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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 10 February

High Energy Astrophysical Phenomena

X-ray Timing and Spectral studies of the bare AGN Mrk 110

Deblina Lahiri, K. Sriram and Vivek Kumar Agrawal

The origin of the soft X-ray excess below 2 keV in active galactic nuclei (AGNs) remains debated, with relativistic reflection from the inner accretion disk and warm Comptonization in an optically thick corona being the leading explanations. We investigate the timing and spectral properties of the Seyfert galaxy Mrk 110 using six XMM-Newton observations. A frequency-dependent lag analysis in the 7-9 $\times 10^{-5}$ Hz range reveals a soft X-ray lag of 889-3000s in the combined 2019 data, detected with a significance of 80%. The cross-correlation function analysis, supported by simulations, also detects lags of similar nature. Spectral modeling performed by adopting both proposed black hole masses in the literature for Mrk 110 confirms the presence of a warm corona in all observations, along with a weak relativistic reflection component and the reflection fraction remains low (Rf < 1). Interpreting the measured soft lag in terms of light travel time implies an emission radius 4.5 Rg for a supermassive black hole mass of $M = 1.4 \times 10^8$ solar mass , favoring a reflection scenario. However, if a lower mass of $M = 2 \times 10^7$ solar mass is adopted, the inferred radius increases, and both relativistic reflection and warm Comptonization can plausibly contribute to the observed soft lag. The warm corona radius appears larger in the high accretion state and smaller in a lower accretion state, although no trend can be established. The persistently low reflection fraction suggests an outflowing inner corona in Mrk 110, consistent with the recent detection of jet activity in this source.
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Astrophysics of Galaxies

Herschel/HIFI Observations of Molecular Lines Toward G10.47+0.03

Indrajit Mondal, Prasanta Gorai, Ankan Das et al. (+6 more)

We present a spectral line analysis of the hot molecular core G10.47+0.03 (hereafter, G10). Our aim is to determine molecular abundances and excitation conditions across a wide spectral range inaccessible to ground-based observatories. We utilize archival data from the Herschel Space Observatory, obtained with the Heterodyne Instrument for the Far-Infrared (HIFI). We report here the detection of high-excitation CO, 13CO, and C18O, H2O isotopologues, HCO+, HCN, HNC, CS, C34S, SO, SO2, H2CS, and CH3OH. CO, p-H2O, CS, and HCN show similar velocity profiles with a narrow, blueshifted component, which may be linked to the outer outflow layer. Redshifted wings may indicate inner outflow activity. A Markov Chain Monte Carlo framework is employed to infer column densities and temperatures accurately. We also performed spectral energy distribution fitting to constrain the global physical parameters of G10, providing essential context for interpreting the molecular emission. The MCMC analysis revealed two excitation temperature components: a warm component (30-65 K) and a hot component (90-250 K). The higher temperatures indicate dense, hot gas typical of massive hot cores. The lower temperatures correspond to the warm, less dense envelope around the core. Transitions of H2O, high-excitation CO, and HCN indicate outflowing gas and high-density shocked regions. These findings highlight G10's complex dynamical environment.
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All authors Indrajit Mondal, Prasanta Gorai, Ankan Das, Suman Kumar Mondal, Ruben Fedriani, Xiaohu Li, Parama Mahapatra, Sabyaasachi Banik, Sheng-Li Qin

Cosmology and Nongalactic Astrophysics

Microlensing events and primordial black holes in the axionlike curvaton model

Kentaro Kasai, Masahiro Kawasaki, Kai Murai et al. (+1 more)

Recently, Subaru Hyper Suprime-Cam (HSC) observations found 12 candidates for microlensing events. These events can be explained by primordial black holes (PBHs) with masses of $10^{-7}$-$10^{-6} M_\odot$ and a fraction of all dark matter of $f_\mathrm{PBH} = \mathcal{O}(10^{-1})$. In this paper, we consider the PBH production in two types of the axionlike curvaton models, which predict an enhancement of the curvature perturbations on small scales. We show that the microlensing events can be explained in the axionlike curvaton model and discuss the cosmological implications such as gravitational waves.
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All authors Kentaro Kasai, Masahiro Kawasaki, Kai Murai, Shunsuke Neda

Earth and Planetary Astrophysics

A Narrowband Technosignature Search Toward the Hycean Candidate K2-18b Using the VLA and MeerKAT

C. D. Tremblay, S. Chaudhary, Megan G. Li et al. (+12 more)

K2-18b, a sub-Neptune exoplanet located in the habitable zone of its host star, has emerged as an important target for atmospheric characterization and assessments of potential habitability. Motivated by recent interpretations of JWST observations suggesting a hydrogen-rich atmosphere consistent with Hycean-world scenarios, we conducted a coordinated, multi-epoch search for narrowband radio technosignatures using the Karl G. Jansky Very Large Array equipped with the COSMIC backend and the MeerKAT telescope with the BLUSE backend. Our observations span frequencies from 544MHz to 9.8GHz and include multiple epochs that cover at least one full orbital period of the planet. In this work, we outline, create, and apply a comprehensive post-processing framework that incorporates observatory-informed RFI masking, drift-rate filtering based on the expected dynamics of the K2-18 system, multibeam spatial discrimination, primary and secondary transit filtering (when applicable), and SNR-based excision of weak and strong spurious signals. Across all bands and epochs, no signals consistent with an astrophysical or artificial origin were identified at a limit of 10^12 to 10^13W. These non-detections allow us to place upper limits on the presence of persistent, isotropic narrowband transmitters within the K2-18 system, providing the first interferometric technosignature constraints for a Hycean-planet candidate. Our results demonstrate the efficacy of coordinated multiepoch interferometric searches and establish a methodological framework for future technosignature studies of nearby potentially habitable exoplanets.
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All authors C. D. Tremblay, S. Chaudhary, Megan G. Li, Sofia Z. Sheikh, T. Myburgh, D. Czech, D. E. MacMahon, P. B. Demorest, R. A. Donnachie, A. P. V. Siemion, V. Gajjar, M. Lebofsky, K. Wandia, K. I. Perez., Nikku Madhusudhan

