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Physics Astrophysics Astrophysics of Galaxies

astro-ph.GA Watch Astrophysics of Galaxies

Monday 5 October

Astrophysics of Galaxies

The star-forming past and quenching of brightest cluster galaxies in TNG-Cluster

Sunna Gottschewski, Joey Braspenning, Annalisa Pillepich et al. (+2 more)

The Brightest Cluster Galaxies (BCGs) in the most massive galaxy clusters of our Universe are, at present, mostly quiescent, elliptical, and red. However, their formation histories are unclear and likely different from those of massive ellipticals in lower-mass haloes. Simulations face the challenge of simultaneously requiring large volumes to sample massive clusters and sufficient resolution to model their stellar populations. Therefore, we make use of TNG-Cluster, one of the highest-resolution cosmological simulations of galaxy clusters, which returns 352 BCGs at $z=0$ with stellar masses $M_{*, <30 \mathrm{pkpc}} = 10^{11.6-12.9} ~\mathrm{M}_\odot$ and total halo masses $M_{\mathrm{200c}} = 10^{14.3-15.4}~\mathrm{M}_\odot$. 93 per cent of the BCGs are quenched at $z=0$, whereas at redshift $z>3$ all their main progenitors were still star forming. The star-formation histories of individual BCGs are complex, including multiple (re)quenching episodes. They rejuvenate on average $2.1 \pm 1.8$ times since $z=3$. BCGs quench for the first time $9.9^{+0.9}_{-1.4} ~\mathrm{Gyr}$ ago (10th-90th percentiles; $z=1.7^{+0.5}_{-0.5}$), while the last and final quenching event occurred $7.0^{+2.8}_{-5.0} ~\mathrm{Gyr}$ ago ($z=0.8^{+0.8}_{-0.6}$). We find a large scatter in the halo, stellar, and SMBH masses at both first and last quenching, suggesting no characteristic mass at which quenching occurs. Instead, BCGs quench for the first time when the cumulative kinetic energy injected by their SMBH equals the BCG binding energy, corresponding to a delay of $2.3^{+1.2}_{-1.2} ~ \mathrm{Gyr}$ after the first SMBH kinetic energy injection. Namely, TNG-Cluster BCGs quench when they experience significant gas expulsion. Our work shows that BCGs have complex and varied star-formation histories, with multiple rejuvenation episodes, but they ultimately quench due to SMBH feedback.
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All authors Sunna Gottschewski, Joey Braspenning, Annalisa Pillepich, Katrin Lehle, Dylan Nelson

Astrophysics of Galaxies

Rotational excitation of SiC$_6$ by collisions with helium: cross sections, rate coefficients and non-LTE modeling

Liman Tian, Ziyu Xiang, Chuangang Ning et al. (+1 more)

Rotational transitions of SiC$_6$ in the $j=26$–$40$ range have been detected in IRC+10216, yet collisional rate coefficients for SiC$_6$ with He or H$_2$ were previously unavailable. This paper reports rate coefficients for rotational excitation of SiC$_6$ induced by collisions with He, calculated using a two-dimensional potential energy surface (PES) constructed at the RCCSD(T)-F12 level under the rigid-rotor approximation. The close-coupling (CC) method was employed for low rotational energy levels, while the coupled-states (CS) approximation was used for higher rotational levels. Systematic convergence tests were conducted, and the resulting CC and CS scattering cross sections were compared. The rate coefficients obtained via the CS method cover rotational levels up to $j=40$ and temperatures of 3–100\,K. Although the CC and CS rate coefficients differ by up to a factor of $\sim 2$ for some transitions, particularly those influenced by weak coupling and resonances, the two methods yield nearly identical excitation and brightness temperatures for the high-$j$ transitions (e.g., $19\rightarrow18$) examined, and the CS-based line fluxes agree with the CC-based results to within 6.5% for $n(\mathrm{H_2}) \ge 10^{3}$\,cm$^{-3}$; this demonstrates that the CS approximation is reliable for the non-LTE modelling of high-$j$ SiC$_6$ transitions considered here, for which fully converged CC calculations are computationally impractical. Using the calculated SiC$_6$–He rate coefficients and reduced-mass scaling to estimate the corresponding SiC$_6$–H$_2$ rates, we further investigate the excitation of the observed high-$j$ transitions. Under typical low-density conditions in IRC+10216 ($n(\mathrm{H_2}) \approx 10^4$\,cm$^{-3}$), the $j=40\to39$ transition is subthermally excited, highlighting the importance of non-LTE effects when interpreting the emission of high-$j$ SiC$_6$ transitions.
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All authors Liman Tian, Ziyu Xiang, Chuangang Ning, Xiaolin Chen

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

Detection of knots in the supernova type Iax remnant Pa 30

Tim Cunningham, Ilaria Caiazzo, John C. Raymond et al. (+1 more)

We present deep, narrowband Gemini North/GMOS images of the Pa 30 nebula that reveal rich small-scale structure in the ejecta filaments. In [S II], the number of detected filaments increases by about an order of magnitude compared to previous studies. The imaging further reveals that the filaments are not smooth radial streaks, but instead are composed of cascades of knots or clumps. The images in [O III] yield the first confirmation that previously detected diffuse [O III] emission in fact originates from the same [S II] filaments. We measure a nebula center consistent with the position of the central star, indicating that the remnant has not received a large transverse kick. The 3$\sigma$ upper limit on the velocity of the stellar kick is $\lesssim$100 km/s. Cross-sectional profiles of the filaments in [S II] and [O III] show a central peak on top of a nebular background, the latter being likely due to diffuse emission or unresolved filaments. The median [S II] width of 0.7” is slightly broader than the 0.50” seeing, providing some evidence of partially resolved filaments and implying a characteristic knot diameter of ${\sim}10^{16}$ cm. The $\approx$1” widths measured in [O III] are consistent with the poorer seeing of the oxygen images. The discovery of this clumpy substructure provides a new observational constraint on models for the origin and evolution of the remarkable filamentary ejecta of Pa 30.
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All authors Tim Cunningham, Ilaria Caiazzo, John C. Raymond, Scott J. Kenyon

Astrophysics of Galaxies

Tentative Detection of FeS toward Orion SrcI

Aitana Tasa-Chaveli, Holger S. P. Müller, Álvaro Sánchez-Monge et al. (+3 more)

