Solar and Stellar Astrophysics
Comprehensive MHD modelling of ten successive CMEs driving a historic geomagnetic storm – The 2024 Mothers Day event
Shirsh Lata Soni, Anwesha Maharana, Sanchita Pal et al. (+1 more)
Interacting coronal mass ejections (CMEs) result in complex heliospheric structures that can dramatically enhance their geoeffectiveness compared to isolated events. A striking example of such complex structures is that of the Mothers Day event, which occurred during 10-14 May 2024, leading to the strongest geomagnetic storm in decades. It was driven by at least ten interacting CMEs accompanied by
flare and filament eruptions from the
solar western hemisphere. We aim to understand its
solar and heliospheric origins, variation in
plasma and
magnetic characteristics, and predict its geoeffectiveness. Furthermore, we focus on bringing to the community the challenges and limitations faced during themodelling of such a complex, yet important environment. We use multi-point remote observations of CMEs and employ different methods to estimate their speeds and geometry. These parameters drive the 3D magnetohydrodynamic simulations of CME
evolution and heliospheric propagation in the framework of the EUHFORIA model. The best-performing simulation reproduced the arrival time of the storm and peak intensity with a lead of 2 hours, and estimated the storm strength with about 70% accuracy. This work underscores the requirements and challenges involved in accurately modelling extreme events. The major bottleneck was to constrain the CME input parameters that dictate the accuracy of the data-driven simulations. Predicting the impacts of the complex heliospheric structures during this event required the modelling of the CME-CME interactions accurately. As a community, we need to invest more in observational infrastructure while improving the speed and accuracy of our MHD
forecasting models.
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All authors Shirsh Lata Soni, Anwesha Maharana, Sanchita Pal, Stefaan Poedts
High Energy Astrophysical Phenomena
Giant radio pulses in the magnetar XTE J1810-197 detected with the IAR's telescopes
S. B. Araujo Furlan, G. E. Romero, E. Zubieta et al. (+4 more)
[...] We observed XTE J1810-197 between 29 September 2022 and 14 July 2023 with the
radio telescopes at the Argentine Institute of Radioastronomy (IAR). We searched for single pulses in time series at a DM range of 100-400 pc cm-3 , with a threshold in signal-to-noise ratio (S/N) of 8. [...] We found 249
giant pulses at a DM mean value of 178.8$\pm$0.1 pc cm-3 . We measured peak flux densities up to 119 Jy, and fluences up to 58 Jy ms. We fitted a power law distribution to the flux density, obtaining an index of -4.0$\pm$0.3. We observed a maximum rate of approximately 15 pulses per hour on 20 February 2023, followed by an abrupt disappearance of transient
radio emission, indicating a transition to a less active state. The brightest single pulses are limited to a $\sim$2$\%$ of the rotational phase and have similar fluence values to the reported intermediate FRB-like bursts of SGR 1935+2154. No significant X-ray activity in the MAXI data was detected during the
radio observing period. This is the first study of single
radio pulses of a magnetar using IAR data, showing the potential of the upgraded
telescopes for investigating the transient
radio sky. The properties of the single pulses detected here show the magnetar transient nature and capability to emit high-luminosity pulses. We compared the detected emission to FRB-like bursts and single pulses emitted by SGR 1935+2154. Even though the mechanism producing all the events should be coherent, the luminosity of the events, features on the dynamic spectra, and the difference between being phase confined or not, indicate that XTE J1810-197 presents GP emission, while SGR 1935+2154 only shows normal single pulses or FRB bursts. This could indicate that the conditions for producing each type of event differ.
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All authors S. B. Araujo Furlan, G. E. Romero, E. Zubieta, G. Gancio, F. García, S. del Palacio, C. O. Lousto
High Energy Astrophysical Phenomena
Upper Limits on Pulsed Radio Emission from Unseen Compact Objects in Six Galactic Stellar Binaries
Melanie Ficarra, Fronefield Crawford and T. Joseph W. Lazio
We have conducted a search for
radio pulsars in six
Galactic stellar binary systems having unseen primary
stars. All six systems have estimated primary masses in the range that could be consistent with
neutron stars. We used the Green Bank
Telescope at a center frequency of 350 MHz to search for dispersed periodicities and single pulses across a range of possible dispersion measures (DMs) and binary accelerations. No astrophysical signals were detected in our search. The estimated 400-MHz luminosity upper limits from the search are comparable to or smaller than the lowest values observed for almost all the known
Galactic binary
pulsars having cataloged 400 MHz
radio luminosities. This implies that the systems we observed either do not harbor
radio-emitting
pulsars, contain
pulsars that do not beam in our direction, or contain
pulsars with luminosities that are significantly lower than this subset of the known
Galactic binary
pulsar population.
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Astrophysics of Galaxies
EMBERS I: Low redshift post-starburst galaxies are frequently depleted in molecular gas relative to star forming progenitors
Ben F. Rasmussen, María Jesús Jiménez-Donaire, Sara L. Ellison et al. (+10 more)
The cold gas content of post-starburst
galaxies (PSBs) provides important insight into the mechanisms that drive rapid quenching, but a multiphase assessment of both the atomic and molecular gas in PSBs does not yet exist. We introduce the Ensemble of Multiphase
Baryons Evolving in Rapidly-quenching Systems, or EMBERS, a homogeneously selected, nearly mass- and
redshift-complete survey of the global atomic (HI) and molecular gas (H2) in PSBs, observed with the Five Hundred-metre Aperture Spherical
Telescope (FAST) and the Institut de radioastronomie millimetrique (IRAM) 30m
telescope. We present new CO(1-0) observations for 52 PSBs with the IRAM 30m, which, combined with 9 archival observations, gives a total H2 sample of 61, of which 58/61 have ancillary HI measurements. We detect CO(1-0) in 34/61
galaxies, corresponding to molecular gas fractions (fH2 = MH2/M*) ranging from two to 250 per cent. By comparing with a
stellar-mass matched
star-forming (SF) control sample from xCOLD GASS, we find that PSBs on average are 0.3-0.6 dex depleted in H2. However, considering both HI and H2, individual PSBs host diverse gas reservoirs ranging from gas-rich in both phases, elevated in one phase, or gas-poor, the latter of which is common at lower
stellar mass. The existence of gas-normal and gas-depleted PSBs in both phases suggests that some PSBs may rejuvenate their
star formation, but the rapid shutdown of
star formation in others is likely terminal. Despite this diversity, the majority of EMBERS PSBs are gas-poor compared to SF controls, with the typical PSB hosting gas reservoirs intermediate to those found in
star-forming and quenched
galaxies.
