357 research outputs found
Mass Estimates of X-Ray Clusters
We use cosmological gas dynamic simulations to investigate the accuracy of
galaxy cluster mass estimates based on X-ray observations. The experiments
follow the formation of clusters in different cosmological models and include
the effects of gravity, pressure gradients, and hydrodynamical shocks. A subset
of our ensemble also allows for feedback of mass and energy from galactic winds
into the intracluster medium. We find that mass estimates based on the
hydrostatic, isothermal beta-model are remarkably accurate when evaluated at
radii where the cluster mean density is between 500-2500 times the critical
density. Applied to 174 artificial ROSAT images constructed from the
simulations, the distribution of the estimated-to-true mass ratio is nearly
unbiased and has a standard deviation of 14-29%. The scatter can be
considerably reduced (to 8-15%) by using an alternative mass estimator that
exploits the tightness of the mass-temperature relation found in the
simulations. The improvement over beta-model estimates is due to the
elimination of the variance contributed by the gas outer slope parameter. We
discuss these findings and their implications for recent measurements of
cluster baryon fractions.Comment: TeX, 24p; 11 Postscript figs. Submitted to the Astrophysical Journa
Weak Gravitational Lensing and Cluster Mass Estimates
Hierarchical theories of structure formation predict that clusters of
galaxies should be embedded in a web like structure, with filaments emanating
from them to large distances. The amount of mass contained within such
filaments near a cluster can be comparable to the collapsed mass of the cluster
itself. Diffuse infalling material also contains a large amount of mass. Both
these components can contribute to the cluster weak lensing signal. This
``projection bias'' is maximized if a filament lies close to the line-of-sight
to a cluster. Using large--scale numerical simulations of structure formation
in a cosmological constant dominated cold dark matter model, we show that the
projected mass typically exceeds the actual mass by several tens of percent.
This effect is significant for attempts to estimate cluster masses through weak
lensing observations, and will affect weak lensing surveys aimed at
constructing the cluster mass function.Comment: 4 pages, 3 figures. LaTeX2e, uses emulateapj.sty and onecolfloat.sty.
To be submitted to the Astrophysical Journal Letter
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