Astrophysics of Galaxies
High-Redshift Galaxy Candidates at z > 6 as Revealed by JWST Observations of MACS0647
Keduse Worku, Tiger Yu-Yang Hsiao, Dan Coe et al. (+9 more)
We present a catalog of 57 high-
redshift $z>6$
galaxy candidates, including 14 spectroscopic confirmations ($z = 6.10$ – 9.25), 2 Little Red Dots ($z = 4.77$, 5.81), and 2 interlopers ($z = 3.23$, 3.72), based on \JWST\ NIRCam imaging (7 filters), NIRSpec spectroscopy (PRISM and G395H), and archival \HST\ imaging (17 filters) of the strong
lensing galaxy cluster MACS0647. Our highest
redshift confirmation ($z = 9.25$) is an Extremely Blue
Galaxy (presented in~\citealt{Yanagisawa2024}), and here we identify a spectral turnover likely due to damped Lyman-$\alpha$. We identify an overdensity of
galaxies with spectroscopic
redshifts $z = 6.1$, confirming the $z \sim 6$ overdensity identified in \HST\ images. In one of these
galaxies, our high-resolution G395H spectroscopy reveals two spatially resolved components with a velocity difference of $\sim$90 km/s; if these components are gravitationally bound, this would imply a dynamical mass on the order of $\sim 10^8\ M_\odot$ given their projected separation. We present spectral line fluxes, widths, and derived physical properties, including
stellar masses ($10^8 - 10^9 \ \mathrm{M}_{\odot}$) and
metallicities ($10\% - 40\% \ \mathrm{Z}_{\odot}$) for our spectroscopic sample. We note half of our NIRSpec data was obtained with standard 3-slitlet nods and half was obtained with single slitlets yielding similar results, demonstrating the power to observe more sources on a densely packed NIRSpec MSA.
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All authors Keduse Worku, Tiger Yu-Yang Hsiao, Dan Coe, Abdurro'uf, Tom Resseguier, Rebecca L. Larson, Jacqueline Antwi-Danso, Gabriel Brammer, Vasily Kokorev, Larry D. Bradley, Lukas J. Furtak, Masamune Oguri
Instrumentation and Methods for Astrophysics
Semantic search for 100M+ galaxy images using AI-generated captions
Nolan Koblischke, Liam Parker, Francois Lanusse et al. (+3 more)
Finding scientifically interesting phenomena through slow manual labeling campaigns severely limits our ability to explore the billions of
galaxy images produced by
telescopes. In this work, we develop a pipeline to create a semantic search engine from completely unlabeled image data. Our method leverages
Vision-
Language Models (VLMs) to generate descriptions for
galaxy images, then contrastively aligns a pre-trained astronomy foundation model with these embedded descriptions to produce searchable
embeddings at scale. We find that current VLMs provide descriptions that are sufficiently informative to train a semantic search model that outperforms direct image similarity search. Our model, AION-Search, achieves state-of-the-art zero-shot performance on finding rare phenomena despite training on randomly selected images with no deliberate curation for rare cases. Furthermore, we introduce a VLM-based re-ranking method that nearly doubles the recall for our most challenging targets in the top-100 results. For the first time, AION-Search enables flexible semantic search for over 100 million
galaxy images, enabling discovery from previously infeasible searches, including the identification of 36 new extragalactic
stellar stream candidates. More broadly, our work provides an approach for making large, unlabeled scientific image archives semantically searchable, expanding data exploration capabilities in fields from Earth observation to microscopy. The code, data, and app are publicly available at https://github.com/NolanKoblischke/AION-Search
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All authors Nolan Koblischke, Liam Parker, Francois Lanusse, Jo Bovy, Irina Espejo, Shirley Ho
High Energy Astrophysical Phenomena
Multimessenger Probes of the Supermassive Black Hole Binary Population: The Role of Pulsar Timing Arrays
Nima Laal, Stephen R. Taylor, Cayenne Matt et al. (+1 more)
By inferring the gravitational wave background (GWB) from a population of supermassive black hole binaries (SMBHBs),
pulsar timing arrays (PTAs) enable the study of massive black holes. In many ways, PTAs manifest the promise of a multimessenger approach to astronomy: they can constrain SMBHB population characteristics that are otherwise difficult to constrain using electromagnetic observations, such as hardening mechanisms at sub-parsec separations. In this work, we quantify this multimessenger promise using
Bayesian inference of many realizations of simulated PTA data, while adopting a model for the SMBHBs that has been successfully applied to the 15-year data set of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). Our analyses of 200 realistic, simulated NANOGrav data sets show that there is a greater than 50% chance of reducing the prior uncertainty in the SMBHB hardening rate by more than 50%, and in the SMBHB evolutionary lifetime by 25–75%. Additionally, there is an 88% chance that PTA data can reduce the prior uncertainty in the characteristic mass variable of the
galaxy stellar mass function (GSMF) by 25–50%. For $M_{\text{BH}}$–$M_{\text{Bulge}}$ parameters (in a model without
redshift evolution) and the overall normalization parameter of the GSMF, PTA data can provide only marginal information gain beyond the constraints from electromagnetic observations. Our work delineates the domains over which electromagnetic and gravitational-wave data constrain the demographics and dynamics of the supermassive black-hole binary population, offering a clearer picture of the impact of population multi-messenger astrophysics probes with PTAs.
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All authors Nima Laal, Stephen R. Taylor, Cayenne Matt, Kayhan Gultekin
Instrumentation and Methods for Astrophysics
The MeerKLASS On-the-Fly continuum survey: pipeline design and validation
Suman Chatterjee, Mario G. Santos, Kristof Rozgonyi et al. (+8 more)
The MeerKAT Large Area Synoptic Survey (MeerKLASS) is designed to map large areas of the Southern sky for cosmology using the single-dish HI intensity mapping (IM) technique, while simultaneously delivering a wide, high angular-resolution interferometric survey. We present the design and first results of the MeerKLASS On-the-Fly (OTF) continuum data, which exploits the visibilities recorded during fast, constant-elevation scans. This observing mode enables fast commensal imaging over several hundred of square degrees on a nightly basis. We describe the OTF survey strategy and pipeline, focusing on handling challenges introduced by the current MeerKAT fixed-delay correlation observing mode, which causes decorrelation (smearing). We implement a correction scheme based on time-dependent phase rotation, direction-dependent PSF modeling, and wide-band faceted deconvolution with DDFacet. Using UHF-band and pilot L-band data, we demonstrate the recovery of high-quality 2-second snapshot images and deep mosaics over hundreds of square degrees. After smearing correction we are able to achieve a resolution of $23.3$arcsec and $14$ arcsec with an rms sensitivity of $35 \mu {\rm Jy\,beam}^{-1}$ and $ 33 \mu {\rm Jy\,beam}^{-1}$ in the UHF and L-band respectively. The full survey will cover $10,000 \, {\rm deg}^{2}$ at 544-1088 MHz, and after the delay tracking fix implemented we expect to reach $\sim 25 \mu {\rm Jy\,beam}^{-1}$ at $14$ arcsec resolution. The continuum OTF data products will support diverse science goals, including
galaxy and AGN
evolution, diffuse cluster emission, large-scale structure and cosmology, rotation-measure synthesis, and transient searches. MeerKLASS-OTF thus establishes an efficient path to wide-area commensal surveys with MeerKAT and provides a key technical precursor for SKA-Mid.
