Astrophysics of Galaxies
Something green beneath the surface: The dynamical nature of Fossil Structures in IllustrisTNG-100
Mary Verdugo-Santos, Facundo A. Gómez, Diego Pallero et al. (+2 more)
Fossil structures (FS) have traditionally been considered dynamically relaxed end-products of group
evolution, characterized by a large magnitude gap ($\Delta m_{1,2} \geq 2$). However, recent observations and simulations suggest this picture is incomplete. We investigate whether FS are dynamically relaxed systems and how their
galaxy populations differ from non-fossil systems (non-FS), focusing on system dynamics and
evolution of the
galaxies inside them. Using IllustrisTNG-100, we select 182 structures ($M_{200} > 10^{13}\,M_{\odot}$) at $z = 0$, classifying them as FS/non-FS based on $\Delta m_{1,2}$ in the $r$-band. We track $\Delta m_{1,2}$
evolution over 9\,Gyr and analyze: (1) the emergence of $\Delta m_{1,2}$, (2) the fraction of quenched
galaxies (sSFR $< 10^{-11}$\,yr$^{-1}$), (3) the distribution of
galaxies in color–
stellar mass space, and (4) the gas–BSG centroid shift as a dynamical proxy. The magnitude gap in FS is primarily driven by the absence of massive recent
accretion: FS exhibit significantly lower BSG-to-satellite
stellar mass ratios ($\mu^{\rm{FS}}{\star}$=0.17 vs. $\mu^{\rm{NFS}}{\star}$=0.39) for the most massive satellite accreted within the last 6\,Gyr. FS also host a more prominent red sequence and marginally higher quenched fractions than non-FS. Our findings indicate that while the magnitude gap effectively identifies systems that have ceased major mergers in the last 3-6 Gyr, it is a poor proxy for their current global dynamical state. Both FS and non-FS populations exhibit intermediate gas-BSG offsets ($D_{BSG-CM} \approx 0.15 R/R_{200}$), failing to reach full relaxation. This decoupling suggests that the magnitude gap traces the assembly history of massive components rather than the overall stability of the intra cluster medium.
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All authors Mary Verdugo-Santos, Facundo A. Gómez, Diego Pallero, Franklin Aldás, Cristian A. Vega-Martínez
Cosmology and Nongalactic Astrophysics
Statistical Field Theory for Weak Gravitational Lensing
Zheng Zhang, Philip Bull, Chris Clarkson et al. (+1 more)
Standard weak-
lensing calculations treat
lensing as a linear remapping of the matter field along the line of sight. We instead formulate
lensing as a
stochastic field theory for the Sachs optical scalars, driven by random
Ricci-focusing and Weyl-shearing fields. With convergence and shear expressed linearly in the Sachs-scalar fluctuations, the resulting path integral generates a diagrammatic expansion for their $n$-point correlation functions, organised into linear response, nonlinear propagation, and driving-field cumulants. The conventional calculation emerges as the lowest-order, linear-propagation limit. Beyond it, nonlinear Sachs
evolution couples to driving-field non-Gaussianity, mixing the matter cumulant hierarchy into the
lensing hierarchy. A selection rule governs the couplings: an $n$-point observable receives a direct contribution from the $n$-point driving-field cumulant, and its leading hierarchy-mixing correction from the $(n+1)$-point cumulant via one nonlinear Sachs interaction, with higher cumulants entering only at higher order. The two-point function, for instance, receives corrections from three-point cumulants of
Ricci focusing and Weyl shearing through nonlinear Sachs
evolution. Rather than a restrictive approximation scheme, the formalism is a paradigm shift: a unified framework naturally accommodating path corrections, higher-order matter statistics, stochasticity, and small-scale effects.
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All authors Zheng Zhang, Philip Bull, Chris Clarkson, Andrina Nicola
Astrophysics of Galaxies
On the later evolution of observationally selected protocluster candidates at $z\,{\gtrsim}\,5$
Seunghwan Lim
Recent observations have revealed numerous protocluster candidates at $z\,{\gtrsim}\,5$, yet whether these systems will eventually evolve into today's
galaxy clusters remains an open question. Using the FLAMINGO simulations – resolving protocluster cores up to $z\,{\simeq}\,10$ – we track the later
evolution of observationally selected protocluster candidates, comparing three selection methods against observational samples. The observed number density falls between our mass-selected and abundance-matched samples, implying that current searches pick up both genuine cluster progenitors and significant interlopers that will not reach cluster masses by $z\,{=}\,0$. We find that candidates at $z\gtrsim5$ are heavily clustered, hosting 2$-$10 neighbors within 10\,cMpc. Consequently, a candidate with a neighbor at 5\,cMpc (10\,cMpc) faces a $\gtrsim50\%$ ($\gtrsim30\%$) probability of later merging into a larger system, mostly at $z\,{\lesssim}\,2$. The merger count converges beyond ${\sim}10$\,cMpc, pointing to a fundamental scale in structure formation. Observations show markedly weaker clustering than our simulations predict, suggesting clustering offers a currently overlooked diagnostic. Each candidate undergoes roughly 2$-$6 later major mergers, mostly with systems too small to be recognized as massive at the selection epoch. Hence, relying solely on high-$z$ mass and
galaxy overdensity to forecast a candidate's fate is prone to severe scatter and systematic error. A robust identification of true cluster progenitors demands a total mass sum of
galaxies down to the faintest levels within a 10\,cMpc radius. Upcoming surveys with both depth and area will be key to reliably linking high-$z$ protocluster candidates to their ultimate destiny.
