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Physics Astrophysics Cosmology and Nongalactic Astrophysics

astro-ph.CO Watch Cosmology and Nongalactic Astrophysics

Monday 28 September

Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

KiDS-DR5: Exploring dust transport in dark matter halos of galaxies

Eray Genc, Angus H. Wright, Hendrik Hildebrandt et al. (+12 more)

We analyse a well-defined sample of galaxies from the final data release of the Kilo-Degree Survey (KiDS-DR5), selected using magnitude, photometric redshift, and stellar mass cuts, to measure their mean halo mass and circumgalactic dust content as a function of stellar mass. Our goal is to provide empirical constraints on dust transport mechanisms, such as stellar- and AGN-driven outflows, operating in galaxy halos. We develop and validate a new measurement and modelling framework using the MICE2 simulation, incorporating a realistic circumgalactic dust extinction scenario. Using this framework, we jointly model multiband ($ugriZYJHK_{\rm s}$) magnitude shifts and galaxy–galaxy lensing signals to infer the mean halo mass and dust mass of lens galaxies at $z_{\rm B} < 0.4$, analysed in five stellar-mass bins in KiDS-DR5. The modelling jointly describes the halo mass distribution and dust extinction, including dust associated with neighbouring halos. We demonstrate that the inclusion of a satellite fraction and dust extinction from neighbouring halos is required by the data. We find a linear relation between stellar mass and dust mass, consistent with previous observational studies, but flatter than predictions from the semi-analytic model Dusty-SAGE. This difference may indicate that current implementations of dust-related feedback in galaxy formation models require further refinement.
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All authors Eray Genc, Angus H. Wright, Hendrik Hildebrandt, Dian P. Triani, Dominik J. Bomans, Benjamin Stölzner, Marika Asgari, Henk Hoekstra, Benjamin Joachimi, Shahab Joudaki, Konrad Kuijken, Lauro Moscardini, Mario Radovich, Robert Reischke, Ziang Yan

Cosmology and Nongalactic Astrophysics

Field-level inference of growth rate from DESI BGS galaxy and ZTF supernova simulations

Corentin Ravoux, Bastien Carreres, Julian Bautista et al. (+60 more)

Galaxy peculiar velocities are a powerful probe of the growth rate of structure $f$ at low redshifts ($z < 0.2$), measured through the combination $f\sigma_8$. These constraints are improved by combining peculiar velocities with redshift space distortion measurements from the galaxy density field. We create a dedicated simulation to test growth rate measurement from the combination of Type Ia supernova peculiar velocities from the Zwicky Transient Facility (ZTF) with the Bright Galaxy Survey (BGS) of the Dark Energy Spectroscopic Instrument (DESI), using projections for 6 years of ZTF data and the Data Release 3 (DR3) of DESI. We apply a wide-angle likelihood-based field-level inference to combine ZTF velocity and DESI BGS density fields simultaneously. This procedure is performed while varying the different density and velocity field configurations. Adding DESI galaxy density information to the ZTF supernovae improves the constraint on nuisance parameters and yields up to a 50 % reduction in the growth-rate uncertainty without introducing bias. If we consider the conservatively best DESI density configuration, the mean error bar achievable by a DESI ZTF measurement is $\sigma_{f\sigma_8} = {}^{+0.047}_{-0.048}$ corresponding to a 10 % error. These measurements will play a critical role for testing modified gravity theories.
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All authors Corentin Ravoux, Bastien Carreres, Julian Bautista, Damiano Rosselli, Jessica Aguilar, Steven Ahlen, Melissa Amenouche, Uendert Andrade, Eric Armengaud, Alejandro Aviles, Florian Beutler, Davide Bianchi, David Brooks, Umut Burgaz, Aurelio Carnero Rosell, Edmond Chaussidon, Todd Claybaugh, Andrei Cuceu, Axel de la Macorra, Georgios Dimitriadis, Andreu Font-Ribera, Daniel Felipe Forero Sánchez, Jaime E. Forero-Romero, Enrique Gaztañaga, Satya Gontcho A Gontcho, Ariel Goobar, Gaston Gutierrez, Hiram K. Herrera-Alcantar, Cullan Howlett, Mustapha Ishak, Joel Johansson, Stephanie Juneau, Ofer Lahav, Martin Landriau, Laurent Le Guillou, Alexie Leauthaud, Marc Manera, Ramon Miquel, Seshadri Nadathur, Jakob Nordin, Hernan Enrique Noriega, Enrique Paillas, Nathalie Palanque-Delabrouille, Will Percival, Francisco Prada, Ignasi Pérez-Ràfols, Mickael Rigault, Antoine Rocher, Philippe Rosnet, Graziano Rossi, Rossana Ruggeri, Lado Samushia, Eusebio Sanchez, Christoph Saulder, David Schlegel, Michael Schubnell, Hee-Jong Seo, Joseph Silber, Małgorzata Siudek, Mathew Smith, Gregory Tarlé, Benjamin A. Weaver, Pauline Zarrouk

Cosmology and Nongalactic Astrophysics

Reconstructing the evolution of deceleration parameter with the Lagrange interpolation method

Kaituo Zhang, Bing Xu, Hongwei Yu et al. (+1 more)

In this paper, we reconstruct the evolution of the deceleration parameter using cubic and quartic Lagrange interpolation methods, based on the latest observational data. This data includes baryon acoustic oscillation (BAO) measurements from DESI, cosmic microwave background (CMB) distance priors from Planck 2018, and three datasets of type Ia supernovae (SNe Ia): DES-Dovekie, Pantheon+, and Union3. To mitigate the impact of the nonuniform distribution of data in redshift, we carry out the reconstruction not only in the standard redshift $z$ but also in the $y$-redshift $y\equiv z/(1+z)$ and the log-redshift $\zeta\equiv\ln(1+z)$. The cubic and quartic reconstructions of $q(z)$ from the DESI BAO+CMB+SNe Ia datasets indicate a clear deviation from the $\Lambda$CDM model at low redshift ($z<0.3$), supporting a weaker present-day cosmic acceleration than the predictions of the $\Lambda$CDM model. The reconstructed $q(z)$ exhibits an overall oscillatory pattern around the $\Lambda$CDM model throughout its evolution. Only the cubic-$y$ and cubic-$\zeta$ reconstructions with the DESI BAO+CMB+Union3 data provide evidence that the cosmic acceleration appears to have already reached its maximum value and is beginning to slow down. However, when incorporating the measurement of the Hubble constant $H_0$ from the Supernovae and $H_0$ for the Equation of State (SH0ES) Collaboration, the evolution of $q(z)$ from cubic reconstructions shifts toward the $\Lambda$CDM prediction. Regardless of the presence or absence of the $H_0$ prior, all reconstructions imply that the deceleration-acceleration transition occurred earlier than predicted by the $\Lambda$CDM model. Nevertheless, the Bayesian evidence still favors $\Lambda$CDM, while the frequentist analysis indicates a $>2\sigma$ preference for the Lagrange-interpolation reconstructions, hinting at the existence of dynamical dark energy.
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All authors Kaituo Zhang, Bing Xu, Hongwei Yu, Puxun Wu

