Astrophysics of Galaxies
Electron temperature and emission measure of HII regions in the central molecular zone (CMZ) from H40 \alpha recombination line and continuum emissions by ALMA CMZ Exploration Survey - ACES -
Yoshiaki Sofue, Steven N. Longmore, Daniel Walker et al. (+40 more)
Star formation activity in the Central Molecular Zone (CMZ) directly manifests itself as
radio continuum free-free emission (Bremsstrahlung) and
radio recombination line emission from HII regions surrounding newly formed massive
stars. We derive the overall distribution of the HII regions and their fundamental properties: electron temperature ($\Te$) and emission measure ($EM$), and hence electron density in the form of two dimensional distribution maps over the CMZ by analyzing the ACES (ALMA CMZ Exploration Survey) \h40 (99.02 GHz) recombination line and 99.6 GHz continuum emission data with synthesized beam widths of $2''.45$ (0.097 pc at 8.2 kpc) and $2''.14$, respectively. We apply the 'TeEM' method ($\Te$–$EM$ mapping), which creates $\Te$ and $EM$ maps from input 2D maps of the continuum and integrated line intensity. The analysis covers the entire ACES field from $l\sim -0^\circ.6$ to $+0^\circ.8$ and from $b\sim -0^\circ.2$ to $+0^\circ.1$. The area analyzed is complete and includes previously known HII regions such as Sgr B2, Sgr B1, the Sickle, the Pistol, thermal filaments (Bridges), Sgr A HII regions, the Minispiral, and many other known HII regions. Sgr C is not included in the analysis due to the insufficient signal-to-noise ratio in the recombination line map. The mean electron temperature over the CMZ is determined to be $\Tcmz= 5872 \pm 78 ~{\rm (SE)} ~\pm 3682~{\rm (SD)}$ K (SE:standard error of the mean, SD: pixel-to-pixel standard deviation). Some HII regions, such as Sgr B2 Main and the Minispiral, exhibit large scatter and an internal $\Te$ gradient of several thousand K per parsec. The $EM$ distribution is more diverse, varying by orders of magnitude from $\sim 10^5$ to $\sim 3\times 10^8$ \emunit within the CMZ, as well as within individual HII regions.
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All authors Yoshiaki Sofue, Steven N. Longmore, Daniel Walker, Adam Ginsburg, Jonathan D. Henshaw, John Bally, Ashley T. Barnes, Cara Battersby, Laura Colzi, Paul Ho, Izaskun Jimenez-serra, Elizabeth Mills, Maya A. Petkova, Mattia C. Sormani, Jennifer Wallace, Robin G. Tress, Nazar Budaiev, Rojita Buddhacharya, Christoph Federrath, Zi-xuan Feng, Pablo García, Savannah Gramze, Christian Henkel, Pei-ying Hsieh, Fengwei Xu, Katharina Immer, Dani Lipman, Dariusz C. Lis, Álvaro Sánchez-Monge, Xing Lu, Mark R. Morris, Francisco Nogueras-Lara, JÜrgen Ott, Dylan M. Paré, Jaime E. Pineda, Víctor M. Rivilla, Jairo Armijos-Abendaño, Qizhou Zhang, 6Denise Riquelme-vásquez, Howard a. Smith, Marco Donati, Q. Daniel Wang, N. Bijas
Astrophysics of Galaxies
The Rotation Curve of the Milky Way: State of the Art, the Keplerian Decline Debate, and Implications for Dark Matter
Alessandro Melchiorri and Ruchika
For four decades, the roughly flat rotation curve (RC) of the Milky Way (MW) stood as local evidence for an extended dark matter (DM)
halo. Gaia DR3 has changed the picture: several analyses now find a velocity decline beyond R \approx 15\kpc, and the most radical interpretation \citep{jiao2023} claims a nearly Keplerian fall-off (\vc \propto R^{-1/2}) that excludes a flat RC at 3\sigma and implies a total dynamical mass of only \sim 2 \times 10^{11}\Msun—three to five times below pre-Gaia estimates. Taken at face value, this would make the MW exceptional among comparable spirals and challenge both \Lambda-CDM and MOND. It would also alter predictions for direct-detection experiments, although the local DM density is not fixed by virial mass alone. The Keplerian claim rests on the delicate assumptions of axisymmetric Jeans modelling, while stellar streams, globular clusters, satellite kinematics, and the Local Group timing argument generally favour a substantially heavier
halo, and cosmological simulations reveal potentially substantial biases in Jeans-inferred outer RCs. This review offers a self-contained, pedagogical account of the debate: we derive the full formalism from first principles—the Jeans equations, the asymmetric drift correction, the standard DM
halo and baryonic mass models, the MOND flat-RC prediction, and the timing argument—present an illustrative phenomenological MCMC fit and a Gaussian Process reconstruction of the RC, and critically assess which features of the decline can be regarded as established and which remain open.
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Astrophysics of Galaxies
Constructing X-ray Spectral Models of Galaxies: Varying Contributions from X-ray Binary Populations with Host Galaxy Properties
Emerson Gehr, Bret D. Lehmer, Antara R. Basu-Zych et al. (+7 more)
Recent work has shown that the emission from X-ray binary (XRB) populations in
galaxies varies with stellar mass ($M_\star$),
star formation rate (SFR), and
metallicity ($Z$). Such scaling relations are widely used to predict the XRB contributions to
galaxy-integrated X-ray luminosities including studies focused on dwarf active galactic
nuclei (AGN) and the X-ray radiation field during the epoch of heating in the early ($z \geq 8$) universe. However, as
galaxies approach low SFR and low $Z$, the relatively shallow slope of the XRB luminosity function (XLF) can yield very large
stochastic variations in the total X-ray luminosity expected from the XRB population, for fixed values of $M_\star$, SFR, and $Z$. We have created a procedure to statistically sample any XLF and model total X-ray spectra for XRB populations and their
stochastic uncertainties. We demonstrate the accuracy of this procedure using data for
galaxies ranging from high to low $M_\star$, SFR, and $Z$ and generating X-ray spectral models consistent with Chandra observations. For
galaxies that lie on the galactic main-sequence, we can relate SFR and $Z$ to $M_\star$ using established $M_\star$-SFR and $M_\star$-$Z$ relations. Applying these relations, we construct main-sequence (MS) XRB spectral models, which provide typical XRB spectral shapes, normalizations, and uncertainties as a function of $M_\star$. The spectral model library associated with this work is available at https://doi.org/10.5281/zenodo.20126734.