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Astrophysics of Galaxies
Characterizing the Formation and Evolution of S0-galaxies (CaFES-0): Their formation pathways around Galaxy Clusters
Diego Pallero, Yara L. Jaffé, Amelia Fraser-McKelvie et al. (+7 more)
The formation pathways of lenticular
galaxies (S0s), which lie morphologically between elliptical and spiral
galaxies, remain a topic of active research. Environmental effects, merging histories, and pre-processing mechanisms are often proposed as key factors influencing their transformation. However, the relative importance of these processes remains unclear, particularly when compared with other
galaxy types. We use the Hydrangea cosmological zoom-in simulation suite to analyse the environmental histories of S0
galaxies, defined here as central and satellite quenched disk
galaxies. We find that the vast majority (>85%) of our sample of S0s are satellites in massive
haloes (log$_{10}$M$_{200}/$M$_\odot$ > 13), while only $\sim10\%$ are centrals in low-mass
haloes. Satellite S0s exhibit a highly quiescent merging history, with $\sim60\%$ experiencing no significant mergers since $z=2$. Centrals show more varied merging histories, although our results may be affected by limited sample size. Contrary to expectations, no clear trends in merger ratios with morphology are observed. However, mergers involving lenticular and spiral
galaxies tend to occur in low-density environments and are likely gas-rich, enabling disk reformation. Pre-processing effects in groups are critical, influencing both quenching and morphological transformation.} Our results strongly suggest that S0
galaxies predominantly form from faded/stripped spirals in clusters, with a minority forming via mergers in smaller
haloes. These results are in agreement with previous observations of lenticular
galaxies around
galaxy clusters.
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All authors Diego Pallero, Yara L. Jaffé, Amelia Fraser-McKelvie, Lodovico Coccato, Facundo A. Gómez, Yannick Bahé, Evelyn J. Johnston, Ciria Lima-Dias, Arianna Cortesi, Maria Emilia De Rossi
Cosmology and Nongalactic Astrophysics
Fireworks at Cosmic Dawn: relieving BAO-CMB tensions with the Pop III.1 Flash
Yash Aggarwal, Christopher Cain, Garett Lopez et al. (+4 more)
A
Cosmic Microwave Background (CMB) optical depth of $\tau \sim 0.09$, several $\sigma$ in excess of the latest Planck low-$\ell$ EE polarization measurement, has been proposed as a way to reconcile the preference for a sub-minimal
neutrino mass sum in a combined analysis with CMB and Dark Energy Spectroscopic Instrument (DESI) three-year data. Reionization, however, is not just probed by $\tau$. It is also constrained by Ly$\alpha$ forest observations that indicate a late end of reionization, and the patchy kinetic Sunyaev-Zel'dovich (pkSZ) effect which prefers a short duration. We explore whether an early phase of reionization can achieve a high $\tau$ while remaining consistent with both Ly$\alpha$ forest and pkSZ constraints. As a concrete example, we consider supermassive Pop III.1
stars, dark-matter-powered metal-free
stars proposed as progenitors of supermassive black holes. Within this framework, self-regulating ionizing feedback imposes a minimum source separation of $\sim 1 \, \text{cMpc}$, consequently limiting large-scale ionization fluctuations and reducing the pkSZ power on observationally relevant scales. Our fiducial model realizes an optical depth of $\tau = 0.087$ with a Pop III.1-driven flash ionization phase centered at $z = 20$, while evading the most conservative $2\sigma$ upper limits on the pkSZ signal from the most recent South Pole
Telescope data release. More broadly, our findings motivate further exploration of early reionization models with weakly clustered sources as a possible resolution of tensions between BAO and CMB measurements.
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All authors Yash Aggarwal, Christopher Cain, Garett Lopez, Hy Trac, Anson D'Aloisio, Philip Tanedo, Jonathan C. Tan
High Energy Astrophysical Phenomena
Short-Range Forces Can Catalyze Extreme Orbital Evolution in Hierarchical Triples
Ygal Y. Klein and Chris Hamilton
Hierarchical triples are promising environments for producing exotica such as black hole mergers and hot Jupiters, because of the von Zeipel-Lidov-Kozai (ZLK) effect, whereby a distant tertiary can torque an inner binary to high eccentricity over secular timescales. In the double-averaged (DA) approximation to ZLK, this eccentricity excitation is suppressed by apsidal precession due to "short-range forces" (SRFs) like relativity and
tidal/rotational bulges. Here we show that, when the DA approximation breaks down, SRFs often catalyze, rather than suppress, extreme eccentricity behavior. This occurs because SRFs can drive large, discrete jumps in the binary's effective "adiabatic invariants" during high-eccentricity episodes. These nonadiabatic jumps can dramatically alter the maximum/minimum eccentricity and secular period of astrophysically relevant triples, including some for which SRFs were previously thought irrelevant. Even the angular momentum component j_z evolves secularly – to our knowledge, this is the first time such
evolution has been demonstrated from a test-particle quadrupole-order, three-body mechanism. In short, binaries may explore much more of phase space than is implied by any (semi-)analytic ZLK theory of which we are aware. We demonstrate this at the test-particle quadrupole level; in a companion work we show how even more-extreme behavior occurs when the jumps are combined with octupolar ZLK
evolution.
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Solar and Stellar Astrophysics
X-Shooter survey of disk accretion in Upper Scorpius II. A lack of correlation between accretion rates and disk properties
A. Empey, C.F. Manara, R. Garcia Lopez et al. (+19 more)
The
evolution of protoplanetary discs is intertwined with the process of
planet formation, growth and migration. Studies of nearby
star forming regions of different ages and properties provide the necessary information needed to understand the processes dictating their
evolution. This paper presents the results of a spectroscopic study of the
stellar and
accretion properties of a large sample of 127
stars with protoplanetary discs in the Upper Scorpius region with disc
dust masses inferred from ALMA continuum measurements. The
accretion luminosity is derived from the excess UV continuum emission with respect to the photospheric and chromospheric one self-consistently with the
stellar spectral types, extinction and luminosity, using FRAPPE. We apply a new method to evaluate upper limits to the
accretion luminosity. In ~50% of cases we evaluate upper limits on the
accretion luminosity, either because the S/N of the data is insufficient or because the measured value of the
accretion luminosity is below the estimate of the emission due to chromospheric activity. The results show that the mass
accretion rate has a weak correlation with the
stellar mass, while no correlation is observed with disc properties such as
dust mass or gas disc radius. The dispersion is larger than what is found in younger
star forming regions such as Lupus and Cham. I, and suggests a fading of the correlations with age. We find no evidence that membership to Upper Scorpius sub-groups, nor the properties of known binary or transition discs can explain the origin of this dispersion. The lack of correlation and large dispersion of
accretion rates challenge the current expectations of evolutionary models. The observed properties point to a decoupling of the inner and outer disc by the age of Upper Scorpius and a fading of the relations observed in younger
star forming regions.
