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Physics Astrophysics Astrophysics of Galaxies

astro-ph.GA Watch Astrophysics of Galaxies

Monday 7 September

Astrophysics of Galaxies

A new clump-based star formation model for galaxy simulations: implications for high-redshift compact star clusters

Shu Horie and Hidenobu Yajima

We develop a new star formation model for galaxy simulations in which star-forming gas clumps are identified on-the-fly and converted into stars with an efficiency $\epsilon_{\rm SF}$ set by the clump surface density $\Sigma_{\rm c}$, calibrated against radiation hydrodynamics simulations of star cluster formation. Applying this model to isolated disc galaxies embedded in haloes of $M_{\rm h}=10^{9}$, $10^{10}$ and $10^{11}\,\mathrm{M_\odot}$, with disc compactness corresponding to redshift $z=0$–$10$, we find that more compact discs form more massive and denser clumps. The maximum clump mass increases from $\sim 10^{5}$ to $\sim 10^{7}\,\mathrm{M_\odot}$, and the fraction of clumps exceeding the surface density of $300\,\mathrm{M_\odot\,pc^{-2}}$ rises from $0.25$ to $0.38$ between $z=0$ and $10$ in $10^{10}\,\mathrm{M_\odot}$ haloes. Star formation becomes correspondingly bursty, and the global star formation efficiency after three disc rotations increases from $5 \times 10^{-3}$ to $2 \times 10^{-1}$ in $10^{10}\,\mathrm{M_\odot}$ haloes and from $2 \times 10^{-2}$ to $4 \times 10^{-1}$ in $10^{11}\,\mathrm{M_\odot}$ haloes as the redshift increases from $z=0$ to $10$. The accompanying feedback disrupts the gas discs of the most compact systems, while prominent stellar spiral arms emerge. Self-gravitationally bound star clusters form only in compact discs. We find no bound star clusters at $z \leq 2$ in $10^{10}\,\mathrm{M_\odot}$ haloes, whereas the bound cluster mass fraction reaches $\approx 40$ per cent at $z \geq 8$ and $\approx 70$ per cent in the most compact $10^{11}\,\mathrm{M_\odot}$ halo. These fractions are broadly consistent with those inferred for high-$z$ clumpy galaxies observed by the James Webb Space Telescope.
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Astrophysics of Galaxies

ALMA Reveals an Explosive Outflow Candidate in IRAS 16119–5048

Yongquan Luo, Jianjun Zhou, Tie Liu et al. (+24 more)

We present a multiwavelength study of the massive star formation region IRAS 16119-5048 (I16119) using ALMA ATOMS Band 3 and QUARKS Band 6 observations, complemented by archival ATCA radio continuum and Spitzer mid-infrared data. The CO (2-1) emission reveals a system of high-velocity streamer-like structures around the central region. Using dendrogram analysis of velocity-channel maps followed by linking in position-position-velocity space, we identify 16 approximately radially distributed streamers whose projected trajectories converge toward a common central region. The kinetic energy of the outflows is at least an order of magnitude lower than those of most known explosive outflows, while their mass entrainment and momentum rates are high compared with typical protostellar outflows, suggesting that I16119 may represent a low-energy explosive outflow candidate. Dense-gas and photodissociation-region tracers reveal shell-like structures associated with the 8 $\mu$m emission, indicating that feedback from the H II region may influence the streamer morphology. The 1.3 mm continuum resolves 27 dense cores along a fragmented filamentary structure. Their separations are consistent with thermal Jeans or cylindrical fragmentation, while the collect-and-collapse scenario is unsupported. The dense cores also show evidence of mass segregation, with the most massive cores concentrated near the inferred explosive centre. We suggest that I16119 is a plausible low-energy explosive outflow candidate, possibly triggered by dynamical interactions among centrally concentrated massive cores. However, the complex velocity structure and possible contamination from individual core-driven outflows prevent a definitive classification. More sensitive, higher angular-resolution observations are required to confirm the nature of the outflow.
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All authors Yongquan Luo, Jianjun Zhou, Tie Liu, Jarken Esimbek, Siju Zhang, Xindi Tang, Sami Dib, Prasanta Gorai, Mika Juvela, Leonardo Bronfman, Patricio Sanhueza, Jihye Hwang, Fengwei Xu, Kee-Tae Kim, Guido Garay, Chang Won Lee, Tapas Baug, L. Viktor Tóth, Gang Wu, Dalei Li, Yuxin He, Yingxiu Ma, Dongdong Zhou, Toktarkhan Komesh, Weiguang Ji, Dezhao Meng, Jiasheng Li

Astrophysics of Galaxies

Irreducible-Mass Balance for Magnetized Null Horizons with an Internal Current Sheet

Remo Ruffini and Giorgio Sonnino

We begin with a general question: how does the irreducible mass of a magnetized black hole change when the horizon is not stationary? The null Raychaudhuri equation gives an exact area balance for any smooth null horizon, without assuming stationarity or axisymmetry. When the horizon is axisymmetric and admits an integrable quasilocal Hamiltonian, this geometrical identity becomes an energy balance. The equation keeps area growth, rotational and electromagnetic work, nonstationary focusing, canonical-flux corrections, and internal-boundary terms separate. We then turn to Wang's self-gravitating split-monopole Blandford-Znajek engine. In the weak-field and slow-rotation regime, P/M_H\ll1 and a/M_H\ll1, our general balance reproduces Wang's mass- and angular-momentum loss rates. The irreducible mass, M_{irr}=\sqrt{A_H/(16\pi)}, reveals what those rates do not show by themselves. It measures the part of the rotational work absorbed irreversibly by the horizon. At fixed magnetic flux and under impedance matching, half of the instantaneous rotational work leaves as electromagnetic power. The other half increases the horizon area and M_{irr}. The assumptions behind this reduction are derived explicitly. A minimal nondissipative world-volume action makes the current-sheet contribution vanish through O(p^2\epsilon^2). Direct power counting of Wang's perturbative fields, together with a compatible canonical-flux prescription, gives a relative focusing and canonical correction of O(p^2)+O(\epsilon^2). These estimates mark the range in which the reduced Blandford-Znajek trajectory remains controlled. Extending that trajectory to high spin requires an additional extrapolation. Relating the quasilocal horizon loss to energy measured at infinity requires a separate asymptotic flux calculation.
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Astrophysics of Galaxies · Cross-listed from astro-ph.SR

