Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Dark matters are Inert, or FIMPy, or WIMPy or UFOy: An inflationary gravitational particle production
Ayan Chakraborty, Debaprasad Maity and Rajesh Mondal
In this letter, we explore the phenomenological impact of inflationary gravitational particle production in the physics of Dark Matter (DM). Large-scale DM fluctuations generated during inflation behave as gravitational particles upon their post-inflationary horizon reentry and alter the conventional Boltzmann dynamics of DM with a non-conserving source term, thereby producing significant phenomenological consequences. Within this framework, we analyze four distinct types of DM classified according to their production mechanisms. Dark matter may be completely non-interacting with the thermal bath, behaving as Inert Dark Matter. Alternatively, depending on the strength of its interactions with bath particles, DM may exhibit WIMPy, UFOy, or FIMPy behavior, sharing characteristics with their conventional counterparts. The late-time enhancement of the DM number density, driven by the successive horizon reentry of gravitationally produced low-momentum modes, enlarges the viable parameter space for both thermal and non-thermal DM scenarios. Remarkably, this expanded parameter space remains consistent with current constraints from $\Delta N_{\rm eff}$ and Lyman-$\alpha$ bound.
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Instrumentation and Methods for Astrophysics
New Robotic Telescope: The big eye to observe the transient Universe
C. M. Gutiérrez, J. Barrera, J. Bento et al. (+20 more)
NRT is an international project to build and operate the world's largest robotic
telescope. The
telescope will have a segmented primary mirror with an equivalent diameter of 4 m, a set of simultaneously mounted optical and near-infrared instruments, and a response time of less than 30 seconds. The project builds on the experience gained with the successful twenty-year operation of the Liverpool
telescope, and with the GTC optics and control system. All of the above together with the excellent conditions for astronomical observation of La Palma, represents a solid base and guarantees that NRT will be one of the leading facilities in the field of time domain astronomy. This contribution will analyze the current status of the project with special emphasis on the development of its optics, and the plans for its construction and operation.
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All authors C. M. Gutiérrez, J. Barrera, J. Bento, D. Copley, C. M. Copperwheat, F. J. De Cos, M. Escriche, J. J. Fernández-Valdivia, A. P. Garner, J. Gracia, D. G. Heffernan-Clarke, H. E. Jermak, J. León Gil, A. M. McGrath, C. Miossec, A. Oria, A. Ranjbar, R. Rebolo, C. Rodríguez-Pereira, F. Sánchez-Lasheras, R. J. Smith, I. A. Steele, M. Torres
Solar and Stellar Astrophysics
The Making of Delta Sunspots
Ronald L. Moore, Sanjiv K. Tiwari, V. Aparna et al. (+2 more)
We explore what fraction of delta sunspots in which the polarity inversion line (PIL) is sharp in photospheric magnetograms are made from a writhe kink in an emerging twisted flux rope. We searched simultaneous full-disk magnetograms and continuum images from Helioseismic and
Magnetic Imager (HMI) on
Solar Dynamics Observatory (SDO) to find 28 random sharp-PIL delta sunspots that are born well on the disk. Only one of these is made from a single newly emerged bipolar
magnetic region (BMR) and therefore is a candidate for being made from a single emerging writhe-kinked flux rope. That outcome indicates that few, if any, sharp-PIL delta sunspots are made by a single emerging writhe-kinked flux rope. That is the main new finding of this paper. Each of the other 27 is made by merging of two or more emerging or emerged BMRs. We name delta-sunspot genesis from a single BMR Type I genesis. We identify another three genesis types among the other 27 delta sunspots: Type II, Type III, and Type IV. We present an observed example genesis for each of the four genesis types, and for each example present schematic drawings depicting our scenario(s) for the cause of that example genesis. The core idea of each scenario is that the delta sunspot is made by packing opposite-polarity
magnetic flux together by advection into a convection downflow.
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All authors Ronald L. Moore, Sanjiv K. Tiwari, V. Aparna, Navdeep K. Panesar, Alphonse C. Sterling
Astrophysics of Galaxies
A new wideband radio polarization observation of the Supernova Remnant G315.4$-$2.3
X. Chen, X. Sun, J. F. Kaczmarek et al. (+3 more)
The
supernova remnant (SNR) G315.4$-$2.3 (MSH 14$-$63 or RCW 86) exhibits strong emission across the electromagnetic spectrum.