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

Freeze-in of anapole and charge-radius inelastic dark matter: X-ray probes of a decoupled vector portal

Krzysztof Jodłowski and Chih-Ting Lu

We study freeze-in production and experimental probes of inelastic dark matter (iDM) coupled to the Standard Model through dimension-6 transition anapole and charge-radius operators. These interactions arise upon integrating out the heavy dark photon of a broken $U(1)_D$ vector portal. We focus on mass splittings below the dielectron threshold, where the excited-state decay is cosmologically long-lived and decays predominantly through $\chi_1\to\chi_0+3\gamma$, producing a distinctive keV–MeV photon spectrum. We calculate the decay rate and photon spectrum analytically in the Euler–Heisenberg limit and evaluate finite-electron-mass corrections using the full one-loop amplitude. We then combine X-ray limits with freeze-in relic density targets and complementary direct detection (DD) and accelerator constraints. The surviving $\chi_1$ population also leads to exothermic downscattering signatures at DD experiments, including the possibility of explaining the LZ signal, while the three-photon decay is constrained by X-ray data. At $\Delta=900\,\mathrm{keV}$, INTEGRAL/SPI probes the Boltzmann-suppressed high-mass branches of the freeze-in targets, whereas the NuSTAR limits at $\Delta=100\,\mathrm{keV}$ are substantially weaker because of the steep splitting dependence of the decay width. Our results demonstrate the potential of X-ray observations as a probe of freeze-in through a decoupled vector portal and of the reheating temperature governing the iDM production.
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Sunday 27 September

Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.IM

Lidar-monitoring of atmospheric fluctuations for millimeter-wave astronomical observations

Jacques Delabrouille, Patrick Chazette, Étienne Burtin et al. (+15 more)

Ground-based millimeter-wave astronomical observations suffer from strong contamination by the emission of inhomogeneous water vapor in the Earth's atmosphere. This emission reduces the observing efficiency and data quality even from a high-altitude, dry location such as the Atacama plateau in Chile. We propose to continuously monitor atmospheric water vapor with a co-pointing dedicated Raman lidar system. We show, with numerical simulations and proof-of-concept observations, how a synergistic use of atmospheric lidar data has the potential to substantially improve the quality of astronomical data sets.
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All authors Jacques Delabrouille, Patrick Chazette, Étienne Burtin, Christophe Chailan, Josquin Errard, Shamik Ghosh, Manuel Gonzalez, John Groh, Reijo Keskitalo, Valérian Le Lorec, Sotiris Loucatos, Christophe Magneville, Jean-Baptiste Melin, Michel Piat, Damien Prêle, Julien Tang, Timothée Tollet, Julien Totems

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

Heavy Higgsino Dark Matter With Low Reheating in View of the LZ High-Recoil Event

C. Pallis

We show that a heavy higgsino $\tilde h$ with mass $m_{\tilde h}\sim0.1~{\rm PeV}$, which can be made consistent with the recent LUX-ZEPLIN event avoiding constraints from direct and indirect detection, can account for the present cold dark matter abundance of the universe, if the reheating temperature is bounded as $T_{\rm rh}\lesssim 595~{\rm GeV}$. These values can be achieved by a possible out-of-equilibrium decay of a modulus $\phi$ with mass $m_{\phi}\gg m_{\tilde h}$ and a non-vanishing branching ratio into $\tilde h$'s which plays a decisive role in reducing $T_{\rm rh}$ below its upper limit via the non-thermal $\tilde h$ production. The modulus $\phi$ can be identified with the scalar component of the goldstino superfield which is involved in the generation of the $\mu$ parameter of MSSM (with $\mu\simeq m_{\tilde h}$) via the Giudice-Masiero mechanism.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

Constraining the galaxy-halo connection at $z>10$ using the neighbors of UV-bright galaxies

Ivan Nikolić and Charlotte A. Mason

JWST has discovered an overabundance of UV-luminous galaxies compared to extrapolations from pre-JWST galaxy formation models. Distinguishing between proposed theoretical explanations requires constraining the halo masses of these systems, which can be probed through clustering. However, at $z>10$, low galaxy number densities render traditional clustering measurements challenging. We introduce a novel formalism that uses information about the local environments ($\lesssim$2 arcmin) of individual UV-bright galaxies at $z>10$ to test the galaxy-halo connection implied by theoretical models for the UVLF excess. We create mock JWST observations using (500 cMpc)$^3$ 21cmFAST simulations to forward-model the spatial distribution of fainter photometric candidates around UV-bright galaxies. We find that the distance to the nearest neighbor is sensitive to the stochasticity of the UV luminosity-halo mass relation, and can distinguish between models where UV luminosity is boosted uniformly in galaxies versus models with high stochasticity in UV luminosity at fixed halo mass. As a proof-of-concept, we apply our framework to observations around the two brightest confirmed galaxies at $z>10$, GN-z11 and JADES-GS-z14-0, and find that the lack of neighbors within $<0.5$ arcmin of these sources disfavors models where UV luminosity is boosted uniformly, suggesting that stochasticity is important for explaining their high UV luminosities. We forecast that distinguishing between these models at high significance requires deep imaging surveying $<1.1$ arcmin around $7$-$15$ bright galaxies ($M_{\rm UV}\lesssim-21$) at $z =10$-$12$, dropping to $\lesssim5$ at $z\sim14$, capable of detecting their neighbors down to $M_{\rm UV,lim}\approx-18$. These observations are within reach of JWST, Roman and Euclid surveys, providing a path to constraining the galaxy-halo connection at our redshift frontier.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.HE