An Eccentric Massive Protobinary Assembled via a Core-merger Parabolic Encounter

Yao Wang, Yichen Zhang, Rubén Fedriani et al. (+14 more)

Most massive stars form in binary systems, which profoundly influence their subsequent evolution. However, how such systems form remains poorly understood, with several competing scenarios proposed, including disk fragmentation, core fragmentation and capture. Determining the orbital architectures of massive binaries, particularly during their earliest embedded phases, is therefore crucial for distinguishing among these formation pathways, but direct measurements of their three-dimensional motions have remained exceptionally challenging. Here we present high-resolution, multi-epoch sub-millimeter-to-centimeter ALMA and JVLA observations of the massive protobinary IRAS 07299$-$1651, complemented by JWST and VLT infrared imaging. We detect orbital proper motion of the binary components, enabling a full three-dimensional orbital reconstruction. Combining orbital fitting, multi-wavelength continuum modelling, hydrogen recombination line kinematics and jet observations, we find that the preferred orbital solutions are highly eccentric and close to parabolic, while both circumstellar disks are strongly misaligned with the orbital plane. These properties are naturally explained by a “core-merger” scenario in which the two protostars originated independently from initially unbound cores that recently underwent a near-parabolic encounter, producing an eccentric binary with a current separation of about 200 au. These findings suggest that the core-merger process may represent an important pathway for forming eccentric massive binaries.
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All authors Yao Wang, Yichen Zhang, Rubén Fedriani, Kei E. I. Tanaka, Viviana Rosero, Kai Yang, Morten Andersen, Maria T. Beltrán, Mélisse Bonfand, Yu Cheng, James M. De Buizer, Yihuan Di, Guido Garay, Prasanta Gorai, Zhi-Yun Li, Yao-Lun Yang, Jonathan C. Tan

Astrophysics of Galaxies

Recovering the characteristic halo mass of rare populations from clustering: a benchmark using the Millennium Simulation

Amrita Banerjee and Darren Croton

We measure how accurately the characteristic halo mass of a rare, massive population can be recovered from clustering alone, using dark matter haloes in the Millennium simulation, where the true masses are known. Massive samples of 25 to 10000 haloes are cross-correlated against field reference samples of 5000 to 50000 haloes at six redshifts over $0 \leq z \leq 5.29$. The bias is measured at $r = 8\,h^{-1}\,\mathrm{Mpc}$ and inverted to return a characteristic mass, which we compare with the mean logarithmic halo mass measured directly from the simulation. Across 192 configurations the characteristic mass is recovered with a median absolute offset of $0.103$ dex. We show that (i) accuracy depends only weakly on the number of rare objects while the uncertainty falls from $\pm 0.71$ dex at 25 objects to $\pm 0.08$ dex at 10000; (ii) enlarging the smallest samples gives the greatest return, with a doubling from 25 to 50 objects reducing the uncertainty by about a third, against a tenth from 5000 to 10000; and (iii) the reference population carries an error of its own, which propagates coherently into every cross-correlation measured against it and is not reduced by observing more rare objects. Working with haloes rather than galaxies isolates the clustering measurement from the galaxy–halo connection, providing a benchmark before population-specific complications are introduced. For the best configurations, the uncertainty contributed by the calibration of the bias–mass relation, at $\sim 0.07$ dex, already matches that of the measurement itself.
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Astrophysics of Galaxies

Between Little Red Dots and Star-Forming Galaxies: A Sequence in the Optical Continuum Slope

Kristiphong Boonmee, Akio K. Inoue, Masafusa Onoue et al. (+1 more)

The "Little Red Dots" (LRDs) uncovered by JWST are typically analyzed as a distinct class of objects; however, whether they are separated from ordinary star-forming galaxies by a genuine boundary has not been tested at the population level. Using a sample of $\sim3,500$ galaxies at $3 \lesssim z \lesssim 8$ with NIRSpec/PRISM spectra from the DAWN JWST Archive, we modeled their rest-frame UV-to-optical continuum emission with power laws and located the sources in the $\beta_{\rm{UV}}$-$\beta_{\rm{opt}}$ plane. Alongside a dense locus of star-forming galaxies and a diagonal sequence which can be explained by dust reddening and/or quiescence, we identify a vertical sequence extending from the locus of star-forming galaxies into the LRD region. This sequence is smoothly and continuously populated, with no clear boundary between the two populations. Its middle section, $-1 \lesssim \beta_{\rm{opt}} \lesssim 0$, hosts an intermediate population of $\sim50$ sources that falls outside the LRD selection boundary and has been largely overlooked; NIRCam imaging shows their rest-frame UV and optical median stacked images lie between point-like LRDs and extended star-forming galaxies. We modeled the vertical sequence as linear mixtures of stacked star-forming spectra and a black hole star (BH*) template derived from "The Cliff", one of the most compelling BH* candidates, and we infer black hole-to-stellar mass ratios $\eta = M_{\rm{BH}}/M_* \approx 0.006-0.1$ at the LRD end. We propose $-1 \lesssim \beta_{\rm{opt}} \lesssim 0$ as a practical selection window for possible transition candidates and argue that LRDs may be the compact, BH*-dominated extreme of a continuous population in which the relative contributions of the host and BH* vary smoothly.
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All authors Kristiphong Boonmee, Akio K. Inoue, Masafusa Onoue, Xingyao Cai

Astrophysics of Galaxies

Catching Up with the Fastest Star in the Galaxy: A Two-Passage GRAVITY+ Campaign to Detect S301's Schwarzschild Precession