High Energy Astrophysical Phenomena

Systematic Study of the Simultaneous Events Detected by GECAM

Yang-Zhao Ren, Feng-Rong Zhu, Shao-Lin Xiong et al. (+45 more)

GECAM is a constellation of all-sky monitors in hard X-ray and gamma-ray band primarily aimed at high energy transients such as gamma-ray bursts, soft gamma-ray repeaters, solar flares and terrestrial gamma-ray flashes. As GECAM has the highest temporal resolution (0.1~$\mu$s) among instruments of its kind, it can identify the so-called simultaneous events (STE) that deposit signals in multiple detectors nearly at the same time (with a 0.3~$\mu$s window). However, the properties and origin of STE have not yet been explored. In this work, we implemented, for the first time, a comprehensive analysis of the STE detected by GECAM, including their morphology, energy deposition, and the dependence on the geomagnetic coordinates. We find that these STE probably result from direct interactions between high-energy charged cosmic rays and satellite. These results demonstrate that GECAM can detect, identify, and characterize high-energy cosmic rays, making it a Micro Cosmic-Ray Observatory (MICRO) in low Earth orbit.
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All authors Yang-Zhao Ren, Feng-Rong Zhu, Shao-Lin Xiong, Yan-Qiu Zhang, Chen-Wei Wang, Jia-Cong Liu, Hao-Xuan Guo, Shuo Xiao, Dong-Ya Guo, Zheng-Hua An, Ce Cai, Pei-Yi Feng, Min Gao, Ke Gong, Yue Huang, Bing Li, Xiao-Bo Li, Xin-Qiao Li, Xiao-Jing Liu, Ya-Qing Liu, Xiang Ma, Wen-Xi Peng, Rui Qiao, Li-Ming Song, Xi-Lei Sun, Wen-Jun Tan, Jin Wang, Jin-Zhou Wang, Ping Wang, Yue Wang, Xiang-Yang Wen, Sheng-Lun Xie, Wang-Chen Xue, Sheng Yang, Qi-Bin Yi, Zheng-Hang Yu, Da-Li Zhang, Fan Zhang, Hong-Mei Zhang, Jin-Peng Zhang, Peng Zhang, Shuang-Nan Zhang, Wen-Long Zhang, Zhen Zhang, Xiao-Yun Zhao, Yi Zhao, Chao Zheng, Shi-Jie Zheng

Instrumentation and Methods for Astrophysics

A new strategy for achieving multiple continuous cooling stages in an adiabatic demagnetization refrigerator

Yanan Li, Ke Li, Teng Pan et al. (+2 more)

This paper presents a three-stage continuous adiabatic demagnetization refrigerator (CADR) simultaneously providing cooling platforms at two different temperatures. Unlike conventional CADR with two continuous stages, this system does not require an extra continuous stage. It is achieved with carefully designed heat switch operations and stage sequences. This new strategy significantly reduces system complexity and mass. The detailed implementation of the two cooling platforms is described, and factors limiting system performance are analyzed. This CADR system has achieved a cooling power of 20 {\mu}W@1 K and 4 {\mu}W@300 mK simultaneously, offering a new design strategy for the development of CADR with multiple continuous stages.
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All authors Yanan Li, Ke Li, Teng Pan, Yaxuan Wang, Wei Dai

Solar and Stellar Astrophysics · Cross-listed from nucl-th

Three-Body Barrier Dynamics of Double-Alpha Decay in Heavy Nuclei

Shulin Tang, Tao Wan, Yibin Qian et al. (+6 more)

The simultaneous emission of two $\alpha$ particles–double-$\alpha$ decay–represents a long-predicted but unobserved mode of nuclear radioactivity. Here we formulate this process as a genuine three-body problem within the hyperspherical coordinate framework and evaluate decay probabilities by numerically solving the corresponding hyperradial Schrödinger equation, combined with large-scale random sampling of the potential parameters; the latter treatment ensures that the present results are more convincing. Inspired by this, we demonstrate that the penetrability ratio between simultaneous and sequential $\alpha$ emission exhibits a strikingly linear dependence on $ZQ_{\alpha\alpha}^{-1/2}$, extending the barrier penetration dynamics into the correlated few-body regime. The nuclei $^{108}$Xe, $^{218}$Ra, $^{224}$Pu, $^{222}$U, $^{216}$Rn, and $^{220}$Th are suggested as the most promising candidates for the observation of double-$\alpha$ decay, with predicted half-lives potentially accessible within present detection limits. Our results provide a unified framework for multi-$\alpha$ decay and open a pathway to probing nuclear clustering and few-body correlations in heavy nuclei.
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All authors Shulin Tang, Tao Wan, Yibin Qian, Chong Qi, Ramon A. Wyss, Roberto J. Liotta, Dong Bai, Bo Zhou, Zhongzhou Ren

Astrophysics of Galaxies

A deep MeerKAT view of associated HI absorption in radio AGNs at intermediate redshift: Role of absorber geometry and conditions of the gas

Raffaella Morganti, Tom Oosterloo, Clive Tadhunter et al. (+1 more)

