Astrophysics of Galaxies
Probing departures from Schwarzschild geometry with the S301 star and kilometre-baseline interferometry
Rodrigo P. Silva, Alexandre C. M. Correia and 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 much smaller departures, establishing S301 as a powerful test of the spacetime geometry of Sgr A*.
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Instrumentation and Methods for Astrophysics
Armillary: A Label-Free Coordinate System for Stellar Spectra
Yuan-Sen Ting and 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 the coordinates, and the same graph transfers the labels of a few
stars to all the others. The coordinates are more nearly linear in $T_{\rm eff}$ and $\log g$ than principal components, t-SNE, UMAP or an autoencoder. The label transfer, without deep learning, is more precise than the first three and comparable to the autoencoder. On 202,932 APOGEE DR17
stars, an illustrative draw of 32 training
stars recovers the ASPCAP $T_{\rm eff}$, $\log g$ and [M/H] of held-out dwarfs and giants, with $1\sigma$ errors of 100 K, 0.18 and 0.083 dex. Resolving the two $\alpha$ sequences of the disc in [$\alpha$/M] for giants takes 128 training
stars, and with 2048 the four errors improve to 33 K, 0.06, 0.026 and 0.022 dex. On 104,799 DESI
stars, 32 training labels from APOGEE recover the stellar parameters to 129 K, 0.25 and 0.203 dex, even for spectra degraded to a signal-to-noise of about 20. At a signal-to-noise of about 100, 2048 training labels resolve the two $\alpha$ sequences of the disc in DESI giants, with errors against APOGEE of 51 K, 0.07, 0.047 and 0.026 dex. The code is public at https://github.com/tingyuansen/armillary.
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Astrophysics of Galaxies
EMIR confirmation of the high-z Ly{\alpha} blob SHARDS20018464
S.Zarattini, F. Garzón and C. Muñoz-Tuñón
A spectroscopic follow-up of the Ly$\alpha$ blob SHARDS20018464 was performed using the infrared spectrograph EMIR (Espectrógrafo Multiobjeto Infra-Rojo) at the 10.4 m GTC
telescope, equipped with its newly upgraded H2RG focal plane array detector. We observed the blob in the Ks band, which corresponds, at the photometric
redshift of $z=3.49$ presented in the literature, to the rest-frame visible part of the spectrum. Thanks to the sensitivity of EMIR, we were able to identify the [OIII] emission doublet at the position of the blob and the companion
galaxy. The flux of the detected lines is of the order of $10^{-17}$ erg s$^{-1}$ cm$^{-2}$, obtained with 4-hour exposure. The mean
redshift derived by analysing the two lines individually is $z=3.59\pm0.01$, slightly higher than the photometric one, although in agreement within the uncertainties. We also estimated the flux of the two lines and their ratio, which was found to be $R = 2.92$, very close to the theoretical prediction of 2.98. This is a strong analytical confirmation that the observed emissions correspond to the [OIII] doublet. Within uncertainties, the
redshift of the blob confirms the photometric one reported in the literature, as well as the physical properties inferred for it. Its remarkably small size (5-8 kpc vs. $\sim 100$ kpc for typical samples) and its position aside the companion
galaxy also confirm the previously-proposed idea that this object could be the first of a new class of compact Ly$\alpha$ emitters. Moreover, the data support the scenario of photo-ionisation due to a cluster of young and massive
stars.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Lunar radio emission from dark photon dark matter
Ariel Arza
The dielectric surface of the Moon provides an efficient interface for the conversion of dark matter dark
photons into
radio waves. This work explores a novel detection strategy that aims to capture this
radio emission using standard
radio telescope antennas. Detailed sensitivity projections are presented that demonstrate the power of this technique. It is found that both current and future
radio observatories, including large arrays such as the Atacama Large Millimeter/submillimeter Array (ALMA) and the Square Kilometer Array (SKA), as well as large single dishes like the Five-hundred-meter Aperture Spherical
Telescope (FAST) and the Green Bank
Telescope (GBT), can explore a substantial and previously inaccessible parameter space for these dark matter candidates.
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Instrumentation and Methods for Astrophysics
A Technosignature Survey Of The Anti-Solar Point: The SETI Institute's Largest-Ever Campaign With The Allen Telescope Array
Isabel Gerrard and Sofia Z. Sheikh
The ATA-ASP campaign is a
radio technosignature survey of the Anti-Solar Point as a "Schelling point", using the Allen
Telescope Array (ATA) in the Search for Extraterrestrial Intelligence (SETI). We borrow from game theory the concept of Schelling points to hypothesize spacetime coordinates where both we and an extraterrestrial
agent might send and search for a signal. From the perspective opposite the Sun, an extraterrestrial
agent could detect Earth transiting within the habitable zone, thus this Anti-Solar Point (ASP) poses a shared and salient Schelling point. This campaign uses the ATA, tuned to 2356-3700 MHz, to observe Earth's ecliptic, and searches for sky-localized, narrowband, Doppler-drifting signals. Analysis is conducted using the Allen
Telescope Survey Agnostic Technosignature pipeline (ATSAT), which integrates software packages bliss and NBeamAnalysis with
radio frequency interference removal and outputs spectrograms. Narrowband signals and their Doppler-drift rates indicate technological and distant origin, while comparing beamformed beams localizes signals to the ASP. The plots are visually inspected and cataloged into six signal morphologies to distinguish potential signals-of-interest and
radio frequency interference. To date, the survey has observed approximately 12% of the projected coordinate coverage over 126 observations; 67% of sessions have been analyzed, producing more than 11,000 plots, all of which have been inspected and 75% labeled. 25 of these labeled spectrograms contain narrowband drifting signals sky-localized to the ASP, and the 10 corresponding coordinates will be re-observed. Although SETI literature has long proposed searching for beacons at the ASP, this campaign provides the first observational coverage. Observing Earth's ecliptic will require a multi-year effort and produce over 11 petabytes of data, making it the ATA's largest survey ever.
