Cosmology and Nongalactic Astrophysics
Audible curvaton: modulated phase transition as the origin of large-scale curvature perturbations and gravitational wave anisotropies
Wen-Yuan Ai, Gabriele Franciolini, Xin Wang et al. (+1 more)
We propose a post-inflationary first-order phase transition modulated by a light spectator field as the origin of primordial large-scale
curvature perturbations. Spectator fluctuations acquired during inflation modulate the bubble nucleation history, generating
curvature perturbations together with correlated intrinsic gravitational-wave (GW) anisotropies. We show that this mechanism can reproduce the observed amplitude of
curvature perturbations while producing a loud
stochastic GW background in the frequency bands of space-based detectors such as LISA, Taiji, and TianQin. A concrete
benchmark yields strongly enhanced intrinsic GW anisotropies and a local primordial non-Gaussianity signal within reach of future large-scale-structure surveys.
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All authors Wen-Yuan Ai, Gabriele Franciolini, Xin Wang, Xiang-Xi Zeng
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Spinformation: do gravitational-wave events carry information beyond effective spins?
Cailin Plunkett, Jack Heinzel, Noah E. Wolfe et al. (+2 more)
While the
spin vectors of binary black holes offer insight into the astrophysical formation channels of these systems, individual
spins are less precisely measured through gravitational-wave observations than the effective inspiral
spin $\chi_\mathrm{eff}$ and the effective precession
spin $\chi_\mathrm{p}$. Reducing to effective parameters discards information in the data, but how much information is lost has yet to be demonstrated. Here we show how to quantify whether individual mergers carry information about component
spins beyond the constraints implied by effective parameters (a.k.a. spinformation) and apply the technique to GWTC-5. Thresholding on information loss $\gtrsim 0.25$ bits, over $80\%$ of gravitational-wave events in GWTC-5 have component
spin posteriors described by $\chi_\mathrm{eff}$ alone. Only $\sim3\%$ of gravitational-wave events have substantial
spin information not explained by $\chi_\mathrm{eff}$ and $\chi_\mathrm{p}$. The catalog's component
spin information is effectively two-dimensional in $\chi_\mathrm{eff}$ and $\chi_\mathrm{p}$. Using simulated signals, we find the noise realization can create or destroy over a bit of beyond-$\chi_\mathrm{eff}$ information: the structure in real data may therefore be driven by noise. At current sensitivity, component
spins provide interpretive\textemdash rather than informational\textemdash advantage over effective parameters.
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All authors Cailin Plunkett, Jack Heinzel, Noah E. Wolfe, Davide Gerosa, Salvatore Vitale
High Energy Astrophysical Phenomena
The Second Catalog of Low-Energy Fermi-LAT Sources
The Fermi-LAT Collaboration
We used 14 years of Fermi-Large Area
Telescope (LAT) data to derive a catalog of sources detected between 20 MeV and 200 MeV. For each source we provide localization, spectral, and association information. The Second Catalog of Low-Energy Fermi-LAT sources (2FLE) contains 450 sources detected at $TS>25$, with median energy flux of $F_{20-200 \, \text{MeV}} = 1.9\times10^{-11}$ erg cm$^{-2}$ s$^{-1}$. Using a
Bayesian and likelihood-ratio method, we associate 377 2FLE sources with a known counterpart. Of the 325 objects associated with extragalactic sources, the dominant source class represented in the 2FLE are flat-spectrum
radio quasars (FSRQ). Additionally, 52 sources are associated with Galactic sources. Three associated sources have not been previously detected in any $\gamma$-ray catalog and represent new $\gamma$-ray sources of known origin. We find that 387 2FLE sources have a positional cross-match with the 4FGL-DR4 sources. For the sources with a 4FGL counterpart, we compare the spectrum of the 2FLE source to the 4FGL spectral energy distributions. Of the 73 2FLE sources without multi-wavelength associations, 13 have a 4FGL counterpart that lacks classification, while 60 are newly discovered $\gamma$-ray sources. Among these 60 sources, 51 are found at high latitudes ($|b|>10^{\circ}$), and 38 are detected at $>10\sigma$. Additionally, we find that out of the 450 2FLE sources 45 are TeV emitters, and 6 are spatially coincident with a 1LHAASO source. The 2FLE helps us pave the way for reducing the “MeV gap", and provides the most sensitive catalog between 20-200 MeV to date.
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Astrophysics of Galaxies
Wave Cold Dark Matter Can Reproduce the Radial Acceleration Relation in X-ray Elliptical Galaxies
Runyu Meng and Xiaobo Dong
Wave cold dark matter (wave CDM) is a well-motivated variant within the collisionless CDM paradigm, in which the de~Broglie wavelengths of ultralight
bosons become relevant on galactic scales. While many of the previous tests of wave CDM have focused on small-scale tensions involving solitonic cores and certain
soliton–
halo relations in
galaxies, the radial acceleration relation (RAR) provides a complementary test: for a given baryonic mass distribution, it probes whether the DM
halo can reproduce the observed total gravitational field. In this work we test wave CDM against the RAR using eight X-ray elliptical
galaxies from the compilation of Lelli et al. We perform a suite of 3D Schrödinger–Poisson simulations and evolve the wave-CDM
halos to virialized quasi-stationary states. For each
galaxy and each adopted
boson mass, we select the realization whose final snapshot most closely matches the empirical RAR. We find that the selected wave-CDM realizations for these elliptical
galaxies can reproduce the RAR without including baryonic feedback or dark-matter self-interactions. At the
boson mass $m_a=10^{-23}$eV, the combined fit to the eight
galaxies gives $a_0=1.19\times10^{-10}\,\mathrm{m\,s^{-2}}$, consistent with the canonical value inferred from disk
galaxies. When the
boson mass is varied over $3\times 10^{-24}$ eV $\le m_a \le 2\times 10^{-23}$ eV, the best-fit value of $a_0$ changes by only $\sim 11\%$, and this variation shows no systematic trend with $m_a$. This insensitivity to
boson mass arises because, over the radial range relevant for the RAR, the virialized
halos are supported mainly by their velocity field, whereas the
boson-mass-dependent
quantum-pressure term is dynamically subdominant. These results show that wave CDM can reproduce the RAR in elliptical
galaxies, and provide a new galactic-scale test of the model beyond the previous focus on solitonic cores.