We present MeerKAT observations searching for HI absorption in a sample of 17 powerful ($L_{\rm 1.4GHz}> 10^{27}$ W Hz$^{-1}$) radio sources at intermediate redshifts ($0.25<z<0.7$). The sample is well characterised at radio and optical wavelengths, allowing us to connect the presence (or absence) of HI to the properties of the AGN and its host galaxy. The sample consists mostly of core-dominated sources and quasars. Half of the targets have a UV luminosity $L_{\rm UV} = 10^{23}$ W Hz$^{-1}$, above this limit, the gas would be expected to be ionised by this radiation. We obtained 15 spectra free (or almost free) of radio frequency interference, reaching extremely low optical depths ($\tau_{\rm peak} < 0.005$) resulting in three new HI absorption detections. Two are associated HI absorptions, giving a detection rate of such systems of $13\%\pm 7\%$. Both are found in young radio sources (PKS 1151-34 and PKS 1306-09), confirming the trend that this type of sources are more often detected in HI compared to more evolved ones. The UV luminosity of both these sources is below $10^{23}$ W Hz$^{-1}$. Surprisingly, one of the detections (PKS 1151-34) is hosted by a quasar, suggesting that the radio lobes are still embedded in the circumnuclear disc. In the second source (PKS 1306-09), the HI is highly blueshifted and likely part of a jet-driven outflow. A third detection is a 'local intervening' system, caused by a galaxy in the local environment of PKS 0405-12 and located in front of the southern radio lobe of this source, about 100 kpc in projection from this quasar. Overall, the results indicate a variety of plausible situations, which resemble what is seen at low redshifts. For the associated absorption, a combination of evolutionary status of the radio sources, physical conditions, and geometry of the gas structure determine the detection rate of HI absorption.
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All authors Raffaella Morganti, Tom Oosterloo, Clive Tadhunter, Suma Murthy

Earth and Planetary Astrophysics

The compositions of the HR 8799 planets reflect accretion of both solids and metal-enriched gas

Jerry W. Xuan, Jean-Baptiste Ruffio, Yayaati Chachan et al. (+24 more)

With four giant planets ($m\sim5-10~M_{\rm Jup}$, $T_\rm{eff}\sim900-1200$ K) orbiting between 15-70 au, HR 8799 provides an unparalleled testbed for studying giant planet formation and probing compositional trends across the protoplanetary disk. We present new JWST/NIRSpec IFU observations ($2.85-5.3~\mu$m, $R\approx2700$) that now include the spectrum of HR 8799 b, and higher S/N spectra for HR 8799 c, d, and e compared to that in Ruffio & Xuan et al. We detect CO, CH$_4$, H$_2$O, H$_2$S, CO$_2$, and for planet b, NH$_3$. We combine the NIRSpec spectra with $1-5 \mu$m photometry to perform atmospheric retrievals that account for disequilibrium chemistry and clouds, and allow C/H, O/H, N/H, and S/H to scale independently. While the four planets are similarly enriched in carbon and oxygen, with C/H and O/H between $3-5\times$ stellar, we observe a tentative trend of increasing S/H - a tracer of refractory solids - from $2-5 \times$ stellar with increasing orbital distance. From HR 8799 b's NH$_3$ abundance, we estimate $\rm N/H=21.2^{+16.2}_{-8.8}\times$ stellar, suggesting the outer planet accreted significant amounts of N-rich gas. Overall, the elemental abundance patterns we observe are consistent with a picture where planet b formed between the CO snowline and the more-distant N$_2$ snowline, while the inner planets accreted $3 \times$ stellar CO-enriched disk gas within the CO snowline. The excess volatile mass from pebble drift and evaporation implies an integrated pebble flux of $750 \pm 200~M_{\oplus}$. The increase in the planets' S/H with orbital distance implies more solid accretion further out, which is quantitatively compatible with expectations from both pebble and planetesimal accretion ($2 \times$ Minimum Mass Solar Nebula) paradigms.
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All authors Jerry W. Xuan, Jean-Baptiste Ruffio, Yayaati Chachan, Kazumasa Ohno, Aurora Y. Kesseli, Ruth A. Murray-Clay, Eve J. Lee, Julianne I. Moses, William O. Balmer, Aneesh Baburaj, Geoffrey A. Blake, Doug Johnstone, Yapeng Zhang, Heather A. Knutson, Dimitri Mawet, Charles Beichman, Klaus W. Hodapp, Marshall D. Perrin, Quinn M. Konopacky, Michael R. Meyer, Geoffrey Bryden, Thomas P. Greene, Jarron Leisenring, Marie Ygouf, Björn Benneke, Julie Inglis, Nicole L. Wallack

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

A Small Patch Hypothesis in Cosmology

Meir Shimon

If our observable Universe is only a tiny region of a vastly larger and conformally older spacetime, then the usual formulations of the classical flatness and horizon problems of the Hot Big Bang can be reinterpreted as artifacts manifesting an observational selection effect; we occupy a small causal domain of a much larger causally-connected and possibly non-flat spacetime. A sufficiently large positive cosmological constant, $\Lambda$, sets the future asymptotic horizon scale of the observable Universe, $\sim$$\Lambda^{-1/2}$, thereby implying that the observable Universe may simply be a minute patch of a far larger pre-existing one, hereafter a Small Patch Hypothesis. Importantly, this observational bound is purely geometric; regardless of when the Universe is observed, the maximum accessible scale is finite and fixed by $\Lambda$, independent of inflationary dynamics, anthropic arguments, or assumptions about the global hosting spacetime. In this sense, inflation becomes one viable realization of the proposed Small Patch Hypothesis. Here, one particular non-inflationary alternative is considered for illustrative purposes in which a primordial spectrum grows logarithmically toward large scales, and in fact diverges at some finite $k_{c}$. If $k_{c}\ll \Lambda^{-1/2}$, then our local cosmic patch probes only the linear regime and appears exceptionally smooth. Over the comparatively narrow observable window, this power spectrum mimics a slightly red-tilted, inflation-like spectrum. Rather than introducing high-energy new fields, this perspective frames large-scale homogeneity, isotropy, Gaussianity, adiabaticity, and the observed thermodynamic Arrow of Time as possible consequences of restricted observational access to a much larger Universe in equilibrium, rather than signatures of a unique early-Universe mechanism. [abridged]
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Astrophysics of Galaxies

A Monopolar Jet from Protostar HOPS 10: Evidence for Asymmetric Magnetized Launching

