Peer Revenue An exchange of ideas

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Astrophysics

astro-ph Watch Astrophysics

Saturday 27 June

Solar and Stellar Astrophysics

Center-to-limb variations of solar active regions: Observations of spots, faculae, and network in the 6173 Å\ continuum

A.G.M. Pietrow, S. Sumra, D.J.M. Petit dit de la Roche et al. (+3 more)

Accurate modeling of stellar active regions (ARs) remains a major bottleneck for radial-velocity and transmission-spectroscopy studies aimed at finding Earth-like planets. While much effort has been devoted to AR modeling, their center-to-limb variations (CLV) have been largely overlooked. We take a step toward remedying this by measuring the CLV of the 6173 Å continuum intensity for sunspots (the whole spot, and separate umbrae and penumbrae), faculae, network, and the quiet Sun using the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). This study is based on four simple round $\alpha$-sunspots and their surroundings, as well as one strongly evolving region. After correcting for stray light, we find that relative to the quiet Sun, all components except for the umbra display reduced darkening towards the limb. Additionally, strongly evolving active regions do not appear to display significantly altered CLV profiles compared to stable active regions. Faculae and network show contrast enhancements that peak near $\mu \approx 0.3$ before declining toward the limb, reaching maxima of approximately 4% and 2% respectively in contrast excess relative to the quiet Sun, while the spot-to-quiet-Sun contrast rises to approximately 15% near the limb. For both types of AR, this change in CLV behavior near the limb is likely related to the three-dimensional structure of the active regions and the rapidly changing viewing geometry. This behavior is not captured by synthetic CLVs based on PHOENIX and ATLAS model atmospheres with solar values and a different effective temperature, underscoring the need for more realistic treatments of stellar activity.
Read the full abstract

All authors A.G.M. Pietrow, S. Sumra, D.J.M. Petit dit de la Roche, E. J. Lößnitz, C. Denker, M. Aßmus

Instrumentation and Methods for Astrophysics

Energy estimation of cosmic rays by air shower radio signals

Fateme Latifian and Gohar Rastegarzadeh

We present a method for reconstructing the primary energy of cosmic ray air showers using radio emission. The approach is based on CoREAS simulations performed for both the SURA experiment and a dense reference array of antennas. By comparing the simulated electric field intensity from the dense array with that obtained for the SURA configuration, we derive a scale factor (Ci j). This scale factor exhibits a correlation with the primary energy, decreasing as energy increases. Unlike previous approaches employed by various experiments, our technique shows limited sensitivity to the shower core location. Even for the farthest core positions allowed by the array, the scale factor remains effectively independent of the core location. We also examined the accuracy and reliability of the reconstruction method. Finally, we reconstructed the primary energy of cosmic rays using our method with a maximum error of about 11% in our simulation tests.
Read the full abstract

Astrophysics of Galaxies

Stellar Surface Density Modulates MgII Cool-gas Outflow Absorption in DESI Star-forming Galaxies

Yu Rong and Shihong Liu

Galaxy outflows are usually ordered by stellar mass and star-formation rate (SFR), but the same feedback budget may couple differently to gas in diffuse and compact galaxies. We use Dark Energy Spectroscopic Instrument (DESI) Data Release 1 stacked spectra of massive star-forming galaxies at $0.35<z<1.0$ to test whether stellar surface density, $\Sigma_\star=M_\star/(2\pi R_e^2)$, is an independent empirical coordinate of down-the-barrel singly ionized magnesium (MgII) cool-gas absorption. In AGN-clean samples matched in stellar mass, and in a stricter sample matched in both stellar mass and a Balmer-line SFR proxy, the MgII outflow equivalent width (EW) rises monotonically with $\Sigma_\star$ in every redshift bin. From the lowest to highest $\Sigma_\star$ tertile, EW increases by 0.37-0.61 Angstrom, while the absolute outflow velocity changes only weakly. DESI therefore shows that cool-gas outflow strength in massive star-forming galaxies is not set only by how much stellar mass or star formation a galaxy has, but also by how tightly the galaxy is built. The structural dependence points to changes in the absorbing velocity distribution and/or the effective covering fraction of cool outflowing gas.
Read the full abstract

Cosmology and Nongalactic Astrophysics

Cosmological structure growth in energy-momentum squared gravity

Alvaro de la Cruz-Dombriz, Peter K. S. Dunsby and Payel Sarkar

We investigate the cosmological evolution of matter perturbations in the modified gravity model $f(R,T^2)$, where $T^2=T_{\mu\nu}T^{\mu\nu}$ denotes the quadratic contraction of the energy–momentum tensor. Using the gauge-invariant 1+3 covariant formalism, we study the evolution of the matter density contrast and analyze several growth observables, including the growth factor, the growth index, and the weighted growth rate $f\sigma_8$. We consider representative values $n=1/2$ and $n=1/4$, which probe different regimes of the matter–geometry coupling. We show that the growth index decreases with increasing redshift and approaches the standard matter-dominated behavior at early times, while mild scale-dependent deviations from the $\Lambda$CDM model emerge at late times. The model predicts small departures from General Relativity for $n=1/4$, whereas stronger deviations appear for $n=1/2$ and larger values of the coupling parameter $\alpha$. We further compare the theoretical predictions for $f\sigma_8$ with current observational data and find that viable parameter choices remain within the observational $\pm2\sigma$ bounds. These results indicate that $f(R,T^2)$ gravity can provide a viable description of late-time cosmic acceleration and large-scale structure formation while remaining consistent with current growth observations.
Read the full abstract

Instrumentation and Methods for Astrophysics

TOA_SP: A Multi-Strategy Framework for Single-Pulse Timing

Songbo Zhang and Xuan Yang

Precision pulsar timing typically relies on the stability of average pulse profiles, enabling time-of-arrival (TOA) estimation through template cross-correlation. This assumption breaks down for highly variable radio sources such as Rotating Radio Transients (RRATs) and fast radio bursts (FRBs), where individual pulses could exhibit strong variability in morphology and amplitude, and no single averaged profile may represent the underlying emission process. We present toa_sp, an open-source Python package for extracting TOAs directly from PSRFITS search-mode data without requiring profile folding into a stable template. The framework implements a suite of complementary single-pulse timing strategies, including parametric profile fitting, non-parametric estimators, and adaptive sub-band and time-resolution optimisation, together with empirical diagnostics for assessing model consistency. We apply toa_sp to 688 single pulses from a 3-hour FAST observation of RRAT~J1913+1330. The resulting TOAs residual achieve a weighted RMS residual of 1.33\,ms, a 24% improvement over a standard template-based PSRCHIVE pipeline, while retaining all pulses without statistical outlier rejection. A set of bright FRB 20220529 bursts provides a controlled test of the framework across regimes of increasing pulse complexity, revealing frequency-dependent substructure not captured by band-integrated profiles. We introduce an empirical convergence diagnostic that identifies well-constrained pulses and guides the transition between parametric and non-parametric regimes. Full multi-strategy processing of 688 pulses requires approximately 7.6\,s per pulse on a 10-thread CPU. The package is publicly available via pip install toa_sp.
Read the full abstract

Cosmology and Nongalactic Astrophysics

Cosmological inference from the eBOSS QSO full-shape analysis with optimal redshift weights

Xiaoyong Mu, Zhuo-Heng Li, Wentao Luo et al. (+2 more)