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All authors Emerson Gehr, Bret D. Lehmer, Antara R. Basu-Zych, Konstantinos Kovlakas, Vianney Lebouteiller, Erik B. Monson, Izabela Pavel, Chris Richardson, Maxime Varese, Zachary Wilson
Astrophysics of Galaxies
The Extended Mapping Obscuration to Reionization with ALMA (Ex-MORA) Survey: A Molecular Gas Line Search
V. Catán, J. González-López, M. Aravena et al. (+9 more)
Current investigations of cold gas in the interstellar medium face selection biases, as optical/near-infrared surveys favor massive, low-obscuration
galaxies and miss gas-rich passive or inefficient
star-forming systems. Overcoming this requires large-volume line surveys selected by molecular gas rather than stellar luminosity. We present a molecular gas census across $0.5 < z < 5$ using ALMA Band 4 observations from the Extended Mapping of Obscuration to Reionization Survey (Ex-MORA), covering 577 arcmin$^2$. Combining an unbiased search for bright emitters with a targeted search using spectroscopic
redshift priors, we detect 52
galaxies in CO or \ci transitions (two showing two lines). Physical properties were derived via CIGALE with non-parametric
star-formation histories, and gas masses were estimated using
metallicity-dependent conversion factors. The sample is dominated by main-sequence (MS)
galaxies with high stellar masses (median $\log M_*/\text{M}_{\odot} = 10.83$) and large gas reservoirs ($>10^{10}\,\text{M}_{\odot}$). Gas fraction ($\mu_{\text{gas}}$) increases with
redshift for active populations, though high-
redshift trends are influenced by a gas-rich protocluster at $z \approx 2.4$. Conversely, an overdensity at $z \approx 0.73$ mirrors the field population. Five Green Valley (GV)
galaxies exhibit a $\mu_{\text{gas}}$ peak at
cosmic noon, suggesting stellar feedback may suppress
star formation by heating gas rather than rapidly depleting it in at least some transitional systems. Resolved kinematics show a prevalence of rotating disks. These results demonstrate that wide-area line searches effectively recover massive gas reservoirs across diverse evolutionary stages
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All authors V. Catán, J. González-López, M. Aravena, A.S. Long, C.M. Casey, D.L. Clements, E. da Cunha, M. Franco, A.M. Koekemoer, A. Man, J. Spilker, E. Treister
Astrophysics of Galaxies · Cross-listed from astro-ph.CO
CORN – Chronometers of Relic Nature I: The first estimate of the expansion rate of the Universe using compact relic galaxies
Krzysztof Lisiecki, Nicola Principi Cavaterra, Agnieszka Pollo et al. (+9 more)
Measuring the expansion rate of the Universe is a central challenge in cosmology. Independent and robust methods are essential to validate existing measurements and assess potential systematic effects. We employ the
cosmic chronometer (CC) approach, which uses the differential age
evolution of quiescent
galaxies to measure the Hubble parameter H(z) without assuming an underlying cosmological model. In contrast to previous CC studies, we restrict our analysis to relics – ultra compact massive
galaxies (UCMGs) hosting the oldest stellar populations – thereby minimising uncertainties related to
star formation history and merger history. We select a sample of 189 relic
galaxies in the
redshift range 0.07< z <0.22 from the E-INSPIRE UCMGs catalogue. Using the D_n4000 spectral index of relic
galaxies and its
redshift evolution, combined with MILES stellar population synthesis models, we derive the differential age relation required to infer H(z). We account not only for
metallicity effects but also for the impact of alpha-element enhancement, which has not been explicitly propagated into the systematic uncertainty budget of the D_n4000
cosmic chronometer method. We obtain an independent measurement of H(z=0.15) = 85\pm53 km/s/Mpc. The total uncertainty is dominated by statistical limitations. The systematic component is 13% (8.7% when alpha-enrichment is not propagated), among the tightest estimates in current CC studies. We find that alpha-enrichment plays a major role in the systematic error budget, particularly in the high
metallicity regime, and must be properly accounted for in future analyses. We demonstrate the proof of concept that relic
galaxies provide a promising pathway to reduce systematic uncertainties in the CC method. The statistical uncertainties, which dominate the error budget, can be significantly reduced by the increase of data volume expected during the next years.
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All authors Krzysztof Lisiecki, Nicola Principi Cavaterra, Agnieszka Pollo, Chiara Spiniello, Laura Hunt, Charlie Rosen, Marek Biesiada, Darko Donevski, Patryk Matera, Giuliano Lorenzon, Katarzyna Małek, John Mills
Astrophysics of Galaxies
Does IRS13 require an intermediate-mass black hole?
Václav Pavlík, Vladimír Karas, Florian Peißker et al. (+2 more)
We investigate whether the Galactic-centre association IRS13 requires an intermediate-mass black hole (IMBH) to remain bound. Using high-precision $N$-body calculations of IRS13-like systems orbiting the Milky Way supermassive black hole (SMBH), as well as simulations of more massive infalling clusters, we find that an IRS13-sized cluster dissolves on a very short timescale even when an IMBH of $4\times10^4\,M_\odot$ is present. The observed velocity dispersion can arise naturally from the tidal field of Sgr A* and the infall event itself; therefore, it need not imply a central IMBH. In the infalling-cluster runs, tidal stripping produces transient disks, spiral-like structures, and ring-like overdensities. These features suggest a broader interpretation: IRS13 is best viewed as a temporary phase-space overdensity, analogous in mechanism (though not in scale) to phase-wrapped shells and streams in disrupted
galaxies.
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All authors Václav Pavlík, Vladimír Karas, Florian Peißker, Bhavana Bhat, Andreas Eckart
Astrophysics of Galaxies
From Cluster Core to Splashback: Linking Dynamical Structure to Multidimensional Galaxy Evolution in the Coma Cluster
Mohamed H. Abdullah, S. W. El-Sogheir, Gillian Wilson et al. (+2 more)
We investigate
galaxy evolution across the full dynamical structure of the Coma cluster using the GalWCat19 spectroscopic cluster catalog combined with SDSS-based value-added
galaxy properties. We measure a splashback radius of $R_{sp} = 2.94 \pm 0.16~h^{-1}\, Mpc$. Using specific
star formation rate (sSFR), color offset from the red sequence ($\Delta(g-r)_{RS}$), and bulge-to-total ratio ($B/T$) as independent diagnostics, we find a coherent environmental transition from quiescent, red, bulge-dominated
galaxies in the cluster core to increasingly
star-forming, blue, disk-dominated populations at larger radii. We further introduce a three-dimensional framework in the joint $(\log sSFR, \Delta(g-r)_{RS}, B/T)$ space and develop a peak-based classification scheme that extends beyond traditional one-dimensional
galaxy classifications. This framework identifies two dominant populations: red, quiescent, bulge-dominated
galaxies, which account for $51\%$ of the joint-analysis sample, and blue,
star-forming, disk-dominated
galaxies, which account for $29\%$. The remaining $\sim20\%$ of
galaxies occupy transitional or mixed states that connect these two principal populations. The relative fractions of these populations change strongly near the splashback radius, where the red, quiescent, bulge-dominated population declines rapidly and the blue,
star-forming, disk-dominated population becomes increasingly dominant. These results show that the splashback boundary is not only a dynamical boundary, but also a critical evolutionary transition zone. Overall, our findings suggest that
galaxy evolution in Coma is not a purely binary transformation, but instead proceeds through continuous multidimensional pathways in which
star formation quenching, color
evolution, and morphological transformation occur on different timescales while remaining closely linked to the cluster dynamical structure.