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Instrumentation and Methods for Astrophysics
XuYi Interferometer Observation Simulator
M. Hadjara, T. Xu, Y. Sun et al. (+21 more)
The XuYi Interferometer is the first Chinese long-baseline optical interferometer currently under development by the National Institute of Astronomical Optics and Technology (NIAOT) of the Chinese Academy of Sciences. In preparation for future scientific operations, we developed the XuYi Interferometer Observation Simulator (XIOS), a lightweight MATLAB-based software package designed to assist observers in planning interferometric observations. The simulator combines target observability calculations, interferometric baseline geometry, delay-line constraints, (u,v)-coverage prediction, and visibility estimation into a single graphical user interface. It incorporates astronomical routines from the MAAT toolbox and adopts visualization concepts inspired by ASPRO2. The software allows users to evaluate observing opportunities, predict interferometric performances, and generate realistic observing configurations before
telescope operations. We present the architecture of the simulator, its principal modules, and representative simulation results obtained for the current three-
telescope XuYi interferometric configuration operating in the near-infrared H band.
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All authors M. Hadjara, T. Xu, Y. Sun, W. Wei, C. Liu, H. Zhang, J. Huang, C. Zeng, J. Yuan, J. Perdigon, A. Boskri, S. Lagarde, R. Petrov, R. Ligi, B. Lopez, F. Millour, J. Dejonghe, F. Baron, J. Wang, X. Wu, H. Zhao, Y. Hou, Z. Hua, X. Cui
Instrumentation and Methods for Astrophysics
BRICS Southern Observatory (BRICS-SO) Project: Invitation to African countries to invest in Chile
Massinissa Hadjara, Amokrane Berdja, Swagat R. Das et al. (+6 more)
Recently, the BRICS countries created a promising astronomy consortium (https://www.bricsastronomy.org/), which was joined last year by some emerging countries, including two African countries, namely: Egypt and Ethiopia. Certainly, other African countries will join BRICS+ in the years to come. Thus, by pooling their efforts, emerging countries (BRICS+) are sure to quickly catch up with their technological delay in the field of astronomy, particularly through ambitious and large-scale projects. Chile, due to the exceptional climatic conditions of its North, is recognized as the world capital of astronomy where all the largest consortia have settled there and applied all their know-how. The official launch of BRICS (and then its expansion to other countries; BRICS+) is welcomed as an excellent opportunity to think big in the development of astronomy. China has shown great determination in being the first country in the South to establish astronomical facilities in Chile, thus opening a possible opportunity for BRICS+ astronomers. Ambitious astronomical instrumentation is essential for the future of Astronomy and Astrophysics. Access to existing facilities is becoming more and more difficult because of saturation. Existing programs like the VLT-I/ELT and their instruments necessitated decades of collaboration between international institutions. It is therefore necessary for the BRICS+ astronomical community to collaborate together on ambitious projects without wasting time in order to offer a new pole with new opportunities for the researchers. This pole (BRICS-SO), in addition to attracting highly qualified people, will also help train new generations in all our countries, and encourage exchanges and collaborations.
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All authors Massinissa Hadjara, Amokrane Berdja, Swagat R. Das, Elisson S. G. de Almeida, Slobodan Jankov, Vladmir Lukin, Abdelkarim Boskri, Zouhair Benkhaldoun, Jinghui Zheng
Cosmology and Nongalactic Astrophysics
Testing Refracted Gravity with the kinematics of stacked galaxy clusters
Dario Primignani, Lorenzo Pizzuti, Antonaldo Diaferio et al. (+1 more)
We test Refracted
Gravity (RG), a phenomenological modified
gravity model that modifies the Poisson equation by introducing an effective gravitational permittivity $\epsilon(\rho_{\rm bar})$ which depends on the baryonic matter density $\rho_{\rm bar}$ and mimics the behaviour of dark matter in
cosmic structures. We perform a kinematical analysis of member
galaxies for a sample of 74
galaxy clusters, compiled from the Cluster Infall Regions in the Sloan Digital Sky Survey (CIRS). We stack the clusters in three bins of increasing velocity dispersion to mitigate the effects of systematic errors induced by deviations from dynamical
equilibrium and from the assumption of spherical
symmetry. By means of the MG-MAMPOSSt code, we reconstruct the gravitational potential in RG and infer the model parameters jointly with the gas and stellar mass-profile parameters, adopting broad, physically informed priors on the baryonic components. The estimates of the main parameter in Refracted
Gravity, the
vacuum permittivity $\epsilon_0$, range from $0.04$ to $0.37$, across the three main stacks, depending on the model adopted for the hot gas component. The constraints are mutually compatible within the quoted uncertainties and overlap with previous cluster-scale estimates. The agreement becomes less sensitive to gas parametrisation when selecting the less-disturbed clusters for building the stacks. These results characterize the sensitivity of cluster-scale RG constraints to baryonic modelling and sample selection
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All authors Dario Primignani, Lorenzo Pizzuti, Antonaldo Diaferio, Valeria Broccolato
Solar and Stellar Astrophysics
Production of White Dwarf Debris Disks from Planetary Collisions and Poynting-Robertson Drag
Fred C. Adams and 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 $s\sim1$ cm. The rocky debris disk evolves through the action of Poynting-Robertson drag, driven by the stellar luminosity, which is initially large but steadily decreases with time. This scenario provides an alternate channel for delivering rocky material to the immediate vicinity of a white dwarf.