Iron sulfide (FeS) is a key refractory compound in astrophysical environments. It is commonly found in meteorites and evidence of FeS has only been reported in solid form in a protoplanetary environment. Furthermore, FeS is of astrobiological interest since it acts as a precursor to the formation of pyrite (FeS$_2$), which plays a key role in anaerobic metabolism. We present millimeter-wave spectroscopic calculations for gaseous FeS and report its tentative detection toward the massive disk Orion SrcI. If confirmed, this would constitute the first ever detection of gaseous FeS in the interstellar medium. Our data are consistent with a FeS column density of $\sim1.7 \times 10^{15}$ cm$^{-2}$. Comparing to other sulfur reservoirs, the amount of sulfur locked in FeS is more than three orders of magnitude lower than that contained in SO$_2$ and SiS. However, FeS emission may arise from a different region as it is the case for the metallic salt NaCl. Our results support the presence of FeS in interstellar grains and are consistent with grain destruction playing an important role in the origin of the FeS emission. The observations, however, are still insufficient to discern whether FeS is a main sulfur reservoir in molecular clouds or a primary carrier of refractory iron-bearing material.
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All authors Aitana Tasa-Chaveli, Holger S. P. Müller, Álvaro Sánchez-Monge, Asunción Fuente, Adam Ginsburg, Thomas Möller

Astrophysics of Galaxies

Water Abundance and Ortho-Para Ratio in the S140 Photon Dominated Region

Dariusz C. Lis, Sofia Lawsky, Emeric Bron et al. (+2 more)

We analyzed archival far-infrared to submillimeter Herschel PACS, SPIRE, and HIFI spectroscopic observations of the S140 photon dominated region (PDR) to constrain the water vapor abundance and ortho-para ratio in this region. Toward the high-mass protostar IRS1, 52 spectral lines, including 15 water lines, are detected with the PACS and SPIRE instruments. PDR modeling suggests a UV radiation field G0 ~ 1 x 10^3 Habing units, and a thermal gas pressure of 5 x 10^8 K cm^-3 in this region. The models strongly underestimate intensities of high-J CO lines, which may indicate the presence of hot shocked gas associated with outflows along the line of sight, in addition to the UV irradiated gas. The spectral resolution of the PACS and SPIRE spectrometers is insufficient to separate the PDR and shock contributions. The PDR models further suggest that optically thick ground-state water lines trace primarily surface layers of the PDR. The gas temperature in this region is predicted to be ~ 800 K and the water abundance with respect to hydrogen nuclei reaches ~ 10^-5. However, the bulk of gas-phase water is located in a more shielded region, deeper inside the PDR, with a gas temperature ~ 24 K, and a gas-phase H_2O abundance of ~ 10^-7. A comparison of the observed water line fluxes toward IRS1 with PDR model predictions shows no evidence for departures from the LTE ortho-para ratio at the local gas temperature, which is assumed in the models. The sensitivity of the Herschel instruments was insufficient to measure the water ortho-para ratio toward the externally illuminated edge-on PDR at the surface of the S140 molecular cloud. Such observations will be possible with the next generation far-infrared spectroscopic space missions currently in development.
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All authors Dariusz C. Lis, Sofia Lawsky, Emeric Bron, Franck Le Petit, Javier R. Goicoechea

Astrophysics of Galaxies · Cross-listed from gr-qc

Black Hole Horizon Fluctuations from Unruh Quantum Noise

Kashif Ammar Yasir

The mean Hawking flux does not determine how quantum stress fluctuations perturb a black-hole geometry. That information resides in field correlations, including vacuum contributions absent from the outgoing luminosity. Here we connect the complete exterior Unruh Wightman function to a finite-band stochastic reconstruction of Schwarzschild geometry. We retain the incoming vacuum and both outgoing frequency branches, form the connected stress covariance before angular projection, and propagate its monopole through a density-driven radial response. A shared Gaussian reconstruction then resolves how the value and derivative of the lapse control different geometric observables. For the specified covariance and noise amplitude, 2,200 realizations give relative widths of 0.0185 for the local horizon radius and 0.0483 for the surface-gravity temperature parameter, consistently across histograms and reconstruction checks. Covariance derivatives explain this unequal sensitivity. The construction separates the quantum-state input from the gravitational closure and spatial sampling assumptions, providing a reproducible finite-resolution description of how Hawking-field correlations affect horizon positions and surface-gravity statistics.
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Astrophysics of Galaxies

Broadband radio continuum and host galaxy properties of extremely inverted spectrum compact radio galaxies

Mukul Mhaskey, Barenya Dev, Aritra Basu et al. (+3 more)

We present broadband radio continuum spectra spanning 0.15-8 GHz for a sample of ten Extremely Inverted Spectrum Extragalactic Radio Sources (EISERS), selected from narrowband, low-frequency surveys below 1.4 GHz. In these surveys, EISERS show unusually steep low-frequency spectral indices, approaching or exceeding the synchrotron self-absorption (SSA) limit of $\alpha$= +2.5, expected for homogeneous synchrotron sources. We have performed follow-up quasi-simultaneous radio observations of these sources using uGMRT (0.150-1.4 GHz) and VLA (1.0-8.0 GHz). The new observations provide improved frequency coverage and consistent flux calibration across both the optically thick and optically thin spectral regimes. We find that the spectral slopes of EISERS in optically thick regime are flatter than the two frequency spectral indices obtained using TGSS and WENSS and lie in the range +1.6 to +3, suggesting that heterogeneous survey data can introduce biases through flux-scale offsets, intrinsic variability of these compact sources and diverse angular resolutions between surveys. We modelled the broadband radio spectra as synchrotron emission affected by synchrotron self-absorption and subsequently modified by free-free absorption in an external ionised medium. The estimated physical parameters based on the best-fits indicate that the magnetic fields and thermal electron densities are similar to the general class of peak spectrum sources, with $B_{SSA}$ spanning over a large range of values from 20 mG to 8 G and $n_{e} \sim 29-128{cm}^{-3}$. Optical and infrared analysis further indicates that the EISERS are preferentially associated with dusty starburst galaxies, composite starburst-AGN systems, or obscured AGN embedded in dense circumnuclear environments, supporting a scenario in which at least a fraction of these sources represent young or environmentally confined radio AGN.
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All authors Mukul Mhaskey, Barenya Dev, Aritra Basu, Helmut Meusinger, Surajit Paul, Matthias Hoeft

Astrophysics of Galaxies

Linking simulations and observations of star-forming regions I. Masses and temperatures of ALMAGAL-like cores

Birka Zimmermann, Álvaro Sánchez-Monge, Stefanie Walch et al. (+1 more)