Observations of Repeating Tidal Disruption Events

Iair Arcavi and Thomas Wevers

The disruption of stars by supermassive black holes (SMBHs) as tidal disruption events (TDEs) can produce transient flares across the electromagnetic spectrum. Such flares can be used to probe SMBH properties, accretion physics and stellar dynamics in galactic nuclei. However, it can be difficult to distinguish TDE flares and those arising from other accretion phenomena around SMBHs, such as active galactic nuclei disk instabilities. Repeated flares from the same location can be produced by either such instabilities or by repeated partial disruptions of the same star, with the former expected to be at random intervals and the latter roughly periodic. Repeating nuclear transients can thus be used to distinguish between full and partial TDEs, as well as between TDEs and other accretion phenomena. Here we review observations of such repeating nuclear flares at various wavelengths. As time domain surveys become wider, deeper and faster, and as they accumulate longer baselines of data, more repeating phenomena at various time scales are being revealed. While these events show the potential for constraining several open questions regarding SMBH accretion phenomena, the small number of cases so far, the limited observational coverage for many of them, and the overall diversity of emission and repetition properties observed make it difficult to robustly associate most cases with physical scenarios at this stage. However, in the near future, as more data accumulate, the nature of various classes of repeating nuclear transients should become more clear, and with it the nature of many of the one-time flares as well.
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Cosmology and Nongalactic Astrophysics

Dark energy and negative compressibility of the Universe: A study based on cosmic equations of state

Felipe A. Asenjo, Ósmar Rodríguez, Ariel Órdenes Morales et al. (+1 more)

All cosmological models are defined through energy and matter, which describe the evolution of the targeted Universe. Whether the content is simple or complex, it can be defined through an effective equation of state (EoS). We study different cosmological models by analyzing the properties of the complete EoS of their fluid contents. We obtained general expressions for the ratio between pressure $p$ and energy density $\rho$, and for their derivative $dp/d\rho$ in terms of deceleration and jerk parameters. We show that, in general, a cosmology whose energy density is constructed from multiple ideal gases cannot be described by the EoS of a single, ideal gas. This is directly related to a variation in the deceleration parameter during the evolution of the Universe. Furthermore, we studied the effective compressibility properties of the EoS, demonstrating that dark energy features of the fluid should be related to the negative compressibility of the contents. These features depend on the dynamics of the jerk parameter for each cosmological system, implying that the knowledge of dark energy evolution is encoded in the third-order derivatives of the scale factor. This approach to understanding the properties of cosmological models indicates that the accelerating evolution of some models, such as the lambda-cold dark matter model ($\Lambda$CDM) or the Chaplygin gas model, is due to the EoS of their nonideal content fluids rather than an associated anomalous (dark energy) nature. On the contrary, models such as $w$-cold dark matter ($w$CDM), $w_0$$w_a$-cold dark matter ($w_0$$w_a$CDM), or Dvali-Gabadadze-Porrati models, include by construction fluids with anomalous content, implying a negative compressibility and an effective dark energy behavior. Our work highlights the importance of treating all contents of the Universe as a nonideal fluid system, with a unique EoS.
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All authors Felipe A. Asenjo, Ósmar Rodríguez, Ariel Órdenes Morales, Alejandro Clocchiatti

Saturday 26 September

Cosmology and Nongalactic Astrophysics

Constant-Roll Inflation as a Competitive Alternative to Slow-Roll Inflation

Sandip Biswas, Rajib Saha and Kaushik Bhattacharya

Starting from the constant-roll condition, which involves the constant-roll parameter $\beta$, which is a fundamental constant in the constant-roll inflationary models, we derive the scalar power spectrum and obtain an analytic expression for the scalar spectral index $n_s$ in terms of $\beta$ and the number of remaining e-folds $\tilde N$. The resulting relation is non-monotonic in $\beta$, allowing two distinct constant-roll branches, one with $\beta<0$ and one with $\beta>0$, to reproduce nearly the same observed scalar tilt. We constrain $\beta$ using Planck 2018 CMB data, and further using the combined Planck 2018 + ACT DR6 data. For Planck 2018, the posterior distribution of $\beta$ exhibits a bimodal structure associated with the two analytical branches, while the combined Planck+ACT analysis tightens the allowed range of $\beta$ and shows continued consistency with the $\beta=0$ slow-roll-like spectral point. The data constrain $\beta$ to be small, but do not require it to vanish exactly. We also estimate the inflationary mass scale $M$ by using the observed scalar-amplitude normalization at the pivot scale. Both the negative and positive $\beta$ branches give a high-scale inflationary normalization of order $M\sim10^{-5}M_{\rm Pl}$. We show that the $\beta \to 0$ limit is only spectrally slow-roll like, but does not reproduce standard slow-roll dynamics. Our results show that constant-roll inflation is observationally competitive with the usual slow-roll inflationary paradigm. The constant roll inflation model is supported by the latest CMB observations equally well or marginally better when compared with the slow roll inflation model.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

Cool Embeddings: Predicting Galaxy Cluster Cooling Times in IllustrisTNG and TNG-Cluster with AstroCLIP

Rawan Karam, Carter Lee Rhea, Julie Hlavacek-Larrondo et al. (+4 more)

Foundation models trained on optical astronomical data have not previously been applied to X-ray cluster thermodynamics. We show that embeddings from AstroCLIP, a contrastive vision-language model trained on optical galaxy images and spectra, retain physically meaningful structure when applied to mock Chandra X-ray images of simulated galaxy clusters - a significant shift in observational modality and physical scale. We target the central cooling time ($t_{\mathrm{cool},0}$) of the intracluster medium, a key diagnostic of cluster thermodynamics traditionally requiring X-ray spectroscopy. We present a machine learning framework that predicts $t_{\mathrm{cool},0}$ directly from X-ray images, applied to 711 projections from TNG300 and 993 from TNG-Cluster from the IllustrisTNG simulations. AstroCLIP embeddings form a structured latent space in which clusters with similar thermodynamic properties are naturally grouped, with no equivalent separation by halo mass. Building on this, we introduce a dot-product $k$-nearest neighbour attention model that retrieves similar clusters from the training set and adaptively reweights their cooling times. This model achieves root-mean-square errors of 0.24 (TNG300) and 0.23 (TNG-Cluster) in $\log(t_{\mathrm{cool},0})$, and demonstrates strong out-of-distribution generalisation, outperforming a fine-tuned convolutional neural network trained on raw images (RMSE 0.50 versus 0.73). These results demonstrate that pretrained foundation model embeddings transfer across astrophysical domains and encode thermodynamic information sufficient for inference of cluster cooling properties - offering a scalable path toward cool-core characterisation in all-sky surveys such as eROSITA.
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All authors Rawan Karam, Carter Lee Rhea, Julie Hlavacek-Larrondo, Laurence Perreault-Levasseur, Marine Prunier, Adam Alexandre, Hyunseop Choi

