Baryonic Effects Research Articles

A deconstruction of methods to derive one-point lensing statistics

Gravitational lensing is a crucial tool for exploring cosmic phenomena, providing insights into galaxy clustering, dark matter, and dark energy. Given the substantial computational demands of N-body simulations, approximate methods like 𝙿𝙸𝙽𝙾𝙲𝙲𝙷𝙸𝙾 and 𝚝𝚞𝚛𝚋𝚘𝙶𝙻 have been proposed as viable alternatives for simulating lensing probability density functions (PDFs). This paper evaluates these methods and their effectiveness across both weak and strong lensing regimes, with a focus in the context where baryonic effects are negligible. Our comparative analysis reveals that these methods are effective for applications where lensing is mild, such as the majority of sources of electromagnetic and gravitational waves. However, both 𝙿𝙸𝙽𝙾𝙲𝙲𝙷𝙸𝙾 and 𝚝𝚞𝚛𝚋𝚘𝙶𝙻 break down for large values of convergence and magnification due to their loss of accuracy in capturing small-scale nonlinear matter fields, owing to oversimplified assumptions about internal halo structures and reliance on perturbation theory. 𝙿𝙸𝙽𝙾𝙲𝙲𝙷𝙸𝙾 yields second-to-fourth moments of the lensing PDFs, which are 6–10% smaller than those resulting from N-body simulations in regimes where baryonic effects are minimal. These findings aim to inform future studies on gravitational lensing of point sources, which are increasingly relevant with upcoming supernova and gravitational wave datasets.

Surviving the waves: evidence for a dark matter cusp in the tidally disrupting Small Magellanic Cloud

ABSTRACT We use spectroscopic data for ${\sim }6000$ red giant branch stars in the Small Magellanic Cloud (SMC), together with proper motion data from Gaia Early Data Release 3, to build a mass model of the SMC. We test our Jeans mass modelling method (binulator + gravsphere) on mock data for an SMC-like dwarf undergoing severe tidal disruption, showing that we are able to successfully remove tidally unbound interlopers, recovering the dark matter density and stellar velocity anisotropy profiles within our 95 per cent confidence intervals. We then apply our method to real SMC data, finding that the stars of the cleaned sample are isotropic at all radii (at 95 per cent confidence) and that the inner dark matter density profile is dense, $\rho _{\rm DM}(150\ {\rm pc}) = 1.58_{-0.58}^{+0.80}\times 10^8 \ {\rm M}_{\odot }\, \rm kpc^{-3}$, consistent with a $\Lambda$ cold dark matter cusp. Our model gives a new estimate of the SMC’s total mass within 3 kpc $(M_{\rm tot} \le 3\ {\rm kpc})$ of $2.29\pm 0.46 \times 10^9 \ {\rm M}_{\odot }$. We also derive an astrophysical ‘J-factor’ of $18.99\pm 0.16$ GeV$^2$ cm$^{-5}$ and a ‘D-factor’ of $18.73\pm 0.04$ GeV$^2$ cm$^{-5}$, making the SMC a promising target for dark matter annihilation and decay searches. Finally, we combine our findings with literature measurements to test models in which dark matter is ‘heated up’ by baryonic effects. We find good qualitative agreement with the Di Cintio et al. model but we deviate from the Lazar et al. model at high $M_*/M_{200} > 10^{-2}$. We provide a new, analytical, density profile that reproduces dark matter heating behaviour over the range $10^{-4} < M_*/M_{200} < 10^{-1}$.

The Nearly Universal Disk Galaxy Rotation Curve

The universal rotation curve (URC) of disk galaxies was originally proposed to predict the shape and amplitude of any rotation curve (RC) based solely on photometric data. Here, the URC is investigated with an extensive set of spatially resolved RCs drawn from the PROBES-I, PROBES-II, and MaNGA databases with matching multiband surface brightness profiles from the DESI-LIS and Wide-Field Infrared Survey Explorer surveys for 3846 disk galaxies. Common URC formulations fail to achieve an adequate level of accuracy to qualify as truly universal over fully sampled RCs. We develop neural network (NN) equivalents for the proposed URCs that predict RCs with higher accuracy, showing that URC inaccuracies are not due to insufficient data but rather nonoptimal formulations or sampling effects. This conclusion remains even if the total RC sample is pruned for symmetry. The latest URC prescriptions and their NN equivalents trained on our subsample of 579 disk galaxies with symmetric RCs perform similarly to the URC/NN trained on the complete data sample. We conclude that a URC with an acceptable level of accuracy (ΔV circ ≲ 15%) at all radii would require a detailed modeling of a galaxy’s central regions and outskirts (e.g., for baryonic effects leading to contraction or expansion of any dark-matter-only halo).

