Dense Cores in Dark Clouds . XIV . N 2 H + ( 1 – 0 ) maps of dense cloud cores

We present results of an extensive mapping survey of N2H (1–0) in about 60 low mass cloud cores already mapped in the NH3(1,1) inversion transition line. The survey has been carried out at the FCRAO antenna with an angular resolution of 54, about 1.5 times finer than the previous ammonia observations made at the Haystack telescope. The comparison between N2H + and NH3 maps shows strong similarities in the size and morphology of the two molecular species indicating that they are tracing the same material, especially in starless cores. Cores with stars typically have map sizes about a factor of two smaller for N2H + than for NH3, indicating the presence of denser and more centrally concentrated gas compared to starless cores. The mean aspect ratio is ∼ 2. Significant correlations are found between NH3 and N2H + column densities and excitation temperatures in starless cores, but not in cores with stars, suggesting a different chemical evolution of the two species. Starless cores are less massive (< Mvir > ≃ 3 M⊙) than cores with stars (< Mvir > ≃ 9 M⊙). Velocity gradients range between 0.5 and 6 km/s/pc, similar to what has been found with NH3 data, and the ratio β of rotational kinetic energy to gravitational energy have magnitudes between ∼ 10 and 0.07, indicating that rotation is not energetically dominant in the support of the cores. “Local” velocity gradients show significant variation in both magnitude and direction, suggesting the presence of complex motions