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Physics Astrophysics Astrophysics of Galaxies

astro-ph.GA Watch Astrophysics of Galaxies

Tuesday 8 September

Astrophysics of Galaxies

Triaxiality of the Milky Way dark matter halo and the microlensing optical depth towards the Large Magellanic Cloud

J. García-Bellido and M. R. S. Hawkins

The microlensing optical depth towards the Large Magellanic Cloud (LMC), $\tau_{\rm LMC}$, bounds the compact-object fraction of the Galactic dark matter halo, but is almost always evaluated for a spherical halo. We compute it for triaxial haloes and show that the shape dependence is carried entirely by the projection of the line of sight onto the halo principal axes: for a scale-free halo $\rho\propto R^{-\alpha}$ at fixed local density it factorises exactly as $\tau/\tau_{\rm sph}=S_\odot^{\alpha}\langle S^{-\alpha}\rangle_w$, with $S(\Omega)$ the ellipsoidal shape function. The LMC lies only $0\fdg78$ from perpendicular to the Sun-Galactic Centre line, making it a near-optimal probe of in-plane elongation and a poor probe of vertical flattening. For the halo shapes favoured by Gaia we find $\tau_{\rm LMC}/\tau_{\rm sph}=0.95$–$1.15$ at fixed local density, $1.57$ for the Law-Majewski logarithmic potential, and $0.67$–$1.54$ when the major-axis azimuth is left free. For the Einasto halo required by the declining Gaia DR3 rotation curve, truncation near $25\kpc$ is offset by the larger local density it implies and $\tau$ falls by only $7$–$15$ per cent; but the median lens distance moves inwards from $13.4$ to $8.5\kpc$, where the logarithmic slope is steep and rising, amplifying the shape sensitivity: the Gaia RR~Lyrae enhancement grows from $15$ to $23$ per cent and the orientation-free range widens to $0.62$–$1.62$. The systematic on the inferred MACHO or primordial-black-hole fraction is two-sided, of order $\pm15$ per cent for the measured shapes and a factor $2.6$ under full orientation freedom, exceeding the statistical errors of the EROS-2 and OGLE bounds.
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Astrophysics of Galaxies

Euclid: Quick Data Release (Q1) – Exploring the detailed visual morphology of galaxies in clusters

P. Mas-Buitrago, S. Kruk, D. O'Ryan et al. (+167 more)

Galaxy clusters provide unique laboratories for studying environmental effects on galaxy evolution. The morphology–density ($T$–$\Sigma$) and morphology–cluster-centric radius ($T$–$R$) relations trace how galaxy morphology is influenced by the environment, but previous studies at intermediate redshifts have been limited in both sample size and radial coverage. We use the Euclid Quick Data Release 1 (Q1) visual morphology catalogue to measure the $T$–$\Sigma$ and $T$–$R$ relations for smooth, featured-or-disc, and barred galaxies in known clusters at $0.2\leq z\leq 0.5$, extending this analysis to large cluster-centric distances ($3 R_{500c}$) and studying their dependence on stellar mass. Using photometric redshifts and stellar masses provided by Euclid, we identify 1754 cluster members within $1.5 R_{500c}$, distributed across 71 clusters. We classify the identified galaxies as smooth, featured-or-disc, or barred using the predicted vote fractions provided by the Zoobot deep learning foundation model in the Q1 visual morphology catalogue. We confirm the $T$–$\Sigma$ relation in all the stellar mass ranges studied, with a stronger influence of the cluster environment on galaxy morphology in the densest parts of the cluster and closer to the cluster centre. Beyond $1.5 R_{500c}$, the morphological segregation weakens, with featured-or-disc galaxies overtaking smooth galaxies at the lowest densities, consistent with the growing contribution of field interlopers in the cluster outskirts. For barred galaxies, we find a tentative decline of the bar fraction toward lower densities that is most pronounced for the most massive galaxies. In conclusion, our results show that the cluster environment drives a progressive transformation of galaxy morphology, with the loss of disc structure becoming more pronounced towards the cluster core, where environmental processes act most efficiently.
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All authors P. Mas-Buitrago, S. Kruk, D. O'Ryan, M. T. Nardone, A. La Marca, P. Awad, M. Baes, M. Fossati, T. Géron, Z. Ghaffari, M. Girardi, C. J. Lintott, J. G. Sorce, B. Altieri, F. Durret, V. Pettorino, B. Y. Irureta-Goyena, B. Simmons, J. Reerink, H. Domínguez Sánchez, J. H. Knapen, F. Shankar, E. Duran-Camacho, J. M. Pérez-Martínez, M. Walmsley, N. Auricchio, C. Baccigalupi, M. Baldi, S. Bardelli, P. Battaglia, A. Biviano, M. Bolzonella, A. Bonchi, E. Branchini, M. Brescia, J. Brinchmann, S. Camera, G. Cañas-Herrera, V. Capobianco, C. Carbone, J. Carretero, M. Castellano, G. Castignani, S. Cavuoti, A. Cimatti, C. Colodro-Conde, G. Congedo, C. J. Conselice, L. Conversi, Y. Copin, A. Costille, F. Courbin, H. M. Courtois, M. Cropper, H. Degaudenzi, G. De Lucia, H. Dole, F. Dubath, X. Dupac, S. Dusini, A. Ealet, M. Fabricius, M. Farina, R. Farinelli, S. Ferriol, P. Fosalba, S. Fotopoulou, M. Frailis, E. Franceschi, M. Fumana, S. Galeotta, K. George, B. Gillis, C. Giocoli, P. Gómez-Alvarez, J. Gracia-Carpio, A. Grazian, F. Grupp, S. Gwyn, W. Holmes, I. M. Hook, F. Hormuth, A. Hornstrup, M. Huertas-Company, K. Jahnke, M. Jhabvala, B. Joachimi, S. Kermiche, A. Kiessling, B. Kubik, M. Kümmel, M. Kunz, H. Kurki-Suonio, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, G. Mainetti, O. Mansutti, O. Marggraf, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, S. Maurogordato, E. Medinaceli, M. Melchior, M. Meneghetti, E. Merlin, G. Meylan, A. Mora, M. Moresco, L. Moscardini, E. Munari, C. Neissner, S.-M. Niemi, J. W. Nightingale, C. Padilla, S. Paltani, F. Pasian, K. Pedersen, W. J. Percival, A. Pezzotta, S. Pires, G. Polenta, M. Poncet, L. A. Popa, L. Pozzetti, F. Raison, A. Renzi, J. Rhodes, G. Riccio, E. Romelli, M. Roncarelli, B. Rusholme, R. Saglia, Z. Sakr, A. G. Sánchez, D. Sapone, B. Sartoris, P. Schneider, T. Schrabback, M. Scodeggio, A. Secroun, E. Sihvola, P. Simon, C. Sirignano, G. Sirri, P. Tallada-Crespí, A. N. Taylor, H. I. Teplitz, I. Tereno, N. Tessore, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, J. Valiviita, T. Vassallo, G. Verdoes Kleijn, A. Veropalumbo, Y. Wang, J. Weller, A. Zacchei, G. Zamorani, F. M. Zerbi, E. Zucca, J. Macias-Perez, M. Sereno