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All authors Suman Chatterjee, Mario G. Santos, Kristof Rozgonyi, Keith Grainge, Sarvesh Mangla, Joseph J. Mohr, Sourabh Paul, Yvette Perrott, Oleg M. Smirnov, Cyril Tasse, Laura Wolz
Solar and Stellar Astrophysics
Residual energy in weakly compressible turbulence with a mean guide field
R. Skalidis, A. Tritsis, J. R. Beattie et al. (+1 more)
The energy distribution is a fundamental property of magnetohydrodynamic (MHD)
turbulence. In strongly magnetized
turbulence energy imbalances arise and are quantified by the residual energy: $E_r~=~(E_{kin}~ - ~E_{mag})$; $E_{kin}$ and $E_{mag}$ stand for the volume-averaged kinetic and
magnetic energy, respectively. We explore the properties of $E_r$ in weakly compressible MHD
turbulence in the presence of an initially strong (guide)
magnetic field, investigating how the driving mechanism and the
magnetic field strength affect the cascade of $E_r$. We run a suite of direct numerical simulations with the PENCIL code. The sonic Mach number is approximately equal to 0.1 in all simulations, whereas the
plasma beta varies. We drive
turbulence by either injecting velocity or
magnetic fluctuations at large scales and study the power spectra of kinetic,
magnetic, density, and $E_r$. Magnetically driven simulations show locally imbalanced Alfvénic fluctuations and a $\propto k^{-3/2}$ cascade, consistent with the dynamic
alignment theory. In the inertial range, $E_r \approx$ 0. Kinetically driven simulations give rise to a $\propto k^{-1}$ scaling, consistent with weakly interacting modes that preserve a high level of coherence throughout the inertial range. Residual energy is positive at all scales of the inertial range. The spectral slope of the $E_r$ cascade steepens systematically with increasing magnetization, varying from approximately -1 at $\beta = 0.3$ to between -2.0 and -5/3 at $\beta = 4.0$. The energy partition in weakly compressible
turbulence is strongly influenced by the forcing mechanism, even when the global sonic and Alfvénic Mach numbers are comparable across simulations.
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All authors R. Skalidis, A. Tritsis, J. R. Beattie, P. F. Hopkins
Earth and Planetary Astrophysics
JWST/NIRSpec Detects Warm CO Emission in the Terrestrial-Planet Zone of HD 131488
Cicero X. Lu, Isabel Rebollido, Sean Brittain et al. (+12 more)
We have obtained a high-resolution, JWST NIRSpec $2.87$ – $5.14$ $\mu$m spectrum of the debris disk around HD 131488. We discover CO fundamental emission indicating the presence of warm fluorescent gas within $\sim10$ AU of the
star. The large discrepancy in CO's vibrational and rotational temperature indicates that CO is out of thermal
equilibrium and is excited with UV fluorescence. Our UV fluorescence model gives a best fit of $1150\,$K with an effective temperature of $450$, $332$, and $125\,$K for the warm CO gas kinetic temperature within $0.5$, $1$, and $10\,$AU to the
star and a gas vibrational temperature of $8800\,$K. The newly discovered warm CO gas population likely resides between sub-AU scales and $\sim\,10\,$AU, interior to the cold CO reservoir detected beyond $35\,$AU with HST STIS and ALMA. The discovery of warm, fluorescent gas in a debris disk is the first such detection ever made. The detection of warm CO raises the possibility of unseen molecules (H$_2$O, H$_2$, etc) as collisional partners to excite the warm gas. We estimated a lower mass limit for CO of $1.25\times 10^{-7}\text{M}_{\oplus}$, which is $10^{-5}$ of the cold CO mass detected with ALMA and HST. We demonstrate that UV fluorescence emerges as a promising avenue for detecting tenuous gas at $10^{-7}$ Earth-mass level in debris disks with JWST.
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All authors Cicero X. Lu, Isabel Rebollido, Sean Brittain, Tracy Beck, Christine H. Chen, Kadin Worthen, Joan Najita, Chen Xie, Aoife Brennan, Amaya Moro-Martin, John Debes, Kevin France, Luca Matrà, Marshall Perrin, Aki Roberge
Earth and Planetary Astrophysics
From Earths to Super-Earths: Five New Small Planets Transiting M Dwarf Stars
Jonathan Gomez Barrientos, Heather A. Knutson, Morgan Saidel et al. (+39 more)
Earth-sized
planets transiting M
dwarf stars present one of the best opportunities with current facilities for studying the atmospheric and bulk compositions of terrestrial worlds. Here, we statistically validate five new transiting Earth and super-Earth sized
planets orbiting M
dwarf stars using a combination of light curves from the Transiting
Exoplanet Survey Satellite, multi-color observations from Palomar and Las Cumbres Observatory, high-resolution imaging, and
stellar spectroscopy. The sample includes: TOI-5716 b, an Earth-sized
planet (R_p = 0.96 $\pm$ 0.05 Rearth) with a 6.766-day orbit around a metal-poor thin-disk
star ([Fe/H] = -0.54 $\pm$ 0.10); TOI-5728 b, a super-Earth (R_p = 1.31 $\pm$ 0.05 Rearth) on an 11.497-day orbit; and TOI-5736 b, a larger
planet (R_p = 1.56 $\pm$ 0.07 Rearth) with an ultra-short period of just 0.649 days. We also statistically validate a multi-
planet system, TOI-5489, hosting two similarly-sized super-Earths: TOI-5489 b (R_p = 1.40 $\pm$ 0.05 R_earth) and TOI-5489 c (R_p = 1.28 $\pm$ 0.07 R_earth) with orbital periods of 3.152 and 4.921 days, respectively. Due to their longer orbital periods, TOI-5716 b and TOI-5728 b both have
equilibrium temperatures $\leq$ 400 K, making them useful test cases for studies of atmospheric mass loss. If TOI-5728 b is confirmed to have an Earth-like bulk composition, it would join the very small sample of rocky
planets orbiting mid- to late-M
dwarfs that lie below the
cosmic shoreline and therefore may have retained high mean molecular weight atmospheres.