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All authors A. Empey, C.F. Manara, R. Garcia Lopez, A. Natta, R. Claes, F. Zagaria, J.M. Alcalá, R. Anania, G. Beccari, J. Carpenter, S. Facchini, D. Fedele, G. Lodato, K. Mauco, A. Miotello, B. Nisini, I. Pascucci, L. Piscarreta, G. Rosotti, A. Scholz, L. Testi, M. Vioque
Astrophysics of Galaxies
Baryonic mass budgets in the central regions of the Bullet Cluster and their consistency with strong lensing in MOND
Dong Zhang, Hosein Haghi, Elena Asencio et al. (+8 more)
Strong
lensing observations of the Bullet Cluster have traditionally been regarded as strong evidence for dark matter and a major challenge to Milgromian dynamics (MOND). The offset between the
lensing mass and the X-ray gas centroids implies a substantial amount of unseen mass near the brightest cluster
galaxies (BCGs). However, the high
metallicities observed in both the intracluster gas and the massive early-type member
galaxies suggest a past
stellar population dominated by massive
stars, whose evolved remnants contribute additional baryonic mass. This effect is naturally incorporated in the integrated
galaxy-wide initial mass function (IGIMF) theory, which predicts substantially larger baryonic masses than a canonical IMF. In this work, we re-estimate the baryonic masses of the three BCG-centred core regions of the Bullet Cluster using recent JWST photometry and compare them with MOND strong-
lensing masses. We derive IGIMF masses using
stellar population synthesis models with constant and (self-) enriched
metallicities, representing lower and upper mass limits, respectively. We find that the MOND strong-
lensing masses of all three cores lie within the range predicted by the IGIMF models. These results suggest that the baryonic mass budget is consistent with MOND requirements from strong-
lensing observations in the core regions of the Bullet Cluster. However, the physical viability of this scenario also depends on the spatial distribution and dynamical behavior of the remnant population, which remain to be established. More generally, regardless of the validity of MOND, the results imply that less dark matter may be required than previously inferred.
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All authors Dong Zhang, Hosein Haghi, Elena Asencio, Indranil Banik, Akram Hasani Zonoozi, Sangjun Cha, Boseong Young Cho, Hyungjin Joo, Pavel Kroupa, Anastasia Lazutkina, Eda Gjergo
Cosmology and Nongalactic Astrophysics
Validation of the Hybrid Bias Expansion model for the galaxy bispectrum
Marcos Pellejero Ibáñez, Raul E. Angulo, Laila Linke et al. (+8 more)
The Hybrid Bias Expansion model (also known as Hybrid Effective Field Theory, HEFT) provides a promising way to extend the range of validity of perturbative large-scale structure modelling by replacing perturbative gravitational
evolution with the nonlinear displacement field measured from $N$-body simulations. While this approach has already been shown to improve the modelling of the power spectrum, its validity at the bispectrum level has not yet been established. In this work we perform a first systematic real-space validation of the Hybrid bispectrum model using DESI-like LRG and ELG mock catalogues constructed at fixed cosmology on volumes similar to those of DESI's LRG samples. We find that the model remains self-consistent up to $k_{\rm max}^B \simeq 0.25\,h\,{\rm Mpc}^{-1}$, while clear signs of breakdown appear for a similar EFT tree-level bispectrum approach at $k_{\rm max}^B \gtrsim 0.13\,h\,{\rm Mpc}^{-1}$. We also show that adding matter cross-statistics significantly improves the precision of the recovered bias parameters, while a partial third-order extension including only the $\delta^3$ operator does not extend the validity range. Finally, we find a strong hierarchy among the bispectrum basis terms when grouped by total bias-operator order, with the lowest-order sectors dominating the total amplitude, which has important implications in emulation strategies.
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All authors Marcos Pellejero Ibáñez, Raul E. Angulo, Laila Linke, Sara Ortega-Martinez, Maria Tsedrik, Sergio Contreras, John A. Peacock, Kate Storey-Fisher, Jens Stücker, Rodrigo Voivodic, Matteo Zennaro
High Energy Astrophysical Phenomena
Nonlinear Decay of Fast Magnetosonic Waves through Weak Turbulence: Force-Free Electrodynamics Simulations
Siddhant Solanki, Jens Mahlmann and Alexander Philippov
We investigate the propagation of low-frequency fast-magnetosonic (FMS) waves in highly magnetized environments. Such conditions are relevant to the escape of GHz fast
radio bursts potentially produced in the inner magnetospheres of magnetars. It remains an open question whether such waves can escape without substantial reprocessing. Using relativistic force-free electrodynamics simulations, we confirm the key theoretical predictions of Golbraikh & Lyubarsky (2023) and demonstrate that FMS waves undergo efficient nonlinear conversion into secondary FMS and Alfvén waves via the parametric decay instability. This process continues to drain energy from the primary FMS waves even after approximate energy equipartition between the FMS and Alfvén components is established. The resulting spectrum of excited waves is broad, extending across much of the inertial range in $k$-space within the simulation domain. Our results indicate that FMS waves likely do not escape magnetar magnetospheres without substantial dissipation and spectral broadening.