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All authors Mohamed H. Abdullah, S. W. El-Sogheir, Gillian Wilson, Magdy Y. Amin, A. Ahmed
Astrophysics of Galaxies
Spiral Morphology and Radial Migration: Kinematically heating, cooling, and cold
Kathryne J. Daniel, M. E. Wisz, Karen L. Masters et al. (+3 more)
Transient spiral arms are known to drive radial redistribution of
stars and thus could play a central role in shaping disk
galaxies, including modifying, over time, the age, chemical, and kinematic (chrono-chemo-dynamic) distributions in the Milky Way. However, the physical factors governing the efficiency of such processes remain poorly understood. This paper investigates how the morphology of spiral arms – the number, pitch angle, lifetime, and radial dependence of the pattern speed – influences orbital redistribution through 'cold torquing' at the corotation resonance(s). Analytic expressions are derived for the maximum radial excursion of
stars trapped at corotation that explicitly account for spiral morphology, predicting that the efficiency of cold torquing for a density-wave like spiral is greater for more open spiral patterns. Tracer-particle simulations confirm the analytic prediction, in both two- and three-dimensional galactic potentials. In contrast, spirals that have a radially dependent pattern speed such that they corotate with the disk at all radii exhibit the opposite behavior, with cold torquing becoming more efficient as the spiral winds to smaller pitch angles over time. This study further finds that resonant interactions from the same transient spiral causing cold torquing naturally also produces both kinematic heating and cooling of orbits away from corotation. These results demonstrate that spiral morphology alone cannot predict the efficiency of cold torquing and suggest that the relationship between spiral pitch angle and radial redistribution provides a potential diagnostic for distinguishing between competing theories of spiral structure.
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All authors Kathryne J. Daniel, M. E. Wisz, Karen L. Masters, Rosemary F. G. Wyse, Amy Smock, Lipika Chatur
Astrophysics of Galaxies · Cross-listed from astro-ph.EP
SMA Observations Reveal Abundant HNC Chemistry in Transition Disks
Kyle Gresko, Charles J. Law, Deryl E. Long et al. (+8 more)
The physical and chemical conditions of protoplanetary disks shape the properties of nascent planetary systems. The line ratios and relative abundances of the HCN-HNC isomer pair are well-suited for tracing these gas conditions, since isomer chemistry is linked to the underlying temperature, elemental abundances, and irradiation environment of the emitting gas. While HCN emits bright lines regularly observed in disks, the fainter HNC lines are targeted significantly less often, precluding our ability to calibrate the HNC-to-HCN ratio as a tracer of disk properties. Here, we present new Submillimeter Array observations of five transition disks around the T Tauri
stars GM Aur, J1604, LkCa 15, GG Tau, and V4046 Sgr, covering the J=3-2 and J=4-3 lines of HCN and HNC. We detected at least one line of both HCN and HNC in each source and measured disk-integrated HNC-to-HCN flux and column density ratios of $\approx$0.1-0.7 and 0.1-0.4, respectively. For all sources, measured HNC fluxes exceed predictions from models of full (non-transition) disks by $\approx$3-10x, while HCN fluxes appear typical. The relative brightness of HNC vs. HCN in transition disks strongly suggests a link between the presence of a cavity and efficient HNC production. We corroborate this trend using chemical models of the DM Tau transition disk, showing HNC production and destruction are connected to the radiation environment. In our sample, disk-integrated HNC-to-HCN column density ratio shows no trend with disk gas temperature but positively correlates with disk mass due to increased HNC abundance in the larger reservoirs of cooler gas in more massive disks.
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All authors Kyle Gresko, Charles J. Law, Deryl E. Long, L. Ilsedore Cleeves, Feng Long, Yuri Aikawa, Jennifer B. Bergner, Romane Le Gal, Viviana V. Guzmán, Karin I. Öberg, David J. Wilner
Astrophysics of Galaxies
An X-ray Absorption-Line Survey of the Circumgalactic Medium of M31 with XMM-Newton
Kaile Wang, Zheng Zhou, Taotao Fang et al. (+1 more)
X-ray absorption line spectroscopy provides a powerful method for probing the extended hot circumgalactic medium (CGM) of individual
galaxies. In this study, we present the first survey of \osv and \oeit absorption lines toward the hot
halo of M\,31, using $15$ and $18$ background active galactic
nuclei, with impact parameters ranging from $R_{\rm imp}\sim300$–$730$~kpc and $\sim190$–$730$~kpc, respectively. We find a marginal excess absorption above the expected Milky Way (MW) foreground toward the innermost sightlines, consistent with an additional hot-CGM contribution associated with M\,31. Comparing sightlines inside and outside $R_{\rm imp}=300$–$350$~kpc, the excess corresponds to a mean equivalent width of $\sim4$–$9$~mÅ\ for the inner \osv sightlines at $R_{\rm imp}\sim310$~kpc and $\sim17$~mÅ\ for the inner \oeit sightlines at $R_{\rm imp}\sim200$~kpc, with a nominal combined significance level of $2.2$–$2.3\,\sigma$. The hot-CGM mass inferred from this excess is highly model dependent, especially on the assumed CGM boundary, and therefore does not yet provide a robust baryon census. Attributing the excess entirely to hot gas confined within approximately the virial radius of M\,31 would require a CGM mass exceeding the nominal “missing” baryon budget. The inferred mass decreases to a few $\times10^{11}~M_\odot$ when the assumed CGM boundary is extended to $400-500$~kpc. Deeper observations, both through longer exposures of existing sightlines and the inclusion of additional inner-
halo targets, will be essential to robustly constrain the properties of the hot CGM of M\,31.
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All authors Kaile Wang, Zheng Zhou, Taotao Fang, Fabrizio Nicastro
Astrophysics of Galaxies · Cross-listed from astro-ph.SR
Filling the Gap: Calibrating Gyrochronology at 1.3 Gyr with the Benchmark Cluster NGC-752
Andrew W. Boyle and Andrew W. Mann
Empirical gyrochronology relies on co-eval stellar associations to map stellar rotation as a function of mass and age. The accuracy of its age predictions is therefore limited by the number and quality of
benchmark rotation sequences. The well-characterized clusters NGC-6811 (t ~ 1 Gyr) and NGC-6819 (t ~ 2.5 Gyr) bracket an intermediate-age interval in which stellar
spin-down remains poorly constrained due to lack of available rotation data. At t ~ 1.3 Gyr, NGC-752 provides a critical
benchmark within this gap, but previous measurements could not define the G- and K-dwarf rotation sequence needed for calibration. Here, we combine Gaia-based NGC-752 membership lists with literature rotation periods to map NGC-752's slow-rotator sequence for the first time. We identify a well-defined sequence intermediate between those of NGC-6811 and NGC-6819.