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All authors Ben F. Rasmussen, María Jesús Jiménez-Donaire, Sara L. Ellison, Vivienne Wild, Kate Rowlands, Qifeng Huang, Jing Wang, Dong Yang, Scott Wilkinson, Blake Ledger, Toby Brown, Ho-Hin Leung, Shoshannah Byrne-Mamahit
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Cosmological and Astrophysical Constraints on Late First-Order Phase Transitions
Kylar Greene, Daven Wei Ren Ho, Soubhik Kumar et al. (+1 more)
First-order cosmological phase transitions (PT) can take place in a dark sector at relatively late times between the big-bang nucleosynthesis and recombination epochs. Because bubble nucleation is
stochastic, the PT completes at different times in different regions of the Universe. This fluctuation sources a
curvature perturbation whose (dimensionless) power spectrum ${\cal P}_\zeta(k)$ features a universal infrared tail, independent of the microscopic details of the PT. Even in the absence of any non-gravitational interaction between the dark sector and the Standard Model, these additional
curvature perturbations at small scales impact a variety of observables. We derive new constraints on dark sector phase transitions using Planck,
baryon acoustic oscillation (BAO), Lyman-$\alpha$ observations, spectral distortion limits from FIRAS, constraints on early reionization, and the existence of ultra-faint
dwarf galaxies.
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All authors Kylar Greene, Daven Wei Ren Ho, Soubhik Kumar, Yuhsin Tsai
High Energy Astrophysical Phenomena
AT 2024ahzi: A Type IIP Supernova Discovered by the LSST Commissioning Camera
Kaylee de Soto, V. Ashley Villar, Jared A. Goldberg et al. (+25 more)
As part of its commissioning, the Vera C. Rubin Observatory observed several fields repeatedly for a month with ComCam, an instrument that uses the same hardware as the LSST camera but covers a smaller field of view. We photometrically classify AT 2024ahzi, a transient discovered by ComCam, as a Type IIP
supernova (SN IIP) using both ComCam and DECam photometry. We find that the duration, luminosity, and color of AT 2024ahzi's photometric plateau are all consistent with those from a large sample of SNe II. By comparing its multi-band light curves to SN II models and analytic relations, we place constraints on the SN progenitor, explosion dynamics, and circumstellar environment. We argue that the progenitor has an extended density profile indistinguishable from a slowly accelerating CSM. We discuss how a similar workflow can identify and characterize future Rubin SNe II.
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All authors Kaylee de Soto, V. Ashley Villar, Jared A. Goldberg, Anya Nugent, Yize Dong, Ryan J. Foley, Tobias Geron, Luca Izzo, C. Tanner Murphey, Katie Auchettl, David A. Coulter, Thomas de Boer, Kenneth C. Chambers, Diego A. Farias, Christa Gall, Hua Gao, Jens Hjorth, Willem B. Hoogendam, David O. Jones, Gauri Nair, Gautham Narayan, Armin Rest, Kishore C. Patra, Haille M. L. Perkins, Margaret E. Verrico, Qinan Wang, Amanda R. Wasserman, Yossef Zenat
Astrophysics of Galaxies
A dynamical attractor in the evolution of dwarf spheroidal galaxies
Jorge Peñarrubia and Ethan O. Nadler
We use controlled $N$-body experiments to study the dynamical
evolution of
dwarf spheroidal
galaxies (dSphs) embedded in dark-matter (DM)
haloes containing a large population of dark subhaloes. We show that
stellar orbits subject to
stochastic force fluctuations irreversibly gain energy and expand toward a dynamical attractor characterized by a
stellar half-light radius $r_{\rm half} \approx r_{\rm max}$ and a velocity dispersion $\sigma \approx 0.5\,v_{\rm max}$, where $v_{\rm max}$ is the peak circular velocity of the host
halo at radius $r_{\rm max}$. This state is reached both in isolation and under
tidal stripping, although
tidal mass loss significantly accelerates the
evolution. Assuming that the Milky Way (MW) dSphs have reached this state, we find that the inferred
halo masses collapse onto narrow sequences as a function of $r_{\rm half}$. Under this assumption, MW satellites with $r_{\rm half} \lesssim 1\,\mathrm{kpc}$ follow the
tidal tracks of cuspy
haloes, while larger systems deviate in a manner consistent with cored DM profiles. Moreover, the mass–luminosity relation follows the slope expected from abundance matching, but with
halo masses systematically lowered from their peak values at fixed luminosity. These results suggest that the structural diversity of dSphs is largely an evolutionary outcome driven by internal heating and tides, rather than by the conditions of
star formation. This framework predicts that isolated, early-quenched dSphs should have systematically larger sizes than satellites, a prediction testable with upcoming surveys.
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Earth and Planetary Astrophysics
${}^{12}$CO Ro-vibrational Spectroscopy of AB Aurigae – A Potential Point Source is Present
Janus Kozdon, Jeffrey Fung, Sean D. Brittain et al. (+4 more)
The Herbig Ae
star AB Aurigae hosts a vast, low-inclination protoplanetary disk that exhibits a plethora of substructures, including the protoplanet candidate AB Aur b. We present M-band spectroscopic data taken with NASA IRTF from Feb 2024 covering multiple position angles that captured emission from an off-centered, low temperature, and compact source. Analysis of the ${}^{12}$CO $\nu=$1-0 low-J ro-vibrational emission line profiles and spectroastrometric signals localizes the source at around an orbital radius of 65 au and a position angle of 143$^\circ$. These coordinates are distinctly different from those of AB Aur b, which was not detected. Although there is no obvious explanation for the detected source, if we assume it was a circumplanetary disk, then its maximum temperature would be about 550 K and its maximum radius would be about 5 au. Our results alludes to a previously unknown companion that may be residing in the AB Aurigae system.