Cosmology and Nongalactic Astrophysics

Bimodal mass primordial black holes in three-field inflation

M. M. Nasrolahzadeh and N. Khosravi

In this paper, we study the evolution of curvature and entropy perturbations in three-field inflation with non-canonical kinetic terms. Using the kinematic basis in field space, we characterize the background trajectory through its turning rate and non-planar torsion. We also emphasize the inherited structure of perturbations from the kinematic system, which detaches the distinct roles of turning rate and torsion in the interactions among perturbations. We present and study numerically a three-phase model with an intermediate decelerated expansion stage in which two separated transient epochs amplify two distinct families of modes, generating a double-peaked curvature power spectrum. This double-peaked power spectrum leads to the formation of primordial black holes with two characteristic masses, $M_1\sim2\times10^{-12}M_\odot$ and $M_2\sim52M_\odot$ explaining, simultaneously, both dark matter and the LIGO-Virgo-KAGRA binary black hole mass range.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Exact Solutions for Chiral Gravitational Waves from Spin-2 Mixing

Mohammad Ali Gorji and Yuhang Zhu

A spectator spin-2 field can mix linearly with the metric tensor perturbations. We study the coupled tensor system in an inflationary background, including a parity violating effect parametrised by $\theta$. Without expanding in the linear mixing between the two fields, we solve the system exactly for arbitrary mass while treating the mixing strength nonperturbatively. The mode functions of both helicities are constructed by acting with an operator-valued Gauss hypergeometric function ${}_2F_1$ on Whittaker modes, and the late-time power spectrum of each graviton helicity is expressed in closed form in terms of the generalised hypergeometric function ${}_3F_2$. We find that one helicity is exponentially enhanced, showing that strong mixing with a spectator spin-2 field can generate a large and highly chiral primordial gravitational wave spectrum. The degree of circular polarisation is bounded by $\tanh(\pi\theta)$, independently of the spin-2 mass and the mixing strength. The same solution also gives the late-time power spectrum of the spectator field and its cross spectrum with the graviton. In the weak mixing limit, our exact result reproduces the perturbative Schwinger-Keldysh result. These solutions provide a nonperturbative framework for studying primordial gravitational waves sourced by additional tensor modes.
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Cosmology and Nongalactic Astrophysics

AGN hosting jets. II: Deriving fundamental information from semi-analytical models and the LoTSS sample

Pau Beltrán-Palau, Manel Perucho, José-María Martí et al. (+1 more)

Galactic activity has been shown to play a fundamental role in galaxy and cluster evolution throughout the history of the Universe. In the last decades, a number of works have tackled the determination of radio luminosity functions and their evolution, with the aim to understand and quantify this role. In this work we propose a different approach, based on the application of a semi-analytical model to produce mock populations of radio loud active galaxies throughout several orders of magnitude in power, and the comparison with observational samples. The aim of this work is to test the ability of our semi-analytical model to reproduce luminosity and size distributions of large numbers of sources from the radio-loud active galactic nuclei sample from the LoTSS survey. We apply our semi-analytical model for the evolution of radio galaxies and generate hundreds of thousands of sources applying random selection of parameters within probability distributions for each of them. Our results show that the model is able to reproduce the main features of the observed sample, and identifies jet mass-load included in our model and activity periods as critical parameters that should be addressed in more detail in future work. These initial results allow us to establish a maximum activity period ranging from 10 to 200 Myr within an active time distribution probability p(t_max) \propto 1/t_{max}. We also reproduce the radio luminosity function for the z<0.6 population, and the jet power spectrum from 10^{34.5} W to 10^{38} W. Our results show that mass-load is a fundamental parameter in the determination of radio source luminosities with distance, mainly in the low-power regime. Our model predicts that at least 3-4 x 10^{5} radio galaxies must exist in the LoTSS field in order to obtain the 17045 observed ones. This population is vastly dominated by low power sources.
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All authors Pau Beltrán-Palau, Manel Perucho, José-María Martí, Xavier López-López

Cosmology and Nongalactic Astrophysics

Observing population III stars in the pristine region

Sung Kei Li, Jose M. Diego and Jose M. Palencia

The detection of the long-sought Population III (Pop III) stars is, perhaps, one of the most intriguing missing links in modern astronomy. Caustic crossing events (CCE) – extreme magnification at the critical curves of galaxy clusters of individual stars at cosmological distances – are postulated to allow for the direct detection of individual Pop III stars. However, in the usual CCE regime, the abundant existence of intracluster stars as microlenses limits the maximum magnification attainable, thus limiting the theoretical detection of luminous stars to relatively low redshifts, significantly smaller than the redshifts where Pop III stars are expected to exist. Here in this letter, we propose to observe Pop III stellar populations as CCEs in the pristine regions of merging clusters. Pristine regions are defined as areas in the lens where the intracluster light, and hence the corresponding stelalr microlenses, is exceptionally low. In thes regions, the low density of microlenses allows background stellar populations to achieve magnification closer to the theoretical limit (whitout microlenses). We show that the maximum magnification in the pristine region scales inversely with the surface mass density of stellar microlenses. Adopting Pop III isochrones, regular James-Webb $\sim29\,$mag observations are sufficient to detect individual Pop III stars in pristine regions, offering a unique observational strategy to detect Pop III stars with the incoming cluster observations. The intermediate regions between high-redshift merging clusters (such as El Gordo) are naturally devoid of microlenses and constitute exceptional targets for the search of Pop III stars.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

The Physical Origins of Scatter in the Dust Attenuation Scaling Relation of Star-Forming Galaxies: Star–Dust Geometry

Zongfei Lyu, Xian Zhong Zheng, Zhizheng Pan et al. (+11 more)

Characterising the physical drivers of dust attenuation in star-forming galaxies (SFGs) is essential for interpreting their spectral energy distributions and star formation histories. The infrared excess (IRX$\equiv$$L_{\rm IR}/L_{\rm UV}$) follows a universal scaling relation with metallicity, star formation rate, galaxy size, and inclination. However, the origin of the scatter around this relation remains poorly understood. We revisit this relation using $\sim$32,000 local SFGs from SDSS, GALEX, and WISE, and investigate why some galaxies deviate systematically from the best-fit relation. We find that the deviations are systematically linked to UV luminosity. UV-faint SFGs ($\log(L_{\rm UV}/{\rm L}_\odot)\le 9$) exhibit a median IRX excess of +0.23 dex, while UV-bright SFGs ($\log(L_{\rm UV}/{\rm L}_\odot)\ge 10$) show a median deficit of $-$0.20 dex relative to the relation defined by the dominant UV-intermediate population (86.38 percent of the sample). These offsets are not driven by metallicity, total infrared luminosity, or specific star formation rate. Instead, the deviations are closely linked to systematic differences in star–dust geometry. UV-faint SFGs are compact (median $R_{\rm e} = 2.90$ kpc) and preferentially viewed edge-on (median $b/a = 0.41$), leading to high effective dust column densities along the line of sight. UV-bright SFGs are extended (median $R_{\rm e} = 5.99$ kpc) and preferentially viewed face-on (median $b/a = 0.74$), allowing UV photons to escape efficiently. Galaxies with significant bulge components ($B/T > 0.4$) populate the envelope of the relation, exhibiting larger scatter. We conclude that the scatter in the IRX relation can be largely explained by variations in the three-dimensional star–dust geometry, with UV luminosity acting as an effective tracer of these geometric and physical differences.
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All authors Zongfei Lyu, Xian Zhong Zheng, Zhizheng Pan, Antonios Katsianis, Stijn Wuyts, Haiguang Xu, Pedro Cataldi, Wenhao Liu, Man Qiao, Dong Dong Shi, Yuheng Zhang, Shuang Liu, Run Wen, Chao Yang

