Solar and Stellar Astrophysics
Stellar rotation and binaries in open clusters with Gaia DR3
Elena Pancino, Elisabetta Reggiani, Silvia Marinoni et al. (+14 more)
Stellar rotation is a fundamental ingredient in shaping the
evolution of
stars and it can also be used to trace past
stellar interactions. Yet, systematic studies of
stellar rotation in large samples of
stars belonging to different populations have only recently been made possible, thanks to spectroscopic surveys. We profit from the catalogue of rotational broadening and rotation periods released with
Gaia DR3. We focus on open clusters to study the rotational behaviour of several interesting populations including, among others, blue stragglers and extended main sequence turnoffs (eMSTO). We use literature lists of almost a million member
stars in several thousand open clusters in the Milky Way. We collect properties of
stars and clusters from large surveys, including
Gaia, and from various literature sources. We include a comprehensive collection of known variables and binary
stars from various databases. We manually select (exotic)
stellar populations from the color-magnitude diagrams of individual clusters and study their rotational properties. Our catalogue contains more than 44 000 rotationally characterised
stars, almost 57 000 variables (excluding binaries) and more than 22 000 binary
stars. We find several interesting results, including a few hundred new blue stragglers, several fast rotating red
giants, and we increase the number of clusters with an eMSTO to 96. We discover that most clusters more massive than $10^3$ $M_{\odot}$ display an eMSTO. We present a new parametrization of the number of blue stragglers as a function of cluster mass and age. We find that the percentage of binary
stars in the equal-mass binary sequence and in the main sequence are similar. We present the first large-scale statistical exploration of
stellar rotation in open clusters, which already yielded new interesting results and which can be used as the basis for several detailed follow-up studies.
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All authors Elena Pancino, Elisabetta Reggiani, Silvia Marinoni, Paola M. Marrese, Deimer Alvarez Garay, Aleksandra Avdeeva, Maite Echeveste, Ellen I. Leitinger, Sneha Nedhath, Sharmila Rani, Nicoletta Sanna, Sara Saracino, Laurenz F. Steinbauer, Alessio Turchi, Vikrant V. Jadhav, Sebastian Kamann, Monica Rainer
High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Monochromatic neutrinos from scotogenic dark matter
Ricardo Cepedello, Pablo de la Torre and Manuel Masip
The scotogenic model defines a framework for radiative
neutrino masses and provides a viable dark matter candidate. Since the scotogenic dark matter is leptophilic, indirect searches appear as an especially interesting possibility. Here we propose a simple variation of the model with a very distinct phenomenology. The scotogenic
fermion singlets are naturally grouped into pseudo-Dirac pairs of mass of 0.1-1 TeV. We show that the lightest one constitutes a dark matter candidate that near threshold annihilates with a 90% branching ratio into
neutrino pairs. The model gives the observed relic abundance consistently with the bounds from direct searches and with all
neutrino and charged
lepton data. We also show that, for a sub-MeV dark matter particle, the model suggests a scenario that could address the lithium problem.
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Cosmology and Nongalactic Astrophysics
Constraints on the inflationary vacuum and reheating era from NANOGrav
Debtosh Chowdhury, Rounak Nath and Sudipta Show
NANOGrav and various
pulsar timing array experiments recently reported compelling evidence for a
stochastic gravitational wave background (SGWB). Such a background may originate from several astrophysical or cosmological sources. Assuming an inflationary origin, we use the latest NANOGrav 15-year
dataset to constrain inflationary parameters, including the tensor spectral index ($n_t$), tensor-to-scalar ratio ($r$), and explore the implications for reheating through constraints on the reheating equation of state ($\omega_{\text{re}}$) and reheating temperature ($T_{\text{re}}$). We find a preference for an extremely blue-tilted tensor spectrum and a non-instantaneous reheating epoch. Despite no concrete evidence on
primordial vacua, inflationary
vacuum is commonly assumed to be the Bunch-Davies
vacuum. In this work, we study modifications to the GW spectrum arising from a two-parameter Bogoliubov family of non-Bunch-Davies
vacua. Within this framework, we find that NANOGrav observations favour a subclass of non-Bunch-Davies
vacuum, known as the alpha-
vacuum. In addition, our analysis demonstrates that the observations strikingly narrow the range of the parameter $\alpha$ that characterizes the
vacua. Our analysis indicates that the NANOGrav data can accommodate both matter- and radiation-like reheating scenarios for the standard Bunch-Davies
vacuum case. However, within the non-Bunch-Davies framework considered here, a non-matter-like reheating is preferred because matter-like reheating requires relatively large $\alpha$, violating both the NANOGrav upper bound and the backreaction constraint. We further show that a frequency-dependent parametrization of $\alpha$ beyond a threshold frequency can yield a minimal solution that alleviates the blue-tilted issue. Finally, we highlight the possibility of testing such frequency dependence of $\alpha$ through future GW experiments.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
On the equivalence of unitarization prescriptions for the Sommerfeld enhancement
Barry E. Cimring and Tracy R. Slatyer
The annihilation of self-interacting dark matter with long-range interactions can be significantly enhanced at low velocities through the Sommerfeld effect. At special points in parameter space, where near-zero-energy resonances exist in the spectrum of the theory, the standard calculation of this enhancement appears to violate unitarity. Recently, several approaches have been proposed to regulate this behavior, some introducing explicit ultraviolet (UV) scales and others not, raising the question of whether these prescriptions are consistent. In this paper, we compare these approaches and show that even in nominally cutoff-dependent methods, the regulated Sommerfeld-enhanced cross sections are independent of the UV regulator to a good approximation, and that when the unitarity-preserving corrections are large, the regulation schemes coincide to leading order. We use these insights to write down a regulator-independent prescription for unitarization applicable to multi-state systems, where the modified enhancement can be written solely in terms of the standard enhancement factor, the hard annihilation amplitude, and the $S$-
matrix for scattering in the long-range potential.