Stars near Teff ~ 4500 K rotate more slowly than their counterparts in NGC-6811, indicating that
stars experiencing stalled
spin-down at ~1 Gyr have resumed appreciable
spin-down by the age of NGC-752. Adopting an age of 1.3 Gyr for NGC-752, we further show that existing empirical gyrochronology models overestimate the ages of many G and early-K dwarfs by 20–50% because they lack intermediate-age calibration data, although uncertainty in the absolute age of NGC-752 may account for part of this offset. NGC-752 therefore provides a necessary anchor for improving rotational age estimates. This calibration is especially timely because Gaia DR4, Roman, and PLATO are expected to yield rotation periods for tens of millions of
stars, making the age coverage of
benchmark sequences a principal limitation on large-scale gyrochronology.
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Astrophysics of Galaxies
Discovery of four Narrow-line Type-1 Quasars at z = 2.54 – 6.06 with Subaru 'Onohi'ula PFS-SSP
Ayumi Takahashi, Yoshiki Matsuoka, Yoshiki Toba et al. (+21 more)
We report the discovery of four narrow-line type-1
quasars (NLQ1s) from the Subaru 'Onohi'ula
Prime Focus Spectrograph Subaru Strategic Program (PFS-SSP). To extend a comprehensive understanding of this population to the distant universe, we searched for broad-line AGNs (
quasars) whose rest-UV spectral shapes resemble those of local NLS1
galaxies, utilizing the Ly$\alpha$ line profile. We identified four NLQ1s, including one candidate, at $z=2.54$ – $6.06$. The obtained spectra show a prominent Ly$\alpha$ emission line with a very low continuum level. The measured full width at half maximum (FWHM) of Ly$\alpha$ ranges from $1410 \ \mathrm{km\,s^{-1}}$ to $1510 \ \mathrm{km\,s^{-1}}$ with a mean of $\sim 1430 \,\mathrm{km\,s^{-1}}$. Although we used only line width information for the NLQ1 selection, the resulting equivalent widths (EW) of Ly$\alpha$ are higher (the mean $\sim 190$\,Å \ in the rest frame) than the typical values of
quasars. Two
quasars have exceptionally large Ly$\alpha$ luminosity, accounting for $\sim 3$ – $4$% of the bolometric luminosity. We measured black hole masses and Eddington ratios for three objects whose C\,iv line is available. The resulting black hole masses are $\sim 10^{6.9}$ – $10^{7.7}\, M_{\odot}$ with high Eddington ratios ($> 0.1$), consistent with those of NLS1
galaxies reported in the low-$z$ universe. N\,v and C\,iv broad absorption lines are detected in one object. This
quasar can be classified as a mini-BAL
quasar, which further supports the idea that this NLQ1 is indeed a luminous version of an NLS1
galaxy.
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All authors Ayumi Takahashi, Yoshiki Matsuoka, Yoshiki Toba, Tohru Nagao, Toshihiro Kawaguchi, Hiroaki Sameshima, Alberto Rodríguez-Ardila, Andy D. Goulding, Masayuki Akiyama, Denimara Dias dos Santos, Atsushi Hoshi, Kohei Ichikawa, Masatoshi Imanishi, Kazushi Iwasawa, Mitsuru Kokubo, Huynh Anh N. Le, Khee-Gan Lee, Masafusa Onoue, Masayuki Tanaka, Patrice Theulé, Hao Zhang, Jialai Wang, Xinfeng Xu, Yongquan Xue
Astrophysics of Galaxies
Flat Galactic Rotation Curves Interpreted as Evidence for the Mach's Principle
Andres Escala
We explore the possibility of a Machian interpretation for the phenomena associated with asymptotically flat rotation curves in disk
galaxies, providing an alternative to both the Lambda-Cold Dark Matter ($\Lambda$CDM) paradigm and MOdified Newtonian Dynamics (MOND). We argue that the MOND acceleration scale $a_0$ is likely not a new fundamental constant, but rather a manifestation of the cosmological scales of the observable Universe ($a_0 \sim c^2/R_u \sim c^4/GM_u \sim c/t_u$). We rewrite the Baryonic Tully-Fisher Relation (BTFR) in a cosmological format, $\frac{M_{\rm bar}}{M_{u}} = \left( \frac{V}{c} \right)^4$, suggesting that the transition to the non-Newtonian regime occurs when local accelerations become small enough to feel the global
cosmic boundary, and showing that any Machian interpretation must fulfill a relation of this form. Furthermore, this framework naturally predicts a cosmological
evolution of the BTFR normalization as the mass in the observable Universe evolves. We test these predictions against recent high-
redshift observations ($z \sim 2$ and $z \sim 5$), finding that the data favor a flat, baryon-only, $\Lambda$-dominated quasi-de Sitter universe ($\Omega_m \approx 0.05$, $\Omega_\Lambda \approx 0.95$) over standard MOND or $\Lambda$CDM parameters. These results suggest that flat galactic rotation curves may be interpreted as compelling evidence in favor of Mach's Principle, in at least some of its versions.
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Astrophysics of Galaxies
A cosmic collision in the making: JWST/NIRISS reveals a merging and maturing protocluster core at z~3 around a red quasar
C. Bertemes, D. Wylezalek, G. Noirot et al. (+10 more)
We report the discovery of “The Step”, a dense protocluster at z=3 revealed by JWST/NIRISS Wide-Field Slitless Spectroscopy (WFSS) of the field around the luminous
quasar and starburst SDSSJ165202.64+172852.3. The protocluster contains at least 18 member
galaxies and exhibits two substructures in the 3D position-velocity space - notably a distinctive step-like distribution, from which the nickname derives. We propose that the Step may be undergoing a merger of two
haloes, which could also explain the large velocity span (700-850km/s) between
galaxies along the densest line of sight. This sightline contains seven
galaxies within 70 projected kpc from the
quasar, consistent with a remarkably dense protocluster core. We derive a
galaxy overdensity of a factor >100 in the core and >15 within 1 Mpc$^2$, making it one of the densest structures known at this
redshift, and a very massive
halo of $13.1 < log M_{\rm halo}/ M_\odot < 13.8$, which suggests the structure could potentially evolve into a massive, Coma-like cluster at z=0. Compared to the field, the
star-forming
galaxies in the Step show slightly elevated levels of
star formation. Yet, we find two quiescent
galaxies with strong D4000 breaks and no evidence for ongoing
star formation. Compared to other z=3 protoclusters, the Step exhibits similar or slightly suppressed
star-forming activity. We also identify two new AGN candidates and find tentative evidence for an enhanced AGN fraction (10-20%) compared to the field. The protocluster constitutes one of the emerging handful of maturing structures at 2 < z < 4 that host both
star-forming and quenched
galaxies. This
redshift regime may thus be a key transitional epoch for cluster studies, where overdensities transition from being the most active sites of
star formation in the early Universe towards shaping the massive passive ellipticals seen in the cores of today's clusters.