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

An analysis of four stellar rings

E. Paunzen, J. Florian, A. Gütl-Wallner et al. (+9 more)

About 50 years ago, one thousand ring-like structures (called stellar-rings) were discovered by Isserstedt (1968). They were believed to be groups of young stars formed by shell-like triggered star formation, which would make them excellent tracers of spiral arms, for example. Neglected for 40 years, we used highly accurate kinematic, astrometric, and photometric data to investigate the four most prominent stellar rings. The aim is to investigate if those structures are indeed physically related groups of stars. We used proper motions and parallaxes from the Gaia DR2 to calculate distances and to search for common properties. Color-magnitude diagrams using BVJHKs measurements were investigated and isochrones fitted. None of the four stellar rings consists of a physically related group of young stars. The location of stars in the line-of-sight mimics a ring-like structure on the sky. The color-magnitude diagrams are typical for an integrated field population and not for a young star cluster, for example. The currently available data are sufficient to analyze ring-like structures with a high statistical significance. This allows a new search for such structures in the Milky Way.
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All authors E. Paunzen, J. Florian, A. Gütl-Wallner, A. Herdin, E. Kralofsky, K. Leschinski, M. Mach, H.M. Maitzen, M. Prišegen, M. Rockenbauer, M. Rode-Paunzen, S. Wallner

Astrophysics of Galaxies

Turbulence Cascade in Cygnus X Revealed by Multi-point VDF Method

Junjie Huang, Yangjun Pu, Keping Qiu et al. (+3 more)

Turbulence plays a crucial role in regulating star formation activities within molecular clouds, yet few methods can directly reveal its properties and underlying processes. We use molecular line data from the Nobeyama 45m Cygnus X CO Survey to study the turbulence properties and their relationships with star-forming activities and/or other non-thermal motions. In this work, we apply the multi-point velocity dispersion function (VDF), rather than direct linewidth measurements, to investigate the non-thermal properties of molecular cloud motions. We filter out the large-scale ordered structure and isolate a relatively small-scale turbulence component. Through the Friends In Velocity (FIVe) algorithm, we identify 10 substructures of the clouds and derive the turbulent properties of each cloud using the VDF method. We find that both the cloud-complex regions and the 10 velocity substructures exhibit turbulence correlation lengths of $\sim 2$–5 pc. This plateau scale suggests a parsec-scale turbulence correlation or driving scale in Cygnus X. Below this scale, the rising VDFs trace the velocity scaling of the turbulent cascade, whereas larger-scale VDF variations likely reflect cloud-scale motions. The comparison between cloud complexes and substructures further suggests that, in observational data, the VDF may constrain the turbulence correlation scale more robustly than the turbulence velocity dispersion.
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All authors Junjie Huang, Yangjun Pu, Keping Qiu, Junhao Liu, Yingxi Li, Mengke Zhao

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

Why Azimuthal Averaging Works in Halo Lensing: Symmetry and Power Counting for Nonlinear Shear and Magnification

Keiichi Umetsu

Cluster weak-lensing analyses often compress two-dimensional lensing fields into azimuthally averaged radial profiles and evaluate nonlinear observables from the averaged convergence and shear. However, the ring average of a nonlinear observable generally differs from the mean-field prediction formed from the averaged fields. This difference, divided by the mean-field prediction, defines the fractional residual. For a complete ring, the difference begins at second order in angular fluctuations. For centered elliptical halos, rotational symmetry makes the shape contribution even in signed ellipticity, while the leading miscentering dipole is orthogonal to the shape quadrupole. We test these predictions using projected triaxial NFW halos at six mass-redshift grid points spanning $3\leq M_{200\mathrm c}/(10^{14}\,h^{-1}M_\odot)\leq20$ and $0.2\leq z_l\leq0.5$, for $z_s=1$. For the reference offset model, centering offsets follow a Rayleigh distribution with scale $0.05r_{200\mathrm c}$. For $0.366\leq R/r_{200\mathrm c}\leq1$, where at least $95\%$ of each population satisfies a conservative subcriticality criterion, we calculate the median of the fractional residuals across the retained halos for each population and radius. The largest population-median magnitudes are $0.90\%$ for reduced shear, $0.0093\%$ for inverse magnification, $0.64\%$ for magnification, and $0.18\%$ across the two magnification-bias cases $\mu^{\alpha-1}$ ($\alpha=0.3, 1.4$). In the paired calculation at $z_s=2$, the maximum magnitude increases for every observable, consistent with weak-lensing power counting. Across both source planes and the common radial domain, every population median remains below $2\%$ in magnitude. This accuracy follows from first-order cancellation, rotational symmetry, and harmonic orthogonality, with further weak-lensing suppression of the remaining nonlinear terms.
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Astrophysics of Galaxies · Cross-listed from astro-ph.HE

Compton-induced HE – VHE $\gamma$-rays from pair cascade emissions in the SEDs of radio galaxies: NGC 1275

Mfuphi Ntshatsha, Markus Böttcher and Soebur Razzaque

In the scheme of active galactic nuclei (AGNi), the blazar subclass is particularly bright in $\gamma$-rays. This is because of their emissions being beamed into our line of sight, as opposed to their misaligned parent population, radio galaxies. This work presents results of a Monte-Carlo code that propagates jet-collimated $\gamma$-rays through the magnetized AGN environment, leading to secondary cascade emissions from relativistic electron-positron pairs. The resulting multi-wavelength emissions are used to fit the broadband spectral energy distribution (SED) of the radio galaxy NGC 1275. Using known physical parameters of NGC 1275 from the literature, we find that cascade emissions from stochastic processes have the potential to reproduce the broadband SEDs of radio galaxies. We also find that the interplay between accretion disk and broad-line region (BLR) photons may provide insights into the production region(s) of $\gamma$-rays in AGNi. While dense accretion disk and BLR radiation fields are vital to the development of cascades, excessive densities lead to the suppression of cascade synchrotron emission and attenuation of \,TeV $\gamma$-rays. Furthermore, the magnetic field is important in shaping the cascade $\gamma$-ray spectrum.
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Astrophysics of Galaxies

Design and commissioning of a windowless gas-target system for high-current beams at JUNA

Xuyang Wang, Fuqiang Cao, Weike Nan et al. (+20 more)

Windowless gas targets avoid the beam-energy loss and straggling introduced by entrance foils and are therefore well suited for direct measurements of low-energy nuclear reactions. A windowless gas-target system designed for operation with milliampere beams has been developed for the Jinping Underground Nuclear Astrophysics facility (JUNA). The system combines three-stage differential pumping, closed-loop gas recovery and purification, a constant-temperature power-compensation calorimeter, and a position-resolved target-thickness monitor based on secondary elastic scattering. Stable operation was achieved over a target-pressure range of 1-3 mbar, with pressure fluctuations below 1% during 8 h of continuous circulation, while the accelerator-side pressure was maintained at approximately \(10^{-4}\) Pa. The closed-loop gas-circulation system maintained stable target conditions, while gas-transport calculations indicated that the axial pressure nonuniformity remained within approximately 1.6% under representative operating conditions. Calorimeter measurements were consistent with the thermal calculations, supporting the sensitivity correction used for beam-power determination. Beam commissioning with \(^{14}\mathrm{N}(p,\gamma)^{15}\mathrm{O}\) and \(^{12}\mathrm{C}(p,\gamma)^{13}\mathrm{N}\) at the 600 kV Cockcroft-Walton accelerator of the China Institute of Atomic Energy (CIAE) demonstrated stable operation of the gas-target and \(\gamma\)-ray detection systems and provided information on the influences of reaction position and beam heating. These results demonstrate the operating stability and diagnostic capability of the system for future high-current, low-energy nuclear-reaction measurements at JUNA.
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All authors Xuyang Wang, Fuqiang Cao, Weike Nan, Gang Lian, Wei Nan, Hongwei Huang, Yuchen Jiang, Jingyu Dong, Minghao Zhu, Yuwen Chen, Yihui Liu, Jinlong Ma, Yueran Wang, Jie Chen, Yunju Li, Shengquan Yan, Youbao Wang, Xiao Fang, Luohuan Wang, Yangping Shen, Bing Guo, Weiping Liu, JUNA collaboration