Somnath Dutta

A fundamental challenge in star formation is understanding how a protostar accretes mass from its circumstellar disk while removing excess angular momentum. Protostellar jets are widely invoked as the primary channels for angular momentum removal, yet the mechanism by which they are launched and extract angular momentum remains poorly constrained. Here we report high-resolution ALMA Band 7 (345 GHz) and Band 6 (230 GHz) observations of CO (3-2), CO (2-1), and SiO (5-4) emission from the protostar HOPS 10 (G209.55-19.68S2). The combined data trace both the entrained outflow and the collimated jet with excellent spatial and velocity resolution, revealing a uniquely monopolar protostellar jet, the clearest example reported to date. The system exhibits a distinctly unipolar high-velocity jet with velocity offsets of +44 to +66 km s-1, unlike the predominantly bipolar morphology characteristic of most protostellar jets. While the low-velocity outflow, with velocity offsets of -20 to +30 km s-1, is detected in both directions, the high-velocity jet appears only on one side, and this monopolarity is consistent across all tracers. Given the nearly edge-on geometry and low submillimeter extinction, comparable emission would normally be expected from both lobes. The shock tracer SiO emission confirms a genuine, highly collimated jet rather than cloud contamination, and no ambient structure is capable of obscuring a counterjet. We argue that intrinsically asymmetric mass loading along the disk magnetic field lines provides the most plausible explanation for the observed monopolarity.
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High Energy Astrophysical Phenomena

Mass-Radius Constraints for 2S 0918-549 from an RXTE Superexpansion Burst: A Direct Cooling-Tail Analysis

Hongbin Fan, Helei Liu, Zhaosheng Li et al. (+6 more)

Thermonuclear (Type I ) X-ray bursts from accreting neutron stars offer a means to determine neutron-star (NS) mass ($M$) and radius ($R$) and thereby probe the properties of matter at supranuclear density. A subset of these events, photospheric radius-expansion (PRE) bursts, provide a particularly powerful tool to constrain the neutron-star $M$ and $R$. Here, we apply the direct cooling-tail method to 2S~0918$-$549, using a rare superexpansion burst observed by RXTE. We fit only the post-touchdown data within \(F/F_{\rm td}\in[0.6,0.95]\), employing modern atmosphere models (pure He and metal-enriched). The pure-He atmosphere yields a good description of the cooling tail (\(\chi^{2}/\nu=18.12/14\)), whereas metal-rich models fail; information-criterion tests (AIC/BIC) disfavor adding a free absorption edge in every time bin, indicating that heavy-element ashes are unnecessary. The joint fit gives a distance \(d=4.1-5.3\) kpc and mass-radius constraints \(M=1-2\,M_\odot\) and \(R=9.7-11.9\) km (99% confidence). These results suggest that representative families of both gravity-bound and self-bound equations of state remain viable at the $1\sigma$ confidence level.
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All authors Hongbin Fan, Helei Liu, Zhaosheng Li, Yupeng Chen, Shoutao Ban, Guoliang Lü, Akira Dohi, Chunhua Zhu, Renxin Xu

Solar and Stellar Astrophysics

Spectroscopic He I 1083 nm prominence eruption observations in the middle corona with MLSO/UCoMP

Chloe Pistelli, Momchil E Molnar, Giuliana de Toma et al. (+1 more)

Coronal mass ejections (CMEs) are a major driver of space weather as they propagate through the heliosphere. Many CMEs have associated prominence material entangled in their magnetic structure which contains cooler plasma. This cooler CME component contains significant amounts of neutral elements, which emit brightly in permitted atomic lines. It has been hypothesized that permitted transitions of neutral elements in eruptions could be used for inferring the magnetic field in CMEs, which is crucial for space weather forecasting. We present observations made with the Upgraded Coronal Multi-channel Polarimeter (UCoMP) in He I 1083 nm that clearly show the presence of neutral helium in eruptive prominences associated with CMEs as they propagate through the lower and middle corona. We find that solar prominence eruptions can be detected in He I 1083 nm observations up to the edge of the instrument field of view at about 2 solar radii, providing valuable spectral information that complements existing extreme ultraviolet and white-light coronal imaging observatories. These results illustrate the capability of UCoMP to probe the dynamic behavior of prominence eruptions, allowing for their line-of-sight velocity estimation, and potentially improving space weather forecasting by enabling earlier and more accurate identification of Earth-directed eruptions.
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All authors Chloe Pistelli, Momchil E Molnar, Giuliana de Toma, Joseph Plowman

Solar and Stellar Astrophysics

Orbital Period Changes of Recurrent Nova T Pyxidis Demonstrate that M_ejecta >> 11.3xM_accreted and Is Not a Type Ia Supernova Progenitor

Bradley E. Schaefer

Recurrent nova (RN) T Pyxidis (T Pyx) has a complex history of mass accreting-onto and ejection-from the white dwarf, with a classical nova eruption around 1866 kick-starting a RN-phase with six RN eruptions from 1890–2011. T Pyx is a primary progenitor candidate for Type Ia supernovae (SNIa). This is chiefly a question of whether the mass accreted by the white dwarf ($M_{\rm accreted}$) is more-or-less than the mass ejected by the nova eruptions ($M_{\rm ejecta}$) over the entire eruption cycle. Prior attempts to measure $M_{\rm ejecta}$ from the traditional methods have a scatter of $>$130$\times$, so only a new technique can provide a measure of adequate accuracy and reliability. This new technique is the timing experiment of measuring the orbital period from 1986 to 2025, where the period increased by $+$50.3$\pm$7.9 parts-per-million across the 2011 eruption. With simple and sure physics, the best estimate for the mass ejected by one RN event is $>$2400$\times$10$^{-7}$ M$_{\odot}$, with an extreme inviolate limit of $\gg$354$\times$10$^{-7}$ M$_{\odot}$. Over all eruptions in a cycle, $M_{ejecta}$$>$17120$\times$10$^{-7}$ M$_{\odot}$, with an inviolate limit of $M_{ejecta}$$\gg$2144$\times$10$^{-7}$ M$_{\odot}$. Over the full eruption cycle, the white dwarf accreted 220$\times$10$^{-7}$ M$_{\odot}$. So M$_{\rm ejecta}$$\gg$11.3$\times$M$_{\rm accreted}$, and T Pyx can never become a SNIa. This paper is the seventh in a series proving that each of various popular candidate SNIa progenitors cannot possibly evolve to a supernova; including V445 Pup, U Sco, T CrB, all symbiotic stars, FQ Cir, V1405 Cas, and now T Pyx.
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2602.09377 · 10 Feb · 7th in a series of ApJ papers, each proving that popular progenitor candidates cannot become Type Ia supernovae: 1. V445 Pup (arXiv:2412.17286), 2. T CrB (arXiv:2510.01587), 3. U Sco (arXiv:2510.01589), 4. FQ Cir (arXiv:2511.16594), 5. all symbiotic stars (arXiv:2511.19948), 6. V1405 Cas (ApJ submitted), 7. T Pyx (ApJ in press)