We present a full-shape power-spectrum analysis of the eBOSS DR16 quasar sample with optimal redshift weights. The DR16 QSO catalog contains 343,708 quasars over $0.8<z<2.2$, a redshift interval broad enough to contain useful light-cone evolution but not naturally captured by a single effective-redshift measurement. We construct Karhunen–Loève weights for the parameters of interest and measure the resulting monopole and quadrupole with a cross-correlation estimator, which remains well defined for sign-changing weights. The theoretical spectra are convolved with the measured Fourier-space survey-window kernels for each Galactic cap and weighting scheme, and both the covariance matrix and the end-to-end validation are based on 1000 EZ light-cone mock catalogs. In $\Lambda$CDM, the redshift-weighted and standard analyses give consistent constraints, as expected from the near-standard effective redshifts of the weights targeting $h$, $\Omega_{\rm m}$, and $A_s$. In the Chevallier–Polarski–Linder (CPL) model, the redshift-weighted DR16 analysis reduces the marginalized uncertainties on $H_0$, $\sigma_8$, and $w_0$ by $43.3\%$, $19.7\%$, and $20.5\%$, respectively, and turns the standard one-sided constraint on $w_a$ into a bounded posterior, $w_a=-0.98^{+1.0}_{-1.3}$. The gain is therefore concentrated where the model contains genuine redshift evolution, demonstrating that optimal redshift weighting can recover tomographic information from a wide QSO light cone while keeping the full-shape data vector compact.
Read the full abstract

All authors Xiaoyong Mu, Zhuo-Heng Li, Wentao Luo, Yuting Wang, Gong-Bo Zhao

Solar and Stellar Astrophysics

Radio Diagnostics of Particle Acceleration in Solar Flares with SKAO Observations

Rohit Sharma, Marina Battaglia, Sijie Yu et al. (+3 more)

Particle acceleration is a fundamental astrophysical process occurring across diverse systems and scales, producing electromagnetic emission across all wavelengths. Radio bursts from astrophysical systems like active galaxy jets, solar flares, pulsars, etc., provide a probe into the emission mechanism and particle acceleration processes. Among all astrophysical phenomena, magnetically driven solar flares provide unique diagnostics of nonthermal particles due to the advantage of multiple spatial-temporal and spectral measurements. The subsequent emitted radiation spans various sections of the radio spectrum. Based on brightness temperature and spectrum, one can distinguish between bright plasma emission or 'nonthermal' emission. Nonthermal radio bursts in meter and microwave bands arise from suprathermal particles, while the surrounding plasma produces fainter thermal emission. High spatial-temporal studies along with polarimetry will enable tracking of electron beams in evolving magnetic fields and constrain coronal properties such as magnetic strength, density, and temperature. Fine spectral structures from gyrosynchrotron bursts allow mapping of magnetic fields along acceleration tracks. However, emissions from the more numerous, weaker particle populations remain difficult to observe. Particles in solar flares follow a power-law energy distribution, with weaker populations being more common. The Square Kilometre Array Observatory (SKAO) will provide high-fidelity data that will enable detailed characterisation of these populations, statistical studies of particle beams, and insights into their interaction with magnetic topologies. Its high-resolution (especially SKA-Mid) and multi-wavelength synergy (EUV, X-rays) will refine diagnostics of coronal and acceleration-region properties. This chapter reviews particle acceleration models and expected advances from SKAO.
Read the full abstract

All authors Rohit Sharma, Marina Battaglia, Sijie Yu, Hamish Reid, Eduard Kontar, Bin Chen

Astrophysics of Galaxies

Low cosmic-ray ionisation at parsec scales in G035.39-00.33

Andrea Socci, Ashley Barnes, Jaime Pineda et al. (+11 more)

Cosmic rays (CRs) regulate the chemical evolution of the gas and its coupling to the magnetic field in the densest and coldest regions of the interstellar medium (ISM). However, the CR ionisation rate of H$_2$ ($\zeta_2$) is one of the most debated parameters characterising molecular clouds due to the uncertainties in its estimation. We developed a new analytical framework based on the chemistry of N$_2$H$^+$, N$_2$D$^+$ and DCO$^+$ to overcome observational limitations in current estimates of $\zeta_2$ and to probe the latter and the electron fraction, $x(e)$, in the gas across multiple density regimes. We applied this method towards the parsec-scale filament of the infrared dark cloud (IRDC) G035.39-00.33 with new observations from the NOrthern Extended Array (NOEMA) at a resolution of $3''$ (or $\sim9000$ au). Ancillary observations of C$^{18}$O complete this survey to measure $x(e)$ and $\zeta_2$ in G035.39-00.33. CO depletion is widespread in G035.39-00.33 with factors, $f_\mathrm{D}$, positively correlated with column and number densities of H$_2$ in the cloud. The deuterium fractions ($R_\mathrm{D}$) are enhanced towards these same sites in which the corresponding electron fraction values cluster below $\lesssim10^{-8}$. $\zeta_2$ varies by three orders of magnitude in G035.39-00.33 ($\sim10^{-18}-10^{-15}$ s$^{-1}$) with a median of $\sim2.3\times10^{-18}$ s$^{-1}$, consistent with those reported for other IRDCs and giant filaments, but on average lower than the typical $\zeta_2$ for the ISM. $\zeta_2$ shows a functional dependence on $N(\mathrm{H_2})$, but with absolute values lower compared to those predicted by theoretical models. This behaviour suggests the presence of an overall attenuation of the CR flux taking place in G035.39-00.33. The CR flux appears to be reduced by the change in magnetic field strength and morphology previously reported in the region.
Read the full abstract

All authors Andrea Socci, Ashley Barnes, Jaime Pineda, Olli Sipilä, Caroline Gieser, P. Caselli, Alvaro Hacar, Giuliana Cosentino, Chi-Yan Law, Morgan T. Owen, Prasanta Gorai, Francesco Fontani, Isazkun Jiménez-Serra, Jonathan C. Tan

Astrophysics of Galaxies

Radio Galaxies and Jet Duty Cycles

M. J. Hardcastle, C. Konar, S. Dutta et al. (+10 more)

Radio-luminous active galactic nuclei, or radio galaxies, are the brightest population of objects in the extragalactic radio sky and will be seen in large numbers in essentially every SKA observation. Despite having been studied for more than seventy years, some aspects of radio galaxy physics are still poorly understood, and the SKA will shed light on this by enabling the generation of very large samples of high-resolution, sensitive, broad-band images of radio galaxies, allowing us to probe, for example, regions of particle acceleration, spectral ageing, and the magnetic field structures both internal and external to the radio lobes. A key feature of the radio galaxy population is that observations of extended sources probe the past history, and thus the duty cycles, of accretion onto the central supermassive black hole, and we discuss ways in which the SKA will improve our understanding of episodic and dying radio galaxies in particular.}
Read the full abstract

All authors M. J. Hardcastle, C. Konar, S. Dutta, D. V. Lal, R. D. Baldi, M. Brienza, A. Hota, M. Kunert-Bajraszewska, B. Mingo, M. Pandey-Pommier, K. Rubinur, S. Shabala, E. Vardoulaki

Instrumentation and Methods for Astrophysics

Enhancing VLBI Capability with the SKA-Mid and the Jingdong 120-m Radio Telescope

Wen Chen, Jun Yang, Zhixuan Li et al. (+2 more)