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Cosmology and Nongalactic Astrophysics
A self-consistent analytical model for both the photoionization rate and reionization history
Christopher Cain, Kevin S. Croker, Anson D'Aloisio et al. (+4 more)
Recent developments at the intersection of cosmology and astrophysics have highlighted the need for improved analytical models of observables that probe the Epoch of Reionization. With few exceptions, fast analytical treatments of reionization suitable for use in
Bayesian inference have been limited to modeling the reionization history, $x_i(z)$. Such models cannot take full advantage of observables that constrain $x_i$ indirectly. One such observable is the photoionization rate of neutral hydrogen, $\Gamma_{\rm HI}(z)$, which can be inferred from the mean transmission of the Lyman-$\alpha$ forest of high-
redshift quasars and
galaxies. It has been shown by several prior works that the
evolution of $\Gamma_{\rm HI}$ at $5 \lesssim z \lesssim 6$ is highly sensitive to the tail end of reionization, potentially providing a tight astrophysical constraint on the reionization timeline. We present a new analytical formalism, based on the cosmological radiative transfer equation, that self-consistently predicts $x_i$ and $\Gamma_{\rm HI}$. We test our model against detailed radiative transfer simulations and find it to be percent-level accurate in $x_i$ and $20-30\%$ accurate in $\Gamma_{\rm HI}$ at $z \lesssim 6$ - better than or comparable to existing observational uncertainties. Finally, we demonstrate that modest shifts in the ionizing
photon output of high-
redshift galaxies and/or the endpoint of reionization lead to differences in $\Gamma_{\rm HI}$ much larger that the model's intrinsic uncertainty, highlighting its utility for interpreting existing data. We explore the origin of modeling uncertainty in $\Gamma_{\rm HI}$ and comment on future pathways for improvement.
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All authors Christopher Cain, Kevin S. Croker, Anson D'Aloisio, Ivelin Georgiev, Hurum Maksora Tohfa, Yongda Zhu, Rogier Windhorst
High Energy Astrophysical Phenomena
Damping of Fast Radio Bursts in the Inner Magnetospheres of Magnetars
Siddhant Solanki, Jens Mahlmann, Alexander Philippov et al. (+1 more)
We investigate the propagation of fast
radio bursts (FRBs) through magnetar magnetospheres. Previous work showed that, in the inner magnetosphere, GHz
radio waves propagate as fast magnetosonic waves and undergo resonant three-wave interactions that transfer their energy into trapped Alfvén waves. Using three-dimensional force-free electrodynamics simulations, we demonstrate that FRBs would excite Alfvénic fluctuations, leading to strong nonlinear attenuation of the
radio signal. In quiescent dipolar magnetospheres, the nonlinear decay stays efficient within $\sim10$–$100$ magnetar radii; charge starvation of the excited Alfvén waves stops the decay at larger radii. For FRBs propagating within relativistic
magnetic outflows launched during magnetospheric eruptions, three-wave interactions remain efficient and constrain the escape radius to $\gtrsim10^2$–$10^3$ magnetar radii for luminous bursts. Our results confirm that nonlinear
plasma processes strongly limit the escape of FRBs from the inner magnetospheres of magnetars.
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All authors Siddhant Solanki, Jens Mahlmann, Alexander Philippov, Andrei Beloborodov
Astrophysics of Galaxies
Reimagining SED Fitting with Cosmological Galaxy Simulations and Machine Learning
Dhruv T. Zimmerman and Desika Narayanan
SED fitting is the most common technique to recover
galaxy physical properties from observed photometry. However, SED fitting requires many assumptions that essentially collapse a
galaxy from a three-dimensional spatially varying object with complex structure into a scalar point. Moreover, modern inference techniques are computationally intensive, which presents a unique challenge in the era of extremely large
datasets. We present Phot-Gal, a new
galaxy SED modeling tool that solves the inverse problem of SED fitting by training a machine learning model on photometry generated from 3D radiative transfer of simulated
galaxies with a wide range of implemented physics. Phot-Gal is designed to accept an arbitrary amount of input photometry by utilizing a $K$-nearest neighbors imputation strategy. Our fiducial model predicts
redshift,
stellar mass,
dust mass, and
star formation rate with uncertainties based on the provided input photometry. We evaluate the performance of Phot-Gal relative to the commonly-used SED fitting tool prospector in successfully recovering each of these properties with several metrics for the inferred values and uncertainties and find that it outperforms the accuracy of standard SED fitting software on the testing set. However, with fewer photometric constraints, Phot-Gal is more likely to have output uncertainties that do not reflect the offset from the ground truth. We dissect the components of Phot-Gal to find reasonable physical justifications for the photometry it relies on most, understand how each step in its workflow contributes to the eventual output posterior, and evaluate its ability to generalize to novel data.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Dynamical tidal response of neutron stars: From effective field theory to gravitational waveforms
Thomas Apostolidis, Valerio De Luca, Leonardo Gualtieri et al. (+3 more)
We investigate the fully relativistic dynamical
tidal response of
neutron stars up to second order in the frequency. Combining the worldline effective field theory for extended gravitating bodies with perturbation theory of relativistic
stellar models, we derive the
tidal deformation induced by an external time-dependent field, including a universal logarithmic running term. In the effective theory, we work in dimensional regularization and, through a consistent matching procedure, obtain for the first time the complete leading-order dynamical
tidal corrections to both the conservative dynamics and the gravitational-wave signal of compact binaries, including the scheme-dependent finite terms in addition to the running. We show that, in the relativistic regime, dynamical effects cannot be fully captured by mode excitations alone. The magnitude of the additional contribution depends on the
stellar compactness, the equation of state, and the running term. Dynamical Love numbers are significantly enhanced with respect to their static counterparts for relatively small compactness. As a result, although they formally enter the gravitational-wave phase at eighth post-Newtonian order, dynamical
tidal effects yield a nonnegligible contribution during the late inspiral. Using a Fisher-
matrix analysis, we show that third-generation detectors such as the Einstein
Telescope could measure dynamical Love numbers for a range of
neutron-
star masses and equations of state. Conversely, neglecting these effects can lead to significant biases in the inference of static Love numbers, and hence on the
nuclear equation of state. Our results highlight the importance of dynamical
tidal effects for high-precision gravitational-wave modeling with future detectors.
