scale structure probes at higher and lower
redshifts and are competitive with those derived from UV luminosity function data. Interestingly, the best current Lyman-$\alpha$ forest data prefers a non-zero contribution from isocurvature modes.
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All authors Olga Garcia-Gallego, Vid Iršič, Matteo Viel, Martin G. Haehnelt, James S. Bolton
Cosmology and Nongalactic Astrophysics
Exploring gas thermodynamics around galaxies from the Sunyaev-Zel'dovich effects: impact of galaxy-halo connection, 2D projection and velocity field
Sadaf Kadir, Bernardita Ried Guachalla, Sihan Yuan et al. (+2 more)
A complete picture of the gas thermodynamics around
galaxies is imprinted on the
cosmic microwave background (CMB). Indeed, the thermal, kinematic, and relativistic Sunyaev-Zel'dovich effects (tSZ, kSZ, rSZ) measure the gas density, temperature, pressure of baryonic feedback and bulk velocity around
galaxies, along with the gravitational potential it sits in. This full thermodynamic picture promises to constrain
galaxy formation models and gas related uncertainties in the impact on
galaxy lensing. Recent kSZ measurements around
galaxies suggest that the gas may be more extended than anticipated, pointing to powerful feedback processes and large baryonic corrections to
lensing. How robust are these conclusions about the
galaxy-
halo connection, including satellite fraction and high-mass outliers, or to 2D projection effects and large-scale velocity modes? In this paper, we give estimates for these effects using a simulated sample of DESI-like luminous red
galaxies within the IllustrisTNG hydrodynamical simulation and the Abacus N-body simulation. We show that analyzing projected 2D profiles can lead to biases when computing quantities like the gas fraction. We also find that in the absence of spatial filtering, the 2-
halo term is non-negligible for kSZ even at the smaller radii where the 1-
halo term dominates. We show that a 1% uncertainty in the satellite fraction of
galaxies can propagate into uncertainties of $\pm$1%, $\pm$3% and $\pm$5% in the 1-
halo terms of the kSZ, tSZ, and rSZ signals, respectively. We show that masking the 2% most massive objects in the sample reduces the profile amplitudes by up to 10%, 40%, and 75% for the kSZ, tSZ, and rSZ signals, respectively. Finally, we show that naive simulations of the kSZ effect can be biased by an artificial Doppler term, which is automatically removed when high-pass or compensated aperture filtering is applied.
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All authors Sadaf Kadir, Bernardita Ried Guachalla, Sihan Yuan, Emmanuel Schaan, Risa H. Wechsler
Instrumentation and Methods for Astrophysics
SELDON: Supernova Explosions Learned by Deep ODE Networks
Jiezhong Wu, Jack O'Brien, Jennifer Li et al. (+6 more)
The discovery rate of optical transients will explode to 10 million public alerts per night once the Vera C. Rubin Observatory's Legacy Survey of Space and Time comes online, overwhelming the traditional physics-based inference pipelines. A continuous-time
forecasting AI model is of interest because it can deliver millisecond-scale inference for thousands of objects per day, whereas legacy MCMC codes need hours per object. In this paper, we propose SELDON, a new continuous-time variational autoencoder for panels of sparse and irregularly time-sampled (gappy) astrophysical light curves that are nonstationary, heteroscedastic, and inherently dependent. SELDON combines a masked GRU-ODE encoder with a latent neural ODE propagator and an interpretable Gaussian-basis decoder. The encoder learns to summarize panels of imbalanced and correlated data even when only a handful of points are observed. The neural ODE then integrates this hidden state forward in continuous time, extrapolating to future unseen epochs. This extrapolated time series is further encoded by deep sets to a latent distribution that is decoded to a weighted sum of Gaussian basis functions, the parameters of which are physically meaningful. Such parameters (e.g., rise time, decay rate, peak flux) directly drive downstream prioritization of spectroscopic follow-up for astrophysical surveys. Beyond astronomy, the architecture of SELDON offers a generic recipe for interpretable and continuous-time sequence modeling in any time domain where data are multivariate, sparse, heteroscedastic, and irregularly spaced.