Dense cores and clumps in massive star-forming regions are studied through (sub-)millimetre continuum observations, but inferred masses and temperatures can be biased by limited resolution, interferometric filtering, projection, and uncertain dust temperatures. We quantify how reliably core masses and temperatures can be inferred from ALMA-like continuum data using synthetic observations of such clumps. We post-processed radiation-hydrodynamic simulations of collapsing 1000 M$_\odot$ clumps with RADMC-3D and CASA to generate synthetic ALMAGAL-like images. Cores were defined around sink particles, enabling comparison of masses from the 3D simulations, idealised RADMC-3D maps, and synthetic ALMA images. We quantified how resolution, projection, and viewing angle affect core masses, and tested three dust-temperature estimators (clump-scale L/M, a L/M+flux model, and a supervised machine-learning estimate). Projection effects cause line-of-sight integrated core masses within 1500 au to exceed spherical masses by factors of two to three. The empirical L/M temperature prescription follows the global thermal evolution but misses the core-to-core scatter, producing core-mass errors of a factor of a few. Including local flux improves temperature and mass estimates, while a gradient-boosting machine-learning model suggests further improvement. Synthetic ALMAGAL-like images recover the global core structure, but flux-reconstruction uncertainties introduce mass errors up to a factor of three and limit reliable core-mass recovery to $\gtrsim 0.3$ M$_\odot$, comparable to the ALMAGAL completeness limit. Individual core masses are typically uncertain by a factor of three to five, mainly due to dust-temperature assumptions and flux reconstruction. Reducing these biases requires temperature estimates that include local core information rather than a single clump-scale L/M-based prescription.
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All authors Birka Zimmermann, Álvaro Sánchez-Monge, Stefanie Walch, Gary A. Fuller

Astrophysics of Galaxies

Cusps, cores, and one acceleration: dark-matter haloes versus modified dynamics across the full SPARC sample

Mikhael Da Silva

The rotation curves of the 175 disk galaxies in the SPARC database are confronted, one by one and under identical conditions, with the two mass models that have dominated the missing-mass debate for four decades: a cold dark-matter halo of Navarro-Frenk-White (NFW) form, and Milgromian dynamics (MOND) with the acceleration constant held at $a_0=1.2\times10^{-10}$ m s$^{-2}$. Stellar mass-to-light ratios, distances and inclinations are treated as nuisance parameters with priors set by the 3.6 $\mu$m photometry and by the SPARC error budget, and every galaxy is sampled with a Markov-chain Monte Carlo. Three findings emerge. (i) Judged by the Bayesian information criterion, the free NFW halo is preferred in 96 galaxies and MOND in 79; once the halo is required to obey the $\Lambda$CDM concentration-mass relation the score becomes 86 to 89, i.e. a draw. The two theories fail in different places: MOND loses in massive, high-surface-brightness, bulge-dominated systems, NFW loses in slowly rising dwarf rotation curves. (ii) The NFW concentrations demanded by the data sit a median 0.24 dex below the $\Lambda$CDM expectation, and 53% of the sample lies more than $2\sigma$ below it, independent of halo mass; this is the core-cusp problem expressed as a scaling-relation offset rather than as a handful of anecdotes. (iii) The radial acceleration relation built from the full sample has $a_0=(1.13\pm0.02)\times10^{-10}$ m s$^{-2}$ and an observed scatter of 0.14 dex, yet the value of $a_0$ preferred by individual galaxies spans more than a decade and correlates with surface brightness. The two statements are not in contradiction: the population-level relation is tight because it averages over exactly the degeneracies with mass-to-light ratio and distance that make $a_0$ ill-determined galaxy by galaxy. The full table of fits is provided.
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Astrophysics of Galaxies · Cross-listed from astro-ph.SR

From the Milky Way to the Early Universe: How Metallicity Shapes the Formation of Double Neutron Stars

Abhishek Chattaraj, Jeff J. Andrews, Monica Gallegos-Garcia et al. (+9 more)

Among the compact binaries detected through gravitational wave (GW) emission, double neutron stars (DNSs) hold the unique distinction of having well-characterized local analogs in the Milky Way. However, understanding their broader cosmological population remains challenging due to the complex metallicity-dependent evolution of their progenitors. Using the detailed binary population synthesis code POSYDON, we model DNS formation across a cosmological range of metallicities. We find that while DNSs are predominantly formed through common envelope evolution, metallicity-dependent radial expansion and stellar wind mass loss bifurcates the pathway into distinct subchannels, producing systematically distinct merging populations at different metallicities. Notably, our best representative Galactic models predict local merger rates in broad agreement with the latest GWTC-5 constraints, suggesting that the populations observed via radio pulsar surveys and through GW emission need not be in tension. Contrary to previous studies, we demonstrate that the intrinsic merger efficiency increases toward low metallicities, a trend robust across varying binary evolution assumptions, although the magnitude and the underlying stellar processes driving this enhancement vary across metallicity regimes. When convolved with the cosmic star formation history, our models reveal that the majority of merging DNSs originate from progenitors in the range $\sim 0.1\,Z_\odot - Z_\odot$, with significant supersolar contributions. Furthermore, we show that weaker stellar winds at low metallicities produce DNS mergers with systematically more symmetric mass ratios ($q \gtrsim0.9$). Additionally, we assess detectability within proposed configurations for third-generation GW observatories. Our study provides a framework for interpreting the cosmological DNS population in the upcoming multi-messenger era.
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All authors Abhishek Chattaraj, Jeff J. Andrews, Monica Gallegos-Garcia, Max M. Briel, Michael Zevin, Tassos Fragos, Emmanouil Zapartas, David R. Aguilera-Dena, Seth Gossage, Anarya Ray, Philipp M. Srivastava, Zepei Xing

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

Unravelling the Nature of AT 2025abao: From Precursor to Final Fate

Zhuo Chen, Yingzhen Cui, Tianshu Wu et al. (+9 more)

Luminous red novae (LRNe) are potential signatures of common envelope evolution (CEE), a critical yet poorly understood phase in compact binary formation. AT 2025abao, an LRN in the Andromeda galaxy, originated from an asymptotic giant branch (AGB) progenitor and exhibited a prolonged pre-outburst transient. Lacking direct constraints on the companion, however, the system's evolutionary fate remains unclear. Here, we unravel the binary nature of AT 2025abao by modeling its complete evolution, from precursor to final outcome. We show that the eight-year infrared precursor arises from a $\approx1.4^{+0.2}_{-0.3}\,M_{\odot}$ main-sequence companion inspiralling through the wind of a $\approx 6.9\,M_{\odot}$ AGB star. As CEE commences, the companion plunges into the envelope and launches a shock. Radiation hydrodynamic modeling of this outburst constrains the total ejecta mass to $\approx 0.92\,M_{\odot}$ and energy to $\approx 1.25\times 10^{47}\,$erg, revealing that only $\approx 0.57\,M_{\odot}$ becomes unbound. Subsequent radiative transfer simulations successfully reproduce the evolving spectral energy distribution. Crucially, our models indicate the main-sequence companion and AGB core survive in an eccentric orbit without merging at least 400 days after CEE onset. AT 2025abao may therefore be the first observed CEE event caught forming a close compact binary, bridging a long-standing observational gap in compact binary formation.
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All authors Zhuo Chen, Yingzhen Cui, Tianshu Wu, Yongzhi Cai, Hongwei Ge, Andrea Reguitti, Minxuan Cai, Lulu Fan, Ji-An Jiang, Tinggui Wang, Zelin Xu, Jie Lin