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All authors C. Bertemes, D. Wylezalek, G. Noirot, R. Hviding, D. S. N. Rupke, N. L. Zakamska, S. Veilleux, L. Gatto, W. Liu, A. Vayner, Y. Ishikawa, Y. Chen, S. Sankar
Astrophysics of Galaxies · Cross-listed from astro-ph.HE
Decoding the jet of BL Lacertae using relativistic magneto-hydrodynamics
G. F. Paraschos, J. A. Kramer, I. Liodakis et al. (+5 more)
Blazars are a highly variable subclass of active galactic
nuclei, whose relativistic jet is pointed towards our line of sight at a small angle. Their variability is often characterised by multi-band
flares. BL Lacertae (BL Lac), the namesake of a blazar subclass recently exhibited the highest recorded linearly polarised optical
flare. We investigate the origin of this
flare via very-long-baseline interferometry observations. Our analysis shows that the sweeping, helical motion of the BL Lac jet, which is known to exhibit kink-like instabilities, can explain the observed flux density spike and polarisation angle rotation, as also confirmed by our state-of-the-art relativistic magneto-hydrodynamic simulations. As a by-product of these simulations we find that baryon loading of the jet is required to optimally replicate the observed jet morphology.
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All authors G. F. Paraschos, J. A. Kramer, I. Liodakis, S. G. Jorstad, A. P. Marscher, I. Myserlis, I. Agudo, N. R. MacDonald
Astrophysics of Galaxies
Unveiling and Characterising Ubiquitous Nitrogen Enhancement in $6 \leq z \leq 10$ Galaxies with JWST Spectroscopy
Raunaq Singh Rai and Guido Roberts-Borsani
The James Webb Space
Telescope (JWST) has revealed a growing number of $z>6$
galaxies with enhanced N/O ratios that challenge standard chemical enrichment frameworks. We test whether this is exclusive to extreme systems or a generic feature of $6 \leq z \leq 10$ populations through a stacking analysis of 135
galaxies with JWST/NIRSpec $R\sim1000$ spectroscopy, probing the origin of N, C and O enrichment and its dependence on recent
star formation. A full-sample composite reveals prominent C III], C IV, N IV] and He II emission, demonstrating a ubiquity of high-ionisation UV lines. Auroral [O III]$\lambda$4363 electron temperatures and multi-ionisation zone modelling yield direct-$T_e$ abundances with supersolar $\log(\mathrm{N/O}) = -0.57^{+0.09}_{-0.10}$ and subsolar $\log(\mathrm{C/O}) = -0.80^{+0.03}_{-0.03}$ at $12 + \log(\mathrm{O/H}) = 7.79^{+0.03}_{-0.03}$, in contrast with local samples and suggesting significant nitrogen enhancement within the first billion years. Stacking further by recent
star formation activity over burst timescales of $\Delta t = 3$–$20$~Myr, we find that sources caught in a recent burst are less enriched in both N/O and
metallicity than those in a relative lull, with the largest contrasts confined to the shortest timescales. C/O, however, remains largely invariant across all metrics. We interpret these observations as the result of delayed AGB enrichment across multiple burst episodes, together with dilution by pristine gas inflows. Cosmological simulations reproduce this trend with CCSNe and AGB yields alone, without the need for shorter-lived (super-)massive
stars. Enhanced N/O therefore appears to be a generic feature of high-
redshift systems, produced by standard enrichment processes rather than requiring new physical frameworks.
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Astrophysics of Galaxies · Cross-listed from astro-ph.CO
Realization Variance of Gravitational Wave Background Anisotropies from Shot Noise for Pulsar Timing Arrays
Meng-Xiang Lin, Adam Lidz and Chung-Pei Ma
Shot-noise anisotropies in the nHz gravitational wave background (GWB) are a promising target for
pulsar timing arrays (PTAs). If the nHz GWB is sourced by merging supermassive black hole binaries (SMBHBs), as current evidence suggests, the shot-noise signal is expected to be large, potentially of order unity at observing frequencies of $f \sim 1 \, \mathrm{yr}^{-1}$. In this regime, the signal is dominated by rare bright binaries, and Poisson fluctuations in the discrete SMBHB population produce significant spatial anisotropies. Here, we use Monte Carlo simulations to model the realization-to-realization scatter in the shot-noise, sampling from empirically calibrated models of the SMBHB source populations. We find that the probability distribution of shot-noise amplitudes is broad, spanning a factor of $\sim 50$ (95% interval) at fixed frequency, with a long tail towards high amplitudes. The most probable and median amplitudes lie significantly below the ensemble means by factors of $\sim 2-3$, implying that the shot-noise in typical realizations is smaller than the mean. The ensemble-averaged shot-noise also differs from simple estimates based on moments of the strain, $\langle h^4 \rangle/\langle h^2 \rangle^2$, because the average of a ratio is not equal to the ratio of the averages (i.e., $\langle X/Y \rangle \ne \langle X \rangle/\langle Y \rangle$). This difference is a factor of $\sim 3$ at $f = 0.1 \, \rm{yr}^{-1}$, growing to larger than two orders of magnitude by $f \sim 1 \, \rm{yr}^{-1}$, where the GWB is dominated by low abundance, high-strain sources. Shot-noise nevertheless provides a powerful diagnostic for understanding the GWB and SMBHB populations; interpreting PTA measurements, however, requires modeling its full probability distribution.
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Astrophysics of Galaxies · Cross-listed from astro-ph.SR
IPA: Morphology and Kinematics of Molecular Hydrogen Winds in Five Young Protostars across the Mass Spectrum Observed with JWST
Himanshu Tyagi, P. Manoj, Mayank Narang et al. (+29 more)
Molecular winds may play a key role in governing angular momentum transport and
accretion during the early
evolution of protostars. We present the morphology and kinematic properties of the H$_2$ emission in five young, envelope-dominated, protostars across a broad bolometric luminosity range, from 0.2 to $10^4~L_{\odot}$, observed with the NIRSpec/IFU and MIRI/MRS onboard JWST as part of the Investigating Protostellar
Accretion (IPA) program. A rich set of pure rotational lines of H$_2$, up to $v=0-0$ S(18), and a few ro-vibrational lines are detected in the winds, revealing bipolar structures. The H$_2$ lines show a stratified/onion-like structure morphologically and kinematically, where the lines with higher $E_{\rm up}$ show a higher degree of collimation and higher velocities. Additionally, the wind velocity scales with the $L_{\rm bol}$ of the host protostellar system. In 4 out of 5 protostars, H$_2$ emission fills the outflow cavity without showing pronounced limb brightening. We also report a tentative detection of H$_2$ wind rotation in IRAS 16253, which suggests a launch radius of $\sim4$ au and the
magnetic lever arm parameter of $\sim5-10$. Taken together, these properties of the H$_2$ winds can be explained by the magnetohydrodynamic disk wind models. We detect a collimated, high-velocity H$_2$ jet toward HOPS 370, which is more evolved than the extremely young source HH 211, but is accreting at a high
accretion rate. This suggests that the presence of collimated molecular jets in protostars is more closely connected to
accretion rate than system age.
