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 H-2 column density for prestellar cores, N(p-NH3)/N(H-2) similar to 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.