Revisiting the effects of baryon physics on small-scale redshift space distortions

Abstract Redshift space distortions are an important probe of the growth of large-scale structure and for constraining cosmological parameters in general. As galaxy redshift surveys approach percent level precision in their observations of the two point clustering statistics, it is timely to review what effects baryons and associated processes such as feedback may have on small-scale clustering in redshift space. Contrary to previous studies in the literature, we show using the large-volume Bahamas hydrodynamic simulations that the effect of baryons can be as much as 1 per cent in the k ∼ 0.1 h Mpc−1 range for the monopole and 5 per cent for quadrupole, and that this could rise to as much as 10 per cent at k ∼ 10 h Mpc−1 in both measurements. For the halo power spectra, this difference can be as much 3-4 per cent in the monopole on scales of 0.05 < k < 0.3 h Mpc−1 for 1013 h−1 M⊙ haloes. We find that these deviations can be mitigated to the sub-percent level in the both the monopole and quadrupole up to k ∼ 0.3 h Mpc−1 if the baryon corrected halo masses are used to calculate the redshift space power spectra. Finally, we use the cosmo-OWLS simulation suite to explore the changes in the redshift space power spectra with different feedback prescriptions, finding that there is a maximum of 15-20 per cent difference between the redshift space monopole and quadrupole with and without baryons at k ∼ 1–2 h Mpc−1 within these models.

Cosmic shear with small scales: DES-Y3, KiDS-1000 and HSC-DR1

We present a cosmological analysis of the combination of the DES-Y3, KiDS-1000 and HSC-DR1 weak lensing samples under a joint harmonic-space pipeline making use of angular scales down to ℓmax=4500, corresponding to significantly smaller scales (δθ ~ 2.4') than those commonly used in cosmological weak lensing studies. We are able to do so by accurately modelling non-linearities and the impact of baryonic effects using Baccoemu. We find S 8 ≡ σ 8√(Ωm/0.3) = 0.795+0.015 -0.017, in relatively good agreement with CMB constraints from Planck (less than ~1.8σ tension), although we obtain a low value of Ωm =0.212+0.017 -0.032, in tension with Planck at the ~3σ level. We show that this can be recast as an H0 tension if one parametrises the amplitude of fluctuations and matter abundance in terms of variables without hidden dependence on H0. Furthermore, we find that this tension reduces significantly after including a prior on the distance-redshift relationship from BAO data, without worsening the fit. In terms of baryonic effects, we show that failing to model and marginalise over them on scales ℓ ≲ 2000 does not significantly affect the posterior constraints for DES-Y3 and KiDS-1000, but has a mild effect on deeper samples, such as HSC-DR1. This is in agreement with our ability to only mildly constrain the parameters of the Baryon Correction Model with these data.

The effect of AGN feedback on the Lyman-α forest signature of galaxy protoclusters at z∼ 2.3