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Astrophysics of Galaxies
The Dance of the Little Red Dots: Spectroscopy of Two Blue Companions at z = 3.9 and 5.5 Reveals Young, Metal-Poor Starbursts Merging with Their LRDs within a Few Hundred Myr
Fabio Pacucci and Pierluigi Rinaldi
The Little Red Dots (LRDs) are compact, red sources, abundant at $4 \lesssim z \lesssim 9$ and likely powered by massive black holes. Photometric studies have found blue companions around them, but none has yet been confirmed spectroscopically. This Letter presents the only two LRD-companion pairs with spectroscopy of both members in the literature: "Waltz" at $z = 3.9$ and "Tango" at $z = 5.5$, with projected separations of $3.6$ and $2.5$ kpc. Both companions lie at the
redshift of their LRD, within $132 \, \rm km \, s^{-1}$ and $57 \, \rm km \, s^{-1}$, and are physically identical, but $524$ Myr apart: starbursts $\lesssim 50$ Myr old, metal-poor ($0.2 \, \rm Z_\odot$), dust-free, dynamically cold, and as bright as the LRDs themselves in the rest-frame UV. The LRD in Waltz hosts a $\approx 3 \times 10^{6} \, \rm M_\odot$ black hole accreting at half the Eddington rate, a factor of a few above the birth mass of a direct collapse black hole, and is embedded in gas as metal-poor as its companion. Orbital modeling shows that Tango is bound in $81\%$ of the allowed orbits and that Waltz is bound if its host
halo exceeds $5 \times 10^{10} \, \rm M_\odot$. Both blue companions then merge with their respective LRD within a few hundred Myr. We conclude that we are observing what heavy seeding requires: a young black hole beside the metal-poor starburst that the synchronized-pair scenario predicts, in the last steps of a
cosmic dance that ends in a merger, and in a
galaxy seeded by its black hole.
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Solar and Stellar Astrophysics
Any colour you like: The diverse chromaticities of white dwarfs
Mark A. Hollands, Boris T. Gaensicke, Pier-Emmanuel Tremblay et al. (+1 more)
Main sequence
stars have perceived colours ranging from orange to white to blue with increasing effective temperature. This is because their atmospheric opacities cause only minor deviations from blackbody colours when integrated over the broadband sensitivity curves of the human visual system. White dwarfs can have much denser atmospheres, reaching ~ 1 g/cm3 for the coolest known objects. If metals such as carbon, calcium, or sodium are present in these ultra-dense atmospheres, extreme broadening of atomic and molecular opacities can produce optical spectra that diverge significantly from blackbodies. We investigated how the combination of temperature and chemical composition can affect the perceived colours (chromaticity) of white dwarfs. While we found that most white dwarfs are similar in colour to blackbodies, we also demonstrate examples of known
stars that would appear yellow, green, cyan, pink, or purple if viewed close enough for their stellar discs to be resolved. We examined the chromaticity distribution for the volume-limited 20 pc local sample of white dwarfs finding a median correlated colour temperature of ~= 6800 K, establishing that, on average, white dwarfs are indeed white in colour. Finally we show how white dwarf spectral models can be used to generate colour-accurate images of their stellar discs as they would appear from up close.
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All authors Mark A. Hollands, Boris T. Gaensicke, Pier-Emmanuel Tremblay, Detlev Koester
Astrophysics of Galaxies
EMRIs in Kerr Spacetime: The Role of Inclination Diffusion
Yael Alush, Nicholas C. Stone and Scott A. Hughes
Extreme mass ratio inspirals (EMRIs) are expected to be a major source of gravitational waves (GWs) for the future
Laser Interferometer Space
Antenna (LISA). An EMRI occurs when a compact object, driven by the emission of gravitational radiation, slowly inspirals into a massive black hole (MBH). The classical formation channel involves repeated two-body interactions within dense nuclear
star clusters. However, both EMRI event rates and the expected distribution of their orbital parameters remain highly uncertain. A major source of this uncertainty is the poorly constrained ratio between gradually inspiraling EMRIs and direct plunges, which do not produce detectable GWs. While most studies of astrophysical EMRI production focus on the Schwarzschild limit, previous work examining the Kerr metric found that the
spin of the central MBH can significantly affect the EMRI-to-plunge ratio. This enhancement depends sensitively on orbital inclination, yet earlier studies held inclination fixed. In this work, we develop the mathematical framework describing inclination
evolution driven by two-body encounters evolving along Kerr geodesics. By implementing 3D
diffusion into Monte Carlo simulations, we show that initially prograde orbits may evolve into retrograde states, thereby converting potential EMRIs into plunges or vice versa. We estimate the EMRI-to-plunge ratio and find that substantial MBH
spin enhances the EMRI rate by a factor of $\sim 2.5$. Additionally, even for a non-spinning MBH, modeling the orbits as relativistic geodesics rather than Newtonian trajectories increases the number of EMRIs by a similar factor of $\sim 2.5$. The distribution of Kerr EMRI inclinations has a substantial prograde bias that may aid in identifying the subset of loss cone EMRIs within large future EMRI samples.
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High Energy Astrophysical Phenomena
Identity Crisis: Untangling Mass-Ordering Artifacts from Compact-Object Pairing in Gravitational-Wave Populations
Soumendra Kishore Roy, Asad Hussain, L. A. C. van Son et al. (+3 more)
Mass distributions of binary black hole mergers inferred from gravitational-wave observations offer clues to how binaries form. These distributions conventionally label the heavier component as the primary, with mass $m_1$, and the lighter as the secondary, with mass $m_2$, such that $m_1 \geq m_2$. This ordering folds the physically labeled mass distribution along the equal-mass line, potentially reshaping the underlying population structure. In this Letter, we determine which population features can arise from mass ordering and which require genuine astrophysical structure. We show that ordering alone can produce (1) an $m_2$ distribution that declines more rapidly than the $m_1$ distribution, without intrinsic differences between the physically labeled components, and (2) an apparent concentration along equal masses, without correlations that preferentially pair black holes of equal mass. Moreover, different physically labeled populations can produce the same ordered mass distribution. Crucially, however, a preferred companion mass that remains constant as $m_1$ increases requires a characteristic mass scale already present in the physically labeled population. Applied to binary black hole mergers in the fifth Gravitational-Wave Transient Catalog, our model recovers such a scale near $m_2 \simeq 50\,\mathrm{M}_\odot$. Around this scale, the merger-rate density declines much more rapidly toward higher $m_2$ than toward lower $m_2$, ruling out an equal or weaker high-$m_2$ decline at 99.45% credibility. This structure therefore requires a characteristic mass scale in at least one physically labeled component, but masses alone cannot determine which component carries it. Any formation model reproducing the observed high-mass binary black hole merger population must contain such a scale.