Radio polarization observations probe
magnetic fields and will help to understand the
evolution of the SNR. We aim to investigate the
radio spectrum and
magnetic field properties of the SNR. We observed G315.4$-$2.3 using the Australia
Telescope Compact Array (ATCA), covering the frequency range of 1.1-3.1 GHz. We performed rotation measure (RM) synthesis on the $Q$ and $U$ frequency cubes to obtain polarized intensity and RM. The regular component of the line-of-sight
magnetic field was estimated from RM. The fractional polarization versus wavelength squared was used to constrain the properties of the turbulent
magnetic field. We obtained image cubes of Stokes $I$, $Q$, and $U$, along with images of polarized intensity $P$, RM, and fractional polarization $p$. The
radio spectra are very similar for different areas of the SNR. The foreground RM was estimated to be 55 rad m$^{-2}$, and the internal RM of most SNR areas is less than about 50 rad m$^{-2}$. The regular
magnetic field along the line of sight was estimated to be about 1.4 $\mu$G in the southwest, much smaller than the total
magnetic field. For most parts of the southwest and northeast, $p$ is less than 8% and is nearly constant with $\lambda^2$. We estimated the ratio of turbulent to regular
magnetic field to be larger than about 3. The scale of the turbulent
magnetic field for some area in the northwest might be smaller than about 0.4 pc. The
radio characteristics, including spectrum and turbulent
magnetic field, are very similar in the northeast and southwest, even though the
evolution is quite different for these two regions based on the current models. These should be taken into account for future modeling of the
evolution of the SNR.
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All authors X. Chen, X. Sun, J. F. Kaczmarek, B. M. Gaensler, P. Slane, J. L. West
Instrumentation and Methods for Astrophysics
The 4 meter New Robotic Telescope project: an updated report
C. M. Gutiérrez, M. Torres, A. Oria et al. (+23 more)
The New Robotic
Telescope (NRT) is an international collaboration to build and operate a 4 m diameter fully robotic
telescope. The
telescope will take advantage of the superb atmospheric conditions at the Observatory of the Roque de los Muchachos (ORM). In conjunction with a large aperture, entirely robotic operation, quick response, and a set of versatile instrumentation in the optical and near-infrared this guarantees a high scientific impact focused mainly in the area of time domain astronomy. This paper presents the scientific motivation and the status of the project, discussing possible technical solutions under evaluation for the optics, mechanics and control system.
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All authors C. M. Gutiérrez, M. Torres, A. Oria, J. J. Fernández-Valdivia, D. Arnold, D. Copley, C. Copperwheat, J. de Cos Juez, A. Franco, Y. Fan, A. García Piñero, E. Harvey, H. Jermak, X. Jiang, J. H. Knapen, A. McGrath, A. Ranjbar, R. Rebolo, R. Smith, I. A. Steele, Z. Wang, X. Wu, D. Xu, S. Xue, W. Yuan, Y. Zheng
Earth and Planetary Astrophysics
Saturn's rings age I.: Reconsideration of the exposure age
Gregorio Ricerchi and Aurélien Crida
At the end of the Cassini mission, Saturn's rings have been claimed to be spectacularly young compared to the age of the
Solar System: their unusual ice-rich composition corresponds to initially pure ice rings polluted by interplanetary
dust particles for 100 to 400 Myr. Since then, this exposure age has been commonly accepted as the real age of the rings. In this paper, we review the processes that are involved in determining the exposure age. We aim to see how the exposure age depends on various parameters and how relevant it is to define the real rings age. First, a new expression for the gravitational focusing onto planar rings, important parameter but crudely defined in the literature, is derived. Then, an analytical formula describing how the
dust fraction varies with time in static or viscously evolving rings is provided, including possible vaporisation at impact. Finally, we introduce a cleaning process from space weathering to possibly alter
dust and reduce its amount to make rings look younger than they are. We first found that the gravitational focusing is 5 times less important than previously thought, which automatically increases the exposure age from 0.5 to 2 Gyr. Moreover, depending on the impact properties (vaporisation rate, space weathering efficiency), several billion years can easily be reached. Finally, we find that the
dust fraction in the rings converges towards a finite value which, in particular with an efficient space weathering mechanism, can be close to the observed one in the current rings. In this case, neither the age nor the initial composition of the rings can be derived, and the measure of the
dust fraction and bombardment rate only constrains the physical parameters of the impacts and the efficiency of the space weathering. As long as the latter parameters are not known, the exposure age argument in favour of young rings is completely undercut.
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Instrumentation and Methods for Astrophysics
Modified-gradient methods for exact divergence-free in meshless magnetohydrodynamics
Xiongbiao Tu, Qiao Wang, Liang Gao et al. (+1 more)
We present a novel gradient regularization to completely eliminate the
magnetic divergence error in meshless magnetohydrodynamics (MHD), which offers a high spatial resolution and conservative advantage, due to its Lagrangian nature. Comparing with the counterpart of constrained-gradient (CG) technique, we reform $\nabla \cdot \mathbf{B}=0$ by an implicit projection method to modify the
magnetic-field gradients. The accuracy of modified-gradient (MG) method is verified and it achieves exact divergence-free results with round-off precision, by using tests of shock tube, 2D and 3D
vortex, magneto-rotational instability, and especially, advection experiment, compared with CG method and the GIZMO code. It leads to noticeable improvement in pattern, amplitude and numerical dissipation of divergence error of
magnetic field.