The Jingdong Radio Telescope (JRT) is a 120-meter fully steerable radio telescope currently under construction in Jingdong County, Yunnan Province, China. Located at a relatively low latitude (24.5 degree), the JRT will enable observations of nearly 90% of the sky. Equipped with two broadband single-pixel receivers covering 1-8 GHz and 6-18 GHz, and a powerful digital backend, the telescope will support single-dish studies of various radio sources-particularly millisecond pulsars for enhancing the detection of nanohertz gravitational waves. In addition to single-dish capabilities, the JRT is expected to contribute approximately 800 hours annually to international Very Long Baseline Interferometry (VLBI) observations via a standard VLBI backend. When operating in conjunction with the phased-up SKA-Mid, the JRT will significantly enhance the technical and scientific capabilities of existing VLBI networks. This paper presents a comprehensive overview of the JRT's VLBI module and explores its potential to improve joint VLBI observations with current VLBI networks. Our analysis suggests that coordinated VLBI observations involving both the SKA-Mid and the JRT have the potential to significantly advance the field. For early sciences, we also highlight a few highly promising scientific cases, e.g. measuring the distance to PSR J0437-4715 with <1 ly accuracy and exploring jet formation with an event-horizon-scale resolution in M60*.
Read the full abstract

All authors Wen Chen, Jun Yang, Zhixuan Li, Yingjie Li, Niu Liu

Instrumentation and Methods for Astrophysics

VLBI-Enabled Localization of Continuous GW Sources

Keitaro Takahashi, Takuya Akahori, Kenta Fujisawa et al. (+8 more)

Pulsar timing arrays (PTAs) are opening the nanohertz gravitational-wave (GW) band by timing millisecond pulsars (MSPs) to target signals from supermassive black hole binaries (SMBHBs). Beyond evidence for a stochastic background, a central SKA-era objective is detecting individual continuous-wave (CW) sources. The scientific payoff hinges on localization: conventional PTA searches yield uncertainties of tens-hundreds of deg$^2$, too large to identify a unique host, obtain a redshift, infer intrinsic masses, or pursue electromagnetic counterparts. This limitation is chiefly geometric: the CW response includes Earth and pulsar terms, and poorly known pulsar distances make the pulsar-term phase a free parameter that degrades triangulation. If distances to a few MSPs are known to better than a GW wavelength ($\sim$ 1 pc), these phases are fixed and localization improves by orders of magnitude. Simulations indicate that with sub-parsec distances for a handful of nearby MSPs, the uncertainty can shrink to $\sim 10^{-3}$ deg$^2$ (arcminute scale), enabling unique host association and multi-messenger follow-up. Achieving such distances requires $\sim$ 10 $\mu$arcsec parallaxes for MSPs within a few hundred parsecs, a precision now approached with Very Long Baseline Interferometry (VLBI) and expected to become practical with phased-array SKA1-Mid operating as a sensitive VLBI element. SKA1's multi-beam, multi-calibrator astrometry will provide the independent distance priors needed for PTAs to localize nanohertz GW sources and measure SMBHB parameters and environments. We assess VLBI's role in PTA CW searches and propose a concrete SKA1-Mid observing strategy for nearby MSPs to deliver the required sub-parsec distances.
Read the full abstract

All authors Keitaro Takahashi, Takuya Akahori, Kenta Fujisawa, Hiroshi Imai, Hajime Kita, Hideyuki Kobayashi, Hiroaki Misawa, Kotaro Niinuma, Tomoaki Oyama, Kazuhiro Takefuji, Fuminori Tsuchiya

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Gravitational waves from graviton bremsstrahlung in scalar leptoquark decays

Qian-Jiu Wang, Hua Tong and Zhao-Huan Yu

We study the stochastic gravitational wave background originated from graviton bremsstrahlung in decays of scalar leptoquarks, which are colored scalar bosons simultaneously coupling to a quark and a lepton. We take the scalar leptoquarks in the $\mathrm{SU}(5)$ grand unified theory as a concrete example. Stringent experimental bounds on proton decay force these particles to be superheavy, which in turn renders their graviton bremsstrahlung, induced by quantum gravity effects, less suppressed. By solving the relevant Boltzmann equation, we trace the evolution of the scalar leptoquark number density in the early universe and use it to compute the resulting gravitational wave spectrum. We find that high-frequency gravitational wave detectors employing resonant cavity techniques offer a promising means to probe such signals.
Read the full abstract

Friday 26 June

Instrumentation and Methods for Astrophysics

GOATS: The next generation software infrastructure for time-domain astronomy at Gemini/NOIRLab. Application to alerts from Vera C. Rubin Observatory's Legacy Survey of Space and Time

Monika Soraisam, Louis Avner, Miguel Gómez et al. (+38 more)

Time-domain and multimessenger astronomy (MMA/TDA) targets demand rapid-response follow-up observations. In many cases, it is the only way to make discoveries and advance our understanding of the astrophysical phenomena, for example, kilonovae accompanying gravitational waves from compact object mergers, shock breakout in supernovae, prompt emission from GRBs, etc. Presently the MMA/TDA follow-up workflow requires wrangling disparate software packages and user interfaces. We present an end-to-end software tool for the community, the Gemini Observation and Analysis of Targets System (GOATS), which unifies and simplifies the workflow, particularly for Gemini follow-up observations. GOATS achieves this by integrating services from Gemini Observatory and its parent organization, NSF NOIRLab. From a single platform, GOATS enables enhanced target selection via NOIRLab's ANTARES alert broker, triggering of Gemini (and other facilities within the Astronomical Event Observatory Network), automated data retrieval from the Gemini Observatory Archive, and interactive data reduction and analysis through Gemini's DRAGONS software and NOIRLab's Astro Data Lab science platform. GOATS was successfully deployed in an end-to-end demonstration of real-time follow-up of Rubin/LSST alerts with NOIRLab facilities. As part of this demonstration, we selected targets from the Rubin alert stream and triggered follow-up observations within minutes of the Rubin detections. We obtained spectra for several targets and classified them as supernova of various types (Ia, IIP, Ib/c) with redshifts ranging from 0.05 to 0.35. By eliminating the need to manually connect tools and automating repetitive tasks, GOATS lowers the entry barrier and allows users to focus on the scientific interpretation of the observation results.
Read the full abstract

All authors Monika Soraisam, Louis Avner, Miguel Gómez, William Vacca, Bryan Miller, Andrew Stephens, Arturo Núñez, Andrew Adamson, César Briceño, Hernán Chacana, Guillermo Damke, Nicolás Esquivel, Paul Hirst, Kathleen Labrie, Thomas Matheson, Chadd Myers, Robert Nikutta, Abhijit Saha, Chris Simpson, Olesja Smirnova, D. J. Teal, Sergio Troncoso, James Turner, Sebastián Vicencio, Hubert Condoretti, Scott Dahm, Tómas Ahumada, Eric Bellm, Robert Blum, Aleksandar Cikota, Hannah Crayton, Diego Gómez, Melissa Graham, Stephen Heathcote, Leanne Guy, Fredrik Rantakyrö, Kevin Reil, Rachel Street, Sandrine Thomas, Simón Torres, Kathy Vivas

Solar and Stellar Astrophysics · Cross-listed from physics.space-ph

Wave Activity at MHD-ion Scales Associated with Switchbacks

Kyung-Eun Choi, Oleksiy V. Agapitov, Forrest Mozer et al. (+9 more)