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All authors Soumendra Kishore Roy, Asad Hussain, L. A. C. van Son, Maya Fishbach, Carl L. Rodriguez, Will M. Farr
Astrophysics of Galaxies
How JWST is Revolutionizing Our View of Early Galaxy Formation
Rychard Bouwens
The James Webb Space
Telescope (JWST) has been revolutionizing our understanding of early
galaxy formation over its first four years of science operations. With un- precedented sensitivity, spatial resolution, and wavelength coverage from the near- to mid-infrared, JWST has enabled astronomers to identify hundreds of
star-forming
galaxies at
redshifts z>~8 (within ~650 million years of the Big Bang) through strong spectral breaks and characterize these
galaxies through sensitive spectroscopy. These capabilities have provided new insights into the stellar populations, neutral gas, nebular continuum emission, chemical enrichment, dust content, and ionization conditions of
galaxies during
cosmic dawn, revealing more numerous and brighter systems than anticipated from pre-JWST models. We discuss the implications of these discoveries for reionization, the buildup of stellar mass and metals, and the
evolution of
galaxy populations and luminosity functions. JWST is also revealing a new physical picture of early
galaxies, characterized by compact, clumpy
star formation, high gas fractions, and intense radiation fields. Despite much progress, many open questions remain, including the efficiency, intermittency, and stellar initial mass function (IMF) of early
star formation, conditions in the interstellar medium (ISM), masses, and structure of the earliest
galaxies, and the
topology of reionization. Resolving these open questions will require
lensing magnification, sensitive spectroscopy to > 5 micron, including with the Atacama Large Millimeter Array (ALMA), exploration to higher
redshifts, and larger, more complete samples, helping to clarify how the first
galaxies formed and evolved.
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Cosmology and Nongalactic Astrophysics
TNGC-SIDM I: Evolution of massive cluster mergers under the self-interacting dark matter paradigm
Wonki Lee, Dylan Nelson, Myungkook J. Jee et al. (+8 more)
Merging
galaxy clusters provide an ideal laboratory for testing the self-interacting nature of dark matter. In this paper, we present a pilot study of magnetohydrodynamical cosmological zoom-in simulations of two cluster mergers selected from TNG-Cluster, with $M_{\rm 200c} \sim 9\times10^{14}~M_\odot$ and $M_{\rm 200c}\sim 2\times10^{14}~M_\odot$. The simulations are performed with both standard collisionless cold dark matter (CDM) and self-interacting dark matter (SIDM), assuming an isotropic, velocity-independent cross-section of $\sigma_{\rm T}/m_\chi = 1~\rm cm^2~g^{-1}$, with an additional $0.5~\rm cm^2~g^{-1}$ run for the low-mass system, and the mass resolution and
galaxy formation model are unchanged from TNG-Cluster. We show how dark matter self-interactions produce an isothermal core in the dark matter
halo, generate unique substructures in the intracluster light, and introduce variation in the multi-wavelength observables of the intracluster
plasma. Using these simulations, we test the validity of observational probes for dark matter self-interactions in cluster mergers. We find that the shock-to-shock separation shows similar
evolution in the self-interaction models tested here, providing a reference for distinguishing the $\sim100-200~\rm kpc$-scale difference in
halo separation induced by self-interactions. Moreover, the dark matter
halo centroid of the main cluster in the massive cluster merger is offset from the brightest cluster
galaxy by as much as $\sim20~\rm kpc$, larger than the offset in the sub-cluster. This offset persists beyond 4 Gyr after the first pericenter passage. Our results indicate that sample selection plays a key role in testing the possible self-interacting nature of dark matter using cluster mergers, and that double
radio relic cluster mergers and massive clusters with evidence of an ancient major merger offer a promising testbed for this purpose.
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All authors Wonki Lee, Dylan Nelson, Myungkook J. Jee, Giulia Despali, Mark Vogelsberger, Annalisa Pillepich, Cian Roche, Kyle Finner, Hyungjin Joo, Daisuke Nagai, John ZuHone
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Nonlinear Perturbations of Relativistic Stars
K. J. Kwon, Abhishek Hegade K. R., Tejaswi Venumadhav et al. (+2 more)
We extend the general relativistic Lagrangian perturbation formalism of Friedman and Schutz [Astrophys. J. 200, 204 (1975)] beyond linear order, retaining full time dependence of the perturbations. We provide general formulae to relate the Lagrangian and Eulerian perturbations to any general perturbative order. As a proof of principle, we apply the framework to tidally perturbed relativistic
stars in Regge-Wheeler gauge and reduce the second-order field and conservation equations to master equations with a nonlinear source. Projecting the source onto the
star's eigenmodes, we obtain a nonlinear equation of motion for the mode amplitudes and the coupling coefficients, which describe the interactions among the eigenmodes and with the external tidal field. Approximating the tidal field and the coupling coefficients, we compute the static quadratic Love number from the quadrupolar fundamental mode alone and find that it reproduces the direct metric-matching value to a reasonable accuracy of $4\%$, up to a further correction arising from the
Hamiltonian and momentum constraints of the second-order tidal field.
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All authors K. J. Kwon, Abhishek Hegade K. R., Tejaswi Venumadhav, Hang Yu, Nicolás Yunes
Earth and Planetary Astrophysics
Simulations of the Evolving Ozone Layer: Implications for the Early Earth, Exoplanets, and the Search For Life
Akhil Kumar and Gregory J. Cooke
Over 4 billion years, Earth's atmosphere has been transformed from a composition devoid of molecular oxygen (O$_2$) to one where O$_2$ is now 21% of our modern atmosphere by volume. With high quantities of O$_2$, an ozone (O$_3$) layer can form and partially shield the surface from biologically harmful ultraviolet radiation (UV). The
evolution of the O$_3$ layer has previously been simulated under the modern Sun by independent groups with separate models. Here, we present simulations of Earth's atmosphere from four open-source one-dimensional (1D) photochemical models and a 3D chemistry-
climate model, focussing on O$_3$. We find that the O$_3$ layer thickness exhibits a clear deviation between the 1D models and the 3D model due to several factors, including treatments of O$_2$ photolysis, chemical networks, H$_2$O microphysics and 3D transport. We find that 1D models introduce a bias for unobserved
climate states and show how these biases may propagate to calculations of biological UV damage and surface habitability. We show that when applied to specific
exoplanet atmospheres, these discrepancies can become more pronounced, propagating through to observational predictions for the next generation of
telescopes, such as HWO and LIFE, that will search for habitable and inhabited
exoplanets.