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All authors Jonathan Gomez Barrientos, Heather A. Knutson, Morgan Saidel, Michael Greklek-McKeon, W. Garrett Levine, Nicholas Saunders, Howard Isaacson, Renyu Hu, Karen A. Collins, David R. Ciardi, Polina A. Budnikova, Dmitry V. Cheryasov, Samuel W. Yee, Diogo Souto, Aida Behmard, Akihiko Fukui, Avi Shporer, Akanksha Khandelwal, Bob Massey, Brice-Oliver Demory, Catherine A. Clark, Chris Stockdale, Emily A. Gilbert, Enric Palle, Francis P. Wilkin, Felipe Murgas, Francis Zong Lang, Ilse Plauchu-Frayn, Jessie L. Christiansen, Jon M. Jenkins, Joseph D. Twicken, Keith Horne, Michaël Gillon, Monika Lendl, Michael B. Lund, Norio Narita, Pam Rowden, Ramotholo Sefako, Richard P. Schwarz, Steven Giacalone, Urs Schroffenegger, Yilen Gómez Maqueo Chew
High Energy Astrophysical Phenomena
Detection of Partial Coherence due to Multipath Propagation for FRB 20220413B with CHIME/FRB
Zarif Kader, Evan Davies-Velie, Matt Dobbs et al. (+7 more)
Fast
radio bursts (FRBs) are a $\sim$ millisecond-long transient phenomenon that propagate across extragalactic distances and are effectively a point source.
Radio wave propagation through inhomogeneous distributions of
plasma can act as a lens, generating multiple images of the emitted electric field. A lens can produce images of a point source where the phase of the electric field between images remains coherent when observed by a
radio telescope. FRB 20220413B shows a complicated pulse structure with time separated components that may be image copies of the main components due to
plasma lensing. We perform several analyses to determine if FRB 20220413B is consistent with expectations of a
plasma lensed FRB. We analyze and fit the morphology of the burst to a
plasma lens model and find consistency in the spectro-temporal profile but not the observed flux. Using the complex-valued channelized voltage data from the CHIME
telescope, we perform a time-lag correlation analysis and report correlation signatures present in the electric field of FRB 20220413B. We find that there exists an excess correlation signature only in absolute power and not in phase. We perform a frequency-lag correlation analysis on the spectra of all subcomponents of the burst and find a consistent scintillation bandwidth across all components. We find the scintillation bandwidth is consistent with expectations of scattering due to the Milky Way. We interpret this as all burst components propagating through the same scintillation screen located in the Milky Way, which would generate the excess variance signature observed, even in the absence of phase coherence between burst components. We find that while the burst morphology can be modeled by a
plasma lens, the coherent signature present in the time-lag correlation is consistent with the expectations of a common scattering screen, but not coherent
plasma lensing.
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All authors Zarif Kader, Evan Davies-Velie, Matt Dobbs, Afrokk Khan, Calvin Leung, Robert Main, Kiyoshi W. Masui, Kenzie Nimmo, Ue-Li Pen, Mawson Sammons
Astrophysics of Galaxies
The MeerKLASS UHF On-the-Fly Continuum Survey – Data Release I
Sourabh Paul, Keith Grainge, Mario G. Santos et al. (+9 more)
We present the first public data release (DR1) from the interferometric component of the MeerKAT Large Area Synoptic Survey (MeerKLASS) UHF survey, a legacy program demonstrating a novel on-the-fly (OTF) mapping technique. This release is based on 12 hours of early science observations covering approximately 800 deg$^2$ of the southern sky. We describe the data processing pipeline developed to calibrate and image these fast-scanning observations, producing high-fidelity continuum images at a central frequency of 816 MHz. The resulting mosaic reaches an RMS sensitivity of $\sim$35 $\mu$Jy beam$^{-1}$ in its deepest regions, with a typical angular resolution of $\sim32'' \times 17''$. In these images, we identify $95483$
radio sources. We validate the catalogue through cross-matching with external surveys, confirming sub-arcsecond astrometric accuracy and a robust flux density scale. We compute the differential source counts, finding excellent agreement with existing measurements and validating our end-to-end processing. The success of this pilot study serves as a crucial proof of concept for the OTF observing strategy, and the public release of the images and source catalogue provides a valuable resource for a wide range of astrophysical studies. This work paves the way for the full MeerKLASS OTF survey and future large-area survey projects with the SKA.
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All authors Sourabh Paul, Keith Grainge, Mario G. Santos, Suman Chatterjee, Sarvesh Mangla, Laura Wolz, Joseph J. Mohr, Oleg Smirnov, Cyril Tasse, Kristof Rozgonyi, Matthias Hoeft, Yvette Perrott
High Energy Astrophysical Phenomena
Probing jet-induced optical variability across timescales in radio-loud NLSy1 galaxies
Vivek Kumar Jha, Anshul Kumar Sharma, Madhu Sudan et al. (+1 more)
We investigate optical variability across multiple timescales in a sample of
radio-loud narrow-line Seyfert~1 (RL-NLSy1)
galaxies, including $\gamma$-ray detected, $\gamma$-ray undetected, and non-jetted systems along with a comparison set of highly polarised core-dominated
quasars (HPQs). Using Zwicky Transient Facility light curves, we measure fractional variability ($F_{\rm var}$) and rest-frame structure functions (SFs) to test whether short-term jet-linked variability is reflected in long-term behaviour. $\gamma$-ray detected RL-NLSy1s and HPQs show steeply rising SFs, revealing strong long-term coherence despite modest $F_{\rm var}$, consistent with Doppler-boosted synchrotron emission from relativistic jets. Non-jetted RL-NLSy1s exhibit the highest $F_{\rm var}$ but plateauing SFs, indicative of
stochastic, disc-driven fluctuations lacking long-term coherence. $\gamma$-ray undetected RL-NLSy1s show the lowest $F_{\rm var}$ and nearly flat SFs, consistent with weak or absent jet activity across all timescales. Colour-magnitude trends show that jet-dominated sources exhibit redder-when-brighter behaviour, whereas disc-dominated systems exhibit bluer-when-brighter trends. These results show that SF-derived temporal coherence, rather than variability amplitude alone, is a promising diagnostic of jet dominance and orientation, offering a framework for interpreting AGN variability in forthcoming time-domain surveys.
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All authors Vivek Kumar Jha, Anshul Kumar Sharma, Madhu Sudan, Hum Chand
Astrophysics of Galaxies
Cosmic Duets I. High-spatial resolution spectroscopy of dual and lensed AGN with MUSE-NFM
M. Scialpi, F. Mannucci, Q. D'Amato et al. (+34 more)
We present the first-year results of the MUSE Large Program "
Cosmic Duets", whose goal is to obtain adaptive-optics assisted MUSE observations with an angular resolution of 0.1"-0.2" in order to provide integral-field spectroscopy of sub-arcsec separation dual and lensed active
galactic nucleus (AGN) candidates. These observations reveal previously unexplored properties of dual and lensed systems that are key to understanding
galaxy evolution, supermassive black hole mergers, and strong-
lensing modeling. Targets were efficiently selected using the
Gaia multipeak (GMP) technique, which identifies pairs of point-like sources with separations below 0.8" in the
Gaia catalog. MUSE spatially resolved spectroscopy provides accurate
redshifts, ionization diagnostics, and identification of absorption systems along the line of sight. We report results for 30 GMP targets at z=0.5-3.5. All systems show at least 2 spatially resolved components. 19 objects are confirmed as AGN multiplets, including 6 dual AGN, 10 doubly lensed
quasars, and 3 quadruply lensed systems, while the remaining 11 correspond to chance
alignments with foreground
stars. Among all the spectroscopically confirmed dual AGN in the literature, 27 pairs have projected separations below 7kpc in this
redshift regime, and our sample accounts for 22% of the total. We studied dual and lensed AGN distributions as a function of
redshift, magnitude, and projected separation while accounting for selection effects, and we find that bright systems are dominated by lensed
quasars, whereas the relative fraction of dual AGN increases at fainter magnitudes. This first-year sample demonstrates the high efficiency of GMP selection combined with MUSE spectroscopy for identifying sub-arcsec dual and lensed AGN. The full program, targeting 150 systems, will enable statistical studies of dual AGN and constraints on mass distribution in
lensing galaxies.