Joseph Catanzarite

S301 is the fastest known star in the Galaxy. It orbits Sgr A* every 8.68 yr on an e = 0.9832 orbit that carries it within 136 Schwarzschild radii at 25,600 km/s (GRAVITY Collaboration 2026). An orbit like that must precess, by the same Schwarzschild effect that turns Mercury's perihelion, whatever the spin of the black hole. We ask whether an astrometry-only GRAVITY+ campaign covering the 2031.8 and 2040.5 periapsis passages can catch it. We validate a relativistic light-curve model, design a 131-epoch Fisher-optimal cadence with a periapsis floor, fit a seven-parameter orbit including the light-travel-time delay, and build a systematic error budget. With white noise at the 207 microarcseconds achieved on S301, the fit recovers the injected rate, 0.2307 deg/yr, as 0.2324 +/- 0.0023 deg/yr (+/-0.0012 at the forecast 100 microarcseconds). Real astrometric noise is not white. We add per-run calibration offsets and a wandering Sgr A* photocentre at GRAVITY's published amplitudes, marginalize over the reference zero point, mass and distance, add the bounded systematics in quadrature, and inflate by the excess scatter of real GRAVITY orbit fits. What survives is 0.0074 deg/yr, a 31 sigma detection. The Sun hides the first periapsis for 153 d, at a cost to the period and periapsis epoch but not to the precession rate. Radial velocities are out of reach at S301's magnitude; photometry only validates the light-curve model. The spin of Sgr A* could shift the rate by 5.17-5.74 per cent and cannot be bounded, so the campaign is a spin-agnostic test of general relativity, and a forecast until the star comes round.
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Astrophysics of Galaxies · Cross-listed from astro-ph.CO

Little Red Dot Cosmology: A Matter-Era Baryon Acoustic Oscillations Probe of $\Lambda$CDM

Jessica A. Zebrowski and Rohan P. Naidu

The discovery of Little Red Dots (LRDs) with JWST provides a new source population for cosmology in a largely unmapped period of cosmic history. LRDs are most numerous at $4\lesssim z\lesssim9$, thereby bridging existing low-redshift large-scale-structure measurements and the cosmic microwave background. In this epoch, the Universe is deep in the matter-dominated era, where dark energy is dynamically negligible and the expansion history is tightly predicted in $\Lambda$CDM, making these redshifts a clean test of the standard cosmological model. Recent measurements indicate that LRDs have number densities of $\bar n\sim10^{-4}$ $h^3$ Mpc$^{-3}$, a bias rising from $b\sim 3$ to $\sim8$ over this interval, and distinctive spectrophotometric signatures – a remarkably favorable combination for baryon acoustic oscillation (BAO) measurements. Using a Fisher forecast with these fiducial inputs, we find that a wide-field spectroscopic survey of LRDs over a DESI-like (14,000 deg$^2$) footprint delivers a percent-level isotropic distance scale measurement of $D_V/r_d$ across four bins spanning $4\lesssim z\lesssim9$. LRDs are therefore a compelling target for future wide-field near- to mid-infrared spectroscopy aimed at mapping large-scale structure deep into the matter-dominated era.
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Astrophysics of Galaxies

A Unified Magnetohydrodynamic Scaling Relation for the Multiphase Interstellar Medium

Mengke Zhao, Guang-Xing Li and Keping Qiu

The interplay of magnetic fields, turbulence, and gravity governs the structural evolution of the interstellar medium (ISM) and the initial conditions of star formation, yet observational gaps have long enforced a broken power-law description of the magnetic field–density relation. Here we assemble a unified dataset spanning ten orders of magnitude in density ($10^{-26}$–$10^{-16}\,\mathrm{g\,cm^{-3}}$) by combining pulsar and Zeeman observations. The unified data are consistent with a continuous magnetic-field evolution organised by the Alfvén Mach number $\mathcal{M}_{\rm A}=\sqrt{E_K/E_B}$. Within this interpretation, the low-density gas is magnetically dominated ($\mathcal{M}_{\rm A}<1$), whereas the high-density gas becomes kinetically dominated ($\mathcal{M}_{\rm A}>1$) as gravity increasingly contributes to the kinetic-energy budget, with magnetic tension continuing to influence the collapse geometry. Within the Gradual Transition interpretation, the empirical break density traces the vicinity of the trans-Alfvénic equipartition point, $\mathcal{M}_{\rm A}=1$. This Gradual Transition model makes three predictions tested here. Its exponent and background field are fixed in advance by turbulent physics and recovered by the fits ($\beta\approx0.15$–$0.21$ against a predicted $0.147$; $B_c\approx2.0\,\mu$G). A dense-gas fit, extrapolated blindly across four decades, passes through the diffuse pulsar data. And, under the adopted scale mappings, the implied magnetic-energy spectrum approaches a $k^{-5/3}$-like scaling on large scales and departs from this extrapolation on small scales, where gravitational compression amplifies the field. The broken power law can therefore be viewed as a piecewise approximation to the continuous magnetic equation of state, with its fitted transition density potentially retaining a physical connection to the onset of gravity-driven motions.
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Sunday 6 September

Astrophysics of Galaxies · Cross-listed from astro-ph.SR

Elusive helium stars in the gap between subdwarfs and Wolf-Rayet stars III. Formation of the Galactic population of stripped helium stars

L.R. Yungelson, A.G. Kuranov and A.V. Mishakina

Population synthesis based on the grid of pre-computed evolutionary sequences for close binaries is applied to the problem of formation of the Galactic population of stripped helium stars, the remnants of $5 \lessapprox M/M_\odot \lessapprox 24$ primary components of close binaries after RLOF. Stellar rotation is taken into account. For the current star formation rate in the Galaxy $2\,M_\odot yr^{-1}$, the estimate of the number of 1 to $7\,M_\odot$ objects with $T_{eff} \gtrapprox $25000K ranges from 14700 to 28500, while for the number of objects with masses from $2\,M_\odot$ to $7\,M_\odot$ it is 3200 to 5500, depending on the assumptions about formation of common envelopes and their outcomes. Other factors influencing the estimate are adopted star formation rate, distributions of close binaries over initial masses of primary components, mass ratios of components, orbital periods. Observational selection may severely limit the number of detectable objects. Angular velocities of rotation of companions to stripped helium stars are 60 to 80 per cent of the critical one. Using the models of initially homogeneous helium stars as approximations for the remnants after mass loss results in the underestimate of pre-supernovae masses.
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Astrophysics of Galaxies

Fractional Bose-Einstein Condensate Dark Matter Cores: Numerical GPP Solutions and SPARC Rotation Curves

Akila Labadi, Mohamed Benarous and Ahmed Hocine

We investigate a fractional Bose Einstein condensate dark matter scenario in which an ultralight bosonic component forms a self gravitating core embedded in a predominantly cold dark matter halo. The stationary GPP system solved numerically beyond the TF approximation leads to energetically bound equilibrium configurations and good phenomenological fits to the selected rotation curves from 30 SPARC galaxies.
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Astrophysics of Galaxies · Cross-listed from astro-ph.EP