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All authors Janus Kozdon, Jeffrey Fung, Sean D. Brittain, Stanley Jensen, Josh Kern, Cory Padgett, Yasuhiro Hasegawa
Astrophysics of Galaxies
HST view of NGC 5044: Constraints on Filament Widths, Magnetic Support, Multiphase Structure, and Comparison with Cluster Environments
Prathamesh Tamhane, Ming Sun, William Waldron et al. (+12 more)
We present new Hubble Space
Telescope (HST) imaging of ionised filaments in the brightest group
galaxy NGC 5044. These filaments extend several kiloparsecs and have widths of $\sim$50–120 pc, with some as narrow as those in cluster cores and others broader, reflecting the lower confining pressure in groups. Filament width ($W$) scales with ambient pressure ($P$) as $W \propto P^{-0.4}$. Combining HST, ALMA, and MUSE data, we measure column densities and
magnetic field strengths. Equipartition fields decline from $\sim$40 $\mu$G at the centre to $\sim$20 $\mu$G at 5 kpc, about 2–3 times weaker than in clusters. Dynamical stability requires stronger radial fields ($\sim$10$^2$ $\mu$G), consistent with simulations and
magnetic draping, though such high values exceed Faraday Rotation Measure limits.
Turbulence and
cosmic rays also contribute support. Group and cluster filaments are stable against gravitational collapse, and ultraviolet imaging reveals no
star formation in NGC 5044 ($<$10$^{-3}$ M$_\odot$ yr$^{-1}$). NGC 5044 hosts an ionised gas core within its Bondi radius with $n_e \propto r^{-1}$ and filling factor $f \gtrsim 3 \times 10^{-3}$, that is connected to the extended filaments, suggesting a channel for gas inflow toward the black hole. Group and cluster filaments likely share a common origin, with
magnetic fields and AGN feedback preserving their structure. Ambient pressure and
dust survival regulate molecular gas formation. Lower-pressure groups favour broader, more diffuse filaments with sporadic molecular clumps and weaker
dust shielding, whereas higher-pressure clusters host narrower strands with stronger molecular-ionised gas
alignment. We predict that (i) filament width scales with ambient pressure, (ii) filament-coincident Faraday rotation structures emerge at $\leq 0.1$ kpc resolution, and (iii) molecular/ionised gas co-spatiality is weaker in groups than in clusters.
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All authors Prathamesh Tamhane, Ming Sun, William Waldron, Kokoro Hosogi, Patricia da Silva, Huan Le, Massimo Gaspari, Francoise Combes, Norbert Werner, Gerrit Schellenberger, Andrew Fabian, Rebecca Canning, Laurence David, Megan Donahue, Mark Voit
Astrophysics of Galaxies
SIMPLIFI-Study of Interstellar Magnetic Polarization: A Legacy Investigation of Filaments. II. Enhancement of grain alignment near embedded protostars in the DR21 Ridge
S. Kumar, T.G.S. Pillai, G. V. Panopoulou et al. (+10 more)
Thermal
dust continuum polarimetry is a powerful indirect probe of
magnetic field geometry in dense molecular clouds while at the same time providing information on the
alignment of
dust grains with the
magnetic field. The leading theory of grain
alignment, Radiative Torque
Alignment (RAT), has been successful in explaining a variety of observations, including the loss of polarization fraction toward high column densities. One prediction of RAT is that an increase in grain
alignment efficiency should be observed in the environments surrounding protostars, due to radiation from the embedded source. However, observational confirmation of this prediction remains scarce. In this study, we sought to test the theoretical prediction of enhanced grain
alignment near protostars in the high-mass
star forming region DR21 using 214 $\mu m$ SOFIA/HAWC+ observations. We investigated the correlation of the polarization fraction of
dust emission, $p$, and the polarization angular dispersion, $S$, with respect to total intensity. We also probed intrinsic
dust polarization properties using the product $S\times p$ as a proxy. We detected significant polarization fractions even at the highest intensities, where strong depolarization is typically expected. The polarization fraction-intensity trend flattens at $I > 1.6^{+0.3}_{-0.3} \times 10^4$ MJy/sr ($N_{H_2}$ $\sim 2\times 10^{23}$ ${cm}^{-2}$). We compared the observed trends with predictions from an analytical model of a centrally heated envelope surrounding an embedded luminous protostar. The predictions from the simple model agree well with the observed trends. Our results provide strong support for enhancement of grain
alignment by local radiation from embedded sources.
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All authors S. Kumar, T.G.S. Pillai, G. V. Panopoulou, J. Kauffmann, L. N. Tram, S. Reissl, D. Clemens, V. J. M. Le Gouellec, M. Heyer, L. M. Fissel, P. F. Goldsmith, D. Seifried, G. A. P. Franco
Cosmology and Nongalactic Astrophysics
Halving and Doubling: Boosting the Detection of Relativistic Effects in the Galaxy Bispectrum with Optimal Subsample Selection
Samantha Josephine Rossiter, Stefano Camera, Federico Montano et al. (+3 more)
On the scale of the
cosmic horizon, signatures that are unique to general relativity are concealed within the statistics of the large scale distribution of
galaxies. These were thought to be beyond the reach of all but the most ambitious
galaxy surveys, as they are substantially suppressed relative to standard
redshift-space distortions. We show that the detectability of these higher-order relativistic effects can be dramatically enhanced by a sampling strategy that splits a
galaxy catalogue into faint and bright subsamples and then combines their auto-bispectra. For current surveys such as DESI, this implies that this new signal will be detectable for the first time using our new strategy.
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All authors Samantha Josephine Rossiter, Stefano Camera, Federico Montano, Chris Clarkson, Dionysios Karagiannis, Roy Maartens
Astrophysics of Galaxies
The Star Formation History of WLM from Asymptotic Giant Branch Stars and The Discovery of a Candidate Accreted System in its Outer Disk
Abigail J. Lee, Daniel R. Weisz, Andrew E. Dolphin et al. (+1 more)
We measure the
star formation history (SFH) of Local Group
dwarf galaxy WLM using wide-area ($\sim4$ half-light radii) ground-based near-infrared (NIR) imaging of bright ($M_{J}<-4.9$ mag) asymptotic
giant branch (AGB)
stars. From our NIR color-magnitude diagram (CMD) of 825
stars, we find that our recovered SFH is in excellent agreement with literature SFHs of WLM measured from much deeper CMDs ($M_{F090W}\sim+4.3$ mag) based on JWST imaging. We find good agreement in the qualitative shape of the SFHs as well as quantitative metrics such as the timescales for which 50% and 90% of the
stellar mass formed with $\tau_{50,{\rm AGB}}=5.16_{-0.50}^{+2.07}$ Gyr ago and $\tau_{90,{\rm AGB}}=1.33_{-0.09}^{+0.11}$ Gyr ago versus $\tau_{50,{\rm JWST}}=5.94_{-0.31}^{+0.37}$ Gyr ago and $\tau_{90, {\rm JWST}}=1.55_{-0.13}^{+0.03}$ Gyr ago. The coarser precision of the AGB
star-based values is driven by the low number of AGB
stars. We derive an age-
metallicity relation (AMR) from the AGB
star CMD fitting that is similar to the JWST-based AMR and is consistent with other reported
metallicities in WLM (i.e., spectroscopy, RR Lyrae). From our wide-area AGB
star map and SFH, we identify a
stellar over-density ($M_*\sim2.0\times10^6 M_{\odot}$, $r_h\sim340$ pc) in WLM's northwestern outer disk. Despite WLM having long been considered an isolated
galaxy, the mass, size, and age of this over-density are highly suggestive of an accreted
dwarf galaxy. Overall, our findings illustrate the power of NIR observations of AGB
stars for efficiently and accurately measuring SFHs and for identifying and characterizing substructures in nearby
galaxies.