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All authors Thomas Apostolidis, Valerio De Luca, Leonardo Gualtieri, Takuya Katagiri, Paolo Pani, Luca Santoni
High Energy Astrophysical Phenomena
Evidence for protostellar jets as a population of hadronic gamma-ray sources
Javier Méndez-Gallego, Rubén López-Coto, Emma de Oña Wilhelmi et al. (+3 more)
Stars are born in darkness, deep within cold, dense molecular clouds where
gravity drives the collapse of gas and
dust, giving rise to protostars, the earliest stages of
stellar evolution. Once considered purely thermal sources, these young systems are now emerging as sites of energetic non-thermal activity. While
radio synchrotron jets hinted at the presence of relativistic electrons, direct confirmation of
proton acceleration remained elusive. Here we report a statistically significant detection of gamma rays from a population of young
stellar objects, revealing a
Galactic class of Gamma-Loud Protostars. Observations point towards particle acceleration within protostellar jets, where gamma-ray emission arises from
protons interacting with surrounding molecular clouds via pion decay. We find a correlation between
cosmic-ray output and bolometric luminosity, suggesting that particle acceleration scales with the system's mechanical power. These findings open a new observational window into the role of non-thermal processes in protostellar
evolution and suggest that gamma-ray studies of protostars can provide critical insights into
accretion, ejection, and feedback in
star formation. This previously overlooked emission traces the energetic feedback that young
stars inject into their surroundings, shaping the conditions for subsequent
star and
planet formation.
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All authors Javier Méndez-Gallego, Rubén López-Coto, Emma de Oña Wilhelmi, Stefano Menchiari, Iván Agudo, Rubén Fedriani
Cosmology and Nongalactic Astrophysics
The impact of evolving cosmic filaments on mass and spin evolution of dark matter halos
Hannah Jhee, Hyunmi Song, Clotilde Laigle et al. (+3 more)
The
evolution of
galaxies is closely tied to that of their host dark matter
halos, which is in turn strongly modulated by the surrounding large-scale environment.
Cosmic filaments are expected to influence the peculiar motions, mass assembly and angular momentum of nearby
halos through highly anisotropic matter flows. In order to fully capture the dynamic interplay between the filaments and
halos, we develop an
algorithm to trace the progenitors of individual filaments identified at z=0 with DisPerSE in a cosmological N-body simulation, by quantifying the spatial similarity between a descendant filament and progenitor candidates. This enables us to reconstruct filament-by-filament evolutionary histories, including their bulk drift and the
evolution of density profiles, from which splashback radii and core overdensities are derived. Using these time-dependent properties, we re-examine
halo phase-space trajectories in a filament-centric frame that evolves with time. This eliminates biases inherent to static models by separating
halo motions from the motion of the filaments, allowing trajectories to be identified more reliably. We find that as
halos approach high-density filaments, their mass
accretion rates are systematically suppressed beginning at the filament outskirts, suggestive of
tidal stripping or suppressed net
accretion. Furthermore, the
evolution of
halo spin alignments exhibits a clear departure from
stochastic random-walk expectations. This suggests that distinct mass flow regimes in and around filaments exert different torques on infalling
halos, thereby changing their angular momentum. Our findings, derived from a sample screened for major mergers, highlight the pure dynamical impact of the filamentary environment. Ultimately, we demonstrate that tracking the simultaneous co-
evolution of filaments and
halos is essential for accurately characterizing environmental effects.
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All authors Hannah Jhee, Hyunmi Song, Clotilde Laigle, Christophe Pichon, Corentin Cadiou, Ena Choi
Astrophysics of Galaxies
Eppur non si trovano Vol. 3: Phoebe – a Mirage of a Primordial Black Hole
Andrzej Udalski and Przemek Mróz
Recent preprints by Key et al. reported the discovery of a short-lived brightening of a
star (nicknamed "Phoebe") located in the Large Magellanic Cloud that was interpreted as a short-timescale gravitational microlensing event produced by a lunar-mass
primordial black hole (PBH) in the Milky Way dark matter
halo. Here, we present an independent re-analysis of the publicly available DECam observations of this object, incorporating additional data from 2020 and 2021. The object underwent at least three distinct, low-amplitude brightenings (one of which was misinterpreted as a short-timescale microlensing event) in addition to long-term variations of its mean magnitude. These characteristics indicate that Phoebe is an ordinary variable
star rather than a microlensing event. This finding resolves the apparent tension with the results from earlier microlensing experiments that rule out the hypothesis that a substantial fraction of dark matter is composed of lunar- and planetary-mass PBHs.
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Solar and Stellar Astrophysics
An Ultramassive White Dwarf with a Likely Oxygen-Neon Core
Stefan M. Arseneau, J.J. Hermes, Vedant Chandra et al. (+4 more)
The core composition of ultramassive white
dwarfs remains an open question in
stellar evolution. The carbon content of white
dwarf cores is critical to their role as progenitors of Type Ia
supernovae. However, because the
stellar photosphere only extends to the outermost layer of the
star, observational probes of core compositions are limited. Here we present gravitational
redshift measurements of an ultramassive white
dwarf, SDSS J060851.44-005950.3, which indicate the likely presence of an oxygen-neon core. We measure the mass ($1.226_{-0.025}^{+0.024} M_\odot$) and radius ($0.491_{-0.009}^{+0.009}~R_\oplus$) of the white
dwarf using gravitational
redshifts from high-resolution UVES and MagE spectra paired with independent constraints from photometry. By comparing to state-of-the-art mass-radius relations for ultramassive white
dwarfs, we find preference for a oxygen-neon core over a carbon-oxygen core, with a Bayes factor of $2.7$. This is a white
dwarf which is likely structurally incapable of producing a Type Ia
supernova, according to current understanding of
supernova physics. This object provides evidence that white
dwarfs which pass through the Q-branch without experiencing a delay in cooling compared to the normal white
dwarf cooling sequence likely have oxygen-neon cores.