Cosmology and Nongalactic Astrophysics

Universality classes of sharp gravitational production of light particles

Kanta Ito, Yusuke Mikura and Shuichiro Yokoyama

We establish a classification of the gravitational production of light particles across sharp transitions connecting different asymptotic forms of the scale factor. A family of smooth scale factors with a transition duration $\Delta\eta$ is characterized by its regularity in the sharp-transition limit $\Delta\eta\to 0$, leading to three qualitatively different universality classes: $C^0$, $C^1$, and $C^2$-or-smoother. We find that the $C^0$ class exhibits a quadratic enhancement in the energy density of produced particles, $\rho\propto\Delta\eta^{-2}$, while the $C^1$ class shows a logarithmic enhancement, $\rho\propto\ln(1/\Delta\eta)$. No sharp-transition enhancement occurs for the $C^2$-or-smoother class. Using a specific $C^\infty$ model of the scale factor, we derive the energy density analytically and confirm both the predicted quadratic scaling and its coefficient by numerically solving the mode equation. These results identify the regularity of the scale factor in the sharp limit as the key property controlling the sharp-transition enhancement.
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Cosmology and Nongalactic Astrophysics

Cross-correlation between CMB B-modes and Faraday Rotation as a Novel Probe of Primordial Magnetic Fields

Toshiya Namikawa and Guanming Liang

We investigate the cross-bispectrum between the cosmic microwave background (CMB) $B$-mode polarization and two Faraday rotation (FR) angles as a new probe of primordial magnetic fields (PMFs). Assuming Gaussian PMFs with both non-helical and helical components, we derive the $B\alpha\alpha$ bispectrum and decompose it into parity-even and parity-odd contributions. The mixed non-helical–helical contribution appears in the parity-even sector, whereas the purely non-helical and purely helical contributions contribute to the parity-odd sector. This parity dependence provides sensitivity to PMF helicity that is absent in the FR power spectrum alone. We then forecast the detectability of the cross-bispectrum for SO-like and LiteBIRD-like CMB experiments, and find that future observations can probe PMFs with amplitudes at the sub-nG level. The $B\alpha\alpha$ bispectrum is dominated by the helicity-sensitive parity-even sector and provides a promising avenue for constraining both the amplitude and helicity of PMFs.
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Friday 25 September

Cosmology and Nongalactic Astrophysics

Galaxy and Halo Assembly Bias in Alternative Dark Matter Models

Yikun Wang, Idit Zehavi, Sergio Contreras et al. (+6 more)

The clustering of dark matter halos depends not only on halo mass but also on secondary halo properties, a phenomenon known as halo assembly bias. Coupled with variations in halo occupation, this dependence impacts galaxy clustering, an effect termed galaxy assembly bias. While previous studies have found only weak cosmological dependence of assembly bias within the $\Lambda$CDM framework, its sensitivity to the underlying dark matter physics remains largely unexplored. We use the matched dark-matter-only and hydrodynamical simulations from the AIDA-TNG suite to measure assembly bias across four dark matter models: cold dark matter, warm dark matter, and self-interacting dark matter with constant cross-sections and velocity-dependent cross-sections. We find that at z = 0, halo assembly bias is nearly identical across the four models for concentration-selected halos, as is the concentration dependence of the halo occupation distribution. The resulting galaxy assembly bias signals likewise show only weak model dependence. For stellar-mass-selected galaxy samples with $n = 0.0586 h^{3} Mpc^{-3}$ at z = 0, the velocity-dependent self-interacting dark matter scenario exhibits the largest deviation from the fiducial cold dark matter model: its assembly bias contribution to galaxy clustering is enhanced by up to $\sim 6\%$, corresponding to a $\sim 3\%$ difference in the assembly bias amplitude. Although statistically distinguishable, this difference is small and unlikely to be detected in current analyses. The weak model dependence persists across different galaxy number densities and redshifts. Overall, within the TNG galaxy-formation framework, these results indicate that assembly bias is largely insensitive to the dark matter models explored here, providing a robust baseline for future studies of the galaxy-halo connection in alternative dark matter scenarios.
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All authors Yikun Wang, Idit Zehavi, Sergio Contreras, Jonás Chaves-Montero, Giulia Despali, Carlo Giocoli, Lauro Moscardini, Massimiliano Romanello, Mark Vogelsberger

Cosmology and Nongalactic Astrophysics

CMB Data Analysis in the example of the POLARBEAR experiment and the LiteBIRD experiment

Kolen Cheung

In this dissertation, I briefly go through my subject areas — from Astrophysics, Cosmology, to Cosmic Microwave Background (CMB) radiation; and Data Science & High-Performance Computing. I go through the beginning of the Universe briefly in part I and introduce the Physics of the CMB in part II. Then I move on to how it can be observed experimentally, mathematically, and computationally in part III. In parts IV to VI, I write about 2 specific CMB experiments — POLARBEAR & LiteBIRD, together with my research involved in them. In part V, original research on a measurement of the CMB $B$-mode at sub-degree scales is presented using the 3rd-5th seasons of POLARBEAR observations. This demonstrates the capability of a single medium aperture telescope with a Continuously Rotating Half-Wave Plate (CRHWP) to target both the low-$\ell$ and high-$\ell$ $B$-mode science at $50 \leq \ell \leq 3000$. In part VI, the effect of detector crosstalk systematics on the CMB power-spectra is studied in detail in the example of the LiteBIRD experiment. An analytical, map-domain solution is developed, a computational simulation method is implemented, and the two predictions are compared using the LiteBIRD experiment design specification. The general agreement of the two shows that the analytical model well describes the LiteBIRD experiment, and can be used to calculate the systematic effects without performing time-consuming time-domain simulations with a high degree of accuracy. This can be used to forecast the amount of crosstalk systematics and to develop mitigation strategies. A mitigation strategy is presented, which is a hardware-based mitigation method that minimizes the crosstalk systematic effects in the 2pt power-spectra.
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2609.32037 · 25 Sep · PhD thesis, University of California, Berkeley, 2022. 241 pages, 66 figures, 6 tables. Filed version: https://escholarship.org/uc/item/0hh4w9v6. v2 corrects errors: fig. 4.1 overstated the FIRAS 1{\sigma} uncertainty tenfold; fig. 13.2 showed a simulated CMB map, not the Planck one; the fig. 36.8 discussion named the wrong ordering as the worst. All changes are listed in the ancillary changelog