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High Energy Astrophysical Phenomena
Seeing Double: The Theory Defying Twin Flares of TDE 2022dbl
Xinze Guo, Ryan Chornock, Raffaella Margutti et al. (+13 more)
Partial tidal disruption events, in which a
star survives a close passage by a supermassive black hole and may be disrupted again on a subsequent encounter, provide a unique probe of supermassive black hole properties and
accretion physics. We examine TDE 2022dbl, a partial tidal disruption event candidate that exhibits two separate UV/optical
flares, using 11 new optical spectra, updated UV/optical photometry, and a Keck-II/ESI host-
galaxy spectrum. We trace the
evolution of the prominent blended N III + He II feature across both
flares and find that the blend evolves from N III-dominated to He II-dominated emission, which may reflect changing ionization conditions and a declining efficiency of Bowen fluorescence. The two
flares show similar thermal
evolution and spectral features, supporting a partial-disruption scenario. The second
flare exhibits a broader, plateau-like peak, a longer decline timescale, and less extreme line velocities than the first
flare. We suggest that these differences arise from the interaction between debris from the second disruption and an
accretion disk formed during the first
flare. From the host-
galaxy velocity dispersion, we infer a black hole mass of $\log_{10}(M_{\rm BH}/M_\odot)=6.01\pm0.45$. No third
flare has been detected at the expected recurrence epoch, leading us to propose a new interpretation in which a positive-energy kick during ballistic core reformation delays the return of the surviving remnant.
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All authors Xinze Guo, Ryan Chornock, Raffaella Margutti, Yuhan Yao, Erica Hammerstein, Natalie LeBaron, S. Bradley Cenko, Matthew J. Graham, Dina Ibrahimzade, Itai Sfaradi, Jean Somalwar, Robert Stein, Eli Wiston, Joahan Castaneda Jaimes, Mansi M. Kasliwal, Russ R. Laher
Earth and Planetary Astrophysics
Peering into the Midplane of the DM Tau Disk using N2H+ and DCO+
Amina Diop, Kevin Flaherty, Chunhua Qi et al. (+7 more)
Planets form in the midplanes of protoplanetary disks, thus investigating the properties of the midplane region can shed light on the physical and chemical processes governing the
evolution of planetary systems. In this work, we study the conditions near the midplane of the disk around DM Tau using 0."3 (~43 au) ALMA observations of N2H+ (J = 3 - 2) and DCO+ (J = 4 - 3). The radial profiles reveal that DCO+ is centrally peaked, with a depression near 120 au, while N2H+ exhibits a central depression and a peak near 100 au. In addition, both molecules display extended emission out to 400 au. Using parametric models to interpret our observations, we note that a fiducial model based on CO-derived parameters captures the features within 200 au, but fails to reproduce the outer disk emission. We explore various mechanisms that could account for this extended emission and conclude that it is best reproduced by an increased external UV penetration and
cosmic ray/X-ray ionization rate, possibly enhanced by radial drift. These processes affect the precursors of N2H+ and DCO+ : increased UV leads to the photodesorption of CO and N2, while ionization enhances H3+ abundance. Besides, the observed N2H+ and DCO+ features are broadly consistent with previous CO snowline constraints, but can also be shaped by processes such as ionization, CO depletion, and multiple chemical pathways. Thus, using these molecular ions as robust CO snowline tracers requires additional constraints from complementary molecular tracers and detailed chemical modeling.
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All authors Amina Diop, Kevin Flaherty, Chunhua Qi, Ilse Cleeves, A. Meredith Hughes, Agnes Kospal, Sean Andrews, David J. Wilner, Jacob B. Simon, Deryl E. Long
Solar and Stellar Astrophysics
Differential Luminosity Response of Balmer-Line Profiles in Galactic B/A Luminous Stars
N. L. Vaidman, S. A. Khokhlov, Sh. T. Nurmakhametova et al. (+3 more)
We investigate the differential luminosity response of the optical Balmer series from H8 to H-alpha in Galactic B5-A5 luminous
stars using homogeneous measurements of central depth, FWHM, and equivalent width at a resolving power of approximately 12,000. Direct line-to-line comparisons show a systematic change in the central-depth response toward the lower-order transitions. For the primary 72-
star luminosity sample, the fitted luminosity coefficients show an overall positive trend with upper-level
quantum number, with a point-estimate gradient of dq/dn = 0.0419. A joint Monte Carlo analysis with 10,000 realisations gives a median dq/dn = 0.0387 and a 95 percent interval from 0.0253 to 0.0532, with no non-positive gradients obtained. The higher-order H8-H-delta coefficients form a statistically unresolved plateau, followed by a well-supported increase in response magnitude from H-delta toward H-alpha. The result is robust to the adopted effective-temperature scale. The FWHM coefficients show no comparable Balmer-order progression, and the directly fitted profile-shape response is consistent with zero from H8 through H-beta. For H-alpha, the full logarithmic sample is not formally significant, whereas removal of the three remaining strongly filled-core profiles yields a significantly negative shape response. The observed behaviour is qualitatively compatible with the systematic variation of pressure broadening across the Balmer series, while the enhanced H-alpha response may additionally reflect non-LTE and wind-related effects.