Calibration of CNEOS Fireball Velocities and the Robustness of Nominally Hyperbolic Events

Volkan Duran and Abraham Loeb

The NASA/JPL CNEOS Fireball Data catalogue provides a near-global record of bright atmospheric entries but does not report per-event velocity covariance. We calibrate its kinematic accuracy using 19 events with independent reference trajectories and use optical, satellite, radar, and infrasound catalogues as source-specific controls. For nine modern high-quality comparisons, the CNEOS-minus-reference speed residual has mean -1.00 km s$^{-1}$ and standard deviation 0.86 km s$^{-1}$; variance decomposition assigns 0.77 km s$^{-1}$ to the CNEOS component. The radiant residuals have a 0.74 degree per-axis core plus one 16.3 degree outlier, so the extreme tail remains poorly determined. Seven of 354 complete CNEOS states are nominally hyperbolic without correction. A +0.9935 km s$^{-1}$ atmospheric-stage shift produces five additional crossings, but these are treated only as sensitivity cases. Polar-IM (2026 April 1) is the strongest post-2018 CNEOS anomaly, whereas independent GLM-LI stereo solutions yield 57.3 +/- 2.0 and 56.7 +/- 3.0 km s$^{-1}$, close to their direction-specific parabolic thresholds. We conclude that CNEOS can identify priority candidates, but secure interstellar classification requires an independent, uncertainty-bearing three-dimensional trajectory for the same event.
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Astrophysics of Galaxies

ADF22-WEB: Massive galaxy formation shaped by cosmic web filaments in the z = 3.1 proto-cluster core

Hideki Umehata, Ian Smail, Charles C. Steidel et al. (+7 more)

We present a census of dust, molecular gas, and galaxy structure in 18 dusty star-forming galaxies (DSFGs) at $z=3.09$ embedded in Ly$\alpha$-traced cosmic web filaments in the core of the SSA22 proto-cluster, using multi-band ALMA, JWST imaging, and JVLA CO(1–0). Using up to six ALMA bands and Herschel/SPIRE data, we construct rest-frame far-infrared spectral energy distributions. The DSFGs span two orders of magnitude in far-infrared luminosity ($L_{\rm FIR}\sim10^{11}$–$10^{13}L_\odot$), with median values of $\log(L_{\rm FIR}/L_\odot)=11.56^{+0.32}_{-0.37}$ and $T_{\rm dust}=25^{+6}_{-3}{\rm K}$. For eight DSFGs with high-resolution ($\sim1$ kpc) JWST and ALMA imaging, we measure stellar and dust surface densities and find a positive correlation, suggesting that structural compaction of the stellar component proceeds together with that of the interstellar medium. We report 12 detections of CO(1–0), 18 of CO(3–2), four each of CO(8–7) and CO(9–8), and one of CO(12–11). The median brightness temperature ratio between CO(3–2) and CO(1–0) is $r_{31}=0.66^{+0.05}_{-0.04}$, consistent with field galaxies at similar redshifts. The high-$J$ CO lines show relatively low excitation, and the CO(8–7)/CO(3–2) ratio correlates with star-formation rate surface density, suggesting that molecular gas excitation is primarily regulated by star formation. Lower-mass galaxies show excess molecular gas fractions and depletion times relative to field scaling relations. By combining quiescent galaxy samples in the same field, we identify a sequence from gas-rich systems with low stellar surface density to gas-poor, compact systems with high stellar surface density. These results suggest that massive galaxy evolution in dense environments is governed by a baryon cycle linking gas supply, star formation, and structural transformation within the cosmic web environment.
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All authors Hideki Umehata, Ian Smail, Charles C. Steidel, Bret D. Lehmer, Kouichiro Nakanishi, Bunyo Hatsukade, Mariko Kubo, Norika Okauchi, Yoichi Tamura, Masato Hagimoto

Astrophysics of Galaxies · Cross-listed from astro-ph.HE

Chandra X-ray imaging and IC/CMB model for the inner jet of PKS 0637-752

Jaya Maithil, Daniel A. Schwartz, Aneta Siemiginowska et al. (+2 more)

We present the X-ray surface brightness maps of the jet from the quasar PKS 0637-752, using two epochs of archival Chandra observations (1999 and 2017). We present, for the first time, a model of the faint inner jet extending from 3.4 to 7 arcsec from the core, interpreting its X-ray emission as inverse Compton scattering of cosmic microwave background photons by the synchrotron-emitting relativistic electrons. The inner jet contrasts with the bright outer part of the jet, dominated by several discrete knots for which upper limits to the Fermi gamma-ray flux rule out the inverse Compton mechanism. It is the first detailed inverse Compton model published for this inner jet. We examine three physically motivated scenarios, distinguished by the high-energy cutoff of the electron distribution, that can account for the observed radio, millimeter/submillimeter, and X-ray emission while remaining consistent with optical and gamma-ray upper limits. We also report for the first time X-rays from the radio lobe at the end of the receding jet.
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All authors Jaya Maithil, Daniel A. Schwartz, Aneta Siemiginowska, Diana M. Worrall, Preeti Kharb

Astrophysics of Galaxies

A Direct DESI–SDSS Two-Fibre Test of Aperture Bias in Optical Emission-Line Diagnostics

Shihong Liu and Yu Rong

Fixed angular apertures sample different physical regions of nearby galaxies and can therefore bias optical emission-line diagnostics. We use 20,545 high-confidence emission-line galaxies observed by both the Dark Energy Spectroscopic Instrument (DESI) and the Sloan Digital Sky Survey (SDSS) as a two-fibre experiment, in which the DESI 1.5 arcsec fibre is nested within the SDSS 3 arcsec fibre. To isolate aperture effects from line-measurement systematics, we refit every spectrum using the same eMILES stellar-continuum and emission-line model while preserving the wavelength-dependent line-spread function of each spectrum. This common refit yields 20,200 quality-controlled matched galaxies. Relative to SDSS, the smaller DESI aperture produces small but highly significant offsets: $\Delta\log({\rm N2})=+0.0067\pm0.0002$, $\Delta\log({\rm S2})=-0.0148\pm0.0003$, $\Delta\log({\rm O3})=-0.0246\pm0.0006$, $\Delta{\rm O3N2}=-0.0327\pm0.0007$, and $\Delta\log({\rm H}\alpha/{\rm H}\beta)=-0.0195\pm0.0003$, where $\Delta$ denotes DESI minus SDSS. These offsets persist in Baldwin–Phillips–Terlevich-selected star-forming galaxies and in a near-concentric subset. Their amplitudes vary across the redshift distribution and retain a measurable dependence on apparent fibre coverage after redshift is controlled, showing that redshift and relative aperture coverage jointly modulate the aperture terms. We conclude that, for high-S/N emission-line galaxies, DESI–SDSS comparisons carry measurable, diagnostic-dependent fibre-aperture terms even when continuum modelling, emission-line fitting, and spectral-resolution treatment are held fixed.
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Astrophysics of Galaxies · Cross-listed from astro-ph.IM