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Cosmology and Nongalactic Astrophysics
AI-assisted super-resolution cosmological simulations V: Cosmology-aware super-resolution
Xiaowen Zhang, Patrick Lachance, Rupert A.C. Croft et al. (+2 more)
We present a cosmology-aware generative model for super-resolution (SR) of cosmological $N$-body simulations in particle phase space. The model jointly generates displacements and velocities, conditioning a generative
adversarial network (GAN) based generator and discriminator on evolved low-resolution (LR) fields and five $\Lambda$CDM parameters $(\Omega_m,\Omega_b,h,n_s,\sigma_8)$. We train a single model on 100 matched low-high resolution pairs from the Quijote Latin-hypercube suite at $z = 0$, mapping $512^3$ to $1024^3$ particles in $1\,h^{-1}\,\mathrm{Gpc}$ boxes. On ten cosmologies excluded from SR training, the model reproduces the broad matter distribution and the cosmological variation of clustering and
halo abundances. Over $0.1<k<3\,h\,\mathrm{Mpc}^{-1}$, the mean of the per-cosmology maximum absolute power-spectrum errors is $3.6\%$, while FoF
halo abundances agree with HR to within $15\%$ in the analyzed mass bins below $10^{14.8}\,h^{-1}M_\odot$. Satellite abundances and occupations retain larger, mass-dependent discrepancies. Corrections measured at one near-fiducial cosmology reduce a shared component of these systematic errors when applied to the other nine test cosmologies. A power spectrum based inference test also shows that calibration reduces the mean shifts in all parameters. These results extend our SR model across cosmologies and provide 6D phase space realizations for subsequent studies of non-linear structure and field-level cosmological inference.
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All authors Xiaowen Zhang, Patrick Lachance, Rupert A.C. Croft, Tiziana Di Matteo, Francisco Villaescusa-Navarro
Astrophysics of Galaxies
Unveiling the Origins of the Molecular Gas Reservoirs in Recently Quenched Massive Galaxies
E. Savitch, D. Narayanan, D. J. Setton et al. (+13 more)
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)
star formation is ongoing but heavily obscured by dust. Across $M_*>3\times10^9M_\odot$
galaxies from $z=0-2$, we find that all three mechanisms are plausible. Many seemingly quiescent, molecular gas-rich
galaxies host dust-obscured
star formation, with visual optical depths increasing on average from $\tau_V\sim0.5-2.3$ from $z=0-2$. Assuming a Milky Way-like CO-to-H$_2$ conversion factor can overestimate molecular gas masses by a factor of $\sim\!5$ in non-
star-forming
galaxies, compared to $\sim\!1.45$ in
star-forming
galaxies. Temporary quiescence can also occur in gas-rich transitioning
galaxies on timescales ranging from $100\,\text{Myr}-2\,\text{Gyr}$, although this is most prominent at high
redshift and is relatively rare overall. Further work is needed to disentangle the relative contributions of these mechanisms across
cosmic time.
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All authors E. Savitch, D. Narayanan, D. J. Setton, K. E. Whitaker, R. Bezanson, E. Cenci, R. Davé, V. R. D'Onofrio, R. Feldmann, J. E. Greene, M. Kriek, M. Parente, J. S. Spilker, K. A. Suess, D. Valentín-Martínez, D. Zimmerman
Astrophysics of Galaxies
Forming Molecular Hydrogen in a Galaxy Halo Through Star Formation Wind Interactions
Brad Koplitz, Sanchayeeta Borthakur, Timothy Heckman et al. (+5 more)
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 hydrogen ratio (2%) and an accompanying low neutral hydrogen column density (log$_{10}[N($H I$)/\mathrm{cm}^{-2}] = 18.52^{+0.13}_{-3.58}$). Our measurements reveal that the H$_2$ bearing cloud is traveling at $\sim$100 km s$^{-1}$ relative to the host
galaxy, has a super-solar
metallicity, and excites at a single, cold temperature ($245^{+25}_{-21}$ K) indicating a lack of the ”typical” core-envelope structure seen in other H$_2$ clouds. Furthermore, our analysis points to the H$_2$ likely being formed through interactions between galactic winds and the gaseous
halo surrounding the
galaxy. The properties of this cloud suggest that the H$_2$ is short-lived, yet it presents crucial information on the microphysics of the wind-CGM interactions.
