研究動向

astro-ph.EP2026年10月6日

Exploring the ultrahot Neptune LTT 9779 b with CRIRES+. Non-detection of helium transmission spectra and detection of H$_2$O on the dayside

S. Liu, F. Yan, L. Nortmann, B. Guo, D. Cont, F. Lesjak, D. Shulyak, A. Reiners et al.

Ultrahot Neptunes reside in the most extreme irradiation regime of the hot Neptune desert and remain challenging targets for atmospheric characterization because of their low planet-to-star flux ratios. We present high-resolution transit and dayside thermal emission spectroscopy of the ultrahot Neptune LTT 9779 b obtained with CRIRES$^+$, to probe atmospheric escape and dayside molecular emission. No significant absorption is detected in the metastable He I $λ1083$ nm triplet during transit, yie…

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astro-ph.GAastro-ph.CO2026年10月6日

Hierarchical Black Hole Mergers at High Redshift: Predictions for LISA and LGWA from SEEDZ

Daxal H. Mehta, Lewis R. Prole, John A. Regan, Rüdiger Pakmor, Sophie Koudmani, Ricarda S. Beckmann, Michael Tremmel, John H. Wise et al.

We investigate the hierarchical assembly of black holes (BHs) in the early Universe using the next-generation SEEDZ cosmological zoom-in simulations. Our suite follows two independent regions (\textsc{Rarepeak} and \textsc{Normal1}) evolved with three BH feedback prescriptions: no feedback (NoFB), weak feedback (WeakFB), and standard thermal isotropic feedback (FidBH). Focusing on BH mergers at $z \geq 10$, we explore merger-driven BH growth and detectability with next-generation gravitational-w…

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astro-ph.GA2026年10月6日

Spectroscopic Confirmation of the Milky Way Satellites Boötes V and Leo Minor I and the LMC Satellite DELVE 2: Three Small Ultra-Faint Dwarf Galaxies

W. Cerny, M. Geha, J. D. Simon, T. S. Li, A. B. Pace, R. P. van der Marel, N. Kallivayalil, A. P. Ji et al.

We present the first multi-object spectroscopy of Boötes V, Leo Minor I, and DELVE 2 -- three small (20 pc $\le r_{1/2}\le$ 26 pc), ultra-faint ($-3.2\le M_V\le-2.1$) stellar systems in the outer Galactic halo (71 kpc $\le D_\odot\le$ 102 kpc) with heretofore ambiguous classifications. Leveraging at least two epochs of Keck/DEIMOS or Magellan/IMACS observations targeting each satellite, we identify 13, 7, and 7 spectroscopic members in the three systems, respectively. We tentatively resolve a $σ…

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astro-ph.EPastro-ph.IM2026年10月6日

Enhancing the Interpretability of Radial Velocity Analysis Using Leave-one-out Cross-validation

Matthew C. Nixon, Ritvik Basant, Rafael Luque, Luis Welbanks, Pierrot Lamontagne

Radial velocity (RV) observations are reaching increasingly high precision, enabling the targeting of low-amplitude signals. Assessing results obtained at the limits of our capabilities requires understanding the relationship between data, models and inference. Leave-one-out cross-validation (LOO-CV) has become an increasingly popular tool for interpretable model criticism in astronomical data analysis. In this work, we demonstrate how LOO-CV can provide insight into the RV analysis of exoplanet…

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astro-ph.GAastro-ph.EPcond-mat.mes-hallphysics.comp-ph2026年10月6日

Molecular hydrogen formation on dust: The impact of gas-dust drift on formation efficiency

Stefan Reissl, Simon C. O. Glover, Ralf S. Klessen, Liam S. Morrissey, Mordecai-Mark Mac Low

Molecular hydrogen is predominantly formed on dust-grain surfaces in the interstellar medium, where relative gas-dust motion can arise in dynamically active environments. While the dependence of H$_2$ formation on grain temperature and surface properties is well studied, the impact of gas-dust drift has received little attention. We investigate how gas-dust drift modifies H$_2$ formation, focusing on the competition between the drift-enhanced H-atom collision rate and reduced sticking at higher…

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astro-ph.GA2026年10月6日

DIGging into HII regions: the role of ionizing photon leakage and spectral hardening in coupling HII regions and diffuse ionized gas

Dalya Baron, Kathryn Kreckel, Gwen C. Rudie, Karin M. Sandstrom, Alberto D. Bolatto, Guillermo A. Blanc, Oleg V. Egorov, Eva Schinnerer et al.