Astrophysics of Galaxies

Weak cool core, weak turbulence: XRISM, XMM-Newton and Chandra spectroscopy of the core of Abell 1413

Egemen Gormez and Murat Hudaverdi

We present the first XRISM spectroscopy of the core of Abell 1413 (z = 0.143), combining 104.7 ks of Resolve with archival XMM-Newton and Chandra spectra of a matched sky region. A1413 is hot, massive and relaxed but lacks a strong cool core (t_cool = 6.4 Gyr), a regime in which the low turbulence reported to date has been tested only once, in A3571. The Resolve spectrum requires a single velocity-broadened component with kT = 7.06 (+0.33, -0.43) keV and a line-of-sight velocity dispersion sigma_v = 170 (+25, -24) km/s (M_3D = 0.217). The bulk velocity relative to the brightest cluster galaxy, v_bulk = -24 +/- 26 (z_ICM) +/- 71 (z_BCG) km/s, is limited by the optical redshift rather than by Resolve, and disfavours coherent line-of-sight sloshing. The non-thermal pressure fraction, 2.5 +/- 0.7 per cent, implies a hydrostatic mass bias b < 2.5 per cent, comparable to the strong cool-core cluster A2029 (2.6 +/- 0.3 per cent) and, at matched sampling scale, if anything below it. With A3571 (1.3 +/- 0.3 per cent), to which A1413 rescales within 0.2 sigma, two weak cool cores now show that this quiescence does not require central cooling. The resolved Fe-K He-alpha complex gives Fe = 0.38 +/- 0.03 (stat) +/- 0.04 (sys) solar; Ni/Fe, separated from Fe K-beta for the first time, is solar, as is the pattern as a whole. The Ne, Mg and Si lines that set Ne/Fe, Mg/Fe and Si/Fe lie below 2 keV, where our instruments disagree by 10-20 per cent; we therefore do not regard the SNIa fraction as constrained.
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Astrophysics of Galaxies

Detection prospects for heavy WIMP dark matter around M31* in microwave band

Andrei E. Egorov

This work analyzes the detection prospects for weakly interacting massive particles (WIMPs) in dark matter (DM) density spike around the supermassive black hole (SMBH) in Andromeda galaxy M31 in microwave band. WIMP annihilation produces relativistic electrons and positrons, which generate the synchrotron emission in strong magnetic field of the accretion flow medium at microwave frequencies. Properties of this emission, as well as their dependence on DM and medium parameters, were modeled. Atacama Large Millimeter Array (ALMA) sensitivity to this emission and underlying WIMP parameters was estimated. It was obtained that M31* in microwave band represents the unique target, where DM spike signal can be detected in case of realistic spike and halo density profiles. In such case ALMA may reach the thermal s-wave annihilating WIMPs with masses up to around 1 TeV with just 10–100 hours exposure. Optimistic parameter configurations may allow probing all possible WIMP masses up to 100 TeV. Related systematic uncertainties are discussed.
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Astrophysics of Galaxies

The environmental dependence of the circumgalactic medium in a high-resolution cosmological simulation

Georg Herzog, Rajeshwari Dutta and Michele Fumagalli

There is increasing evidence from observations that the circumgalactic medium (CGM) of galaxies depends on the large-scale structure in which they are embedded. When probing the CGM in absorption using quasar sightlines, studies find an enhanced sky coverage in the CGM of galaxies in overdensities compared to galaxies in isolation. However, the exact reason for this environmental dependence is still unclear. In this work we aim to model for the first time the influence of the large-scale structure on the cool and warm ($T\sim10^{4-5}$ K) gas phases of the CGM. We use a high-resolution ($m_{gas}\approx 4.5\times 10^4$ M$_{\odot}$, $m_{dm}\approx 2.4\times 10^5$ M$_{\odot}$) cosmological simulation based on the EAGLE model of galaxy formation. We select all galaxies at $z=0$ with stellar mass $M_*>10^8$ M$_\odot$ and split them into galaxies in overdensities (group galaxies) and galaxies in isolation using a Friends-of-Friends algorithm. For these two samples, we investigate how the large-scale structure influences the physical properties of the CGM and the measured covering fractions of the cool and warm gas phases. When the two samples of group and isolated galaxies are matched in stellar mass, halo mass, and we use only central galaxies, we do not find any significant difference in the physical properties of the CGM and the measured covering fractions. However, when satellite galaxies are included, we recover the observational trends in the difference of covering fractions with the environment. The difficulty of recovering the observational trends shows the complexity of capturing the multiphase CGM in simulations. However, since our results concerning the admixture of satellites are independent of the employed subgrid physics, this work shows that central galaxies and satellites need to be disentangled in observational studies to clearly discern the role of the environment on the CGM.
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Astrophysics of Galaxies · Cross-listed from astro-ph.EP

Radial velocity follow-up of Gaia astrometric substellar companions: six confirmed brown dwarfs and 13 impostor binaries

Marcus L. Marcussen, Simon H. Albrecht, Kamil K. Kalinowski et al. (+7 more)

With microarcsecond precision, Gaia has made the astrometric discovery of substellar companions feasible. However, follow-up observations are needed to check on orbital solutions and rule out astrophysical false positives. We validate and characterise a sample of 20 Gaia Data Release 3 (DR3) astrometric candidates for substellar companions, with the dual goal of identifying false positives and deriving robust physical parameters for genuine companions. We performed high-resolution spectroscopy using FIES, NIRPS, and NEID at the Nordic Optical Telescope, the ESO 3.6m telescope, and the WIYN Telescope, respectively. Double-lined spectroscopic binaries were identified as false positives, and surviving systems were characterised through joint Gaia astrometry and radial velocity modelling. Thirteen of the candidates proved to be near-twin binary stars for which the astrometric motion of the center of light is small enough to mimic that of a single star in response to a substellar companion. We confirm that six companions are brown dwarfs with masses in the range ${\sim}26$–$68\,M_\mathrm{Jup}$, two of them for the first time. In contrast to earlier studies of lower-mass Gaia candidates, we find that the astrometric orbital solutions are generally reliable to within the stated uncertainties.
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All authors Marcus L. Marcussen, Simon H. Albrecht, Kamil K. Kalinowski, Joshua N. Winn, Gu{\dh}mundur Stefánsson, Jens Reersted Larsen, Julie Gadeberg, Evan Fitzmaurice, Kevin Schlaufman, Suvrath Mahadevan

Astrophysics of Galaxies · Cross-listed from cs.SC

Physical Law Ecology: mapping multi-mechanism ecologies as the zeroth step of data-driven scientific discovery

Xiongheng Bian, Xiangyu Cui, Ma Feng et al. (+1 more)

Every data-driven equation discovery method assumes (implicitly and without verification) that the target system obeys a single governing law ($K{=}1$). Here we show that this assumption is the primary bottleneck limiting scientific discovery in multi-mechanism systems, and introduce Physical Law Ecology, a framework that makes $K^*$ (the number of coexisting independent mechanisms) itself the first quantity to be determined from data. The framework automatically mines a pool of topologically distinct candidate equations, constructs a continuous dominance weight field across parameter space, and discovers analytic evolution laws governing mechanism succession—with optional monotonicity constraints encoding irreversible physics. Across four unrelated systems (elastomer mechanics, pool boiling, galactic dynamics, and droplet evaporation), BIC consistently identifies $K^*{=}3$ independent governing topologies. Applied to 163 SPARC galaxies (3,269 spatially resolved measurements), the framework autonomously recovers three gravitational laws whose coexistence provides evidence against the single-universal-acceleration hypothesis of MOND ($p<10^{-34}$). In engineering applications, multi-law weighted prediction reduces error by 67-72% over single-equation baselines while retaining full interpretability. By establishing the determination of $K^*$ as the zeroth step of scientific discovery-prior to and independent of equation search—this work opens a direction orthogonal to existing symbolic regression: not finding better equations, but mapping the ecology of mechanisms that govern complex systems.
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All authors Xiongheng Bian, Xiangyu Cui, Ma Feng, Xiaoyan Shen