DustRover: A Python Package for Modelling Dust Extinction Curves (Phase I)

Amir E. Bazkiaei, Tayyaba Zafar, Nuria P. F. Lorente et al. (+2 more)

We introduce DustRover, an open-source Python package designed to model dust extinction curves using multi-wavelength regimes. DustRover supports optical/infrared spectroscopy, broadband photometry, and X-ray data within a unified framework, enabling robust analysis of dust extinction curves in distant galaxies. The software features a modular architecture that strictly decouples data management, dust models, and Markov Chain Monte Carlo (MCMC) based statistical fitting. The package is highly user-oriented, using simple YAML configuration files and offering built-in visualisation tools for SEDs and extinction curves.
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All authors Amir E. Bazkiaei, Tayyaba Zafar, Nuria P. F. Lorente, Anilkumar Mailvaganam, Arihant Raidani

Astrophysics of Galaxies · Cross-listed from astro-ph.IM

PERRY: A Human-in-the-Loop GUI for Precision Alignment of MUSE Data

Amir E. Bazkiaei, Brent Miszalski, Jesse van de Sande et al. (+3 more)

The Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope produces high-dimensional data-cubes where even minor astrometric misalignments between multiple exposures can introduce severe artifacts and compromise data quality. While automated pipelines provide a crucial baseline, subtle offsets require human intervention. To address this, we introduce PERRY, an interactive, Python-based Graphical User Interface (GUI) explicitly designed for the visual inspection and manual fine-tuning of MUSE image alignments. Playing an essential role of finding manual offset adjustments for data-cubes within the Pythonic AAO Reduction Environment (PARE), PERRY ingests automatically pre-aligned data, provides synchronized visual and quantitative diagnostics, and enables real-time coordinate translation and rotation updates. The resulting precise adjustments are preserved in reproducible configuration files, maximizing the scientific return and efficiency of advanced data reduction pipelines.
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All authors Amir E. Bazkiaei, Brent Miszalski, Jesse van de Sande, Nuria P. F. Lorente, Simon O'Toole, Kate Sheng

Astrophysics of Galaxies

Deep learning from the crowd Fundamentals of morphological galaxy classification

Luis Enrique Sucar, Carlos del Burgo and Jonathan Serrano-Pérez

Aims. The objective of this work is to adapt a deep neural network model to perform galaxy morphological classification trained from crowd annotations, considering the training scheme, the agreement between the annotators, and the hierarchy. Methods. We use Galaxy Zoo 1 as our experimental testbed and trained a convolutional neural network (CNN) for the automatic classification of galaxies' morphologies. We analyze the impact of the following aspects on the classification accuracy and training efficiency: (i) Training only the last layer vs. training all the network; (ii) Classification with only the CNN vs. considering the hierarchy; (iii) Comparing the models trained with different amounts of data and levels of agreement between the annotators; (iv) Training by stages, transferring knowledge from one model to another; and (v) Combining several models as an ensemble. Results From the experiments, we derive the following results: (i) Training all the layers in the network significantly improves the accuracy (10% increase in exact match), compared to training only the last layer; (ii) There is a tradeoff between the amount of data and the level of agreement between the annotators used for training; (iii) Using the hierarchy can improve accuracy when the amount of training data is reduced; (iv) Training by stages through transfer learning (curriculum learning) produces higher accuracy for limited data; (v) Ensembles can improve accuracy; (vi) Models achieve a low accuracy for the most difficult cases, but, if we consider hierarchical measures, we can derive useful results for upper levels in the hierarchy. An accuracy above 99% is achieved when training all layers of the network and considering a high agreement between the annotators. Conclusions. Training deep learning models from crowd annotations involves additional challenges than learning from hard annotations.
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Saturday 5 September

Astrophysics of Galaxies

Interstellar Complex Organic Molecules and Molecular Outflows in NGC 1333 IRAS 4B and 4B' Observed Using NOEMA

C. C. Sarver, M. M. Giese, D. C. Lis et al. (+1 more)

We present interferometric observations with the Northern Extended Millimeter Array (NOEMA) of NGC 1333 IRAS 4B and 4B', two young stellar objects (YSOs) within the Perseus molecular cloud. YSOs, especially Class 0 protostars, are rich in gas-phase interstellar complex organic molecules (iCOMs), but relatively little is known about the spatial distribution of these important prebiotic molecules. Various molecules were imaged within IRAS 4B and the surrounding area in the 145 GHz spectral range, revealing hundreds of molecular transitions within the warm inner envelope of IRAS 4B. This work provides derived physical parameters (rotational temperature, column density, velocity shift with respect to local standard of rest, and full-width at half-maximum spectral line width) for 11 molecules toward IRAS 4B including methanol (CH$_3$OH and isotopologues), methyl formate (HCOOCH$_3$), dimethyl ether (CH$_3$OCH$_3$), acetaldehyde (CH$_3$CHO), ethanol (C$_2$H$_5$OH), glycolaldehyde (CH$_2$OHCHO), acetone (CH$_3$COCH$_3$), and isocyanic acid (HNCO). Out of these molecules, 10 are iCOMs (excluding HNCO) that trace the inner envelope of IRAS 4B and mark it as a rich source of organic material. There is a strong spatial correlation between the continuum emission of IRAS 4B and iCOM molecular emission and among various iCOMs with each other. Physical parameter and integrated intensity maps show that IRAS 4B is a binary protostar system that drives a jet in a north-south orientation and an outflow in a northwest-southeast orientation. IRAS 4B' also drives a west-east outflow but shows no evidence of molecular emission cospatial with its continuum emission.
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All authors C. C. Sarver, M. M. Giese, D. C. Lis, S. L. Widicus Weaver