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All authors M. Scialpi, F. Mannucci, Q. D'Amato, C. Marconcini, G. Cresci, A. Marconi, L. Ulivi, M. Fumagalli, P. Rosati, G. Tozzi, M.V. Zanchettin, L. Battistini, E. Bertola, C. Bracci, S. Carniani, E. Cataldi, M. Ceci, A. Chakraborty, C. Cicone, A. Ciurlo, A. De Rosa, G. Di Rosa, A. Feltre, M. Ginolfi, I. Lamperti, E. Lusso, B. Moreschini, E. Nardini, M. Parvatikar, M. Perna, K. Rubinur, P. Severgnini, J. Singh, C. Spingola, G. Venturi, C. Vignali, M. Volonteri
Instrumentation and Methods for Astrophysics
The automation of optical transient discovery and classification in Rubin-era time-domain astronomy
Nabeel Rehemtulla, Michael W. Coughlin, Adam A. Miller et al. (+1 more)
Robotic wide-field time-domain surveys, such as the Zwicky Transient Facility and the Asteroid Terrestrial-impact Last Alert System, capture dozens of transients each night. The workflows for discovering and classifying transients in survey data streams have become increasingly automated over decades of development. The recent integration of machine learning and artificial intelligence tools has produced major milestones, including the fully automated end-to-end discovery and classification of an optical transient, and has enabled automated rapid-response space-based follow-up. The now-operational Vera C. Rubin Observatory and its Legacy Survey of Space and Time are accelerating the rate of transient discovery and producing large volumes of data at incredible rates. Given the expected order-of-magnitude increase in transient discoveries, one promising path forwards for optical time-domain astronomy is heavily investing in accelerating the automation of our workflows. Here we review the current paradigm of real-time transient workflows, project their
evolution during the Rubin era and present recommendations for accelerating transient astronomy with automation.
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All authors Nabeel Rehemtulla, Michael W. Coughlin, Adam A. Miller, Theophile Jegou du Laz
Astrophysics of Galaxies
Modeling the Milky Way Circumnuclear Disk: Rosettes and Rings
Asad Ukani, Lena Murchikova and Mark D. Gorski
The Milky Way
Galactic Center hosts a $\sim4\times10^{6}\,M_\odot$ supermassive black hole (SMBH), Sagittarius A* (Sgr A*). The dominant structures in its immediate vicinity are the
nuclear star cluster (NSC), whose enclosed mass at 2 pc is approximately half that of the SMBH, and the circumnuclear disk (CND)/ring, which extends between $\sim0.5$ pc and $\sim3$ pc from Sgr A* and is the largest reservoir of molecular gas in this region. Existing models of the CND commonly use one circular orbit to describe the motion of its gas. Here, we explore a much broader range of models. In the combined potential of Sgr A* and the NSC, we consider non-Keplerian rosette orbits as well as a circular disk, which is formed using a finely spaced set of concentric rings. For both systems, we test various inner/outer radii, inclinations, and position angles, sampling a total of $\sim3.3 \times 10^{5}$ models. We then conduct mock observations of all models to construct velocity maps, which we compare with HCN ($J=1{-}0$) observations of the CND. We find that the best-fitting model is a circular disk with inner and outer radii of 1.0 pc and 2.9 pc, an inclination of $i=60^{\circ}$, and a position angle of $\text{PA} = 35^{\circ}.$
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Instrumentation and Methods for Astrophysics
Pre-training vision models for the classification of alerts from wide-field time-domain surveys
Nabeel Rehemtulla, Adam A. Miller, Mike Walmsley et al. (+15 more)
Modern wide-field time-domain surveys facilitate the study of transient, variable and moving phenomena by conducting image differencing and relaying alerts to their communities. Machine learning tools have been used on data from these surveys and their precursors for more than a decade, and convolutional neural networks (CNNs), which make predictions directly from input images, saw particularly broad adoption through the 2010s. Since then, continually rapid advances in computer
vision have transformed the standard practices around using such models. It is now commonplace to use standardized architectures pre-trained on large corpora of everyday images (e.g., ImageNet). In contrast, time-domain astronomy studies still typically design custom CNN architectures and train them from scratch. Here, we explore the effects of adopting various pre-training regimens and standardized model architectures on the performance of alert classification. We find that the resulting models match or outperform a custom, specialized CNN like what is typically used for filtering alerts. Moreover, our results show that pre-training on
galaxy images from
Galaxy Zoo tends to yield better performance than pre-training on ImageNet or training from scratch. We observe that the design of standardized architectures are much better optimized than the custom CNN baseline, requiring significantly less time and
memory for inference despite having more trainable parameters. On the eve of the Legacy Survey of Space and Time and other image-differencing surveys, these findings advocate for a paradigm shift in the creation of
vision models for alerts, demonstrating that greater performance and efficiency, in time and in data, can be achieved by adopting the latest practices from the computer
vision field.
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All authors Nabeel Rehemtulla, Adam A. Miller, Mike Walmsley, Ved G. Shah, Theophile Jegou du Laz, Michael W. Coughlin, Argyro Sasli, Joshua Bloom, Christoffer Fremling, Matthew J. Graham, Steven L. Groom, David Hale, Ashish A. Mahabal, Daniel A. Perley, Josiah Purdum, Ben Rusholme, Jesper Sollerman, Mansi M. Kasliwal
Earth and Planetary Astrophysics
The Brown-dwarf Desert Persists as a Mass-ratio Desert around Low-mass Stars
Keming Zhang
Sun-like
stars are known to host a paucity of brown
dwarf companions at close separations. Direct imaging surveys of intermediate-mass
stars have suggested that the brown
dwarf desert may be fundamentally a feature in the mass ratio. Microlensing surveys provide a unique opportunity to investigate the nature of this desert around low mass
stars, as microlensing hosts have typical masses of 0.05-0.8 $M_\odot$. Here, we perform a statistical analysis of homogeneously selected binary-lens microlensing events in the literature, and identify a companion mass-ratio desert at $0.02\lesssim q\lesssim0.05$ and projected separations around 1-5 au. We derive a statistically significant truncation to the
giant-
planet mass-ratio distribution at $q\simeq0.02$, above which the occurrence rate density drops by approximately an order of magnitude. Due to the possibility that the small number of detected companions in this desert orbit white
dwarfs, this mass-ratio desert may be closer to being completely dry around main-sequence
stars. Below this desert, we derive a
giant-
planet ($q>4\times10^{-4}$) occurrence rate density of $5.8\pm0.8$% per decade of projected separation. Our analysis furthers the hypothesis that the brown
dwarf desert is fundamentally a feature in the mass ratio, separating distinct populations of planetary and non-planetary companions that are likely formed via core
accretion and gravitational instability, respectively. The persistence of this desert across
stellar types suggests that both gas-
giant planets and sub-
stellar companions form in a scale-invariant fashion, with
planets growing to a maximum of approximately 2% their host masses.