Astrophysics of Galaxies

J023721.13$-$010528.5: A Giant $S$-shaped Radio Galaxy Showing Four Episodes of Jet Activity

Pavan Vijay Khadekar, Dharam Vir Lal and Ramana Athreya

We present high-sensitivity, high-resolution radio observations of J023721.13$-$010528.5 using the upgraded Giant Metrewave Radio Telescope in band-3 (250–500\,MHz) and band-4 (550–950\,MHz), along with MeerKAT (1280\,MHz) and VLA (3\,GHz) survey images. The radio source, hosted by a bright cluster galaxy at redshift $z=0.372$, is a giant radio galaxy with a projected linear size between the outermost hotspots of 1.2~Mpc and is one of the largest $S$-shaped radio sources known. Its radio morphology revealed four pairs of components straddling the radio core, which were also local maxima in profiles of radio flux densities and equipartition energy density measured along the radio lobes. Spatially resolved multi-frequency spectral analysis showed progressively older emission from the inner to the outer components, spanning approximately 4–21 Myr. The high degree of symmetry of the inner three component-pairs with respect to the radio core makes it improbable that these are randomly located knots in the radio jet. Therefore, we present J023721.13$-$010528.5 as the prototype of a new class of radio galaxies with four episodes of jet activity — a quadruple-double radio galaxy. We suggest that giant $S$-shaped radio sources may be among the most promising targets for identifying and studying multi-epoch radio jet activity, since their large linear sizes and jet-axis evolution can spatially separate hotspots from successive episodes, making them easier to detect and analyse.
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Astrophysics of Galaxies

The Impact of Circumgalactic Rotation on Ly$\alpha$ Radiative Transfer

Hee-Gyeong Kym, Seok-Jun Chang, Max Gronke et al. (+1 more)

Hydrogen Lyman-alpha (Ly$\alpha$) is a prominent emission line from the circumgalactic medium (CGM). Due to its resonant nature, Ly$\alpha$ carries imprints of the physical properties and kinematics of the cold CGM. In particular, CGM rotation can modify the Ly$\alpha$ peak separation, which is often interpreted as a tracer of H I column density. We present 3D Monte Carlo Ly$\alpha$ radiative-transfer simulations in a CGM-like rotating medium and examine how the emergent spectra depend on rotational velocity ($V_{\rm rot}$), H I column density ($N_{\rm HI}$), viewing angle, clumpiness, and intrinsic source width. We find that rotation broadens the integrated spectra and increases the peak separation, with the strongest viewing-angle dependence when rotational Doppler shifts dominate over frequency diffusion. At high $N_{\rm HI}$, numerous scatterings reduce the sensitivity of integrated spectra to rotation, producing a degeneracy between $V_{\rm rot}$ and $N_{\rm HI}$. Consequently, Ly$\alpha$ peak separation alone can overestimate $N_{\rm HI}$ in a rotating medium. Spatially resolved halo spectra provide a clearer diagnostic: opposite sides of the rotating medium show systematic redshifted and blueshifted asymmetries associated with the line-of-sight velocity of the last-scattering gas. Such rotation-driven signatures can also contribute to velocity-map patterns often interpreted in terms of inflow or outflow, highlighting the need to consider rotation in spatially resolved Ly$\alpha$ observations. We further show that the main signatures persist in simple clumpy media, while the halo signatures are largely insensitive to the intrinsic source width. Our results demonstrate that spatially resolved Ly$\alpha$ observation is essential for disentangling CGM rotation from radiative-transfer effects.
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All authors Hee-Gyeong Kym, Seok-Jun Chang, Max Gronke, Kwang-Il Seon

Astrophysics of Galaxies

Series of core collapse numerical simulations (SOLANUM) I: Modelling the early and late infall in a sun-like protostar

D. Navarro-Almaida, B. Commerçon, U. Lebreuilly et al. (+5 more)

Magnetohydrodynamical simulations and interferometric observations toward young stellar objects reveal the accretion of gas that may alter the physical properties and chemical composition of protostellar disks. Our goal is to constrain the physical history and properties of late infalling gas, and assess its potential to change the physical and chemical properties of the disk. We carried out a core collapse simulation of 5 M$_{\odot}$ of gas endowed with tracer and sink particles during $\sim 3.6\times 10^{5}$ yr. We analyzed the properties of the rotationally supported disk, and the origin and physical history of the gas from which it is initially formed. We also selected the tracer particles that describe the late infall to analyze their origin and physical history, and compare them to the information obtained from the disk. The final mass of the sink reaches 1.02 M$_\odot$, while the mass of the disk stays fairly constant around 0.02 M$_\odot$. Throughout its evolution, the disk radius increases up to $\sim 40$ au and its density is reduced by a factor of $\sim 8$. Filaments that channel gas from the envelope to the disk and sink appear as a result of the magnetic interchange instability. Tracer particles can identify late infalling gas, whose physical properties resemble that of observed streamers and are only accreted in the final snapshots of the simulation. The origin and physical history of the late infalling gas are different from those of the gas that initially forms the disk. Core collapse simulations predict the appearance of filaments that connect the envelope to the disk. The late accretion of gas through these channels has properties similar to those of streamers and brings gas to the disk with a different physical history that could translate into a different chemical composition.
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All authors D. Navarro-Almaida, B. Commerçon, U. Lebreuilly, P. Hennebelle, A. Ahmad, A. Fuente, P. Rivière-Marichalar, J. E. Pineda

Astrophysics of Galaxies

Low-Redshift Interlopers in the SDSS DR16 $z > 5$ Quasar Catalogue

Vivek Kumar Jha, Harikumar N and Yogesh Wadadekar

High-redshift quasars ($z>5$) are crucial for studying early black hole growth and reionisation. SDSS Data Release 16 catalogues 655 such sources with multiple redshift estimators. We systematically examined this subsample and found 480 sources (73.2%) where pipeline redshift (Z\_DR16Q) disagrees with the derived estimate (Z\_FIT) significantly. Visual inspection confirms that 125 of these (19.1% of the total) are actually low-redshift active galactic nuclei. In 114 cases, broad Mg\,ii with C\,iii and C\,iv was misidentified as Ly$\alpha$; in 11 cases, H$\alpha$ was misidentified as Ly$\alpha$. This error is immediately revealed by the absence of Gunn–Peterson trough blueward of Ly$\alpha$. Crucially, Z\_FIT recovers correct redshift in the affected sources where emission lines are prominent, indicating the algorithm is sound; the issue lies in community preference for Z\_DR16Q or Z\_SPEC. We urge caution against uncritical use of pipeline redshifts for $z>5$ DR16Q sources and recommend Z\_FIT as the preferred estimator.
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Astrophysics of Galaxies

AEON-z5: A Candidate AGN-driven Outflow Enriching the Circumgalactic Medium at $z\simeq5.23$

Xiaoyang Wei, Zheng Cai, Shiwu Zhang et al. (+6 more)