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All authors Brad Koplitz, Sanchayeeta Borthakur, Timothy Heckman, Frances H. Cashman, Evan Scannapieco, Jason Tumlinson, Hsiao-Wen Chen, Molly Peeples
Astrophysics of Galaxies
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 et al. (+7 more)
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, robustly tracing
stars from the centres of 107 present-day clusters back through the merger hierarchy. We find that the majority of the final BCG stellar mass is typically contributed by the central
galaxies of only 3 to 5 progenitor
haloes. Most accreted
galaxies contribute no
stars to the BCG, instead surviving as satellites or depositing stellar material throughout the cluster. This naturally leads to a definition of the BCG stellar population as originating from the central
galaxies of the most massive infalling systems. These are delivered to the cluster centre via efficient dynamical friction and subsequently undergo violent relaxation. The ICL arises from the complementary population of
stars tidally stripped from the outskirts of all infalling systems. We therefore develop a forecasting method, identifying
stars in the BCG and ICL via the dynamical fates of their originating stellar systems. Applying this to 261 clusters, we find the resulting components remain spatially interleaved, but occupy distinct regions of phase space. Our physically defined BCG matches conventional aperture-based selections with high completeness, while providing a direct interpretation in terms of hierarchical assembly.
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All authors Frazer R. Pearce, Steven P. Bamford, Garreth Martin, Yannick M. Bahé, Harley J. Brown, Madeline Butler, Ana Contreras-Santos, Weiguang Cui, Nina Hatch, Alexander Knebe
Astrophysics of Galaxies
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 et al. (+4 more)
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$\mu$m PAH emission at our targeted
redshift. We observe a bimodal distribution of similar nature in both f$_{\rm PAH}$ and q$_{\rm PAH}$, suggesting that PAH enrichment in
galaxies goes through a rapid transition phase from a PAH-poor to a PAH-rich system, at about 70% solar
metallicity. For the
star-forming
galaxies (SFGs; i.e., $\sim$78% of the total sample), we find that f$_{\rm PAH}$ increases with stellar mass and rest-frame FUV luminosity, identifying massive, UV-bright
galaxies to have higher PAH mass fraction. However, the majority of the massive quiescent
galaxies (QGs) show lower PAH mass fraction relative to that of SFGs of similar mass, suggesting PAH and smaller dust grains are more susceptible to destruction during quenching processes. Among SFGs, we observe an anti-correlation between f$_{\rm PAH}$ and the O32 emission line ratio, suggesting PAH photo-dissociation in strongly ionized ISM. This anti-correlation, along with a correlation between f$_{\rm PAH}$ and gas-phase
metallicity 12+log(O/H), indicates that low-mass, metal-poor SFGs, which are increasingly common at even higher
redshifts, host more extreme conditions less favorable for PAH production and survival.
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All authors Chayan Mondal, Chian-Chou Chen, Kanak Saha, Thomas S.-Y. Lai, Irene Shivaei, Hiddo S. B. Algera, Bovornpratch Vijarnwannaluk
Cosmology and Nongalactic Astrophysics
Optimizing Color Selection for Cluster-Member Identification with SuperBIT
Leila Ohashi, Sayan Saha and Jacqueline E. McCleary
Galaxy richness maps provide a useful tracer of the stellar mass distribution in
galaxy clusters, but identifying cluster members from multiband photometric data can be challenging. In this work, we investigate multiband imaging data obtained with the Super-Pressure Balloon-borne Imaging
Telescope (SuperBIT) during its science flight in April 2023. Using spectroscopically identified cluster members across the SuperBIT cluster sample, we
benchmark the performance of the three colors available from the three SuperBIT bands: $(u-b)$, $(b-g)$, and $(u-g)$. We quantify the performance of each color using the $1\,\sigma$ scatter of the spectroscopically identified members in color and the purity of our cluster-member identification
algorithm. We find that $(b-g)$ consistently exhibits the smallest color scatter and highest purity across the sample and over the
redshift range probed by SuperBIT. We therefore identify $(b-g)$ as the preferred color for red-sequence-based cluster-member identification, providing a basis for future analyses of the cluster
galaxy population using SuperBIT multiband photometry.
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Astrophysics of Galaxies
The star-forming past and quenching of brightest cluster galaxies in TNG-Cluster
Sunna Gottschewski, Joey Braspenning, Annalisa Pillepich et al. (+2 more)
The Brightest Cluster
Galaxies (BCGs) in the most massive
galaxy clusters of our Universe are, at present, mostly quiescent, elliptical, and red. However, their formation histories are unclear and likely different from those of massive ellipticals in lower-mass
haloes. Simulations face the challenge of simultaneously requiring large volumes to sample massive clusters and sufficient resolution to model their stellar populations. Therefore, we make use of TNG-Cluster, one of the highest-resolution cosmological simulations of
galaxy clusters, which returns 352 BCGs at $z=0$ with stellar masses $M_{*, <30 \mathrm{pkpc}} = 10^{11.6-12.9} ~\mathrm{M}_\odot$ and total
halo masses $M_{\mathrm{200c}} = 10^{14.3-15.4}~\mathrm{M}_\odot$. 93 per cent of the BCGs are quenched at $z=0$, whereas at
redshift $z>3$ all their main progenitors were still
star forming. The
star-formation histories of individual BCGs are complex, including multiple (re)quenching episodes. They rejuvenate on average $2.1 \pm 1.8$ times since $z=3$. BCGs quench for the first time $9.9^{+0.9}_{-1.4} ~\mathrm{Gyr}$ ago (10th-90th percentiles; $z=1.7^{+0.5}_{-0.5}$), while the last and final quenching event occurred $7.0^{+2.8}_{-5.0} ~\mathrm{Gyr}$ ago ($z=0.8^{+0.8}_{-0.6}$). We find a large scatter in the
halo, stellar, and SMBH masses at both first and last quenching, suggesting no characteristic mass at which quenching occurs. Instead, BCGs quench for the first time when the cumulative kinetic energy injected by their SMBH equals the BCG binding energy, corresponding to a delay of $2.3^{+1.2}_{-1.2} ~ \mathrm{Gyr}$ after the first SMBH kinetic energy injection. Namely, TNG-Cluster BCGs quench when they experience significant gas expulsion. Our work shows that BCGs have complex and varied
star-formation histories, with multiple rejuvenation episodes, but they ultimately quench due to SMBH feedback.