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Solar and Stellar Astrophysics
The diverse outcomes of binary white dwarf mergers and connections to Galactic LISA sources
Kyle Kremer, Katelyn Breivik and Claire S. Ye
In the coming decade, the millihertz gravitational wave observatory LISA will provide the best constraints yet on the tens of thousands of close white
dwarf binaries in the Milky Way, yielding unprecedented insights into the most abundant class of compact object binaries. Following inspiral via gravitational wave emission, interacting white
dwarf binary pairs can lead to a multitude of outcomes, including AM Canum Venaticorum (AM CVn) binaries, R Coronae Borealis
stars, young, rapidly-spinning single white
dwarfs, (millisecond) magnetars, and a variety of explosive transients, most notably Type Ia
supernovae. Current and future electromagnetic observations of these various outcomes coupled with the forthcoming flood of data from LISA place us on the precipice of a significant advance in our understanding of the long-term fate of white
dwarf binaries. In this paper, we present a suite of mock catalogs of the Milky Way's white
dwarf merger history, created using the population synthesis code $\texttt{COSMIC}$ combined with a
metallicity-dependent
star formation history from FIRE-2
galaxy simulations. We summarize the various merger outcomes expected (based upon varying white
dwarf masses and chemical compositions) and explore ways the rates of these outcomes may vary with model uncertainties pertaining to binary
evolution. We publicly release these merger catalogs as a tool for facilitating connections between gravitational wave science and white
dwarf binary astrophysics.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Nonthermal leptogenesis via cosmological gravitational particle production is tested by inflationary gravitational waves
Tammi Chowdhury, Leah Jenks, Edward W. Kolb et al. (+2 more)
We explore the coincidence of scales between
cosmic inflation and right-handed
neutrinos in seesaw models. We show that inflation models, which will be tested by next-generation CMB experiments, can produce right-handed
neutrinos in sufficient abundance to explain the observed
baryon asymmetry of the universe. The model can be tested by gravitational wave signatures from
cosmic inflation and particle production.
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All authors Tammi Chowdhury, Leah Jenks, Edward W. Kolb, Andrew J. Long, Evan McDonough
High Energy Astrophysical Phenomena
Multi-wavelength outburst activity from EP J174942.2-384834: a very faint X-ray transient discovered by Einstein Probe
F. Coti Zelati, A. Marino, Y. L. Wang et al. (+27 more)
We report the discovery and multi-wavelength characterization of the
Galactic transient EP J174942.2$-$384834, first detected by the Einstein Probe during a faint X-ray outburst in March 2025. Coordinated follow-up observations revealed two major outbursts and a rebrightening over a seven-month period. Broadband X-ray spectral modeling shows that the outburst emission was dominated by thermal Comptonization of very soft seed
photons. The absence of a detected thermal disk component, together with the low inferred seed-
photon temperature, is consistent with a cool and possibly truncated
accretion disk. The X-ray spectrum remained consistently hard throughout the outburst activity, with a power-law
photon index of $\Gamma \approx 1$-2, gradually softening as the flux declined. The optical/UV counterpart brightened in tandem with the X-ray emission and exhibited a blue continuum with broad Balmer absorption features. Together with the optical/UV - X-ray luminosity correlation, this supports a disk-dominated origin of the optical/UV outburst emission, with viscous heating likely playing a major role and irradiation possibly contributing, especially in the UV. No
radio counterpart was detected, implying at most very faint jet activity. Taken together, the observed properties support the classification of EP J174942.2$-$384834 as a very faint X-ray transient black hole candidate. This study demonstrates the ability of Einstein Probe to uncover and characterize the faintest accreting compact objects in the
Galaxy.
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All authors F. Coti Zelati, A. Marino, Y. L. Wang, M. Veresvarska, N. Rea, S. Guillot, D. A. H. Buckley, N. Rawat, S. E. Motta, Y. Xu, Z. Li, Y.-F. Huang, H. Feng, L. Tao, M. Imbrogno, G. Illiano, M. C. Baglio, H. Q. Cheng, C. C. Jin, H. Sun, W. Yuan, F. Carotenuto, R. P. Fender, A. Coleiro, D. Götz, H. L. Li, P. Maggi, Y. L. Qiu, J. Wang, L. P. Xin
Astrophysics of Galaxies
From gas to stars along the spiral wave: CO, HCN, and star formation variations across the spiral arms in NGC 4321 and M51
Minou Greve, Lukas Neumann, Mallory Thorp et al. (+17 more)
Molecular clouds form
stars from the interstellar medium via gravitational collapse, following a sequence from low-density gas to high-density cores and eventually the formation of
stars. In classical density wave theory, gas clouds orbiting the
galaxy experience gas compression and triggered
star formation, while encountering the gravitational well of spiral arms. We aim to trace these different phases of the molecular cloud life cycle via tracers of molecular gas (CO), dense molecular gas (HCN), and
star formation (H$\alpha$, 24 $\mu$m) within the spiral arms of two grand-design spiral
galaxies: NGC 4321 and M51 (NGC 5194). In the spiral arms of these
galaxies, we investigate the relation between molecular gas, dense gas, and
star formation (CO-HCN-SFR) at matched physical resolutions of 270 pc and 125 pc in NGC 4321 and M51, respectively. We employed spiral arm masks for these
galaxies and investigate trends of HCN/CO and SFR/HCN (SFR/CO), which serve as proxies for the dense gas fraction and dense (molecular) gas
star formation efficiency, perpendicular to the spiral arm spines. We find that HCN/CO, SFR/CO, and SFR/HCN increase from the upstream towards the downstream side of both spiral arms of NGC 4321, while their trends are less prominent in M51. Our results indicate that large-scale
galactic dynamics (e.g. density waves) can induce a sequence of gas density and
star formation-to-gas density variations perpendicular to the spiral arms. This sequence contributes to the increased scatter seen among spectroscopic ratios such as HCN/CO and SFR/HCN at sub-kiloparsec scales.