Abstract PDF $DWRF ×3$SNOV ×3$STAR ×1

Astrophysics of Galaxies

Selecting Post-Starburst Galaxies Based on Star Formation History

Sara Starecheski, K. Decker French, Vicente Villanueva et al. (+6 more)

Post-StarBurst (PSB) galaxies are galaxies that have undergone a large burst of star formation followed by rapid quenching. Understanding their properties as a population can help us better understand how galaxies evolve to quiescence. This project aims to use Star Formation History (SFH) measurements from the Integral Field Spectroscopy (IFS) surveys MaNGA, CALIFA, and AMUSING++ processed with the Pipe3D analysis pipeline in order to select PSB galaxies as well as PSB regions in galaxies. Most PSB selection methods use cutoffs determined by spectral features, but in this work we introduce a new PSB selection method based directly on the property we are most interested in; inferred SFHs. IFS data allows us to probe a galaxy's star formation on a spatially resolved scale, enabling us to examine the size, shape, and location of PSB regions within a galaxy. We select 107 PSB galaxies, only 7 of which are among known PSBs selected by other methods. Unlike traditional PSB selection methods, our approach is not biased against Active Galactic Nuclei (AGN). Despite this, we still find no evidence for a significant Seyfert 2 PSB population, suggesting that strong AGN activity is uncommon throughout the PSB phase. Our spatially-resolved SFH selection identifies a wide range of galaxies, including globally quiescent elliptical galaxies with centrally-concentrated PSB spaxels, galaxies with ring-like PSB spaxels and a preference for inside-out age gradients (contrary to what has previously been observed in the literature), and galaxies with widespread PSB regions that have significant star formation elsewhere in the galaxy.
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All authors Sara Starecheski, K. Decker French, Vicente Villanueva, Sebastion F. Sanchez, Tony Wong, Margaret E. Verrico, Alex Green, Akshat Tripathi, Keaton Donaghue

Monday 9 February

Cosmology and Nongalactic Astrophysics · Cross-listed from physics.hist-ph

Dark Matter in Zwicky's Cosmology: Towards an Epistemological Reconstruction

Simon Beyne and Christian Marinoni

A new contextualised reading of Fritz Zwicky's 1933 article ”The redshift of extragalactic nebulae” about the virial analysis of the velocity dispersion of galaxies in the Coma cluster leads to a reconsideration of the traditional discourse on the introduction of dark matter. We argue that this component of matter was not only already on the stage of the scientific debates of the time, but also, in a more concealed form, played a central role in Zwicky's epistemic context. We thus reject the narration that dark matter is the result of a “naïve” astrophysical observation and emphasise the cosmological motivations that prompted Zwicky to presciently search for it. Moreover, with regard to its abundance, we argue that the discrepancy between the observed amount of luminous matter in the Coma Cluster and Zwicky's higher mass estimate derived from virial analysis was not, in fact, astonishing. What Zwicky described as a surprising excess of dark matter was of precisely the order of magnitude he had set out to identify. Consequently, we challenge the widespread view that dark matter was merely an ad hoc hypothesis introduced to rescue Newtonian theory. Instead, we suggest it may represent one of the earliest cosmological indications supporting a new emerging theory of gravitation: General Relativity. This reinterpretation contributes to ongoing debates in the philosophy of science concerning the epistemic status of ad hoc hypotheses.
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Instrumentation and Methods for Astrophysics · Cross-listed from cs.MA

Agent Mars: Multi-Agent Simulation for Multi-Planetary Life Exploration and Settlement

Ziyang Wang

Artificial Intelligence (AI) has transformed robotics, healthcare, industry, and scientific discovery, yet a major frontier may lie beyond Earth. Space exploration and settlement offer vast environments and resources, but impose constraints unmatched on Earth: delayed/intermittent communications, extreme resource scarcity, heterogeneous expertise, and strict safety, accountability, and command authority. The key challenge is auditable coordination among specialised humans, robots, and digital services in a safety-critical system-of-systems. We introduce Agent Mars, an open, end-to-end multi-agent simulation framework for Mars base operations. Agent Mars formalises a realistic organisation with a 93-agent roster across seven layers of command and execution (human roles and physical assets), enabling base-scale studies beyond toy settings. It implements hierarchical and cross-layer coordination that preserves chain-of-command while allowing vetted cross-layer exchanges with audit trails; supports dynamic role handover with automatic failover under outages; and enables phase-dependent leadership for routine operations, emergencies, and science campaigns. Agent Mars further models mission-critical mechanisms-scenario-aware short/long-horizon memory, configurable propose-vote consensus, and translator-mediated heterogeneous protocols-to capture how teams align under stress. To quantify behaviour, we propose the Agent Mars Performance Index (AMPI), an interpretable composite score with diagnostic sub-metrics. Across 13 reproducible Mars-relevant operational scripts, Agent Mars reveals coordination trade-offs and identifies regimes where curated cross-layer collaboration and functional leadership reduce overhead without sacrificing reliability. Agent Mars provides a benchmarkable, auditable foundation for Space AI.
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Cosmology and Nongalactic Astrophysics

A non-perturbative framework for N-point functions of locally non-Gaussian fields

Hardi Veermäe

We present a non-perturbative approach to correlation functions and polyspectra of locally non-Gaussian fields and develop a semi-perturbative framework that does not rely on a local expansion. This enables the computation of $N$-point functions of non-Gaussian fields even when the mapping between the auxiliary Gaussian field $\zeta_{\rm G}$ and the non-Gaussian field $\zeta({\bf x}) = F(\zeta_{\rm G}({\bf x}))$ is non-analytic. As an example, we consider non-Gaussian fields with exponentially tailed distributions, which can arise, for instance, in ultra-slow-roll models of inflation, and derive some exact analytic results in the strongly non-Gaussian regime.
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Earth and Planetary Astrophysics