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All authors Xiongbiao Tu, Qiao Wang, Liang Gao, Yifa Tang
Astrophysics of Galaxies
Properties of Galaxies with Counter-rotating Stellar Disks in the MaNGA Survey
Min Bao, Zhenyu Tang, Yanmei Chen et al. (+2 more)
Gas
accretion process can fuel both
star formation and black hole activity, playing a critical role in
galaxy evolution. The counter-rotating structures are believed to originate from gas
accretion, serving as an ideal laboratory for studying its impact on
galaxy evolution. Based on the Mapping Nearby
Galaxies at Apache Point Observatory (MaNGA) survey, we built a sample of 147
galaxies with counter-rotating
stellar disks (CRDs). This is the largest CRD sample to date, accounting for $\sim$1.5% of the MaNGA survey. For a subset of 138 CRDs, global
stellar mass ($M_\ast$) and
star formation rate (SFR) were measured in reference. We constructed a control sample with similar $M_\ast$ and SFR but lacking counter-rotating structures. The CRDs relatively exhibit more bulge-dominated morphology, lower molecular gas mass fraction and reside in less dense environment, supporting the hypothesis that they primarily originate from gas
accretion. We classified 96 out of 138 CRDs into four types based on their
stellar and gas kinematics following the criteria from Bao et al. (2022). There are two additional CRD types: 8 CRDs show misalignment between both
stellar disks and gas disk, indicating multiple gas
accretion events with differing angular momentum directions; 34 CRDs lack ionized gas emission, showing the highest $M_\ast$ among all the CRD types, which may represent a final stage of CRD
evolution. We compared the radial gradients of gas-phase
metallicity and
stellar population properties between CRD types, and found that the impact of gas
accretion on
galaxy evolution primarily depends on the abundance of pre-existing gas in progenitors.
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All authors Min Bao, Zhenyu Tang, Yanmei Chen, Yong Shi, Qiusheng Gu
Astrophysics of Galaxies
OPTIMus-Survey of massive star-forming regions at OPTical, Infrared, and Millimeter wavelengths
M. S. Kirsanova, A. V. Moiseev, A. M. Tatarnikov et al. (+3 more)
This work presents a description of the scientific goals and objectives of OPTIMus (OPTical, Infrared, Millimeter survey of massive
star-forming regions), a survey of massive
star-forming regions in the optical, infrared, and millimeter wavelengths. The survey is aimed at constructing a comprehensive characterization of the multicomponent and structurally complex interstellar medium in the vicinity of young massive
stars, combining both observational and theoretical aspects. Using multi-wavelength observational data, we will reconstruct the three-dimensional structure and determine the physical parameters of HII regions, photodissociation regions, and the surrounding molecular clouds. The paper describes the observational data obtained with the BTA 6-m and Zeiss-1000
telescopes of the Special Astrophysical Observatory of the Russian Academy of Sciences, the 2.5-m
telescope of the Caucasian Mountain Observatory of the Sternberg Astronomical Institute of Moscow State University, and the 20-m
telescope of the Onsala Space Observatory.
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All authors M. S. Kirsanova, A. V. Moiseev, A. M. Tatarnikov, A. S. Gusev, A. D. Yarovova, D. S. Wiebe
Astrophysics of Galaxies
Morphologies for DECaLS Galaxies through a combination of non-parametric indices and machine learning methods: A comprehensive catalog using the Galaxy Morphology Extractor (galmex) code
V. M. Sampaio, Y. Jaffé, C. Lima-Dias et al. (+5 more)
Galaxy morphology encodes key information about formation and
evolution. Large imaging surveys require automated, reproducible methods beyond visual inspection. Non–parametric indices provide an useful framework, but their performance must be quantitatively assessed. We present a homogeneous catalog of non–parametric morphological indices for DECaLS
galaxies with effective radii larger than 2 arcsec. Our goal is to evaluate the reliability of indices in separating spirals and ellipticals, test their consistency with existing classification schemes, and establish their applicability for the upcoming surveys focused in the southern hemisphere. We developed galmex, a modular Python package for preprocessing images and measuring a variety of non–parametric indices. Using bona-fide spirals and ellipticals as control samples, we assessed the discriminatory power of each index, and compared them with CNN-based T-Types and
Galaxy Zoo DECaLS labels. We use the indices as input for a Light Gradient Boosted Machine (LightGBM) to obtain probabilistic classifications. Concentration is the most reliable parameter from the Concentratiom + Asymmetry + Smoothness system (CAS), while asymmetry–based indices (A and S) are limited to detecting disturbed morphologies. MEGG indices (M20,
Entropy, Gini, G2) provide stronger separation and trace a gradient with T–Type. By using a simple binary (0/1) label for ellipticals/spirals, classifiers trained on non–parametric indices achieve high accuracy and well–calibrated probabilities, dominated by
entropy, concentration, and Gini. We release the first public catalog of CA[A_S]S+MEGG indices for DECaLS, together with galmex. We combine the non-parametric indices with machine learning framework to derive spiral/elliptical separation for
galaxies below z~0.15 through a probabilistic approach.