The dispersal of chemically enriched gas from galaxies into their surroundings is a key process in galaxy evolution, yet direct observational evidence at z>5 remains scarce. We present AEON-z5, a galaxy at z~5.23 in the COSMOS field comprising a compact continuum-emitting core surrounded by an extended, line-dominated ionized nebula. JWST/NIRCam imaging shows that H$\alpha$+[N II] and H$\beta$+[O III] emission extends to projected radii of >4 kpc - 2-2.5 times the typical effective radius at the host stellar mass - reaching the outer ISM and the inner CGM. F444W grism data reveal a highly asymmetric H$\alpha$+[N II] profile, which we interpret as a bipolar outflow and decompose into three kinematic components. The dominant component has a flux-weighted velocity offset of ~+489 km/s and FWHM~630 km/s, with a wing reaching $v_{84}$~792 km/s. A tentative detached feature at $\Delta v_{LOS}$~2800 km/s, detected at 1.5$\sigma$ in the 1D spectrum (2.4$\sigma$ in the 2D fit), may trace an outflow clump. These kinematics are most coherently explained by an AGN in the core. For the extended nebula, we derive a velocity curve shifting redward with radius, reaching 200-400 km/s at $r_p$~1.3-2.5 kpc - a trend that may reflect an accelerating outflow, corotating gas, or recycled inflow viewed in projection. Crucially, the measured [N II]/H$\alpha$ ratios imply near-solar N2-based abundances (0.7-1.0 $Z_\odot$), remaining >0.37 $Z_\odot$ after allowing for AGN excitation and calibration systematics. The combination of large extent, enrichment, and extreme kinematics identifies AEON-z5 as a candidate snapshot of feedback-driven metal transport, offering a direct view of how early AGN activity may redistribute chemically processed gas into the CGM within the first ~1.1 billion years.
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All authors Xiaoyang Wei, Zheng Cai, Shiwu Zhang, Fujiang Yu, Yunjing Wu, Shuaiyi Li, Xiaojing Lin, Mingyu Li, Xuelun Mei

Astrophysics of Galaxies

The Roman eXtreme Deep Field (RXDF)

Haojing Yan, Anton M. Koekemoer, Yue Shen et al. (+127 more)

The Roman eXtreme Deep Field (RXDF) program is one of the five General Astrophysics Survey (GAS) programs approved for observing time with the Nancy Grace Roman Space Telescope in Cycles 1 and 2. It has been allocated 386.41 hours to carry out an imaging survey to AB = 30 mag (5-sigma) over ~140x larger area than the Hubble eXtreme Deep Field (HXDF) full-depth area (ACS+WFC3/IR). The RXDF will cover the full Roman wavelength range with 7 bands, reaching AB = 30 mag in RZYJH, 29 mag in F, and 28 mag in K, over a full-depth area of 678.75 arcmin^2 embedded in a total area of 1,243 arcmin^2, and far exceeding the depths of the Roman Core Community Surveys (CCS). The RXDF is within the Euclid Ultra Deep Field (EUDF) near the North Ecliptic Pole (NEP), a strategic long-term field for generational space facilities, with a wealth of multi-wavelength data including extensive coverage from the James Webb Space Telescope (JWST) NEXUS Treasury program. The observations will cover 3 epochs at a 1-year cadence, each epoch divided into 3 sub-epochs ~10 days apart, enabling time-domain studies on time baselines from ~10 days to over ~2 years. The RXDF is uniquely positioned to address critical questions in reionization, large scale structure (LSS), growth of supermassive black holes (SMBHs), little red dots (LRDs), and high-z supernovae (SNe); the volumes probed by HST+JWST are too small at these extreme depths, and even the deepest CCS tiers are too shallow. In addition to our key objectives, a wealth of additional science will be enabled by engaging the community with our rapidly released datasets, revolutionizing a wide range of science for a lasting legacy. This short document, which is converted from the approved RXDF proposal, aims to provide the community with a summary of the program.
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All authors Haojing Yan, Anton M. Koekemoer, Yue Shen, Bangzheng Sun, Norman A. Grogin, Zihao Wu, Christian Kragh Jespersen, Rachel Somerville, Kyoung-Soo Lee, Dale D. Kocevski, Adam J. Burgasser, Pedro H. Bernardinelli, Yicheng Guo, Charles Steinhardt, Xiaohui Fan, Duncan Farrah, Gisella De Rosa, Feige Wang, Jinyi Yang, Lifan Wang, Fengwu Sun, Christopher N. A. Willmer, John David Silverman, Steven L. Finkelstein, Seth H. Cohen, Rolf A. Jansen, Rogier A. Windhorst, Brent M. Smith, Stefano Casertano, Anthony H. Gonzalez, Michael A. Strauss, Ray A. Lucas, Katherine E. Whitaker, Mingyang Zhuang, Rodrigo Angulo, Chloe Aurin, Micaela Bagley, Franz E. Bauer, Jessica M. Berkheimer, Rachel Bezanson, Alejandro S. Borlaff, Rebecca A. A. Bowler, Larry D. Bradley, W. N. Brandt, Denis Burgarella, Timothy Carleton, Delondrae D. Carter, Caitlin M. Casey, Christopher J. Conselice, Kyle W. Cook, Jeff Cooke, David A. Coulter, Tyler Desjardins, Tim Dewachter, Nicole E. Drakos, Simon P. Driver, Qiao Duan, Eiichi Egami, Andreas Faisst, Travis C. Fischer, Adriano Fontana, Ori Fox, Brenda Frye, Yoshinobu Fudamoto, Eric Gawiser, Mauro Giavalisco, Yuichi Harikane, Thomas Harvey, Nimish P. Hathi, Benne W. Holwerda, Taylor Hutchison, Olivier Ilbert, Akio K. Inoue, Lucy R. Ivey, Kartheik Iyer, Mathilde Jauzac, Ignas Juodzbalis, Jeyhan S. Kartaltepe, Daichi Kashino, Susan Kassin, Patrick Kelly, Kotaro Kohno, Stephanie LaMassa, Erini Lambrides, Rebecca Larson, Junyao Li, Zhiyuan Ma, Sangeeta Malhotra, Elizabeth McGrath, Peter Melchior, Marcio Melendez, Hironao Miyatake, Bahram Mobasher, Mireia Montes, Thomas Moore, Takahiro Morishita, Takashi Moriya, Leonidas Moustakas, Rohan Naidu, Rosalia O'Brien, Pascal A. Oesch, Masafusa Onoue, Rafael Ortiz III, Masami Ouchi, Robert G. Pascalau, Molly Peeples, Andreea O. Petric, Sara Petty, Justin Pierel, Marc Rafelski, Eniko Regos, Armin Rest, Mitchell Revalski, James Rhoads, Pierluigi Rinaldi, Aaron Robotham, Kate Rowlands, Pablo M. Sanchez-Alarcon, Paola Santini, Alice E. Shapley, Raymond C. Simons, Swara Ravindranath, Takahiro Sumi, Takumi S. Tanaka, Masayuki Tanaka, Scott Tompkins, Christina C. Williams, Edward J. Wollack, John F. Wu, L. Y. Aaron Yung

Monday 7 September

Astrophysics of Galaxies

Extreme Kerr Newman Black Holes: Differential Geometry, Symmetry, and the Golden Ratio

