Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996mnras.279.1303l&link_type=abstract
Monthly Notices of the Royal Astronomical Society, vol. 279, p. 1303
Astronomy and Astrophysics
Astronomy
Cosmology: Theory, Dark Matter, Large-Scale Structure Of Universe
Scientific paper
Previous studies have shown that the bulk velocity of a sample of elliptical galaxies nearer than 60 h^-1^ Mpc is observed to be high (599 km s^-1^ ), whereas the velocity of a shell of galaxies at a distance ~30 h^-1^ Mpc is much smaller, 224 km s^-1^, and consistent with shot noise only. We investigate the significance of the small ratio of these velocities in the context of Gaussian fluctuation theories for galaxy formation. We find that the shell and bulk velocities are significantly correlated for plausible power spectra, and the possibility of such a large discrepancy between them is small (~1.5 per cent). However, the probability rises to about 14 per cent since the shell at 30 h^-1^ Mpc is the most extreme of a sample of ten, and we conclude that the small ratio itself does not present a serious problem for the standard model of galaxy formation from gravitational instability of Gaussian fluctuations. We also investigate the joint distribution of the shell speed and bulk speed, as this allows us to put constraints on the density parameter of the Universe. Using the power spectrum of IRAS-selected galaxies as a (possibly biased) indicator of the underlying mass power spectrum, we find acceptable solutions provided that {OMEGA}_0_^0.6^/b ~> 1, where b is the IRAS bias parameter.
Heavens Alan F.
Loke Hung Yean
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