ABSTRACT The intergalactic medium in the vicinity of galaxy protoclusters are interesting testbeds to study complex baryonic effects such as gravitational shocks and feedback. Here, we utilize hydrodynamical simulations from the SIMBA and The Three Hundred suites to study the mechanisms influencing large-scale Lyman-$\alpha$ transmission in $2\lt z\lt 2.5$ protoclusters. We focus on the matter overdensity-Lyman-$\alpha$ transmission relation $(\delta _m-\delta _F)$ on Megaparsec-scales in these protoclusters, which is hypothesized to be sensitive to the feedback implementations. The lower density regions represented by the SIMBA-100 cosmological volume trace the power-law $\delta _m-\delta _F$ relationship often known as the fluctuating Gunn–Peterson approximation. This trend is continued into higher density regions covered by simulations that implement stellar feedback only. Simulations with active galactic nucleus (AGN) thermal and AGN jet feedback, however, exhibit progressively more Lyman-$\alpha$ transmission at fixed matter overdensity. Compared with the seven protoclusters observed in the COSMOS field, only two display the excess absorption expected from protoclusters. The others exhibit deviations: four show some increased transparency suggested by AGN X-ray thermal feedback models while the highly transparent COSTCO-I protocluster appears to reflect intense jet feedback. Discrepancies with the stellar-feedback-only model suggests processes at play beyond gravitational heating and/or stellar feedback as the cause of the protocluster transparencies. Some form of AGN feedback is likely at play in the observed protoclusters, and possibly long-ranged AGN jets in the case of COSTCO-I. While more detailed and resolved simulations are required to move forward, our findings open new avenues for probing AGN feedback at Cosmic Noon.

No Catch-22 for fuzzy dark matter: testing substructure counts and core sizes via high-resolution cosmological simulations

ABSTRACT Fuzzy dark matter (FDM) has recently emerged as an interesting alternative model to the standard cold dark matter (CDM). In this model, dark matter consists of very light bosonic particles with wave-like behaviour on galactic scales. Using the N-body code ax-gadget, we perform cosmological simulations of FDM that fully model the dynamical effects of the quantum potential throughout cosmic evolution. Through the combined analysis of FDM volume and high-resolution zoom-in simulations of different FDM particle masses ($m_{\chi }$$\sim$$10^{-23}\!-\!10^{-21}$ eV c−2), we study how FDM impacts the abundance of substructure and the inner density profiles of dark matter haloes. For the first time, using our FDM volume simulations, we provide a fitting formula for the FDM-to-CDM subhalo abundance ratio as a function of the FDM mass. More importantly, our simulations clearly demonstrate that there exists an extended FDM particle mass interval able to reproduce the observed substructure counts and, at the same time, create substantial cores ($r_{c} \sim 1$ kpc) in the density profile of dwarf galaxies ($\approx 10^{9}\!-\!10^{10}$ M$_{\odot }$), which stands in stark contrast with CDM predictions even with baryonic effects taken into account. The dark matter distribution in the faintest galaxies offers then a clear way to discriminate between FDM and CDM.

The influence of baryons on low-mass haloes

ABSTRACT The Voids-within-Voids-within-Voids project used dark-matter-only (DMO) simulations to study the abundance and structure of dark matter (DM) haloes over the full mass range populated in the standard Lambda cold dark matter cosmology. Here, we explore how baryonic effects modify these results for $z=0$ halo masses in the range $10^4$–$10^7~\mathrm{M_\odot }$, below the threshold for galaxy formation. Our main study focuses on three simulations from identical initial conditions at $z=127$, one following DMO, one including non-radiative gas, and one additionally including the baryonic physics relevant in this halo mass range (cooling and photoheating). In the non-radiative simulation, above $10^{5.5}~\mathrm{M_\odot }$, halo abundance and internal structure are very similar to the DMO simulation, and the baryon to DM ratio is everywhere close to the cosmic value. At lower mass, this ratio drops and haloes are less concentrated and less massive in the non-radiative case. Test simulations at higher resolution show this to be mainly a resolution effect; the expected drop in baryon content due to residual pressure effects only becomes substantial for $z=0$ haloes below ${\sim}10^{2.7}~\mathrm{M_\odot }$. However, gas is heated by reionization at $z=6$ in our ‘full physics’ run, and this results in almost complete expulsion of gas from all haloes in our simulated mass range. This suppresses the halo mass function by ${\sim}30{{\ \rm per\ cent}}$, lowers halo concentration, and consequently weakens the DM annihilation signal by ${\sim}40{-}60{{\ \rm per\ cent}}$.

