Characterizing hydrostatic mass bias with mock-X Barnes, David J; Vogelsberger, Mark; Pearce, Francesca A ...
Monthly notices of the Royal Astronomical Society,
09/2021, Letnik:
506, Številka:
2
Journal Article
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ABSTRACT
Surveys in the next decade will deliver large samples of galaxy clusters that transform our understanding of their formation. Cluster astrophysics and cosmology studies will become ...systematics limited with samples of this magnitude. With known properties, hydrodynamical simulations of clusters provide a vital resource for investigating potential systematics. However, this is only realized if we compare simulations to observations in the correct way. Here we introduce the mock-X analysis framework, a multiwavelength tool that generates synthetic images from cosmological simulations and derives halo properties via observational methods. We detail our methods for generating optical, Compton-y and X-ray images. Outlining our synthetic X-ray image analysis method, we demonstrate the capabilities of the framework by exploring hydrostatic mass bias for the IllustrisTNG, BAHAMAS, and MACSIS simulations. Using simulation derived profiles we find an approximately constant bias b ≈ 0.13 with cluster mass, independent of hydrodynamical method, or subgrid physics. However, the hydrostatic bias derived from synthetic observations is mass-dependent, increasing to b = 0.3 for the most massive clusters. This result is driven by a single temperature fit to a spectrum produced by gas with a wide temperature distribution in quasi-pressure equilibrium. The spectroscopic temperature and mass estimate are biased low by cooler gas dominating the emission, due to its quadratic density dependence. The bias and the scatter in estimated mass remain independent of the numerical method and subgrid physics. Our results are consistent with current observations and future surveys will contain sufficient samples of massive clusters to confirm the mass dependence of the hydrostatic bias.
Recent results by the Planck Collaboration have shown that cosmological parameters derived from the cosmic microwave background anisotropies and cluster number counts are in tension, with the latter ...preferring lower values of the matter density parameter, Ωm, and power spectrum amplitude, σ8. Motivated by this, we investigate the extent to which the tension may be ameliorated once the effect of baryonic depletion on the cluster mass function is taken into account. We use the large-volume Millennium Gas simulations in our study, including one where the gas is pre-heated at high redshift and one where the gas is heated by stars and active galactic nuclei (in the latter, the self-gravity of the baryons and radiative cooling are omitted). In both cases, the cluster baryon fractions are in reasonably good agreement with the data at low redshift, showing significant depletion of baryons with respect to the cosmic mean. As a result, it is found that the cluster abundance in these simulations is around 15 per cent lower than the commonly adopted fit to dark matter simulations by Tinker et al. for the mass range 1014-1014.5 h
−1 M. Ignoring this effect produces a significant artificial shift in cosmological parameters which can be expressed as Δσ8(Ωm/0.27)0.38 −0.03 at z = 0.17 (the median redshift of the Planck cluster sample) for the feedback model. While this shift is not sufficient to fully explain the Planck discrepancy, it is clear that such an effect cannot be ignored in future precision measurements of cosmological parameters with clusters. Finally, we outline a simple, model-independent procedure that attempts to correct for the effect of baryonic depletion and show that it works if the baryon-dark matter back-reaction is negligible.
ABSTRACT
Recent high-resolution cosmological hydrodynamic simulations run with a variety of codes systematically predict large amounts of entropy in the intra-cluster medium at low redshift, leading ...to flat entropy profiles and a suppressed cool-core population. This prediction is at odds with X-ray observations of groups and clusters. We use a new implementation of the EAGLE galaxy formation model to investigate the sensitivity of the central entropy and the shape of the profiles to changes in the sub-grid model applied to a suite of zoom-in cosmological simulations of a group of mass M500 = 8.8 × 1012 M⊙ and a cluster of mass 2.9 × 1014 M⊙. Using our reference model, calibrated to match the stellar mass function of field galaxies, we confirm that our simulated groups and clusters contain hot gas with too high entropy in their cores. Additional simulations run without artificial conduction, metal cooling or active galactic nuclei (AGN) feedback produce lower entropy levels but still fail to reproduce observed profiles. Conversely, the two objects run without supernova feedback show a significant entropy increase which can be attributed to excessive cooling and star formation. Varying the AGN heating temperature does not greatly affect the profile shape, but only the overall normalization. Finally, we compared runs with four AGN heating schemes and obtained similar profiles, with the exception of bipolar AGN heating, which produces a higher and more uniform entropy distribution. Our study leaves open the question of whether the entropy core problem in simulations, and particularly the lack of power-law cool-core profiles, arise from incorrect physical assumptions, missing physical processes, or insufficient numerical resolution.