Magnetic switchbacks (SB) – the localized magnetic structures with magnetic field direction inclined at an angle $\theta$ relative to the background $B_0$ – in the young solar wind have been associated with enhanced ion-scale wave activity and local plasma heating. It remains debated whether the apparent wave-power increase is intrinsic or mainly caused by sampling geometry. In this work, we analyze magnetic and electric field fluctuations measured by Parker Solar Probe, focusing on the 0.1–3~\(f_{cp}\) frequency band that spans the transition from the MHD inertial range to ion-kinetic scales. By decomposing magnetic fluctuations into field-aligned and transverse components and comparing SB and non-SB intervals at the same local magnetic field angle, we test whether SBs sample an anisotropic cascade from different viewing angles or host intrinsically amplified wave activity. We find that the transverse magnetic power $\delta B_{\perp}$ is systematically enhanced inside switchbacks across a wide range of magnetic field rotation angles $\theta$. The enhancement persists even at small and intermediate deflections, where geometric projection alone predicts weak power, indicating an intrinsic origin beyond sampling geometry. The inertial-range spectral indices also remain similar between SB and non-SB intervals despite the enhanced wave power inside SBs, suggesting that the underlying turbulence cascade is largely preserved. This excess $\delta B_{\perp}$ coincides with elevated proton temperatures and enhanced electric-field fluctuations, supporting the interpretation that SBs act as localized sites of cross-scale energy transfer and ion-scale dissipation in the near-Sun solar wind.
Read the full abstract

All authors Kyung-Eun Choi, Oleksiy V. Agapitov, Forrest Mozer, Seung-Ju Yang, Dae-Young Lee, Richard D. Sydora, Lucas Colomban, Liudmyla Kozak, Mingzhe Liu, Marc Pulupa, Jia Huang, Shaosui Xu

High Energy Astrophysical Phenomena

Identifying Observational Signatures of Flux Eruption Events in Supermassive Black Hole Accretion Flows with Machine Learning

Angelo Ricarte, Erandi Chavez, Franc O et al. (+1 more)

Simulated black hole accretion flows with strong magnetic fields often exhibit "flux eruption events" (FEEs), transient and localized expulsions of matter near the event horizon due to magnetic reconnection. It may now be possible to image them with the Event Horizon Telescope (EHT), a global network of millimeter-wave observatories that images black holes. Here we use machine learning as an interpretable inference tool to identify observational signatures of FEEs that could be accessible to the EHT. First, we train a convolutional neural network to learn task-relevant representations of FEEs in uncorrupted simulated images. After using this network to label a larger set of images, we then train interpretable models (random forest and logistic regression) to determine observational signatures. We find that during a FEE, images in the millimeter tend toward more diffuse emission, higher linear polarization, and lower total fluxes, but these signatures are weak for most FEEs compared to the usual time variability of these features. Moreover, the Q-U loop rotation rate decreases during FEEs, contrary to a picture in which FEEs could jointly cause both millimeter Q-U loops and flares. Our random forest trained on observable summary statistics achieves ~80% class-weighted accuracy, suggesting that the CNN learns FEE structure not fully mapped onto these traditional summary statistics. Our results imply that image size and polarization fraction can be used to flag candidate FEEs, but high-resolution, high-dynamic range images will still be important to confirm FEEs and test accretion flows for this phenomenon.
Read the full abstract

All authors Angelo Ricarte, Erandi Chavez, Franc O, Pavlos Protopapas

Astrophysics of Galaxies

Interaction-induced star formation boosts stellar mass assembly in $z\sim5$ galaxies

Kiyoaki C. Omori, Marcin Sawicki, Rosa M. Mérida et al. (+10 more)

Galaxy interactions are a key ingredient in galaxy evolution; not only are they a primary pathway of galaxy growth and mass assembly, but also a key driver of processes such as star formation and quenching. We investigate the impact of galaxy-galaxy interactions on stellar mass assembly using JWST/NIRCam observations of a spectroscopically selected sample of galaxies at $5.0<z_{spec}<5.6$ from the Canadian NIRISS Unbiased Cluster Survey (CANUCS). Of the 48 galaxies in our parent sample, we visually classify 21 ($44\%$) as closely-interacting ($\lesssim$ 5 kpc) systems with two or more components. We evaluate the non-parametric star formation histories (SFHs) of these systems' components using the spectral energy distribution fitting code Dense Basis. We find that the components in these systems experience brief intervals ($\sim0.2$ Gyr) of strongly enhanced star formation that grow their stellar mass by $\sim2.66\pm0.85\times$, forming $\sim1.71\pm0.37\times$ of excess mass than expected compared to if there was no burst. Attributing these star formation rate enhancements to interactions and assuming that the components will merge, we find that mergers are responsible for $\sim42^{+20}_{-25}\%$ of the total stellar mass growth of galaxies at $z\sim5$. While about half of this contribution comes from the merging of the pre-existing stellar masses of the merging galaxies, half is due to stellar mass that is newly-formed during the interaction. We conclude that mergers, and their associated star formation bursts, are an important pathway for stellar mass growth in high-$z$ galaxies.
Read the full abstract

All authors Kiyoaki C. Omori, Marcin Sawicki, Rosa M. Mérida, Guillaume Desprez, Roberto Abraham, Maruša Bradač, Nicholas S. Martis, Adam Muzzin, Gaël Noirot, Ghassan T. Sarrouh, Christopher J. Willott, Danilo Marchesini, Katherine Myers

High Energy Astrophysical Phenomena

The NANOGrav 15 yr Data Set: Customized Chromatic Noise Models

Bjorn Larsen, Jeremy G. Baier, Daniel J. Oliver et al. (+53 more)

Pulsar timing arrays conduct low-frequency gravitational wave searches, which require comprehensive accounting of various noise sources to achieve robust results. Interstellar propagation effects (e.g., dispersion and scattering) are especially complex noise sources, introducing chromatic delays that can reduce sensitivity to gravitational waves and bias their inference if left unmodeled. These delays also strongly depend on the line of sight properties to each individual pulsar. To address this, we present customized chromatic noise models for 67 pulsars in the NANOGrav 15 yr dataset. These models are selected from an expanded suite of Gaussian processes to simultaneously characterize multiple types of chromatic delays and are tailored to each pulsar's dataset. Alongside probing the interstellar medium, we use these models to infer the solar wind electron density over the course of $\sim 1.5$ solar cycles. We also find evidence for non-dispersive chromatic delays in 21 out of 67 NANOGrav pulsars. After applying our chromatic models, we observe significant impacts on the inference of achromatic noise in 19 out of 67 pulsars, finding in several cases that a previously significant achromatic noise process can be partially or entirely described as chromatic. These results demonstrate that refined noise modeling is essential to enhance the sensitivity and accuracy of low-frequency gravitational wave searches with pulsar timing arrays.
Read the full abstract

All authors Bjorn Larsen, Jeremy G. Baier, Daniel J. Oliver, Kalista Wayt, Yu-Ting Chang, Jeffrey S. Hazboun, Chiara M. F. Mingarelli, Joseph Simon, Matthew T. Miles, Gabriella Agazie, Akash Anumarlapudi, Anne M. Archibald, Zaven Arzoumanian, Paul T. Baker, Paul R. Brook, H. Thankful Cromartie, Kathryn Crowter, Megan E. DeCesar, Paul B. Demorest, Timothy Dolch, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Nate Garver-Daniels, Peter A. Gentile, Joseph Glaser, Deborah C. Good, Ross J. Jennings, Megan L. Jones, David L. Kaplan, Matthew Kerr, Michael T. Lam, Duncan R. Lorimer, Jing Luo, Ryan S. Lynch, Alexander McEwen, Maura A. McLaughlin, Natasha McMann, Bradley W. Meyers, Cherry Ng, David J. Nice, Timothy T. Pennucci, Benetge B. P. Perera, Nihan S. Pol, Henri A. Radovan, Scott M. Ransom, Paul S. Ray, Ann Schmiedekamp, Carl Schmiedekamp, Brent J. Shapiro-Albert, Ingrid H. Stairs, Kevin Stovall, Abhimanyu Susobhanan, Joseph K. Swiggum, Haley M. Wahl

