17 research outputs found
SZE Observables, Pressure Profiles and Center Offsets in Magneticum Simulation Galaxy Clusters
We present a detailed study of the galaxy cluster thermal \ac{sze} signal
and pressure profiles using {\it Magneticum} Pathfinder hydrodynamical
simulations. With a sample of 50,000 galaxy clusters () out to , we find significant
variations in the shape of the pressure profile with mass and redshift and
present a new generalized NFW model that follows these trends. We show that the
thermal pressure at accounts for only 80~percent of the pressure
required to maintain hydrostatic equilibrium, and therefore even idealized
hydrostatic mass estimates would be biased at the 20~percent level. We compare
the cluster \ac{sze} signal extracted from a sphere with different virial-like
radii, a virial cylinder within a narrow redshift slice and the full light
cone, confirming small scatter () in the sphere and
showing that structure immediately surrounding clusters increases the scatter
and strengthens non self-similar redshift evolution in the cylinder.
Uncorrelated large scale structure along the line of sight leads to an increase
in the \ac{sze} signal and scatter that is more pronounced for low mass
clusters, resulting in non self-similar trends in both mass and redshift and a
mass dependent scatter that is at low masses. The scatter
distribution is consistent with log-normal in all cases. We present a model of
the offsets between the center of the gravitational potential and the \ac{sze}
center that follows the variations with cluster mass and redshift.Comment: 20 pages, 15 figures, submitted to MNRA
Toward Unbiased Galaxy Cluster Masses from Line of Sight Velocity Dispersions
We study the use of red sequence selected galaxy spectroscopy for unbiased
estimation of galaxy cluster masses. We use the publicly available galaxy
catalog produced using the semi-analytic model of De Lucia & Blaizot (2007) on
the Millenium Simulation (Springel et al. 2005). We explore the impacts on
selection using galaxy color, projected separation from the cluster center, and
galaxy luminosity. We study the relationship between cluster mass and velocity
dispersion and identify and characterize the following sources of bias and
scatter: halo triaxiality, dynamical friction of red luminous galaxies and
interlopers. We show that due to halo triaxiality the intrinsic scatter of
estimated line of sight dynamical mass is about three times larger (30-40%)
than the one estimated using the 3D velocity dispersion (~12%) and a small bias
(~1%) is induced. We find evidence of increasing scatter as a function of
redshift and provide a fitting formula to account for it. We characterize the
amount of bias and scatter introduced by dynamical friction when using
subsamples of red-luminous galaxies to estimate the velocity dispersion. We
study the presence of interlopers in spectroscopic samples and their effect on
the estimated cluster dynamical mass. Our results show that while cluster
velocity dispersions extracted from a few dozen red sequence selected galaxies
do not provide precise masses on a single cluster basis, an ensemble of cluster
velocity dispersions can be combined to produce a precise calibration of a
cluster survey mass observable relation. Currently, disagreements in the
literature on simulated subhalo velocity dispersion mass relations place a
systematic floor on velocity dispersion mass calibration at the 15% level in
mass. We show that the selection related uncertainties are small by comparison,
providing hope that with further improvements this systematic floor can be
reduced.Comment: submitted to Ap
Velocity Segregation and Systematic Biases In Velocity Dispersion Estimates With the SPT-GMOS Spectroscopic Survey
The velocity distribution of galaxies in clusters is not universal; rather,
galaxies are segregated according to their spectral type and relative
luminosity. We examine the velocity distributions of different populations of
galaxies within 89 Sunyaev Zel'dovich (SZ) selected galaxy clusters spanning . Our sample is primarily draw from the SPT-GMOS spectroscopic
survey, supplemented by additional published spectroscopy, resulting in a final
spectroscopic sample of 4148 galaxy spectra---2868 cluster members. The
velocity dispersion of star-forming cluster galaxies is % greater than
that of passive cluster galaxies, and the velocity dispersion of bright () cluster galaxies is % lower than the velocity dispersion of
our total member population. We find good agreement with simulations regarding
the shape of the relationship between the measured velocity dispersion and the
fraction of passive vs. star-forming galaxies used to measure it, but we find a
small offset between this relationship as measured in data and simulations in