Remo Ruffini and Giorgio Sonnino

We investigate the geometry of extreme Kerr-Newman black holes and its role in selecting distinct black hole states. Motivated by Smarr's question of what physical information is encoded in event-horizon symmetries, we identify, besides the Smarr extreme family, a special family in which the mass, charge, angular momentum, and irreducible mass are constrained by a single irrational number. In the Christodoulou diagram, this family is selected by a discrete symmetry of appropriately scaled charge and angular-momentum variables. The local differential geometry of the event horizon provides an additional selection principle, which, up to the discrete symmetries (Q \rightarrow\pm Q) and (J \rightarrow\pm J), identifies a unique extreme Kerr-Newman black hole exhibiting the highest degree of local spherical symmetry compatible with the rotating Kerr-Newman geometry. Remarkably, for this distinct extreme configuration, all relevant physical and geometrical quantities, including the energy, electric charge, angular momentum, and irreducible mass, are solely related through the golden ratio. We also examine reversible and irreversible transformations and the associated extractable energy. Intrinsic horizon geometry can therefore constrain the macroscopic parameters and single out distinct extreme Kerr-Newman configurations.
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Astrophysics of Galaxies

Origins of complex organic molecules in L1551 IRS 5: Interplay of thermal heating and accretion shocks

Ji-hyun Kang, Jeong-Eun Lee, Seokho Lee et al. (+1 more)

Complex organic molecules (COMs) are typically observed in the warm inner envelopes of Class 0 protostars. In more evolved Class I sources, COM emission is confined to the compact inner disk and obscured by high dust opacity, but the FU Orionis-type binary L1551 IRS 5 offers a valuable opportunity to probe disk chemistry, as its outburst luminosity thermally sublimates ices out to large radii. We sought to spatially resolve the origins of COMs in this system to distinguish between central radiative heating and shock-induced chemistry driven by heterogeneous accretion pathways. We analyzed high-angular-resolution ALMA archival data, focusing on COMs (e.g., CH3OH, CH3OCHO) and the shock tracer SO, and compared their spatial morphologies and kinematics to diagnose the excitation conditions associated with different accretion flows. We find that the COM emission in L1551 IRS 5 arises from both radiative heating and localized accretion shocks. In the northern source, the widespread low-excitation COM emission is primarily consistent with thermal heating by the recent outburst. This source also exhibits dual-mode accretion with distinct chemical signatures, with COMs along the spiral arm tracing steady equatorial circumbinary disk-to-circumstellar disk accretion and high-excitation COMs with bright SO along the eastern disk surface tracing a vertical envelope-to-disk streamer impact. In the southern source, methanol is confined to the southeastern streamer impact site, whereas SO forms a ring-like structure at the tidal truncation radius. We attribute this difference to differential chemical survival timescales. L1551 IRS 5 thus serves as an ideal laboratory to investigate how shock chemistry and binary-regulated accretion shape the chemical structure of protostellar disks.
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All authors Ji-hyun Kang, Jeong-Eun Lee, Seokho Lee, Shigehisa Takakuwa

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

Precise physical and kinematical parameters of massive eclipsing binaries in the Small Magellanic Cloud

M. Kaya, Ö. Çak{\i}rl{\i}, B. Hoyman et al. (+3 more)

The formation of massive stars serves an important field of study, requiring research into whether these stars need to form together within clusters of low-mass stars or if they are able to form independently. Currently, there has been an increase in the number of massive stars found far from clusters in the Milky Way (MW) and Small Magellanic Cloud (SMC). The existence of isolation and composition in binary systems is an uncommon phenomenon among massive stars, and their rare occurrence presents valuable insights that are regarded as evidence in this field. This research looks for ways to increase the catalogue of identified massive stars in eclipsing binaries, particularly those that show significant indications of isolation. For the definition of the first step, we are analysing the eight double-lined spectroscopic binaries in the SMC, as detailed in the OGLE variable star catalogues, with the goal of identifying their astrophysical properties. Later, we examine the expected locations and characteristics of binary stars thought to be part of a cluster, using absolute parameters and a cross-validation approach to determine the connection between kinematic analysis and these parameters. If the kinematic connection with the cluster and the physical parameters match precisely with the cluster's isochrone, such stars could act as reliable standard candles for determining the cluster's distance and age.
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All authors M. Kaya, Ö. Çak{\i}rl{\i}, B. Hoyman, O. Özdarcan, T. Yontan, R. Canbay

Astrophysics of Galaxies

The Role of Dark Matter in Driving Disk Perturbations: Application to LMC-SMC Like Galaxy Interactions

Himansh Rathore, Hayden R. Foote, Gurtina Besla et al. (+6 more)

Dark-matter (DM) models predict that satellite galaxies distort their host's DM halo. As such, both the satellite and the distorted halo can perturb the host's stellar disk. The LMC-SMC system is a nearby $\sim1:10$~mass-ratio binary with a well-constrained orbit and well-characterized LMC disk perturbations. Hence, the system offers unique opportunities to test DM theory, provided the impact of halo torques on the LMC's disk can be characterized along with the SMC's torques. We use halo Basis Function Expansions (BFEs) of an N-body simulation of an isolated LMC-SMC-like interaction to quantify the time-dependent torques exerted on the LMC's disk by the SMC and the LMC's DM halo. We find that the halo torques arise from the quadrupole halo distortion, and the inner (R$<6$ kpc) LMC disk warps are the most promising probe of this quadrupole. For the first time, we construct a BFE to quantify the LMC's disk perturbations resulting from the SMC and halo torques. We find that the LMC's disk is significantly perturbed prior to the Clouds' Milky Way infall, possessing warps with a mean vertical extent of $\sim1$ kpc. Finally, we apply multi-channel singular spectral analysis (mSSA) to the time-series of the disk BFE coefficients, halo quadrupole, and the LMC-SMC orbit. mSSA successfully separates the temporal evolution of the LMC warps into components correlated with the halo versus the SMC. Our framework identifies correlated evolution between the LMC's halo distortions and the LMC's disk perturbations, enabling the Clouds to be a precision laboratory for DM physics.
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All authors Himansh Rathore, Hayden R. Foote, Gurtina Besla, Silvio Varela-Lavin, Nicolas Garavito-Camargo, Martin D. Weinberg, Facundo A. Gomez, Kathryne J. Daniel, Chervin F.P. Laporte

Astrophysics of Galaxies

A pilot submillimeter search for IceCube neutrino counterparts: JCMT follow-up and dusty-galaxy catalog associations

Yuji Urata and Kuiyun Huang

The submillimeter band offers a complementary route to identifying electromagnetic counterparts of high-energy neutrinos, tracing relativistic transients and persistent dust-obscured galaxies. We present a pilot search combining JCMT/SCUBA-2 follow-up of IceCube events with catalog searches for bright high-redshift dusty systems. Among nine rapidly observed IceCube fields, sources of particular interest were found in three: JCMT0402-0424 ("Shadow Blaster") in IC 210922A, a transient-like source following IC 220115A, and two known blazars in IC 240105A. ALMA resolved the Shadow Blaster into a strongly lensed dusty star-forming galaxy at z=2.988 with a compact gas-rich starburst core. Motivated by this result, we cross-matched IceCube localizations with the Herschel Bright Sources (HerBS) and Planck High-Redshift Source Candidate (PHZ) catalogs. Among 51 historical IceCube events with A_bbox,90 <= pi deg^2, four fields contain at least one HerBS source, compared with 0.723 expected from right-ascension scrambling (fixed-cut p=4.18e-3). Scanning the localization-area threshold gives p_global,A=0.0135. Applying the same IceCube selection to PHZ gives four associated fields versus 3.544 expected (p=0.478). Because the focused HerBS selection followed a broader exploratory analysis with trials-corrected p_global=0.130, the focused result is suggestive rather than definitive. The four well-localized HerBS fields contain six high-redshift DSFGs with apparent L_IR~10^13 L_sun. ALMA imaging and published spectroscopy reveal compact or multiple-component morphologies, extreme molecular-gas kinematics, and possible obscured nuclear activity. These results support a hierarchical strategy: identify luminous submillimeter candidates through wide-field imaging and catalogs, then characterize them at high angular resolution to test for compact gas-rich calorimetric conditions and obscured AGN activity.
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Astrophysics of Galaxies

