Deviations from the fundamental plane of early-type galaxies and large-scale cluster motions

Details Deviations from the fundamental plane of early-type galaxies and large-scale cluster motions Deviations from the fundamental plane of early-type galaxies and large-scale cluster motions

Nov 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002phdt........14g&link_type=abstract

Thesis (PhD). UNIVERSITY OF MARYLAND COLLEGE PARK, Source DAI-B 64/01, p. 248, Jul 2003, 227 pages.

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Scientific paper

We fit the fundamental plane, FP, to over 400 early-type galaxies in 20 nearby clusters with cz ˜ 4000 11000 km s -1 using our own photometry and spectroscopy its well as measurements culled from the literature. We find that the duality-of- fit, rms(log σ), to the average fundamental plane, , varies substantially among these clusters. A statistically significant gap in the distribution of rms(log σ) separates the clusters with which fit well from those that do not. The average redshift, of the sample is 7200 km s-1 and the mean redshifts of the two subsamples are 6700 and 8000 km s -1 respectively. Both samples show a mean peculiar velocity of zero, within their errors. However, the 9 high-rms clusters exhibit a significantly higher scatter in their peculiar velocities compared to the other 11 clusters. Assuming early-type galaxies in clusters are drawn from a single underlying population, there should be no correlation between the scatter in peculiar velocity and rms(log σ). The source of the high values of rms(log σ) in this subset of clusters is not entirely known, but these clusters tend to have a problematic combination of intrinsic properties indicative of the presence of substructure, which could potentially bias the measured peculiar velocities. On the other hand, we find that all X-ray bright clusters in our sample fit the well. The evidence suggests that all-sky surveys which mix together both classes of clusters, as characterized by rms(log σ), may artificially inject signal into the observed peculiar velocity field. We therefore suggest using cluster X-ray luminosity or FP scatter to preselect clusters to derive relative distances via the FP. When such a pre-filter is applied to our sample a relatively quiescent Hubble flow is revealed and we are able to rule out some large bulk flows reported by other authors. The resulting subset of clusters exclude the Lauer & Postman (1994) and Willick (1999) frames as the natural rest frame of the local universe and disagree with the Hudson et al. (1999) result at the 97% level. Finally, if the low FP scatter clusters, which includes the most massive, better trace the underlying mass distribution, their random motions imply W0.60 σ8 < 0.43, a value which agrees with most recent measurements made via independent methods.

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