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All authors N. L. Vaidman, S. A. Khokhlov, Sh. T. Nurmakhametova, N. A. Litvinov, A. T. Agishev, D. A. Alimbetova
Earth and Planetary Astrophysics
A Spatial Map of the Atmospheric Limb of a Hot Jupiter
Lili Alderson, Hannah R. Wakeford, David Grant et al. (+18 more)
Planets are inherently three-dimensional objects shaped by their thermal structure and dynamics. Observations of transiting
exoplanets have begun to uncover this three-dimensional nature, with JWST measuring their dayside atmosphere structure with eclipse mapping, and exploring spectroscopic asymmetries in the limbs of
planets during transit. We apply the novel mapping method of transmission strings to the hot Jupiter WASP-17b. With this method, we are not only able to extract hemispheric limb asymmetries from east-to-west, but can map equator-to-pole variations around the transmitting atmosphere as a function of angle, spanning 0.6-12$\mu$m. We find a clear transition in the thermal scale height around the limb of the atmosphere, with a $\sim$650K temperature difference between the morning (T=858$^{+434}_{-233}$K) and evening (T=1522$^{+116}_{-114}$K). These results are consistent with both nightside emission and dayside eclipse mapping measurements, and represent a fully comprehensive set of observations for a transiting
exoplanet. We are also able to constrain the abundances of H$_2$O and CO$_2$ to constant values around the limb, providing observational constraints to results from global circulation models. The transmission string technique combined with the outstanding observability of WASP-17b pushes the study of
exoplanet atmospheres further into a three-dimensional understanding of hot Jupiter dynamics and chemistry
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All authors Lili Alderson, Hannah R. Wakeford, David Grant, Nikole K. Lewis, Avinash Verma, Jayesh Goyal, Mark Hammond, Daniel Valentine, Natalie H. Allen, Ana Glidden, Amélie Gressier, Jingcheng Huang, Maura Lally, Dana R. Louie, Jacob Lustig-Yaeger, Cathal Maguire, Elijah Mullens, Kristen S. Sotzen, Jeff A. Valenti, Roeland P. van der Marel, Tiffany Kataria
Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc
Turning Selection Bias into a New Statistic: Asymmetry and Fringes of Lensed Gravitational Waves
Juno C. L. Chan and Elwin K. Y. Li
Gravitational waves (GWs) propagating across the Universe can be distorted by intervening lenses, producing characteristic wave-optics signatures. These effects are not incorporated into current matched-filtering searches and can therefore substantially reduce detection efficiency. The underlying mechanism is the signal-consistency test, which measures deviations between the observed and expected signal-to-noise ratio (SNR) distributions. We report a systematic study of the impact of gravitational
lensing on signal-consistency tests, using a two-image interference model and representative signal-consistency statistics in both the time and frequency domains. We find that overlapping images produce sharply localized SNR residuals in the time domain, breaking the reflection
symmetry of the autocorrelation about the merger time. Although interference fringes produce broadband SNR residuals in the frequency domain, both domains exhibit a minimum for high-mass signals when the fringe structure becomes comparable to the signal bandwidth. This highlights a limitation of current strategies that search for distorted lensed signals only among GW events detected by matched-filtering searches. Exploiting this asymmetry, we develop a statistic that separates selected down-ranked lensed injections from noise-background triggers and paired nonlensed injections, without extending the template bank. Our results establish the first connection between
lensing observables and detection, paving the way for the discovery of lensed GWs.
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Cosmology and Nongalactic Astrophysics
Enabling Polyspectra via Stochastic Realizations of Inverse Decay Curvature Perturbations in Axion Inflation
Matthew A. Reinhard, Zachary Slepian and Atsushi Taruya
Current and upcoming
galaxy-
redshift surveys offer a promising path for constraining inflationary physics. These constraints are often imposed by relating correlations of the primordial
curvature perturbation to the late-time
galaxy correlation functions. The primordial correlators can either be computed analytically, or via realizations of the primordial
curvature perturbations that are initialized on a grid and evolved numerically according to the classical equations of motion. In this work we take a hybrid approach, initializing the fields in the Bunch-Davies
vacuum; and then imposing time
evolution through direct numerical integration. Our method efficiently generates realizations of the inverse decay primordial
curvature perturbations for
axion inflation—an inflationary model in which a pseudoscalar inflaton field couples to a $U(1)$ gauge field via a Chern-Simons interaction. Depending on the choice of parameter $\xi\in\{2, 2.5, 3\}$, which controls gauge field particle production in this model, our method generates realizations with an average runtime of a few hours on 1 CPU core. We compute the power spectrum and bispectrum from these realizations and find a surprisingly large discrepancy between our result and previous work that used an approximation for the gauge field mode functions—up to a factor of $\sim4$ difference for the bispectrum in the case of $\xi=2$. This new method enables not only rapid computation of higher order polyspectra, but also generation of initial conditions for large-scale structure analyses.
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High Energy Astrophysical Phenomena
Evidence for Distinct One-Off and Repeating Subpopulations in CHIME/FRB Catalog 2
Sloane Sirota and Duncan R. Lorimer
The Canadian Hydrogen Intensity Mapping Experiment (CHIME) has published its second catalog of 3,641 fast
radio bursts (FRBs). While this sample includes 981 bursts from 83 repeating sources, only 2.3% of CHIME FRBs are observed to repeat. This raises the question of whether the FRB population truly consists of a single repeating population or includes a distinct subpopulation of one-off sources. We apply Simulation Based Inference (SBI), a likelihood-free machine learning framework, to model the CHIME/FRB Catalog 2
dataset, testing eight FRB population models, half of which include a subpopulation of truly one-off sources. The current catalog strongly and decisively favors models including such a subpopulation, with the best-fitting model combining a log-normal burst rate distribution, a Poissonian wait-time distribution, and a one-off subpopulation. This preference is corroborated by an independent random forest classifier and by the ability of one-off models to naturally reproduce the hyperactive repeating sources present in the catalog without having been trained on them. We place upper limits on the potentially observable CHIME/FRB population of 36,000 repeating sources and 19 one-off sources per day in the CHIME sky. Models with a one-off subpopulation naturally account for the hyperactive repeating sources present in the catalog without having been trained on them, providing an independent consistency check on our results. We predict the repeater percentage will fall below 2% in the next five years, eventually declining to ~0.5% as the sample saturates with one-off detections.