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Astrophysics of Galaxies
Eccentric Binaries Accreting from Thin Disks: Orbital Evolution
Alexander J. Dittmann, Geoffrey Ryan and Luciano Combi
Circumbinary disks crucially affect the orbital and electromagnetic properties of binary systems across the universe, from
stars in our
galactic neighborhood to supermassive black hole binaries formed as the result of tumultuous
galactic mergers. Previous simulations have focused nearly exclusively on thick
accretion disks, appropriate for studying
stellar binaries, and have found encouraging agreement with observations thereof. We present herein the first systematic study of eccentric binary systems accreting from thin disks, focusing on binary orbital
evolution. Our main results are that (1) thinner disk not only drive binaries to rapidly inspiral, but also excite binary eccentricities at much higher rates; (2) while thick disks may drive binaries to a stable fixed point of $e\approx0.425$, thinner disks pump binary eccentricities to $e\gtrsim0.6$; (3) the range of near-zero eccentricities that are damped towards zero depends on both disk thickness and viscosity, thinner disks and those with $\alpha$ viscosities driving binaries towards circularity over a much narrower range of eccentricities. These differences follow largely from the effects of pressure support on
accretion streams and shocks within the inner regions of the
accretion flow. Our results suggest that accreting binary black holes should have high eccentricities well into the frequency range probed by
pulsar timing arrays and space-based gravitational wave interferometers, affecting the spectrum and isotropy of the gravitational wave background. Our results also suggest that circumbinary disks may play an important role in shaping the orbits of close binary
stars, but much less so those of wider binaries.
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Cosmology and Nongalactic Astrophysics
Solving the Cosmological Vlasov-Poisson Equations with Physics-Informed Kolmogorov-Arnold Networks
Nicolas Cerardi, Emma Tolley and Ashutosh Mishra
Cold dark matter (CDM) evolves as a collisionless fluid under the Vlasov-Poisson equations, but N-body simulations approximate this
evolution by discretising the distribution function into particles, introducing discreteness effects at small scales. We present a physics-informed neural network approach that evolves CDM fields without any use of N-body data or methods, using a Kolmogorov-Arnold network (KAN) to model the continuous displacement field for one-dimensional
halo collapse. Physical constraints derived from the Vlasov-Poisson equations are embedded directly into the loss function, enabling accurate
evolution beyond the first shell crossing. The trained model achieves sub-percent errors on the residuals even after seven shell crossings and matches N-body results while providing a resolution-free representation of the displacement field. In addition, displacement errors do not grow over time, a very interesting feature with respect to N-body methods. It can also reconstruct initial conditions through backward
evolution when sufficient final-state information is available. Although current runtimes exceed those of N-body methods, this framework offers a new route to high-fidelity CDM
evolution without particle discretisation, with prospects for extension to higher dimensions.
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Astrophysics of Galaxies
GLIMPSE-D: An Exotic Balmer-Jump Object at z=6.20? Revisiting Photometric Selection and the Cosmic Abundance of Pop III Galaxies
Seiji Fujimoto, Yoshihisa Asada, Rohan P. Naidu et al. (+19 more)
We present deep JWST/NIRSpec G395M spectroscopy of GLIMPSE-16043, a promising $z\sim6$ Pop III candidate originally identified through NIRCam photometry as having weak [OIII]$\lambda\lambda4959,5007$ emission. Our follow-up reveals clear [OIII] emission, ruling out a genuine zero-
metallicity nature. However, the combination of the measured line fluxes and photometry indicates that its spectral energy distribution requires an extraordinarily strong Balmer jump ($-1.66 \pm 0.47$ mag) and H$\alpha$ equivalent width ($3750\pm1800$ Å), features that cannot be reproduced by current
stellar+nebular or pure nebular photoionization models. The only models approaching the observations to almost within $1\sigma$ involve a hot ($T_{\rm eff}\!\simeq\!10^{4.7}$ K) single blackbody embedded in a low-$T_{\rm e}$ nebular environment, suggestive of scenarios such as a
tidal-disruption event or a microquasar with strong disk winds. This cautions that photometric Pop~III selections are vulnerable to contamination when the rest-frame optical continuum is undetected. Motivated by this, we refine the photometric Pop III selection criteria to exclude the locus of extreme Balmer-jump objects. The revised criteria also recover the recently reported spectroscopic candidate AMORE6, demonstrating that the updated selection preserves sensitivity to genuine Pop III-like sources while removing key contaminants. Applying the refined criteria across legacy survey fields and five newly released CANUCS
lensing cluster fields, we revisit the Pop III UV luminosity function and estimate the Pop III
cosmic star-formation rate density to be $\approx[10^{-6}$–$10^{-4}]$~$M_{\odot}$~yr$^{-1}$~cMpc$^{-3}$ at $z\simeq6$–7, falling in the range of current theoretical predictions.
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All authors Seiji Fujimoto, Yoshihisa Asada, Rohan P. Naidu, John Chisholm, Hakim Atek, Gabriel Brammer, Danielle A. Berg, Daniel Schaerer, Vasily Kokorev, Lukas J. Furtak, Johan Richard, Alessandra Venditti, Volker Bromm, Angela Adamo, Adelaide Claeyssens, Miroslava Dessauges-Zavadsky, Qinyue Fei, Tiger Yu-Yang Hsiao, Damien Korber, Julian B. Munoz, Richard Pan, Alberto Saldana-Lopez
Astrophysics of Galaxies
The Effect of a Non-universal Extinction Curve on the Wesenheit Function and Cepheid Distances
D. M. Skowron, M. L. Fouesneau, R. Drimmel et al. (+1 more)
The Wesenheit function is widely used to reduce the effects of interstellar reddening in distance measurements. Its construction, however, relies on the assumption of a universal extinction curve and on fixed values of the total-to-selective extinction ratio, Rv. Recent studies have shown that Rv varies significantly across the Milky Way and between different
galaxies, raising concerns about systematic biases in Wesenheit magnitudes and period-Wesenheit relations. In this work, we discuss the impact of non-universal extinction on Wesenheit indices by combining the Rv-dependent extinction curve with a grid of
stellar atmosphere models. We compute the integrated extinction in optical and near-infrared passbands, derive Rv-dependent R coefficients for multiple Wesenheit indices, and examine how changes in Rv propagate into Wesenheit magnitudes and Cepheid distances in our
Galaxy. We find that the R coefficients in the Wesenheit functions vary strongly with Rv. For classical Cepheids in the Milky Way disk, variations of Rv within the typical observed range (2.6-3.6) can lead to substantial differences in the Wesenheit function, reaching +-0.7 mag from the mean for the
Gaia-based Wesenheit index W_G and resulting in distance errors of almost 40%. Near-infrared Wesenheit indices are much less sensitive to Rv changes. Our results clearly show that accounting for variable Rv is essential when applying period-Wesenheit relations, particularly in the optical regime, or that near or mid infrared based distances should be used. While we present this effect for classical Cepheids, it applies to all pulsating
stars for which period-Wesenheit relations are used to infer distances.
