5 research outputs found
Gas clumping and its effect on hydrostatic bias in the MACSIS simulations
We use the MACSIS hydrodynamical simulations to estimate the extent of gas
clumping in the intracluster medium of massive galaxy clusters and how it
affects the hydrostatic mass bias. By comparing the clumping to the azimuthal
scatter in the emission measure, an observational proxy, we find that they both
increase with radius and are larger in higher-mass and dynamically perturbed
systems. Similar trends are also seen for the azimuthal temperature scatter and
non-thermal pressure fraction, both of which correlate with density
fluctuations, with these values also increasing with redshift. However, in
agreement with recent work, we find only a weak correlation between the
clumping, or its proxies, and the hydrostatic mass bias. To reduce the effect
of clumping in the projected profiles, we compute the azimuthal median
following recent observational studies, and find this reduces the scatter in
the bias. We also attempt to correct the cluster masses by using a non-thermal
pressure term and find over-corrected mass estimates ( to )
from 3D gas profiles but improved mass estimates ( to )
from projected gas profiles. We conclude that the cluster-averaged mass bias is
minimised from applying a non-thermal pressure correction () with
more modest reductions from selecting clusters that have low clumping
() or are dynamically relaxed (). However, the latter
selection is most effective at minimising the scatter for individual objects.
Such results can be tested with next generation X-ray missions equipped with
high-resolution spectrometers such as Athena.Comment: 13 pages, 10 figures, submitted to MNRA
Galaxy cluster rotation revealed in the MACSIS simulations with the kinetic Sunyaev-Zeldovich effect
The kinetic Sunyaev-Zeldovich (kSZ) effect has now become a clear target for
ongoing and future studies of the cosmic microwave background (CMB) and
cosmology. Aside from the bulk cluster motion, internal motions also lead to a
kSZ signal. In this work, we study the rotational kSZ effect caused by coherent
large-scale motions of the cluster medium using cluster hydrodynamic
cosmological simulations. To utilise the rotational kSZ as a cosmological
probe, simulations offer some of the most comprehensive data sets that can
inform the modeling of this signal. In this work, we use the MACSIS data set to
specifically investigate the rotational kSZ effect in massive clusters. Based
on these models, we test stacking approaches and estimate the amplitude of the
combined signal with varying mass, dynamical state, redshift and map-alignment
geometry. We find that the dark matter, galaxy and gas spins are generally
misaligned, an effect that can cause a sub-optimal estimation of the rotational
kSZ effect when based on galaxy catalogues. Furthermore, we provide
halo-spin-mass scaling relations that can be used to build a statistical model
of the rotational kSZ. The rotational kSZ contribution, which is largest in
massive unrelaxed clusters (100 K), could be relevant to studies
of higher-order CMB temperature signals, such as the moving lens effect. The
limited mass range of the MACSIS sample strongly motivates an extended
investigation of the rotational kSZ effect in large-volume simulations to
refine the modelling, particularly towards lower mass and higher redshift, and
provide forecasts for upcoming cosmological CMB experiments (e.g. Simons
Observatory, SKA-2) and X-ray observations (e.g. \textit{Athena}/X-IFU).Comment: Submitted to Monthly Notices of the Royal Astronomical Society.
Comments and discussions are welcome. Data and codes can be found at
https://github.com/edoaltamura/macsis-cosmosi
EAGLE-like simulation models do not solve the entropy core problem in groups and clusters of galaxies
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
Inferring the dark matter splashback radius from cluster gas and observable profiles in the FLAMINGO simulations.
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- (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
Inferring the dark matter splashback radius from cluster gas and observable profiles in the FLAMINGO simulations
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