paper

FAUST VII. Detection of A Hot Corino in the Prototypical Warm Carbon-Chain Chemistry Source IRAS 15398-3359

arXiv:2303.03564 · doi:10.3847/1538-4357/acc1e5

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 $_{3, 15} - 1 8_{2, 16}$ , A ( $E_{u} =$ 447 K), 19 $_{3, 16} - 1 9_{2, 17}$ , A ( $E_{u} =$ 491 K), and 20 $_{3, 17} - 2 0_{2, 18}$ , 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 $\sim$ 10 au) and warm carbon-chain chemistry (WCCC) rich in carbon-chain species on large scales ( $\sim$ 100-1000 au). A possible implication of the small emitting region is further discussed in relation to the origin of the hot corino activity.

20pages, 3figures