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All authors D. M. Skowron, M. L. Fouesneau, R. Drimmel, S. Khanna
Astrophysics of Galaxies
The low-mass and structured stellar halo of M83 argues against a merger origin for its starburst and extended neutral hydrogen disk
Eric F. Bell, Benjamin Harmsen, Matthew Cosby et al. (+12 more)
A merger origin has been suggested for M83's massive, metal-rich extended HI disk and
nuclear starburst. We observe M83's
stellar halo to test this idea. We train nearest-neighbor
star-
galaxy separation on wide-area Subaru imaging with Hubble Space
Telescope data to map M83's
halo in resolved
stars. We find that M83 has an extended, very low density smooth
stellar halo of old and metal-poor [M/H]$\sim -1.15$ RGB
stars with a mass between 15 and 40 kpc of $\log_{10}M_{*,15-40,maj}/M_{\odot}=8.02\pm0.10$. In addition to M83's well-known Northern Stream, our ground-based Subaru imaging reveals a new stream to M83's south, which modeling suggests could be its trailing arm. The combined stream masses are $\log_{10}M_{stream}/M_{\odot}=7.93\pm0.10$, with
metallicity [M/H]$= -1.0\pm0.2$. The stream progenitor was only recently accreted, as its
stellar populations suggest that it formed
stars until $2.1\pm1.3$ Gyr ago. M83 lies on the
stellar halo mass-
metallicity correlation seen for other Milky Way mass
galaxies, albeit with low
stellar halo mass. We infer a total accreted mass of $\log_{10}M_{*,accreted}/M_{\odot}=8.78^{+0.22}_{-0.28}$, with the most massive past merger having $\log_{10}M_{*,dom}/M_{\odot}=8.5\pm0.3$. We identify plausible M83 analogs in TNG-50 with similar
stellar halos, finding that while a recent
accretion can create a prominent
stellar stream, such accretions do not trigger starburst activity, nor do they deliver enough gas to form M83's extended Hi disk. We conclude that other non-merger mechanisms, such as secular
evolution or
accretion of gas from the IGM, are likely to be responsible for M83's remarkable properties.
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All authors Eric F. Bell, Benjamin Harmsen, Matthew Cosby, Paul A. Price, Sarah Pearson, Antonela Monachesi, Roelof S. de Jong, Richard D'Souza, Katya Gozman, Jacob Nibauer, Michael P. Busch, Jeremy Bailin, Benne W. Holwerda, In Sung Jang, Adam Smercina
Solar and Stellar Astrophysics
The Impact of Initial Mass Dependent Convective Boundary Mixing on the Structure and Fates of Massive Stars
Emily E. Whitehead, Raphael Hirschi, Vishnu Varma et al. (+4 more)
While convection has been known to play a key role in
stars for many decades, its implementation in one-dimensional
stellar evolution codes still represents a major uncertainty today. The purpose of this work is to investigate the impact of initial mass dependent convective boundary mixing (CBM), often referred to as overshooting, on the frequency and type of
nuclear burning shell interactions that occur in low
metallicity massive
stars and the subsequent effect on their fates. Two grids of models were calculated using the Modules for Experiments in
Stellar Astrophysics (MESA) code and a 22-isotope
nuclear network, each with a different strength of CBM applied. One grid uses the typical CBM value for diffusive overshooting used in literature whereas the other grid uses CBM values guided by the results of 3D convection simulations. Interactions between the carbon, neon and oxygen shells (C-Ne-O) are common throughout both grids. The higher CBM grid also exhibits more frequent H-He and He-C interactions at lower initial masses than in the lower CBM grid. Several models also undergo multiple interaction events during
evolution. While future work will be needed to fully assess the impact of the new CBM and the interactions it leads to, one expects interesting effects like unusual nucleosynthesis including more common or enhanced i- and gamma-process nucleosynthesis. Furthermore, SN precursors and a significant change to the pre-SN structure are also expected, with many models not having the commonly expected onion-ring like structure and having a different explosion probability.
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All authors Emily E. Whitehead, Raphael Hirschi, Vishnu Varma, Bernhard Mueller, Federico Rizzuti, Cyril Georgy, W.D. Arnett
Astrophysics of Galaxies
Looking into the faintEst WIth MUSE (LEWIS): on the nature of ultra-diffuse galaxies in the Hydra I cluster. V. Integrated stellar population properties
Goran Doll, Chiara Buttitta, Enrichetta Iodice et al. (+19 more)
Context: This paper presents new results from the ESO Large Programme Looking into the faintEst WIth MUSE (LEWIS). The sample consists of low-surface brightness (LSB) and ultra-diffuse
galaxies (UDGs) located inside 0.4 R$_{vir}$ of the Hydra I cluster. Integral field spectroscopy is acquired for 24
galaxies with the MUSE spectrograph mounted on the Very Large
Telescope (VLT). Aims: Our main objective is to analyse possible correlations between the environment and the integrated
stellar population properties. Methods: For each
galaxy, we extract the 1D stacked spectrum in an aperture of one effective radius and adopt previously published
stellar kinematics to derive age,
metallicity and [Mg/Fe] through a full spectral fitting technique. Results: We find that the analysed LEWIS sample has a mean
metallicity of [M/H] = -0.9 dex, a mean age of 10 Gyr, comparable to results of UDGs in other clusters. According to the projected phase-space,
galaxies can be classified into two groups: early infallers, with slightly higher
metallicities ([M/H]$_{early} = -0.8 \pm 0.1$ dex), and late infallers, with slightly lower values ([M/H]$_{late} = -1.0 \pm 0.1$ dex). Two types of
galaxies are found in the early-infall region: half of them have
metallicities consistent with the
dwarf mass-
metallicity relation, while the other half show higher values. Moreover, they display different timescales for
stellar mass assembly. Conclusions: We identified different classes of UDGs in the Hydra I cluster, which suggest different formation mechanisms taking place. Almost all of the UDGs and LSBs in the cluster are consistent with the puffed-up
dwarf formation scenario, having
dwarf-like
metallicities and being consistent with the
dwarf mass-
metallicity relation. In the innermost regions of the cluster, where metal-richer UDGs lie,
tidal or environmental effects might have influenced their formation and
evolution.