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All authors Jiezhong Wu, Jack O'Brien, Jennifer Li, M. S. Krafczyk, Ved G. Shah, Amanda R. Wasserman, Daniel W. Apley, Gautham Narayan, Noelle I. Samia
Solar and Stellar Astrophysics
Synthetic disk-integrated absorption lines isolating stellar granulation for high-precision RV studies
Ginger Frame, Heather Cegla, Cis Lagae et al. (+6 more)
We present a novel method for constructing high-accuracy, time-varying disk-integrated
stellar absorption line profiles that isolate the effects of granulation alone. This framework provides an effectively unlimited supply of physically consistent training data, offering a unique opportunity to study granulation-driven velocity variability with no contamination from other
stellar processes or instrumental systematics. Our interpolation scheme enables accurate profile generation at arbitrary limb angles and successfully reproduces observed disk integrated
solar bisector shapes from IAG spectra. Using four Fe I lines (525.0, 615.2, 617.3, and 627.1 nm), we produce 1000 model
star disk-integrated realisations per line and find an isolated granulation-induced RV scatter of 0.16-0.21 m s^-1. Using our synthetic profiles and assuming infinite signal-to-noise, we find strong correlations between various line-shape metrics and convective blueshift, demonstrating that line-shape diagnostics can, in principle, trace granulation effects. Equivalent width proves the strongest diagnostic, achieving up to 60% scatter reduction. However, the strength of all simple line shape diagnostics rapidly diminishes once
photon noise is injected. Even when artificially boosting the signal to represent a spectrum containing ~1000 spectral lines, the achievable improvement with these metrics remains below 10% at typical signal-to-noise ratios. Our results highlight the need for more robust, noise-resilient diagnostics and position our synthetic
dataset as a valuable testbed for developing and benchmarking such methods.
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All authors Ginger Frame, Heather Cegla, Cis Lagae, Veronika Witzke, Christopher Watson, Sergiy Shelyag, Vatsal Panwar, Michael Palumbo, Alexander Shapiro
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Non-Hermitian Quantum Mechanics with Applications to Gravity
Oem Trivedi, Alfredo Gurrola and Robert J. Scherrer
Hermiticity is usually treated as a foundational axiom of
quantum mechanics, guaranteeing real spectra and
unitary time
evolution. In this work we argue that Hermiticity is more naturally understood as a
symmetry law arising from the global conservation of an inner product current. We show that in spacetimes admitting complete Cauchy surfaces without boundary flux this conservation reduces to the familiar Hermiticity condition of the canonical inner product. However, in the presence of causal horizons, most strikingly in black hole geometries, this conservation law becomes obstructed for restricted observers. Tracing over inaccessible degrees of freedom then inevitably yields completely positive trace preserving dynamics with an effective non-Hermitian generator. Using
quantum thermodynamics and the monotonicity of relative
entropy, we demonstrate that the generalized second law may be reinterpreted as an
entropy balance that compensates precisely for the flux of inner product charge through the horizon. The structure of Einstein equations, through the Bianchi identity and the Raychaudhuri focusing equation, provides the
geometric mechanism underlying this balance. We also show that black hole ringdown can serve as a realistic observational probe of this idea and may provide quantitative upper bounds on the strength of horizon-induced inner product flux. In this way
gravity,
entropy production, and effective non-Hermiticity are unified under a single structural principle, with Hermiticity emerging as the special case of globally conserved inner product
symmetry.
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Solar and Stellar Astrophysics
Improved Stark Broadened Profiles for Neutral Helium Lines Using Computer Simulations
Patrick Tremblay, Alain Beauchamp, Pierre Bergeron et al. (+1 more)
The study of Stark broadening of neutral helium lines, despite significant advances over recent decades, has not led to updated large grids of helium line profiles relevant to the spectroscopic study of helium-rich
stars. While the semi-analytical approach based on the standard Stark broadening theory is efficient for generating such grids, it presents challenges in incorporating additional physical effects into the model. Motivated by recent studies that highlight potential issues with line profiles in the context of white
dwarf stars, this paper leverages advances in computer simulations to create a new grid of line profiles for 13 neutral helium lines in the optical range. These profiles cover densities ranging from 10^14 to 6 x 10^17 cm^-3 and temperatures from 10,000 K to 40,000 K, with the exception of the narrower He I 4713 line, for which the profile grid begins at 10^15.5 cm^-3. The primary goal of this research is to present the new grid and compare it with both the semi-analytical approach and other simulation results. By doing so, corrections to the previous grid will be explored, providing a foundation for future studies that utilize this updated grid. We also examine the impact of these new profiles on the determination of physical parameters for a range of astrophysical objects, including DB white
dwarfs and other helium-rich
stars.