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All authors Minou Greve, Lukas Neumann, Mallory Thorp, Dario Colombo, Frank Bigiel, Miguel Querejeta, Sharon E. Meidt, Ashley T. Barnes, Zein Bazzi, Ralf S. Klessen, Adam K. Leroy, Hsi-An Pan, Jérôme Pety, Marina Ruiz-García, Eva Schinnerer, Rowan Smith, Sophia Stuber, Jiayi Sun, Antonio Usero, Thomas G. Williams
High Energy Astrophysical Phenomena
An X-ray and optical spectral study of the changing-look narrow-line Seyfert 1 2MASX J0413-0050
A. Vietri, A. Tortosa, D. Ilić et al. (+12 more)
Active
galactic nuclei (AGN) showing dramatic spectral and flux variations, either due to changes in the
accretion rate (changing-state, CS-AGN) of the supermassive black hole or in the line-of-sight column density (changing-obscuration, CO-AGN), have been classified as changing-look (CL) AGN. Here we present a peculiar source, 2MASX J0413-0050, first identified as a narrow-line Seyfert 1 (NLS1s)
galaxy in 2004. When re-observed twice in 2021, it showed a transition in the spectral type (towards a Seyfert 1.9) and the complete and mysterious disappearance of the Hbeta line while source was in a high
accretion state. In the meantime, the X-ray flux decreased between observations taken in 2020 and 2022, and again in the most recent spectrum of 2023. Shortly after this, another optical spectrum revealed the re-emergence of both the narrow and broad Hbeta components (Seyfert 1.8). Despite the fact that it was not possible to retrieve the line-of-sight column density from the X-ray spectra, which would have helped in assessing whether this event could be attributed to a CO AGN scenario, the observational evidence does not necessarily support such an interpretation. J0413-0050 may have undergone several switch-on switch-off phases over the past 20 years, on an unknown timescale, which could have affected the
accretion power and, consequently, the optical continuum and so the emission lines coming from the broad-line region (BLR). For these reasons, it is reasonable to classify this source as a CS-AGN. The case of J0413-0050 supports the hypothesis that NLS1s can indeed experience CL phenomena.
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All authors A. Vietri, A. Tortosa, D. Ilić, S. Ciroi, M. Berton, E. Järvelä, C. Ricci, E. Sani, L. Crepaldi, B. Dalla Barba, S. Chen, E. Congiu, P. Condò, I. Varglund, G. Rodighiero
High Energy Astrophysical Phenomena
No model-independent evidence for a peak in binary black hole spin (mis)alignments
Noah E. Wolfe, Salvatore Vitale and Michael Zevin
The degree of black-hole
spin-orbit misalignment ("tilts") in the astrophysical population could be a powerful diagnostic to distinguish between binary formation in isolation, in dynamical environments, or in hierarchical triples. However, robust population-level
spin tilt measurements are complicated by model misspecification as well as numerical and Poisson variance, ultimately owing to poor single-event constraints on tilts. Motivated by reports of a possible peak in the
spin tilt distribution, we analyze the fourth LIGO-Virgo-KAGRA gravitational-wave transient catalog to test for preferred
spin orientations at different black hole masses. We find that a peak in
spin tilts is not statistically significant nor model independent. Since the data cannot be used to reliably identify subpopulations based on their
spin tilt properties, we also consider a complementary approach: measuring the
spin magnitude and tilt distributions at fixed mass scales. We find no confident correlation between mass and
spin tilt, but we do confirm a confident correlation between
spin magnitude and mass, corroborating recent analyses.
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Astrophysics of Galaxies
Kinematic Stratification in Extremely Red Quasars Revealed by JWST
Jack M. M. Neustadt, Nadia L. Zakamska, Yu-Ching Chen et al. (+7 more)
We analyze the spectra of the central
nuclei of extremely red
quasars (ERQs) observed as part of the JWST ERS Q3D program. We focus on the complex kinematic structures of the prominent rest-frame optical emission lines. Our modeling allows us to deblend the lines and separate the emission into distinct kinematic components that imply velocity- and density-stratified gas structures on a range of physical scales within the ERQs. Supplementing the JWST data with archival data, we analyze the spectral energy distributions (SEDs) of the ERQs and find they are consistent with a significantly
dust-obscured central source with a small amount of relatively-unobscured UV/optical flux that is scattered into our line-of-sight. While the kinematics of the UV and optical emission lines largely agree, the UV lines are dominated by scattered light. In contrast, the optical emission-line ratios indicate a combination of scattered and obscured emission. Our analysis focuses on one ERQ, J0834, because its distinct spectroscopic features allow the emission to be easily decomposed into separate kinematic components.
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All authors Jack M. M. Neustadt, Nadia L. Zakamska, Yu-Ching Chen, Andrey Vayner, Fred Hamann, Marie Wingyee Lau, Serena Perrotta, Kate Rowlands, Sylvain Veilleux, Dominika Wylezalek
Earth and Planetary Astrophysics
Life is But a Stream: The Distribution of Planetary Systems Along Stellar Streams and their Properties
Jeremy J. Webb, Milica Ivetic, Maxwell X. Cai et al. (+2 more)
The majority of discovered
exoplanets have been observed orbiting field
stars as opposed to within a
star cluster. To determine whether the lack of observed
exoplanets in
star clusters is due to gravitational perturbations or observational limitations, we consider the possibility of studying
exoplanets in
stellar streams. We present the results of direct $N$-body simulations of planetary systems around
stars that orbit within a
star cluster. Our simulations demonstrate that
stars with early cluster escape times tend to retain all their
planets as they spend most of their time orbiting in the cluster's low-density outskirts. Alternatively,
stars with later escape times can have a wide range of survival fractions as they are subjected to a range of local densities and encounter types. With respect to the
stellar stream that forms as the result of the cluster's dissolution,
stars near the edge of the stream are therefore more likely to have unperturbed planetary systems. Conversely,
stars near the centre of the stream have a higher chance of having
planets pushed to eccentric orbits, inclined orbits, or stripped from the system entirely. From our suite of simulations, we provide an estimate of the probability that a
star will host a
planet with a given initial semi-major axis $a_0$ based on the
star's location along a
stellar stream $\Delta \phi$.