Origin of Hyperion and Saturn's Rings in A Two-Stage Saturnian System Instability

Matija Ćuk, Maryame El Moutamid, Jim Fuller et al. (+1 more)

The age of the rings and some of the moons of Saturn is an open question, and multiple lines of evidence point to a recent (few hundred Myr ago) cataclysm involving disruption of past moons. The main driver of the evolution of the Saturnian system is the relatively rapid tidal expansion of its largest moon, Titan, which is likely driven by resonant tides within Saturn. The obliquity of Saturn and the orbit of the small moon Hyperion both serve as a record of the past orbital evolution of Titan. Saturn's obliquity was likely generated by a secular spin-orbit resonance with the planets, while Hyperion is caught in a mean-motion resonance with Titan, with both phenomena driven by Titan's orbital expansion. We propose that the breaking of Saturn's spin resonance was also the event in which Hyperion formed, when an outer mid-sized satellite (“Proto-Hyperion”) was destabilized and collided with Titan, with some of the debris accreting into Hyperion. During the instability Proto-Hyperion's perturbations produced the observed orbital inclination of Iapetus. The same event also excited the eccentricity of Titan, which then, through Titan's resonant interaction with the inner moons, led to destabilization, collisional disruption and re-accretion of the inner moon system, including the rings. We present numerical integrations that show that this chain of events has a relatively high probability, and discuss how it fits within our knowledge of the Saturnian system.
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All authors Matija Ćuk, Maryame El Moutamid, Jim Fuller, Valéry Lainey

Astrophysics of Galaxies

Are carbon deflagration supernovae triggered by dark matter ?

Jeremy Mould

Collisions between stellar remnants and dark matter in the Galactic bulge are frequent, and the kinetic energy of a primordial black hole incident on a white dwarf, if it is all thermalized, will raise the degenerate core's temperature, by at least a degree in the case of a lunar mass black hole. This is an underestimate in two ways: the specific heat is less than 3k/2 per particle, and the incoming object is accelerated by gravitational focusing. Detailed physical models have recently been made of this triggering event. Present observational data are equivocal as to whether the radial distribution of type Ia supernovae in galaxies follows the starlight in the galaxies, or is more concentrated towards the center, as collisional triggering would suggest. But future samples of millions of supernovae from the Rubin telescope will change that.
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Astrophysics of Galaxies

ALMA [CI] Image of the Circumnuclear Disk of the Milky Way: Inflowing Low-density Molecular Gas

Kunihiko Tanaka, Makoto Nagai and Kazuhisa Kamegai

We present ALMA [\ion{C}{1}]~$^3P_1$–$^3P_0$ imaging of the central $6.6\times4.2~\mathrm{pc}^2$ region of the Galaxy encompassing the circumnuclear disk (CND). The data reveal low-density ($n_\mathrm{H_2}\sim10^3~$cm$^{-3}$) molecular gas with inward motion, widespread both inside and outside the CND. The normalized [\ion{C}{1}] to CS~7–6 intensity difference decreases inwardly from $R=4$~pc to 1.7~pc and azimuthally along the CND's rotation, likely tracing paths of low-density gas inflow. By projecting spaxels into orbital coordinates assuming a velocity field model, we identify four kinematic features: a pair of spiral outer streamers toward the CND, inner streamers extending to 0.5~pc from Sgr~A$^*$, an outer disk at $ R\sim3$–6~pc, and the rotating ring at $R=2$~pc. $P$–$P$–$V$ correlation between the inner streamers and H42$\alpha$ indicates gas supply to the mini-spiral through the western arc (WA) and northern arm (NA). The total inflowing mass is $1.5\times10^4~M_\odot$, 1.7 times the mass of the rotating ring. The identified flows can be organized into two main pathways connecting the CND exterior and interior: “WA flow” feeding the mini-spiral WA via the CND, and “NA flow” bypassing the purely rotating orbit. The inflow rate along the former is approximately constant (0.1–0.16~$M_\odot~\mathrm{yr}^{-1}$), implying a CND dwelling time comparable to its orbital period and supporting the CND's transient nature. We also identify two [\ion{C}{1}]-bright clumps (CBCs) lacking dense-gas counterparts near the contact point between the northern outer streamer and the CND. Apparently intact against tidal disruption despite subcritical densities, the CBCs may represent a chemically young phase shortly after formation in colliding flows.
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Astrophysics of Galaxies

Towards a general field equation for galaxies and galaxy clusters

Albert Raymond Penner

The MONDian theory of AQUAL (AQUAdratic Lagrangian) and the theory of GRAS (GRavitational Anti-Screening) are alternatives to the theory of dark matter. When these theories are applied to galaxy dynamics they are in excellent agreement with observations including the galactic RAR (Radial Acceleration Relationship). However, when applied to galaxy clusters they do not explain the bulk of the missing mass. This manuscript develops a modified version of the GRAS/AQUAL field equation that can be extended to galaxy clusters. It involves just a single free parameter. The new field equation is then applied to a sample of galaxy clusters and checked against modeled galaxies and solar system constraints. Further to this, the modified field equation leads to an understanding of the difference between the galactic RAR and the RAR recently found for clusters.
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High Energy Astrophysical Phenomena

Transient Relativistic Iron Emission Line from an X-ray Flaring Supermassive Black Hole

Xiurui Zhao, Marco Ajello, Francesca Civano et al. (+16 more)