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All authors Stefan M. Arseneau, J.J. Hermes, Vedant Chandra, Roberto Raddi, Maria E. Camisassa, Alberto Rebassa-Mansergas, Santiago Torres
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Moduli Stabilisation for ADD and the Dark Dimension Scenario
Andreas P. Braun, Michele Cicoli, Riccardo Milioli et al. (+1 more)
We provide a
moduli stabilisation mechanism for realising anisotropic string compactifications with one or two large extra dimensions, corresponding to the ADD and Dark Dimension scenarios. This is achieved within the type IIB Large Volume Scenario, where an exponentially large Calabi-Yau volume in string units can naturally generate a parametrically low Kaluza-Klein scale. Anisotropy is realised by considering a Calabi-Yau threefold which is a K3 fibration over a $\mathbb{P}^1$ base. The volume of the 4D K3 fibre is stabilised at relatively small values by perturbative corrections to the effective action, in particular string loops and higher-derivative effects, leaving an exponentially large volume of the 2D $\mathbb{P}^1$ base. We argue that complex structure
moduli stabilisation can dynamically deform the $\mathbb{P}^1$ base, corresponding to a Tyurin degeneration limit where the internal geometry effectively develops a single large 1D cycle. Within a unified description, the ADD case is instead recovered as a symmetric alternative limit. The potential can feature either a dS
vacuum or a quintessence runaway, although in both cases some degree of tuning is required to match the observed cosmological constant scale. We also present an explicit Calabi-Yau orientifold example with consistent brane setup, tadpole cancellation and
moduli stabilisation. We analyse the resulting
moduli spectrum and associated phenomenological constraints, including supersymmetry breaking, cosmological
moduli overproduction and fifth force bounds.
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All authors Andreas P. Braun, Michele Cicoli, Riccardo Milioli, Roberto Valandro
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
From Rags to Jeans: Axion Miniclusters from Early matter domination
Ariel Angulo, Paola Arias, Nicolás Bernal et al. (+1 more)
In an early matter-dominated era, density and temperature inhomogeneities of the radiation bath grow more efficiently than in the standard radiation-dominated history. If the
axion mass depends on temperature, these inhomogeneities induce spatial fluctuations of the
axion mass, providing a new source term for
axion density perturbations. We show that this mechanism is most efficient when the reheating temperature lies just below the mass-saturation scale $T_\Lambda$, and can drive
axion overdensities to order unity by matter–radiation equality. For the QCD
axion saturating the observed dark matter abundance, the nonlinear spectrum at equality exhibits two characteristic regions: one associated with the gravitational enhancement already present in
moduli-driven cosmologies, and another produced by the temperature dependence of the
axion mass. We estimate the resulting minicluster masses and discuss the possible formation of
axion miniclusters and
axion-
star substructure.
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All authors Ariel Angulo, Paola Arias, Nicolás Bernal, Javier Redondo
Cosmology and Nongalactic Astrophysics
Testing X-ray selection effects with four rich, yet X–ray–faint, galaxy clusters
S. Andreon and A. Moretti
A robust understanding of selection effects in
galaxy cluster studies is crucial for both astrophysical and cosmological applications. Examining clusters identified through different observational strategies, even in small numbers, helps to illuminate potential biases inherent to each method. We selected four rich
galaxy clusters in the Northern Hemisphere whose early Swift X-ray
Telescope (XRT) observations indicated unusually low central X-ray emission, making them unlikely to be detected in X-ray surveys. Spectroscopic follow-up confirms that all four systems are genuine
galaxy clusters, rather than projections of multiple clusters or groups along the line of sight. Their optical richness, estimated using one of the baseline Euclid cluster richness
estimators, implies masses of $\log M_{200}/M_\odot \sim 14.6$ and independently confirms the absence of additional massive structures along the line of sight. Deep XRT follow-up reveals highly disturbed X-ray morphologies: three clusters exhibit at least two distinct X-ray peaks, while the remaining cluster has an axis ratio exceeding 1.5. Spectroscopy shows that
galaxies associated with different parts share the same
redshift, demonstrating that these substructures are physically connected rather than chance projections. These clusters display low central X-ray surface brightness and total X-ray luminosities suppressed by roughly one dex for their richness, making them undetectable in X-ray surveys as eROSITA. We estimate $\sim$20% as a lower limit for the poorly sampled population, albeit based on a small sample. Our results demonstrate that even rich clusters in the northern $z<0.3$ Universe can be missed by X-ray selection and that the X-ray variety captured by X-ray surveys underestimates the true cluster diversity.
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Cosmology and Nongalactic Astrophysics
BayeSN $\times$ Dovekie: Joint Photometric Cross-calibration and SED Modelling of Type Ia Supernovae
M. Grayling, B. Popovic, M. Ginolin et al. (+2 more)
We present a new framework for BayeSN, the hierarchical
Bayesian SED model for type Ia
supernovae (SNe Ia), incorporating cross-calibration of samples observed across heterogeneous
telescopes. This framework is the first to parametrise the filter wavelength and zero-point offsets commonly used in SN~Ia cosmology within SN SED model training, enabling additional constraint on cross-calibration from SNe beyond the standard
stellar-based cross-calibration pipeline. We apply this framework to train a new G26 BayeSN model on the same SED model training sample used in recent cosmological analyses, an order-of-magnitude increase over previous BayeSN training samples, and include a novel training methodology to leverage high-
redshift SNe Ia in BayeSN training. We present the G26 model and apply it to the DES-SN5YR sample to assess performance, finding a 12 per cent reduction in $\sigma_{\rm NMAD}$ scatter when compared with SALT3$.$Dovekie; 0.164 mag compared with 0.185 mag for a sample of likely SNe Ia at $z < 0.7$, without bias corrections. We additionally present constraints on cross-calibration wavelength and zero-point shifts from our framework when using the latest `Dovekie' calibration constraints as a prior. This work is a key step towards a full end-to-end cosmological analysis with BayeSN; the new G26 model is incorporated within the public BayeSN code.
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All authors M. Grayling, B. Popovic, M. Ginolin, A. Do, K. S. Mandel
Cosmology and Nongalactic Astrophysics
Cooling, conduction, compact objects: Gravothermal evolution of dissipative self-interacting dark matter halos
Ludwig D. Schmidt, Moritz S. Fischer and Mathias Garny
Many proposed self-interacting dark matter (SIDM) models give rise to radiative processes that can dissipate energy. Understanding their impact on astrophysical objects through simulations and comparing the results with observations may thus constrain SIDM models. In this work, we systematically investigate how dissipation alters the gravothermal
evolution of isolated SIDM
halos by independently varying dissipation and heat conduction and identify potential observational signatures. To this end, we present the first extension of the $N$-body formalism for frequent small-angle self-interactions (fSIDM) to include effective dissipation. We compare all results for isolated
halos with a dissipative gravothermal fluid model to assess its validity and limitations. We find that dissipation qualitatively changes the gravothermal
evolution of SIDM
halos beyond simply accelerating collapse. Sufficiently strong central cooling can invert the usual role of heat conduction: the formation of an isothermal core is suppressed such that conduction remains directed inward throughout the
evolution. Outer
halo regions beyond the scale radius can cool efficiently rather than being heated by conduction, resulting in a larger region of mass infall and a less pronounced indentation between the core and the outer
halo in the final density profile. These effects depend strongly on the cooling rate but are comparatively insensitive to the angular dependence of the self-interaction cross section. We further show that weakly dissipative self-interactions can explain the properties of the recently observed strong lens perturber in JVAS~B1938+666 with significantly shorter
evolution times or, equivalently, smaller cross sections compared to the elastic case. Our results open a new route to connecting
halo structure and recently reported compact objects to dark-sector microphysics.