Sunday 4 October

Astrophysics of Galaxies

ALMA Observations of Molecular Complexity in the Large Magellanic Cloud: The N83 Star-Forming Region

Marta Sewiło, Amanda Broadmeadow, Roya Hamedani Golshan et al. (+9 more)

We report the results of the 1.2 mm continuum and molecular line $\sim$0.1 parsec-scale observations with the Atacama Large Millimeter/submillimeter Array of two fields in the star-forming region N83 in the Large Magellanic Cloud (LMC). This study is third in a series of investigations exploring molecular complexity in a low-metallicity and high UV flux environment of the LMC. We determine the physical and chemical properties of five sources detected with ALMA based on spectral modeling with XCLASS and the analysis of the continuum emission. The temperatures exceeding 100 K, small sizes, and high H$_2$ volume densities of sources N83A-mm A and B indicate that they are hot cores. N83A-mm A/B are associated with complex organic molecules: methanol (CH$_3$OH), methyl cyanide (CH$_3$CN), and dimethyl ether (CH$_3$OCH$_3$). We also found CH$_3$OH in three cold cores, and extended cold CH$_3$OH emission in both fields. We detected SO, $^{33}$SO, SO$_2$, OCS, H$_2$CS, CS, C$^{33}$S, HC$^{15}$N, H$^{13}$CN, HNCO, HDCO, H$^{13}$CO$^{+}$, SiO, and CH$_2$CO in at least one core. Molecular abundances with respect to H$_2$ fit into the trends previously reported for the Magellanic hot cores: the CH$_3$OH abundance varies significantly, while the abundances of S-bearing species show small variations. We found evidence for strong UV radiation and complex kinematics in both ALMA fields in N83. The feedback-produced shocks are important drivers of the chemistry of S-bearing species, SiO, and CH$_3$OH in and outside hot cores. Local effects have a large impact on the chemical composition and abundances of star-forming cores in the LMC.
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All authors Marta Sewiło, Amanda Broadmeadow, Roya Hamedani Golshan, Steven B. Charnley, Lee Mundy, Kazuki Tokuda, Thomas Möller, Jennifer Wiseman, C.-H. Rosie Chen, Remy Indebetouw, Joana M. Oliveira, Peter Schilke

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

AI Agents as a Research Team: A Human-Supervised Case Study in Stellar Spectroscopy

Marwan Gebran and Ian Bentley

We present a qualitative case study of a human-supervised team of specialized AI agents supporting an astronomy research project. The Bot Spectroscopist team, described in the project record as operating through Grok Bot powered by xAI Grok, divided work among orchestration, numerical implementation, data curation, spectroscopy critique, literature search, figure preparation, manuscript editing, and review. Human decisions determined scientific scope, model changes, and manuscript inclusion. The scientific application is CondGen, a deterministic label-to-spectrum network extending our previous work to five individual elemental abundances. The reported baseline assessment achieved a mean absolute error (MAE) of 0.003681 in continuum-normalized flux on 21,657 synthetic test spectra. Existing binned diagnostics show that reconstruction error varies with effective temperature and abundance. The bots also flagged a non-monotonic cool-star magnesium response for further investigation; a matched SYNSPEC abundance sweep is needed to assess its physical fidelity. Building on a pre-existing spectral database, notebooks, and research program, the authors estimate that the reported analysis, diagnostics, figure preparation, and initial manuscript drafting were assembled in less than a week through human prompting and exchanges among agents. No comparison with a human team starting from the same resources was performed, so this elapsed-time account does not establish a productivity or labor saving. The study illustrates task delegation, artifact exchange, critique, and correction under human supervision.
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Astrophysics of Galaxies · Cross-listed from astro-ph.HE

A Brush with Turbulence: Probing the ICM Dynamics in the Merging Toothbrush Cluster using XRISM

Anjali Madangarli, Aurora Simionescu, Huub Röttgering et al. (+11 more)

The Toothbrush Cluster (1RXS J0603.3+4214) is known for its northern radio relic, radio halo, and highly disturbed X-ray morphology. It shows features of both shock-driven and turbulent reacceleration, the latter of which is invoked to explain its radio halo. However, how kinetic energy from the merger is distributed into gas motions across spatial scales remains unclear. We probe the intracluster medium (ICM) dynamics in the southern, X-ray-brightest region of the cluster using a 167 ks XRISM/Resolve observation. We conduct both full-array and quadrant sub-array analyses by fitting the spectra with single and multi-component thermal models in the 3-8 keV band. The full-array spectrum favours two ICM components with a transonic line-of-sight (LOS) velocity difference of $\Delta v_{\mathrm{bulk}}=1635^{+165}_{-110}$ km s$^{-1}$, while the velocity dispersions are much lower, at $\sigma_{v,1\mathrm{D}}\sim$245-310 km s$^{-1}$. The sub-array analysis likewise reveals multiple components in at least three quadrants, with LOS bulk velocities ranging from $-2520^{+295}_{-230}$ to $+930^{+70}_{-110}$ km s$^{-1}$. The velocity dispersions remain modest at $\sim$215 km s$^{-1}$, corresponding to a turbulent pressure support of about 3-6% on scales dominating the observed line broadening. Cooler gas is detected in the NE and SW, with $kT_{\mathrm{NE}}=3.13^{+0.33}_{-0.30}$ keV and $kT_{\mathrm{SW}}=2.32^{+0.43}_{-0.37}$ keV, likely associated with a third, northern subcluster identified in weak-lensing and optical studies. Our results indicate a complex ICM kinematic structure, with evidence for at least three subclusters exhibiting supersonic bulk velocity offsets and much smaller velocity dispersions. This shows that the merger geometry has a significant line-of-sight component and may indicate that the cluster collision is relatively young, with the turbulent cascade not yet fully established.
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All authors Anjali Madangarli, Aurora Simionescu, Huub Röttgering, Anwesh Majumder, Soeda Haruse, Kazuhiro Nakazawa, Yuusuke Uchida, Daisuke Ito, Gianfranco Brunetti, Reinout van Weeren, Congyao Zhang, Kamlesh Rajpurohit, Priyanka Chakraborty, Hiroki Akamatsu