which suggests that our dispersions are systematically low by as much as 3\%
relative to simulations. We argue that this offset could be interpreted as a
measurement of the effective velocity bias that describes the ratio of our
observed velocity dispersions and the intrinsic velocity dispersion of dark
matter particles in a published simulation result. Measuring velocity bias in
this way suggests that large spectroscopic surveys can improve dispersion-based
mass-observable scaling relations for cosmology even in the face of velocity
biases, by quantifying and ultimately calibrating them out.Comment: Accepted to ApJ; 21 pages, 11 figures, 5 table
nIFTy galaxy cluster simulations - IV. Quantifying the influence of baryons on halo properties
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-matteronly
(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 R200. However, we see larger differences for quantities within R2500,
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
nIFTy galaxy cluster simulations – I. Dark matter and non-radiative models
We have simulated the formation of a galaxy cluster in a Ʌ 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
Cosmology dependence of galaxy cluster scaling relations
The abundance of galaxy clusters as a function of mass and redshift is a well known powerful cosmological probe, which relies on underlying modelling assumptions on the mass-observable relations (MOR). Some of the MOR parameters can be constrained directly from multi-wavelength observations, as the normalization at some reference cosmology, the mass-slope, the redshift evolution, and the intrinsic scatter. However, the cosmology dependence of MORs cannot be tested with multi-wavelength observations alone. We use magnet i cum simulations to explore the cosmology dependence of galaxy cluster scaling relations. We run fifteen hydrodynamical cosmological simulations varying Omega(m), Omega(b), h(0), and sigma(8) (around a reference cosmological model). The MORs considered are gas mass, baryonic mass, gas temperature, Y and velocity dispersion as a function of virial mass. We verify that the mass and redshift slopes and the intrinsic scatter of the MORs are nearly independent of cosmology with variations significantly smaller than current observational uncertainties. We show that the gas mass and baryonic mass sensitively depends only on the baryon fraction, velocity dispersion, and gas temperature on h(0), and Y on both baryon fraction and h(0). We investigate the cosmological implications of our MOR parametrization on a mock catalogue created for an idealized eROSITA-like experiment. We show that our parametrization introduces a strong degeneracy between the cosmological parameters and the normalization of the MOR. Finally, the parameter constraints derived at different overdensity (Delta(500c)), for X-ray bolometric gas luminosity, and for different subgrid physics prescriptions are shown in the appendix
Halo mass function: Baryon impact, fitting formulae, and implications for cluster cosmology
We use a set of hydrodynamical and dark matter-only (DMonly) simulations to calibrate the halo mass function (HMF). We explore the impact of baryons, propose an improved parametrization for spherical overdensity masses, and identify differences between our DMonly HMF and previously published HMFs. We use the Magneticum simulations, which are well suited because of their accurate treatment of baryons, high resolution, and large cosmological volumes of up to (3818 Mpc)3. Baryonic effects globally decrease the masses of galaxy clusters, which, at a given mass, results in a decrease of their number density. This effect vanishes at high redshift z 3c 2 and for high masses M200 m 73 1014 M&09. We perform cosmological analyses of three idealized approximations to the cluster surveys by the South Pole Telescope (SPT), Planck, and eROSITA. We pursue two main questions. (1) What is the impact of baryons? - for the SPT-like and the Planck-like samples, the impact of baryons on cosmological results is negligible. In the eROSITA-like case, however, neglecting the baryonic impact leads to an underestimate of \u3a9m by about 0.01, which is comparable to the expected uncertainty from eROSITA. (2) How does our DMonly HMF compare with previous work? - for the Planck-like sample, results obtained using our DMonly HMF are shifted by 06(\u3c38) 43 06(\u3c38(\u3a9m/0.27)0.3) 43 0.02 with respect to results obtained using the Tinker et al. fit. This suggests that using our HMF would shift results from Planck clusters towards better agreement with cosmic-microwave-background anisotropy measurements. Finally, we discuss biases that can be introduced through inadequate HMF parametrizations that introduce false cosmological sensitivity