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All authors Sunna Gottschewski, Joey Braspenning, Annalisa Pillepich, Katrin Lehle, Dylan Nelson
High Energy Astrophysical Phenomena
Pair echo model of CTAO/LST-1 signal from GRB 221009A
Andrii Neronov, Ievgen Vovk, Teneman Keita et al. (+1 more)
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 1.33 days after the burst can be interpreted as the pair echo produced by very-high-energy gamma-rays propagating through intergalactic medium with
magnetic field of the strength log(B/G)=-16.2+/- 0.7, if its correlation length lambda_B is larger than 20 kpc. If the field correlation length is shorter than 20 kpc, the field strength estimate is modified upwards by a square root of (20 kpc / lambda_B). In the specific case of short correlation length IGMF that is relic from cosmological phase transitions, the pair echo model of the LST-1 signal implies the field strength in the 1e-14-1e-12 G range. Such
magnetic field parameters are consistent with all known constraints on IGMF, including the lower bounds from gamma-ray observations of active galactic
nuclei.
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All authors Andrii Neronov, Ievgen Vovk, Teneman Keita, Davide Miceli
High Energy Astrophysical Phenomena
Can Historic Measurements cast light on the Spectral Differences found between the Pierre Auger Observatory and the Telescope Array?
Quentin Luce and 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 same, it is found that historic data are in good agreement with measurements made at the Pierre Auger Observatory above 30 EeV. Thus, the tensions between the spectra measured by the
Telescope Array and the Auger Observatory remain.
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Solar and Stellar Astrophysics
Ap stars with resolved magnetically split lines: Mean magnetic field modulus measurements 1999–2004
Gautier Mathys, John D. Landstreet and 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 <B> 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, observatory archive data. We determine the values of <B> and of the radial velocity by measuring the
magnetic splitting and the wavelength shift of the Fe lambda 6149.2 Å line in high-resolution spectra recorded in natural light. Combining our measurements with published ones, we characterise the variability of both quantities. We derived for the first time the accurate, unambiguous values of the rotation periods of HD 29578 and HD 165474. We set lower limits of years to decades to the rotation periods of six
stars and identified four more that have not shown any significant <B> variations over timescales of 13 to 33 years. We established that HD 47103 is the first Ap
star with a rotation period of years known to have a
magnetic field significantly exceeding 7.5 kG. We achieved the first determination of the orbital elements of HD 116114, HD 142070, and HD 144897, and we refined the orbital elements of six other binaries.
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High Energy Astrophysical Phenomena
Centaurus A: Opportunities to unveil particle acceleration with the CTAO
Cainã de Oliveira and 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 from Cen A. Using simulated observations based on the CTAO Instrument Response Functions (IRF) for the Alpha Configuration of
telescopes, we investigate both the spectral and morphological domains to assess the observatory's potential to constrain competing models of particle acceleration in the kiloparsec-scale jet and the Southern Giant Lobe. For the jet, we explore CTAO observations with t=50 and 200h for different leptonic and hadronic origin scenarios for the very-high-energy gamma-ray emission. We show that longer observation campaigns (t=200h) would probe the presence of hard spectral components extending to tens of TeV. Morphological simulations demonstrate that CTAO can resolve the extended gamma-ray emission along the jet, discriminating between point-like and Gaussian spatial models within t=50h, assuming a known background model and an optimistic zenith angle $\vartheta=$20{\deg}. Under similar hypotheses, we studied the Giant Lobes evaluating both diffuse and filamentary emission templates for the S1 region detected by Fermi-LAT. We found that CTAO-South can be sensitive to hadronic scenarios with
proton energies extending beyond 10 TeV, for the Alpha Configuration and $\vartheta=$20{\deg}. Overall, our results indicate that CTAO observations of Cen A can provide a decisive step toward unveiling the mechanisms driving the high-energy emission and particle acceleration in
radio galaxies
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Cherenkov Bursts are Memory Steps
Jann Zosso, Guangzi Xu and Vitor Cardoso
We show that the familiar Cherenkov burst from a finite superluminal charge track can be understood as a pair of interfering electromagnetic
memory transitions. Endpoint accelerations of the track produce opposite
memory steps in the transverse vector potential, such that the corresponding finite-frequency radiation is universally fixed, below the endpoint-acceleration-scale, by the
memory amplitude and the time for which the temporary
memory offset persists. As the Cherenkov direction is approached, the
memory amplitudes grow while their separation in observer time shrinks, until the two vector-potential steps overlap and their divergent contributions cancel into a finite Cherenkov burst. This perspective opens the door to using the Askaryan effect as a setting in which individual macroscopic
memory transitions may be resolved, providing a new experimental arena for
memory-linked infrared physics.