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All authors Himanshu Tyagi, P. Manoj, Mayank Narang, S. Thomas Megeath, Robert Gutermuth, Lee Hartmann, Alessio Caratti o Garatti, Dan M. Watson, David A. Neufeld, Ewine F. Van Dishoeck, Neal J. Evans II, Vinod Chandra Pathak, Samuel A. Federman, Tyler L. Bourke, Yao-Lun Yang, Guillem Anglada, Henrik Beuther, Leslie W. Looney, Rolf Kuiper, Pamela Klaassen, Pooneh Nazari, Bihan Banerjee, Joel Green, Sujay Vijay Jadhav, Mayra Osorio, B. Shridharan, Amelia M. Stutz, Thomas Stanke, John J. Tobin, Lukasz Tychoniec, Scott Wolk, Manya Arora
Astrophysics of Galaxies
An emerging baryon cycle in a galaxy 500 million years after the Big Bang
Shengzhe Wang, Xin Wang, Hang Zhou et al. (+17 more)
The emergence of stellar feedback as a regulator of
galaxy growth marks a fundamental transition in
cosmic history. At early times, rapid gas
accretion and collapse may induce intense
star formation before feedback becomes effective, producing feedback-free starbursts. When and how such bursts subsequently develop into self-regulated baryon cycles remain observationally unknown. Here we show that Gz9p3, a merging
galaxy at $z=9.311$, is caught in this transition only 500 million years after the Big Bang. Deep JWST spectroscopy reveals a substantial neutral-gas reservoir along its merger-driven tidal structure and a multiphase outflow. Fine-structure absorption provides the first direct measurement of the electron density of the cool outflowing gas at high
redshift ($\approx\,17\,{\rm cm^{-3}}$), yielding a mass-loading factor among the highest yet measured for
galaxies of comparable stellar mass. The emergence of such efficient feedback after an intense burst is consistent with the delayed onset of feedback expected in feedback-free starburst models. The cool outflowing gas is unlikely to escape the host
halo, implying that much of this metal-enriched material may remain available for future recycling through the circumgalactic medium. Gz9p3 therefore provides an early view of a baryon cycle being established through the interplay of merger-driven gas redistribution, bursty
star formation and stellar feedback, suggesting that feedback-regulated recycling was already shaping
galaxy growth during the epoch of reionization.
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All authors Shengzhe Wang, Xin Wang, Hang Zhou, Zhijie Qu, Zhaozhou Li, Yuxuan Pang, Qianqiao Zhou, Shouyi Wang, Yangyao Chen, Yuguang Chen, Karl Glazebrook, Glenn G. Kacprzak, Nicha Leethochawalit, Houjun Mo, Themiya Nanayakkara, Huiyuan Wang, Weida Hu, Xunda Sun, Chao-Wei Tsai, Hu Zhan
Astrophysics of Galaxies · Cross-listed from astro-ph.HE
Recoiling Black Holes I. Burst of Observables
Erwan Hochart and Simon Portegies Zwart
We aim to investigate the tidal disruption and gravitational wave events shortly after a massive black hole binary merges in the galactic centre and whose remnant black hole is ejected from the
galaxy. Using computational methods, black holes of mass $M_{\bullet}=10^{5}$ M$_\odot$ and $4\times10^{5}$ M$_\odot$ embedded in a nuclear
star cluster are kicked at velocities of $v_k=300$ and $600$ km s$^{-1}$. Systems are integrated for $0.1$ Myr using a $4$th-order Hermite scheme. The kick instantaneously repopulates the loss cone, producing a strong burst of tidal disruption events and gravitational wave mergers. The anisotropy in the apsidal orientation of bound
stars prolongs this burst phase. Rates increase for lower $v_k$, larger $M_{\bullet}$ and for steeper nuclear
star cluster density profiles at moment of merger. Assuming binary black holes scour a Bahcall-Wolf density profile during coalescence, ejected remnants with mass between $10^{5}\leq M_{\bullet}$ [M$_\odot] \leq 4\times10^{5}$ generate observable offset events at a forecasted rate of $\dot{N}\lesssim290$ yr$^{-1}$ up to
redshift $z=3$. If, at the moment of merger, the milliparsec scales of the nuclear
star cluster are described by a shallow density profile ($\gamma=1$), this decreases to $\dot{N}\lesssim30$ yr$^{-1}$. The strong dependence on the initial density profile and recoil kick makes observables powerful probes of the nuclear
star cluster post-massive black hole binary coalescence, and provides test for numerical relativity.
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Astrophysics of Galaxies
A Chemical Inventory of the Disk around the Class 0 Protostar L1527 IRS with ALMA
Merel L.R. van 't Hoff, Łukasz Tychoniec, John J. Tobin et al. (+1 more)
Planet formation starts in disks that are still embedded within their natal envelopes. Here, we compile an extensive inventory of the chemical composition of the disk and envelope ($<$ 3500 au) around the Class 0 protostar L1527 IRS. Using all publicly available ALMA (Atacama Large Millimeter/submillimeter Array) data, we report the detection of 40 molecules, including isotopologues. Of these, 23 are different molecular species and 29 are reported here for the first time toward L1527 in ALMA observations. CH$_3$OH is the only complex organic molecule detected, while the hydrocarbon CH$_3$CCH is the largest molecule detected. Overall, only a few programs are sensitive enough to detect emission unambiguously originating from the disk based on the kinematics. Nitrogen-bearing molecules are predominantly detected on more extended scales, while hydrocarbons show a distinct tail roughly along the southeastern outflow cavity wall, probably due to a stronger UV field in the eastern outflow lobe. The L1527 IRS protostellar system is not rich in sulfur-bearing molecules, with only strong emission observed for CS and SO. Overall, the envelope appears dominated by a carbon-rich chemistry, which seems to transition into an oxygen-rich chemistry in the disk. We calculate column densities of all detected species, providing a starting point to quantify the chemical diversity among young disks and the chemical
evolution of the
planet-forming material.
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All authors Merel L.R. van 't Hoff, Łukasz Tychoniec, John J. Tobin, Daniel Harsono
Astrophysics of Galaxies
Ubiquitous Interstellar Neutral Helium Detected with JWST
Jane R. Rigby, D. Koutroumpa, M. Galeazzi et al. (+8 more)
We report the discovery of ubiquitous neutral helium emission in sky spectra taken with JWST's NIRSpec instrument. The emission, with a wavelength of 1.0833 micron, resembles one of the "sky lines" that are seen by ground-based observatories. We examine this emission in all suitable NIRSpec spectra in the public archive, totaling 22 days of exposure time. We find that this He I emission is almost always present: it is well-detected in 80 percent of the observations, and in 53 percent of the individual exposures. The emission is highly time-variable: at a given pointing, the line intensity can vary by factors of several over the course of a day. The He I emission is strongest when JWST crosses through the cone of interstellar neutral helium that is gravitationally focused by the sun; intensity during the cone crossing is anti-correlated with solar activity. The low
redshift and narrow velocity width of the He I line, and the elevated intensity when JWST crosses through the focusing cone, together indicate that origin of the He I emission is cold Milky Way gas passing through our solar system. JWST provides a new way to study this interstellar gas, revealing new insights such as extreme variability on timescales of hours to days, which has not been previously reported.