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All authors Abigail J. Lee, Daniel R. Weisz, Andrew E. Dolphin, Alessandro Savino
Astrophysics of Galaxies
Small hosts, big appetites: unveiling rapid and early low-mass black hole growth in cosmological zoom-in simulations of dwarf galaxies
Giulia Ortame, Martin A. Bourne, Sophie Koudmani et al. (+3 more)
Dwarf galaxies are ideal laboratories to probe the interplay between
galaxy formation and the growth of black holes (BHs) in the early Universe. Mounting observational evidence reveals the presence of BHs in low-mass
galaxies across
cosmic time, with $\textit{JWST}$ uncovering a likely population of $\textit{overmassive}$ BHs at $2 \lesssim z \lesssim 11$. Simulations struggle to reproduce this high-
redshift regime, motivating revisions to models of BH
accretion and feedback from active
galactic nuclei (AGN). To address this, we present high-resolution cosmological zoom-in simulations of a
dwarf galaxy based on FABLE physics, introducing novel sink-based BH
accretion models and relaxing the fiducial assumption of strong
supernova feedback. BHs accrete more efficiently in the sink-based runs compared to the `traditional' Bondi-based counterparts, with AGN feedback leading to early, rapid quenching maintained by fast, hot and metal-enriched
outflows. These
outflows pollute the outer circumgalactic medium, yielding flat
metallicity gradients down to $z=0$. We further assess the performance of two widely used virial
estimators and find significant departures from the true dynamical mass, especially during the high-
redshift dwarf assembly. Since our
galaxy is dark-matter-dominated at all times and radii, BH growth, tied to the
baryon cycle, shows no clear correlation with global dynamical properties. Efficient AGN feedback is produced by overmassive BHs relative to extrapolated local $M_\bullet - M_\star$ relations, raising the possibility that dormant, overmassive BHs in local quenched
dwarfs and those probed by $\textit{JWST}$ may reflect a common mode of early and rapid BH growth in low-mass
galaxies.
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All authors Giulia Ortame, Martin A. Bourne, Sophie Koudmani, Debora Sijacki, Francesco D'Eugenio, Roberto Maiolino
Solar and Stellar Astrophysics
Spectroscopic follow-up of hot subdwarf variables found in ZTF – Atmospheric and fundamental properties of radial-mode sdB pulsators
Corey W. Bradshaw, Thomas Kupfer, Alekzander R. Kosakowski et al. (+2 more)
Hot subdwarf variables (sdBVs) that display large-amplitude ($>$1%), short-period variability, as a result of radial-mode pulsations, have recently become objects of interest as they show unique properties among the sdBV classes. Since the discovery of objects such as Balloon 090100001 and CS 1246, twelve more have been discovered in the Zwicky Transient Facility (ZTF) survey that display similar characteristics. However, due to lack of broad spectroscopic investigations, it remains unclear whether these objects constitute a distinct class of radial-mode dominant sdBVs that share common atmospheric and fundamental properties. Here we aim to spectroscopically define these peculiar sdBVs as a population. We collected low-resolution spectroscopy on a sample of sdBVs discovered in the ZTF survey, including time-series observations. We fitted the spectra to a grid of theoretical models to determine their mean effective temperature, surface
gravity and helium abundance and any corresponding variability. We then use these properties to estimate the mass, radius and luminosity using a spectral energy distribution fitting method. We show that the resulting properties are similar to the radial-mode dominant sdBVs, Balloon 090100001 and CS 1246, and that they are distinguishable from other similar radial-mode pulsators, such as blue large-amplitude pulsators. We find that these
stars, on average, have mean effective temperatures of 28,300 K and surface
gravity measurements of $\log\,g=5.56$, with changes in these parameters on the order of 1000 K and 0.10 dex, respectively. The location of these
stars on the $T_{\textrm{eff}}$ – $\log\,g$ plane places them on the boundary region between the low-amplitude, multi-periodic V361 Hya and V1093 Her
stars, where the hybrid DW Lyn pulsators lie. The masses and radii of the majority of the sdBVs in our sample align with canonical-mass sdB properties.
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All authors Corey W. Bradshaw, Thomas Kupfer, Alekzander R. Kosakowski, Brad N. Barlow, Matti Dorsch
High Energy Astrophysical Phenomena
Variance of gravitational-wave populations
Alessia Corelli, Davide Gerosa, Matthew Mould et al. (+1 more)
We quantify the impact of finite catalog size, or "catalog variance," on current gravitational-wave population analyses. The distribution of merging binary black holes is commonly reconstructed via hierarchical
Bayesian inference, with uncertainties reported as credible intervals. Such intervals are conditioned on the specific realization of the observed events and are therefore themselves subject to variability arising from the finite size of the catalog. We estimate this "uncertainty on the uncertainty" using statistical bootstrapping applied to data segments containing both detected events and sensitivity injections. Applying this framework to GWTC-4, we find that the inferred population distributions exhibit substantially broader uncertainties than those obtained in a standard single-catalog analysis. In particular, the $\sim 35\,M_\odot$ peak in the primary-mass distribution is largely absorbed by statistical fluctuations once catalog variance is taken into account. Unlike other studies that rely on simulating catalogs by assuming an underlying population, this work provides the first data-driven assessment of the uncertainty intrinsic to the observed gravitational-wave catalog. Accounting for catalog variance is important for drawing robust astrophysical conclusions from gravitational-wave data, avoiding inferences driven by a particular finite realization rather than genuine population features.