Nearest neighbour analysis as a new probe for fuzzy dark matter

ABSTRACT Fuzzy dark matter (FDM) is a promising candidate for dark matter (DM), characterized by its ultra-light mass, which gives rise to wave effects at astrophysical scales. These effects offer potential solutions to the small-scale issues encountered within the standard cold dark matter (CDM) paradigm. In this paper, we investigate the large-scale structure of the cosmic web using FDM simulations, comparing them to CDM-only simulations and a simulation incorporating baryonic effects. Our study employs the nearest neighbour (NN) analysis as a new statistical tool for examining the structure and statistics of the cosmic web in an FDM universe. This analysis could capture the information absent in the two-point correlation functions. In particular, we analyse data related to the spherical contact, nearest neighbour distances (NND), and the angle between the first and second nearest neighbours of haloes (NNA). Specifically, we utilize probability distribution functions, statistical moments, and fitting parameters, as well as G(x), F(x), and J(x) functions to analyse the above data. Remarkably, the results from the FDM simulations differ significantly from the others across these analyses, while no noticeable distinction is observed between the baryonic and CDM-only simulations. Moreover, the lower FDM mass leads to more significant deviations from the CDM simulations. These compelling results highlight the efficiency of the NN analysis – mainly through the use of the J(x) function, $s_3$, $l_{3}$, and $a_4$ parameters – as a prominent new tool for investigating FDM on large scales and making observational predictions.

Forecast constraints on the baryonic feedback effect from the future kinetic Sunyaev-Zel'dovich effect detection

The baryonic feedback effect is an important systematic error in the weak lensing (WL) analysis. It contributes partly to the S 8 tension in the literature. With the next generations of large scale structure (LSS) and CMB experiments, the high signal-to-noise kinetic Sunyaev-Zel'dovich (kSZ) effect detection can tightly constrain the baryon distribution in and around dark matter halos, and quantify the baryonic effect in the weak lensing statistics. In this work, we apply the Fisher matrix technique to predict the future kSZ constraints on 3 kSZ-sensitive Baryon Correction Model (BCM) parameters. Our calculations show that, in combination with next generation LSS surveys, the 3rd generation CMB experiments such as AdvACT and Simon Observatory can constrain the matter power spectrum damping S(k) to the precision of σ S (k) < 0.8%√(37.8 Gpc3h-3-3/V) at k ≲ 10h/Mpc, where V is the overlapped survey volume between the future LSS and CMB surveys. For the 4th generation CMB surveys such as CMB-S4 and CMB-HD, the constraint will be enhanced to σ S (k) < 0.4%√(37.8 Gpc3h-3/V). If extra-observations, e.g. X-ray detection and thermal SZ observation, can effectively fix the gas density profile slope parameter δ, the constraint on S(k) will be further boosted to σ S (k) < 0.3%√(37.8 Gpc3 h -3/V) and σ S (k) < 0.1%√(37.8 Gpc3 h -3/V) for the 3rd and 4th generation CMB surveys.

Atomic hydrogen shows its true colours: correlations between H i and galaxy colour in simulations

ABSTRACT Intensity mapping experiments are beginning to measure the spatial distribution of neutral atomic hydrogen H i to constrain cosmological parameters and the large-scale distribution of matter. However, models of the behaviour of H i as a tracer of matter are complicated by galaxy evolution. In this work, we examine the clustering of H i in relation to galaxy colour, stellar mass, and H i mass in IllustrisTNG at z = 0, 0.5, and 1. We compare the H i-red and H i-blue galaxy cross-power spectra, finding that H i-red has an amplitude 1.5 times greater than H i-blue at large scales. The cross-power spectra intersect at ≈3 Mpc in real space and ≈10 Mpc in redshift space, consistent with z ≈ 0 observations. We show that H i clustering increases with galaxy H i mass and depends weakly on detection limits in the range MH i ≤ 108 M⊙. In terms of M⋆, we find massive blue galaxies cluster more than less massive ones. Massive red galaxies, however, cluster the weakest amongst red galaxies. These opposing trends arise from central-satellite compositions. Despite these M⋆ trends, we find that the cross-power spectra are largely insensitive to detection limits in galaxy surveys. Counter-intuitively, all auto and cross-power spectra for red and blue galaxies and H i decrease with time at all scales. We demonstrate that processes associated with quenching contribute to this trend. The complex interplay between H i and galaxies underscores the importance of understanding baryonic effects when interpreting the large-scale clustering of H i, blue, and red galaxies at z ≤ 1.