High Energy Astrophysical Phenomena

JWST observations of SN 2024abup: First Detection of CO in a broad-lined Type Ic Supernova and Constraints on r-process Nucleosynthesis

Manisha Shrestha, Lindsey A. Kwok, David J. Sand et al. (+42 more)

SN 2024abup is a nearby broad-lined Type Ic supernova (SN Ic-bl) in NGC 0681 at a distance of 23.3 \pm 1.6 Mpc. As energetic explosions of massive stars, SNe Ic-bl are considered a plausible site for rapid-neutron capture nucleosynthesis (r-process) and chemical enrichment from short-lived progenitors. They may also contribute to dust production in the early Universe. We present JWST near- to mid-infrared (NIR+MIR) observations (1-14 micron) of SN Ic-bl 2024abup at +41 days after the V band maximum (+54 days after explosion), the first-ever JWST+MIR observation of a SN Ic-bl along with radio and optical data. Using the spectral synthesis code SUMO, we identify the observed broad IR line features in SN 2024abup and find significant contributions from C, O, Mg, and carbon monoxide (CO) – the earliest detection of molecules in a core-collapse SN so far. The spectrum shows continuum emission at wavelengths greater than 1.5 micron, which could be explained by dust – preexisting, newly formed, or a combination-heated by the SN. We do not find compelling evidence for infrared signatures of r-process elements, though our search is hampered by the presence of many broad and blended features from the non-r-process elements. These new observations indicate that SNe Ic-bl could be a contributor to early-universe dust production, and suggest that if r-process elements are produced, revealing their presence from spectra requires very high-quality data and models to disentangle blends.
Read the full abstract

All authors Manisha Shrestha, Lindsey A. Kwok, David J. Sand, Stan Bartmentloo, Collin Christy, Anders Jerkstrand, K. Azalee Bostroem, Jennifer E. Andrews, Kate D. Alexander, Yize Dong, Carl E. Fields, Emily Hoang, Griffin Hosseinzadeh, Brian Hsu, Daryl Janzen, Saurabh W. Jha, Joel Johansson, Jeniveve Pearson, M. J. Lundquist, Darshana Mehta, Aidan Martas, Maryam Modjaz, Bernhard Müller, Conor L. Ransome, Aravind P. Ravi, Mathieu Renzo, Nicolás Meza Retamal, Bhagya Subrayan, Nathan Smith, Stefano Valenti, Sergiy Vasylyev, Giacomo Ricigliano, Peter J. Brown, Moira Andrews, Joseph Farah, D. Andrew Howell, Curtis McCully, Megan Newsome, Kathryn Wynn, Ryan Chornock, Natalie LeBaro, Raffaella Margutti, Melissa Shahbandeh, Chris Ashall, Peter Hoeflich

Cosmology and Nongalactic Astrophysics

DESI DR2 Reference Mocks: Clustering results from UCHUU ELGs and QSOs

R. Vaisakh, J. Lasker, R. Kehoe et al. (+44 more)

High-redshift galaxy clustering provides a powerful probe of the growth of structure, testing models of dark matter, dark energy, and galaxy formation during the epoch when the Universe was rapidly evolving. Emission line galaxies (ELGs) and quasars (QSOs) are used as tracers of dark matter by the Dark Energy Spectroscopic Instrument (DESI) to probe this redshift regime. We present results from ELG and QSO mock catalogs created from the Uchuu N-body simulation and tuned to DESI Data Release 2 (DR2) clustering. Employing a modified subhalo abundance matching (SHAM) technique, we populate Uchuu halos and subhalos with QSOs between 0.8 < z < 2.1. For ELGs, we modify this method to select satellite galaxies with low velocities relative to their associated central halos, and populate a separate set of Uchuu halos and subhalos with ELGs between 0.8 < z < 1.6. In this paper, we reproduce the redshift evolution of number density and clustering statistics across the fitted range of scales. We also measure the large-scale clustering bias of both the data and mock samples. These results improve simulated lightcone construction from cosmological models and enhance our understanding of the galaxy-halo connection.
Read the full abstract

All authors R. Vaisakh, J. Lasker, R. Kehoe, A. Amalbert, N. Khan, E. Fernandez-Garcia, F. Prada, M. S. Wang, J. DeRose, S. Bailey, A. J. Ross, J. Aguilar, S. Ahlen, D. Bianchi, D. Brooks, F. J. Castander, T. Claybaugh, K. S. Dawson, A. de la Macorra, S. Ferraro, J. E. Forero-Romero, E. Gaztanaga, Satya Gontcho A Gontcho, G. Gutierrez, C. Hahn, M. Ishak, R. Joyce, S. Juneau, T. Kisner, A. Kremin, C. Lamman, M. Landriau, M. E. Levi, M. Manera, R. Miquel, A. D. Myers, S. Nadathur, W. J. Percival, I. Perez-Rafols, G. Rossi, E. Sanchez, D. Schlegel, H. Seo, G. Tarle, B. A. Weaver, R. Zhou, H. Zou

Cosmology and Nongalactic Astrophysics

The NANOGrav 15 yr Data Set: Impacts of Customized Chromatic Noise Models on Gravitational Wave Analyses

Nikita Agarwal, Gabriella Agazie, Alessandra Amosso et al. (+120 more)

We report updated nHz gravitational wave (GW) significance, characterization, and interpretations using the customized chromatic-noise models (CNMs) developed in Larsen, Baier et al. (2026). for the NANOGrav 15-year data set. We find increased evidence for the Hellings-Downs (HD) correlation signature of the stochastic gravitational wave background (GWB), with a Bayes factor of $1571\pm14$ for HD-correlations over a common uncorrelated red-noise process using a power-law model with $14$ Fourier modes. We find this $\sim8\times$ increase in Bayes factor from Agazie et al. (2023a) is a result of improved noise mitigation. Assuming an analytic null distribution for the frequentist interpulsar correlation statistic, this corresponds to a slightly more significant measurement from $3.16\sigma$ to $3.32\sigma$ against the no-correlation scenario. Spectral inference with CNMs brings the power-law GWB amplitude down to $A_{\rm GWB} = 2.1^{+0.6}_{-0.5}\times10^{-15}$ at fixed $\gamma_{\rm GWB} = 13/3$. In a varied-$\gamma$ analysis, the spectral index increases to $\gamma_{\rm GWB}=3.5^{+0.7}_{-0.6}$. We report updates on an all-sky continuous gravitational wave (CW) search as well as select targeted searches and calculate a $3.2\times$ larger detection volume for the NANOGrav detector. With CNMs, we find reduced evidence for a non-Einsteinian, scalar-transverse mode of gravity. Finally, we reinterpret the GWB first with the assumption of an astrophysical background sourced by SMBHBs and then assuming the more exotic origins of cosmic inflation, a first-order cosmological phase transition, and stable cosmic strings. Under both the SMBHB hypothesis and the cosmological hypotheses, we see only marginal shifts in model parameter posteriors which are consistent with the slightly quieter and steeper power-law GWB spectrum.
Read the full abstract