Abstract PDF $CSMC ×1$TSCP ×1

Cosmology and Nongalactic Astrophysics

SLICE: Unveiling the Multi-Component Merging Core of SPT-CLJ1150-2805 Through Strong-Lensing Mass Modelling

James R. Betts, Benjamin Beauchesne, Mathilde Jauzac et al. (+16 more)

We present a new strong-lensing and X-ray mass model of the merging galaxy cluster SPT-CLJ1150-2805 ($z=0.383$), combining JWST NIRCam, HST, Chandra, and VLT/MUSE data to robustly decompose its collisionless and collisional components. Exploiting JWST, we expand the multiple-image catalogue with 66 new images (30 comprising 6 new systems). Our baseline model uses 118 spectroscopically confirmed images from 20 systems, achieving an image-plane root-mean-square offset of $0.56''$. An expanded model incorporating 31 additional photometric images from 8 additional systems yields a near-identical mass distribution, confirming excellent model stability. We resolve a complex multi-axis post-merger system requiring five cluster-scale dark matter haloes, including a bimodal core with distinct haloes coincident with each brightest cluster galaxy. The remaining mass components are independently supported by kinematics of 291 cluster members ($\sigma_v=1960^{+84}_{-92}$ km s$^{-1}$), which reveal two new galaxy substructures - the northernmost of which we tentatively identify as the baryonic counterpart to our fifth dark matter halo. The cluster is an extraordinarily efficient lens, possessing an effective Einstein radius $\theta_E=42.41^{+0.05}_{-0.04}{''}$ and an enclosed mass $M(<\theta_E)=3.35^{+0.04}_{-0.03}\times10^{14}M_\odot$ for a source at $z_s=2$. For a high-redshift source at $z_s=9$, it produces a magnification cross-section of $A(>10)\simeq0.15$ arcmin$^2$ and $A(>30)\simeq0.020$ arcmin$^2$. This global lensing power surpasses all Hubble Frontier Fields clusters. In a regime where systematic uncertainties between mass models dominate high-redshift magnification errors, the stability of our reconstruction sets this lens apart. This combination of extreme lensing power and a robust mass model establishes SPT-CLJ1150-2805 as a premier cosmic telescope for high-redshift studies.
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All authors James R. Betts, Benjamin Beauchesne, Mathilde Jauzac, David Lagattuta, Guillaume Mahler, Jean-Paul Kneib, Gavin Leroy, Marceau Limousin, Priyamvada Natarajan, Sameeksha Saini, Keren Sharon, Stephane V. Werner, Catherine Cerny, Isaque Dutra, Dominique Eckert, Alaina Einsig, Michael D. Gladders, Gourav Khullarm, Manon Regamey

Cosmology and Nongalactic Astrophysics

Observational Evidence of Velocity Anisotropy Assembly Bias in Galaxy Clusters

Facundo Rodriguez, Andrea Biviano, Ravi K. Sheth et al. (+2 more)

Cosmological simulations show that halo clustering depends on secondary internal properties beyond mass, an effect known as assembly bias. In particular, numerical models have shown that internal velocity anisotropy ($\beta$) is the halo property most tightly linked to secondary halo bias: at fixed mass, haloes with isotropic velocity profiles are more strongly clustered, whereas haloes in which radial motions dominate are more weakly clustered. Despite this robust theoretical prediction, direct observational detection of velocity anisotropy assembly bias has remained elusive. Here we present observational evidence for this effect using a sample of massive galaxy clusters from the eROSITA and DESI surveys. We measure the internal orbital anisotropy $\beta$ for 91 clusters via Jeans dynamical modelling with MAMPOSSt, considering three anisotropy profile models to ensure robustness. We divided the sample into two subpopulations: isotropic and radially anisotropic, verifying that they show no significant differences in halo mass. To quantify their large-scale clustering, we measured the projected cross-correlation function with We report evidence of velocity anisotropy assembly bias: clusters with isotropic internal kinematics exhibit stronger clustering than radially dominated ones, a segregation that is unlikely to be attributable to residual differences in cluster mass. This trend shows varying significance across three anisotropy profiles, from a mild tendency to a highly pronounced signal. Furthermore, the assembly bias remains distinct when restricting the sample to clusters consistently classified across all three models.
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All authors Facundo Rodriguez, Andrea Biviano, Ravi K. Sheth, Antonio D. Montero-Dorta, Manuel Merchán

Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

$\textit{N\=ap\=owaw\=a`enakaulua}$: a close quasar pair at cosmic dawn in the Aether survey

Silvia Onorato, Emanuele Paolo Farina, Roberto Decarli et al. (+32 more)

We present the discovery and first characterization of $\textit{N\=ap\=owaw\=a`enakaulua}$: the most compact known quasar pair candidate in the Epoch of Reionization, with a projected separation of only $0.98^{\prime\prime}$ ($\approx 5.56$ pkpc at $z \sim 6.08$) and a velocity offset of $\Delta v \simeq 15 \text{ km s}^{-1}$. Using spectroscopy from JWST/NIRSpec IFU, as part of the $\textit{Aether survey}$, Gemini/GNIRS and GMOS we characterize the continuum and emission line properties of the two quasars, enabling constraints on their black hole masses ($M_{\text{BH}} \simeq 1.5 \times 10^9$ and $4.0 \times 10^8\,M_\odot$), accretion states ($\lambda_{\text{Edd}} \simeq 1.23$ and $1.07$), and systemic redshifts ($z_{\rm sys} \simeq 6.0781$ and $6.0785$). We place this pair in the cosmological context by comparing the chance of occurrence to extrapolations of high-$z$ quasar clustering measurements at larger scales, resulting in a $\sim 2-3$ order of magnitude excess with respect to expectations. This excess hints at an underlying population of merger-triggered quasar pairs at cosmic dawn or to a denser-than-average galactic environment. $\textit{N\=ap\=owaw\=a`enakaulua}$ thus represents a crucial signpost to investigate the mass assembly of the first massive galaxies and black holes.
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All authors Silvia Onorato, Emanuele Paolo Farina, Roberto Decarli, Klaudia Protušová, Elia Pizzati, Debora Pelliccia, Devin S. Chu, Larry Lindsey Kimura, Leinani Lozi, Emily Peavy, Fabrizio Arrigoni-Battaia, Eduardo Bañados, Aaron J. Barth, Silvia Belladitta, Manuela Bischetti, Sarah E. I. Bosman, Hyunseop Choi, Tiago Costa, Anna-Christina Eilers, Xiaohui Fan, Simona Gallerani, Thomas R. Geballe, Anniek J. Gloudemans, Eunchong Kim, Brian C. Lemaux, Weizhe Liu, Yoshiki Matsuoka, Chiara Mazzucchelli, Atsuko Nitta, Jan-Torge Schindler, Andrew W. Stephens, Hyewon Suh, Fabian Walter, Feige Wang, Jinyi Yang