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All authors Jeremy J. Webb, Milica Ivetic, Maxwell X. Cai, Simon Portegies Zwart, Daniella Morrone
High Energy Astrophysical Phenomena
On the Origin of Mass Ejection in Failed Supernovae
Daniel A. Paradiso, Sarah Vallejo and Eric R. Coughlin
Some high-mass
stars likely end their lives in underluminous implosions that leave behind a black hole, known as failed
supernovae (FSNe). However,
neutrinos radiated during proto-
neutron star formation generate a weak (Mach $\gtrsim 1$) shockwave in the outer layers of the
star, which produces a unique transient as it breaks out of the dying
star and signals its imminent disappearance. It was recently shown that there are two self-similar solutions that describe the propagation of this weak shockwave, and these solutions simultaneously contain outward-moving ejecta and fallback
accretion onto the black hole. Here we show that the larger Mach number solutions are unstable, such that the Mach number of the shock grows with time $t$ and deviates from the self-similar prediction as $\propto t^{\alpha}$, with $\alpha \lesssim 0.1$, whereas the smaller Mach number solutions are stable. We also show that, above a critical mass loss that is readily achievable in core-collapse
supernovae, the shock asymptotically strengthens and approaches the strong limit. Our results imply that it is the mass lost to
neutrinos relative to the mass enclosed by the shockwave, as well as the
stellar density gradient where the shock forms, that primarily dictate its strength and the amount of material it ejects. These criteria explain why red supergiants, which have relative mass losses well in excess of the critical value at the time of shock formation, more readily eject material and create more luminous explosions compared to more compact progenitors.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Extended thermodynamics and $P-v$ Criticality of Kalb-Ramond black hole coupled with nonlinear electrodynamics
D. V. Singh, S. Upadhyay, P. Paul et al. (+1 more)
We present an exact black hole solution in anti-de Sitter (AdS) spacetime with a Kalb-Ramond field coupled to nonlinear electrodynamics (NLED), characterized by mass,
magnetic monopole charge, and Lorentz-violating parameters. The geometry admits two horizons (inner and outer) that coalesce into a degenerate horizon at a critical monopole charge. Beyond this critical point, no black hole solutions exist. In the limit of vanishing Lorentz-violating parameters, the solution reduces to the modified Kalb-Ramond and Bardeen black holes, while suitable parameter choices reproduce the Reissner-Nordström-AdS and Schwarzschild-AdS geometries. We analyze the thermodynamics of the solution by computing the Hawking temperature,
entropy, specific heat, and Gibbs free energy. The NLED source introduces nontrivial modifications: the Hawking temperature displays nonmonotonic behavior with possible local extrema, the
entropy deviates from the standard area law, and the specific heat may assume negative values, signaling thermodynamic instabilities. The Gibbs free energy exhibits swallow-tail structures, indicative of first-order phase transitions. Furthermore, we derive the first law of black hole thermodynamics in the extended phase space, together with the Smarr relation, and confirm their validity for the Kalb-Ramond black holes with NLED sources. Our findings highlight the rich thermodynamic structure induced by Lorentz-violating effects and nonlinear electrodynamics in AdS black hole backgrounds.
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All authors D. V. Singh, S. Upadhyay, P. Paul, K. Myrzakulov
Cosmology and Nongalactic Astrophysics
Non-conservation and time non-locality of biased tracers
Lawrence Dam
We study the effect of ongoing formation and merger on the assumed number conservation of biased tracers. Using a Lagrangian approach we present a model of the number density which accounts for such effects. The model is nonlocal in time, reflecting the gradual assembly of tracers from the underlying matter. The loss of tracers through merger is modelled by an environmentally-dependent sink, such that the merger rate is proportional to the local number density (higher probability of an event in higher density regions). We derive from our model a formula for the linear bias of non-conserved tracers, showing that such tracers debias more rapidly than conserved ones. Over time the large-scale power becomes increasingly suppressed relative to the conserved prediction, behaviour which has been observed in simulations elsewhere. Implications for current modelling approaches are discussed.
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Astrophysics of Galaxies
J1248+4826: A diffuse radio source consistent with re-energized fossil plasma in a galaxy group
M. Polletta, A. L. Coil, B. L. Frye et al. (+1 more)
High-resolution, sub-gigahertz
radio surveys have revealed a growing number of diverse, diffuse
radio sources, presenting new challenges in classifying them and deciphering their nature. We report the discovery of J1248+4826, a complex diffuse
radio source in the Low Frequency Array (LOFAR) Two Metre Sky Survey and investigate its physical origin. We analyzed the
radio morphology and spectrum of J1248+4826 and studied its environment and optical counterparts using multiwavelength data. After subtracting the
radio emission of the bright
radio galaxies in the field to isolate the diffuse component, we compared it with known diffuse
radio sources including odd
radio circles (ORCs), diffuse circular sources, cluster
halos, and remnant lobes to establish its nature and formation mechanism. The apparent ring-like morphology, high
radio luminosity, and steep spectrum of J1248+4826 initially suggested that this source might be a new ORC or a diffuse circular source. However, the residual
radio emission reveals a compact (~30 kpc radius) horseshoe-shaped inner structure, embedded in an extended (~200 kpc) diffuse envelope, with an ultra-steep spectrum (alpha=1.7+/-0.2), which we interpret as a re-energized remnant lobe. The analysis of the multiwavelength data reveals a possible association with a
galaxy group at z=0.2 and points to its most massive known member, a currently inactive early type
galaxy located ~55 kpc from the structure's center, as the progenitor. Moderate shocks associated with the group dynamics provide a plausible reacceleration mechanism, although the details of such a process remain uncertain with the current data. J1248+4826 highlights the increasing diversity of diffuse
radio phenomena and the challenges in their study and classification, while also revealing their potential to study the interplay between
galaxies and their environment on large scales.