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All authors Jane R. Rigby, D. Koutroumpa, M. Galeazzi, T. Hutchison, K. D. Kuntz, Rosalia O'Brien, Marshall Perrin, F. S. Porter, Yu. Ralchenko, B. M. Walsh, Brian Welch
Astrophysics of Galaxies · Cross-listed from astro-ph.SR
Sector-based morphological analysis of four planetary nebulae (J 320, NGC 2610, A 6672 and PRTM 1) observed with UVIT/ASTROSAT
Anisha Hazra, Ranjan Kumar, Sonika Piridi et al. (+1 more)
Four planetary nebulae (PNe), Jonckheere 320, NGC 2610, A 6672, and PRTM 1, have been imaged in the far-ultraviolet (FUV) filter F148W ($\lambda_{\mathrm {eff}} = 1481\, \mathring{A} $) using the Ultraviolet Imaging
Telescope (UVIT) onboard ASTROSAT. The FUV images reveal faint extended emission structures surrounding the bright central
star. A novel sector-based structural analysis technique was employed to examine the detailed FUV morphologies of PNe. In this method, sector strengths were calculated for each nebula and used to classify their structures. Our results show that Jonckheere 320 exhibits a polypolar morphology, while NGC 2610 and PRTM 1 display spherical structures. In contrast, A 6672 shows irregular or elliptical features in the FUV.
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All authors Anisha Hazra, Ranjan Kumar, Sonika Piridi, Ananta C. Pradhan
Astrophysics of Galaxies
Searching for low-surface-brightness galaxies with compact neural networks A parameter-efficient approach to first-pass selection of diffuse galaxy in HSC-SSP imaging
Günther K. Heemann, Henri Cecatka and Dominik J. Bomans
Low-surface-brightness
galaxies (LSBGs) trace a diffuse and observationally challenging regime of
galaxy formation that remains highly susceptible to selection effects in optical surveys. We present a hybrid LSBG detection pipeline that integrates compact convolutional neural networks (cCNs) as a morphological validation stage within a multi-step detection framework applied to HSC-SSP imaging. Permissive low-threshold source detection with SEP is followed by cCN-based morphological filtering, physically motivated consistency checks, and parametric surface-brightness modelling with galfitm. The cCN is deliberately constrained to ${\sim}10^4$ trainable parameters to match the spatial scales of diffuse emission and ensure computational efficiency at survey scale. The cCN reduces the initial detection set of ${\sim}77\times10^6$ objects by more than four orders of magnitude while recovering essentially all literature LSBGs that pass the detection stage. The resulting Gold catalog of 5156 candidates occupies the characteristic loci of LSBGs in colour-colour and structural parameter space, in close agreement with previously published HSC-SSP based samples. Cross-matching with SDSS and DESI spectroscopic
redshifts confirms that the pipeline identifies genuine nearby diffuse
galaxies. Compact neural networks provide a robust and computationally scalable morphological filter for LSBG searches, effectively bridging classical detection pipelines and large general-purpose deep architectures. The pipeline is detection-limited rather than selection-limited, identifying the initial source extraction stage as the primary target for future improvement.
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Astrophysics of Galaxies
Dust production in the harsh environment of Sgr A* - MIRI/JWST observation of the O-rich asymptotic giant branch star IRS~3
F. Peißker, M. García Marín, A. Eckart et al. (+18 more)
Studies of the interstellar medium (ISM) have frequently revealed signatures of the dust produced in the envelopes of asymptotic giant branch (AGB)
stars, demonstrating a connection between the dust composition of the ISM and that of AGB stellar envelopes. Investigating this relationship in the extreme, radiation-dominated environment surrounding Sgr A*, the center of our own
galaxy, reveals how such conditions might influence dust composition and the recycling of material in galactic centers. IRS 3, the brightest L band source in the Galactic center and most prominent AGB
star within the inner parsec of the Milky Way, is embedded in a dusty envelope with an estimated radius of $\sim$10000 AU. We aim to conduct a comprehensive spectral analysis to more tightly constrain the dust composition and line-emitting species within the envelope of IRS 3 in the immediate vicinity of Sgr A*. In 2025, we observed the inner parsec of the Milky Way with the Mid-Infrared Instrument (MIRI) on board the James Webb Space
Telescope (JWST) as part of the guaranteed time observations (GTO) program Mid-Infrared Characterisation of Nearby Iconic
galaxy Centres (MICONIC). We used the MIRI Medium Resolution Spectrometer (MRS) to study the spectroscopic characteristics of the AGB
star IRS 3, located about 0.17 parsecs in projection from Sgr A*.
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All authors F. Peißker, M. García Marín, A. Eckart, G. Wright, O. C. Jones, D. Dicken, A. Alonso Herrero, D. Rouan, D. Law, T. Böker, T. Henning, M. Baes, A. Labiano, L. Pantoni, L. Hermosa Muñoz, P.O. Lagage, P. van der Werf, G. Östlin, J. A. D. L. Blommaert, M. Güdel, P. Guillard
Astrophysics of Galaxies · Cross-listed from astro-ph.HE
Global simulations of accretion flows onto perturbers embedded in magnetized disks -I. MRI and jet formation in ideal MHD
Raúl O. Chametla, F. J. Sánchez-Salcedo, Martin E. Pessah et al. (+1 more)
We present the highest resolution global MHD simulations to date of gas flow around a low mass a perturber with mass ratio $q\in[10^{-4},10^{-3}]$, embedded in an
accretion disk around a massive central object. We find that gas flow onto the secondary self-consistently forms a turbulent, magnetized mini-
accretion disk. The mini-
accretion disk sustains a large-scale
magnetic field generated by the dynamo effect of the MRI and the
accretion flow into the perturber. Simultaneously, a bipolar, collimated, magnetized outflow is launched, extending beyond the perturber's Hill sphere. The bipolar outflows are driven by the combined action of
magnetic pressure, in the innermost regions of the mini-
accretion disk, and the magnetocentrifugal acceleration of gas, which may attain speeds comparable to the escape velocity from the massive central object. Our results establish an important conceptual connection in
accretion disk physics across a wide range of astrophysical systems -from mini-
accretion disks to circumstellar and black hole
accretion disks-by demonstrating that no fine-tuning is required for small-scale disks to naturally enter an outflow-launching regime. Beyond identifying the physical mechanism responsible for launching small-scale outflows, our framework lays the groundwork for developing more sophisticated physical models of mini-
accretion disks around embedded low-mass perturbers.