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Astrophysics of Galaxies
Rotational excitation of SiC$_6$ by collisions with helium: cross sections, rate coefficients and non-LTE modeling
Liman Tian, Ziyu Xiang, Chuangang Ning et al. (+1 more)
Rotational transitions of SiC$_6$ in the $j=26$–$40$ range have been detected in IRC+10216, yet collisional rate coefficients for SiC$_6$ with He or H$_2$ were previously unavailable. This paper reports rate coefficients for rotational excitation of SiC$_6$ induced by collisions with He, calculated using a two-dimensional potential energy surface (PES) constructed at the RCCSD(T)-F12 level under the rigid-rotor approximation. The close-coupling (CC) method was employed for low rotational energy levels, while the coupled-states (CS) approximation was used for higher rotational levels. Systematic convergence tests were conducted, and the resulting CC and CS scattering cross sections were compared. The rate coefficients obtained via the CS method cover rotational levels up to $j=40$ and temperatures of 3–100\,K. Although the CC and CS rate coefficients differ by up to a factor of $\sim 2$ for some transitions, particularly those influenced by weak coupling and resonances, the two methods yield nearly identical excitation and brightness temperatures for the high-$j$ transitions (e.g., $19\rightarrow18$) examined, and the CS-based line fluxes agree with the CC-based results to within 6.5% for $n(\mathrm{H_2}) \ge 10^{3}$\,cm$^{-3}$; this demonstrates that the CS approximation is reliable for the non-LTE modelling of high-$j$ SiC$_6$ transitions considered here, for which fully converged CC calculations are computationally impractical. Using the calculated SiC$_6$–He rate coefficients and reduced-mass scaling to estimate the corresponding SiC$_6$–H$_2$ rates, we further investigate the excitation of the observed high-$j$ transitions. Under typical low-density conditions in IRC+10216 ($n(\mathrm{H_2}) \approx 10^4$\,cm$^{-3}$), the $j=40\to39$ transition is subthermally excited, highlighting the importance of non-LTE effects when interpreting the emission of high-$j$ SiC$_6$ transitions.
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All authors Liman Tian, Ziyu Xiang, Chuangang Ning, Xiaolin Chen
Solar and Stellar Astrophysics
Three-dimensional magnetic reconnection in unipolar regions. A case study of coronal bright points in the Sun
D. Nóbrega-Siverio, F. Moreno-Insertis and A.S.H. To
Magnetic reconnection is a fundamental mechanism underlying the heating and a wide variety of eruptive phenomena in the solar atmosphere; however, characterizing its 3D aspects remains challenging. Our aim is to understand how 3D
magnetic reconnection in unipolar regions drives localized heating and
plasma ejections. To this end, we used a self-consistent 3D radiation-MHD simulation of a coronal bright point (CBP) performed with the Bifrost code. We focused on localized, intense heating events and upflows near a unipolar CBP footpoint associated with its parasitic polarity. 3D reconnection diagnostics were carried out using the parallel electric field and its integral along
magnetic field lines. We then compared the resulting upflows with spectroscopic observations from Hinode/EIS. We find recurrent episodes of 3D
magnetic reconnection without nulls at the footpoints of loops rooted near the CBP's parasitic polarity. A detailed analysis of one representative event places the reconnection region at heights z=[1.0,2.5] Mm, within a predominantly vertical
magnetic field with localized concentrations of electric current. The dissipation of these currents efficiently heats the
plasma to about 2 MK and produces strong gas-pressure gradients that drive upflows of a few tens of km/s. Blueshifts observed with Hinode/EIS near the parasitic polarity of an observed CBP are consistent with this scenario. The recurrence of these reconnection events are essential for heating CBP loops to million-degree temperatures. This form of 3D reconnection may operate more generally in the solar atmosphere, dissipating
magnetic stress around strong flux concentrations and contributing to heating in apparently unipolar regions. The resulting pressure-driven upflows offer an indirect spectroscopic diagnostic of localized reconnection heating, which future observations with MUSE and Solar-C will be able to test.
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Solar and Stellar Astrophysics
Detection of knots in the supernova type Iax remnant Pa 30
Tim Cunningham, Ilaria Caiazzo, John C. Raymond et al. (+1 more)
We present deep, narrowband Gemini North/GMOS images of the Pa 30 nebula that reveal rich small-scale structure in the ejecta filaments. In [S II], the number of detected filaments increases by about an order of magnitude compared to previous studies. The imaging further reveals that the filaments are not smooth radial streaks, but instead are composed of cascades of
knots or clumps. The images in [O III] yield the first confirmation that previously detected diffuse [O III] emission in fact originates from the same [S II] filaments. We measure a nebula center consistent with the position of the central
star, indicating that the remnant has not received a large transverse kick. The 3$\sigma$ upper limit on the velocity of the stellar kick is $\lesssim$100 km/s. Cross-sectional profiles of the filaments in [S II] and [O III] show a central peak on top of a nebular background, the latter being likely due to diffuse emission or unresolved filaments. The median [S II] width of 0.7” is slightly broader than the 0.50” seeing, providing some evidence of partially resolved filaments and implying a characteristic
knot diameter of ${\sim}10^{16}$ cm. The $\approx$1” widths measured in [O III] are consistent with the poorer seeing of the oxygen images. The discovery of this clumpy substructure provides a new observational constraint on models for the origin and
evolution of the remarkable filamentary ejecta of Pa 30.