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All authors Patrick Tremblay, Alain Beauchamp, Pierre Bergeron, Antoine Bédard
Astrophysics of Galaxies
A Selection Aware View of Black Hole-Galaxy Coevolution at High Redshift
Francesco Ziparo, Stefano Carniani, Simona Gallerani et al. (+1 more)
The large population of broad-line Active
Galactic Nuclei (AGN) observed with the James Webb Space
Telescope (JWST) at $z \gtrsim 4$ opens a new window onto the black hole-
galaxy connection in the first Gyr of
cosmic history. We use the JADES survey-level
dataset and develop a forward-modeling
Bayesian framework that explicitly accounts for broad H$\alpha$ detectability, ensuring that selection effects are incorporated into the likelihood function. With this approach, we constrain the black hole-
stellar mass ($M_{\mathrm{BH}}$-$M_\star$) relation to be $\log M_{\rm BH} = -4.06^{+0.50}_{-0.51} + 1.17^{+0.06}_{-0.06}\,\log M_\star$, with an intrinsic orthogonal scatter of $\sigma_{\rm int} = 0.63^{+0.14}_{-0.11}$ dex. The slope and normalization are consistent with local determinations, indicating that the average scaling was already established by $z \sim 4$-6. This suggests that the primary
evolution of the relation occurs in its dispersion rather than in its mean normalization. In contrast, the substantially larger intrinsic scatter relative to the nearby Universe reveals a wider diversity of black hole-
galaxy growth histories, likely driven by bursty
accretion, delayed feedback, and differences in merger or seeding histories. Future JWST samples will be crucial to test whether this increased scatter is a persistent feature of the high-
redshift Universe.
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All authors Francesco Ziparo, Stefano Carniani, Simona Gallerani, Bartolomeo Trefoloni
High Energy Astrophysical Phenomena
A Broker Integrated Algorithm for Gravitational Wave - Electromagnetic Counterpart Searches in O4a and O4b Runs
Hemanth Bommireddy, Francisco Forster, Isaac McMahon et al. (+6 more)
We present an automated framework to search for optical counterparts of LIGO-Virgo-KAGRA (LVK) gravitational wave (GW) superevents using public Zwicky Transient Facility (ZTF) alerts processed through the ALeRCE broker. The goal is to filter and identify optical transients potentially associated with binary black hole (BBH) mergers during the LVK O4a and O4b observing runs. Using the Automatic Learning for the Rapid Classification of Events (ALeRCE) infrastructure, we spatially query ZTF alerts within GW localization regions and apply machine learning classifiers, host-
galaxy crossmatching, and temporal cuts within 200 days post-merger to isolate plausible candidates. Our search yielded one candidate in O4a and four in O4b, several consistent with the
supernova or
tidal disruption event regime. This work demonstrates that public alert brokers can establish a robust baseline for systematic searches for electromagnetic counterparts to GW superevents in current and future observing runs. Our
algorithm provides a systematic approach to search for BBH counterparts for all significant LVK GW superevents using survey
telescope alerts. The search, together with the accompanying analysis, demonstrates the significance of the counterpart candidates, with one candidate ultimately identified as a transient event consistent with a Bowen fluorescence
flare in a now discarded active
galactic nucleus (AGN).
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All authors Hemanth Bommireddy, Francisco Forster, Isaac McMahon, Manuel Pavez Herrera, Regis Cartier, Felipe Olivares Estay, Lorena Hernández García, Mary Loli Martínez Aldama, Alejandra Muñoz Arancibia
Solar and Stellar Astrophysics
Hunting for methanol in the water rich, planet forming disk around HL Tau
Alessandro Soave, Margot Leemker, Stefano Facchini et al. (+3 more)
Methanol, the simplest complex organic molecule found in space, is considered a key compound necessary for the formation of chemical species of prebiotic interest. Methanol detections in protoplanetary disks remain scarce, even though it is frequently detected in the material surrounding other Young
Stellar Objects. We investigate the presence of methanol in the protoplanetary disk around the HL Tau protostar, motivated by the detection of spatially resolved warm water emission. Given the similar
volatility of methanol and water, thermally desorbed gas-phase methanol is expected to emit from the same region of the HL Tau disk where water vapour has been observed. Accordingly, we selected and imaged the most promising ALMA archival observations to search for rotational methanol lines. We found no methanol emission in the analysed archival
datasets. Assuming optically thin emission and LTE, we derive stringent upper limits on the methanol column density for different excitation temperatures: < 7.2 x 10^(14) cm^(-2) at 100 K and < 1.8 x 10^(15) cm^(-2) at 200 K, assuming a circular emitting region with a radius of 17 au (~ 0.12”). Furthermore, we obtain a stringent upper limit on the methanol-to-water column density ratio (< 0.55 x 10^(-3) at 100 K and < 1.4x 10^(-3) at 200 K), which is, on average, an order of magnitude lower than the values measured for other Young
Stellar Objects and
Solar System comets. We argue that the most likely explanation for the methanol non-detection in HL Tau is the presence of optically thick
dust in the central region of the disk, which obscures part of the methanol emission. The upper limit on the methanol-to-water ratio in the HL Tau disk is at least an order of magnitude smaller than most clouds, YSOs and comets, possibly due to radiative transfer and/or excitation effects, or due to a different chemical
evolution compared to the other sources.