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All authors V. M. Sampaio, Y. Jaffé, C. Lima-Dias, S. Véliz Astudillo, M. Martínez-Marín, H. Méndez-Hernández, R. Herrera-Camus, A. Monachesi
Cosmology and Nongalactic Astrophysics
Weak Lensing by Photometric Density Ridges
Mehraveh Nikjoo, Joe Zuntz and Ben Moews
Ridges in
galaxy density fields measured by photometric surveys are 2D projections of filaments in the
cosmic web, and so should lens light from background
galaxies. We report on a detection of this effect in Dark Energy Survey Year 3 data at high significance, though not independently of
galaxy-
galaxy lensing. We describe improvements to the existing subspace-constrained mean shift
algorithm to locate these ridges efficiently at scale, and examine the dependence of the signal in simulations on cosmological and algorithmic parameters. We find that it depends primarily on $S_8=\sigma_8 \left( \Omega_m / 0.3 \right)^{1/2}$, and discuss improvements to our methodology that would be needed to allow precision parameter estimation.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Observational Constraints on the Structure-Induced Dark Energy Model
A. Kaz{\i}m Çaml{\i}bel
A new phenomenological dark energy model, originally associated to the large-scale structure formation and considered as a solution to the fine-tuning and coincidence problems related to the cosmological constant, was analyzed within the framework of General Relativity in a Friedman-Robertson-Walker spacetime and its model parameters were estimated using
cosmic chronometers and recent DESI data. It turns out that the proposed model can serve as an alternative evolving dark energy model with a novel equation of state function, apart from other popular propositions in the literature. Due to the form of this phenomenological energy density ansatz, which starts to rise with the nonlinear structure growth in the universe and falls with the domination of
cosmic voids, we prefer to call it structure-induced dark energy. Observational constraints show that it is not only a suitable solution for the fundamental problems such as coincidence or fine-tuning problems, it gives flexibility, when considering the
cosmic tensions and presents a new perspective on the evolving dark energy models.
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High Energy Astrophysical Phenomena
Global Structure of Accretion Flows in Sgr A*
Shenyue Yin and Siming Liu
Sagittarius A* (Sgr A*) is a compact
radio source at the
Galactic center. Observations have confirmed that its mass is approximately (4.1)*10$^{6}$ M$_{\odot}$, and Sgr A* is generally believed to be powered by gas
accretion onto a supermassive black hole. Multifrequency
radio observations of the
pulsar J1745-2900, about 0.12 pc away from Sgr A*, reveal an unusually large Faraday rotation. Combined with X-ray observations, this indicates that there is a strong
magnetic field (greater than 8 mG) leading to a low $\beta$
plasma at large scales.We show that the gas starts to be captured by the black hole below tens of thousands of the Schwarzschild radii $r_S$, where the gas pressure starts to dominate. Assuming that the
accretion rate along
magnetic fields at large scales decreases with the distance to the black hole following a power law, it is shown that, with an
accretion disk below tens of $r_S$, as revealed with the EHT observations, there should be a supersonic wind above such a small
accretion disk, and the
accretion flow may be convection-dominated from tens of $r_S$ to tens of thousands of $r_S$. Detailed modeling is warranted.
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High Energy Astrophysical Phenomena
A Possible Short-Timescale Optical Quasi-Periodic Oscillation in PKS\,0805$-$07 from High-Cadence TESS Observations
Sikandar Akbar, Zahir Shah, Athar A. Dar et al. (+1 more)
We present a timing analysis of the high-cadence optical light curve of the high-
redshift flat-spectrum
radio quasar PKS\,0805$-$07 obtained during TESS Sector~34 (MJD~=~59230.90–59239.90). We search for short-timescale quasi-periodic oscillations (QPOs) using complementary time-series techniques, including the Lomb–Scargle periodogram (LSP) and the weighted wavelet $Z$-transform (WWZ), and evaluate their significance against red-noise variability using Monte Carlo simulations. The LSP reveals a dominant modulation at $f \approx 0.6\,\mathrm{d^{-1}}$ ($P \approx 1.7$\,d) exceeding the $99.99\%$ confidence level, while the WWZ independently recovers a consistent timescale at the $\sim$99.9% level and shows that the signal is temporally localized rather than persistent. The modulation spans $\sim$5 coherent cycles, indicating a transient feature. However, the significance only marginally exceeds the highest WWZ confidence threshold, and the limited number of cycles is insufficient for a firm confirmation. In a disk-based scenario, orbital motion of a hotspot near the innermost stable circular orbit implies a black hole mass of $M_{\rm BH} \sim 7.2 \times 10^{8}\,M_\odot$, consistent with typical FSRQ values. Alternatively, magnetohydrodynamic kink instabilities in the relativistic jet can naturally produce day-scale variability for standard blazar parameters and account for its transient character. Compact SMBH binary and
tidal disruption event scenarios are disfavoured by the jet-dominated nature of the source, the optical rather than X-ray character of the modulation, and a black hole mass well above that of confirmed QPE hosts. The candidate modulation is consistent with a compact, short-lived structure embedded within
stochastic jet variability, and high-cadence multiwavelength monitoring will be essential to confirm its recurrence and constrain its physical origin.
