FAUST. VII. Detection of a Hot Corino in the Prototypical Warm Carbon-chain Chemistry Source IRAS 15398–3359

Abstract

Abstract We have observed the low-mass protostellar source IRAS 15398−3359 at a resolution of 0.″2–0.″3, as part of the Atacama Large Millimeter/Submillimeter Array Large Program FAUST, to examine the presence of a hot corino in the vicinity of the protostar. We detect nine CH3OH lines including the high-excitation lines with upper-state energies up to 500 K. The CH3OH rotational temperature and the column density are derived to be 119 − 26 + 20 K and 3.2 − 1.0 + 2.5 × 10 18 cm−2, respectively. The beam filling factor is derived to be 0.018 − 0.003 + 0.005 , indicating that the emitting region of CH3OH is much smaller than the synthesized beam size and is not resolved. The emitting region of three high-excitation lines, 183,15–182,16, A (E u = 447 K), 193,16–192,17, A (E u = 491 K), and 203,17–202,18, A (E u = 537 K), is located within the 50 au area around the protostar and seems to have a slight extension toward the northwest. Toward the continuum peak, we also detect one emission line from CH2DOH and two features of multiple CH3OCHO lines. These results, in combination with previous reports, indicate that IRAS 15398−3359 is a source with hybrid properties showing both hot corino chemistry rich in complex organic molecules on small scales (∼10 au) and warm carbon-chain chemistry rich in carbon-chain species on large scales (∼100–1000 au). A possible implication of the small emitting region is further discussed in relation to the origin of the hot corino activity.