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All authors Alessandro Soave, Margot Leemker, Stefano Facchini, Luke Maud, Kazi Lucie Jessica Rygl, Leonardo Testi
Solar and Stellar Astrophysics
Collective Vortex Dynamics: From Isolated Vortices to their Communities
Lauren McClure, Suzana Silva, Gary Verth et al. (+2 more)
Small-scale vortical motions in the upper
solar atmosphere are abundant and occupy about 2.8% of the photosphere at any given time. Although considerable work has focused on the detection and analysis of individual
solar vortices, the interconnected and multi-scale behaviour of these coherent structures remains largely unexplored. We present a methodology for studying this behaviour through
vortex interactions, to improve our understanding of how small- and large-scale photospheric flows contribute to energy transfer into the upper
solar atmosphere and to the driving of
solar activity. We represent
vortices as a network of interacting structures. We apply a community detection
algorithm to derive an optimal reduced network composed of highly interconnected
vortex groups. From the interaction patterns and group structure, we define three roles within each community: peripheral, connector and hub. We then track both
vortex communities and their member
vortices from the photosphere into the chromosphere and across their lifetimes. On average,
vortices assigned to these roles persist to greater heights in the chromosphere and have longer lifetimes than unclassified
vortices. This shows that community detection can identify
vortices with greater dynamical influence on the upper
solar atmosphere. We also find that 32% to 58.6% of
vortex communities exhibit global periodic behaviour following a helical path. This collective vortical motion may indicate an enhanced mechanism for wave excitation.
Solar vortical community detection, therefore, offers a new framework for studying
solar vortices and a new perspective on the importance of collective
vortex dynamics.
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All authors Lauren McClure, Suzana Silva, Gary Verth, Istvan Ballai, Viktor Fedun
Solar and Stellar Astrophysics
Near-infrared spectroscopy of RS Ophiuchi in 2021: the calm, the storm, and the abatement
C. E. Woodward, A. Evans, D. P. K. Banerjee et al. (+4 more)
We present near-infrared (NIR) observations of the 2021 eruption of the recurrent nova RS Ophiuchi. The
dataset provides both pre- and post-eruption perspectives on the eruption, as well as NIR spectra at high cadence. The spectrum obtained in 2020 June (14.3 years after the 2006 eruption, and 428.1 days before the 2021 eruption), is that of the red
giant secondary, on which are superimposed several emission lines which most likely arise in the red
giant wind. Spectra obtained during the eruption consist of emission (including coronal) lines, superimposed on a bremsstrahlung continuum at 8900K. The temperature of the coronal gas is estimated to be $10^{6.0}$K on day 11.7, and $10^{5.9}$K on day 31.7. The high cadence observations, obtained on day 31.7 of the eruption, provide no conclusive evidence for rapid ($<\sim1$~minute) variations in the HeI 1.0833$\,\mu$m line. Data obtained about one year after the eruption show that there may have been changes in the spectral type of the secondary after the 2021 eruption.
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All authors C. E. Woodward, A. Evans, D. P. K. Banerjee, B. Kaminsky, S. Starrfield, K. L. Page, R. M. Wagner
Cosmology and Nongalactic Astrophysics
DESI DR2 Baryon Acoustic Oscillations from the Lyman Alpha Forest Multipoles
N. G. Karaçayl{\i}, A. Cuceu, J. Aguilar et al. (+55 more)
We present an alternative measurement of the
Baryon Acoustic Oscillation (BAO) using the Legendre multipole representation of the Ly$\alpha$ forest correlation functions from the second data release (DR2) of the Dark Energy Spectroscopic Instrument survey. Compressing the auto- and cross-correlation functions into Legendre multipoles yields a positive-definite covariance
matrix without any smoothing – unlike the baseline DR2 analysis – thanks to a significantly reduced data vector size. We introduce the statistical corrections required to debias the finite-sample covariance
matrix estimate and demonstrate that monopole and quadrupole terms for both auto- and cross-correlations can be used even when the correlation functions are distorted by continuum errors and contaminated by metals. This formalism has slightly diminished the constraining power of the BAO scale, while considerably weakening constraints on nuisance parameters. We measure the isotropic BAO scale with $0.93\%$ precision at $z_\mathrm{eff}=2.35$, the Hubble parameter $H(z_\mathrm{eff})=(239.5\pm3.4)~(147.09~\mathrm{Mpc}/r_d) ~\mathrm{km~s}^{-1}~\text{Mpc}^{-1}$, and the transverse comoving distance $D_M(z_\mathrm{eff})=(5.80 \pm 0.10)~(r_d/147.09~\mathrm{Mpc})$~Gpc for a given value of the sound horizon ($r_d$). Our BAO results are entirely consistent with the baseline DR2 analysis.