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Cosmology and Nongalactic Astrophysics
Physics-guided discovery of dynamical dark-energy equations of state through iterative AI reasoning
Clecio R. Bom, Bernardo M. Fraga, Miguel A. Sabogal et al. (+3 more)
Phenomenological model building has traditionally relied on human
reasoning: equations are proposed from theoretical intuition, analogy, or empirical convenience, and only then tested against data. Here we show that this cycle can be recast as an iterative AI
reasoning process for dynamical dark energy. Our framework uses a large
language model to propose equations of state together with cosmological rationales, grounded by
retrieval from the dark-energy literature and refined through autonomous evaluation. Each candidate is embedded in a cosmological model, optimized against observations, and assessed using likelihood performance and theoretical consistency. An independent
language-model critic scores the physical motivation, novelty, clarity, stability and implementation validity of both the equation and its rationale, allowing subsequent proposals to evolve jointly in mathematical structure and physical
reasoning. Applied to cosmological data combinations including
supernovae,
baryon acoustic oscillations and Planck likelihoods, the framework identifies two parameterizations that, to the best of our knowledge, have not previously been explored and that are competitive with established forms. For Pantheon+
supernovae, DESI DR2
baryon acoustic oscillations and the full Planck 2018 temperature, polarization, and
lensing likelihoods, the best AI-selected model attains larger
Bayesian evidence than the traditional parameterizations considered here by more than one unit. These results show that AI-guided
reasoning can complement physical model building by proposing and evaluating interpretable phenomenological parameterizations for dynamical dark energy.
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All authors Clecio R. Bom, Bernardo M. Fraga, Miguel A. Sabogal, Armando Bernui, Phelipe Darc, Gustavo Schwarz
Instrumentation and Methods for Astrophysics
Characterization of a symmetric-facet dual-ruled grating for spatial heterodyne spectroscopy
Cole Meyer, Joanne Flores, Jason Corliss et al. (+1 more)
Dual-bandpass spatial heterodyne spectrometers (DB-SHS) enable simultaneous high-resolution measurements of widely separated passbands, providing powerful diagnostics of astrophysical and planetary environments. However, DB-SHS instruments require a single incident beam to span two adjacent diffraction gratings with distinct ruling densities and blaze angles, resulting in a large gap between ruled sections that reduces throughput. Dual-ruled gratings solve this problem by integrating multiple ruled panels onto a single substrate, minimizing the dead space between ruled sections. We present experimental validation of a first-generation symmetric-facet dual-ruled grating manufactured by Bach Research, mechanically ruled at $800$ and $\mathrm{2000\;gr\;mm^{-1}}$ with a $13.8^\circ$ blaze angle. Using a stabilized deuterium source alongside a Czerny-Turner monochromator, we measured diffraction efficiencies into the $m = 0, \pm1, \pm2$ orders from $200$ to $\mathrm{700\;nm}$. We compare these results with theoretical predictions from rigorous coupled-wave analysis (RCWA), inferring a facet asymmetry of $\lesssim1^\circ$ and $\sim70\%$ facet duty cycle indicative of minor manufacturing defects. This work demonstrates the viability of mechanically ruled, symmetric-facet, dual-ruled gratings and lays the foundation for laboratory validation of the first DB-SHS, ultimately enabling high-resolution spectroscopy of distinct spectral regions relevant to astrophysical and planetary remote sensing.
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All authors Cole Meyer, Joanne Flores, Jason Corliss, Walter Harris
Solar and Stellar Astrophysics
Steady-state Stellar Winds Driven by Recombination
Eritas Yang and Eliot Quataert
Hydrogen and helium recombination energy has been proposed as a potential driver of mass ejection in common-envelope
evolution and other eruptive
stellar phenomena. We investigate whether recombination can by itself launch a steady, transonic wind from near a
stellar surface. Using a tabulated equation of state, we explore steady-state, adiabatic wind solutions over a broad range of
stellar mass, density, and temperature. We classify a wind as recombination-driven only if the gas is gravitationally bound prior to recombination and if the released energy remains trapped until the flow becomes unbound. Only a small fraction of the solutions satisfy both conditions. In most cases, the gas is either already unbound without recombination or loses the released energy through radiative
diffusion while still bound. The subset of valid solutions require
outflow velocities $\gtrsim 10\,{\rm km\,s^{-1}}$ at $10\,R_\odot$, inconsistent with a wind launched from a hydrostatic
star. We conclude that recombination energy alone is unlikely to produce steady
stellar winds. It can, however, accelerate and unbind a pre-existing
outflow generated by processes such as binary orbital decay, producing mass-loss rates of $\sim \rm M_\odot\,yr^{-1}$.