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All authors Raúl O. Chametla, F. J. Sánchez-Salcedo, Martin E. Pessah, Mauricio Reyes-Ruiz
Astrophysics of Galaxies
The Environmental Dependence of Star Cluster Demographics
Jianling Tang, Kathryn Grasha, Mark R. Krumholz et al. (+1 more)
Both the
star cluster mass function and the lifetimes of clusters may vary with galactic environment, but measuring this variation is challenging because in observational surveys real features of cluster demographics are invariably entangled with catalogue incompleteness. Here we analyse $\approx$ 8300
star clusters in 12
galaxies drawn from the LEGUS survey using the slug
Bayesian forward modelling framework coupled to our new c-4 neural network-based completeness
estimator, which allows us to incorporate realistic catalogue-inclusion probabilities directly into the likelihood and compensate for these biases. We show that this approach allows us to fit observed cluster luminosity functions with excellent fidelity at both galactic and sub-galactic scales. We find that mass function slopes are relatively universal and broadly consistent with a power law $M^{-2}$ form, but high mass truncations vary by orders of magnitude both between and within
galaxies. Our fits also strongly favour models where cluster disruption is mass-independent, but the time at which disruption begins again shows wide environmental variations. Our results demonstrate that young cluster demographics are environmentally dependent, with the clearest signal appearing at the upper end of the cluster mass function, but that these variations are not well-explained by any of the models currently in the literature, and do not correlate straightforwardly with properties such as
star formation rate per unit area or strength of shear.
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All authors Jianling Tang, Kathryn Grasha, Mark R. Krumholz, Tomasz Różański
Astrophysics of Galaxies
A Partial Lyman Limit Absorber in the Halo of a Galaxy Pair: A Possible Signature of Gas Inflow
Sumukha R. Bharadwaj, Anand Narayanan, Sowgat Muzahid et al. (+2 more)
We present an analysis of a partial Lyman limit system at z = 0.87641 detected in the HST/COS spectrum of the background
quasar LBQS 0107-0235. The absorber exhibits a simple kinematic structure, with the metal-lines and the H I Lyman-series absorption well described by a single component. Photoionization modeling yields a gas
metallicity of one-tenth solar and a hydrogen number density of n_H \approx 8.5 \times 10^{-4} cm^{-3} (log_{10}(n_H/cm^{-3}) \approx -3.1). At the absorber
redshift, the VLT/MUSE data show two
galaxies (G1 and G2) at normalized impact parameters of \rho/R_{vir} \approx 0.9 and velocity separations of |\Delta v| = 18 and 99 km s^{-1}, respectively, from the absorber. Both
galaxies have rotating disks with stellar masses of M_* \approx 6 \times 10^9 and \approx 2.2 \times 10^{10} M_{\odot}. Their 100-Myr-averaged
star formation rates are \approx 2.5 and \approx 2.2 M_{\odot} yr^{-1}, though their instantaneous rates place G2 on the
star-forming main sequence and G1 above it, which is actively
star-forming at this
redshift. The absorber is positioned very close to the projected major axis of both
galaxies. The absorber's orientation, kinematics, and sub-solar
metallicity (log_{10}(Z/Z_{\odot}) = -1.05) are consistent with the absorption tracing a sub-solar
metallicity inflowing stream, though a
galaxy-
galaxy interaction origin cannot be excluded. We discuss these scenarios in the context of cosmological simulations of cold-mode
accretion and CGM gas flows around
galaxies with
halos of mass M_h \lesssim 10^{12} M_{\odot}.
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All authors Sumukha R. Bharadwaj, Anand Narayanan, Sowgat Muzahid, Jane C. Charlton, Sebastiano Cantalupo
Astrophysics of Galaxies · Cross-listed from astro-ph.IM
Kratos-linerad: GPU-accelerated Monte Carlo radiative transfer of lines with efficient imaging
Lile Wang
Spectral lines encode the velocity, the temperature, and the chemical structure of astrophysical gas; interpreting them requires radiative transfer that is accurate at high optical depth, consistent with the local excitation, and efficient enough to synthesize velocity-resolved images. We present Kratos-linerad, a GPU-accelerated Monte Carlo radiative transfer code for spectral lines. The level populations can be iterated to statistical
equilibrium together with the escaping
photon distribution, treating angle-dependent partial frequency redistribution through constant-
memory sampling tables. The code adopts the two-step imaging scheme to line transfer, in which a Monte Carlo pass samples a velocity-resolved scattering emissivity, and a deterministic ray-tracing pass synthesizes channel maps decoupled from the scattering geometry. Validation reproduces the analytic scaling of escaped spectra and the imaging double-peak profiles. GPU parallelism enables both stages sufficiently fast for routine application to astrophysically realistic models.
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Astrophysics of Galaxies
Active galactic nucleus activity in nearby disk galaxies: The roles of bar strength and spiral arm morphology
Zh. R. Martirosyan, A. A. Hakobyan, V. Adibekyan et al. (+3 more)
(abridged) We investigate the dependence of AGN activity on bar strength and spiral arm morphology in nearby spiral
galaxies, with a particular emphasis on disentangling their individual and joint effects while controlling for
galaxy stellar mass and color. We constructed a sample of 843 morphologically undisturbed Sa-Sd
galaxies from the MaNGA survey in the
redshift range $0.026 \leq z \leq 0.1$. Bar strengths, stellar masses, colors, and AGN classes were adopted from the literature, while spiral arm classes (ACs), i.e., flocculent (FL), multi-armed (MA), and grand design (GD) systems, were visually determined for the entire sample using optical imaging together with bulge-disk decomposition residual maps. The AGN fraction increases systematically with bar strength, from $0.10^{+0.02}_{-0.02}$ in unbarred
galaxies to $0.34^{+0.03}_{-0.03}$ in strongly barred systems. After controlling for stellar mass and color, a statistically significant enhancement remains detectable primarily at intermediate stellar masses ($10.5 \lesssim \log(M_\star/M_\odot) \lesssim 11.0$), whereas no significant dependence is found at higher masses. In contrast, spiral arm morphology alone does not show a robust independent connection with AGN activity once stellar mass and color are controlled, although a weak enhancement is present in intermediate-mass GD and MA systems. When bar strength and spiral AC are considered jointly, the highest AGN fraction is observed in strongly barred GD$+$MA
galaxies $(0.39^{+0.04}_{-0.04})$, while the lowest AGN fractions are found in unbarred FL systems $(0.09^{+0.03}_{-0.02})$. Our results suggest that stellar mass and color drive the primary trend in AGN activity in nearby disk
galaxies, while stellar bars and spiral arms act as secondary structural drivers.
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All authors Zh. R. Martirosyan, A. A. Hakobyan, V. Adibekyan, L. V. Barkhudaryan, M. H. Gevorgyan, A. G. Karapetyan