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All authors N. G. Karaçayl{\i}, A. Cuceu, J. Aguilar, S. Ahlen, S. Bailey, S. BenZvi, D. Bianchi, A. Brodzeller, D. Brooks, T. Claybaugh, A. de la Macorra, Biprateep Dey, P. Doel, J. Estrada, S. Ferraro, A. Font-Ribera, J. E. Forero-Romero, E. Gaztañaga, S. Gontcho A Gontcho, A. X. Gonzalez-Morales, G. Gutierrez, C. Hahn, H. K. Herrera-Alcantar, K. Honscheid, C. Howlett, M. Ishak, R. Joyce, R. Kehoe, D. Kirkby, T. Kisner, A. Kremin, O. Lahav, M. Landriau, J.M. Le Goff, L. Le Guillou, M. E. Levi, M. Manera, P. Martini, A. Meisner, R. Miquel, J. Moustakas, A. Muñoz-Gutiérrez, S. Nadathur, N. Palanque-Delabrouille, W. J. Percival, F. Prada, I. Pérez-Ràfols, G. Rossi, E. Sanchez, D. Schlegel, M. Schubnell, H. Seo, J. Silber, D. Sprayberry, G. Tarlé, B. A. Weaver, R. Zhou, H. Zou
Cosmology and Nongalactic Astrophysics
Hierarchical cosmological constraints through strong lensing distance ratio
Shuaibo Geng, Shuo Cao, Marek Biesiada et al. (+3 more)
Strong gravitational
lensing provides an independent and powerful probe of
cosmic expansion by directly linking observables to cosmological distances. Upcoming surveys such as LSST will discover large number of
galaxy-
galaxy strong
lensing systems, offering a new route to precise cosmological constraints. In this paper, we propose a Fisher-like sensitivity factor to map how the cosmological information of strong-
lensing distances changes across the lens-source
redshift plane. Applying such factor to the distance ratio $D_{ls}/D_s$, the time-delay distance $D_{\Delta t}$, and the double-source-plane ratio, we determine the “sensitivity valleys” where an observable becomes insensitive to a given parameter. The realistically simulated LSST lens population, which largely lies outside the distance-ratio valleys, covers the most sensitive region for $(w_0,w_a)$ parameter space. We then develop a new hierarchical framework, which could calibrate the
redshift evolution of lens mass-density slopes and constrain cosmological parameters simultaneously. Focusing on the LSST mock data, we demonstrate that ignoring mass-profile
evolution can bias $\Omega_m$ by up to $\sim 10\sigma$, while modeling the lens
evolution could perfectly recovers the fiducial cosmology and yield stringent cosmological constraints (e.g., $\Delta\Omega_m \simeq 0.01$ and $\Delta w \simeq 0.1$ for $\sim 10^4$ lenses).
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All authors Shuaibo Geng, Shuo Cao, Marek Biesiada, Xinyue Jiang, Yalong Nan, Chenfa Zheng
Cosmology and Nongalactic Astrophysics
Joint tomographic measurement of thermal Sunyaev Zeldovich and the cosmic infrared background
Adrien La Posta, David Alonso, Carlos García-García et al. (+1 more)
We present a novel method for the tomographic reconstruction of the bias-weighted mean electron pressure $\langle bP_e \rangle$ and
star formation rate density $\langle b\rho_{\mathrm{SFR}} \rangle$, by simultaneously modelling the contribution from the thermal Sunyaev-Zel'dovich (tSZ) effect and the
Cosmic Infrared Background (CIB) to the cross-correlation between photometric
galaxy samples and multi-frequency
Cosmic Microwave Background (CMB) maps. The resulting measurements are independent of the
galaxy clustering properties and robust against cross-contamination between tSZ and CIB. Applying this method to publicly available data, we reconstruct the
cosmic evolution of $\langle bP_e \rangle$ and $\langle b\rho_{\mathrm{SFR}} \rangle$ out to $z\sim1$, making our measurements publicly available. Our measurements of both quantities are broadly compatible with predictions from the fiducial FLAMINGO hydrodynamical simulation, although we observe a lower gas pressure at low
redshifts, in agreement with other measurements.