LEGGOS: Direct abundances of N, O, Ne, S, and Ar in five lensed galaxies at Cosmic Noon

Brian Welch, Gourav Khullar, Taylor A. Hutchison et al. (+14 more)

We present direct $T_e$ chemical abundances in five strongly lensed galaxies at Cosmic Noon ($2.481 \leq z \leq 3.625$) using JWST/NIRSpec data from the LEGGOS survey. We measure gas-phase abundances of N, O, S, and Ar in all five galaxies, and Ne in two galaxies. Three galaxies have electron temperature constraints from multiple different ionization zones, and we find that these are broadly consistent with temperature scaling relations observed in both local and high-$z$ galaxies. We find a range of oxygen abundances $8.04 \leq 12+\log(\text{O/H}) \leq 8.79$ (22 – 126% $Z_{\odot}$). The ratios of N/O and Ne/O are consistent with trends observed in local galaxies. We do not observe any evidence for significant N enhancement in our sample, though the youngest galaxy in our sample (SGAS-J1050) has a mildly elevated $\log(\text{N/O}) = 1.20 \pm 0.08$, which we suggest may be driven by a population of young massive stars. The ratios of S/O and Ar/O are generally sub-solar, similar to trends observed in other high-$z$ galaxies. We find that the S/O and Ar/O abundances are sub-solar, consistent with enrichment from core-collapse supernovae (CCSNe). Modeling of the star formation histories of the LEGGOS galaxies supports CCSNe enrichment, as each galaxy shows a recent period of star formation lasting $\lesssim 100$ Myr, indicating that type Ia supernovae would not yet have had enough time to contribute significantly to the gas-phase abundances of these galaxies.
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All authors Brian Welch, Gourav Khullar, Taylor A. Hutchison, Keren Sharon, Pedram Abedi, Matthew B. Bayliss, Michael Florian, Dylan Berry, Jacqueline Antwi-Danso, Nikko J. Cleri, Håkon Dahle, Aleena Ebey Panzer, Michael D. Gladders, Rion Oh, Cole Panzer, Jane R. Rigby, T. Emil Rivera-Thorsen

Astrophysics of Galaxies

LEGGOS: A Shocking Lack of Evidence for Shocks at sub-kiloparsec Scales at 2 < z < 4

Nikko J. Cleri, Taylor A. Hutchison, Brian Welch et al. (+11 more)

Here we present the first systematic search for shocks in six gravitationally lensed galaxies at 2.37 < z < 3.625 with JWST/NIRSpec integral field spectroscopy from the LEnsing and Galaxy Growth: Observing Substructures (LEGGOS) survey. We employ diagnostics that utilize the fluxes and kinematics of shock-sensitive rest-frame optical emission lines He̱ta}, [O iii] {\lambda}5008, [O i] {\lambda}6302, H{\alpha}, [N ii] {\lambda}6585, and [S ii] {\lambda}{\lambda}6718, 6733. We find that, on pixel, clump, and galaxy-integrated scales, the LEGGOS spectra show minimal if any evidence for shocks. The image plane pixels are < 8% within the shock regions of the rest-frame optical line ratio diagnostics for any individual galaxy, and the shock-identified pixels do not show a coherent spatial structure. We also leverage MAPPINGS V shock models to infer shock velocities from the observed emission lines, and find that the distributions of inferred shock velocities are inconsistent with those expected for shock-dominated gas. Altogether, none of these methods provide significant evidence for shocks in the six LEGGOS sources. We conclude by discussing the implications of the lack of evidence for shocks in the broader context of galaxy evolution at cosmic noon and earlier epochs.
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All authors Nikko J. Cleri, Taylor A. Hutchison, Brian Welch, Gourav Khullar, Matthew B. Bayliss, Håkon Dahle, Michael Florian, Michael D. Gladders, Connor Luettgenau, Rion Oh, Jane R. Rigby, T. Emil Rivera-Thorsen, Julissa Sarmiento, Keren Sharon

Astrophysics of Galaxies

A New Sample of $\sim$ 100 Intermediate-mass Black Holes Reaching $z \approx 1$

Wen-Juan Liu, Luis C. Ho, Su Yao et al. (+2 more)

We present a systematic search for intermediate-mass black hole (IMBH) active galactic nuclei (AGNs) at $0.5 < z \lesssim 1$ using DESI DR1 spectroscopy.We identify 98 broad-line IMBH AGNs with black hole masses $M_\mathrm{BH}<10^6$ $M_{\odot}$ through quantitative spectral decomposition and broad-H$\beta$ selection. This sample spans $M_\mathrm{BH}=10^{5.5}-10^{6.0}$ $M_{\odot}$ and Eddington ratios from 1.2 to 9.0 extending systematic IMBH AGN searches to intermediate redshift. Compared with a consistently selected $z<0.6$ IMBH sample, the $0.5<z<1$ sources reach higher broad-H$\beta$ luminosities and substantially higher Eddington ratios, indicating more extreme accretion states at earlier cosmic times. They also show broader [O III] profiles and stronger blueshifted wing components, with these kinematic differences persisting after matching in black hole mass and Eddington ratio. These results reveal two distinct signatures of evolution among IMBH AGNs at $z<1$: ability of IMBHs to reach increasingly extreme accretion states toward higher redshift, and systematic changes in their ionized-gas kinematics. The former demonstrates that rapid, including super-Eddington, growth of IMBHs can persist to relatively late cosmic times, while the latter may indicate evolution in the ionized-gas environment and associated outflow activity of actively growing IMBHs. Together, these findings provide new constraints on the evolutionary pathways of IMBHs at $z<1$, and show that seed-mass black holes can continue to undergo rapid growth well after the cosmic dawn.
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All authors Wen-Juan Liu, Luis C. Ho, Su Yao, Xiao-Bo Dong, Yaqi Zhao

Astrophysics of Galaxies

A Dusty Quenching-candidate AGN host at z=5.7: massive quiescent galaxies may quench already during the dust-obscured phase

Francesco D'Eugenio, Matilde Brazzini, Roberto Maiolino et al. (+12 more)

We present a spectro-photometric analysis of RUBIES-EGS-9809, a broad-line AGN host at z=5.7 with a Balmer break and a dominant point source. The source is dust reddened ($A_V>$3 mag), shows hot- and cold-dust emission, and is X-ray Compton thick, with X-ray-to-bolometric ratio consistent with luminous AGN. The large $A_V$ agrees with strong NaI absorption (EW=17$\pm 2 \AA$), possibly from a neutral-gas outflow (3 $\sigma$), while broad [O III] traces an ionized outflow, suggesting AGN feedback may be affecting the host. We estimate a stellar mass log(M*/M$_\odot$)=10.7$\pm$0.3, Lbol$\sim4\times10^{46}$ erg s$^{-1}$ , and black-hole mass log(M$_{BH}/M_\odot)\sim8.1$ (subject to large systematics). The resolved Balmer break (0.1 arcsec, 0.6 kpc) is consistent with a stellar origin, implying the galaxy is already old in stars while still heavily obscured. This shows that massive galaxies can host evolved stellar populations during their compact, dust-obscured phase, consistent with formation in an earlier dusty starburst. SED modelling suggests a declining SFR, but low-resolution spectroscopy alone cannot constrain the recent SFR, so we treat the source as a strong quenching candidate rather than a secure post-starburst system. Because quenching follows the decline in SFR, star-formation-driven outflows are disfavoured, leaving AGN feedback as a plausible driver. We speculate that such rapid feedback ($\sim$100 Myr timescale) may precipitate quenching while the post-quenching phase stays dust-enshrouded, concealing the UV-bright quenched phase that would otherwise be easily detected, if dust free. By the time dust clears, the UV-luminous stars may have already dwindled, leaving a classic dust-free quiescent galaxy. This 'dusty path' to quiescence may explain the lack of intermediate-age quenched progenitors (ages 50-100 Myr) linking dusty starbursts to massive quiescent systems at z=3-7.
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All authors Francesco D'Eugenio, Matilde Brazzini, Roberto Maiolino, Elena Bertola, Stefano Carniani, Xihan Ji, Ignas Juodžbalis, Yixiao Liu, Minjung Park, Eleonora Parlanti, Robert G. Pascalau, Gabriele Pezzulli, Jan Scholtz, Sandro Tacchella, Stefano Zibetti