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

Large offsets of double-neutron-star mergers: degeneracies and implications for host associations

Xiao-Tian Xu, Bin-Bin Zhang, Wenjie Wu et al. (+1 more)

The projected offset of a Gamma-Ray Burst (GRB) from its host galaxy is an important diagnostic of its physical origin, where the host associations are usually evaluated through chance-coincidence probabilities. However, as shown by observations, the host associations given by this approach may be ambiguous in some cases. In this work, we revisit the modelling of the offsets of double-neutron-star (DNS) mergers with controlled numerical experiments using Monte Carlo simulations. To isolate the dynamical effects of the second supernova (SN) from uncertainties in the upstream binary evolution, we parametrise the direct progenitor of DNSs and integrate the post-SN trajectories in galactic potentials using galpy. Complementary to previous population synthesis calculations, our Monte-Carlo tool, GRB-offset, provides a lightweight framework to identify sensitivities and expose degeneracies in offset modelling. With GRB-offset, we have investigated the following physical ingredients, supernova physics (ejected mass and kick velocity), galactic potential (potential shape, galaxy virial mass), DNS birth location, star formation history, and redshift. The offset distributions given by our reference Monte-Carlo simulation peak at around 30 kpc and 1000 kpc for the DNSs bound to and unbound from the host galaxy, which sensitively depends on the considered physical ingredients. A given offset can arise from various combinations of these ingredients, introducing substantial degeneracies when interpreting observed offsets. Therefore, an observed offset alone can hardly constrain the properties of the DNS progenitor and of the host galaxies.
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All authors Xiao-Tian Xu, Bin-Bin Zhang, Wenjie Wu, Suoning Wang

Astrophysics of Galaxies

Spatio-temporal progression of star formation in the Carina OB1 association

C. Göppl and T. Preibisch

The Carina OB1 association, harboring the famous Carina Nebula near its center, is the most massive, well-studied OB association in our Galaxy. Containing several massive star clusters with different ages, it shows a complex spatio-temporal structure. We explore the formation history and kinematic evolution of the eight most massive clusters in Car OB1. We determine the cluster ages, stellar populations, the initial massive star content, and the number of supernova explosions since the time of each cluster's formation. Using Gaia DR3 astrometry, we determine the 3D configuration of the association and perform a traceback analysis of the cluster positions over the last 13 Myr. The traceback analysis places the birth location of the oldest (13 Myr) cluster, NGC 3293, in the Carina spiral arm. Approximately four Myr later, a series of 11 supernova explosions started in NGC 3293. We construct a possible scenario in which the expanding bubble driven by these supernova explosions interacted with the southern part of the original cloud complex and led to the sequential formation of the younger clusters in the central Carina Nebula. Our scenario suggests that the sequence of 16+/-4 supernova explosions in the association during the last 10 Myr played an important role in creating the massive clusters in Car OB1. However, the supernova feedback does not dominate the large-scale expansion of the association; the general expansion rather seems to reflect the initial kinematics of the original unbound cloud complex.
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Astrophysics of Galaxies · Cross-listed from astro-ph.SR

SPHERE/ZIMPOL observations of the symbiotic system R Aquarii. II. Dynamics of the dust in the Mira wind and the Halpha gas in the jet

H.M. Schmid, E. Lagadec, J. Milli et al. (+17 more)

R Aqr is a resolved symbiotic Mira binary and a prototype target for the study of complex hydrodynamic processes including dust-driven mass loss, mass transfer, accretion, and jet outflows and the formation of strongly asymmetric structures. We investigate for R Aqr the central Halpha emission from the ionized gas and the polarization from scattering dust based on SPHERE/ZIMPOL maps with a resolution of about 25 mas (5 AU). Data for four epochs were taken, including the dust eclipse around 2021, to follow structural changes. The central Halpha gas traces the orbital motion of the hot component. The polarization from scattering dust shows interaction effects near the binary (<60 AU), including a flattened distribution in the orbital plane, corotating dust, and a reduction of the scattering signal during the dust eclipse. The polarization shows at >60 AU a steady outflow with about a dozen dust clouds, a few of which have a comet-like core and tail features. The dust velocity is about 20 km/s, and this is faster than for the CO gas measured with ALMA. Several prominent Halpha clouds also show scattering polarization because they are just partly ionized dust clouds from the Mira wind. We also found small faster-moving transient Halpha clouds, pointing to outflow instabilities and shocks. The observed angular shift of Halpha during the dust eclipse, can be explained by strong illumination changes from the hot component. At larger separation, the H$\alpha$ clouds move faster (>100 km/s), in agreement with previous studies. This acceleration is probably a result of gas heating by photoionization and shocks, and the produced overpressure gives rise to the two well-known jet-like features expanding in polar directions. The presented R Aqr data are very useful to clarify the complex hydrodynamics taking place in AGB binaries.
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All authors H.M. Schmid, E. Lagadec, J. Milli, C. Tschudi, J. Ma, N. Engler, J.L. Beuzit, A. Boccaletti, G. Chauvin, R. Claudi, S. Desidera, K. Dohlen, M. Feldt, R. Gratton, Th. Henning, M. Kasper, M. Langlois, F. Ménard, D. Mouillet, A. Vigan

Astrophysics of Galaxies

Large-Scale Stellar Bars and Nuclear Activity in Narrow-Line Seyfert 1 Galaxies

Po-Chieh Yu

We present a statistical comparison between barred and unbarred narrow-line Seyfert 1 galaxies (NLS1s) to investigate the role of large-scale stellar bars in fueling AGN with low-mass black holes. From a parent sample of 492 NLS1s selected from SDSS and Pan-STARRS1 (PS1), we construct a PS1-resolved matched sample of 101 barred and 101 unbarred NLS1s, matched in redshift, inclination, and image quality. Unbarred NLS1s are modestly but consistently brighter than barred NLS1s in several optical AGN luminosity indicators, including $\lambda L_{\lambda}(5100~A)$, broad H$\alpha$, broad H$\beta$, narrow H$\alpha$, narrow H$\beta$, and [O III]~$\lambda 5007$, with typical offsets of $\sim 0.1$–$0.25$ dex; the broad H$\alpha$ and narrow-line offsets are statistically significant, while the continuum and broad H$\beta$ offsets are marginal. Monte Carlo resampling and a Bayesian model support the same direction of offset. In contrast, the main narrow-line diagnostics, including [O III]/H$\beta$, O3N2, and the [S II]-based electron density, are statistically consistent between the subsamples, although barred NLS1s show a higher N2 ratio. Within the barred subsample, the bar strength parameter $e_{\max}$ shows a mild anti-correlation with the optical continuum and broad Balmer-line luminosities. These results indicate that large-scale stellar bars are not associated with enhanced instantaneous optical AGN luminosity. Instead, barred systems may experience more regulated or time-variable inner gas delivery, building circumnuclear gas reservoirs without necessarily increasing accretion power observed at the epoch traced by optical AGN emission.
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Astrophysics of Galaxies · Cross-listed from astro-ph.EP