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All authors Adrien La Posta, David Alonso, Carlos García-García, Sara Maleubre
Cosmology and Nongalactic Astrophysics
Wave-Optics Imprints of Dark Matter Subhalos on Strongly Lensed Gravitational Waves
Shin'ichiro Ando
Wave-optics effects in strongly lensed gravitational waves (GWs) provide a new interferometric probe of dark matter substructure. We compute the full diffraction integral for GWs propagating through statistically generated cold dark matter subhalo populations and quantify the resulting frequency-dependent amplification in the
Laser Interferometer Space
Antenna (LISA) band. We show that realistic
galaxy-scale lenses generically produce percent-level amplitude and phase distortions in strongly magnified images, primarily induced by subhalos in the mass range $10^4$-$10^7\,M_{\odot}$. These signatures arise naturally within the standard cold dark matter paradigm and should be detectable in high signal-to-noise LISA events. Strongly lensed GWs thus offer a direct and complementary window on dark matter structure at subgalactic mass scales inaccessible to electromagnetic measurements.
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Instrumentation and Methods for Astrophysics
Atmospheric effects on cosmic-ray muon rate at high latitude (78.9{\deg}N)
M. Abbrescia, C. Avanzini, L. Baldini et al. (+71 more)
Since 2019, three scintillator detectors of the EEE collaboration have been continuously measuring
cosmic muon rates at 78.9{\deg}N at the Ny-Ålesund Research Station (Svalbard). The resulting six-year time series reveals a pronounced annual modulation, driven primarily by seasonal atmospheric variations. Utilizing routine radiosonde profiles collected above the same site, we applied several established techniques –along with a tailored analysis approach– to investigate the relationship between
muon rate and atmospheric temperature. The temperature-corrected
muon-rates are analysed using the Lomb-Scargle periodogram technique in order to investigate the presence of remaining periodic structures. Finally, the temperature corrections coefficients of our analysis are compared with measurements in other stations located at lower latitudes.
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All authors M. Abbrescia, C. Avanzini, L. Baldini, R. Baldini Ferroli, G. Batignani, M. Battaglieri, S. Boi, E. Bossini, F. Carnesecchi, D. Cavazza, C. Cicalò, L. Cifarelli, F. Coccetti, E. Coccia, A. Corvaglia, A. De Caro, D. De Gruttola, S. De Pasquale, L. Galante, M. Garbini, L.E. Ghezzer, I. Gnesi, F. Gramegna, E. Gramstad, S. Grazzi, E.S. Haland, D. Hatzifotiadou, P. La Rocca, R. Liotino, Z. Liu, A. Lupi, G. Mandaglio, A. Margotti, G. Maron, M. N. Mazziotta, M. Mazzola, A. Mulliri, R. Nania, F. Noferini, F. Nozzoli, F. Ould-Saada, F. Palmonari, M. Panareo, M. P. Panetta, R. Paoletti, C. Pellegrino, L. Perasso, O. Pinazza, C. Pinto, S. Pisano, K. Piscicchia, L. Quaglia, M. Rasà, F. Riggi, G. Righini, C. Ripoli, M. Rizzi, B. Sabiu, G. Sartorelli, E. Scapparone, M. Schioppa, G. Scioli, A. Scribano, M. Selvi, A. Shtimermann, M. Taiuti, G. Terreni, A. Trifirò, M. Trimarchi, C. Vistoli, L. Votano, M. C. S. Williams, A. Zichichi, R. Zuyeuski
Solar and Stellar Astrophysics · Cross-listed from physics.plasm-ph
The self-generation of core fields and electron scattering in flux ropes during magnetic reconnection
Hanqing Ma, J. F. Drake and M. Swisdak
Two-dimensional particle-in-
cell simulations with a realistic mass ratio reveal the generation mechanisms of the out-of-plane
magnetic field in
magnetic islands/flux ropes during
magnetic reconnection. In the absence of an initial guide field, reconnection produces a large electron temperature anisotropy (around 4.5) inside
magnetic islands that drives the Weibel instability. Strong out-of-plane
magnetic fields (Bz/B0 around 0.4, greatly exceeding the
Hall field) with a regular bipolar structure grow inside islands. A space-time analysis reveals a one-to-one correspondence between the temperature anisotropy and the development of the Weibel
magnetic field. The instability relaxes the anisotropy, but island merging leads to anisotropy reemergence and re-excitation. In the presence of a strong ambient guide field (Bg/B0 = 0.5), the electron
outflow from the X-point deflects along the separatrices and forms a circular current loop wrapping the flux ropes. This flux-rope separatrix current generates an out-ofplane
magnetic field that reinforces the ambient guide field, reaching Bz/B0 around 1.4. The current can, in some cases, drive the electron Kelvin-Helmholtz instability, which produces electron
vortices and strengthens the
magnetic field. Mergers significantly broaden the islands and further strengthen the field. These self-generated out-of-plane
magnetic fields scatter electrons and reduce their temperature anisotropy, which can potentially affect electron heating via
Fermi reflection. The simulation results are supported by spacecraft observations suggesting that ambient guide fields can be enhanced within flux ropes in Earth's magnetotail.