We report the discovery of the first transient relativistic iron K{\alpha} line in an Active Galactic Nucleus (AGN) J1047+5907. The line was detected 21.5 days (rest-frame) after an X-ray coronal flare observed in 2008 and it exhibits significant broadening consistent with relativistic reflection from the accretion disk in the vicinity of the central supermassive black hole (SMBH). The line has a width of ~300 eV, corresponding to a Keplerian velocity of 14,000 km s-1, at a distance of 5-41 light-days from the SMBH, strongly implying that the observed coronal flare triggered the emergence of the line. This event provides rare direct evidence of the response of the accretion disk to impulsive coronal illumination and offers a new method to probe the SMBH and disk physics. The relativistic modeling favors a broadened line produced by distant reflection from an accretion disk around a rapidly spinning black hole viewed at an intermediate inclination, consistent with other observations. Systematic monitoring of type 1 AGN following strong X-ray flares may open a new observational window into the innermost regions of AGN, enabling constraints on the physics of SMBH and its accretion disk at different radii that are otherwise challenging to access.
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All authors Xiurui Zhao, Marco Ajello, Francesca Civano, Javier A. Garc{\i}a, Elias Kammoun, Stefano Marchesi, Yue Shen, Daniel Stern, Qian Yang, Peter G. Boorman, Fiona Harrison, Erin Kara, Andrealuna Pizzetti, Ross Silver, Kirill V. Sokolovsky, Zachary Stone, Nuria Torres-Alba, Qiaoya Wu, Peixin Zhu

Cosmology and Nongalactic Astrophysics

Modeling Redshift Uncertainties in Roman Weak Lensing Cosmology

Diogo H. F. de Souza, Boyan Yin, Tim Eifler et al. (+7 more)

Cosmological constraints using weak gravitational lensing measurements from the Roman Space Telescope will require a powerful method for modelling uncertainties in the galaxy redshift distribution. In this work, we use an optimized version of the principal component analysis (PCA) to model uncertainties in the full shape of the redshift distributions, a method proposed by \cite{pca_method} and recently used in the Dark Energy Survey Y6 analysis. Here, we implement this new approach within the Roman High Latitude Imaging Survey (HLIS) Cosmology Project Infrastructure Team (PIT) pipeline, namely Cobaya-Cosmolike Joint Architecture (CoCoA). To validate the PCA in mitigating biases on cosmological parameters, $S_8$ and $\Omega_m$, we use a set of redshift distributions from Cardinal generated for a variety of Roman configurations. Overall, when the simulated cosmic shear data vector is not strongly miscalibrated relative to the fiducial one, both the mean-shift and the PCA-based approaches produce consistent cosmological constraints when marginalizing over nuisance parameters. For mild to strong miscalibration, including additional PCs progressively mitigates biases in $S_8$ and $\Omega_m$, and can achieve comparable performance with fewer parameters than the nine tomographic-bin mean-shift model.
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All authors Diogo H. F. de Souza, Boyan Yin, Tim Eifler, Vivian Miranda, Chun-Hao To, Brett H. Andrews, Katarina Markovič, Eric Huff, Michael A. Troxel, Olivier Doré

Solar and Stellar Astrophysics

Characterisation of starspot structure and differential rotation of Kepler-411

Mikko Tuomi, András Haris and Thomas Hackman

Starspots and their movements on stellar surfaces enable investigating the mechanisms of stellar magnetic activity. Information on the spot distribution and differential rotation provide important constraints for the behaviour of stellar magnetic dynamos. We analyse the Kepler photometry of Kepler-411, a known exoplanet host, to determine the distribution and properties of star spots on the stellar surface with two independent and complementary methods: modelling the photometric effect of rotation of spots on the stellar surface and mapping of spots by transiting planets. By constructing a spot model accounting for geometry, differential rotation and spot evolution, we model the spots of the stellar surface giving rise to the observed brightness variations. We also search for evidence for occultations of starspots in high-cadence photometry. Our spot models reproduce the observed photometric variations well and we are able to obtain information on the distribution and movement of spots on the stellar surface. We do not obtain evidence for differential rotation – the rotational profile is consistent with rigid-body rotation with a period of 10.52$\pm$0.34 days. We detect three occultations of spots by planet c. The positions of these spots coincide well with the positions of larger spot structures identified by our modelling of the rotational modulation of the light curve.
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Instrumentation and Methods for Astrophysics

astromorph: Self-supervised machine learning pipeline for astronomical morphology analysis

Per Bjerkeli, Jouni Kainulainen, Maria Carmen Toribio et al. (+2 more)

Modern telescopes generate increasingly large and diverse datasets, often consisting of complex and morphologically rich structures. To efficiently explore such data requires automated methods that can extract and organize physically meaningful information, ideally without the need for extensive manual interaction. We aim to provide a user-friendly implementation of a self-supervised machine learning framework to explore morphological properties of large datasets, based on the BYOL (Bootstrap Your Own Latents) method. By enabling the generation of meaningful image embeddings without manually labelled data, the framework will enable key tasks such as clustering, anomaly detection, and similarity based exploration. In contrast to existing BYOL implementations, astromorph accommodates data of varying dimensions and resolutions, including both single-channel FITS images and multi-channel spectral cubes. The package is built with usability in mind, offering streamlined pipeline scripts for ease of use as well as deeper customization options via PyTorch-based classes. To demonstrate the utility of astromorph, we apply it in two contrasting science cases representing different astronomical domains: images of protoplanetary disks observed with ALMA, and infrared dark clouds observed with Spitzer and Herschel. In both cases, we demonstrate how astromorph produces scientifically meaningful embeddings that capture morphological differences and similarities across large samples. astromorph enables users to apply a robust, label-free approach for uncovering morphological patterns in astronomical datasets. The successful application to two markedly different datasets suggest that the pipeline is broadly applicable across a wide range of imaging-rich astronomical context, providing a user friendly tool for advancing discovery in observational astronomy.
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All authors Per Bjerkeli, Jouni Kainulainen, Maria Carmen Toribio, Leon Boschman, Otoniel Maya Lucas