ABSTRACT
We determine the inner density profiles of massive galaxy clusters (M200 > 5 × 1014 M⊙) in the Cluster-EAGLE (C-EAGLE) hydrodynamic simulations, and investigate whether the dark matter ...density profiles can be correctly estimated from a combination of mock stellar kinematical and gravitational lensing data. From fitting mock stellar kinematics and lensing data generated from the simulations, we find that the inner density slopes of both the total and the dark matter mass distributions can be inferred reasonably well. We compare the density slopes of C-EAGLE clusters with those derived by Newman et al. for seven massive galaxy clusters in the local Universe. We find that the asymptotic best-fitting inner slopes of ‘generalized’ Navarro–Frenk–White (gNFW) profiles, γgNFW, of the dark matter haloes of the C-EAGLE clusters are significantly steeper than those inferred by Newman et al. However, the mean mass-weighted dark matter density slopes of the simulated clusters are in good agreement with the Newman et al. estimates. We also find that the estimate of γgNFW is very sensitive to the constraints from weak lensing measurements in the outer parts of the cluster and a bias can lead to an underestimate of γgNFW.
ABSTRACT
We examine the outskirts of galaxy clusters in the C-EAGLE simulations to quantify the ‘edges’ of the stellar and dark matter distribution. The radius of the steepest slope in the dark ...matter, commonly used as a proxy for the splashback radius, is located at $\sim \, r_{200 \rm m}$; the strength and location of this feature depends on the recent mass accretion rate, in good agreement with previous work. Interestingly, the stellar distribution (or intracluster light, ICL) also has a well-defined edge, which is directly related to the splashback radius of the halo. Thus, detecting the edge of the ICL can provide an independent measure of the physical boundary of the halo, and the recent mass accretion rate. We show that these caustics can also be seen in the projected density profiles, but care must be taken to account for the influence of substructures and other non-diffuse material, which can bias and/or weaken the signal of the steepest slope. This is particularly important for the stellar material, which has a higher fraction bound in subhaloes than the dark matter. Finally, we show that the ‘stellar splashback’ feature is located beyond current observational constraints on the ICL, but these large projected distances (≫1 Mpc) and low surface brightnesses (μ ≫ 32 mag arcsec−2) can be reached with upcoming observational facilities such as the Vera C. Rubin Observatory, the Nancy Grace Roman Space Telescope, and Euclid.
Building on the initial results of the nIFTy simulated galaxy cluster comparison, we compare and contrast the impact of baryonic physics with a single massive galaxy cluster, run with 11 ...state-of-the-art codes, spanning adaptive mesh, moving mesh, classic and modern smoothed particle hydrodynamics (SPH) approaches. For each code represented we have a dark-matter-only (DM) and non-radiative (NR) version of the cluster, as well as a full physics (FP) version for a subset of the codes. We compare both radial mass and kinematic profiles, as well as global measures of the cluster (e.g. concentration, spin, shape), in the NR and FP runs with that in the DM runs. Our analysis reveals good consistency ⪅20 per cent) between global properties of the cluster predicted by different codes when integrated quantities are measured within the virial radius R
200. However, we see larger differences for quantities within R
2500, especially in the FP runs. The radial profiles reveal a diversity, especially in the cluster centre, between the NR runs, which can be understood straightforwardly from the division of codes into classic SPH and non-classic SPH (including the modern SPH, adaptive and moving mesh codes); and between the FP runs, which can also be understood broadly from the division of codes into those that include active galactic nucleus feedback and those that do not. The variation with respect to the median is much larger in the FP runs with different baryonic physics prescriptions than in the NR runs with different hydrodynamics solvers.