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Astrophysics of Galaxies
Active Galactic Nuclei-driven Metallicity Enrichment in the Interstellar Medium of Mrk 573
D.Ł. Król, P. Zhu, G. Fabbiano et al. (+5 more)
We present the first spatially resolved at $\sim20$ pc scale application of AGN-specific
metallicity diagnostics for the nearby Compton-thick Seyfert 2
galaxy Mrk 573 ($z = 0.017$). We use Hubble Space
Telescope narrow-band imaging, MUSE integral-field spectroscopy and apply AGN strong-line
metallicity diagnostics based on [O III], [S II], H$\beta$, H$\alpha$, and [N II] emission lines. We construct maps of $12 + \log$(O/H) for two different
metallicity calibrations and two different N/O-O/H scaling relations out to $\sim1$ kpc and down to $\sim20$ pc scales. Our analysis reveals
metallicity enhancement in AGN-dominated regions, with oxygen abundances reaching up to few times
Solar. The
metallicity shows a patchy spatial distribution, varying on $\sim100$ pc scales, appears to trace the high Seyfert/LINER index (SLI) value regions and the VLA 6 cm jet/
radio lobe emission. These spatial correspondences and the lack of evidence for
star formation in the bicone region suggest that the enrichment originates from metals transported from the
nuclear AGN regions by winds,
outflows, or jets.
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All authors D.Ł. Król, P. Zhu, G. Fabbiano, M. Elvis, L.J. Kewley, N. Murray, R. Middei, A. Trindade-Falcão
Earth and Planetary Astrophysics
A Global High-Resolution Hydrological Model to Simulate the Dynamics of Surface Liquid Reservoirs: Application on Mars
Alexandre Gauvain, François Forget, Martin Turbet et al. (+3 more)
Surface runoff shapes planetary landscapes, but global hydrological models often lack the resolution and flexibility to simulate dynamic surface water bodies beyond Earth. Recent studies of Mars have revealed abundant geological and mineralogical evidence for past surface water, including valley networks, crater lakes, deltas and possible ocean margins dating from late Noachian to early Hesperian times. These features suggest that early Mars experienced periods allowing
liquid water stability, runoff and sediment transport. To investigate where surface water could accumulate and how it may have been redistributed, we developed a global high-resolution (km-scale) surface hydrological model. The model uses a pre-computed hydrological database that maps topographic depressions, their spillover points, hierarchical connections between basins, and lake volume-area-elevation relationships. This database approach greatly accelerates simulations by avoiding repeated geomorphic processing. The model dynamically forms, grows, merges and dries lakes and putative seas without prescribing fixed coastlines, by transferring water volumes between depressions according to their storage capacities and overflow rules. We explore model behavior over the present-day Mars' topography measured by MOLA (Mars Orbiter
Laser Altimeter) topography for a range of evaporation rates (from 0.1 m/yr to 10 m/yr) and total water inventories expressed as Global Equivalent Layer (from 1 mGEL to 1000 mGEL). 48 Simulations are iterated to reach the steady state. The model outputs the extent and depth of surface water bodies and identifies main drainage pathways using overflow fluxes as runoff indicators. Results show a transition toward a contiguous northern ocean between low (1-10 m) GEL values and increasing concentration of water in northern lowlands and major impact basins at higher GEL.