The optical emission-line ratios of star-forming galaxies are broadly understood in the framework of photoionization, yet some systematic trends remain unexplained. Using 50--100 pc resolution PHANGS-MUSE observations of 19 nearby galaxies, we investigate how escaping ionizing radiation couples HII regions to the diffuse ionized gas (DIG), analyzing thousands of HII regions and DIG sightlines. HII regions and the DIG form a continuous sequence across standard line-ratio diagnostic diagrams (e.g.…

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astro-ph.EPastro-ph.SR2026年10月6日

Discovery of a second-generation planet candidate accreting onto a white dwarf

Jamie T. Williams, Boris T. Gänsicke, Nicholas C. Stone, Detlev Koester, Benjamin D. R. Davies, Christopher Tong, David J. Wilson, Snehalata Sahu et al.

Many white dwarfs accrete the debris of disrupted planetary bodies, detected in the form of metal-enrichment in their atmospheres, dusty or gaseous circumstellar discs, and photometric transits from debris. The composition of accreted debris has been shown to be diverse yet overall closely resembles Solar System bodies. We report the discovery of a white dwarf accreting material that is unlike any Solar System object. The atmosphere of HS 0209+0832 is strongly enriched in trans-iron elements inc…

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hep-phastro-ph.HEhep-exhep-thquant-ph2026年10月6日

Magnus: neutrino oscillation probabilities for any Hermitian Hamiltonian, any number of flavors, and any matter profile

Mauricio Bustamante

Interpreting neutrino oscillation measurements requires computing the probability that a neutrino born with one flavor is detected with another. In vacuum and in matter of constant density, this probability has exact formulas. Where the density varies along the path, as in the Earth, the Sun, or a supernova, it does not. There, the usual approaches either replace the profile by constant-density steps, whose error falls only as the square of their width, or integrate the evolution equation with a…

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astro-ph.HEphysics.plasm-ph2026年10月6日

Power-Law Injection Spectrum from an Ensemble of Reconnecting Current Sheets

Omar French

A collisionless, low-$β$ plasma undergoing strong sub-Alfvénic turbulence is expected to form a broad hierarchy of reconnecting current sheets immersed in a strong guide magnetic field. If the reconnecting field strength of a sheet scales with its length as a power law of index $κ$, and the number of sheets per unit interval of sheet length decreases as a power law of index $x$, the current-sheet ensemble injects nonthermal particles with a power-law energy spectrum $\propto γ^{-s}$, where $s =…

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astro-ph.HEastro-ph.GAastro-ph.SR2026年10月6日

Uncovering the Physical Origins of Black Holes in the Milky Way for Astronomical Surveys

Ilia Kiato, Pierson Lipschultz, Vicky Kalogera, Jeff J. Andrews, Max M. Briel, Abhishek Chattaraj, Seth Gossage, Philipp M. Srivastava et al.

The observational landscape of stellar-mass black holes (BHs) in the Milky Way is expanding beyond X-ray binaries, with Gaia DR4 and Roman expected to open new windows onto BH populations. We use the binary population synthesis framework POSYDON to predict the present-day Galactic BH population and connect it to its evolutionary origins. We test the robustness of these predictions to uncertainties in binary evolution and BH formation, including core-collapse mechanisms, natal kicks, common-envel…

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astro-ph.EPastro-ph.IM2026年10月6日

Detecting multiple planets in Gaia data using Bayesian model selection

Emmanuel J. Greenfield, James E. Owen

Gaia will soon provide a census of cold giant planets. However, an astrometric signal contains the superimposed reflex motion of all companions, so planetary signals cannot be treated individually. We therefore investigate Gaia's planet-detection capabilities for 1-planet and 2-planet systems, with special attention to systems near 2:1 mean-motion resonance. Gaia can detect 2-planet systems, although the lower-S/N planet requires a higher S/N threshold, especially when the outer planet is more m…

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astro-ph.SR2026年10月6日

Unlocking new information in stellar circular polarisation with second-order least-squares deconvolution

