  A measurement of two-particle correlations with a high transverse momentum
trigger particle (p_T^{trig} > 2.5 GeV/c) is presented for Au+Au collisions at
sqrt(s_NN) = 200 GeV over the uniquely broad longitudinal acceptance of the
PHOBOS detector (-4 < \Delta\eta < 2). A broadening of the away-side azimuthal
correlation compared to elementary collisions is observed at all \Delta\eta. As
in p+p collisions, the near-side is characterized by a peak of correlated
partners at small angle relative to the trigger particle. However, in central
Au+Au collisions an additional correlation extended in \Delta\eta and known as
the `ridge' is found to reach at least |\Delta\eta| \approx 4. The ridge yield
is largely independent of \Delta\eta over the measured range, and it decreases
towards more peripheral collisions. For the chosen p_T^{trig} cut, the ridge
yield is consistent with zero for events with less than roughly 100
participating nucleons.