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All authors Alexandre Gauvain, François Forget, Martin Turbet, Jean-Baptiste Clément, Lucas Lange, Romain Vandemeulebrouck
Cosmology and Nongalactic Astrophysics
Excursion-set for Primordial Black Holes I: white noise and moving barrier
Pierre Auclair, Baptiste Blachier and Vincent Vennin
In the excursion-set formalism, the mass distribution of
primordial black holes (PBHs) is derived from the first-passage time of a random walk describing the density contrast as the coarse-graining scale varies. We address two recent concerns that have been raised about this approach. First, it was argued that the random walks are subject to colored (i.e. correlated over time) noise, making the first-passage-time problem cumbersome. We show that this arises from an incorrect separation of drift and noise when sampling on the Hubble-crossing surface: if
Fourier modes are uncorrelated, the noise is strictly white. Moreover, sampling along the Hubble-crossing surface precludes using the density dispersion as a time variable, explaining some pathologies. Sampling instead on a synchronous surface removes both issues. This requires solving a first-passage-time problem with a moving barrier, for which we provide an efficient numerical framework. Second, it was suggested that cloud-in-cloud (i.e. that large black holes may engulf smaller ones) is irrelevant for PBHs and that the excursion set is therefore not needed. While valid for widely separated scales, this statement fails for broad power spectra with enhanced continua of modes. We further show that Press-Schechter estimates neglecting boundary
evolution can break down even without cloud-in-cloud effects.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Non-minimally coupled loop quantum inflation with inverse-volume corrections
Rudranil Roy, Giovanni Otalora, Joel Saavedra et al. (+1 more)
We study slow-roll inflation driven by a scalar field non-minimally coupled to
gravity within the effective framework of Loop
Quantum Cosmology (LQC), including inverse-volume corrections. We consider two physically motivated classes of potentials, a
Higgs-like quartic potential $V\propto\phi^{4}$ and string-inspired fractional monomial potentials $V\propto\phi^{p}$ with $p<1$. Working at first order in the slow-roll expansion, we derive analytic expressions for the inflationary observables, namely the scalar spectral index $n_s$, the tensor-to-scalar ratio $r$, and the running $\alpha_s\equiv dn_s/d\ln k$, and then solve the corrected background dynamics numerically to obtain quantitative predictions. Confronting these results with current observational constraints from Planck 2018 and ACT DR6, we find that the model can lie within the allowed region of the $(n_s,r,\alpha_s)$ parameter space, including a mild preference for slightly larger $n_s$, as suggested by recent ground-based measurements. We also compute the probability of achieving sufficient slow-roll inflation in this setting. Although effective LQC replaces the initial singularity with a nonsingular
quantum bounce, the likelihood of a sufficiently long inflationary phase depends on the pre-inflationary dynamics and on the inflaton potential. Using the canonical Liouville measure on the effective phase space, we determine the fraction of post-bounce trajectories that yield sufficient inflation and find that the non-minimal coupling parameter $\xi$ substantially enlarges the phase-space volume of favorable initial conditions relative to the minimally coupled case, exhibiting an attractor-like enhancement that saturates at large $\xi$.
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All authors Rudranil Roy, Giovanni Otalora, Joel Saavedra, Salvatore Capozziello
Solar and Stellar Astrophysics
Alfvén wave propagation in the partially ionized lower solar atmosphere: a test of the single-fluid approximation
Roberto Soler
Alfvén waves are widely believed to play an important role in the transport of energy from the
solar photosphere to the corona through the partially ionized chromosphere. In previous work, the properties of torsional Alfvén waves were theoretically studied using a multi-fluid model. Here, we compare those multi-fluid results with those obtained using the single-fluid magnetohydrodynamic approximation, as a way to assess the performance of the latter in the context of Alfvénic waves in the lower
solar atmosphere. We consider a broadband photospheric driver that excites torsional Alfvén waves with frequencies ranging from 0.1 mHz to 300 mHz. These waves propagate upwards to the corona along a
magnetic flux tube expanding with height. For both models, we compare the energy flux, chromospheric reflection, transmission and absorption coefficients, and the associated heating rates. In general, the results are almost identical in the two models, with the exception of two minor differences: (1) the net energy flux reaching the corona is approximately 5% larger in the single-fluid model, mainly owing to the higher reflectivity found in the multi-fluid model for wave frequencies exceeding 10 mHz; and (2) in a narrow region around 500 km above the photosphere, the single-fluid model underestimates the
plasma heating rate due to ion-neutral damping by about a factor of two compared with the multi-fluid model. Both discrepancies arise from the approximate treatment of the ion-neutral drift in the single-fluid model and are expected to have a very limited impact on practical applications.
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