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All authors Alessia Corelli, Davide Gerosa, Matthew Mould, Cecilia Maria Fabbri
High Energy Astrophysical Phenomena
Constraining the synchrotron peak and estimating the VHE brightness of a sample of extreme high synchrotron peak blazars
Federica Sibani, Stefano Marchesi, Ettore Bronzini et al. (+5 more)
We present the results of a multi-wavelength study of a population of X-ray bright ($\rm log(F_{0.2-12 \ keV})>-12.5$), non-$\gamma$-ray detected high and extreme high synchrotron peak (HSP, EHSP; $\rm log(\nu_{\rm peak,\ Hz})>16$) BL Lacs to $i$) put stronger constraints on the synchrotron peak location and shape and $ii$) model their expected behaviour in the very high-energy band. First, we performed an X-ray spectral analysis, using XMM-Newton, Chandra, Swift-XRT, and eROSITA data, and fitting the spectra using both a power law and a log parabola model. Out of 78 sources in the initial sample, 17 were best described by a log parabola model, a result that supports a scenario where the synchrotron peak falls in the X-ray band. Among these 17 sources, we further selected the 10 objects dominated by the jet emission, with no significant contamination of the host
galaxy. We performed a $\gamma$-ray analysis of \lat\ data for these objects, obtaining upper limits providing information on their flux in the 100 MeV - 300 GeV energy range. We then modelled the broadband SED of these objects with JetSeT using two models: one assuming a log parabola for the electron distribution and the other one with a broken power law electron distribution, using parameters consistent with those describing the emission of the prototypical EHSP 1ES 0229+200. We found the models to be generally consistent with the available multi-wavelength detections and upper limits. Furthermore, they confirmed that a subsample of sources could display relevant emission in the TeV energy range, even potentially reaching the threshold for detectability by the Cherenkov
Telescope Array Observatory.
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All authors Federica Sibani, Stefano Marchesi, Ettore Bronzini, Marco Ajello, Michele Doro, Lea Marcotulli, Elisa Prandini, Cristian Vignali
Astrophysics of Galaxies
GA-NIFS: Dissecting The Alchemised: JWST reveals turbulent metal-poor gas fuelling a co-spatial starburst in a complex system at $z=10.17$
Robert G. Pascalau, Francesco D'Eugenio, Roberto Maiolino et al. (+25 more)
Recent observations revealed that distant
galaxies have bursty
star formation histories, regulated by
stellar or active
galactic nuclei (AGN) feedback and gas inflows. According to theoretical models, feedback preferentially removes metal-rich gas, while subsequent starbursts are triggered by mergers and newly accreted gas that is generally less enriched than the
galaxy's interstellar medium (ISM). Therefore, gas-phase
metallicity provides key insights into the baryonic processes shaping early
galaxies. We present the first NIRSpec/IFU study of spatially resolved ISM properties in the MACS0647-JD system ($z=10.17$). The system consists of two
stellar components detected in NIRSpec/IFU and NIRCam photometry. The main component ($\log \left(M_{\ast}/M_{\odot}\right)=7.77 \pm0.09$; $12+\log\left(\rm O/H\right)=7.89 \pm 0.16$) is more massive and significantly more metal-rich compared to its companion ($\log \left(M_{\ast}/M_{\odot}\right)=7.42\pm0.07$; $12+\log\left(\rm O/H\right)=7.47 \pm 0.20$), suggesting an older
stellar population and a prolonged chemical enrichment history. We find that the H$\gamma$ line emission centroid is spatially offset by $\sim 0.1^{\prime \prime}$ (150 pc in the source plane) from the
stellar continuum centroid; the latter coincides with the location of the main
stellar component. This offset provides possible evidence of a merger-driven starburst in this system. By comparing the spatial distributions of the
metallicity, velocity dispersion, and the burstiness of
star formation history, we infer the presence of turbulent, metal-poor gas outside the
stellar components. %detected in both NIRSpec/IFU and NIRCam photometry. This metal-poor, dynamically unstable gas is likely responsible for the enhanced recent
star formation in the north-east region of the system.
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All authors Robert G. Pascalau, Francesco D'Eugenio, Roberto Maiolino, Qiao Duan, Yuki Isobe, Santiago Arribas, Andrew J. Bunker, Stéphane Charlot, Michele Perna, Bruno Rodriguez Del Pino, Hannah Ubler, Elena Bertola, Torsten Boker, Stefano Carniani, Dan Coe, Giovanni Cresci, Mirko Curti, Tiger Y.Y. Hsiao, Lucy R. Ivey, Gareth C. Jones, Isabella Lamperti, Eleonora Parlanti, Jan Scholtz, Sandro Tacchella, Lorenzo Ulivi, Giacomo Venturi, Joris Witstok, Sandra Zamora
Solar and Stellar Astrophysics
Calibrating Eruptive Mass Loss in Red Supergiants with Local Group Data
Shelley J. Cheng, Charlie Conroy and Jared A. Goldberg
We calibrate a physically motivated, super-Eddington eruptive mass-loss prescription for red supergiants (RSGs) using Local Group
stellar populations. Building on MESA models that add eruptive mass loss with a free scaling parameter $\xi$, we generate
stellar evolution tracks and isochrones, and synthesize mock populations at
metallicities of $Z/Z_\odot=0.2,\ 0.4$, and $1.0$. We compare model luminosity functions to observations of RSGs in the SMC, LMC, and M31, restricting to $3.5<\log T_{\rm eff}/K<3.75$ and $\log(L/L_\odot)>4.5$. By-eye fits to the observations yield values of $\xi_\mathrm{SMC}=0.0-0.05$, $\xi_\mathrm{LMC}=0.1$, and $\xi_\mathrm{M31}=0.35$, implying a positive, linear trend between the strength of eruptive mass-loss and
metallicity. This calibrated eruptive mass loss prevents
stars with initial masses $\gtrsim 20~M_\odot$ from evolving to become red supergiants, with implications for the mass spectrum of core-collapse progenitors, compact remnants, early
supernova interaction signatures, and the spectral energy distributions of unresolved
galaxies.
