First interferometric study of enhanced N-fractionation in N2H+: the high-mass star-forming region IRAS 05358+3543

Abstract

Nitrogen (N) fractionation is used as a tool to search for a link between the chemical history of the Solar System and star-forming regions. A large variation of ¹⁴N/¹⁵N is observed towards different astrophysical sources, and current chemical models cannot reproduce it. With the advent of high angular resolution radiotelescopes it is now possible to search for N-fractionation at core scales. We present IRAM NOEMA observations of the J=1–0 transition of N₂H^{+, 15}NNH⁺ and N¹⁵NH⁺ towards the high-mass protocluster IRAS 05358+3543. We find ¹⁴N/¹⁵N ratios that span from ∼100 up to ∼220 and these values are lower or equal than those observed with single-dish observations towards the same source. Since N-fractionation changes across the studied region, this means that it is regulated by local environmental effects. We find also the possibility, for one of the four cores defined in the protocluster, to have a more abundant ¹⁵NNH⁺ with respect to N¹⁵NH⁺. This is another indication that current chemical models may be missing chemical reactions or may not take into account other mechanisms, like photodissociation or grain surface chemistry, that could be important.