Spectral Energy Distribution and Polarimetric Properties of Dust in the Interstellar Comet 3I/ATLAS

Seungwon Choi, Masateru Ishiguro, Hiroyuki Naito et al. (+13 more)

The interstellar comet 3I/ATLAS exhibits unusual polarimetric properties compared with Solar System comets, while constraints on its fundamental physical properties, such as dust albedo and grain-size distribution, remain limited. We obtained new optical polarimetry near opposition with the Pirka Telescope, combined it with previously reported polarimetric measurements, and constructed a visible-to-mid-infrared spectral energy distribution (SED) from HST, VLT, SPHEREx, and JWST observations. The SED indicates that the coma is dominated by dark, absorbing dust, with an effective V-band albedo of $p_{\rm eff}\sim0.04$. Modeling the SED with a power-law grain-size distribution yields a size index of $q=3.0$–$3.3$. The mid-infrared spectral structure is better reproduced by adding a minor amorphous-silicate component. The combined polarimetric data further favor a highly porous scattering structure. Despite its unusual polarimetric behavior, the dust of 3I/ATLAS has an albedo and grain-size distribution within the range found for Solar System comets.
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All authors Seungwon Choi, Masateru Ishiguro, Hiroyuki Naito, Yoonsoo P. Bach, Jooyeon Geem, Bumhoo Lim, Moonkuk Hur, Sihu Ahn, Sunho Jin, Hisayuki Kubota, Seiko Takagi, Tatsuharu Ono, Max Mahlke, Carey Lisse, Tomohiko Sekiguchi, Makoto Watanabe

Saturday 3 October

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

The variable mass-loss in low-mass red giant stars: Chromospheric motion across stellar evolution in 47 Tuc

Ian Baeza, L. Monaco, H. Frelijj et al. (+8 more)

Mass-Loss (ML) is a critical process that remains poorly understood despite its broad implications across astrophysics. Our current knowledge is insufficient to reproduce ML consistently across stars, particularly in cool, low-mass giants, where the time-variable nature of chromospheres (CHR) —the region where most physical phenomena powering ML in this regime are expected to occur— is poorly constrained. We characterize the relevant timescales of CHR variability in red giants and explore correlations with intrinsic stellar properties. We analyze the first large temporal spectroscopic monitoring of CHR variability using the H$\alpha$ line in red giants belonging to the globular cluster NGC 104 (47 Tuc) using FLAMES/GIRAFFE data. We find that H$\alpha$ variations increase on average and span a wider range of values with luminosity, together with a systematic blueshift of the line core indicative of outflows for $\log(L/L_\odot) \gtrsim 2.4$, alongside deeper cores consistent with increased CHR optical depth. The characteristic timescale required to observe variations in the H$\alpha$ profile is approximately one day, showing a flat trend with luminosity. While shorter-timescale variations remain consistent with statistical uncertainties, a possible increase toward dimmer stars is found. These trends appear similarly correlated with luminosity and effective temperature. No further correlation is found with different cluster populations, nor are significant differences observed between AGB and RGB stars. The outflow trends closely match previous observations across a wide metallicity range. We discuss whether these observations reflect changes in H$\alpha$ sensitivity to the winds, a genuine atmospheric transition driven by changes in heating efficiency, or continued CHR expansion with geometrically dominated H$\alpha$ formation.
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All authors Ian Baeza, L. Monaco, H. Frelijj, Y. Momany, L. Sbordone, S. Zaggia, I. Yegorova, I. Saviane, A. Mucciarelli, K. Ohnaka, M. Gómez

Astrophysics of Galaxies

Power-law Coupling and Mock Validation of a Surface-density Anisotropy Diagnostic for 85 Rich Galaxy Clusters

Sardor Sharipbayevich Kutlimuratov and Ikram Uralbayevich Tadjibayev

We assess a surface-density anisotropy diagnostic, $A_{\rm ani}$, and its association with the slope $\alpha$ of a power-law galaxy profile. We reprocess 20-annulus profiles of 85 optically rich clusters on a canonical grid, $0 \leq A_{\rm ani} \leq 1.92$, and an extended grid reaching 1.99. Twenty-four canonical fits and 12 extended fits reach their respective upper boundaries; 69 of 85 upper $\Delta\chi^2=1$ bounds remain open, and only four clusters have two-sided intervals. Among 40 preselected power-law fits, the observed $\alpha$-$A_{\rm ani}$ Spearman coefficient is 0.616. In a model-native forward-recovery experiment with 11 injected values, all 935 noiseless profiles recover the input within 0.02. Across 46,750 Poisson catalogs matched to observed count and background conditions, recovery instead has root-mean-square error (RMSE) 0.992 and Spearman $\rho=0.093$; 40.0% of fits reach the canonical upper boundary and 81.4% have an open upper interval. Fixing both background and radial scale improves RMSE to 0.564 in a 9,350-catalog sensitivity test. As a separate structural control, 4,250 Poisson catalogs generated from fitted power laws reproduce the observed slope association: the median mock coefficient for the 40-cluster subset is 0.608 (95% range 0.453-0.731). Thus the diagnostic is numerically recoverable under its defining model without noise, but the available photometry does not reliably identify it for individual clusters. The power-law correlation can arise from shared projected profile shape and is not independent evidence for orbital anisotropy.
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Astrophysics of Galaxies

Diffuse Galactic Backgrounds with SPHEREx: A Pilot Study of Background Modeling and Its Impact on Extinction

Wanggi Lim, Jae Hwan Kang, Keunho J. Kim et al. (+1 more)

We present a spectral analysis of diffuse Galactic background emission using SPHEREx data in a pilot Galactic-plane field, where uncertainty in the estimation of the diffuse infrared background is a major source of systematic uncertainty in extinction studies at near- and mid-infrared wavelengths. We construct channel-resolved background maps across the 0.75–5~$\mu$m range using a Large Median Filter approach and then carry the extinction analysis forward only for the cleaner long-wavelength subset at $\lambda \geq 3~\mu$m. In the present field, comparison against an earlier masked-median background model gives a median channel-by-channel background difference of about 6% and a maximum change of $|\Delta\tau_{\rm norm}|\simeq 7.4$ near 3.205~$\mu$m, underscoring the importance of wavelength-dependent background modeling. These results demonstrate that spectral mapping with SPHEREx provides a practical framework for controlling diffuse background systematics and enables improved constraints on dust opacity and extinction in the Galactic plane.
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All authors Wanggi Lim, Jae Hwan Kang, Keunho J. Kim, Young-Jun Kim

