Dynamics of dense cores in the Perseus molecular cloud

We survey the kinematics of over 150 candidate ( and potentially star-forming) dense cores in the Perseus molecular cloud with pointed N2H+( 1-0) and simultaneous (CO)-O-18( 2-1) observations. Our detection rate of N2H+ is 62%, rising to 84% for SCUBA-selected targets. In agreement with previous observations, we find that the dense N2H+ targets tend to display nearly thermal line widths, particularly those that appear to be starless ( using Spitzer data), indicating that turbulent support on the small scales of molecular clouds is minimal. For those N2H+ targets that have an associated SCUBA dense core, we find that their internal motions are more than sufficient to provide support against the gravitational force on the cores. Comparison of the N2H+ integrated intensity and SCUBA flux reveals fractional N2H+ abundances between 10(-10) and 10(-9). We demonstrate that the relative motion of the dense N2H+ gas and the surrounding (CO)-O-18 gas is less than the sound speed in the vast majority of cases ( similar to 90%). The point-to-point motions we observe within larger extinction regions appear to be insufficient to provide support against gravity, although we sparsely sample these regions.