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Cosmology and Nongalactic Astrophysics
Testing the 4-Point Correlation Function as a Probe of Parity Violation with the Quijote-Odd Simulations
William Ortolá Leonard, Zachary Slepian, Alex Krolewski et al. (+1 more)
We investigate parity violation searches with the 4-Point Correlation Function (4PCF) using the Quijote and Quijote-Odd
halo catalogs. Specifically, we explore the auto- and cross-correlation searching methodologies that have been previously used in the Baryon Oscillation Spectroscopic Survey (BOSS) and the Dark Energy Spectroscopic Instrument (DESI) searches. Although the Quijote-Odd simulations are initialized with a parity-violating primordial trispectrum, we find no statistically detectable parity-odd signal in the
halo 4PCF. Instead, we find that the
halo measurements are dominated by Poisson noise. We are able to distinguish this noise-dominated behavior from the response expected for a parity-odd signal. These results clarify how parity-sensitive 4PCF statistics respond to noise in a controlled simulation setting.
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All authors William Ortolá Leonard, Zachary Slepian, Alex Krolewski, Simon May
Instrumentation and Methods for Astrophysics
Establishing baseline model performances for optical turbulence forecasting
M. De Sepibus, E. Masciadri, C. Weinberger et al. (+4 more)
Accurate forecasting of optical
turbulence (OT) is useful to optimise
telescope scheduling and maximising observing efficiency, as the performance of adaptive optics systems strongly depends on
turbulence conditions. While various numerical weather prediction and machine learning models are developed to predict these complex
turbulence properties, properly evaluating their added value requires well-defined baseline reference models. This study establishes baseline performance thresholds for key astroclimatic parameters using two distinct models: one forecasting the parameter average over a specific timescale, and the other forecasting the temporal
evolution over the same specific timescale. We apply these frameworks to extensive, multi-year
datasets from the sites of the Very Large
Telescope (VLT) and the Large Binocular
Telescope (LBT) and discuss the possibility of extrapolating reference values of forecast performances for other sites based on their optical
turbulence statistical characteristics. Our results show that baseline predictive accuracy varies according to the observing site, the specific parameter, the chosen timescale, and the forecasting approach. Therefore, an OT forecasting model's accuracy cannot be quantified in absolute terms, but relatively to the baseline.
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All authors M. De Sepibus, E. Masciadri, C. Weinberger, A. Otarola, S. Miesske, C. Veillet, S. Ragland
High Energy Astrophysical Phenomena
The compact jets of the black hole X-ray binary Swift J1753.5-0127 during its 2023-2024 outburst
Noa Grollimund, Stéphane Corbel, Lauren Rhodes et al. (+14 more)
X-ray binaries are excellent laboratories to study the coupling between
accretion and ejection phenomena around compact objects through multiwavelength observations. Swift J1753.5-0127 is a black hole low-mass X-ray binary discovered in outburst in 2005 that remained active for 11 years, followed by two mini-outbursts. We investigate the behavior of the compact jets of Swift J1753.5-0127 during its 2023-2024 outburst. We report a dense multiwavelength monitoring in the
radio, NIR/optical/UV and X-ray bands. Using new and archival luminosity measurements, we construct a refined, smoother
radio/X-ray plane that covers the steep/outlier and shallow/transition branches of the
radio/X-ray correlation. We also present spectral energy distributions (SEDs) constructed using quasi-simultaneous observations from four epochs. Swift J1753.5-0127 underwent a faint, hard-only, double-peaked outburst, followed by a re-brightening in the optical. The updated
radio/X-ray plane offers a clear view on the region occupied by this source, similar to MAXI J1348-630, but at lower
radio luminosities than H 1743-322, and we confirm its hybrid behavior. The broad-band SED fitting reveals that a cool, truncated
accretion disk dominates the NIR/optical/UV band. We find that the compact jets have a variable but weak contribution in the NIR, with a break frequency $\nu_\mathrm{break} \lesssim 5 \times 10^{12}~\mathrm{Hz}$, providing additional evidence that
radio-quiet sources are also infrared-quiet. We also find evidence that the
radio spectral index evolves with X-ray luminosity, transitioning from inverted values near quiescence to flatter or negative values at higher luminosities. In the context of adiabatic jet models, this trend may indicate that the jet geometry becomes increasingly confined as the
accretion rate rises.
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All authors Noa Grollimund, Stéphane Corbel, Lauren Rhodes, David M. Russell, M. Cristina Baglio, Francesco Carotenuto, Tristan Bouchet, Payaswini Saikia, Rob P. Fender, Sara E. Motta, Piergiorgio Casella, Kevin Alabarta, Fraser Lewis, Andrew K. Hughes, Fraser J. Cowie, Justine Crook-Mansour, Xian Zhang
High Energy Astrophysical Phenomena
Multimessenger Constraints on Nuclear Acceleration in Neutrino-Emitting Seyfert Coronae
Chengchao Yuan
High-energy
neutrinos from Seyfert
galaxies probe particle acceleration near supermassive black holes, but the accelerated nuclear composition remains uncertain. We connect
stochastic acceleration to nuclear and radiative cascades to assess nuclear contributions. Acceleration and losses limit the energy per nucleon available to nuclear cascades; without secondary reacceleration, fragmentation cannot raise this scale. For NGC~1068, joint
neutrino and gamma-ray constraints depend on the nuclear mixture: helium-dominated injection permits larger nuclear power fractions than the heavier mixtures considered. For the harder candidate {
neutrino} spectrum of NGC~7469, the adopted model yields more energetic nuclear cascades, while the source-specific flux selections allow larger nuclear fractions for the heavier mixtures than in NGC~1068. These results show that composition constraints depend on nuclear yields as well as acceleration conditions and available power.
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Astrophysics of Galaxies
The Connection Between the Growth of Massive Black Holes and Their Dynamical Histories
Lee A. Whitaker, Michael Tremmel, Angelo Ricarte et al. (+1 more)
Massive black holes (MBHs) grow through both gas
accretion and mergers and it remains unclear how variations to MBH growth and dynamical histories contribute to the spread in empirical scaling relations between MBHs and their host
galaxies. We examine the ex- and in-situ growth of MBHs within large-scale cosmological simulations and compare the
evolution of an outlier population of under-grown MBHs to the general population. We use the Romulus25 uniform volume cosmological simulation and the RomulusC cluster zoom-in simulation to examine the growth and merger histories of MBHs. We identify central MBHs that are undergrown relative to other MBHs in similar mass
galaxies and investigate their
accretion, merger, and orbital histories within the simulations. The contribution of ex-situ growth increases with MBH mass, with mergers becoming increasingly important in the most massive
galaxies. We find no difference between cluster and field environments in terms of the importance of ex-situ growth, which is generally very low. Under-grown MBHs have experienced fewer mergers and have had complex dynamical histories, spending significant time 'drifting' within the
galaxy or 'competing' with another MBH. Other under-grown MBHs have experienced a 'late entrance' into a
galaxy which until then had no central MBH. Our results demonstrate that MBH assembly is dominated by in-situ growth, which in turn is impacted by the dynamical histories of MBHs within assembling
galaxies. Prolonged off-centre
evolution can suppress
accretion and contribute to the formation of under-grown central MBHs at $z=0$.