Astrophysics of Galaxies

Connecting the little dots in polarized light

Piero Madau, Roberto Maiolino and Francesco D'Eugenio

Recent observations of the local Little Red Dot (LRD) analog SDSS~J1025+1402 have revealed that the optical continuum is polarized at the ~1.5% level, while broad Halpha has lower polarization (~0.7%) and a different polarization angle. We explain these properties in a scenario in which LRDs are dust-obscured Little Blue Dots (LBDs) viewed at high inclination and powered by super-Eddington accretion. In this framework, electron scattering in the geometrically thick inner accretion flow produces intrinsic continuum polarization, while unpolarized emission from the outer thin disk dilutes the signal, particularly at optical wavelengths. A circumnuclear dust screen contributes dichroic polarization to both the continuum and broad-line emission. Broad Halpha lacks the intrinsic disk component and therefore has lower polarization and a different position angle. We show that this model quantitatively reproduces the observed polarization properties, although degeneracies between accretion rate and inclination remain. These results illustrate the potential of spectropolarimetry as a probe of accretion-flow geometry and orientation in the little-dot population, complementary to spectral-energy-distribution fitting and line diagnostics.
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Astrophysics of Galaxies · Cross-listed from astro-ph.EP

Shaving the Outskirts of Planetary Systems Probed by Roman via Stellar Flybys

Donald Liveoak, Tim Hallatt and Sarah Millholland

The recently launched Nancy Grace Roman Space Telescope (Roman) will soon begin observations that promise to revolutionize our understanding of exoplanet demographics. Roman's Galactic Bulge Time-Domain Survey (GBTDS) will observe the Galactic Bulge via transit and microlensing techniques, providing a unique opportunity to study hot Jupiters as well as long-period/free-floating exoplanets in a dense and kinematically hot stellar environment. In this Letter, we quantify how repeated, impulsive stellar flybys truncate the outskirts of planetary systems in the Bulge. We find that flybys result in ejections on $\sim$Gyr timescales for wide orbits (${\gtrsim} 250\ \text{au}$) around low-mass hosts. Provided these wide orbits are populated, these ejections likely contribute to the population of free-floating planets probed by Roman. Surviving planets outside of ${\sim} 10$ au are placed on eccentric and misaligned orbits. We show that, though systems suffer many close encounters, the evolution is dominated by the single strongest perturbation; planetary orbits (even those that evade ejection) undergo superdiffusion (i.e. a Lévy flight). We comment on the implications of our results for the origin of hot Jupiters amenable to $\textit{Roman}$'s transit search. Our work serves as a quantitative baseline from which future dynamical studies can build to better understand the evolution of planetary systems in the Galactic Bulge.
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Astrophysics of Galaxies

FAST Observations of Filamentary and Compact H I Structure in a Magellanic Stream IV Field

Yuxin Xiao, Qingzheng Yu, Taotao Fang et al. (+3 more)

The Magellanic Stream (MS) is believed to have formed from gas removed from the Large and Small Magellanic Clouds through tidal forces and hydrodynamic interactions with the Milky Way's gaseous halo. It provides an important laboratory for studying how stripped gas fragments, mixes, and evolves in a circumgalactic environment. In this work, we present HI observations of a $3.8^\circ\times2.2^\circ$ field in the MS IV region, using the data from the Commensal Radio Astronomy FasT Survey (CRAFTS). The total HI mass in the analyzed field is $\simeq 5.3 \times 10^{6} (d/120\,{\rm kpc})^{2}\,M_{\odot}$, where $d$ is the distance to the MS IV gas. The data resolve the emission into three coherent filamentary HI structures with related but distinct velocity trends. To characterize the HI structures and study potential multiphase gas, we adopt a Gaussian decomposition procedure to identify and reconstruct sources. Our results indicate that the field is dominated by one major filamentary HI complex, together with several smaller kinematic clump-like components. Among these identified sources, only one source likely shows multiple velocity components. Because several sources appear spatially overlapped in projection, we further examine their apparent overlap regions using position-velocity (P-V) diagrams. P-V diagrams across the apparent overlap region show no clear intermediate-velocity bridge or V-shaped structure, favoring line-of-sight projection over direct cloud-cloud collision. These results demonstrate the value of deep, high-angular-resolution HI observations for resolving faint emission, compact morphologies, and kinematic structure in the MS.
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All authors Yuxin Xiao, Qingzheng Yu, Taotao Fang, Di Li, Shulan Yan, Shuo Zhang

Astrophysics of Galaxies · Cross-listed from gr-qc

Self-supervised reconstruction of transients in data from space-borne gravitational-wave detectors

Yuxiang Xu, Minghui Du, Bo Liang et al. (+3 more)

Space-based gravitational-wave (GW) data may contain transient signals whose waveform morphologies are not known in advance. Extracting these signals is important for characterizing new sources and mitigating instrumental anomalies. However, existing deep neural network (DNN)-based extraction approaches rely on clean training targets and waveform-class-specific examples, which may limit their applicability when the transient morphology is not specified in advance. This work develops a Noise2Noise (N2N)-inspired self-supervised framework that learns from noisy observations without clean training targets and requires no transient-specific waveform templates at inference. A single model trained on noisy massive black-hole binary (MBHB) observations provides high-overlap MBHB recovery and recovers the dominant morphologies of instrumental glitches and other GW transient signals such as cosmic string bursts in source-confused test data. Beyond waveform recovery, when independent information identifies a candidate transient as instrumental, its extracted waveform can be subtracted from the data without an anomaly-specific template. In a simulated continuous data stream, this procedure substantially suppresses the injected-anomaly power within the glitch-dominated frequency band. These results support the use of self-supervised extraction for initial waveform estimation of candidate transients with unknown morphologies, enabling subsequent characterization and, where appropriate, conditional subtraction of instrumental anomalies.
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All authors Yuxiang Xu, Minghui Du, Bo Liang, Zihao Xiao, Tianyu Zhao, Peng Xu

Astrophysics of Galaxies · Cross-listed from astro-ph.SR

A Uniform Census of Variable Stars in M101 Based on HST/ACS Photometry

Jiyu Wang, Xiaodian Chen, Pinjian Chen et al. (+3 more)

