The N2D+/N2H+ ratio as an evolutionary tracer of Class 0 protostars

TL;DR

This study uses the N2D+/N2H+ ratio as an evolutionary tracer for Class 0 protostars, revealing that higher ratios indicate younger, colder objects with signs of infall, thus providing insights into early star formation stages.

Contribution

It introduces the N2D+/N2H+ ratio as a novel chemical marker for determining the evolutionary stage of Class 0 protostars.

Findings

Higher N2D+/N2H+ ratios correlate with younger, colder protostars.

Objects with high ratios show evidence of infall.

Deuterium fractionation exceeds elemental D/H ratios in cold environments.

Abstract

Deuterated ions are abundant in cold (T=10 K), dense (n=10^5 cm^-3) regions, in which CO is frozen out onto dust grains. In such environments, the deuterium fractionation of such ions can exceed the elemental abundance ratio of D/H by a factor of 10^4. In this paper we use the deuterium fractionation to investigate the evolutionary state of Class 0 protostars. In a sample of 20 protostellar objects, we found a clear correlation between the N2D+/N2H+ ratio and evolutionary tracers. As expected, the coolest, i.e. the youngest, objects show the largest deuterium fractionation. Furthermore, we find that sources with a high N2D+/N2H+ ratio show clear indication for infall.