Subarcsecond Multiline Observations of NH 3 with VLA toward the Class 0 Source IRAS 16293−2422

Abstract Ammonia (NH 3 ) is one of the key volatiles that plays a central role in nitrogen chemistry and its evolution during the epoch of star and planet formation. We present subarcsecond ( ∼ 0 . ″ 5 ) resolution observations of NH 3 molecular emission lines with the Karl G. Jansky Very Large Array (VLA) toward the Class 0 multiple system IRAS 16293−2422 including source A and source B as major components. This comprises the most comprehensive set of NH 3 line observations in protostellar sources to date, which includes 17 inversion transitions with a wide range of upper state energies ( E u ) spanning from ∼23 K to ∼1580 K. We detect spatially resolved emission of a number of transitions and find that the high- E u (≳1000 K) lines show compact distributions in the vicinity of protostars while low- E u (≲150 K) lines exhibit more extended emission. Utilizing a two-component model, we constrain the rotation temperature and NH 3 column density for both source A and source B. The rotation temperature of the warmer component reaches ∼200–300 K, indicating that the high- E u lines selectively trace the inner hot region. We suggest that this hot NH 3 gas in source A originated from the local shock heating based on the comparison with the previous high-resolution ALMA observations, while that in source B could be explained by the mass accretion heating in the innermost hot region. We also briefly discuss the chemistry related to NH 3 based on the abundance ratios relative to major icy molecules derived using literature values.