Astrophysics of Galaxies

The MICADO first light imager for the ELT: Simulated Observations of Star Forming Clumps at Cosmic Noon

Matteo Simioni, Carmelo Arcidiacono, Andrea Grazian et al. (+18 more)

Galaxies at redshift z$\sim$2-6 exhibit prominent star-forming regions (clumps). Characterisation of these galactic structures requires both high sensitivity and spatial resolution of $\sim$100 pc or less. Currently, these spatial scales are achievable only with the aid of strong gravitational lensing. However, lensing introduces model-dependent uncertainties and limits the sample to galaxies behind massive clusters. The upcoming 40m-class telescopes, such as the ESO Extremely Large Telescope (ELT), will enable routine studies of clumps in ubiquitous, non-lensed z$\ge$2 galaxies. We assess the capability of MICADO, the first-light imager and spectrograph of the ELT, to characterise clumps in non-lensed z=2 galaxies. Specifically, we focus on two representative observing scenarios, providing the basis for an early scientific exploitation of the instrument. We modelled clumps in an idealised z=2 star-forming galaxy and produced mock MICADO observations in both broad- and narrow-band imaging. The latter leverages the strong emission lines typical of clumps to improve detection and characterisation. Reaching UV rest-frame magnitudes of clumps as faint as M$_{UV} \sim -15$ in optimal observing conditions, MICADO will be able to efficiently characterise clumps in non-lensed z=2 galaxies down to R$_{e} \sim 20$ pc. Moreover, the full MICADO $\sim$1 arcmin$^2$ field of view enables efficient surveys of multiple targets. This study demonstrates MICADO's potential to fill a crucial observational gap, shedding new light on clump formation and evolution at cosmic noon. Accurate PSF reconstruction will be crucial to fully harness this capability as it significantly impacts clump detection and characterisation, especially at the smallest sizes ($<$40 pc).
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All authors Matteo Simioni, Carmelo Arcidiacono, Andrea Grazian, Marco Gullieuszik, Elisa Portaluri, Alvio Renzini, Benedetta Vulcani, Anita Zanella, Francesca Annibali, Michele Cirasuolo, Richard Davies, Natascha Förster Schreiber, Johanna Hartke, Hanindyo Kuncarayakti, Matteo Messa, Stefan Raffetseder, Letizia Scaloni, Elena Valenti, Eros Vanzella, Joël Vernet, Roland Wagner

Astrophysics of Galaxies

Improving constraints on the Yukawa correction at the Galactic Center with multiple stellar orbits

GRAVITY+ Collaboration: A. Foschi, K. Abd El Dayem, N. Aimar et al. (+76 more)

We investigate the presence of a Yukawa-like correction ($\propto \, \alpha e^{- r/\lambda}$) to Newtonian gravity at the Galactic Center, using a multi-star fitting code, including the newly discovered star S$301$, to improve the constraints obtained using S$2$ orbit alone. We perform a Markov Chain Monte Carlo analysis using the astrometric and spectroscopic data of stars S$2$, S$55$, S$29$, S$38$ and S$301$ collected by GRAVITY, GRAVITY$^+$, NACO and SINFONI instruments, covering the period from $1992$ to $2025$. Compared to GRAVITY Collaboration 2025 (Paper I), in which only S$2$ was fitted, the tightest bound on the Yukawa coupling is again reached at $\lambda = 3\cdot10^{13}\,\rm m\ (\sim 200\,AU)$, where we find $|\alpha| < 6 \cdot10^{-4}$, an improvement of roughly a factor five. The addition of S$301$ extends the constraint to short ranges that were inaccessible to S$2$, yielding $|\alpha| < 0.004$ at $\lambda =10^{12}\,\rm m$ and $|\alpha| < 0.006$ at $\lambda =5\cdot 10^{11}\,\rm m$, while S$29$, with its larger apoapsis, gives $|\alpha| < 0.1$ at $\lambda \sim 2\cdot10^{15}\,\rm m$. The latter two represent the tightest limits at these scale lengths on a Yukawa correction obtained to date around a supermassive black hole.
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All authors GRAVITY+ Collaboration: A. Foschi, K. Abd El Dayem, N. Aimar, A. Berdeu, J.-P. Berger, G. Bourdarot, W. Brandner, Y. Cao, C. Correia, S. Cueves Cardona, R. Davies, D. Defrère, F. Delplancke-Ströbele, A. Drescher, F. Eisenhauer, L. Esteras Otal, M. Fabricius, H. Feuchtgruber, S. Flesch, N.M. Förster Schreiber, Q. Fournier, P. Garcia, R. Garcia Lopez, R. Genzel, S. Gillessen, F. Gonté, X. Haubois, S.F. Hönig, M. Houllé, S. Joharle, J. Kammerer, A. Kaufer, P. Kervella, L. Kreidberg, L. Labadie, S. Lacour, O. Lai, R. Laugier, J.-B. Le Bouquin, J. Leftley, R. Li, B. Lopez, D. Lutz, F. Mang, A. Mérand, F. Millour, M. Montargès, N. Morujão, H. Nowacki, M. Nowak, J. Osorno, T. Ott, S. Pappert, C. Paladini, T. Paumard, K. Perraut, G. Perrin, R. Petrov, N. Pourré, S. Rabien, D.C. Ribeiro, S. Robbe-Dubois, M. Sadun Bordoni, J. Sanchez-Bermudez, J. Sauter, J. Scigliuto, J. Shangguan, T.T. Shimizu, F. Soulez, C. Straubmeier, E. Sturm, M. Subroweit, C. Sykes, L.J. Tacconi, P. Thévenet, I. Urso, F.H. Vincent, J. Woillez, G. Zins

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

Approximating the statistics of a gravitational wave background

Mikel Falxa

The astrophysical origin of the gravitational wave background (GWB) reported by pulsar timing array (PTA) collaborations has yet to be confirmed. A GWB signal made of the sum of individual gravitational wave (GW) from the population of supermassive black hole binaries (SMBHB) would show the imprint of a discrete Poissonian statistics in its spectral properties. In this work, we propose a tool based on the saddlepoint approximation method to estimate the distribution of characteristic strain for any given population model. This tool can be used for Bayesian inference or for a quick visualization of the statistics of the GWB from the output of more realistic semi-analytical models. We introduce the general family of variance mixture Gaussian distributions that models heavy-tailed behavior distributions that is expected for a non-Gaussian GWB signal. We show that setting the correct hierarchical priors to a Gaussian free spectrum PTA likelihood is effectively equivalent to a non-Gaussian likelihood. Using ideal simulations, we compare the performance of the saddlepoint approximation with a log-Normal distribution to infer the parameters of the astrophysical model from the statistics of the GWB and show that correctly modeling higher order moments is essential. Future PTA analyses should include the statistics of the GWB in their pipelines.
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