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Astrophysics of Galaxies
The Baryon Budget of Galaxies across the First Billion Years
Umberto Maio and Céline Péroux
We provide a complete census of the
baryons in early
galaxies to investigate the phases in which gas and
stars reside, their corresponding budgets, depletion times, and
stellar return fraction as a function of
redshift and
stellar age. We use the ColdSIM hydrodynamical time-dependent non-
equilibrium chemistry simulations and perform a detailed analysis of the cold, warm, hot, and
stellar phases for both bound structures (
galaxies/CGM) and the diffuse IGM. We investigate in depth the cold HI and H2 components, explicitly computed in our simulations, and their relations with host mass, SFR,
metallicity and depletion times. We also provide observational insights and discuss the implications for
stellar mass functions, PopIII
star formation and changes in the IMF. We find that
cosmic gas prior to reionisation is mostly cold, while at later epochs the warm phase becomes dominant due to enhanced
star formation activity and increasing UV reionising radiation.
Stellar return fractions at these times are ~0.15-0.20, a factor of two lower than the values usually adopted. Cold, warm, and hot gas masses as well as HI and H2 components show increasing trends with mass and SFR, while depletion times decrease down to 0.01-0.1 Gyr with a weak
metallicity dependence. The resulting
star formation efficiency remains at the level of a few per cent and gas-to-
star fractions decline with mass, influenced by local feedback and environment. Our findings are consistent with ALMA, VLA and IRAM surveys at later epochs, including ALFALFA, xCOLDGASS, GASS, xGASS, EDGE-CALIFA, PHIBBS, and ASPECS. Gas phases are quantitatively related to the underlying
stellar populations and can be used to infer unknown quantities. In the appendix we provide fit functions describing the trends of the
stellar return fraction, the main sequence, phase mass relations, gas-to-
star fractions and depletion times.
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Solar and Stellar Astrophysics
Long-term Spectroscopic Survey of the Hyades Cluster: The Binary Population
Guillermo Torres, Robert P. Stefanik and David W. Latham
We report the results of a radial velocity monitoring program in the Hyades region, carried out at the Center for Astrophysics over a period of more than 45 yr. Nearly 12,000 spectra were gathered for 625
stars brighter than $V \approx 14.5$, of which 55% are members or possible members of the cluster. New or updated spectroscopic orbital solutions are presented for more than 100 members and non-members, including several triple systems. In a few cases we incorporate available astrometry. The frequency of binaries in the Hyades with periods up to $10^4$ days is determined to be $40 \pm 5$%, after corrections for incompleteness. This is marginally higher than in other open clusters. The orbital period and eccentricity distributions are found to be similar to those of
solar-type binaries in the field. The mass ratio distribution is essentially flat, or slightly rising toward mass ratios of unity. We revisit the determination of the
tidal circularization period, obtaining a longer $P_{\rm circ}$ value of $5.9 \pm 1.1$ days compared to the previous estimate of 3.2 days, still somewhat short of the value expected if most or all of the action of tides happens during the pre-main-sequence phase. We estimate a line-of-sight velocity dispersion of $0.21 \pm 0.05$ km s$^{-1}$ within 5.5 pc of the cluster center (approximately the half-mass radius) and a larger dispersion beyond that distance. Our velocity measurements are accurate enough to clearly reveal the signatures of gravitational
redshift and convective blueshift among the
dwarfs and
giants in the Hyades.
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High Energy Astrophysical Phenomena
Quasi-periodic Eruptions from Stellar-mass Black Holes Impacting Accretion Disks in Galactic Nuclei
Kun Liu, Shang-Fei Liu, Zhen Pan et al. (+3 more)
We investigate the origins of quasi-periodic eruptions (QPEs) in
galactic nuclei using global three-dimensional meshless finite-mass (MFM) simulations. By modeling
stellar and black-hole impactors traversing
accretion disks under various inclinations and surface densities, we evaluate their consistency with the observed properties of QPEs.
Stellar impacts produce highly asymmetric bipolar ejecta with forward outbursts dominating by over an order of magnitude in energy and luminosity due to the
star blocking downstream flow and creating a low-density wake. This shock-compression mechanism often renders backward events unobservable, implying one detectable burst per orbit, and challenging the standard assumption of two bursts. It also fails to explain alternating long–short recurrence patterns and places several sources near or within twice the
tidal disruption radius for
solar-mass
stars, raising severe stability concerns. Whereas a
stellar-mass black hole (sBH) gravitationally focuses and heats disk gas over an effective interaction scale that extends beyond its Bondi radius $R_{\rm B}$ and is naturally bounded by its Hill radius $R_{\rm H}$ during an impact, yielding nearly symmetric ejecta with mild contrasts. This gravitational-drag mechanism generates higher energy budgets at low inclinations due to enhanced mass accumulation. We suggest an ad hoc effective interaction radius $ R_{\rm eff} \simeq 0.5\, R_{\rm B}^{1/3} R_{\rm H}^{2/3} $ to quantify this trend. Incorporating this effective radius substantially increases the energy that sBH-disk collisions can produce compared to previous Bondi-only estimates, improving the viability of
stellar-mass black holes as the impactors for a wide range of observed QPE energies and properties.
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All authors Kun Liu, Shang-Fei Liu, Zhen Pan, Hongping Deng, Rongfeng Shen, Cong Yu
High Energy Astrophysical Phenomena
Spacetime in motion: an evolving relativistic binary black hole metric for GIZMO
Giacomo Fedrigo, Alessandro Lupi, Alessia Franchini et al. (+1 more)
The last evolutionary stages of massive black hole binaries prior to coalescence is dominated by the emission of gravitational waves, which will be probed by the future
Laser Interferometer Space
Antenna. If gas is present around the two black holes, however, the associated electromagnetic emission can provide additional information about the binary properties and location before the merger event. For this reason, a proper characterisation of the electromagnetic emission during these phases is of fundamental importance, and requires a detailed description of the gas dynamics close to the event horizon of the two black holes, only achievable via numerical simulations. Within this context, we present the implementation of the Superposed Kerr-Schild dynamic metric in the relativistic scheme in the meshless code GIZMO. Our code can now simulate black hole binaries approaching merger with high computational efficiency and accuracy, taking into account relativistic effects on the gas. To validate our implementation, we perform two tests. First, we explore the case of a relativistic Bondi flow around a binary, finding very good agreement with numerical relativity simulations. Then we explore the case of an inviscid relativistic circumbinary disc, comparing our results with a similar simulation run assuming Newtonian
gravity. In this second case, we find moderate differences in the mass
accretion rate and in the inflow dynamics, which suggest that the presence of a non-Keplerian potential and of apsidal precession in the orbiting gas trajectories may produce stronger shocks and boost angular momentum transport in the disc. Our work highlights the importance of accounting for relativistic corrections in
accretion disc simulations around black hole binaries approaching merger, even at scales much larger than those currently probed by numerical relativity simulations.