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All authors Sikandar Akbar, Zahir Shah, Athar A. Dar, Naseer Iqbal
Astrophysics of Galaxies
The influence of galaxy mergers, black-hole growth, and gas processes on the evolution of the stellar mass-gas metallicity relation of galaxies in different cosmic environments
Aaron R. Rowntree, Fiorenzo Vincenzo, Ankit Singh et al. (+3 more)
We study the impact of supermassive black hole (SMBH) growth, $\langle \dot{M}_\mathrm{SMBH}\rangle$, major and minor
galaxy mergers, and gas processes, on the average gas
metallicity of
galaxies within the Horizon Run 5 simulation, with the aim to uncover which of these processes drive the scatter in the gas
metallicity-
stellar mass relation (MZR) at different
redshifts in nodes, filaments and voids. At $z=5$, minor mergers produce the largest differential in $\log[Z_g/Z_\odot]$ where all environments display a maximum $0.22$ dex increase in the average $\log[Z_g/Z_\odot]$ compared to non-merging
galaxies. The node population also displays a consistent $0.1$ dex negative offset in $\mathrm{d} \log[Z_g/Z_{\odot}]$, the residual $Z_g$ from the total MZR of all
galaxies, across all
redshifts, whilst filament and void
galaxies show a smaller offset. Major mergers show little influence on these same properties. This suggests minor mergers regulate
metallicity and contribute to
galaxy mass growth concurrently, accelerating chemical
evolution post merger. Between $z=1-3$, a high $\langle \dot{M}_\mathrm{SMBH}\rangle$ leads to a larger negative offset in $\mathrm{d} \log[Z_g/Z_{\odot}]$ for all environments. Here, node
galaxies show the largest negative offset of approximately $0.25$ dex, suggesting that AGN-driven gas removal may contribute to the MZR scatter at intermediate times. Finally,
galaxies with low $M_{gas}/{M_{tot}}$ show increased $\mathrm{d} \log[Z_g/Z_{\odot}]$ across all
redshifts and environments, again a $0.25$ dex maximum for node
galaxies. These
galaxies also spike in $\mathrm{d} \log[Z_g/Z_{\odot}]$ at late times, below $z=1$. At this time,
galaxies in the nodes show negative $\langle \dot{M}_\mathrm{gas} \rangle$ whilst also showing the largest $\mathrm{d} \log[Z_g/Z_{\odot}]$ values we observe of $0.2$ dex.
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All authors Aaron R. Rowntree, Fiorenzo Vincenzo, Ankit Singh, Gareth Few, Jaehyun Lee, Christophe Pichon
Astrophysics of Galaxies · Cross-listed from physics.flu-dyn
A Robust Compressible APIC/FLIP Particle Grid Method with Conservative Resampling and Adaptive APIC/PIC Blending
Jiansheng Yao and Yingkui Zhao
Modeling inviscid compressible flows with shocks and
vortex dominated dynamics remains challenging for particle grid methods due to moving discontinuities,
cell crossing noise, and quadrature degradation under strong deformation. Building on a FLIP/APIC framework with vorticity aware tensor artificial viscosity, we identify a long time RTI failure mode: particle depletion at spike heads degrades quadrature and particle grid coupling, producing nonphysical, void-like dents. Standard mitigations (CPDI lite and subcell-jittered seeding) reduce but do not eliminate this artifact. We therefore add two sampling-aware controls: (i) conservative split resampling that replenishes depleted
cells while exactly conserving mass, momentum, and internal energy; and (ii) a soft-switch that attenuates only the APIC affine term when local support is insufficient. Tests on the Sod shock tube and single/multi mode RTI show that the method removes spike head voids in long-time RTI while preserving
vortex roll up, and matches reference Euler growth metrics
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Astrophysics of Galaxies
The Stellar Mass Function for Nine Massive Galaxy Clusters in the Local Universe
Jong-In Park, Jubee Sohn, Margaret J. Geller et al. (+2 more)
We measure
galaxy stellar mass functions (SMFs) for nine of the most massive
galaxy clusters in the local universe ($0.07 < z < 0.11$) using deep and complete spectroscopy from the MAssive Cluster Survey with Hectospec (MACH). We construct the cluster SMFs down to $\log(M_*/M_\odot) \gtrsim 8.5$. For comparison, we measure the SMF for field
galaxies, complete to $\log(M_*/M_\odot) \gtrsim 10.5$, based on Sloan Digital Sky Survey (SDSS) spectroscopy over the same
redshift range. The mean MACH SMF shows a shape similar to that of the field SMF but with a significantly higher amplitude at $\log(M_*/M_\odot) < 11.4$. At $\log(M_*/M_\odot) > 11.4$, the MACH SMF shows a clear excess, indicating the contribution of massive
galaxies, including Brightest Cluster
Galaxies (BCGs). Based on homogeneous MACH spectroscopy, we compare SMF shapes for quiescent and
star-forming members as a function of cluster-centric distance. The quiescent SMFs display a curved shape with a peak at $\log(M_*/M_\odot) \approx 10.5$; the
star-forming SMFs decline monotonically with increasing
stellar mass. We further compare the mean MACH SMF with SMFs derived from similarly massive clusters in the IllustrisTNG-300 simulations. The shape of the observed and simulated SMFs agree well overall. However, the MACH clusters contain roughly a factor of two more
galaxies at $9.0 < \log(M_*/M_\odot) < 10.5$. These results demonstrate that constructing cluster SMFs from complete spectroscopic samples can test simulations and provide powerful constraints on
galaxy formation and
evolution in dense environments.