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All authors M. Polletta, A. L. Coil, B. L. Frye, H. Dole
Cosmology and Nongalactic Astrophysics
Are PTA measurements sensitive to gravitational wave non-Gaussianities?
Chiara Cecchini, Jonas El Gammal, Gabriele Franciolini et al. (+1 more)
Observing non-Gaussianities in the timing residuals of
Pulsar Timing Arrays (PTAs) has recently attracted
attention as a potential discriminator between astrophysical and cosmological origins of the observed Gravitational Wave (GW) signal. In this work, we show that even in an idealized signal-dominated setup, after decorrelating the data to avoid spurious detections, statistical tests applied to PTA data cannot distinguish between a Gaussian and a non-Gaussian amplitude distribution of the GWB in a model-agnostic way. In particular, without making strong assumptions on the GW spectrum or the properties of the population, the sensitivity to any distinctive non-Gaussian feature is washed out.
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All authors Chiara Cecchini, Jonas El Gammal, Gabriele Franciolini, Mauro Pieroni
Cosmology and Nongalactic Astrophysics
Exponential Quintessence: Analytic Relationship Between the Current Equation of State Parameter and the Potential Parameter
Naoto Maki and Kazunori Kohri
Motivated by the indications of time-varying dark energy equation of state reported from DESI, we investigate a quintessence model with an exponential potential $V_0 e^{-\lambda\phi/m_{\mathrm{pl}}}$. We derive an analytical relationship between the current equation of state parameter for the quintessence field and the potential parameter $\lambda$ required to realize radiation and matter domination. Our results provide a useful analytical relation for inferring the potential parameter $\lambda$ from the observed current equation of state parameter. Furthermore, based on this framework, we provide a new approximate analytical upper bound on the potential parameter $\lambda$ for current accelerated expansion. Concretely, we obtain $\lambda<1.94$ as an approximate analytic estimate by adopting $\Omega_{\phi0}=0.685$.
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Cosmology and Nongalactic Astrophysics
Effective Field Theory of Large Scale Structure and Newtonian Motion Gauges
Christian Fidler, Julien Lesgourgues, Antonia Mattes et al. (+2 more)
The simplest
flavor of the Effective Field Theory of Large Scale Structure is based on Newtonian equations and describes the nonlinear matter density and velocity using Einstein-de-Sitter kernels. Even in the presence of massive
neutrinos, this has been argued to be sufficient for the analysis of data from Stage-III
galaxy surveys. In this paper, we show that there exists a simple way to extend the validity range of this framework to more complex problems with a scale-dependent growth factor, while incorporating linear general relativistic (GR) corrections as well. For a given cosmology, an Einstein-Boltzmann code can find the exact gauge transformation that brings the full linear equations of motion of the clustering matter components into a form where they are identical to Newtonian equations for a self-gravitating fluid with scale-independent growth. Non-linear clustering can be consistently computed in this gauge, and the results can be transformed back to the initial gauge in order to incorporate GR and scale-dependent-growth effects.
Redshift-space distortions can also be accounted for with a similar strategy. Our method does not incur any additional computational cost. As a showcase, we apply this method to cosmologies with massive
neutrinos. For the real-space one-loop power spectrum, we find that the largest deviation between the accurate and standard methods remains below 0.7% for M_nu<0.30 eV. However, in
redshift space, it reaches 1.7% for the one-loop quadrupole spectrum at k=0.3 h/Mpc and z=0, with the largest contribution coming from the effect of the cosmological constant on the growth of the velocity field. Our method could be applied to a much wider range of models with more significant scale-dependent growth, as long as a self-consistency condition evaluated by the Einstein-Boltzmann code (on the smallness of a gauge transformation field) is fulfilled.
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All authors Christian Fidler, Julien Lesgourgues, Antonia Mattes, Azadeh Moradinezhad Dizgah, Simon Neuland
Solar and Stellar Astrophysics
Turbulent damping of fast tidal oscillations by three-dimensional Rayleigh-Bénard convection with a radiating free surface
Caroline Terquem, Alexander Boone and Enrico Martinez
We present three-dimensional Dedalus simulations of Rayleigh-Bénard convection with a blackbody-radiating free upper surface, subject to a low-amplitude oscillatory forcing that mimics
tidal perturbations in convective envelopes of
stars and
planets. The forcing period is 10-100 times shorter than the convective timescale, $t_{\rm conv}$. Using a Reynolds decomposition of the velocity field averaged over one oscillation period, in which the
tidal oscillations naturally constitute the fluctuating field and convection the mean flow, we elucidate the kinetic energy exchange between the two. Provided the oscillatory Reynolds number exceeds a modest threshold, we find that the oscillations systematically transfer kinetic energy to the mean flow at a volume-averaged rate $D_R \sim u'^2 t_{\rm conv}^{-1}$, where $u'$ is the rms fluctuation velocity. This reflects strong, order-unity correlations between the fluctuation velocities and the mean flow. These arise because the oscillatory forcing displaces fluid elements that are then redirected by buoyancy and incompressibility in the same manner as the mean flow. The transfer is dominated by correlations involving vertical velocity fluctuations and vertical gradients of the mean flow. The resulting energy transfer rate is consistent, within the
equilibrium-tide framework, with the observed
tidal circularisation of
solar-type binaries and with the orbital
evolution of moons of Jupiter and Saturn. This validates the formalism proposed by Terquem (2021) for the dissipation of fast tides, a longstanding problem. Replacing the free surface with a rigid upper boundary significantly and artificially modifies the correlations.