Oleg Kochukhov

Least-squares deconvolution (LSD) is the standard technique for measuring stellar magnetic fields from circular polarisation spectra. It rests on the weak-field approximation and yields the longitudinal field alone. We aim to extend LSD beyond the weak-field limit and interpret departures from a linear field response in terms of the field modulus. The Stokes V absorption coefficient is expanded in odd wavelength derivatives of the intensity profile, with coefficients given by the Zeeman pattern…

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astro-ph.COastro-ph.GA2026年10月6日

And Then There WEre Baryons (ATWEB): The Baryon Budget of the Universe in Halos and the IGM over 13 Billion Years of Cosmic Time

Mohammadreza Ayromlou, G. Mark Voit, Thomas H. Reiprich, Cristiano Porciani, Dominique Eckert

Observations of the local Universe show that, except in the most massive galaxy clusters, the baryon fraction within halos falls below the cosmic mean. This deficit can be characterized using the previously established closure radius, the halocentric distance within which the enclosed baryon fraction reaches the cosmic value. Using the TNG, EAGLE and SIMBA simulations, we examine how, when, and on what scales the baryonic and dark matter distributions diverge. At z=0 less than 30% of cosmic bary…

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astro-ph.GAastro-ph.SR2026年10月6日

Cracking open the "dragon egg": ALMA 1.3mm observations of a compact, young high-mass core candidate at 30mas resolution

A. T. Barnes, J. D. Henshaw, Á. Sánchez-Monge, P. Caselli, I. Jiménez-Serra, J. E. Pineda, K. Immer, M. De Simone et al.

Massive prestellar cores are a central assumption of core-accretion models of high-mass star formation, yet convincing observational examples remain rare. The "dragon egg" (C2c1a) core in the infrared-dark cloud G028.37+00.07 has been proposed as a promising compact high-mass core candidate. We present new ALMA Band 6 observations at $0.035''$-$0.078''$ ($\sim175$-400 au at 5 kpc), providing one of the most stringent high-resolution tests of such a candidate. The region resolves into multiple fr…

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astro-ph.IMastro-ph.HE2026年10月6日

Optimal Photon Counting with Fast, Low Noise Astronomical Imagers

Jack T. Dinsmore, Christopher Layden, Roger W. Romani, Vera L. Berger, Kevin B. Burdge, Geoffrey Mo, Deepto Chakrabarty, Emma T. Chickles et al.

Measuring rapid astrophysical phenomena requires many short exposures, which suffer from repeated read noise. A variety of recent technologies are achieving sub-electron read noise, which enable rapid time-domain studies of faint sources. These data can be analyzed with traditional methods, but the ability to resolve individual electrons enables a new class of more precise, photon-counting techniques. We present a photon-counting method for sub-electron read noise detectors which delivers optima…

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astro-ph.EPastro-ph.GA2026年10月6日

First Direct Identification of a Multi-Star Microlens System Hosting a Planet

Sean K. Terry, David P. Bennett, Jean-Philippe Beaulieu, T. Dex Bhadra, Aparna Bhattacharya, Joshua W. Blackman, Ian A. Bond, Andrew A. Cole et al.

Nearly 25 years have passed since gravitational microlensing delivered its first exoplanet discoveries. The relative proper motion between lens and source systems allows them to be resolved as they separate on the sky over many years. This enables scientists to study light coming directly from the lenses and place tight constraints on the physical properties of these planetary systems. In this paper we present an analysis of high angular resolution images of the microlensing target OGLE-2006-BLG…

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astro-ph.SRastro-ph.EP2026年10月6日

Production of White Dwarf Debris Disks from Planetary Collisions and Poynting-Robertson Drag

Fred C. Adams, Konstantin Batygin

This paper explores the production of debris disks around white dwarfs, which are observed to experience frequent pollution events. In this scenario, planetary collisions occur just outside the surface of a highly evolved AGB star, after the end of its mass loss phase, as it starts its transition into a white dwarf. The collisions vaporize a fraction of the planetary material, which subsequently expands, cools, nucleates droplets, and condenses into rocky bodies with characteristic size of order…

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astro-ph.GAgr-qc2026年10月6日

Probing departures from Schwarzschild geometry with the S301 star and kilometre-baseline interferometry