Hadron-quark transition and chiral symmetry restoration at high density

A simple phenomenological hybrid hadron-quark model with excluded volume effects of baryons and chiral dynamics is investigated. The hybrid equation of state naturally connects the low-density baryonic matter with the high-density quark matter. In the intermediate region, a phase, which cannot be regarded as pure hadron matter or pure quark matter, appears. In this model, there is a possibility that the abrupt first-order-like transition to pure quark matter induces the strong chiral symmetry restoration and the speed of sound has a large peak at considerable large density. Published by the American Physical Society 2024

Multiscale Flow for robust and optimal cosmological analysis

We propose Multiscale Flow, a generative Normalizing Flow that creates samples and models the field-level likelihood of two-dimensional cosmological data such as weak lensing. Multiscale Flow uses hierarchical decomposition of cosmological fields via a wavelet basis and then models different wavelet components separately as Normalizing Flows. The log-likelihood of the original cosmological field can be recovered by summing over the log-likelihood of each wavelet term. This decomposition allows us to separate the information from different scales and identify distribution shifts in the data such as unknown scale-dependent systematics. The resulting likelihood analysis can not only identify these types of systematics, but can also be made optimal, in the sense that the Multiscale Flow can learn the full likelihood at the field without any dimensionality reduction. We apply Multiscale Flow to weak lensing mock datasets for cosmological inference and show that it significantly outperforms traditional summary statistics such as power spectrum and peak counts, as well as machine learning-based summary statistics such as scattering transform and convolutional neural networks. We further show that Multiscale Flow is able to identify distribution shifts not in the training data such as baryonic effects. Finally, we demonstrate that Multiscale Flow can be used to generate realistic samples of weak lensing data.

The contribution of massive haloes to the matter power spectrum in the presence of AGN feedback

ABSTRACT The clustering of matter, as measured by the matter power spectrum, informs us about cosmology, dark matter, and baryonic effects on the distribution of matter in the universe. Using cosmological hydrodynamical simulations from the cosmo-OWLS and BAHAMAS simulation projects, we investigate the contribution of power in haloes with various masses, to the full power spectrum, as well as the power ratio between baryonic and dark matter only (DMO) simulations for a matched (between simulations) and an unmatched set of haloes. We find that the presence of AGN feedback suppresses the power on all scales for haloes of all masses examined (1011.25 ≤ M500, crit ≤ $10^{14.75}\, \mathrm{M_\odot }/h$), by ejecting matter from within $r_{500,\mathrm{c}}\,$ to $r_{200,\mathrm{m}}\,$ and potentially beyond in massive haloes (M500, crit ≳ $10^{{13}}\, \mathrm{M_\odot }/h$), and likely impeding the growth of lower-mass haloes as a consequence. A lower AGN feedback temperature changes the behaviour of high-mass haloes (M500, crit ≥ $10^{{13.25}}\, \mathrm{M_\odot }/h$), damping the effects of AGN feedback at small scales, $k\, {{\gtrsim }}\, {{4}}\, h\mathrm{\, Mpc^{-1}}$. For $k\, {{\lesssim }}\, {{3}}\, h\mathrm{\, Mpc^{-1}}$, group-sized haloes ($10^{{14\pm 0.25}}\, \mathrm{M_\odot }/h$) dominate the power spectrum, while on smaller scales the combined contributions of lower-mass haloes to the full power spectrum rise above that of the group-sized haloes. Finally, we present a model for the power suppression due to feedback, which combines observed mean halo baryon fractions with halo mass fractions and halo-matter cross-spectra extracted from DMO simulations to predict the power suppression to per cent level accuracy down to $k\, {{\approx }}\, {{10}}\, h\mathrm{\, Mpc^{-1}}$ without any free parameters.

How do baryonic effects on the cosmic matter distribution vary with scale and local density environment?