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

Neutrino Direct Simulation Monte Carlo: Accurate modeling of out-of-equilibrium decaying cosmological relics

Kensuke Akita, Miguel Escudero, Oleksii Ihnatenko et al. (+1 more)

We consider nonstandard cosmologies in which decaying relics inject energy at MeV temperatures, driving neutrinos out of equilibrium. The subsequent neutrino evolution shapes predictions for the cosmic radiation density and primordial light element abundances. Earlier work introduced Neutrino Direct Simulation Monte Carlo ($\nu$DSMC), which describes neutrino transport through Monte Carlo sampling of particle interactions. Here, we extend this method by jointly evolving the relic population, neutrino spectra, electromagnetic plasma, and cosmic expansion, and coupling this evolution to Big Bang nucleosynthesis. The framework includes direct and inverse decays of the relic, neutrino flavor conversion, quantum statistics, and pion production by energetic neutrinos. To reveal the physical impact of these effects and independently test $\nu$DSMC, we compare several approaches to neutrino evolution across a range of nonstandard cosmological scenarios. We find excellent agreement with independent solutions of quantum kinetic or quasi-classical Boltzmann equations. Compared with these calculations, $\nu$DSMC includes a broader range of physical processes and is substantially faster for strongly nonthermal neutrino populations. This makes broad, robust parameter scans for nonstandard cosmologies practical. We show that when departures from thermal equilibrium are large, approximations that average over neutrino momenta can give qualitatively incorrect predictions, including the wrong sign of the change in the effective number of neutrino species and substantially incorrect primordial nuclear abundances. We conclude that the extended $\nu$DSMC framework enables reliable cosmological tests of new physics by following neutrino thermalization and its observable consequences.
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All authors Kensuke Akita, Miguel Escudero, Oleksii Ihnatenko, Maksym Ovchynnikov

Cosmology and Nongalactic Astrophysics

Evolving dark energy and a younger Universe from cosmic inhomogeneity

Jacky David Yang and Hans-Otto Carmesin

Joint analyses of baryon acoustic oscillations, type Ia supernovae and the cosmic microwave background show a preference for an evolving dark-energy equation of state, and recent studies suggest that cosmic inhomogeneities can produce an apparent evolution of dark energy within general relativity. Here we examine this effect within a framework in which the possibility that matter can be unevenly distributed enters the expansion dynamics directly. The framework yields redshift-dependent effective values of the Hubble constant and of the dark-energy density parameter without introducing a new free parameter. Using CMB-inferred parameters to fix the homogeneous limit, we find that the dark-energy density parameter increases by about eight percent toward the present, from 0.679 to 0.735, while the inferred Hubble constant shifts from the Planck value toward the range obtained from local measurements. Both trends are broadly consistent with published estimates from supernovae, baryon acoustic oscillations, X-ray clusters and gravitational waves, although a joint analysis of the underlying data is left for future work. Integrating the resulting expansion history gives a present-day cosmic age of 13.521 Gyr, compared with 13.827 Gyr for the homogeneous model; we interpret the difference of 0.306 Gyr as a global time dilation between the two descriptions. The framework also yields the homogeneous-limit dark-energy density parameter, two thirds, from the formation of volume alone. The predicted redshift dependences can be tested against forthcoming measurements of cosmic distances and expansion rates.
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Cosmology and Nongalactic Astrophysics

Kruglov-entropy cosmology from apparent-horizon thermodynamics: background dynamics and observational constraints

Candrasyah Muhammad, Burin Gumjudpai, Nandan Roy et al. (+1 more)

We investigate two late-time cosmological models generated by Kruglov's nonadditive entropy at the apparent horizon. Model I, originally derived by Kruglov, follows the Cai–Kim thermodynamic construction and leads to an implicit modified Friedmann equation, whereas Model II, proposed and derived in this work, is obtained from an entropy-integral prescription and contains an effective vacuum contribution. We formulate both models in terms of the dimensionless Hubble parameter, include radiation, impose exact present-day closure, and evolve the physical branch using analytic derivatives of the implicit Friedmann equations. We constrain the models with DESI DR2 baryon acoustic oscillations and a compressed CMB likelihood, with and without DES-Y5 Type-Ia supernovae. Model I is driven to a markedly lower Hubble constant, $H_0\simeq62.4,\mathrm{km,s^{-1},Mpc^{-1}}$ for the combined data, and remains non-phantom with $w_{\rm DE,0}\simeq-0.814$; it is strongly disfavoured relative to flat $\Lambda$CDM. Model II stays close to $\Lambda$CDM in the standard cosmological parameters and gives $w_{\rm DE,0}\simeq-1.003$, while its two entropy-sector parameters remain strongly degenerate. Its best-fit likelihood is comparable to $\Lambda$CDM, but the additional parameters are not supported by information criteria. These results show that the two thermodynamic realizations of the same nonadditive entropy have sharply different phenomenological consequences at the homogeneous-background level. In summary, the observational plausibility of entropy-based cosmology hinges critically on how the generalized horizon entropy is incorporated into the Friedmann dynamics.
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All authors Candrasyah Muhammad, Burin Gumjudpai, Nandan Roy, Pornrad Srisawad

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

Natural Saturation Of The Sterile Neutrino Dark Matter Resonant Production By a High Lepton Flavor Asymmetry In Primordial Plasma