Astrophysics of Galaxies

Feedback-Driven Interaction of Expanding Molecular Clouds in the LDN 1204-Sh2 145-Sh2 140 Complex

C Rishi, Neelam Panwar, L. K. Dewangan et al. (+1 more)

We present a multi-wavelength study of an extended molecular cloud hosting the LDN 1204, Sh2 145, and Sh2 140 regions to investigate the interplay between stellar feedback, cloud dynamics, and star formation. Infrared images reveal two semi-arc/shell-like structures (extent 14-18 pc) associated with known massive O-type stars. Herschel temperature and column density maps identify one hub-filament system (HFS) candidate toward both LDN 1204A and LDN 1204B sub-regions, with peak column densities of 3.1 x 10^23 and 1.3 x 10^23 cm^-2, respectively. These sub-regions are located at the periphery of the Sh2-145 H ii region. Molecular line data reveal a large arc-/shell-like cloud resolved into two kinematically distinct components spanning -15 to -9.5 km s^-1 and -9 to -3 km s^-1. Each component exhibits an arc-/shell-like morphology, is centered on one of the massive stars, and displays an inverted C-shaped position-velocity structure, indicating expansion driven by its associated H ii region. Both LDN sub-regions are located at the projected interface of the two expanding cloud components. Young stellar objects (YSOs), particularly Class I YSOs, are concentrated toward these sub-regions, while moment 2 maps reveal enhanced velocity dispersion, suggesting increased turbulent motions at the interface. Altogether, the presence of dense filaments, candidate hub-filament systems, and active star formation in LDN 1204 sub-regions demonstrates that feedback driven shell expansion and interaction compressed the gas at the interface, establishing the necessary conditions for filaments and ongoing star formation. These results highlight the important role of feedback-driven cloud interactions in regulating dense structure formation and star formation in molecular clouds.
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All authors C Rishi, Neelam Panwar, L. K. Dewangan, Ajay Kumar Singh

Astrophysics of Galaxies

Finding the evolutionary link between ULIRGs and radio galaxies

Ayisha Fida, Sumana Nandi, Mousumi Das et al. (+4 more)

Ultraluminous infrared galaxies (ULIRGs) are the remnants of the major mergers of gas-rich galaxies. They are dusty systems and are extremely luminous in the infrared. Both starbursts and active galactic nucleus (AGN) activity supply power in these systems, but it is not clear how these two activities are related to the overall evolution of the merger remnant. Studies suggest that there may be an evolutionary link between ULIRGs and radio galaxies. Radio observations of ULIRGs are a useful tool for understanding this evolutionary path as well as studying the energy contributions from starbursts and AGN. We perform a systematic census of these signatures in 38 ULIRGs using upgraded Giant Metrewave Radio Telescope observations and archival radio data. In the sample, 30 sources have enough frequency coverage to obtain their radio spectrum. Of these, 17 sources show a turnover frequency between 63 and 509 MHz and a spectral age variation from 0.009 to 44 Myr. Also, eight sources have extended structures with projected linear sizes varying from 0.7 to 11 kpc. Our results indicate that the primary energy source in these systems is the AGN rather than star formation. The majority of the ULIRGs in our sample, particularly those in the post-merger stage, exhibit gigahertz-peaked spectrum or compact steep spectrum-like characteristics, suggesting that they are evolving into young radio galaxies. We note that six sources with high star formation activity show a low-frequency turnover and a smaller spectral age; we confirm these six sources host buried AGN. This study enables us to trace the evolutionary link between ULIRGs and radio galaxies.
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All authors Ayisha Fida, Sumana Nandi, Mousumi Das, K. Rubinur, S. Shanbhog, Preeti Kharb, Barenya Dev

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

Stellar parameters and abundances for 3.2 million DESI DR1 spectra using machine learning

Nagaraj Vernekar, Michael Hayden and Sara Lucatello

We present a machine-learning pipeline for determining stellar parameters and chemical abundances from spectra observed by the Dark Energy Spectroscopic Instrument (DESI). Building on the model-driven Payne framework, we train an artificial neural network on ~370,000 synthetic spectra spanning FGK stars, and fit the network directly to the flux-calibrated, un-normalised spectral energy distribution (SED) of each star, rather than to a continuum-normalised spectrum as done by DESI's official Stellar Parameter (SP) pipeline. Internal accuracy tests show a median interpolation error of less than 0.3% for 90% of a synthetic verification sample, and the full fitting workflow recovers input labels to high accuracy even at low signal-to-noise ratio (S/N). Validating our method on cross-matched samples of 6719 APOGEE and 3455 GALAH stars observed by DESI with S/N > 20, we recover Teff and logg with smaller systematic offsets than the DESI SP pipeline, an improvement we attribute to fitting the full SED shape rather than a normalised spectrum. We further recover 12 elemental abundances (Na, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Ni, Ba, and Y) to an accuracy that matches or exceeds SP where a comparison is possible, and provide four abundances, Mn, V, Ba, and Y, that SP does not report at all. Applying this pipeline to the DESI Data Release 1 stellar sample, we deliver a catalogue of stellar parameters and abundances for 3.2 million stars.
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Friday 2 October

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

Relaxation of a Vlasov gas to an inhomogeneous state due to phase space mixing in an axisymmetric potential: A Newtonian analogy of the Kerr orbital motion

Ana Laura García-Perciante, Merce Guerrero, Darío Núñez et al. (+1 more)

We explore the dynamics of a Vlasov gas propagating in an external axisymmetric potential consisting of a central potential with an additional quadrupolar component which gives rise to two potential wells along the symmetry axis. Employing independently $N$-particle simulations and statistical methods, we show that an initially homogeneous and isotropic configuration evolves to an inhomogeneous final state with overdensities located at the wells. The quadrupolar component is chosen such that the equations of motion form an integrable Hamiltonian system, which allows one to compute the final state of the gas analytically. On the one hand, this allows one to compare the late-time behaviour of the simulations with an analytic prediction and on the other hand to understand the relaxation process through phase space mixing. Our model constitutes a Newtonian analogue of the particle motion in a Kerr spacetime, and we discuss possible applications to recently observed astrophysical phenomena.
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All authors Ana Laura García-Perciante, Merce Guerrero, Darío Núñez, Olivier Sarbach

