VELOCITY ANISOTROPY AND SHAPE BIAS IN THE CAUSTIC TECHNIQUE
- Department of Astronomy, University of Michigan, 500 Church St., Ann Arbor, MI 48109 (United States)
We use the Millennium Simulation to quantify the statistical accuracy and precision of the escape-velocity technique for measuring cluster-sized halo masses at z {approx} 0.1. We show that in three dimensions one can measure nearly unbiased (<4%) halo masses (>1.5 Multiplication-Sign 10{sup 14} M{sub Sun} h {sup -1}) with 10%-15% scatter. Line-of-sight projection effects increase the scatter to {approx}25%, where we include the known velocity anisotropies. The classical ''caustic'' technique incorporates a calibration factor that is determined from N-body simulations. We derive and test a new implementation that eliminates the need for calibration and utilizes only the observables: the galaxy velocities with respect to the cluster mean v, the projected positions r{sub p} , an estimate of the Navarro-Frenk-White (NFW) density concentration, and an estimate of the velocity anisotropies {beta}. We find that differences between the potential and density NFW concentrations induce a 10% bias in the caustic masses. We also find that large (100%) systematic errors in the observed ensemble average velocity anisotropies and concentrations translate to small (5%-10%) biases in the inferred masses.
- OSTI ID:
- 22130672
- Journal Information:
- Astrophysical Journal Letters, Vol. 768, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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