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All authors Jong-In Park, Jubee Sohn, Margaret J. Geller, Ken J. Rines, Antonaldo Diaferio
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
CFT Perspective On de-Sitter Cosmological Correlators
Sayantan Choudhury
We investigate the principles of
quantum field theory using a stiff de Sitter space. We demonstrate that a non-
unitary Lagrangian on a Euclidean AdS geometry can produce the perturbative expansion of late-time correlation functions to all orders. This discovery greatly simplifies perturbative computations while also allowing us to prove fundamental features of these correlators, which are part of a Euclidean CFT. This allows us to construct an OPE expansion, limit the operator spectrum, and deduce the analytic structure of the spectral density that captures the conformal partial wave expansion of a late-time four-point function. In general, the standard CFT concept of unitarity does not apply to dimensions and OPE coefficients. Rather, the positivity of the spectral density represents the unitarity of the de Sitter theory. This assertion is non-perturbative and does not depend on the use of Euclidean AdS Lagrangians. In a scalar theory, we compute tree-level and entire one-loop-resummed exchange diagrams to demonstrate and verify these characteristics. In the spectrum density, an exchanged particle shows up as a resonant characteristic that may be helpful in experimental searches.
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Earth and Planetary Astrophysics
The Effect of Planetary Rotation Period on Clouds in a Global Climate Model with a Bin Microphysics Scheme
Huanzhou Yang, Eric T. Wolf, Cheng-Cheng Liu et al. (+3 more)
Clouds are the largest source of uncertainty in
climate simulations. For
exoplanets, cloud simulation is particularly challenging because of the lack of observational data to tune parameterized cloud models. Here we apply Community Aerosol and Radiation Model for Atmospheres (CARMA), a size-resolved bin cloud microphysics model, to the atmospheric global
climate model Community Atmosphere Model (CAM6) and simulate
exoplanets with a range of planetary rotation rates. CARMA produces fewer
liquid clouds than the native CAM6 parameterized cloud microphysics scheme (Morrison-Gettelman two-moment microphysics, MG), more ice clouds, and a significantly different ice cloud size distribution. Overall, this leads to a decrease in the magnitude of the net CRE by 4-10 $W/m^2$, which is unlikely to change the determination of habitability from a
climate perspective in most cases. The difference in ice cloud size distribution is likely to strongly affect transmission spectral
retrievals. Our work confirms that the MG parameterized cloud microphysics scheme can produce reasonable
climate simulation when extrapolated to some
exoplanet contexts and highlights the value of resolved cloud microphysics for evaluating parameterized schemes and for interpreting observations.
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All authors Huanzhou Yang, Eric T. Wolf, Cheng-Cheng Liu, Yunqian Zhu, Owen B. Toon, Dorian S. Abbot
High Energy Astrophysical Phenomena
Evolution of Time-Lags of Swift J1727.8-1613 during the Rising Phase of Its Discovery Outburst
Sujoy Kumar Nath, Dipak Debnath and Hsiang-Kuang Chang
We investigate the
accretion dynamics of the black hole X-ray binary Swift J1727.8-1613 during its $2023-2024$ discovery outburst that lasted for $\sim10$ months. Insight-HXMT monitored the rising phase of the outburst of Swift J1727.8-1613 roughly continuously from 2023 Aug 25 to 2023 Oct 05. Strong signatures of type-C Quasi-Periodic Oscillations (QPOs) are observed during this phase of the outburst. In our recent paper, nature of the QPOs are studied with the propagating oscillatory shock (POS) model. In this paper, we report on the observation of both positive (or hard) and negative (or soft) time-lags in the $4-10$ keV (LE), $10-30$ keV (ME), and $30 -150$ keV (HE) bands, computed with respect to the $2-4$ keV reference band. We detect a clear transition from hard to soft lags as the outburst evolves. We show the
evolution of QPOs and associated time-lags between different X-ray energy bands, correlated with changes in the QPO frequency, spectral state, and the size of the Comptonizing region. Our analysis reveals strong anti-correlations between the time-lags and both QPO frequency and
photon index, and a strong positive correlation with the shock location. These evolving lag characteristics and their correlations provide crucial insights into the changing
accretion geometry and the interplay of radiative processes, further supporting dynamic models like the POS in explaining the coupled spectro-temporal
evolution in black hole X-ray binaries.