All authors Nikita Agarwal, Gabriella Agazie, Alessandra Amosso, Akash Anumarlapudi, Anne M. Archibald, Zaven Arzoumanian, Anjana Ashok, Jeremy G. Baier, Paul T. Baker, Bence Becsy, Laura Blecha, Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, Rand Burnette, Robin Case, J. Andrew Casey-Clyde, Yu-Ting Chang, Maria Charisi, Shami Chatterjee, Tyler Cohen, James M. Cordes, Neil J. Cornish, Fronefield Crawford, H. Thankful Cromartie, Kathryn Crowter, Megan E. DeCesar, Paul B. Demorest, Heling Deng, Lankeswar Dey, Timothy Dolch, Graham M. Doskoch, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Emiko C. Gardiner, Nate Garver-Daniels, Peter A. Gentile, Kyle A. Gersbach, Joseph Glaser, Deborah C. Good, Kayhan Gultekin, Aiden Gundersen, C. J. Harris, Doa Hashemi Asl, Jeffrey S. Hazboun, Ross J. Jennings, Aaron D. Johnson, Megan L. Jones, David L. Kaplan, Anala K. Sreekumar, Luke Zoltan Kelley, Matthew Kerr, Joey S. Key, Nima Laal, Michael T. Lam, William G. Lamb, Bjorn Larsen, T. Joseph W. Lazio, Natalia Lewandowska, Tingting Liu, Duncan R. Lorimer, Jing Luo, Ryan S. Lynch, Chung-Pei Ma, Dustin R. Madison, Ashley Martsen, Cayenne Matt, Alexander McEwen, James W. McKee, Maura A. McLaughlin, Natasha McMann, Bradley W. Meyers, Patrick M. Meyers, Matthew T. Miles, Chiara M. F. Mingarelli, Andrea Mitridate, Cherry Ng, David J. Nice, Shania Nichols, Stella K. Ocker, Daniel J. Oliver, Ken D. Olum, Timothy T. Pennucci, Benetge B. P. Perera, Polina Petrov, Nihan S. Pol, Henri A. Radovan, Scott M. Ransom, Paul S. Ray, Joseph D. Romano, Jessie C. Runnoe, Alexander Saffer, Shashwat C. Sardesai, Ann Schmiedekamp, Carl Schmiedekamp, Kai Schmitz, Levi Schult, Brent J. Shapiro-Albert, Xavier Siemens, Joseph Simon, Sophia V. Sosa Fiscella, Ingrid H. Stairs, Daniel R. Stinebring, Kevin Stovall, Robin Strahler, Abhimanyu Susobhanan, Joseph K. Swiggum, Jacob Taylor, Stephen R. Taylor, Mercedes S. Thompson, Jacob E. Turner, Michele Vallisneri, Rutger van Haasteren, Joris P. W. Verbiest, Sarah J. Vigeland, Haley M. Wahl, Kalista Wayt, Kevin P. Wilson, Caitlin A. Witt, David Wright, Olivia Young

Solar and Stellar Astrophysics

Revealing the substellar population of IC 1396: A spectroscopic survey of brown dwarfs in the region

Belinda Damian, Jessy Jose, Aleks Scholz et al. (+7 more)

We present a new spectroscopic view of the brown dwarf population in the young star-forming region IC 1396 and investigate the impact of environment on low-mass star formation. We use deep optical photometry from Subaru-HSC to identify the candidate low-mass stars and brown dwarfs in the region. Our follow-up low-resolution spectroscopic survey with GTC-EMIR and IRTF-SpeX has identified 32 new members in the region with spectral types between M3 and M9, among which 25 are brown dwarfs with spectral types M6 or later. We use the BT-Settl atmospheric models to derive the effective temperatures of the members. Using a comprehensive catalogue of known members and candidates, we estimate the star to brown dwarf ratio for IC 1396 to be 5.0$\pm$0.4, for a mass range between 1-0.03 M$_\odot$. This ratio is largely consistent with measurements in other young clusters spanning a range of UV radiation fields and stellar densities, supporting formation scenarios in which the relative abundance of brown dwarfs is not strongly influenced by the local environmental conditions.
Read the full abstract

All authors Belinda Damian, Jessy Jose, Aleks Scholz, Carlos Román Zúñiga, B. Shridharan, Genaro Suárez, Juan José Downes, Swagat R. Das, Sreeja S. Kartha, Saumya Gupta

Instrumentation and Methods for Astrophysics

A Scalable Path to Astrometric Exomoon Discoveries with the Nautilus Space Observatory

Kevin Wagner, Sumin Seung, Dániel Apai et al. (+13 more)

Moons orbiting exoplanets (exomoons) can be detected through the reflex motion they impart to their host planet, which is recoverable in relative star-planet astrometric time series. The signal grows with moon mass and orbital separation and decreases with distance, so the nearest and least massive imaged planets are the most favorable targets. Recovering small (<Earth-mass) moons requires continuous, long-baseline, high-precision monitoring that is only practical with a dedicated or nearly dedicated facility. Building on recent simulations of astrometric exomoon detection and of the resulting population yields, we argue that the scalable, replicable architecture of the Nautilus Space Observatory is uniquely suited to this problem, and we outline a staged campaign. In an initial phase, one or a few small apertures target the nearest imaged giant planets–a high-reward but low-probability search focused on the closest stars. As the array is built out, the astrometric noise floor decreases and the same technique extends the search to the nearest such systems among nearby stars of spectral type K and earlier. This would be performed in parallel with high-contrast imaging and spectral characterization of the host planets and in synergy with a companion starshade concept for imaging Earth-like planets around the same nearby stars. Nautilus thus provides a scalable path from the first detection of a nearby exomoon toward a systematic search for exomoons around the closest stars.
Read the full abstract

All authors Kevin Wagner, Sumin Seung, Dániel Apai, Enrico Biancalani, Eduardo Bendek, Samantha Hasler, Nadiia Kostogryz, Sowmya Krishnamurthy, Mercedes López-Morales, Peter McGill, Peter Plavchan, Benjamin V. Rackham, Alexander Shapiro, Noah Tuchow, S. Pete Worden, Yifan Zhou

High Energy Astrophysical Phenomena

Lower Your Rates: On Claims of a Binary Black Hole Merger-Rate Crisis

Floor S. Broekgaarden

Recent studies have argued that isolated binary evolution simulations generically overestimate the observed local binary black hole (BBH) merger rate, even after adopting observationally motivated variations in the metallicity-dependent cosmic star-formation history, and have interpreted this as motivation for drastic revisions to binary stellar evolution models. We revisit these claims using a compilation of 1490 simulated BBH merger rates from 57 isolated binary-evolution studies, compared to constraints from the LIGO–Virgo–KAGRA Collaboration through GWTC-5. While $\sim$80% of compiled submodels find rates above the GWTC-5 interval, a substantial subset reproduces or underestimates the observed rate. The literature spans several orders of magnitude, reflecting strong sensitivity to assumptions about natal kicks, common-envelope evolution, mass transfer, angular-momentum loss, remnant formation, stellar winds, initial conditions, and star-formation history. Using 2543 pairwise BBH submodel variations constructed to isolate single physical assumptions, we identify which choices most strongly impact the simulated BBH merger rate. Low BBH merger rates are not uniquely associated with strong natal kicks or reduced low-metallicity star formation. Multiple physically motivated assumptions can independently reduce simulated rates to values consistent with observations. We further show that simulated rates cluster into `simulation silos': frameworks producing apparent consensus within a code that does not generalize beyond it. Our results indicate that claims of a universal BBH merger-rate crisis are strongly model dependent, and underscore the importance of exploring the full parameter space across multiple population-synthesis frameworks before concluding that isolated binary evolution is in tension with gravitational-wave observations.
Read the full abstract