Rodrigo P. Silva, Alexandre C. M. Correia, Paulo J. V. Garcia

The S301 star reaches a pericentre one tenth that of S2, opening a new regime for probing black-hole spin and departures from Schwarzschild. We develop a post-Newtonian secular Hamiltonian framework for bound geodesics in stationary, axisymmetric spacetimes and compute the maximum projected astrometric deviation over one orbit. At the expected GRAVITY+ precision, S301 can probe several nonrotating geometries and sizeable spin-induced deviations, while kilometre-baseline interferometry can probe…

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astro-ph.GA2026年10月6日

Unveiling the Origins of the Molecular Gas Reservoirs in Recently Quenched Massive Galaxies

E. Savitch, D. Narayanan, D. J. Setton, K. E. Whitaker, R. Bezanson, E. Cenci, R. Davé, V. R. D'Onofrio et al.

Observations of quenched galaxies across cosmic time have revealed systems containing substantial molecular gas reservoirs, challenging the traditional picture of gas-poor, red and dead galaxies. Using the Simba cosmological simulation, we investigate three possible hypotheses for the origin of molecular gas-rich quenched systems: (i) quiescence is temporary and the galaxy will rejuvenate, (ii) molecular gas masses are overestimated due to an underestimated CO-to-H$_2$ conversion factor, or (iii…

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astro-ph.GA2026年10月6日

Forming Molecular Hydrogen in a Galaxy Halo Through Star Formation Wind Interactions

Brad Koplitz, Sanchayeeta Borthakur, Timothy Heckman, Frances H. Cashman, Evan Scannapieco, Jason Tumlinson, Hsiao-Wen Chen, Molly Peeples et al.

Molecular hydrogen (H$_2$) is the key ingredient for star formation in galaxies. However, how H$_2$ is distributed in and around galaxies is an open question in astronomy. We report the detection of H$_2$ (covering excitation levels $J = 0$ to 3) in a unique environment at a distance of 139 kpc from a starbursting luminous infrared galaxy. This is the furthest from a galaxy that H$_2$ has been directly detected to date. This H$_2$ system is unlike any seen before, with a high molecular-to-atomic…

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astro-ph.GAastro-ph.CO2026年10月6日

Disentangling the assembly of the central and diffuse stellar components in galaxy clusters through dynamical friction and tidal stripping

Frazer R. Pearce, Steven P. Bamford, Garreth Martin, Yannick M. Bahé, Harley J. Brown, Madeline Butler, Ana Contreras-Santos, Weiguang Cui et al.

In galaxy clusters, it is common to conceptually distinguish the central, brightest cluster galaxy (BCG) from the more diffuse intracluster light (ICL). So far, however, this distinction has lacked a clear physical basis, confusing both theoretical and observational studies. We address this by presenting a dynamically motivated definition of the two stellar components, evaluated using cluster zoom simulations from the Three Hundred project. We start with a motivational hindcasting approach, robu…

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astro-ph.GA2026年10月6日

PAH emission from star-forming and quiescent galaxies at $z=0.5-0.8$ probed by JWST/MIRI

Chayan Mondal, Chian-Chou Chen, Kanak Saha, Thomas S. -Y. Lai, Irene Shivaei, Hiddo S. B. Algera, Bovornpratch Vijarnwannaluk

We investigate emission from polycyclic aromatic hydrocarbon (PAH) dust molecules in 224 MIRI-selected star-forming and quiescent galaxies at $z=0.5-0.8$ in the GOODS-South field using multi-wavelength data from the AstroSat/UVIT, JWST, HST, Herschel, and MUSE. We define an observed diagnostic parameter, f$_{\rm PAH}$, as the ratio of JWST/MIRI F1280W to the average of F770W and F2550W band fluxes, and demonstrate that it effectively traces the PAH mass fraction (q$_{\rm PAH}$) by capturing 7.7$…

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astro-ph.GAastro-ph.CO2026年10月6日

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

Sunna Gottschewski, Joey Braspenning, Annalisa Pillepich, Katrin Lehle, Dylan Nelson

The Brightest Cluster Galaxies (BCGs) in the most massive galaxy clusters of our Universe are, at present, mostly quiescent, elliptical, and red. However, their formation histories are unclear and likely different from those of massive ellipticals in lower-mass haloes. Simulations face the challenge of simultaneously requiring large volumes to sample massive clusters and sufficient resolution to model their stellar populations. Therefore, we make use of TNG-Cluster, one of the highest-resolution…