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Solar and Stellar Astrophysics
Autoencoder-based framework for anomaly detection in stellar spectra: application to the MaNGA Stellar Library
Akihiro Suzuki
A machine-learning-based method is developed to identify objects with unusual
stellar spectra. The method employs an autoencoder, a neural network trained to compress spectral data into a low-dimensional representation and subsequently reconstruct it. Spectra that deviate significantly from the dominant patterns in the training
dataset are identified using the reconstruction error as an anomaly score. The models are applied to selected
datasets from the MaNGA
Stellar Library, an empirical library of
stellar spectra. Several spectra are flagged as anomalous: an object with likely instrumental and/or reduction issues, two carbon
stars, and an oxygen-rich thermally pulsating asymptotic
giant branch
star. The sources of the large reconstruction errors are examined, and the effectiveness and limitations of autoencoder-based approaches for detecting anomalous
stellar spectra are discussed.
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Solar and Stellar Astrophysics
A Generalist Model Including Evolved Star Mass and Age
Mengmeng Zhang, Yude Bu, Siqi Wang et al. (+10 more)
Determining precise
stellar ages and masses for evolved
giants is crucial for
Galactic archaeology but challenged by spectral degeneracies.
Gaia's low-resolution XP spectra offer a unique opportunity to infer these parameters on a massive scale using data-driven methods. We extend a
transformer-based astronomical foundation model to evolved
stars, establishing a unified framework to simultaneously predict atmospheric parameters ($T_{\mathrm{eff}}$, $\log g$, $[\mathrm{M}/\mathrm{H}]$) and evolutionary labels (mass, age) with physical consistency. Treating spectra as
token sequences, we integrated mass and age into the model's vocabulary. The model is trained on
Gaia XP spectra cross-matched with the APOGEE DR17 DistMass catalog. Our generative approach enables flexible input handling, including spectral inpainting and parameter-to-spectrum generation. On an independent test set, the model achieves a prediction scatter of $\sigma \approx 0.114 \, M_{\odot}$ for mass and $\sigma \approx 1.334$ Gyr for age. Beyond numerical accuracy, it successfully reproduces the
giant branch's mass-luminosity relation and autonomously disentangles interstellar extinction from intrinsic temperature variations without explicit physical priors. It also robustly recovers missing spectral data and estimates reliable uncertainties. Validating that foundation models can internalize
stellar physics from data, this physically-aware, probabilistic framework offers a powerful tool for unraveling Milky Way history using large-scale spectroscopic surveys.
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All authors Mengmeng Zhang, Yude Bu, Siqi Wang, Shanshan Li, Jiangchuan Zhang, Jingzhen Sun, Yuhang Zhang, Ke Wang, Jian Liu, Hongliang Yan, Zhenping Yi, Meng Liu, Xiaoming Kong
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Scalar quasinormal modes of rotating black holes in parity-violating gravity
Hiroaki W. H. Tahara, Hayato Motohashi, Kazufumi Takahashi et al. (+1 more)
Recently, an exact rotating black hole solution in a parity-violating theory of
gravity was obtained via a conformal transformation of the Kerr solution in general relativity, with parity-violating effects encoded in the conformal factor. We study the quasinormal modes (QNMs) of a test scalar field minimally coupled to
gravity on this conformal Kerr background, treating the parity-violating effects perturbatively while allowing for arbitrary black hole
spin, from the non-rotating case to the near-extremal regime. For low
spin, we derive a perturbative formula for the QNM frequencies that includes the leading-order parity-violating correction. For high
spin, particularly in the near-extremal regime, we find sizable deviations from the Kerr QNM frequencies. Our results point to a new avenue for probing parity-violating physics in the strong-
gravity regime through black hole QNMs.
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All authors Hiroaki W. H. Tahara, Hayato Motohashi, Kazufumi Takahashi, Vicharit Yingcharoenrat
Solar and Stellar Astrophysics
Stellar Chromospheric Activity Database of Solar-like Stars Based on the LAMOST Low-Resolution Spectroscopic Survey III. Calibrating the Chromospheric Basal Flux and the Connection to Stellar Rotation
Weitao Zhang, Han He and Jun Zhang
Based on the Ca\,II H and K lines observed by LAMOST, we employ the photospheric ($R'_{\rm HK}$) and basal ($R^+_{\rm HK,L}$) flux calibrated chromospheric activity indices to examine the relationship between chromospheric activity and the
stellar rotation rate. We identify the rotation periods of 11,108
stars observed by Kepler and TESS by cross-matching our chromospheric activity catalog with previous studies. Our statistical results show that chromospheric activity increases with the rotation rate until it reaches a saturation level. As the
stellar effective temperature increases from 4950 to 5850 K, the saturation values of the rotation period ($P_{\rm rot}$) vary correspondingly from 4.38 to 1.23 days for $R'_{\rm HK}$ and from 9.88 to 1.33 days for $R^+_{\rm HK,L}$. Similarly, the corresponding saturation Rossby number Ro ranges from 0.200 to 0.032 for $R'_{\rm HK}$ and from 0.302 to 0.107 for $R^+_{\rm HK,L}$. The saturation is also found to be significant in
stars with thick convective zones, whereas it is less apparent in
stars with higher effective temperatures. For
solar-like
stars in the $T_{\rm eff}$ range of 4800 to 6000 K, The values of chromospheric activity indicators are saturated when $P_{\rm rot}<1.45 $ days (Ro$<$0.100) and $P_{\rm rot}<2.85 $ days (Ro$<$0.097) for $R'_{\rm HK}$ and $R^+_{\rm HK,L}$, respectively.