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High Energy Astrophysical Phenomena
Scintillation of the first-known pulsar planetary system
J. M. Yao, L. Zhang, A. Wolszczan et al. (+8 more)
We present a scintillation study of the first-known
pulsar planetary system, PSR~B1257+12, using the Five-hundred-meter Aperture Spherical
radio Telescope (FAST). A total of 31 observations with durations greater than or equal to 30 minutes were analyzed. For 14 longer observations (greater than or equal to 120 minutes), one-dimensional autocorrelation function analyses yielded the scintillation timescale, scintillation bandwidth, and frequency-drift rate for 12 epochs. Two observations show strong periodic modulation in the frequency-domain auto-correlation function, likely caused by astronomical-unit-scale structures along the propagation path, preventing reliable measurements of the scintillation timescale and bandwidth. In three observations, secondary spectra reveal simultaneous detections of inner, middle, and outer arcs. Analysis of the annual modulation of the inner-arc
curvature indicates isotropic scattering, with a screen distance of $233\pm28$~pc and transverse velocity $V_{\rm scr,\alpha}=-7.16\pm2.16$ km~s$^{-1}$, $V_{\rm scr,\delta}=-41.07\pm5.69$ km~s$^{-1}$. Delay-profile analysis for both the inner and outer arcs suggest spectral exponents consistent with, or smaller than, the Kolmogorov value. Under isotropic scattering, the screen–
pulsar distances are $354\pm22$~pc and $166\pm12$~pc for the middle and outer arcs. Combining the results from long-term timing analyses with our scintillation measurements, we find that the dispersion measure (DM) variations are primarily dominated by
plasma located further away from the
pulsar. The low DM-change rate of the outer arc and the absence of nearby scattering screens suggest that the immediate environment of the
pulsar may be relatively clean. Alternatively, scattering screens closer to the
pulsar may exist but remain undetected, requiring higher-sensitivity or longer-duration observations.
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All authors J. M. Yao, L. Zhang, A. Wolszczan, William A. Coles, D. Li, Richard N. Manchester, N. Wang, C. H. Niu, P. Wang, F. F. Kou, J. P. Yuan
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Emergent Gauge Symmetries in Particle Physics and Cosmology
Steven D. Bass
Where do gauge
symmetries come from? These lectures develop the idea that the Standard Model might be emergent, with its gauge
symmetries dissolving in some phase transition deep in the ultraviolet. The (meta-)stability of the
Higgs vacuum may be pointing to some new critical phenomena at very high energy scales, with the
Higgs connecting physics at LHC laboratory energies to that in the deep ultraviolet. In the emergence scenario, the dark energy scale comes out similar to the size of light Majorana
neutrino masses. These two quantities appear at the same order in a low energy expansion in inverse powers of the scale of emergence, about $10^{16}$ GeV. Dark matter candidates include
axions and
phonon like excitations of degrees of freedom above the scale of emergence. Possible tests of these ideas involve
neutrinos as well as gravitational-waves-related signals from the early Universe, which are sensitive to physics at very high energy scales.
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Cosmology and Nongalactic Astrophysics
Constraints on Cosmic Strings from the Curl-Mode CMB Lensing Power Spectrum measured by ACT DR6
A. I. Lonappan, K. Ramesh, T. Namikawa et al. (+2 more)
A network of
cosmic strings is one of the few well-motivated cosmological sources of vector and tensor metric perturbations on the largest observable scales. Such perturbations imprint a characteristic curl component in the deflection angle of
cosmic microwave background (CMB)
photons that, unlike the scalar
lensing potential, vanishes for adiabatic density fluctuations at linear order. We exploit the curl-mode
lensing reconstruction released as part of the Atacama Cosmology
Telescope (ACT) Data Release~6 (DR6), based on five seasons of temperature and polarization data covering $9400~\mathrm{deg}^2$ of sky, to set new constraints on the dimensionless string tension $G\mu$ and the inter-commutation (reconnection) probability $P$. Modelling the string-induced curl power spectrum within the velocity-dependent one-scale framework, we obtain a $2\sigma$ upper bound on the combination $G\mu P^{-1}\le 3.5\times 10^{-5}$ in the small-$P$ regime, and $G\mu \le 5.0\times 10^{-5}$ at $2\sigma$ assuming the canonical Nambu-Goto value $P=1$. Combining the ACT DR6 curl bandpowers with the Planck 2013 curl-mode reconstruction, which extends down to $L_{\rm min}=2$, tightens these bounds to $G\mu P^{-1}\le 3.2\times 10^{-5}$ and $G\mu\le 4.3\times 10^{-5}$ ($2\sigma$). These represent the tightest constraints on
cosmic strings derived from the curl-mode CMB
lensing power spectrum to date. Using the ACT data alone, compared to the ACT 2008-season analysis, the ACT DR6 constraint on $G\mu P^{-1}$ is nearly an order of magnitude tighter.
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All authors A. I. Lonappan, K. Ramesh, T. Namikawa, F. J. Qu, B. Keating
Solar and Stellar Astrophysics
Fine-scale downflows above flare ribbons captured by Solar Orbiter/EUI
Zheng Sun, Alexander G.M. Pietrow, Malcolm K. Druett et al. (+8 more)
In
solar flares,
flare ribbons map chromospheric footpoints where
flare energy deposition occurs. These locations are associated with field aligned energy transport from the corona that results from energy liberated during
magnetic reconnection. Recent chromospheric observations in the H$\alpha$ and H$\beta$ bands have revealed fine-scale downflow structures above
flare ribbons, referred to as riblets. In this study, we identify similar downflow structures in the extreme-ultraviolet (EUV) wavelength using high-resolution observations from
Solar Orbiter/EUI. These fine-scale downflows appear as downward-propagating, bright, and thread-like structures. They exhibit typical velocities of $\sim100~\mathrm{km\ s^{-1}}$, lifetimes of $\sim15$~s, and lengths of $\sim1.6$~Mm. Based on their morphological and dynamical properties, we interpret these observed downflows as the EUV counterparts of the riblets that have previously been reported from chromospheric observations. This study presents EUV imaging of $\sim 10^6$~K downflows above
flare ribbons. We interpret these downflows as a result of (1) the energisation and subsequent compression of pre-existing chromospheric fibrils due to particle beams or (2) adiabatic or shock-driven compression induced by the downward-propagating
plasma from the corona. These fine-scale EUV riblets provide a new diagnostic tool for probing the dynamics of
magnetic reconnection as well as energy transport and deposition during
solar flares.
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All authors Zheng Sun, Alexander G.M. Pietrow, Malcolm K. Druett, Hui Tian, Julián D. Alvarado-Gómez, Song Tan, Alexander Warmuth, Jiasheng Wang, Yuhang Gao, Zhenyong Hou, Alexandros Stork