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astro-ph.HEastro-ph.CO2026年10月6日

Pair echo model of CTAO/LST-1 signal from GRB 221009A

Andrii Neronov, Ievgen Vovk, Teneman Keita, Davide Miceli

Interactions of very-high energy gamma-rays during their propagation through the intergalactic medium result in a delayed secondary ``pair echo'' signal. Detection of such pair echo can be used for measurements of intergalactic magnetic fields (IGMF) in the voids of the Large Scale Structure of the Universe. We notice that a combination of data of LHAASO and CTAO/LST-1 telescopes on the gamma-ray burst GRB 221009A is consistent with the pair echo model. The LST-1 measurement of the source signal…

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astro-ph.HE2026年10月6日

Can Historic Measurements cast light on the Spectral Differences found between the Pierre Auger Observatory and the Telescope Array?

Quentin Luce, Alan A. Watson

The differences between the energy spectra reported by the Pierre Auger Observatory and the Telescope Array Collaboration are well-known. In an effort to understand these differences, we have studied the residuals of the fluxes measured in early work at AGASA, Volcano Ranch and Haverah Park with reference to the spectrum reported by the Auger Collaboration. After an empirical adjustment to the energies in the region before the ankle, where fluxes from the two hemispheres are expected to be the s…

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astro-ph.IMastro-ph.GAastro-ph.SR2026年10月6日

Armillary: A Label-Free Coordinate System for Stellar Spectra

Yuan-Sen Ting, Serat Saad

A stellar spectrum is determined by a few parameters, so a set of spectra lies on a low-dimensional manifold with those parameters as its coordinates. We introduce Armillary, which generalises the Sequencer of Baron and Ménard from an ordering to multidimensional coordinates, constructed from the spectra alone. Two stars are compared by the Wasserstein distance between their signed absorption profiles. Shortest paths through a nearest-neighbour graph measure distance along the manifold and give…

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astro-ph.SR2026年10月6日

Ap stars with resolved magnetically split lines: Mean magnetic field modulus measurements 1999--2004

Gautier Mathys, John D. Landstreet, T. A. A. Sigut

Magnetic Ap stars that have a strong enough field and a sufficiently low v sin i show spectral lines resolved into their magnetically split components. This allows their mean magnetic field modulus to be determined. We complement the existing knowledge of the rotational magnetic variability and of the binarity of a sample of 34 Ap stars with resolved magnetically split lines by analysing observations obtained between 1999 and 2004 that had not been exploited before and, when available, observato…

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astro-ph.HE2026年10月6日

Centaurus A: Opportunities to unveil particle acceleration with the CTAO

Cainã de Oliveira, Edivaldo Moura Santos

As the nearest radio galaxy, Centaurus A (Cen A) has been observed across multiple wavelengths and over a broad range of angular scales, providing valuable insights into the functioning of radio galaxies. However, despite being a known source of gamma rays, the physical mechanisms responsible for these high energy emissions remain unclear. In this study, we explore the capabilities of the Cherenkov Telescope Array Observatory (CTAO) to provide insights into the origin of the gamma-ray emission f…

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gr-qcastro-ph.HEphysics.class-phphysics.optics2026年10月6日

Cherenkov Bursts are Memory Steps

Jann Zosso, Guangzi Xu, Vitor Cardoso

We show that the familiar Cherenkov burst from a finite superluminal charge track can be understood as a pair of interfering electromagnetic memory transitions. Endpoint accelerations of the track produce opposite memory steps in the transverse vector potential, such that the corresponding finite-frequency radiation is universally fixed, below the endpoint-acceleration-scale, by the memory amplitude and the time for which the temporary memory offset persists. As the Cherenkov direction is approa…

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astro-ph.GA2026年10月6日

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

Liman Tian, Ziyu Xiang, Chuangang Ning, Xiaolin Chen

Context. SiC$_6$ was recently identified toward the carbon-rich circumstellar envelope IRC+10216 through rotational transitions with $J=26$--$40$. Reliable collisional rate coefficients are required to model its excitation, but state-to-state rotationally inelastic rates for SiC$_6$ with He or H$_2$ collisions have not been reported. Aims. We provide state-to-state thermal rate coefficients for SiC$_6$--He collisions and assess the applicability of the coupled-states (CS) approximation to the hi…

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