  We report a measurement of the real space (not redshift space) power spectrum
of galaxies over four and a half decades of wavenumber, 0.01 to 300 h/Mpc, from
the IRAS Point Source Catalog Redshift Survey (PSCz). Since estimates of power
are highly correlated in the nonlinear regime, we also report results for the
prewhitened power spectrum, which is less correlated. The inferred bias between
optically-selected APM and IRAS-selected PSCz galaxies is about 1.15 at linear
scales < 0.3 h/Mpc, increasing to about 1.4 at nonlinear scales > 1 h/Mpc. The
nonlinear power spectrum of PSCz shows a near power-law behaviour to the
smallest scales measured, with mild upward curvature in the broad vicinity of
1.5 h/Mpc. Contrary to the prediction of unbiased Dark Matter models, there is
no prominent inflection at the linear-nonlinear transition scale, and no
turnover at the transition to the stable clustering regime. The nonlinear power
spectrum of PSCz requires scale-dependent bias: all Dark Matter models without
scale-dependent bias are ruled out with high confidence.