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Earth and Planetary Astrophysics
A formation pathway for giant planets in S-type discs of {\gamma}-Cephei-like compact binaries
María Paula Ronco, Octavio M. Guilera, Julia Venturini et al. (+2 more)
Planet formation in close binary systems such as $\gamma$-Cephei is strongly challenged by the truncation of the circumprimary disc induced by the
stellar companion, which limits the available reservoir of gas and solids. Recent hydrodynamical studies suggest that a long-lived circumbinary disc may replenish the circumprimary disc with gas and
dust, extending its lifetime and potentially enabling
giant planet formation. However, the long-term
evolution of such systems under viscous
accretion and X-ray photoevaporation, and their coupling with
planet formation, remains largely unexplored. We investigate whether sustained mass inflow from a circumbinary reservoir can prolong the lifetime of circumprimary discs and facilitate gas
giant formation in $\gamma$-Cephei-like binaries, even in the presence of strong photoevaporation. Using our code PLANETALP-B, we model the coupled
evolution of gas,
dust growth, and in-situ
planet formation by pebble and gas
accretion, including viscous
accretion, X-ray photoevaporation, and continuous mass injection. Gas inflow can significantly extend the lifetime of the circumprimary disc, even under strong mass loss. When solids are also transferred, the lifetime of the solid disc increases, enhancing planetary growth. As a result,
planets can reach several Jupiter masses, unlike scenarios without mass replenishment. We show that sustained mass transfer from a circumbinary disc can enable
giant planet formation in $\gamma$-Cephei-like binaries, providing a viable pathway to overcome disc truncation, although its applicability to other systems remains to be tested with dedicated hydrodynamical simulations.
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All authors María Paula Ronco, Octavio M. Guilera, Julia Venturini, Federico Zoppetti, Marcelo M. Miller Bertolami
Astrophysics of Galaxies
Little red dots as obscured little blue dots: relative abundances, luminosities, and black-hole masses
Piero Madau and Roberto Maiolino
We test whether "little red dots” (LRDs) are the
dust-reddened, high-inclination counterparts of bluer compact broad-line active
galactic nuclei, here referred to as "little blue dots” (LBDs), by modeling their relative number densities and luminosities. Using the observed UV luminosity function (LF) of broad-line active
galactic nuclei (BLAGNs) at z>4 as the parent distribution, we forward-model the effects of
accretion rate, anisotropic emission, orientation, and
dust obscuration within our super-Eddington unification framework. We show that a model with a geometrically thick
accretion flow and a dusty circumnuclear cloud population reproduces the LRD LF over the luminosity range currently constrained by JWST. The predicted LRD/BLAGN fraction is strongly luminosity dependent, rising from ~3% at M_{1500}=-21 mag to a peak value of ~20% near M_{1500}=-19. The model also predicts a larger apparent LRD fraction at rest-frame optical wavelengths, reaching 27% at M_{4500}=-20 mag and 39% at M_{6500}=-21. The fiducial solution adopts a baseline host extinction A_V^{host}=0.5 mag, a characteristic per-cloud
nuclear extinction < A_V^c >=3.0 mag, and a gray R_V=5.5 attenuation curve, and yields a mean
dust covering factor < C_{
dust} > ~0.23. This value is conditional on the adopted
dust prescription, since lower per-cloud extinction can be compensated by a larger covering factor. These results may support an orientation-based unification of little dots and identify the LRD LF as a key demographic test of rapid
accretion onto infant black holes at
cosmic dawn. Within this same framework, UV-selected LRDs are predicted to host systematically more massive black holes than unobscured LBDs, not because they represent a distinct parent population, but because
dust attenuation preferentially removes lower-mass obscured systems from the observed UV sample.
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Earth and Planetary Astrophysics
The NUV transit of XO-3 b
Raven Cilley, Lia Corrales, George W. King et al. (+8 more)
Near-UV (NUV) measurements of
exoplanet transits offer a means to probe atmospheric escape, cloud formation, and planetary
magnetic fields. We examine a 2024 XMM-Newton Optical Monitor NUV observation of the transit of XO-3~b, a massive hot Jupiter on an eccentric orbit with a previously observed abnormally large NUV-absorbing atmosphere. We analyze this NUV data jointly with a concurrent ground-based optical observation and all TESS transit observations, and find a NUV transit depth of $R_{p,NUV}/R_{\star} = 0.1371^{+0.016}_{-0.019}$, which is 30-70% deeper than the optical transit. Although the optical transits do not show signs of transit timing variations, the transit center in the NUV is $22^{+13}_{-11}$ minutes late compared to the optical ephemeris. We investigate atmospheric escape as a potential explanation of the properties of this NUV transit by examining X-ray data from XMM-Newton, characterizing the X-ray luminosity of XO-3 for the first time and estimating an extremely small mass-loss rate of $\sim10^4$ g/s ($\sim10^{-19}$ M$_{\text{jup}}$/yr). Finally, we investigate the likelihood of an NUV-absorbent bow-shock by estimating the
magnetic field of the
planet. While such a mechanism is capable of producing NUV transit offsets on the order of tens of minutes, our analytic approximations predict an early rather than late transit, indicating a need for further magnetohydrodynamic simulations.
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All authors Raven Cilley, Lia Corrales, George W. King, Jiayin Dong, Robert Frazier, Kohei Miyakawa, Akihiko Fukui, Teruyuki Hirano, Juliette Becker, James T. Sikora, Lisa Dang
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Phase Transitions and Gravitational Waves
Diego Rios and William H. Kinney
We present a Fisher
matrix forecast for the spectral parameter reconstruction of a
stochastic gravitational wave background generated by a first-order phase transition in the early universe. We use the LISA and DECIGO instruments for reference and model the source spectrum with a double-broken-power-law template, parameterized by the peak amplitude $\Omega_p$, peak frequency $f_p$, break ratio $r_b$, and intermediate slope $b$. For each detector, we construct a fixed fiducial
benchmark with the peak placed in the corresponding sensitivity band, using $f_p=3.0\times10^{-3} \ {\rm Hz}$ for LISA and $f_p=1.0\ {\rm Hz}$ for DECIGO. The LISA baseline includes an unresolved
galactic compact-binary foreground, while for DECIGO we compare foreground cases using a full compact binary, a projected post-subtraction compact-binary residual, and an instrument noise only foreground. We find that both detectors constrain the peak parameters $\ln\Omega_p$ and $\ln f_p$ more robustly than the detailed shape parameters $r_b$ and $b$. For the chosen DECIGO
benchmark, the projected residual foreground produces negligible parameter degradation relative to the instrument noise only case, while the full foreground lowers the signal-to-noise ratio from $\rho=10$ to $\rho\simeq6.06$ and increases the marginalized uncertainty on $b$ by about $51\%$. These results emphasize that
stochastic-background forecasts should distinguish detectability from spectral identifiability.