Dmitry Gorbunov and Dmitry Kalashnikov

Sterile neutrinos remain a well-motivated dark-matter candidate whose cosmological abundance can be enhanced by resonant active–sterile conversion in the presence of a lepton asymmetry in primordial plasma. In the standard picture, a larger initial asymmetry increases the matter potential and can therefore promote resonant production. However, the same increase also shifts the resonance to later stages of the cosmological evolution when the plasma temperature is lower. We show that this delayed production epoch can overlap with the onset of active neutrino oscillations, which redistribute the flavor asymmetries and may substantially reduce, or in some cases nearly erase, the lepton asymmetry needed for a successful resonant sterile-neutrino production. This interplay provides a natural saturation mechanism for the final sterile-neutrino abundance: beyond a certain range of initial asymmetries, increasing the primordial asymmetry no longer leads to a proportional increase in the produced dark-matter density. We identify this effect as an additional constraint on resonant sterile-neutrino production at large lepton asymmetry and discuss its dependence on the flavor structure of the initial asymmetry and on the background cosmological evolution. Our numerical results reveal two order of magnitude range in sterile-active neutrino mixing parameter $\sin^2(2\theta)$ presently consistent with the resonant mechanism of the dark matter sterile neutrino production. It must be investigated by the next generation X-ray telescopes to fully explore this mechanism and corresponding minimal models suggesting sterile neutrinos as viable dark matter. We also consider pion condensation at large flavor lepton asymmetries, which may lead to a first-order QCD phase transition and associated gravitational-wave production in the early Universe.
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Cosmology and Nongalactic Astrophysics

Observational constraints on scalar-vector-tensor dark energy with phantom-divide crossing

Nandan Roy, Shinji Tsujikawa, Ying-li Zhang et al. (+1 more)

We constrain a scalar-vector-tensor (SVT) dark-energy model in which the vector sector drives the dark-energy equation of state below $-1$ at earlier times, while a canonical scalar field subsequently drives it across $-1$ toward a present-day value above $-1$. We confront the model with DES Year 5 supernovae, DESI DR2 baryon acoustic oscillations, and compressed cosmic microwave background information, and then include Gold-2017 redshift-space-distortion (RSD) measurements to probe structure growth. The background posterior assigns substantial weight to crossing histories and gives a better best fit than the flat $\Lambda$-cold-dark-matter ($\Lambda$CDM) model. The RSD analysis preserves this qualitative background evolution, constrains the clustering amplitude, and increases the posterior support for the directional crossing criterion. Since the growth analysis also imposes additional perturbative support conditions, this increase cannot be attributed to the RSD likelihood alone. Matched PolyChord calculations give Bayes factors larger than unity for SVT relative to $\Lambda$CDM under both prior-volume conventions considered here. The quantitative Bayes factor depends on the prior normalization assigned to the regular radiation-era branch and is larger in the RSD analysis under either convention. Overall, current expansion and structure-growth data are consistent with a stable dynamical crossing of the phantom divide in the SVT model.
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All authors Nandan Roy, Shinji Tsujikawa, Ying-li Zhang, Zejun Zhang

Cosmology and Nongalactic Astrophysics

Probing the cosmic web with fast radio bursts: II. Scintillation

Sharon Lapiner, Nir Mandelker, Paz Beniamini et al. (+1 more)

We consider the formation of multiphase gas in cosmic web objects (CWOs) through cooling and fragmentation within the shock-heated medium of cosmic sheets and filaments, and the circumgalactic medium (CGM) of haloes. This leads to dense, cool ($\sim10^{4}\,\mathrm{K}$), small-scale cloudlets in pressure equilibrium with their surroundings. Such ionized overdensities can affect the propagation of radio waves emitted by fast radio bursts (FRBs), allowing us to probe the small-scale structure in CWOs by examining their impact on the scintillation pattern of the observed FRB flux. While we find that the probability of encountering a high-temperature filament or sheet with cold cloudlets is rather small and usually confined to high redshifts, the expected high rates of FRBs may still permit detection through scintillation along rare sightlines. We suggest scintillation from the Milky Way (MW) interstellar medium as a promising probe: CWO plasma screens can suppress it, placing constraints on their cold-gas properties. Filaments and sheets can suppress MW scintillation from sources at $z_\mathrm{S}\gtrsim2$ and $3$, respectively, while cold and turbulent cloudlets in the CGM can be probed by sources at redshifts as low as $z_\mathrm{S}\sim0.5$, constraining remarkably low volume-filling fractions, $f_\mathrm{v}$ (e.g. $f_\mathrm{v}\gtrsim10^{-5}$ for $z_\mathrm{S}\gtrsim2$). To provide testable predictions, we estimate the fraction of FRBs expected to encounter CWOs that may suppress MW scintillation below a given frequency, and express this as a function of the average extragalactic dispersion measure. Future FRB samples could map these constraints onto bounds on the existence and properties of cloudlets in CWOs, such as their density, size, $f_\mathrm{v}$, and turbulence.
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All authors Sharon Lapiner, Nir Mandelker, Paz Beniamini, S. Peng Oh

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Sub-Horizon and Quasi-Static Approximations in Interacting Dark Sector Models Involving Scalar Field Dark Energy

Priyanka Saha, Sharvari Nadkarni-Ghosh and Kaushik bhattacharya

We investigate the validity of the sub-horizon approximation (SHA) and quasi-static approximation (QSA) for linear matter perturbations in interacting scalar-field dark-energy models. We consider both quintessence and phantom scalar fields and derive their full relativistic perturbation evolution to compare with the corresponding SHA and QSA solutions. We find that, while the SHA reproduces the full evolution with percent-level accuracy for non-interacting and weakly interacting models on sufficiently sub-horizon scales, its accuracy progressively deteriorates with increasing interaction strength and towards larger scales. Moreover, unlike in $\Lambda$CDM and non-interacting scalar-field models, applying the SHA to interacting models does not fully recover the standard Newtonian fluid equations. The QSA generally provides a closer description of the full relativistic evolution than the SHA over the scales considered. By comparing the scalar-field model with $\Lambda$CDM using the full relativistic equations and, separately, using the SHA system, we evaluated whether the SHA is capable of capturing the full extent of the physical differences introduced by the alternative model. We find that the difference between these two comparisons becomes increasingly important for stronger interactions and smaller wavenumbers. Finally, we demonstrate that the resulting differences can reach several percent on scales accessible to large-volume hydrodynamical simulations, implying that the validity of the SHA cannot be assumed solely from the sub-horizon condition. Our results highlight the need to benchmark the approximation over the relevant interaction parameter and wavenumber ranges before employing interacting-dark-energy models in large-volume structure-formation simulations and precision comparisons with large-scale-structure observations.
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