ABSTRACT
As progenitors of the most massive objects, protoclusters are key to tracing the evolution and star formation history of the Universe, and are responsible for ${\gtrsim }\, 20$ per cent of ...the cosmic star formation at $z\, {\gt }\, 2$. Using a combination of state-of-the-art hydrodynamical simulations and empirical models, we show that current galaxy formation models do not produce enough star formation in protoclusters to match observations. We find that the star formation rates (SFRs) predicted from the models are an order of magnitude lower than what is seen in observations, despite the relatively good agreement found for their mass-accretion histories, specifically that they lie on an evolutionary path to become Coma-like clusters at $z\, {\simeq }\, 0$. Using a well-studied protocluster core at $z\, {=}\, 4.3$ as a test case, we find that star formation efficiency of protocluster galaxies is higher than predicted by the models. We show that a large part of the discrepancy can be attributed to a dependence of SFR on the numerical resolution of the simulations, with a roughly factor of 3 drop in SFR when the spatial resolution decreases by a factor of 4. We also present predictions up to $z\, {\simeq }\, 7$. Compared to lower redshifts, we find that centrals (the most massive member galaxies) are more distinct from the other galaxies, while protocluster galaxies are less distinct from field galaxies. All these results suggest that, as a rare and extreme population at high z, protoclusters can help constrain galaxy formation models tuned to match the average population at $z\, {\simeq }\, 0$.
ABSTRACT
By using deep observations of clusters of galaxies, it has been recently found that the projected stellar mass density closely follows the projected total (dark and baryonic) mass density ...within the innermost ∼140 kpc. In this work, we aim to test these observations using the Cluster-EAGLE simulations, comparing the projected densities inferred directly from the simulations. We compare the iso-density contours using the procedure of Montes & Trujillo, and find that the shape of the stellar mass distribution follows that of the total matter even more closely than observed, although their radial profiles differ substantially. The ratio between stellar and total matter density profiles in circular apertures shows a slope close to −1, with a small dependence on the cluster’s total mass. We propose an indirect method to calculate the halo mass and mass density profile from the radial profile of the intracluster stellar mass density.
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.
ABSTRACT
We use a set of 45 simulated clusters with a wide mass range (8 × 1013 < M500 M⊙ < 2 × 1015) to investigate the effect of varying hydrodynamics flavours on cluster mass estimates. The ...cluster zooms were simulated using the same cosmological models as the BAHAMAS and C-EAGLE projects, leading to differences in both the hydrodynamics solvers and the subgrid physics but still producing clusters that broadly match observations. At the same mass resolution as BAHAMAS, for the most massive clusters (M500 > 1015 M⊙), we find that changes in the smoothed particle hydrodynamics (SPH) method produce the greatest differences in the final halo, while the subgrid models dominate at lower mass. By calculating the mass of all of the clusters using different permutations of the pressure, temperature, and density profiles, created with either the true simulated data or mock spectroscopic data, we find that the spectroscopic temperature causes a bias in the hydrostatic mass estimates that increases with the mass of the cluster, regardless of the SPH flavour used. For the most massive clusters, the estimated mass of the cluster using spectroscopic density and temperature profiles is found to be as low as 50 per cent of the true mass compared to ∼90 per cent for low-mass clusters. When including a correction for non-thermal pressure, the spectroscopic hydrostatic mass estimates are less biased on average and the mass dependence of the bias is reduced, although the scatter in the measurements does increase.