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

Measuring the Age and Initial Composition of Interstellar Objects

Aster G. Barry-Taylor

Measuring the age and composition of interstellar objects is necessary to understand their origins. However, existing methods for measuring the age are either imprecise or require an unusually bright target, while the composition is confounded by the effects of Galactic cosmic rays, which drive chemical reactions in the cometary matrix. As the Vera C. Rubin Observatory expands the census of interstellar objects, measuring these properties will be critical to understanding the overall population. In this work, I derive a new methodology for simultaneously estimating the age and initial composition of an interstellar object from time-series observations of the coma. Measurements of both the composition and its gradient versus depth into the nucleus are shown to fully constrain both properties in most circumstances. A simple model using only CO and CO$_2$ is discussed and used to demonstrate the properties of this inference process. When applied to 3I/ATLAS, this simple model indicates that this object is at least 0.6 Gyr old and has an initial CO/CO$_2$ ratio of 1.5, supporting a formation outside the CO ice line. Further refinement of the chemical network and improved observational strategies will improve the precision and accuracy of these measurements, enabling a deeper understanding of the interstellar object population and extrasolar planet formation.
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Astrophysics of Galaxies · Cross-listed from astro-ph.CO

Stars Would Remember a Recent Gravitational Transition: Testing G-step Resolutions of the Hubble Tension with Red Dwarfs

Jeremy Sakstein and Harry Desmond

We test the hypothesis that Newton's gravitational constant underwent a rapid transition approximately $73$-$130\,{\rm Myr}$ ago, as proposed in some resolutions of the Hubble tension. Fully convective red dwarf stars with masses below $\sim0.35\,M_\odot$ have thermal timescales comparable to the proposed transition look-back times, so an appreciable present-day memory can remain. We show that a rapid step in $G$ induces measurable changes in their radii and confront these predictions with mass-radius measurements of eight red dwarfs in detached eclipsing binaries. We find that the $G$-step models proposed to resolve the Hubble tension, corresponding to a $4\%$ change in $G$ at a look-back time of $73\,{\rm Myr}$ and an $11\%$ change at $130\,{\rm Myr}$, are excluded at significances of $3.1\sigma$ and $4.0\sigma$, respectively.
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Astrophysics of Galaxies · Cross-listed from astro-ph.HE

A concordance model of neutron star kicks

Cheyanne Shariat, Kareem El-Badry and Smadar Naoz

Neutron stars (NSs) receive natal kicks during supernovae that affect their survival in binaries and motion through the Galaxy. The global distribution of these kick velocities across the NS population remains uncertain. Here, we combine the orbital properties and birth rates of Gaia NS and Be+NS binaries with velocity constraints from young isolated pulsars to construct a concordance model of NS natal kicks. We find that all three populations can be jointly described by a shared bimodal kick distribution. The low-velocity component follows a lognormal distribution with $\mu_{\ln v}=1.87^{+0.65}_{-0.53}$ and $\sigma_{\ln v}=0.55^{+0.85}_{-0.44}$, corresponding to a median speed of $6.5^{+5.9}_{-2.7}~{\rm km~s^{-1}}$. The high-velocity component is consistent with the distribution inferred from young pulsars, which peaks near $200~{\rm km~s^{-1}}$. The low-velocity component contributes only $\sim10\%$ of all NS births, but produces most Gaia NS binaries and roughly half of Be+NS binaries. The same model predicts systemic recoil velocities consistent with the observed kinematics of Gaia NSs, Be+NS binaries, and NS low-mass X-ray binaries. For Gaia NSs, whose formation history remains unknown, we use this kick distribution to constrain their progenitors. We favor pre-supernova binaries containing intermediate-mass stripped stars with $\sim1~{\rm M_\odot}$ companions in au-scale orbits, and predict $\sim300$ such binaries in the Milky Way today, $\sim40$ in the LMC, and $\sim30$ in the SMC. Finally, we consider the implications of these kicks for NSs in hierarchical triples. We find that 2-10$\%$ of Gaia NS triples and 3-23$\%$ of Be+NS triples retain their tertiary after the supernova. Overall, our results suggest that a shared natal kick law can account for isolated pulsars and surviving NS binaries, where most NSs receive large kicks and low kicks are common among surviving binaries.
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Astrophysics of Galaxies

The Merian Survey: A Statistical Census of Bright Satellites of Sub-Milky Way-Mass Galaxies

Lucas S. Mandacarú Guerra, Jiaxuan Li, Yue Pan et al. (+9 more)

Satellite populations provide sensitive tests of the galaxy-halo connection, but studies have largely focused on Milky Way (MW)-mass host galaxies or a small number of nearby dwarf galaxy hosts. Here we present a statistical census of bright, star-forming satellite galaxies around sub-MW-mass hosts using the first data release of the Merian Survey. Our sample consists of 357 hosts with stellar mass $10^{9.5}<M_{\star,\text{host}}<10^{10.5} \ \text{M}_\odot$ at redshifts $0.07<z<0.09$, all selected to be central galaxies. Merian's medium-band imaging isolates H$\alpha$ and [O iii] emission lines for galaxies in this redshift range, enabling efficient selection of star-forming satellites down to $M_{\star,\text{sat}}\gtrsim 10^{7.5} \,\text{M}_\odot$. We identify 471 satellite candidates within the projected virial radii of these hosts. After statistically subtracting the contribution from foreground and background galaxies, we find $148\pm 7$ satellite candidates associated with the host sample. We find that $\mathord{\sim} 60\%$ of hosts have $N_{\rm sat}< 1$ massive satellites within their virial radii, $\mathord{\sim} 22\%$ have $1\leq N_{\rm sat}< 2$, $\mathord{\sim} 10\%$ have $2\leq N_{\rm sat}< 3$, and $\mathord{\sim} 8\%$ have $N_{\rm sat} > 3$. Satellite abundance increases with host stellar mass across the sub-MW regime, extending the observed trend from dwarf to MW-mass galaxies and broadly agreeing with predictions from the TNG50 simulation. The radial distribution of satellites around sub-MW-mass hosts is similar to that around MW-mass hosts and broadly consistent with TNG50. Together, these results extend our empirical view of satellite populations across the previously sparsely sampled transition between dwarf and MW-mass hosts.
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All authors Lucas S. Mandacarú Guerra, Jiaxuan Li, Yue Pan, Jenny E. Greene, Shany Danieli, Joy Bhattacharyya, Alyson M. Brooks, Song Huang, Alexie Leauthaud, Yifei Luo, Annika H. G. Peter, Conghao Zhou