ABSTRACT In this study, we investigate how the baryonic effects vary with scale and local density environment mainly by utilizing a novel statistic, the environment-dependent wavelet power spectrum (env-WPS). With four state-of-the-art cosmological simulation suites, EAGLE (Evolution and Assembly of GaLaxies and their Environments), SIMBA, Illustris, and IllustrisTNG, we compare the env-WPS of the total matter density field between the hydrodynamic and dark matter-only runs at z = 0. We find that the clustering is most strongly suppressed in the emptiest environment of $\rho _\mathrm{m}/\bar{\rho }_\mathrm{m} \ \lt \ 0.1$ with maximum amplitudes ∼67–89 per cent on scales ∼1.86–10.96 hMpc−1, and less suppressed in higher density environments on small scales (except Illustris). In the environments of $\rho _\mathrm{m}/\bar{\rho }_\mathrm{m}\geqslant 0.316$ (≥10 in EAGLE), the feedbacks also lead to enhancement features at intermediate and large scales, which is most pronounced in the densest environment of $\rho _\mathrm{m}/\bar{\rho }_\mathrm{m}\geqslant 100$ and reaches a maximum ∼7–15 per cent on scales ∼0.87–2.62 hMpc−1 (except Illustris). The baryon fraction of the local environment decreases with increasing density, denoting the feedback strength, and potentially explaining some differences between simulations. We also measure the volume and mass fractions of local environments, which are affected by ≳1 per cent due to baryon physics. In conclusion, our results show that the baryonic processes can strongly modify the overall cosmic structure on the scales of k &amp;gt; 0.1 hMpc−1, which encourages further research in this direction.

A full reconstruction of two galaxy clusters intra-cluster medium with strong gravitational lensing

ABSTRACT Whilst X-rays and Sunyaev–Zel’dovich observations allow to study the properties of the intra-cluster medium (ICM) of galaxy clusters, their gravitational potential may be constrained using strong gravitational lensing. Although being physically related, these two components are often described with different physical models. Here, we present a unified technique to derive the ICM properties from strong lensing for clusters in hydrostatic equilibrium. In order to derive this model, we present a new universal and self-similar polytropic temperature profile, which we fit using the X-COP sample of clusters. We subsequently derive an analytical model for the electron density, which we apply to strong lensing clusters MACS J0242.5-2132 and MACS J0949.8+1708. We confront the inferred ICM reconstructions to XMM-Newton and ACT observations. We contrast our analytical electron density reconstructions with the best canonical β-model. The ICM reconstructions obtained prove to be compatible with observations. However they appear to be very sensitive to various dark matter halo parameters constrained through strong lensing (such as the core radius), and to the halo scale radius (fixed in the lensing optimizations). With respect to the important baryonic effects, we make the sensitivity on the scale radius of the reconstruction an asset, and use the inferred potential to constrain the dark matter density profile using ICM observations. The technique here developed should allow to take a new, and more holistic path to constrain the content of galaxy clusters.

Hyperon polarization in heavy ion collisions at STAR

In these proceedings, we present the measurements of global polarization for Λ, ¯Λ with the high-statistics data collected by the STAR experiment for isobar (Ru+Ru, Zr+Zr) collisions at √SNN = 200 GeV and Au+Au collisions at √SNN = 19.6, 27 GeV. These measurements allow us to study possible magnetic field driven effects through the polarization difference between Λ and ¯Λ and system size dependence of global polarization. Furthermore, we present the first measurements of Λ, ¯Λ hyperon local polarization in isobar collisions at √SNN = 200 GeV and Au+Au collisions at √SNN = 19.6, 27 GeV. Comparisons with previous measurements in Au+Au and Pb+Pb collisions at RHIC and LHC provide important insights into the collision system size and energy dependence of the vorticities. The local polarization measurements at lower beam energies can probe the predicted baryonic spin hall effect in a dense baryonic environment in heavy-ion collisions.