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All authors Tim Cunningham, Ilaria Caiazzo, John C. Raymond, Scott J. Kenyon
Earth and Planetary Astrophysics
Dynamics around non-spherical symmetric bodies - III. The case of a spherical body with a crater
P. V. S. Soares, G. Madeira, S. M. Giuliatti Winter et al. (+2 more)
Motivated by the peculiar features of the trans-Neptunian object (TNO) Máni and the discovery of ring systems around Centaurs and trans-Neptunian bodies, we investigate the stability of particles around a small irregular body hosting a deep equatorial crater. This study is the third contribution in a sequence devoted to the dynamics around non-spherically symmetric bodies. Using Máni as a reference model, whose crater depth exceeds 10% of its radius, we map the system stability through complementary methods: Poincaré surfaces of section (PSS), survival maps, and the finite-time Lyapunov exponent (FTLE). In the nominal case, the $1\!:\!1$, $2\!:\!1$, $3\!:\!1$, and $4\!:\!1$
spin-orbit resonances (SORs) are consistently identified by all techniques. The prominent $3\!:\!1$ SOR exhibits a bifurcated structure at high eccentricities, matching structural transitions observed at lower Jacobi constant values in the PSSs. Increasing the rotation rate ($\lambda$) and crater mass ratio ($\mu$) enlarges resonance widths and promotes overlap, making the $2\!:\!1$ and $4\!:\!1$ SORs progressively dominant. Lower rotation rates allow stable trajectories to persist at higher eccentricities, whereas the $1\!:\!1$ SOR is highly sensitive to stronger perturbations and disappears in the most extreme cases. In contrast to mass-anomaly models, which can clear the region interior to the $2\!:\!1$ SOR, the crater configuration considered here preserves stable regions in this vicinity, suggesting alternative scenarios for the formation and maintenance of debris structures around irregular minor bodies.
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All authors P. V. S. Soares, G. Madeira, S. M. Giuliatti Winter, T. Ribeiro, O. C. Winter
Instrumentation and Methods for Astrophysics
Towards a GPU-Accelerated Real-Time Imaging Pipeline for SETI at the Allen Telescope Array
Karen I. Perez, Joe S. Bright, Vishal Gajjar et al. (+1 more)
Traditional technosignature and transient searches commonly operate on beamformed time–frequency products. Interferometric imaging adds spatial context and allows time-domain searches to be performed across many image pixels simultaneously. We report the development and testing of a GPU-accelerated interferometric imaging and image-domain dispersion-measure (DM) search pipeline for Allen
Telescope Array (ATA) post-correlation UVH5 visibility data, integrated with the CyberEther streaming framework to replay recorded visibility data and work toward real-time operation. The pipeline forms Stokes-I dirty images from correlated visibilities, incorporates Inter-Quartile Range Mitigation (IQRM) flags into the imaging weights, images 48 frequency subbands spanning 287.5\,MHz, subtracts a temporal mean over the full observation from each subband and pixel, applies IQRM-informed subband masking, and performs a blind trial-DM search using a short-history image ring buffer. On a controlled 10-minute three-spectral-window test observation containing a periodic dispersed pulsed injection (DM\,$\approx$\,150\,pc\,cm$^{-3}$), the pipeline recovers the injected source at the phase centre with a best-fit DM\,$=$\,150\,pc\,cm$^{-3}$, with individual dispersed pulses reaching a median image-plane S/N of $\approx$52. When integrated into CyberEther, the core processing requires approximately 63\,ms per integration compared with a native integration time of approximately 98\,ms, demonstrating that the core science-processing operations can be completed within the available integration time. The present implementation operates on recorded visibility data and relies on a temporal mean and MAD noise estimate precomputed over the full observation. For live operation, these quantities will instead need to be estimated from data available up to the current integration.
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All authors Karen I. Perez, Joe S. Bright, Vishal Gajjar, Luigi F. Cruz
Astrophysics of Galaxies
Tentative Detection of FeS toward Orion SrcI
Aitana Tasa-Chaveli, Holger S. P. Müller, Álvaro Sánchez-Monge et al. (+3 more)
Iron sulfide (FeS) is a key refractory compound in astrophysical environments. It is commonly found in meteorites and evidence of FeS has only been reported in solid form in a protoplanetary environment. Furthermore, FeS is of astrobiological interest since it acts as a precursor to the formation of pyrite (FeS$_2$), which plays a key role in anaerobic metabolism. We present millimeter-wave spectroscopic calculations for gaseous FeS and report its tentative detection toward the massive disk Orion SrcI. If confirmed, this would constitute the first ever detection of gaseous FeS in the interstellar medium. Our data are consistent with a FeS column density of $\sim1.7 \times 10^{15}$ cm$^{-2}$. Comparing to other sulfur reservoirs, the amount of sulfur locked in FeS is more than three orders of magnitude lower than that contained in SO$_2$ and SiS. However, FeS emission may arise from a different region as it is the case for the metallic salt NaCl. Our results support the presence of FeS in interstellar grains and are consistent with grain destruction playing an important role in the origin of the FeS emission. The observations, however, are still insufficient to discern whether FeS is a main sulfur reservoir in molecular clouds or a primary carrier of refractory iron-bearing material.
