Measuring the escape velocity and mass profiles of galaxy clusters beyond their virial radius

作者：Serra Ana Laura^*; Diaferio Antonaldo; Murante Giuseppe; Borgani Stefano

来源：Monthly Notices of the Royal Astronomical Society, 2011, 412(2): 800-816.

DOI：10.1111/j.1365-2966.2010.17946.x

• gravitation
• galaxies: clusters: general
• techniques: miscellaneous
• cosmology: miscellaneous
• cosmology: dark matter
• cosmology: large-scale structure of Universe

The caustic technique uses galaxy redshifts alone to measure the escape velocity and mass profiles of galaxy clusters to clustrocentric distances well beyond the virial radius, where dynamical equilibrium does not necessarily hold. We provide a detailed description of this technique and analyse its possible systematic errors. We apply the caustic technique to clusters with mass M(200) >= 10(14)h(-1)M(circle dot) extracted from a cosmological hydrodynamic simulation of Lambda CDM universe. With a few tens of redshifts per squared comoving megaparsec within the cluster, the caustic technique, on average, recovers the profile of the escape velocity from the cluster with better than 10 percent accuracy up to r similar to 4r(200). The caustic technique also recovers the mass profile with better than 10 percent accuracy in the range (0.6 - 4)r(200), but it overestimates the mass up to 70 percent at smaller radii. This overestimate is a consequence of neglecting the radial dependence of the filling function F beta(r). The 1-sigma uncertainty on individual escape velocity profiles increases from similar to 20 to similar to 50 percent when the radius increases from r similar to 0.1r(200) to similar to 4r(200). Individual mass profiles have 1-sigma uncertainty between 40 and 80 percent within the radial range (0.6 - 4) r(200). When the correct virial mass is known, the 1-sigma uncertainty reduces to a constant 50 percent on the same radial range. We show that the amplitude of these uncertainties is completely due to the assumption of spherical symmetry, which is difficult to drop. Other potential refinements of the technique are not crucial. We conclude that, when applied to individual clusters, the caustic technique generally provides accurate escape velocity and mass profiles, although, in some cases, the deviation from the real profile can be substantial. Alternatively, we can apply the technique to synthetic clusters obtained by stacking individual clusters: in this case, the 1-sigma uncertainty on the escape velocity profile is smaller than 20 percent out to 4r(200). The caustic technique thus provides reliable average profiles which extend to regions difficult or impossible to probe with other techniques.

• 出版日期2011-4