Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009mnras.398..971m&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 398, Issue 2, pp. 971-984.
Astronomy and Astrophysics
Astronomy
Galaxies: Clusters: General, Large-Scale Structure Of Universe
Scientific paper
Prompted by indications from quasi-stellar object (QSO) lensing that there may be more mass associated with galaxy groups than expected from virial analyses, we have made new dynamical infall estimates of the masses associated with 2dFGRS (2dF Galaxy Redshift Survey) Percolation-Inferred Galaxy Group (2PIGG) groups and clusters. We have analysed the redshift distortions in the cluster-galaxy cross-correlation function as a function of cluster membership, cross-correlating z < 0.12 2PIGG clusters and groups with the full 2dF galaxy catalogue. We have made estimates of the dynamical infall parameter , where b is the galaxy bias parameter and new estimates of the group velocity dispersions for group membership classes out to z < 0.12. We first find that, out to ~20h-1Mpc, the amplitude of the full three-dimensional redshift-space cross-correlation function, ξcg, rises monotonically with group membership. We use a simple linear-theory infall model together with a Gaussian velocity dispersion to fit ξ(σ, π) in the range 5 < s < 25h-1Mpc. We find that in joint fits with the velocity dispersion, β shows a minimum at intermediate group membership n ~ 20 or L ~ 2 × 1011h-2Lsolar. However, with similar fits, the mocks also show a systematic shift between the location of the β minimum and the mass-to-light ratio (M/L) minimum at L ~ 1010h-2Lsolar as initially input. We find improved agreement with the mock when we fix the velocity dispersions to the Eke et al. values in the β fits, tracking the form of the M/L minimum an order of magnitude lower in L. These β estimates also seem to reproduce the mock results better than M/L estimates based on either the fitted or average velocity dispersions and almost as well as the estimates based on median velocity dispersions. With this approach, the β values for the data then appear to track the mock in the range L ~ 1010-1011h-2Lsolar, but then may rise slightly more slowly away from the minimum in the range L ~ 1011-1012h-2Lsolar. Finally, the velocity dispersion degeneracy in fitting β means that the issue of the high group masses implied from QSO lensing currently remains unresolved from these dynamical analyses.
Mountrichas Georgios
Sawangwit Utane
Shanks Tom
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