Astrophysics of Galaxies

A Gravitational Wave Background from Intermediate Mass Black Holes in AGN Disks

Chiara M. F. Mingarelli

Intermediate mass black holes (IMBHs) formed in active galactic nucleus (AGN) disks are expected to inspiral into their central supermassive black holes (SMBHs), generating a stochastic gravitational-wave (GW) background in the mHz–decihertz band. Using the population-agnostic energetic formalism, we treat the AGN-disk channel as a mass-flow pipeline connecting the stellar-mass black hole population observed by LIGO/Virgo/KAGRA (LVK) to the SMBH mass reservoir via IMBHs. By anchoring this estimate to the LVK merger rate densities and the cosmic SMBH mass density derived from scaling relations, we derive a limit on the background amplitude. We show that the total energy density of the background is bounded by the global mass budget of SMBH growth. For fiducial parameters consistent with the fourth Gravitational-Wave Transient Catalog (GWTC-4), this yields a characteristic strain $A_{\rm IMR} \simeq (1.2_{-0.2}^{+0.2})\times 10^{-21}$ at $3\,{\rm mHz}$. While this fiducial amplitude is subdominant to the Galactic white dwarf foreground and the stellar-mass Extreme Mass Ratio Inspiral (EMRI) background, we show it can be distinguished by its non-Gaussian statistics and higher frequency cutoff. This new background may be detectable in the decihertz band where proposed detectors such as the Big Bang Observer or long-baseline lunar interferometers can measure it cleanly. A detection would provide a direct, model-independent constraint on the efficiency with which AGN disks process stellar remnants into SMBH mass growth, linking the LVK and LISA bands.
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Solar and Stellar Astrophysics

Unipolarity of the solar magnetic field in equatorial coronal holes

Khagendra Katuwal and R.T. James McAteer

A study of the unbalanced magnetic polarity distribution of 70 coronal holes was performed. Data from the Helioseismic and Magnetic Imager (HMI) were used to examine the photospheric line-of-sight magnetic field ($B_{\mathrm{LOS}}$) beneath these coronal holes. The skewness ($S$) values of the $B_{\mathrm{LOS}}$ distributions revealed significant asymmetry, characterized by the dominance of one magnetic polarity, with $\sim88\%$ of the coronal holes exhibiting a skewness value ranging from $\pm(0.20~\text{to}~0.40)$. The corresponding magnetic flux imbalance ($\Phi_{\mathrm{imb}}$) ranges from $20\%$ to $45\%$. In contrast, quiet-Sun regions show symmetric magnetic field distributions with skewness values less than$~0.11$ and flux imbalance less than $11.0\%$. A study of a coronal hole as it traverses across the disk shows that the magnetic field distribution does not evolve significantly over this time, remaining stable across half a solar rotation. A moderate correlation ($r = 0.60$) between the magnetic flux imbalance and the speed of associated high speed solar wind streams ($v_{\mathrm{HSS}}$) suggests that flux imbalance may contribute to the generation of these faster solar wind streams. These results imply that regions with higher flux imbalance ($\Phi_{\mathrm{imb}}$), indicative of more open magnetic field structures, present more favorable conditions for plasma acceleration as compared to closed bi-polar field, but the moderate correlation indicates that other factors may also play important roles.
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Astrophysics of Galaxies

Probing Dust Composition in Distant Galaxies with JWST Mid-IR Spectroscopy of Quasars with Foreground 2175 A Absorbers I: Methodology

Viacheslav V. Klimenko, Varsha P. Kulkarni and Monique C. Aller

Interstellar dust plays a crucial role in gas cooling and molecule formation, influencing galaxy evolution. However, the composition and structure of dust in distant galaxies are still poorly understood. We have started a JWST MIRI MRS program investigating the dust features in gas-rich and dusty galaxies at redshifts $z<$1.2, with strong 2175~Å\ bumps detected in absorption along the lines of sight to distant background quasars. Here we describe our program strategy, and present MIRI MRS observations of IR dust features at $z=0.5-1.2$ in five quasar spectra that form the first part of our full sample. We identify artifacts in MIRI MRS data that affect the background in IFU cubes, and propose methods to reduce their effects. We pay special attention to modeling the quasar mid-IR continuum, which shows significant variation depending on AGN morphology, redshift, and black hole mass. Dust in foreground galaxies produces significant absorption from the 10~$\mu$m silicate feature in all five quasar spectra. Compared with the average 10~$\mu$m silicate feature in the diffuse ISM of the Milky Way, we find differences in the absorption peak position, width of the features, and asymmetry of the profiles. A detailed study of these silicate features is presented in our next paper (Klimenko et al. 2026b). In two quasar spectra, we tentatively detect weak IR features near 3.0 and 3.4~$\mu$m. Their strengths are comparable to those seen in the Milky Way ISM, but follow-up observations are required to confirm these detections.
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High Energy Astrophysical Phenomena

A Comparative Study of the Supernova Remnant Cassiopeia A from 2013–2020 Deep [Fe II]+[Si I] Images

Seung-Hoon Jung, Bon-Chul Koo, Yong-Hyun Lee et al. (+2 more)

We present a comparative analysis of supernova remnant Cassiopeia A based on two deep, narrow-band images covering the [Fe II] 1.644um + [Si I] 1.645um lines obtained in 2013 and 2020 with the same instruments on the UKIRT 3.8m telescope. The identical setup and observing procedure allow for direct, accurate measurements of morphological and kinematic changes over a seven-year baseline. We identified 263 compact knots in the 2020 image and, through comparison with the 2013 catalog of Koo et al. 2018 (arXiv:1809.07935), classified them into quasi-stationary circumstellar knots and fast-moving knots (FMKs) of supernova ejecta. The FMKs show significant flux fluctuations, and many of those detected in 2013 are absent in the 2020 image. Proper-motion measurements derived from cross-correlation analysis indicate that most FMKs follow nearly ballistic expansion, whereas some, particularly those just beyond the eastern Fe-rich, X-ray emitting ejecta region, exhibit noticeable deceleration. The proper motions of the main ejecta shell were also measured and modeled as a uniformly expanding shell with a systemic motion, which reproduces the observed geometric and kinematic asymmetries of the remnant.
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All authors Seung-Hoon Jung, Bon-Chul Koo, Yong-Hyun Lee, Hyun-Jeong Kim, Jae-Joon Lee