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

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 CH _3 OH lines including the high-excitation lines with upper-state energies up to 500 K. The CH _3 OH rotational temperature and the column density are derived to be ${119}_{-26}^{+20}$ K and ${3.2}_{-1.0}^{+2.5}\times {10}^{18}$ cm ^−2 , respectively. The beam filling factor is derived to be ${0.018}_{-0.003}^{+0.005}$ , indicating that the emitting region of CH _3 OH is much smaller than the synthesized beam size and is not resolved. The emitting region of three high-excitation lines, 18 _3,15 –18 _2,16 , A ( E _u = 447 K), 19 _3,16 –19 _2,17 , A ( E _u = 491 K), and 20 _3,17 –20 _2,18 , 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 CH _2 DOH and two features of multiple CH _3 OCHO 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.

Keywords

• Interstellar molecules
• Protostars
• Astrochemistry
• Radio astrometry
• Star formation