And Then There WEre Baryons (ATWEB): The Baryon Budget of the Universe in Halos and the IGM over 13 Billion Years of Cosmic Time

Mohammadreza Ayromlou; G. Mark Voit; Thomas H. Reiprich; Cristiano Porciani; Dominique Eckert

Home/Archive/arXiv

arXiv · 2610.07140

And Then There WEre Baryons (ATWEB): The Baryon Budget of the Universe in Halos and the IGM over 13 Billion Years of Cosmic Time

Mohammadreza Ayromlou·G. Mark Voit·Thomas H. Reiprich·Cristiano Porciani·Dominique Eckert

View original source ↗Read source document ↗Export metadata ↓

Abstract

Observations of the local Universe show that, except in the most massive galaxy clusters, the baryon fraction within halos falls below the cosmic mean. This deficit can be characterized using the previously established closure radius, the halocentric distance within which the enclosed baryon fraction reaches the cosmic value. Using the TNG, EAGLE and SIMBA simulations, we examine how, when, and on what scales the baryonic and dark matter distributions diverge. At z=0 less than 30% of cosmic baryons reside within galaxy-hosting halos, compared with ~45% of the dark matter, leaving over 70% of all baryons in the IGM. Building on the closure radius, we introduce three further characteristic scales: the compensation radius, closure envelope, and compensation envelope. The compensation radius marks where the enclosed total mass recovers its gravity-only value, and today it typically lies inside the closure radius in all three models. The closure and compensation envelopes are the largest median radii across halo mass. Galaxy groups provide the largest contribution per dex of halo mass to IGM enrichment with halo-associated baryons and redistribute baryons over the largest distances. They set the closure envelope, which reaches ~2-6.5 Mpc at z=0, depending on the model. The closure radius usually increases with cosmic time at fixed halo mass. Tracking individual halos, we find open baryon cycles with substantial redistribution beyond halo boundaries across all halo masses, while even the progenitors of today's most massive clusters fall below the cosmic baryon fraction. The compensation envelope grows toward low redshift, reaching ~1.5-5.5 Mpc at z=0. Across cosmic time, it coincides with the scale on which the matter power spectrum recovers its gravity-only form, establishing a direct link between the spatial extent of baryon redistribution and the impact of feedback on large-scale structure.

Explore related subjects

astro-ph.CO astro-ph.GA

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Mohammadreza Ayromlou, G. Mark Voit, Thomas H. Reiprich, Cristiano Porciani, Dominique Eckert. 2026-10-05. And Then There WEre Baryons (ATWEB): The Baryon Budget of the Universe in Halos and the IGM over 13 Billion Years of Cosmic Time. https://arxiv.org/abs/2610.07140

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Implications of Cosmic Birefringence for Multi-Field ALP Dark Matter

Cosmic birefringence, characterized by the observed rotation of the polarization plane of the cosmic microwave background (CMB) radiation, serves as a critical probe for testing theories beyond the standard cosmological scenario. As a major component of the universe, dark matter plays a pivotal role in cosmic evolution, particularly in the formation of large-scale structures. However, its fundamental nature remains elusive. Axion-like particles (ALPs), as promising dark matter candidates, possess unique advantages in naturally explaining such phenomena. Previous studies on the implications of cosmic birefringence for these ultralight ALP fields have focused on single-field models with conventional potentials. These models face exclusion due to the washout effect - a suppression of the CMB polarization power spectrum induced by oscillatory dynamics of the scalar field within the mass range of less than $10^{-23}$ eV. To address this limitation, we develop a more general theoretical framework incorporating two ALP fields, providing analytical approximations and numerical calculations. Our findings reveal that the superposition of two ALP fields with distinct masses can relax the constraints imposed by the washout effect and reconcile with observations.

astro-ph.CO↗

arXiv2026

Memoirs of the curvaton: non-perturbative non-Gaussianity and supermassive primordial black holes

The curvaton provides a simple mechanism for generating strongly non-Gaussian curvature perturbations after inflation, with potentially important consequences on small scales. We study curvaton dynamics beyond the standard quadratic potential and construct the local non-Gaussian map $ζ=F(ζ_{\rm G})$ relating the curvature perturbation to an auxiliary Gaussian field $ζ_{\rm G}$. Curvaton self-interactions make the onset of oscillations field dependent and modify the effective equation of state once the curvaton enters the adiabatic regime. We incorporate these effects using the abbreviated action, which provides a compact way to connect the frozen and oscillatory regimes and exposes sources of non-Gaussianity absent in the purely quadratic case. We apply the formalism to quadratic, monomial, quartic, and cosine potentials, for which we derive the mapping $F(ζ_{\rm G})$ and show that self-interactions can either enhance or suppress the resulting non-Gaussianity depending on the potential and initial conditions. We consider non-perturbative aspects in the strongly non-Gaussian regime, and show how strong non-Gaussianity can suppress the power spectrum. As an application, we provide a bottom-up scenario in which strongly positive curvaton non-Gaussianity allows primordial supermassive black hole seeds at peak amplitudes $\mathcal{A}_{\rm pk}\sim10^{-5}$, which are compatible with the COBE/FIRAS $μ$-distortion bounds. This opens a new primordial scenario for the Little Red Dots observed by the JWST. The axion-like curvaton provides a particularly natural setting for this mechanism.

astro-ph.CO↗

arXiv2026

Shear-kSZ: A New Estimator for the Matter-Electron Power Spectrum from kSZ Tomography and Weak Lensing

We propose a new estimator of the electron--matter power spectrum, $P_{me}(k)$, which correlates the kinematic Sunyaev--Zel'dovich (kSZ) temperature with the product of the line-of-sight velocity field and the weak-lensing convergence. Like the stacked kSZ estimator, it factorizes into a calibratable velocity kernel times $P_{me}(k)$, but it probes the full matter distribution rather than the gas around a biased tracer. It therefore measures the baryonic suppression of the matter power spectrum, $S(k)$, one of the dominant astrophysical systematics for Stage-IV cosmic shear. We derive an analytic expression for the estimator, validate it against simulations at the per-cent level, and show that its parity structure cancels cosmic microwave background (CMB) foregrounds. We forecast the detectability with a realistic pipeline: velocities reconstructed from the simulated tracers, with and without photometric-redshift errors; the kSZ signal of all the ionized gas along the line of sight; a CMB map with Simons Observatory (SO) noise; and LSST source samples free of intrinsic alignments. A DESI-like spectroscopic sample at $0.5<z<1$ over the $20\%$ of the sky that DESI, LSST and SO share gives a $4$--$7σ$ detection. Photometric redshifts cost only $5$--$10\%$ of the significance, so LSST can supply its own velocity tracers over its full overlap with SO: with tracers at $0.1<z<1.3$ and five source samples we find $10σ$ in an end-to-end simulation, and $13σ$ with Advanced SO (16$σ$ if extending to $z < 1.5$). This corresponds to a few-per-cent measurement of $S(k)$ at $k\simeq1$--$4\,h\,{\rm Mpc}^{-1}$, the scales that matter most for cosmic shear.

astro-ph.CO↗