Not all subhaloes are created equal: modelling the diversity of subhalo density profiles in TNG50

ABSTRACT In this work, we analyse the density profiles of subhaloes with masses Msh ≥ 1.4 × 108 M⊙ in the TNG50 simulation, with the aim of including baryonic effects. We evaluate the performance of frequently used models, such as the standard Navarro–Frenk–White (NFW), the Einasto, and a smoothly truncated version of the NFW profile. We find that these models do not perform well for the majority of subhaloes, with the NFW profile giving the worst fit in most cases. This is primarily due to mismatches in the inner and outer logarithmic slopes, which are significantly steeper for a large number of subhaloes in the presence of baryons. To address this issue, we propose new three-parameter models and show that they significantly improve the goodness of fit independently of the subhalo’s specific properties. Our best-performing model is a modified version of the NFW profile with an inner log-slope of −2 and a variable truncation that is sharper and steeper than the slope transition in the standard NFW profile. Additionally, we investigate how both the parameter values of the best density profile model and the average density profiles vary with subhalo mass, Vmax, distance from the host halo centre, baryon content, and infall time, and we also present explicit scaling relations for the mean parameters of the individual profiles. The newly proposed fit and the scaling relations are useful to predict the properties of realistic subhaloes in the mass range 108 M⊙ ≤Msh ≤ 1013 M⊙ that can be influenced by the presence of baryons.

The CAMELS Project: Expanding the Galaxy Formation Model Space with New ASTRID and 28-parameter TNG and SIMBA Suites

We present CAMELS-ASTRID, the third suite of hydrodynamical simulations in the Cosmology and Astrophysics with MachinE Learning (CAMELS) project, along with new simulation sets that extend the model parameter space based on the previous frameworks of CAMELS-TNG and CAMELS-SIMBA, to provide broader training sets and testing grounds for machine-learning algorithms designed for cosmological studies. CAMELS-ASTRID employs the galaxy formation model following the ASTRID simulation and contains 2124 hydrodynamic simulation runs that vary three cosmological parameters (Ω m , σ 8, Ω b ) and four parameters controlling stellar and active galactic nucleus (AGN) feedback. Compared to the existing TNG and SIMBA simulation suites in CAMELS, the fiducial model of ASTRID features the mildest AGN feedback and predicts the least baryonic effect on the matter power spectrum. The training set of ASTRID covers a broader variation in the galaxy populations and the baryonic impact on the matter power spectrum compared to its TNG and SIMBA counterparts, which can make machine-learning models trained on the ASTRID suite exhibit better extrapolation performance when tested on other hydrodynamic simulation sets. We also introduce extension simulation sets in CAMELS that widely explore 28 parameters in the TNG and SIMBA models, demonstrating the enormity of the overall galaxy formation model parameter space and the complex nonlinear interplay between cosmology and astrophysical processes. With the new simulation suites, we show that building robust machine-learning models favors training and testing on the largest possible diversity of galaxy formation models. We also demonstrate that it is possible to train accurate neural networks to infer cosmological parameters using the high-dimensional TNG-SB28 simulation set.

The FLAMINGO project: revisiting the S8 tension and the role of baryonic physics

ABSTRACT A number of recent studies have found evidence for a tension between observations of large-scale structure (LSS) and the predictions of the standard model of cosmology with the cosmological parameters fit to the cosmic microwave background (CMB). The origin of this ‘S8 tension’ remains unclear, but possibilities include new physics beyond the standard model, unaccounted for systematic errors in the observational measurements and/or uncertainties in the role that baryons play. Here, we carefully examine the latter possibility using the new FLAMINGO suite of large-volume cosmological hydrodynamical simulations. We project the simulations onto observable harmonic space and compare with observational measurements of the power and cross-power spectra of cosmic shear, CMB lensing, and the thermal Sunyaev-Zel’dovich (tSZ) effect. We explore the dependence of the predictions on box size and resolution and cosmological parameters, including the neutrino mass, and the efficiency and nature of baryonic ‘feedback’. Despite the wide range of astrophysical behaviours simulated, we find that baryonic effects are not sufficiently large to remove the S8 tension. Consistent with recent studies, we find the CMB lensing power spectrum is in excellent agreement with the standard model, while the cosmic shear power spectrum, tSZ effect power spectrum, and the cross-spectra between shear, CMB lensing, and the tSZ effect are all in varying degrees of tension with the CMB-specified standard model. These results suggest that some mechanism is required to slow the growth of fluctuations at late times and/or on non-linear scales, but that it is unlikely that baryon physics is driving this modification.