We present the first results of hydrodynamical simulations that follow the formation of galaxies to the present day in nearly spherical regions of radius ∼20 h−1 Mpc drawn from the Millennium ...Simulation (Springel et al.). The regions have mean overdensities that deviate by (−2, −1, 0, +1, +2)σ from the cosmic mean, where σ is the rms mass fluctuation on a scale of ∼20 h−1 Mpc at z= 1.5. The simulations have mass resolution of up to ∼106 h−1 M⊙, cover the entire range of large-scale cosmological environments, including rare objects such as massive clusters and sparse voids, and allow extrapolation of statistics to the (500 h−1 Mpc)3 Millennium Simulation volume as a whole. They include gas cooling, photoheating from an imposed ionizing background, supernova feedback and galactic winds, but no AGN. In this paper, we focus on the star formation properties of the model. We find that the specific star formation rate density at z≲ 10 varies systematically from region to region by up to an order of magnitude, but the global value, averaged over all volumes, closely reproduces observational data. Massive, compact galaxies, similar to those observed in the GOODS fields (Wiklind et al.), form in the overdense regions as early as z= 6, but do not appear in the underdense regions until z∼ 3. These environmental variations are not caused by a dependence of the star formation properties on environment, but rather by a strong variation of the halo mass function from one environment to another, with more massive haloes forming preferentially in the denser regions. At all epochs, stars form most efficiently in haloes of circular velocity vc∼ 250 km s−1. However, the star formation history exhibits a form of ‘downsizing’ (even in the absence of AGN feedback): the stars comprising massive galaxies at z= 0 have mostly formed by z= 1−2, whilst those comprising smaller galaxies typically form at later times. However, additional feedback is required to limit star formation in massive galaxies at late times.
Recent identification of intestinal epithelial stem cell (ISC) markers and development of ISC reporter mice permit visualization and isolation of regenerating ISCs after radiation to define their ...functional and molecular phenotypes. Previous studies in uninjured intestine of Sox9-EGFP reporter mice demonstrate that ISCs express low levels of Sox9-EGFP (Sox9-EGFP Low), whereas enteroendocrine cells (EEC) express high levels of Sox9-EGFP (Sox9-EGFP High). We hypothesized that Sox9-EGFP Low ISCs would expand after radiation, exhibit enhanced proliferative capacities, and adopt a distinct gene expression profile associated with rapid proliferation. Sox9-EGFP mice were given 14 Gy abdominal radiation and studied between days 3 and 9 postradiation. Radiation-induced changes in number, growth, and transcriptome of the different Sox9-EGFP cell populations were determined by histology, flow cytometry, in vitro culture assays, and microarray. Microarray confirmed that nonirradiated Sox9-EGFP Low cells are enriched for Lgr5 mRNA and mRNAs enriched in Lgr5-ISCs and identified additional putative ISC markers. Sox9-EGFP High cells were enriched for EEC markers, as well as Bmi1 and Hopx, which are putative markers of quiescent ISCs. Irradiation caused complete crypt loss, followed by expansion and hyperproliferation of Sox9-EGFP Low cells. From nonirradiated intestine, only Sox9-EGFP Low cells exhibited ISC characteristics of forming organoids in culture, whereas during regeneration both Sox9-EGFP Low and High cells formed organoids. Microarray demonstrated that regenerating Sox9-EGFP High cells exhibited transcriptomic changes linked to p53-signaling and ISC-like functions including DNA repair and reduced oxidative metabolism. These findings support a model in which Sox9-EGFP Low cells represent active ISCs, Sox9-EGFP High cells contain radiation-activatable cells with ISC characteristics, and both participate in crypt regeneration.
ABSTRACT
The splashback radius, coinciding with the minimum in the dark matter radial density gradient, is thought to be a universal definition of the edge of a dark matter halo. Observational ...methods to detect it have traced the dark matter using weak gravitational lensing or galaxy number counts. Recent attempts have also claimed the detection of a similar feature in Sunyaev–Zel’dovich (SZ) observations of the hot intracluster gas. Here, we use the FLAMINGO simulations to investigate whether an extremum gradient in a similar position to the splashback radius is predicted to occur in the cluster gas profiles. We find that the minimum in the gradient of the stacked 3D gas density and pressure profiles, and the maximum in the gradient of the entropy profile, broadly align with the splashback feature though there are significant differences. While the dark matter splashback radius varies with specific mass accretion rate, in agreement with previous work, the radial position of the deepest minimum in the log-slope of the gas density is more sensitive to halo mass. In addition, we show that a similar minimum is also present in projected 2D pseudo-observable profiles: emission measure (X-ray), Compton-y (SZ), and surface mass density (weak lensing). We find that the latter traces the dark matter results reasonably well albeit the minimum occurs at a slightly smaller radius. While results for the gas profiles are largely insensitive to accretion rate and various observable proxies for dynamical state, they do depend on the strength of the feedback processes.
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