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All authors Lee A. Whitaker, Michael Tremmel, Angelo Ricarte, Priyamvada Natarajan
Astrophysics of Galaxies
Cosmic Evolution Survey: LOFAR 144 MHz imaging of the COSMOS field
E. Vardoulaki, T. Shimwell, M. J. Hardcastle et al. (+18 more)
We present the first deep, targeted LOFAR 144 MHz source catalogue of the COSMOS field, together with the first 144 MHz source counts in this field. The data comprise 48 h of observations. Over the 2.6 sq. deg. region adopted for the catalogue analysis, the final Dutch-array image reaches a median rms sensitivity of ~100 uJy/beam at an angular resolution of 15" x 6". The resulting catalogue contains 1984
radio sources; a peak S/N >= 5 selection is adopted for the resolved/unresolved classification and source-count analysis. We characterised the catalogue using Monte Carlo source-injection and recovery simulations, including dedicated simulations of extended sources, to quantify completeness, flux-density redistribution, and morphology-dependent source-recovery effects. The catalogue reaches 90% completeness at 1.48 mJy. The resulting Euclidean-normalised differential source counts are measured down to ~0.4 mJy and show good agreement with LoTSS DR3 144 MHz source counts and with the VLA-COSMOS 3 GHz counts scaled to 144 MHz, with ~5% of catalogue sources having multiple 3 GHz counterparts within a beam-matched search region. Comparison with the VLA-COSMOS 3 GHz catalogue shows good astrometric agreement, with median offsets of Delta_RA = 0.35" (+0.03"/-0.05") and Delta_Dec = -0.83" (+0.02"/-0.03"), approximately 6% of the corresponding synthesised-beam dimensions, and no significant radial dependence across the field. The resulting catalogue provides a low-frequency view of COSMOS and a reference
dataset for future deeper LOFAR observations and multiwavelength studies of this extensively characterised extragalactic field.
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All authors E. Vardoulaki, T. Shimwell, M. J. Hardcastle, L. Doukas, L. K. Morabito, C. L. Hale, M. T. Sargent, V. Smolčić, G. Zamorani, G. Gozaliasl, F. An, M. Aravena, A. L. Faisst, M. Vaccari, E. Treister, A. Finoguenov, P. Best, J. S. Kartaltepe, C. Casey, S. Jin, V. Mainieri
Solar and Stellar Astrophysics
Anchoring the Chromospheric Activity$-$Rotation Relation: A Study of the Pleiades and Group X
A. Núñez, M. A. Agüeros, J. L. Curtis et al. (+1 more)
We present a study of the rotation and the chromospheric H$\alpha$ activity of low-mass
stars in the $\approx$120 Myr-old Pleiades and the $\approx$400 Myr-old Group X open clusters. We combine published and new rotation periods ($P_\mathrm{rot}$) from TESS and ZTF, and use LAMOST, SDSS, and MDM spectra to measure H$\alpha$ equivalent widths (EWs). While overall the Group X distributions of $P_\mathrm{rot}$ and EWs are as expected, detailed comparisons to the Pleiades and to the 700-Myr-old
benchmark Praesepe produce some surprises. For F through mid K
stars, the Group X color$-$period sequence lies between those of the Pleiades and of Praesepe, as expected. But the $P_\mathrm{rot}$ for its late K and early M dwarfs and the Praesepe slow-rotator sequence overlap, indicating that the 700 Myr-old
stars have not spun down significantly despite being nearly twice as old as their Group X counterparts. In the Rossby number$-L_\mathrm{H\alpha}/L_\mathrm{bol}$ plane, rapid rotators in Group X are saturated, as is seen in older clusters, whereas the rapid rotators in the Pleiades show a weak but measurable dependence of $L_\mathrm{H\alpha}/L_\mathrm{bol}$ on rotation. This implies that the chromospheric activity$-$rotation relation attains its mature form between 120 and 400 Myr. Dividing the sample by color reveals that K, M0, and M1 dwarfs are no longer saturated by $\approx$120 Myr, M2 and M3 dwarfs become unsaturated between $\approx$400 and $\approx$700 Myr, and later M dwarfs remain largely saturated through field ages even as their saturated $L_\mathrm{H\alpha}/L_\mathrm{bol}$ levels decline, indicating that chromospheric
evolution is not determined by rotation period alone.
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All authors A. Núñez, M. A. Agüeros, J. L. Curtis, C. A. Ospinal Achicanoy
High Energy Astrophysical Phenomena
The ePESSTO+ census of ZTF nuclear transients. I. What flares in galactic nuclei?
E. Concepción, T. Petrushevska, G. Leloudas et al. (+21 more)
Transients in galactic
nuclei arise from distinct processes, only some of which trace the supermassive black hole (SMBH). These include tidal disruption events (TDEs), changing-look active galactic
nuclei, Bowen fluorescence
flares (BFFs) and ambiguous nuclear transients, alongside
supernovae that appear nuclear but are unrelated to the SMBH. Reliable classification requires spectroscopy, which will not scale to the alert volumes of the Legacy Survey of Space and Time (LSST). We aim to characterise the population of nuclear transients, to identify early observables capable of distinguishing SMBH-related
flares, and TDEs in particular, from the dominant
supernova background, and to assess the biases this selection introduces. We implemented a real-time filter on the Lasair broker, selecting transients from the Zwicky Transient Facility (ZTF) alert stream by nuclear coincidence with the host
galaxy, with no photometric cuts, to retain SMBH-related
flares in both quiescent and active hosts. The filter ran over 16 months, with candidates reported for classification through ePESSTO+ and other facilities. The filter returned 476 candidates, of which 202 were spectroscopically classified, yielding predominantly
supernovae, 10 confirmed TDEs (5%) and one BFF. The mean g-r colour and the rise time separate TDEs from the
supernova background. Our filter recovers 10 of the 25 TDEs classified in the same period and declination range; most misses are technical or observational rather than physical. Simple real-time filtering combined with basic photometric criteria can already isolate TDEs efficiently from nuclear transient alert streams, and high completeness is achievable. In the LSST era, where samples will be predominantly photometric, selection bias will become as important as contamination, and retaining
flares in active hosts is necessary if unusual events are not to be excluded.