High Energy Astrophysical Phenomena

Dual AGN and Multiple SMBH Systems in the Era of SKAO

Q. D'Amato, L. Cui, R. Deane et al. (+23 more)

We present a radio-oriented review of current strategies for the detection and characterization of dual active galactic nuclei (DAGN) and supermassive black hole binaries (SMBHBs), emphasizing the crucial role of radio interferometry in advancing this field. We discuss how high-resolution radio imaging - particularly through very long baseline interferometry (VLBI) - provides a unique, dust-unbiased tool to identify multiple accreting SMBHs, disentangle AGN-related emission from star formation, and trace components from tens of kpc to sub-parsec scales. We summarize current observational limitations, such as insufficient sensitivity-resolution combination and area coverage. We then outline how the SKAO will overcome these constraints through its unprecedented combination of sensitivity, survey speed, imaging fidelity and angular resolution, enabling the discovery and characterization of dual and binary SMBHs from the nearby Universe to the epoch of reionization. Several science cases are presented, including radio follow-ups of optical/infrared-selected DAGN, direct blind radio selection of DAGN, studies of compact bound SMBHBs, and the link between SMBHB orbital evolution and low-frequency gravitational wave emission. We further emphasize the synergy between SKAO observations and modern and upcoming facilities such as the James Webb and Euclid space telescopes, Rubin Observatory, and gravitational wave detectors including the Laser Interferometer Space Antenna and pulsar timing arrays. These combined capabilities will allow SKAO to enable the first comprehensive radio census of dual and binary SMBH systems, bridge the gap between electromagnetic and gravitational wave observations, and provide a statistically significant view of SMBH pairing, accretion, and merger-driven feedback throughout cosmic history.
Read the full abstract

All authors Q. D'Amato, L. Cui, R. Deane, S. Komossa, C. Pillay, A. Tripathi, P. Kharb, H. Guo, S. Nandi, K. Rubinur, S. Anton, T. An, S. Bonoli, N. Chang, R. Dave, A. De Rosa, M. Habouzit, F. Mannucci, I. Prandoni, P. Severgnini, M. Scialpi, C. Spingola, C. Vignali, W. Xu, X. Yan, Y. Zhang

High Energy Astrophysical Phenomena

Twin Peaks: Resolving Features in the Binary Black Hole Mass Function with COSMIC-METISSE

Duncan B. Maclean, Poojan Agrawal, Katelyn Breivik et al. (+4 more)

Gravitational waves from inspiraling binary black holes (BBHs) provide insights into the lives and deaths of massive stars. Population synthesis allows us to model these binaries through isolated binary evolution, but its predictive power is limited by difficulties in varying the stellar models and their associated uncertainties. We present a new grid of stellar tracks computed with the open-source stellar evolution code MESA, spanning metallicities $10^{-3} \le Z/Z_{\odot} \le 7$. We vary two stellar physics parameters: wind-driven mass loss and the convective boundary mixing (CBM) mechanism. We pair these models with the Method of Interpolation for Single Stellar Evolution (METISSE) and binary population synthesis code COSMIC to obtain synthetic populations of merging BBHs in the local Universe. We find a maximum in the primary mass spectrum near $10M_\odot$ which in most model variations is composed of two sub-populations at $\approx8M_{\odot}$ and $\approx13 M_\odot$, with the higher-mass population dominated by BBHs whose progenitors underwent a mass ratio reversal (MRR). This population also suggests an anticorrelation between higher primary masses and mass ratio, as BBHs with $m_1\gtrapprox10M_\odot$ preferentially undergo MRR and prefer a final mass ratio of $q\approx0.7$. However, the location and relative strength of these two sub-populations is sensitive to our assumed stellar physics: varying both the wind and CBM treatments can merge the MRR and non-MRR populations into a single peak near $9M_\odot$. Variations in our stellar tracks, especially CBM, lead to a factor of $\approx6$ difference in the rate, primarily due to modulation of the common envelope formation channel.
Read the full abstract

All authors Duncan B. Maclean, Poojan Agrawal, Katelyn Breivik, Alexandra G. Guerrero, Michael Zevin, Mathieu Renzo, Carl L. Rodriguez

Solar and Stellar Astrophysics

Euclid: The convective-transition gap of 47 Tuc

M. Libralato, M. Griggio, R. Gerasimov et al. (+140 more)

We report the first detection of the `convective-transition gap' (also known as `M-dwarf gap') in the globular cluster 47 Tuc (NGC 104) thanks to Euclid data. This feature, linked to a change in the physical properties of late-type dwarfs, has remained elusive, with only two detections so far. Leveraging the large number of stars, high resolution, and photometric precision enabled by Euclid, we detect a statistically significant, sharp discontinuity in the main-sequence luminosity function of 47 Tuc at $I_{\rm E} \approx 22.9$, which we identify as the convective-transition gap. We compare the observed properties of the gap in 47 Tuc with theoretical models, showing how the gap can be a powerful diagnostic to probe the internal chemical structure of globular clusters, and their multiple stellar populations. Following its initial discovery in the metal-poor cluster NGC 6397, the identification of a convective gap in the metal-rich 47 Tuc suggests that this feature might be more general than previously thought. These results demonstrate that Euclid can be transformative well beyond cosmology, with impact across multiple areas of astrophysics, including resolved stellar populations.
Read the full abstract

All authors M. Libralato, M. Griggio, R. Gerasimov, L. R. Bedin, I. McDonald, B. Altieri, J. Anderson, F. Annibali, E. Balbinot, G. Battaglia, A. Bellini, P. Casenove, J.-C. Cuillandre, E. Dalessandro, A. M. N. Ferguson, H. R. A. Jones, K. Kuijken, F. Z. Majidi, D. Massari, A. Mohandasan, F. Niederhofer, G. Polenta, J. D. Sakowska, F. Soldano, C. Zerbinati, S. Andreon, N. Auricchio, H. Aussel, C. Baccigalupi, M. Baldi, A. Balestra, P. Battaglia, A. Biviano, E. Branchini, M. Brescia, S. Camera, V. Capobianco, C. Carbone, J. Carretero, M. Castellano, G. Castignani, S. Cavuoti, K. C. Chambers, A. Cimatti, C. Colodro-Conde, G. Congedo, C. J. Conselice, L. Conversi, Y. Copin, F. Courbin, H. M. Courtois, M. Cropper, H. Degaudenzi, G. De Lucia, H. Dole, F. Dubath, X. Dupac, M. Farina, R. Farinelli, F. Faustini, S. Ferriol, M. Frailis, E. Franceschi, S. Galeotta, K. George, B. Gillis, C. Giocoli, J. Gracia-Carpio, A. Grazian, F. Grupp, S. V. H. Haugan, H. Hoekstra, W. Holmes, I. M. Hook, F. Hormuth, A. Hornstrup, K. Jahnke, M. Jhabvala, S. Kermiche, A. Kiessling, B. Kubik, M. Kümmel, M. Kunz, H. Kurki-Suonio, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, O. Mansutti, O. Marggraf, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, E. Medinaceli, S. Mei, M. Meneghetti, E. Merlin, G. Meylan, A. Mora, L. Moscardini, R. Nakajima, R. C. Nichol, S.-M. Niemi, C. Padilla, S. Paltani, F. Pasian, W. J. Percival, V. Pettorino, M. Poncet, L. A. Popa, F. Raison, A. Renzi, J. Rhodes, G. Riccio, F. Rizzo, E. Romelli, M. Roncarelli, R. Saglia, Z. Sakr, D. Sapone, M. Schirmer, P. Schneider, T. Schrabback, A. Secroun, E. Sihvola, P. Simon, C. Sirignano, G. Sirri, L. Stanco, P. Tallada-Crespí, A. N. Taylor, I. Tereno, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, J. Valiviita, T. Vassallo, Y. Wang, J. Weller, D. Scott