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All authors Giacomo Fedrigo, Alessandro Lupi, Alessia Franchini, Matteo Bonetti
Solar and Stellar Astrophysics
Stellar engines and Dyson bubbles can be stable
Colin R McInnes
A range of speculative space ventures envisage the use of ultra-large structures for the collection and reflection of light. Given the length-scale of such structures they cannot be considered as point masses for the calculation of gravitational and radiation pressure forces. Using a simplified model it will be demonstrated that ultra-large reflectors in static
equilibrium levitating above a central
star (so-called
stellar engines) are always unstable if the reflector comprises a uniform disc. However, if the reflector has a non-uniform mass distribution, specifically a ring supporting a reflect or, a
stellar engine can in principle be passively stable. Moreover, while it can be shown that static swarms of reflectors levitating above a central
star (so-called Dyson bubbles) are unstable, in principle they can become passively self-stabilizing if arranged about the
star as a dense cloud. While such ventures are clearly speculative, understanding the orbital dynamics of ultra-large structures, and in particular the conditions for passive stability, can provide insights into the properties of potential technosignatures in search for extraterrestrial intelligence studies.
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Astrophysics of Galaxies
Direct VLBI Detection of Interstellar Turbulence Imprint on a Quasar: TXS 2005+403
Alexander Plavin, Alexander Pushkarev and Yuri Kovalev
We report the first unambiguous detection of refractive substructure in an active
galactic nucleus (AGN) using ground-based Very Long Baseline Interferometry (VLBI). Our analysis of TXS 2005+403 - observed at 1-5 GHz along a line of sight through the Cygnus region - reveals clear signatures of
turbulence-induced substructure on long baselines that cannot be explained by the smooth scatter-broadened profile from diffractive effects alone. This signal persists across multiple observations spanning 2010-2019, demonstrating stable scattering properties along this line of sight. The combination of high flux density, compact intrinsic structure, and strong scattering establishes TXS 2005+403 as an exceptional laboratory for probing
Galactic turbulence. This detection demonstrates that AGNs can serve as
cosmic lighthouses illuminating interstellar
plasma across the sky, complementing
pulsar scintillation studies and informing scattering mitigation for millimeter-wavelength imaging of Sagittarius A*.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Fermion Mass Hierarchy and a High Quality Axion From Gauged U(1) Flavor Symmetry
K.S. Babu, Sai Charan Chandrasekar and Zurab Tavartkiladze
We present a class of models based on a gauged $U(1)_F$
flavor symmetry that explains the hierarchical structure of
fermion masses and mixings via the Froggatt-Nielsen (FN) mechanism, while also solving the strong CP problem by the Peccei-Quinn (PQ) mechanism. A global $U(1)_{\rm PQ}$
symmetry with a nonzero QCD anomaly emerges accidentally in this setup as a byproduct of the gauged $U(1)_F$
symmetry. The resulting
axion is shown to be of high quality, with the
axion potential safeguarded against
quantum gravity corrections by the gauge
symmetry. Three models, which are generalizations of the Dine-Fischler-Srednicki-Zhitnitsky (DFSZ)
axion model, are presented realizing this idea. The right-handed
neutrino mass scale is identified as the Froggatt-Nielsen scale in these models. We present explicit UV completions of the FN sectors of these models and show that they preserve the high quality of the
axion. In these models, the
axion acts as a flavon field, leading to testable predictions in
flavor-changing decays of neutral
mesons. The
axion also serves as the dark matter of the universe with the right amount of relic abundance without causing cosmological domain wall problems.
Baryon asymmetry of the universe is realized via leptogenesis which is calculable in these models and found to be of the right order of magnitude.
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Solar and Stellar Astrophysics
The First Four Ground-Level Enhancements in the 1940s: Investigation, Digitisation, and Analysis of Forgotten Data
Hisashi Hayakawa, Stepan Poluianov, Sergey Koldobskiy et al. (+4 more)
Intense
solar eruptions occasionally accelerate
solar energetic particles (SEPs) and can trigger ground-level enhancements (GLEs). Among the 77 known GLEs, the first four GLEs, #1 – 4 in the 1940s took place before the advent of the standard
neutron monitors and were missing from the International GLE Database. This data gap challenged their quantification. To overcome this difficulty, we systematically gathered, digitised, and quantified contemporaneous
cosmic-ray records pertaining to these GLEs. These data allow us to reconstruct the temporal
evolution, with the 1 – 15 min resolutions, of these GLEs, and broaden their geographical coverage to a global scale. GLEs #1 and #3 exhibited gradual increases in their rise times, measured at 45 +/- 15 and 105 +/- 15 min, respectively. In contrast, GLEs #2 and #4 both exhibited abrupt increases of 15 +/- 15 min. We also compared integral ionisation increase on the standard ionisation chambers and their local geomagnetic cutoff
rigidities Pc to qualitatively compare these GLE's spectral hardness: Our result indicates that their spectra are extremely hard for GLEs #2 and #4 and mildly hard for GLEs #1 and #3. GLE #3 showed the greatest integral ionisations for polar detectors among them.
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All authors Hisashi Hayakawa, Stepan Poluianov, Sergey Koldobskiy, Alexander Mishev, Nicholas Larsen, Inna Usoskina, Ilya Usoskin
Solar and Stellar Astrophysics
In-flight calibration of RADEM, the JUICE mission radiation monitor
Marco Pinto, Francisca Santos, António Gomes et al. (+7 more)
The RADiation-hard Electron Monitor (RADEM) aboard the Jupiter Icy Moons Explorer (JUICE), launched on 14 April 2023, measures high-energy
protons and electrons during the cruise phase and will continue throughout the nominal mission. Initial in-flight observations could not be explained by pre-flight ground calibration, motivating an in-flight calibration campaign. We calibrated the RADEM sensors using
galactic cosmic rays by progressively increasing detector thresholds, thereby modifying their response to high-energy particles. Threshold-dependent in-flight count rates were compared with theoretical expectations derived from the Badhwar-O'Neill 2020
galactic cosmic ray model and corresponding response functions. These results were used to derive new in-flight calibration coefficients and to develop a flux reconstruction
algorithm based on the bow-tie method. In several cases, the in-flight calibration slopes differ by up to an order of magnitude from ground calibration values.