We present a homogeneous HST/ACS F555W/F814W time-series census of variable stars in two M101 disk fields, using a uniform multi-band reduction and reproducible variable-selection workflow for nearby SN-host galaxies. Supplementary archival F555W epochs are used only to refine selected long-period solutions. Candidates are selected with Lomb-Scargle period searches, Fourier light-curve modeling, two-band consistency statistics, artificial-star-test photometric corrections, and mode-aware Cepheid refinement. The final catalog contains 1417 variable-star candidates, including 1102 secure fundamental-mode and 78 secure first-overtone classical Cepheids. Of these secure Cepheids, 420 are newly identified relative to the Shappee & Stanek catalog. The catalog also contains luminous candidates outside the classical Cepheid locus. We release the catalog and source-level two-band light curves for studies of Cepheid physics, stellar variability, and distance-scale applications.
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All authors Jiyu Wang, Xiaodian Chen, Pinjian Chen, Jianxing Zhang, Shu Wang, Licai Deng

Friday 4 September

Astrophysics of Galaxies · Cross-listed from astro-ph.SR

Unresolved triple systems in the aged open cluster Trumpler 19: Discovery, confirmation, and implications

D. Minniti, R. K. Saito, V. D. Ivanov et al. (+31 more)

It is difficult to identify unresolved triple and higher-order systems beyond the solar vicinity. Star clusters yield controlled environments with known physical parameters, providing a way to explore homogeneous stellar samples. Combining modern optical and near-IR surveys, our main goal is to explore the region of the color-magnitude diagrams located above the sequence of equal-mass binaries, which is inhabited by unresolved triple and quadruple systems. Specifically, here we aim to discover and characterize the presence of multiple systems in the aged open star cluster Trumpler 19. We selected cluster members using Gaia astrometry and photometry from the VVVX and DECAPS2 surveys. We made optical and near-IR color-magnitude diagrams to select stars located >0.75 mag above the cluster main sequence, including suitable unresolved triple and quadruple systems. We confirm previous results that there is a sizable sequence of unresolved binaries in Trumpler 19. We also report the discovery of a sequence of unresolved multiple systems in this cluster, and confirm some of these multiple systems via radial velocities measured by the ESO KMOS VVVX-GalCen spectroscopic survey. The fraction of multiple stars in this cluster is comparable to that of the solar neighborhood, with the caveat that the local sample probes deeper down the main sequence. The fraction of unresolved triples and quadruples is also three times higher than that of the open cluster M 67, which is of a similar age and chemical composition. The discovery of unresolved triple systems in Trumpler 19 leads to our main conclusion that these systems were able to survive within the cluster for nearly 4 Gyr. In addition, this cluster contains more multiple systems than M 67, which has a similar total present mass. Further investigations are needed to unveil if this is a primordial feature or the result of dynamical evolution.
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All authors D. Minniti, R. K. Saito, V. D. Ivanov, C. O. Obasi, M. Gómez, P. W. Lucas, J. G. Fernández-Trincado, J. Alonso-García, E. R. Garro, J. Corral-Santana, A. Luna, Z. Guo, R. Kurtev, J. Borissova, V. Fermiano, J. Osses, C. Morris, B. Dias, C. Cáceres, S. Saroon, J. B. Pullen, P. Rodriguez, M. Lad, S. Federle, I. Petralia, D. Bhadrakumar, P. Esteves, M. G. Navarro, T. Palma, L. Baravalle, D. Galdeano, M. V. Alonso, J. L. Nilo Castellon, A. N. Chené

Astrophysics of Galaxies

Tracing the Hidden Molecular Gas in the Small Magellanic Cloud with SOFIA and APEX

K. Rodriguez-Ambler, R. Herrera-Camus, M. Rúbio et al. (+6 more)

In low-metallicity environments, reduced dust abundance weakens molecular cloud shielding against far-ultraviolet radiation, enhancing CO photodissociation and producing extended CO-faint or CO-dark molecular gas. The [CII] 158 $\mu$m line is a key tracer of these CO-faint phases. We characterize the multiphase origin of [CII] emission and quantify the CO-faint molecular gas fraction across several regions of the Small Magellanic Cloud (SMC), the nearest low-metallicity ($\sim 0.2 Z_\odot$) galaxy. We combine high spectral resolution SOFIA/GREAT and upGREAT [CII], APEX CO(2-1), and ASKAP+Parkes H I 21 cm data to decompose [CII] into its atomic and molecular contributions. On average, $(78\pm 1)\%$ of [CII] intensity originates from molecular gas and $(18\pm 1)\%$ from atomic gas. The [CII]-traced H$_2$ accounts for $(77\pm4)\%$ of the total molecular gas column density, indicating that the SMC molecular reservoir is dominated by CO-faint gas. We derive a H$_2$-to-CO conversion factor $X_{CO}\approx 8.9\times10^{20}$ cm$^{-2}$ (K km s$^{-1}$)$^{-1}$ on 4 pc scales in CO-emitting regions, 4.5 times the canonical Galactic value. We find no significant correlation between the CO-dark fraction and either total column density or $\Sigma_{SFR}$, suggesting that the CO-faint fraction is primarily governed by dust and gas shielding rather than current star formation activity. Our results demonstrate that [CII] is the dominant tracer of molecular gas in the SMC and confirm the prevalence of an extended, stable CO-faint molecular phase in low-metallicity environments.
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All authors K. Rodriguez-Ambler, R. Herrera-Camus, M. Rúbio, A. D. Bolatto, D. Riquelme-Vásquez, K. Jameson, C. Muñoz-López, E. J. Tarantino, J. Stutzki

Astrophysics of Galaxies

Reigniting the FUSE I: Star Formation in Massive Elliptical Galaxies

Michael Reefe, Michael McDonald, Eric Miller et al. (+1 more)