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Instrumentation and Methods for Astrophysics
First Detection of Extensive Air Showers Using a Small-Aperture Fluorescence Telescope
M. Zotov, A. Trusov, P. Klimov et al. (+5 more)
We report on the detection of extensive air showers (EAS) generated by ultra-high-energy
cosmic rays using a small-aperture fluorescence
telescope (FT) deployed at the Mount Aragats high-altitude research station. The instrument is equipped with two Fresnel lenses with a diameter of 25 cm and operates with a 2.625 $\mu$s time resolution. To our knowledge, this represents the first-ever observation of EAS achieved with an FT of such a compact aperture. To isolate shower events from the observational data, we implemented two independent event selection pipelines: a conventional cut-based analysis and a deep learning approach utilizing neural networks. Both
algorithms successfully identified over 15 high-confidence EAS tracks from data acquired during clear, moonless nights. We present selected event
topologies and detail the background rejection methodology employed to discriminate true shower tracks from spurious signals mimicking EAS signatures. These results provide an important proof-of-concept for the advancement of fluorescence detection techniques, demonstrating their viability for forthcoming ground-based and space-borne missions. Future efforts will focus on primary energy reconstruction utilizing a previously developed neural-network framework.
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All authors M. Zotov, A. Trusov, P. Klimov, K. Asatryan, A. Belov, G. Gabaryan, V. Kudryavtsev, A. Murashov
High Energy Astrophysical Phenomena
The one and the only: the pulsar - white dwarf system in NGC 6749
Paulo C. C. Freire, Yinfeng Dai, Mario Cadelano et al. (+7 more)
PSR J1905+0154A is a binary millisecond
pulsar located in the globular cluster (GC) NGC 6749. It was discovered in 2004 in a search for
pulsars in GCs carried out with the Arecibo 305-m
radio telescope. The
pulsar has a
spin period of 3.2 ms, an orbital period of 0.81 days, and is in a low-eccentricity orbit with a low-mass WD companion. Combining early Arecibo and latter Five Hundred meter Aperture Spherical
Telescope (FAST) data, we were able to derive a phase-coherent timing solution for this
pulsar, which now spans 20 years. This includes a precise measurement of the astrometric,
spin and orbital parameters of the system. The small range of predicted accelerations expected from the gravitational field of this GC allows an estimate of the intrinsic
spin-down: the inferred
magnetic field at the surface (2.2 - 2.4 * 10^8 G) and characteristic age (2.8 - 3.5 Gyr) are typical of what one finds among MSPs in the
Galactic field. The position of this
pulsar coincides with the position of one of the very few candidate white
dwarfs (WDs) in the whole HST
dataset on this GC. The position of the companion in the colour-magnitude diagram is consistent with a Helium WD with a mass of 0.17 - 0.19 M_sun, a cooling age of 0.4 - 0.7 Gyr, and a surface temperature of 11,600 - 14,800 K. A comparison with the characteristic age of the
pulsar indicates that at the time of Roche lobe detachment, the
spin period was between 1.98 and 2.62 ms.. The velocity of the system relative to the GC, which is 4.5-sigma significant and an order of magnitude larger than the escape velocity, raises the possibility that, despite its location close to the centre of the GC, the
pulsar might not be associated with it. Finally, our effort to confirm a second
pulsar candidate in this GC did not yield a positive confirmation, nor the discovery of any additional
pulsar in this GC.
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All authors Paulo C. C. Freire, Yinfeng Dai, Mario Cadelano, Cristina Pallanca, Zurong Zhou, Zhichen Pan, Luca Rosignoli, Davide Massari, Mattia Libralato and, Craig Heinke
Cosmology and Nongalactic Astrophysics
Capturing statistical isotropy violation with rotational averages
Vaishali R, Dipayan Mukherjee, Akshank Tyagi et al. (+1 more)
Recent high precision cosmological observations have revealed several anomalies in the
Cosmic Microwave Background (CMB), indicating possible violations of statistical isotropy (nSI). Typically, nSI in the CMB sky is studied in the harmonic space, such as, using the Bipolar Spherical Harmonics (BipoSH) formalism, where the BipoSH coefficients capture the general structure of the angular correlation function. In this work, we present a
geometric real space framework to quantify violations of statistical isotropy complementing the BipoSH approach. This
geometric approach involves averaging the angular correlation function over all rotated configurations, weighted by Wigner
matrices. These rotational averages systematically isolate the nSI components of the CMB sky. They also provide a physical space based route to interpretation of how the BipoSH formalism captures breaking of rotational
symmetry. As a demonstration, we consider an analytical dipole modulation model. We numerically implement the rotational average measures and show their agreement with their harmonic space counterparts. The real space approach to quantify nSI could be advantageous in certain scenarios: rotational averages can directly extract nSI information from the correlation function at the level of a given multipole, bypassing the need to compute BipoSH coefficients up to arbitrarily high internal ranks. Importantly, analyzing the temperature map in real space can circumvent the unavoidable partial-sky effects present in CMB observations, which typically complicate harmonic space approaches. We envisage broader applications of this formalism to studies of
primordial non-Gaussianity, CMB polarization, and weak gravitational
lensing, as well as to the characterization of general random fields on a sphere.