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All authors Goran Doll, Chiara Buttitta, Enrichetta Iodice, Anna Ferré-Mateu, Jesus Falcòn-Barroso, Ignacio Martìn-Navarro, Maurizio Paolillo, Luca Rossi, Duncan A. Forbes, Chiara Spiniello, Johanna Hartke, Marco Gullieuszik, Magda Arnaboldi, Michele Cantiello, Enrico Maria Corsini, Giuseppe D'Ago, Michael Hilker, Antonio La Marca, Steffen Mieske, Marco Mirabile, Marina Rejkuba, Marilena Spavone
Cosmology and Nongalactic Astrophysics
The Domain Adaptation problem in photometric redshift estimation: a solution applied to the HSC Survey
M. Treyer, R. Ait-Ouahmed, S. Arnouts et al. (+5 more)
The multi-band HSC-CLAUDS survey comprises several sky regions with varying observing conditions, only one of which, the COSMOS Ultra Deep Field (UDF), offers extensive
redshift coverage. We aim to exploit a complete sample of labeled
galaxies from the COSMOS UDF at i<25 (z<~5) to train a convolutional neural network (CNN) and infer more accurate photometric
redshifts in the other regions than those currently available from SED-fitting methods. To address the severe domain mismatch problem we observed when applying the trained CNN to regions other than the COSMOS UDF, we developed an unsupervised
adversarial domain adaptation network that we grafted onto the CNN. The method is validated by three tests: the predicted
redshifts are compared to the spectroscopic
redshifts that are available for limited samples of mostly bright
galaxies; the predicted
redshift distributions of the entire
galaxy population of a given field in several intervals of magnitude are compared to those of the COSMOS UDF, assumed to be representative; the
redshifts predicted for a sample of
galaxies selected by narrow-band filter observations sensitive to [OII] emitters at z~1.47 are compared to those of confirmed [OII] emission line
galaxies. The results show successful domain adaptation: the network is able to transfer its
redshift classification capability learnt from the COSMOS UDF to other regions of HSC-CLAUDS. Accuracy varies depending on magnitude and
redshift, following that of the labels we used, but far exceeds that of currently available photometric
redshifts. The catalogs of CNN
redshifts we inferred for the XMM, DEEP2 and ELAIS fields and for the remaining COSMOS region (~4 million sources in total at i<25) are made public.
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All authors M. Treyer, R. Ait-Ouahmed, S. Arnouts, J. Pasquet, E. Bertin, G. Desprez, V. Picouet, M. Sawicki
Astrophysics of Galaxies
A Spatially Resolved Evolutionary Sequence of Multi-wavelength AGN Host Galaxies
Gaoxiang Jin, Guinevere Kauffmann, Y. Sophia Dai et al. (+2 more)
We study the spatially resolved
star formation, gas ionisation, and
outflow properties of 1813 active
galactic nuclei (AGNs) from the MaNGA survey, which we classify into infrared (IR), broad-line (BL), narrow-line (NL), and
radio (RD) AGNs based on their mid-infrared colours, optical spectra, and/or
radio photometry. We also provide estimations of AGN power at different wavelengths. AGN incidence is found to increase with
stellar mass following a power-law, with the high-mass end dominated by RDAGNs and the low-mass end dominated by NLAGNs. Compared to their mass-matched non-AGN counterparts, we find that IRAGNs, BLAGNs, and NLAGNs on average show enhanced specific
star formation rates, younger
stellar populations, and harder ionisation towards the centre. RDAGNs, in contrast, show radial profiles similar to quiescent
galaxies. [OIII]
outflows are more common and stronger in BL/IRAGNs, while RDAGNs on average show no
outflow features. The
outflow incidence increases with [OIII] luminosity, and the features in BL/IRAGNs on average extend to ~2 kpc from the
nuclei. We further discuss a possible evolutionary sequence of AGNs and their host
galaxies, where AGNs with strong emission lines or
dust tori are present in
star-forming
galaxies. Later, young compact
radio jets emerge, the host
galaxies gradually quench, and the AGN hosts eventually evolve into globally quiescent systems with larger
radio jets that prevent further gas cooling.
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All authors Gaoxiang Jin, Guinevere Kauffmann, Y. Sophia Dai, Martin J. Hardcastle, Bohan Yue
Instrumentation and Methods for Astrophysics
Nolan Smyth, Laurence Perreault-Levasseur and Yashar Hezaveh
The search for free-floating
planets (FFPs) is a key science driver for upcoming microlensing surveys like the Nancy Grace Roman
Galactic Exoplanet Survey. These rogue worlds are typically detected via short-duration microlensing events, the characterization of which often requires analyzing noisy, irregularly-sampled observations. We present a pipeline for this task using simulation-based inference. We use a
Transformer encoder to learn a compressed summary representation of the raw time-series data, which in turn conditions a neural posterior
estimator. We demonstrate that our method produces accurate and well-calibrated posteriors over three orders of magnitude faster than traditional methods. We also demonstrate its performance on KMT-BLG-2019-2073, a short-duration FFP candidate event.
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Cosmology and Nongalactic Astrophysics
One-loop power spectrum corrections in interacting dark energy cosmologies
Emanuelly Silva, Gabriel Hartmann and Rafael C. Nunes
Interacting Dark Energy (IDE) models offer a promising avenue to explore possible exchanges of energy and momentum between dark matter and dark energy, providing a dynamical extension of the standard $\Lambda$CDM paradigm. Such interactions modify the growth of
cosmic structures, imprinting distinctive signatures on the matter power spectrum that can be tested through large-scale structure (LSS) observations. In this work, we compute the one-loop corrections to the matter power spectrum in IDE models. We then reinterpret these results within the standard framework of the Effective Field Theory of Large-Scale Structure (EFTofLSS), which provides a consistent description of mildly non-linear scales and allows for reliable comparisons with observational data. We investigate two commonly studied forms of the coupling function, $Q$, namely $Q = \xi \mathcal{H} \rho_{\rm m}$ and $Q = \xi \mathcal{H} \rho_{\rm DE}$, and introduce a novel interaction term, $Q = \Gamma \, \rho_{\rm m} \, \rho_{\rm DE} \, \theta_{\rm m}$, characterized by the non-linear coupling constant $\Gamma$, which links the interaction strength to the velocity divergence of dark matter. This coupling function is proposed to isolate the effects solely of the IDE model on mildly non-linear scales. Using Full-Shape (FS) measurements of the
galaxy power spectrum from BOSS DR12, we constrain the interaction rate $\Gamma$, the cosmological parameters, and the bias parameters. We find $\Gamma = 0.0039 \pm 0.0082$, which is highly consistent with the $\Lambda$CDM model. This work opens the possibility of testing IDE models at mildly non-linear scales, potentially providing new insights for this class of models beyond the standard $\Lambda$CDM framework.