In this inaugural paper of our "Reigniting the FUSE" series, we present the data collection & reduction, methodology, and preliminary results for a comprehensive and homogeneous reanalysis of all 30 massive elliptical galaxies that have archival far-ultraviolet (FUV) spectra with the Far Ultraviolet Spectroscopic Explorer (FUSE). We perform SED fitting to these spectra, with aperture-matched photometry from GALEX, SDSS, DES/DECaLS, 2MASS, and WISE, and construct a catalogue of high quality constraints on their stellar masses, star formation histories, stellar and gas-phase metallicities, and dust opacities. As a part of this analysis, we have also compiled a comprehensive modern set of stellar template libraries, with high resolution in the FUV, and broad coverage from $90\,\mathring{\rm A}$ - $1000\,{\rm \mu m}$ at lower resolution, which is made available through modified versions of FSPS and Python FSPS. We find strong evidence to suggest that the youngest stars in these systems do not form out of recycled gas from the old stellar populations, but instead are fueled either by gas cooling out of the hot circumgalactic/intracluster medium, or cool gas stripped from nearby or merging dwarf systems. Future papers in this series will reexamine the O VI $\lambda\lambda$1032,1038 $\mathring{\rm A}$ emission in the context of the cooling flow problem.
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All authors Michael Reefe, Michael McDonald, Eric Miller, Thomas Brown

Astrophysics of Galaxies · Cross-listed from astro-ph.SR

Calibration of the Next Generation Palomar Spectrograph as a Stellar Speedometer

Pranav Nagarajan and Kareem El-Badry

We calibrate the Next Generation Palomar Spectrograph (NGPS) for precision stellar radial-velocity (RV) measurements using repeated observations of 24 Gaia-ESO RV standards spanning $G=11$-$18$. Because NGPS is mounted at the Hale telescope's Cassegrain focus, changes in instrumental flexure produce wavelength-solution shifts of tens of km s$^{-1}$, with substantial time and wavelength dependence. We develop a pipeline that measures these shifts directly from each science exposure, using telluric absorption features in the R and I channels and the [O I] 5577 Å sky-emission line in the G channel. This approach eliminates the need for frequent on-sky arc calibrations. The resulting wavelength-dependent flexure corrections reduce the median absolute discrepancy relative to Gaia-ESO RVs from tens of km s$^{-1}$ to 1.6 km s$^{-1}$. Telluric absorption provides substantially more reliable flexure calibration than sky emission lines, which do not track point-source illumination of the slit. The I channel, which contains both many telluric lines and strong photospheric lines across a range of spectral types, generally yields the most stable RVs. The achieved precision remains above the photon-noise limit, indicating that NGPS RV performance is currently limited by calibration and modeling systematics. These results demonstrate that NGPS is well-suited for accurate and precise stellar RV measurements across a wide range of astrophysical studies.
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Astrophysics of Galaxies · Cross-listed from astro-ph.HE

Rapid radio variability in the $z\sim7$ blazar VLASS J0410$-$0139: Indication of a hidden population of weak radio jets at Cosmic Dawn

Silvia Belladitta, Eduardo Bañados, Anniek J. Gloudemans et al. (+7 more)

Doppler boosting allows blazars to be detected out to high-$z$, making them promising probes of the intergalactic medium through the 21 cm forest. We report 0.144$-$11 GHz observations of the most distant known blazar, VLASS J041009.05$-$013919.88 at z$\sim$7, obtained with the upgraded Giant Metrewave Radio Telescope (uGMRT), the LOw Frequency ARray (LOFAR) and the Very Large Array (VLA). The first uGMRT epoch (300$-$820 MHz, April 2023) revealed an inverted radio spectrum which, combined with earlier (2021$-$2022) VLA data (1.5$-$11 GHz), unveiled a double-peaked spectrum potentially indicative of multi-epoch jet activity. A second uGMRT campaign (August 2023), simultaneous with new VLA observations (1.5$-$11 GHz), instead revealed a flat low-frequency and a peaked high-frequency spectrum, ruling out this interpretation. While limited by the two uGMRT epochs, variability analysis favors intrinsic jet processes, indicating a highly relativistic, closely aligned jet ($\theta<3$ deg, $\delta>19.3$, $\Gamma>9.7$). The equipartition magnetic field ($> 1$ mG) exceeds the equivalent Cosmic Microwave Background field at $z\sim7$ (0.2 mG), indicating synchrotron losses dominate. The inferred Doppler boosting ($\delta>19.3$) implies that J0410$-$0139 is intrinsically radio-weak. As a blazar, it traces a much larger parent population of radio quasars at $z\sim7$, detectable only with deep ($\leq \mu$Jy) next-generation radio observations. LOFAR 144 MHz observations (April and July 2024) yielded $\sim$2 mJy, well below the $\sim$8 mJy predicted from uGMRT epochs, confirming strong variability at rest-frame $\sim$1 GHz. Low-frequency monitoring will be crucial for identifying high radio intensity states suitable for future 21 cm forest studies.
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All authors Silvia Belladitta, Eduardo Bañados, Anniek J. Gloudemans, Timothy W. Shimwell, Emmanuel Momjian, Huib Intema, Chiara Mazzucchelli, Christian Fendt, Bhargav Vaidya, Fabian Walter

Astrophysics of Galaxies

LOFAR radio properties of quasars hosting Extremely High Velocity Outflows

Amy L. Rankine and Paola Rodríguez Hidalgo

Quasar winds are a potential contributor to the radio emission observed in the so-called 'radio-quiet' quasars. Extremely High Velocity Outflows (EHVOs), with bulk velocities >0.1c, represent some of the most energetic of these winds. In this work, we investigate the radio properties of quasars hosting EHVOs in order to assess whether such high-velocity winds contribute to the observed radio emission. We cross-match the catalogue of EHVOs from the Sloan Digital Sky Survey with the high-sensitivity Low-Frequency Array (LOFAR) Two-metre Sky Survey (LoTSS) Data Release 3. We find that EHVO quasars exhibit a significantly higher radio-detection fraction of 38 per cent compared to an underlying parent quasar population at 24 per cent. By constructing control samples using nearest-neighbour matching, we show that matching the C IV emission line blueshift alone is sufficient to reproduce the elevated radio-detection fraction in a global sense; however, differences still remain in the radio-detection fraction as a function of C IV emission blueshift between the EHVO distribution and any matched sample, suggesting that some additional mechanism is at play. Furthermore, composite spectra reveal no significant differences in the ultraviolet absorption profiles between radio-detected and radio-undetected EHVOs, although we identify a mild positive correlation between maximum outflow velocity and radio luminosity. Our results suggest that EHVOs likely represent a subset of the quasars which host fast winds that are observed along particular lines-of-sight, and that radio emission associated with such winds remains a plausible mechanism.
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