Dense Gas Tracers in Perseus: Relating the N2H+, NH3, and Dust Continuum Properties of Pre- and Protostellar Cores

We investigate 35 prestellar cores and 36 protostellar cores in the Perseus molecular cloud. We find a very tight correlation between the physical parameters describing the N₂H⁺ and NH₃ gas. Both the velocity centroids and the line widths of N₂H⁺ and NH₃ correlate much better than either species correlates with CO, as expected if the nitrogen-bearing species are probing primarily the dense core gas where the CO has been depleted. We also find a tight correlation in the inferred abundance ratio between N₂H⁺ and para-NH₃ across all cores, with N(p-NH₃)/N(N₂H⁺) = 22 ± 10. We find a mild correlation between NH₃ (and N₂H⁺) column density and the (sub)millimeter dust continuum derived H₂ column density for prestellar cores, N(p-NH₃)/N(H₂) ~10^-8, but do not find a fixed ratio for protostellar cores. The observations suggest that in the Perseus molecular cloud the formation and destruction mechanisms for the two nitrogen-bearing species are similar, regardless of the physical conditions in the dense core gas. While the equivalence of N₂H⁺ and NH₃ as powerful tracers of dense gas is validated, the lack of correspondence between these species and the (sub)millimeter dust continuum observations for protostellar cores is disconcerting and presently unexplained.