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Astrophysics of Galaxies
Rapid sinking and efficient mergers of supermassive black holes in compact high-redshift galaxies
Atte Keitaanranta, Peter H. Johansson, Alexander Rawlings et al. (+5 more)
We present a cosmological zoom-in simulation targeting the high
redshift compact progenitor phase of massive
galaxies, with the most massive
galaxy reaching a
stellar mass of $M_{\star}=8.5\times 10^{10} \ M_{\odot}$ at $z=5$. The dynamics of supermassive black holes (SMBHs) is modelled from seeding down to their coalescence at sub-parsec scales due to gravitational wave (GW) emission by utilising a new version of the KETJU code, which combines regularised integration of sufficiently massive SMBHs with a dynamical friction subgrid model for lower-mass SMBHs. All nine massive
galaxies included in this study go through a gas-dominated phase of early compaction in the
redshift range of $z\sim 7-9$, starting at
stellar masses of $M_\star\gtrsim 10^8\ \mathrm{M}_\odot$ and ending at a few times $M_{\star}\sim 10^9\ \mathrm{M}_\odot$. The sizes, masses and broad band fluxes of these compact systems are in general agreement with the population of systems observed with JWST known as `Little Red Dots'. In the compact phase, the
stellar and SMBH masses grow rapidly, leading to a sharp decline in the central gas fractions. The outer regions, however, remain relatively gas-rich, leading to subsequent off-centre
star formation and size growth. Due to the very high central
stellar densities ($\rho_{\star}\gtrsim 10^{13}\,\mathrm{M_\odot/kpc^3}$), the SMBHs merge rapidly, typically just $\sim 4-35\ \mathrm{Myr}$ after the SMBH binaries have become bound. Combining KETJU with the phenomenological PhenomD model resolves the complete
evolution of the GW emission from SMBH binaries through the
Pulsar Timing Array frequency waveband up to the final few orbits that produce GWs observable with the future LISA mission.
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All authors Atte Keitaanranta, Peter H. Johansson, Alexander Rawlings, Toni Tuominen, Antti Rantala, Thorsten Naab, Shihong Liao, Bastián Reinoso
Astrophysics of Galaxies
The multiphase interstellar medium as a common origin for magnetic misalignment and TB parity violation
Andrea Bracco, Ari J. Cukierman, Raphael Skalidis et al. (+1 more)
We present an original data analysis and a physical model that provide new insights into the origin of, and relationship between, two observables of the dusty, polarized
Galaxy at intermediate and high latitudes: (i) the misalignment between HI filamentary structures and
magnetic fields and (ii) the positive $TB$ correlation measured in Planck data suggesting parity violation in the interstellar medium (ISM). We confirm an observational link between the two effects and find that both are predominantly produced at large angular scales ($\geq 10^\circ$, multipoles $\ell \leq 20$) with a significantly stronger signal in the northern hemisphere. We propose a model in which filaments and
magnetic fields appear misaligned in projection because they are sourced by cold and warm gas phases distributed in different proportions in the
Solar neighborhood, from the wall of the Local Bubble to larger distances. These projection effects at large angular scales can produce coherent signatures that propagate to smaller scales in power spectra without invoking local, small-scale filament misalignment. Within this frame, HI filaments remain statistically aligned with the
magnetic field in 3D, although with a projected scatter of tens of degrees that requires further investigation. The multiphase, geometrical model presented in this work is supported by Planck polarization data at 30 GHz, where synchrotron radiation dominates, and at 217 and 353 GHz, where
dust emission dominates. Our analysis also incorporates starlight polarization measurements. The model introduced here suggests a new interpretation of two unexplained observables and emphasizes the role of the large-scale magnetized ISM in shaping polarized
Galactic emission, which has important implications for both
Galactic astrophysics and cosmological foreground characterization.
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All authors Andrea Bracco, Ari J. Cukierman, Raphael Skalidis, François Boulanger
Cosmology and Nongalactic Astrophysics
Dark sector interactions in the $w \rightarrow -1$ limit: velocity locking in pure momentum exchange models
Nathan Cruickshank, Robert Crittenden, Kazuya Koyama et al. (+1 more)
Models of interacting dark energy (DE) and dark matter (DM) involving pure momentum exchange are a promising avenue for resolving cosmological tensions. However, the behaviour of these interactions in the theoretically challenging limit where the DE equation of state, $w$, approaches $-1$ is not fully understood. We demonstrate that a generic feature of these models is a $w$-dependent velocity-locking mechanism, which systematically shifts the onset of matter power spectrum suppression to smaller scales as $w \rightarrow -1$. The suppression magnitude depends on the difference in fluid velocities. In this limit, however, the interaction's drag dominates over the DE pressure support and causes the DE velocity to track that of the DM fluid at larger scales. This mechanism provides a physical explanation for the weaker constraints found in the literature when $w\approx-1$ in models where the interaction strength does not explicitly depend on $w$. We also demonstrate that the common approximation of neglecting DE perturbations ($\delta_{\mathrm{DE}}=\theta_{\mathrm{DE}}=0$) fails in this limit. By artificially increasing the velocity difference between the fluids, this simplification incorrectly removes the $w$-dependent velocity-locking mechanism and erases the shift in power spectrum suppression to smaller scales. This leads to an overestimation of the constraining power of cosmological data on the interaction strength.
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All authors Nathan Cruickshank, Robert Crittenden, Kazuya Koyama, Marco Bruni
Instrumentation and Methods for Astrophysics
UK White Paper on Magnetic Reconnection
Alexander J. B. Russell, James A. McLaughlin, Philippa Browning et al. (+25 more)
Magnetic reconnection powers explosive releases of
magnetic energy, heating and particle acceleration throughout the
plasma universe. Knowledge of this universal process is vital to understanding the Heliosphere, as it plays a key role in
solar flares, coronal mass ejections, coronal heating,
solar wind acceleration, geomagnetic storms, and interactions between the
solar wind and planetary magnetospheres. As such, reconnection underpins multiple science objectives of multiple future space missions. The UK plays a leading role in this international field, through a combination of in situ measurements from Earth's magnetosphere and the
solar wind, observations of the
solar corona and chromosphere, and world-class numerical simulations and theory. This white paper identifies: Nine priority science objectives for reconnection research in the next decade; Recommendations to guide investment in theory, simulations and infrastructure; Mission priorities and required measurements to ensure the UK maintains and improves its world-class credentials in reconnection science.
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All authors Alexander J. B. Russell, James A. McLaughlin, Philippa Browning, Jennifer Carter, Luca Franci, Heli Hietala, Andrew Hillier, Gunnar Hornig, David MacTaggart, Sarah Matthews, James McKevitt, Eric Priest, Jack Reid, Ben Snow, Julia Stawarz, Anthony Yeates, Jeffersson Andres Agudelo Rueda, William Bate, Giulio Del Zanna, Jonathan Eastwood, Lucie Green, Anshu Kumari, Mike Lockwood, Thomas Neukirch, David Pontin, Andy Smith, Maria-Theresia Walach, Peter Wyper