ABSTRACT
The Sunyaev–Zeldovich (SZ) effect is a powerful tool in modern cosmology. With future observations promising ever improving SZ measurements, the relativistic corrections to the SZ signals ...from galaxy groups and clusters are increasingly relevant. As such, it is important to understand the differences between three temperature measures: (a) the average relativistic SZ (rSZ) temperature, (b) the mass-weighted temperature relevant for the thermal SZ (tSZ) effect, and (c) the X-ray spectroscopic temperature. In this work, we compare these cluster temperatures, as predicted by the Bahamas & Macsis, IllustrisTNG, Magneticum, and The Three Hundred Project simulations. Despite the wide range of simulation parameters, we find the SZ temperatures are consistent across the simulations. We estimate a $\simeq 10{{\ \rm per\ cent}}$ level correction from rSZ to clusters with Y ≃ 10−4 Mpc−2. Our analysis confirms a systematic offset between the three temperature measures; with the rSZ temperature $\simeq 20{{\ \rm per\ cent}}$ larger than the other measures, and diverging further at higher redshifts. We demonstrate that these measures depart from simple self-similar evolution and explore how they vary with the defined radius of haloes. We investigate how different feedback prescriptions and resolutions affect the observed temperatures, and discover the SZ temperatures are rather insensitive to these details. The agreement between simulations indicates an exciting avenue for observational and theoretical exploration, determining the extent of relativistic SZ corrections. We provide multiple simulation-based fits to the scaling relations for use in future SZ modelling.
ABSTRACT
We investigate the disruption of group and cluster satellite galaxies with total mass (dark matter plus baryons) above $10^{10}\, \mathrm{M}_\odot$ in the Hydrangea simulations, a suite of ...24 high-resolution cosmological hydrodynamical zoom-in simulations based on the EAGLE model. The simulations predict that ∼50 per cent of satellites survive to redshift $z$ = 0, with higher survival fractions in massive clusters than in groups and only small differences between baryonic and pure N-body simulations. For clusters, up to 90 per cent of galaxy disruption occurs in lower-mass subgroups (i.e. during pre-processing); 96 per cent of satellites in massive clusters that were accreted at $z$ < 2 and have not been pre-processed survive. Of those satellites that are disrupted, only a few per cent merge with other satellites, even in low-mass groups. The survival fraction changes rapidly from less than 10 per cent of those accreted at high $z$ to more than 90 per cent at low $z$. This shift, which reflects faster disruption of satellites accreted at higher $z$, happens at lower $z$ for more massive galaxies and those accreted on to less massive haloes. The disruption of satellite galaxies is found to correlate only weakly with their pre-accretion baryon content, star formation rate, and size, so that surviving galaxies are nearly unbiased in these properties. These results suggest that satellite disruption in massive haloes is uncommon, and that it is predominantly the result of gravitational rather than baryonic processes.
Abstract
We present the first simulated galaxy clusters (M200 > 1014 M⊙) with both self-interacting dark matter (SIDM) and baryonic physics. They exhibit a greater diversity in both dark matter and ...stellar density profiles than their counterparts in simulations with collisionless dark matter (CDM), which is generated by the complex interplay between dark matter self-interactions and baryonic physics. Despite variations in formation history, we demonstrate that analytical Jeans modelling predicts the SIDM density profiles remarkably well, and the diverse properties of the haloes can be understood in terms of their different final baryon distributions.
We have simulated the formation of a galaxy cluster in a Λ cold dark matter universe using 13 different codes modelling only gravity and non-radiative hydrodynamics (ramses, ART, arepo, hydra and ...nine incarnations of gadget). This range of codes includes particle-based, moving and fixed mesh codes as well as both Eulerian and Lagrangian fluid schemes. The various gadget implementations span classic and modern smoothed particle hydrodynamics (SPH) schemes. The goal of this comparison is to assess the reliability of cosmological hydrodynamical simulations of clusters in the simplest astrophysically relevant case, that in which the gas is assumed to be non-radiative. We compare images of the cluster at z = 0, global properties such as mass and radial profiles of various dynamical and thermodynamical quantities. The underlying gravitational framework can be aligned very accurately for all the codes allowing a detailed investigation of the differences that develop due to the various gas physics implementations employed. As expected, the mesh-based codes ramses, art and arepo form extended entropy cores in the gas with rising central gas temperatures. Those codes employing classic SPH schemes show falling entropy profiles all the way into the very centre with correspondingly rising density profiles and central temperature inversions. We show that methods with modern SPH schemes that allow entropy mixing span the range between these two extremes and the latest SPH variants produce gas entropy profiles that are essentially indistinguishable from those obtained with grid-based methods.
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