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High Energy Astrophysical Phenomena
High-energy neutrino emission from the Type~IIn supernova SN~2017hcd
Shunhao Ji, Zhongxiang Wang, Litao Zhu et al. (+1 more)
Neutrino astronomy provides another window to exploring the Universe, exemplified by the detection of a megaelectronvolt
neutrino burst from the core-collapse
supernova (CCSN) SN~1987A (refs.~\citenum{hir+87,bio+87}). Commonly discussed theories suggest that some CCSNe could produce
neutrinos with energies a thousand times more than those of SN~1987A \cite{tm18}, which has been probed with new-generation facilities \cite{abb+12,aar+15,abb+23}. The interaction of SN ejecta with a dense circumstellar medium (CSM) or a jet, launched in a CCSN, being choked in the
stellar envelope of the progenitor or an outside CSM are both well-accepted scenarios for the high-energy
neutrino production. Here we report the detection of a high-energy
neutrino flare at a 3.9$\sigma$ significance from SN~2017hcd, made by our analysis of the public track-like
neutrino data taken by the IceCube
Neutrino Observatory \cite{IceCube17}. A Type IIn SN with optical emissions arising from the ejecta–CSM interaction, SN~2017hcd's
neutrino flare lasted $\sim$1–2 month, with its central time $\sim$14-day prior to the SN's optical discovery time. Its estimated isotropic
neutrino energy (all
flavors) is approximately two orders of magnitude higher than the energy ($\sim 10^{50}$\,erg) carried in the SN's ejecta, too high to be explained with the ejecta–CSM scenario. Thus, a choked jet may be the source of the
neutrino flare.
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All authors Shunhao Ji, Zhongxiang Wang, Litao Zhu, Dong Zheng
Solar and Stellar Astrophysics
Long-term activity cycles in planetary M stars observed with SOPHIE
C. G. Oviedo, A. P. Buccino, R.F. Díaz et al. (+5 more)
M
dwarfs are
prime targets for
exoplanet searches due to their low masses and radii, which enable the detection of small
planets in their habitable zones (HZs). However, the
magnetic activity of M
dwarfs can introduce signals in radial velocity measure- ments that may be mistaken for planetary signatures, making the understanding of
stellar activity cycles crucial for accurate
planet detection and characterisation. We aim to identify and characterise long-term
magnetic activity cycles in M
dwarfs using a homogeneous and extensive spectroscopic
dataset in order to better understand their
magnetic variability and its implications for
exoplanet detection. We analysed 13 years of high-resolution spectra obtained with the SOPHIE spectrograph for two early M
dwarfs known to host
exoplanets. We simultaneously monitored chromospheric activity using two indicators, the H{\alpha} index and the Mount Wilson S -index. Long-term trends were modelled using both sinusoidal and low-order
polynomial fits to robustly identify
stellar activity cycles. For GJ 617A, we report a cycle of approximately 4.8 years, while for GJ 411, we find several characteristic timescales of variability of about 4.9 years. In addition, TESS photometric data reveal signs of short-term variability in GJ617A. The periods of the long-term variability detected for GJ 617A and GJ 411 do not coincide with any of the planetary signals previously reported, which reinforces the hypothesis that they are of
magnetic origin. If indeed the variability is due to activity, the cycles detected would not be driven by the same mechanism: The cycle in GJ 617A is consistent with a
solar-like dynamo, while the rotation seems to play a different role in the long-term cycles detected in GJ 411.
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All authors C. G. Oviedo, A. P. Buccino, R.F. Díaz, R. Petrucci, E. Jofré, I. Boisse, P. D. Colombo, X. Delfosse
Cosmology and Nongalactic Astrophysics
Weibel Instability-Driven Seed Magnetic Fields during Reionization
Jorie McDermott, Manami Roy and Christopher M. Hirata
Cosmological reionization was a highly out-of-
equilibrium event that affected every parcel of the intergalactic medium, making it a candidate for astrophysical generation of intergalactic
magnetic fields. During reionization, the first
stars and
galaxies ionized the surrounding, largely neutral, medium in ever-expanding envelopes. Photoionization from sources on one side of the front, combined with the quadrupolar angular dependence of the photoionization cross section, leads to an anisotropic electron velocity distribution. We investigate instabilities in these reionization fronts as a mechanism to generate seed
magnetic fields. The Weibel instability has the potential to create a
magnetic field from these anisotropies. We calculate the magnitude of the isotropic and anisotropic distribution within a simulated reionization front. We find that the fractional anisotropy can grow to $6\times 10^{-3}$ toward the middle of the ionization front. We show that the linear growth timescale of the Weibel instability is fast compared to the crossing time of the ionization front ($\sim 2\times 10^5$ seconds). We briefly speculate on the possible non-linear
evolution of the instability and the implications for cosmological magnetogenesis.
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