Interstellar Nitrogen Isotope Ratios: New NH₃ Data from the Galactic Center out to the Perseus Arm

Abstract Our aim is to measure the interstellar 14 N/ 15 N ratio across Galaxy, establish a standard data set on ammonia isotope ratios, and provide new constraints Galactic chemical evolution. The ( J , K ) = (1, 1), (2, 2), (3, 3) lines of NH 3 were observed with Shanghai Tianma 65 m radio telescope (TMRT) Effelsberg 100 toward large sample 210 sources. One hundred fourty-one these sources detected by TMRT in . Eight them also For 10 36 strong emission, successfully their 1) lines, including (G081.7522, W51D, Orion-KL) detections telescope. Thus, total are both lines. Line physical parameters for derived, optical depths, rotation kinetic temperatures, column densities. ratios determined from / abundance ratios. obtained telescopes agree given source within uncertainties, no dependence heliocentric distance temperature seen. tend increase galactocentric distance, confirming radial nitrogen gradient. This consistent results recent model calculations, impact superasymptotic giant branch stars novae.