Cosmology and Nongalactic Astrophysics

Reheating matters: Starobinsky inflation in light of joint CMB+BAO results and gravitational-wave forecasts

Gláuber C. Dorsch, Lucas P. C. Leão, Lucas M. B. Alves et al. (+2 more)

It has been noted in the literature that, if post-inflationary reheating is dominated by a stiff fluid with equation of state (EoS) $p>\rho/3$, then the predictions of Starobinsky inflation for the scalar spectral index could be made to agree with measurements from the combined CMB+BAO datasets performed by the Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT) collaborations. However, a side-effect of such a stiff epoch is the blue-tilting of the primordial gravitational-wave (GW) spectrum. In this work, we explore the observational consequences of this blue-tilting in three scenarios: (i) a purely stiff-dominated reheating, (ii) a more realistic case where reheating is first dominated by a matter-like fluid (corresponding to inflaton oscillations around the bottom of a quadratic potential well) later followed by a stiff epoch, and (iii) a case analogous to the previous one, but with an earlier radiation-dominated instead of matter-dominated epoch. We show that in all cases the $1\sigma$ region allowed by recent CMB+BAO data is already excluded by constraints on the amount of radiation present during Big Bang Nucleosynthesis (BBN). Moreover, in a considerable fraction of the remaining $2\sigma$ region we find that the blue-tilting would be severe enough to make the primordial spectrum detectable in future interferometers such as Einstein Telescope, LISA, DECIGO, and BBO, thus rendering these scenarios testable by these experiments.
Read the full abstract

All authors Gláuber C. Dorsch, Lucas P. C. Leão, Lucas M. B. Alves, Luiz C. A. Miranda, Beatriz M. D. Sena

Cosmology and Nongalactic Astrophysics

A hierarchical Bayesian framework for cosmology using Type 1 AGN variability

Júlia Laguna-Miralles, Vasily Belokurov and Miles Cranmer

Independent luminosity-distance probes beyond the Type Ia supernova range are needed to test cosmic expansion at high redshift. Type 1 AGN are abundant at \(z>2\), but their use for cosmology requires standardizable observables with controlled scatter, redshift dependence, and measurement uncertainty. We present a hierarchical Bayesian framework for cosmology using AGN variability, based on the empirical anti-correlation between optical/UV variability amplitude and luminosity. The method targets the moderate-baseline regime of current wide-field time-domain surveys, where individual light curves cannot typically identify the full long-timescale stochastic process, but can constrain finite-window brightness and short-lag variability. Each light curve is fitted independently to obtain posterior samples of these summaries, which are then importance-reweighted under a population model relating variability to luminosity, rest-frame wavelength, intrinsic scatter, and the assumed distance-redshift relation. This framework propagates object-level uncertainty while avoiding repeated light-curve likelihood evaluations during cosmological inference, making catalogue-scale analyses feasible. Using Gaia DR3-like G-band simulations matched to real Gaia cadences, noise properties, and quality cuts, we show that finite-baseline light curves are more robustly summarized by window-averaged brightness and short-lag variability than by the separate long-timescale parameters of stochastic models. End-to-end closure tests recover the injected variability-luminosity relation, intrinsic scatter, and distance-redshift parameters up to the expected calibration degeneracies. This Gaia G-band analysis establishes a proof of concept for AGN-variability distances in the moderate-baseline survey regime, with the main gains expected from Gaia DR4, ZTF, DESI-selected AGN samples, and Rubin/LSST-era data.
Read the full abstract

High Energy Astrophysical Phenomena

Stochastic Variability of Binary Accretion

Akhil Nair and Jonathan Zrake

We measure the power spectral density (PSD) of the accretion rate time series in an unequal mass (q = 0.2) binary surrounded by a circumbinary gas disk, using very high-resolution 2D hydrodynamics simulations. Our aim is to identify new signposts of supermassive black hole (SMBH) binaries in active galactic nuclei (AGN), based on the shape of the continuum PSD, to complement well-studied line features in the PSD (periodicities). We find that the continuum PSD is a broken power-law, transitioning from flat (white noise) to a slope of -4 at a break frequency generically ~5 times the binary orbital frequency. This form is expected when (a) delivery of gas from the circumbinary disk to the individual "minidisks" is a damped random walk with correlation time equal to binary orbital period and (b) the minidisks function as low-pass filters acting at the Kepler frequency of the outer edge of the smaller black hole's minidisk; we show numerical evidence for both. The broken power-law PSD is attained in a limit where the secondary black hole is much smaller than its minidisk, realized numerically by a sufficiently small "sink" region; larger sinks lead to excess high-frequency noise seen as accretion rate spikes, and we argue these should be regarded as artificial when the black holes themselves are smaller than the sink regions. The broken power-law PSD is reminiscent of stochastic variability in ordinary AGN, inviting the conjecture that canonical AGN variability could result from widespread binarity, however pulsar timing experiments may exclude this possibility.
Read the full abstract

Astrophysics of Galaxies

Stellar discs and intermediate-mass black holes in galactic nuclei I. Fragmenting the disc in an isotropic stellar potential

Taras Panamarev, Xiang Zou and Bence Kocsis

The origin of the complex orbital structure of young massive stars at the Galactic centre remains an open question. If these stars formed in a single episode from a gaseous accretion disc, they may initially have constituted a single, coherently rotating stellar disc. We investigate whether perturbations from an unseen intermediate-mass black hole (IMBH) could fragment and/or disrupt such a disc into the multiple orbital components observed today. First, we derive a theoretical criterion for when and where the IMBH's torque overcomes the disc's self-torque and tears it apart. We then test this picture with direct $N$-body simulations of a stellar disc interacting with an inclined IMBH around a central supermassive black hole. We find that the outcome depends strongly on the IMBH's orbit and mass. A prograde IMBH rapidly aligns with the stellar disc, while a massive retrograde IMBH ($m_{\bullet} \simeq 0.67\,M_{\rm d}$) anti-aligns relative to the radially overlapping stars and efficiently fragments the original disc into three components in angular-momentum space: an inner disc, a misaligned overlapping region, and an unperturbed outer disc. The IMBH also excites eccentricities in the overlapping region, driving stars away from initially circular orbits. These features emerge for an IMBH mass of $2000\,{\rm M}_{\odot}$ and a disc mass of $3000\,{\rm M}_{\odot}$ within 10–20 Myr, a timescale comparable to the age of the young Galactic centre stellar population, and provide a plausible explanation for the observed multiple orbital planes, warped geometry, and broad eccentricity distribution.
Read the full abstract