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All authors Vaishali R, Dipayan Mukherjee, Akshank Tyagi, Tarun Souradeep
Solar and Stellar Astrophysics
Multi-Dimensional MHD simulations of young Core-Collapse Supernova Remnants
C. J. K. Larkin, J. Mackey, B. Reville et al. (+3 more)
Supernova remnants (SNRs) play a central role in shaping the interstellar medium. Core-Collapse
Supernova (CCSN) progenitors are massive
stars, which produce a dense circumstellar medium (CSM) through intense mass loss in post-main sequence
evolution. The subsequent CCSN produces a strong shock which expands into a highly structured, complex magnetised environment. Magnetohydrodynamic (MHD) consideration of pre- and post-CCSN
evolution in multi-D are desirable to further our understanding of non-thermal aspects. We aim to determine how detailed
stellar evolution treatment influences the shock propagation, focusing on Red Supergiants (RSGs) and Wolf-Rayet (WR)
stars. We use the PION code to perform 3D MHD simulations of these CCSN progenitors. We use a detailed
stellar evolution prescription to accurately and self-consistently model the pre-SN CSM and initialise CCSN explosions to investigate the surrounding environment. Our 2D and 3D treatment, inclusion of radiative cooling and assumption of full photoionization produces CSM features not identified in previous work. In the WR model we produce a coherent set of fast reflected shocks. In both cases we find faster forward shocks than predicted by analytic theory due to additional wind acceleration from photoionization for the RSG case, and accounting for the CSM expansion in the WR case. Model predictions of slowly rotating RSG and WR
stars results in weakly magnetised wind bubbles, limiting potential for their SNRs to become PeV particle accelerators. Detailed multi-D MHD treatment of the CSM is needed to account for SNR
evolution beyond the wind termination shock, where dynamic instabilities can be important. Including self-consistent
stellar evolution is important for determining the CSM density and
magnetic field structure close to the
star, which govern the shock properties and SNR
evolution for the first few hundred yr. (Abridged)
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All authors C. J. K. Larkin, J. Mackey, B. Reville, H. Jin, N. Langer, A. A. C. Sander
Earth and Planetary Astrophysics
Horizontal transport as a source of disequilibrium chemistry on the nightside of a hot exoplanet
Vivien Parmentier, Kevin B. Stevenson, Luis Welbanks et al. (+15 more)
Hot Jupiters have temperature gradients of several hundreds of degrees between their permanent day and nightsides. In
equilibrium, the primary carbon reservoir is expected to transition from CO on the dayside to CH4 on the nightside. Theory predicts that the atmospheric circulation, characterised by km/s winds, can advect chemical species from the dayside to the nightside faster than the time needed for the CO-to-CH4 chemical reaction to reach
equilibrium. However direct evidence of this process has, so far, remained elusive, partly because it is often degenerate with other processes, such as vertical mixing or non-
stellar elemental abundances. Here, we present observational evidence for such day-to-night transport of chemical species by observing both the dayside and the nightside of the hot Jupiter NGTS-10A b with the JWST/NIRSpec instrument. We constrain the presence of H2O and CO with similar abundances on both the dayside and nightside. Our observations are compatible with a
solar-composition atmosphere at chemical
equilibrium on the dayside, but indicative of disequilibrium chemistry for the nightside as it is significantly depleted in CH4 compared to
equilibrium chemistry predictions. We further show that the lack of CH4 on the
planet's nightside cannot be attributed to non-
solar elemental abundances or to vertical mixing mechanisms and must therefore be due to horizontal chemical quenching. Our study shows the fundamental role atmospheric transport plays in shaping the distribution of chemical species on
exoplanet atmospheres.
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All authors Vivien Parmentier, Kevin B. Stevenson, Luis Welbanks, Jake Taylor, Everett Schlawin, Louis-Philippe Coulombe, Yao Tang, Mike Line, Hinna Shivkumar, Xianyu Tan, Jacob L. Bean, Jean-Michel Désert, Jonathan J. Fortney, Peter Gao, Mark Hammond, Eliza M.-R. Kempton, Thaddeus D. Komacek, Megan Weiner Mansfield
Astrophysics of Galaxies
Near-infrared diagnostic diagrams of the gas ionization sources in nearby galaxies: a JWST NIRSpec view
J. H. Costa-Souza, Luis Colina, Rogemar A. Riffel et al. (+6 more)
Buried active
galactic nuclei and obscured young
stellar clusters pose significant challenges to traditional optical diagnostic diagrams. Therefore, developing new tools to trace the excitation sources across the spectrum is a necessary effort for the advancement of the field. Our goal is to explore the full spectral range of the JWST-NIRSpec data, searching for alternative diagnostic diagrams in the less-explored NIR, and to investigate the nature of the ionizing and heating source. We analyze the high-resolution spectra of the circum-
nuclear regions of nine local (z < 0.1) U/LIRGS, investigating potential emission-line ratios to trace the excitation mechanisms acting on the line-emitting gas. We investigate these objects using the well-established [Fe ii]/PaB versus H2/Bry diagram, and attempt to correlate its classifications with other emission features across the spectrum. We then compare the empirical classifications with photo-ionization models, in order to evaluate how accurately the data can be reproduced. Finally, we compare the line width at 80% of the total flux (W80 ) of selected emission lines with the corresponding gas excitation mechanisms. We propose two line-excitation diagnostic diagrams based on [C i]/Pay and H2 1-0 O(5)/PAH 3.3 um ratio, which we found to directly correlate with the hardness of the radiation field, and therefore with the gas excitation mechanisms. In addition, the line-kinematics analysis shows that the W80 values of regions excited by
star formation are on average slightly lower than those of AGN-excited regions, while shock-excited regions display distinctively higher W80 values compared to the other two groups. Our JWST-NIRSpec results reinforce previous studies showing that the H2 emission in the central regions of AGN hosts is complex and likely produced by multiple excitation mechanisms.
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All authors J. H. Costa-Souza, Luis Colina, Rogemar A. Riffel, Santiago Arribas, Michele Perna, Miguel Pereira Santaella, Ismael García-Bernete, Montserrat Villar Martín, Oli L. Dors