Proton fluxes from
solar energetic particle events reconstructed with this method agree within a factor of two with independent measurements from the
Solar and Heliospheric Observatory. These results demonstrate that RADEM provides accurate
proton flux measurements in interplanetary space and is well suited for both single-spacecraft analyses and coordinated multi-mission studies of
solar energetic particles. While electrons were clearly detected during the JUICE Lunar-Earth
gravity assist, reliable reconstruction of their fluxes requires further analysis.
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All authors Marco Pinto, Francisca Santos, António Gomes, Tomás Gonçalves, Luísa Arruda, Patrícia Gonçalves, Laura Rodríguez-García, Rami Vainio, Olivier Witasse, Nicolas Altobelli
Instrumentation and Methods for Astrophysics
Principal Component Analysis for ACS/WFC Superbias Temporal Variation
Alyssa M. Guzman and Norman A. Grogin
We examined the long-term behavior of the superbias calibration frames for the Advanced Camera for Surveys Wide Field Channel (ACS/WFC) aboard the Hubble Space
Telescope (HST). Superbias frames are used to remove detector-level bias structure from science images and are currently generated after an anneal and delivered monthly. The primary goal of this study was to determine whether the frequency of superbias generation could be reduced without compromising calibration quality, potentially aligning with the Wide Field Camera 3 UVIS (WFC3/UVIS) approach of generating only one superbias per year. We analyzed superbias frames produced from 2007 through 2024 to investigate whether these calibration products have changed significantly over time, and whether the frequency of superbias generation and delivery could be safely reduced without loss of calibration accuracy. In addition to visual inspections and pixel-level comparisons, we employed Principal Component Analysis (PCA) to evaluate whether any long-term, global structure exists beneath the apparent noise in these frames. Our findings show that the superbias structure has remained fairly stable post-Servicing Mission 4 (SM4), a 15-year period, and no significant or unexpected global trends or systematic shifts were detected. However, due to unstable hot columns and increasing readout dark observed in ACS/WFC data, it is likely that these calibrations still benefit from more frequent superbias updates than the annual cadence adopted for WFC3/UVIS.
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Astrophysics of Galaxies
First spectroscopic identification of the main sequence in Westerlund 1
R. Castellanos, F. Najarro, M. Garcia et al. (+8 more)
Being the most massive known young
stellar cluster in the Milky Way, Westerlund 1 (Wd1) constitutes an ideal
benchmark for understanding the
evolution of massive
stars. However, the cluster age remains highly controversial (~4-10 Myr), hindering the use of Wd1 as a reference for massive
star evolution. One of the main issues is high foreground extinction, which has so far prevented the detection of the main sequence. Using infrared spectroscopy we seek to detect the cluster's main sequence for the first time, to characterise the Hertzsprung-Russell diagram, and to use the cluster's turn-off to obtain a robust age estimate. We obtained multi-epoch, near-infrared VLT/KMOS spectroscopic observations of Wd1 to map its population of massive
stars. The spectra of ~110 members were analysed with CMFGEN models to derive
stellar parameters, populate the cluster Hertzsprung-Russell diagram, and compare it with isochrones from evolutionary models. Our observations returned 47 new spectroscopically identified cluster members, with spectral types O9-B1 III-V. The cluster turn-off indicates an age of 5.5+/-1.0 Myr at a distance of 4.23+0.23-0.21 kpc, displaying a moderate degree of coevality. We demonstrate that our estimate of the age of Wd1 is robust against reasonable changes in the distance and extinction law, and the adopted rotational velocity and
metallicity of the
stellar isochrones. We further find that ~65% of the OB
stars with multi-epoch coverage exhibit radial-velocity variability. Infrared observations of the unevolved
stellar population support a single episode of
star formation with an age of ~5.5 Myr, reinforcing its potential as a
benchmark for massive
star evolution and providing a reference sample for future binary population studies.
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All authors R. Castellanos, F. Najarro, M. Garcia, I. Negueruela, L.R. Patrick, B. Ritchie, M.G. Guarcello, T. Shenar, C. Evans, R. Prinja, D. Fenech
High Energy Astrophysical Phenomena
Weak emission line quasar SDSS J101353.45+492758.1 I. Continuum fitting
Laetitia Gibaud, Marek Nikołajuk, Piotr Życki et al. (+3 more)
We present a broadband study of the WLQ SDSS J101353.45+492758.1, which displays a nearly featureless UV-optical spectrum with only a weak Mg II line alongside an exceptionally low X-ray flux. We model its spectral energy distribution using the relativistic thin-disk model kerrbb with a power law, and the multicomponent AGN model relagn, a physically motivated extension of agnsed incorporating warm and hot Comptonizing regions. Our fits constrain the black hole mass,
accretion rate, X-ray loudness, and coronal energetics. Both approaches yield consistent BH masses of M_{BH} \approx 2 \times 10^{9} M_\odot and an Eddington
accretion rate of \dot m \approx 0.1. The relagn fit including a warm Comptonizing region provides a significantly improved representation of the UV-soft X-ray continuum. The warm corona, characterized by kTe \simeq 0.20 keV, {\Gamma} \simeq 3.8, and an optical depth {\tau} \simeq 7.26, extends to \sim 34 R_g. The hot corona appears compact and energetically suppressed, leading to an intrinsically weak X ray output with log(L_{X}/L_{bol}) \simeq -4.29, among the lowest reported for WLQs. The {\alpha}_{ox} \sim 2.06 indicates the source to be in high/soft AGN spectral state. The combination of a luminous, standard disk and extremely weak hot corona suggests that this
quasar hosts a highly inefficient inner coronal region. This explains its X-ray faintness and extreme deficit of high-ionization emission lines. The source may represent an AGN analog in "ultrasoft"
accretion state, or a system in which the ionizing continuum is suppressed by a compact or quenched corona. Our study suggests that the source is not accreting at high Eddington ratio, highlighting the physical diversity of WLQs, and supports the view that
geometric and radiative effects jointly shape their extreme spectral properties.
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All authors Laetitia Gibaud, Marek Nikołajuk, Piotr Życki, Agata Różańska, Krzysztof Hryniewicz, Rafał Wojaczyński