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All authors Aitana Tasa-Chaveli, Holger S. P. Müller, Álvaro Sánchez-Monge, Asunción Fuente, Adam Ginsburg, Thomas Möller
Instrumentation and Methods for Astrophysics
Sub 35-ps Single-Photon Stellar Intensity Interferometry of Vega
Verena G. Leopold, Sebastian Karl, Stefan Richter et al. (+7 more)
SII enables measurements of stellar photospheres by correlating intensity fluctuations, offering a robust alternative to amplitude-based techniques. With the advent of modern single-
photon counting detectors, this method has re-emerged as a powerful technique in stellar interferometry exploiting their ultra-high timing resolution. We determine the stellar diameter of Vega at 405 nm using spatial intensity correlations measured at the C2PU facility, part of the Observatoire de la Cote d'Azur. We employed a setup identical to Leopold et al. (2025). The two campaigns in April and August 2024 used hybrid photodetectors (HPDs; 22.7 ps resolution) and new PhotonPix detectors (34.8 ps resolution). A Photonscore TDC integrated
photon arrival times and IRIG-B timestamps for synchronization. Our analysis consisted of calculating auto- and cross-correlation histograms from the recorded data, which were then normalized and corrected for optical path differences. The temporal auto-correlations yield a consistent coherence time of 0.21 ps. This confirms the effectiveness of the PhotonPix detectors despite a slight degradation in timing resolution relative to the HPDs. Combining the data from the two measurement campaigns yields a uniform disk diameter of Vega of 2.97 +/- 0.23 mas. This agrees with the 3.047 mas diameter predicted by the stellar atmosphere model at our observation wavelength, validating our technique and the new PhotonPix detectors for precision SII at sub-35 ps resolution. The integration of advanced single-
photon detectors like the PhotonPix into existing IACT SII instruments promises substantial enhancements in signal-to-noise ratio and observational capabilities, particularly with CTA LSTs. Although challenges such as night sky background saturation and precise positioning and guiding remain, SII observations at apparent magnitudes up to 7.8 are within reach.
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All authors Verena G. Leopold, Sebastian Karl, Stefan Richter, Jean-Pierre Rivet, Yury Prokazov, Evgeny Turbin, Gennady Sintotskiy, Iurii Datii, Jason Aufdenberg, Joachim von Zanthier
Earth and Planetary Astrophysics
Shadows cast by precessing annuli as evidence for an inclined planet in HD 139614
Katie L. Milsom, Tim J. Harries, Evan A. Rich et al. (+3 more)
We analyse scattered-light images at multiple epochs of the protoplanetary disc HD139614 taken with GPI and SPHERE instruments. We show that the azimuthal distribution of the surface brightness of the inner bright ring ($13-21$au) varies with time (likely caused by a structure in the inner-disc at $\sim1$au) and constrain the timescale of this variation to be $<11$months. We show that inner arc ($31-44$au) is likely a spiral and tightly wound, measuring a pitch angle of $6.1\pm1.2^\circ$. Additionally, we construct a physical model to explain the broad shadow across $\sim2/3$ of the outer disc and the azimuthally asymmetric bright ring (which has a shadow not aligned with the broad shadow). We model the disc using 1D warp equations with a fast radiative transfer code to produce scattered-light images. We setup the disc as three annuli separated by gaps with an inclined perturbing
planet between the inner two annuli. The
planet causes the inner annuli to tilt and precess independently casting broad shadows across the outer (un-tilted) annulus. These shadows combine to produce a shadow across $\sim2/3$ of the outer disc and an asymmetric bright ring which matches the observations of HD139614. The precession of the annuli is periodic (so the model matches the observations multiple times) with long precession time-scales ($8.4\times10^3$ and $7.2\times10^4$years for the inner and middle annulus respectively) so the shadows are effectively static over accessible observational time-scales.
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All authors Katie L. Milsom, Tim J. Harries, Evan A. Rich, John D. Monnier, Anna S. E. Laws, Benjamin R. Setterholm
High Energy Astrophysical Phenomena
Continuous Gravitational Waves from Thermo-Elastic Mountains in Ultraluminous X-ray Pulsars
Hong-Bo Li, Ziming Wang, Lijing Shao et al. (+1 more)
Fast-spinning, nonaxisymmetrically deformed
neutron stars (NSs) are promising targets for continuous gravitational-wave (CGW) searches with current and next-generation ground-based detectors. Ultraluminous X-ray
pulsars (ULXPs), characterized by super-Eddington
accretion and strong
magnetic fields, provide extreme environments in which substantial nonaxisymmetric deformations may develop. In this Letter, we investigate thermo-elastic mountains generated by magnetically induced temperature asymmetries in the accreted crusts of ULXPs. We connect the crustal thermal structure to an
accretion-column model and solve the full anisotropic heat-transport equation, extending previous perturbative treatments into the nonlinear, strongly magnetized regime. We find that the weak-field approximation begins to break down near $B_{\rm ref}\sim10^{13}\,{\rm G}$, beyond which nonlinear anisotropic heat transport significantly modifies the quadrupolar thermal response. The resulting thermal asymmetries generate substantial thermo-elastic mass quadrupoles at higher field strengths. Although the currently known ULXPs are unfavorable CGW targets because of their relatively slow
spins and, in most cases, large distances, our illustrative
spin-
evolution calculations show that a NS can enter the super-Eddington accretor phase with a
spin period of order $20\,{\rm ms}$. Such rapidly rotating Galactic ULXPs could lie within the projected sensitivities of next-generation detectors such as the Einstein
Telescope and
Cosmic Explorer. These results extend thermal-mountain physics into the strongly magnetized regime relevant to ULXPs and connect super-Eddington
accretion with prospective CGW observations.
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All authors Hong-Bo Li, Ziming Wang, Lijing Shao, Ren-Xin Xu