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All authors E. Concepción, T. Petrushevska, G. Leloudas, D. Ilić, M. Gromadzki, S. Bhattacharyya, P. Charalampopoulos, A. Gomboc, N. Ihanec, M. Nicholl, P. J. Pessi, D. R. Young, P. Wiseman, T.-W. Chen, M. Dennefeld, Y. Dgany, C. P. Gutiérrez, C. Inserra, L. Makrygianni, T. E. Müller-Bravo, S. Nissen, F. Onori, R. Roy, M. Quilt
Astrophysics of Galaxies
Dynamical formation of dormant black holes: Predictions for Gaia DR4
Daniel Marín Pina, Michela Mapelli, Giuliano Iorio et al. (+1 more)
Dormant black holes (dormant BHs, i.e., X-ray quiet binaries comprising a BH and a companion
star) are probes of the effect of cluster dynamics and binary stellar
evolution on compact-object binaries. A dozen dormant BH binaries are known, a number that will increase substantially with the upcoming Gaia Data Release 4 (DR4). Their origin is uncertain, and dynamical formation is proposed as one possible channel. Here, we study the formation of dormant BHs in low-mass
star clusters, accounting for the interplay of binary stellar
evolution and cluster dynamics. We present new simulations with the $N$-body code PeTar, interfaced with the population synthesis code SEVN for single and binary
star evolution. Our grid spans a range of cluster masses ($300-4800\,$M$_\odot$),
metallicities ($1.4\times10^{-2}$, $1.4\times10^{-4}$), and natal kick models (with and without fallback). We find that almost all dormant BH binaries escape the parent cluster within $\sim1\,$Gyr ($\sim10\,$Myr) when assuming weak (strong) natal kicks. Most ($73\%$) dormant BHs form via the exchange of a BH (or its progenitor
star) into a stellar binary, or of a
star into a binary with a BH. Dormant BHs in low-mass clusters have a wide orbital period distribution (from a few hours to $10^8\,$d), with an upper limit set by natal kicks, a bimodal eccentricity distribution (a first peak at zero eccentricity for circularised systems and a second at high eccentricity), and stellar masses that follow the (evolved) initial mass function. Large BH masses are a smoking gun of dynamical formation, via exchanges and stellar collisions. We expect Gaia DR4 to contain $\sim1-64$ high-
metallicity and $\sim0.4-48$ low-
metallicity dormant BHs, with a period distribution peaking at $\sim10^3\,$d, $\gtrsim90\%$ of them with eccentricity $e>0.1$, and $\sim20\%$ with large BH masses ($m_{\rm BH} \gtrsim 30\,$M$_\odot$).
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All authors Daniel Marín Pina, Michela Mapelli, Giuliano Iorio, Cecilia Sgalletta
Astrophysics of Galaxies
Massive double-exponential galaxies with extended LSB emission: An IllustrisTNG exploration II -are they unique?
Suchira Sarkar, Kanak Saha and Anshuman Borgohain
The massive disk
galaxies (stellar mass >= 10^11 M_solar ) in the local universe (z < 0.1) encode challenging aspects of
galaxy formation physics. We have studied one class of such
galaxies - the giant low surface brightness
galaxies (gLSBs) that show a hybrid morphology - a central Sersic, an inner high surface brightness, exponential stellar disk surrounded by an outer, extended low surface brightness disk, using large volume IllustrisTNG-100 simulation. This is motivated by the recent observation of several such systems and an earlier work by Sarkar & Saha (2025) from IllustrisTNG-50. We find that despite using a ~ 10 times larger volume simulation, only ~11% of massive disk
galaxies show such morphology, consistent with findings from TNG50. This shows robustly that such
galaxies are not common in the local universe. We compared them with the typical disk
galaxies from observations, and single-exponential gLSBs from TNG100. We show that while the inner disk components lie well within the central surface brightness vs. radial scale length distribution of the typical disks, the outer LSB disks lie significantly at the outskirt, occupying a unique space. Their median bulge-to-total ratio is ~ 0.2 making them disk dominated, similar to the typical disks and the single-exponential gLSBs. We find their median dark matter mass fraction to be high (~ 0.9), typical of gLSBs. The outer LSB disks reach fainter central surface brightness and larger scale length values than the single-exponential gLSBs. Our exploration will be useful in understanding their formation mechanism across
cosmic time.
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Solar and Stellar Astrophysics
Star spots mimic the proposed abundance signatures of planet formation
Andrew R. Casey, Megan Bedell, Adam Wheeler et al. (+2 more)
Trends with stellar elemental abundances and condensation temperature have been proposed as a possible tracer of rocky
planet formation. Here we present an alternative explanation, where we show that stellar activity (
star spots) can also cause apparent abundance changes in refractory elements preferentially over volatile elements. This effect arises naturally from atomic physics: refractory (rocky; high-$T_c$) elements preferentially have low first-ionization potentials, with strong transitions that are most sensitive to the cooler, magnetically-perturbed spot conditions, making any spot-induced change in line strength correlated with $T_c$. We re-examine literature on Sun-like
stars in the Solar neighborhood and find that the $\log{R'_{HK}}$ stellar activity indicator is correlated with the so-called $T_c$ slope: the gradient of chemical abundances with respect to condensation temperature. Using 1D LTE Korg.jl simulations of the Sun with spots of varying size and contrast, we show that a wide range of spot configurations can manifest as abundance patterns that mimic a signal of abundance trends with condensation temperature. Finally, we conduct a line-by-line differential analysis of an ambient Solar spectrum relative to a Solar sunspot umbra to represent an extreme case, where we find that elements with high condensation temperature can show a factor of three (0.5 dex) increase. We discuss implications that stellar activity poses for precision spectroscopy, and provide some direction on how this effect might be mitigated.
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All authors Andrew R. Casey, Megan Bedell, Adam Wheeler, Julianne Dalcanton, Lily Zhao