Several studies have indicated that the local cosmic velocity field is rather
cold, in particular in the regions outside the massive, virialized clusters of
galaxies. If our local cosmic environment is taken to be a representative
volume of the Universe, the repercussion of this finding is that either we live
in a low-Ω Universe and/or that the galaxy distribution is a biased
reflection of the underlying mass distribution. Otherwise, the pronounced
nature of the observed galaxy distribution would be irreconcilable with the
relatively quiet flow of the galaxies.
Here we propose a different view on this cosmic dilemma, stressing the fact
that our cosmic neighbourhood embodies a region of rather particular dynamical
properties, and henceforth we are apt to infer flawed conclusions with respect
to the global Universe. Suspended between two huge mass concentrations, the
Great Attractor region and the Perseus-Pisces chain, we find ourselves in a
region of relatively low density yet with a very strong tidal shear. This tidal
field induces a local velocity field with a significant large-scale bulk flow
but a low small-scale velocity dispersion. By means of constrained realizations
of our local Universe, consisting of Wiener-filtered reconstructions inferred
from the Mark III catalogue of galaxy peculiar velocities in combination with
appropriate spectrally determined fluctuations, we study the implications for
our local velocity field. We find that we live near a local peak in the
distribution of the cosmic Mach number, ∣vbulk∣/σv, and that our
local cosmic niche is located in the tail of the Mach number distribution
function.Comment: Contribution to `Evolution of Large Scale Structure', MPA/ESO
Conference, August 1997, eds. A. Banday & R. Sheth, Twin Press. 5 pages of
LaTeX including 3 postscript figures. Uses tp.sty and psfi