The Detection of a Hot Molecular Core in the Large Magellanic Cloud With Alma

Abstract

We report the first detection of a hot molecular core outside our Galaxy based on radio observations with ALMA toward a high-mass young stellar object (YSO) in a nearby low metallicity galaxy, the Large Magellanic Cloud (LMC). are detected from a compact region (∼0.1 pc) associated with a high-mass YSO, ST11. The temperature of molecular gas is estimated to be higher than 100 K based on rotation diagram analysis of SO 2 and 34 SO 2 lines. The compact source size, warm gas temperature, high density, and rich molecular lines around a high-mass protostar suggest that ST11 is associated with a hot molecular core. We find that the molecular abundances of the LMC hot core are significantly different from those of Galactic hot cores. The abundances of CH 3 OH, H 2 CO, and HNCO are remarkably lower compared to Galactic hot cores by at least 1-3 orders of magnitude. We suggest that these abundances are characterized by the deficiency of molecules whose formation requires the hydrogenation of CO on grain surfaces. In contrast, NO shows a high abundance in ST11 despite the notably low abundance of nitrogen in the LMC. A multitude of SO 2 and its isotopologue line detections in ST11 imply that SO 2 can be a key molecular tracer of hot core chemistry in metal-poor environments. Furthermore, we find molecular outflows around the hot core, which is the second detection of an extragalactic protostellar outflow. In this paper, we discuss the physical and chemical characteristics of a hot molecular core in the low metallicity environment.

The Detection of Hot Cores and Complex Organic Molecules in the Large Magellanic Cloud

“…These CH 3 OH fractional abundances are over an order of magnitude larger than an upper limit estimated for the candidate hot core ST11 by Shimonishi et al (2016b). The (CH 3 OCH 3 , CH 3 OCHO) fractional abundances are (2.2±0.7, 1.4 0.4 10 9 ´-) for A1 and (1.7±0.7, 0.5 10 9 <´-) for B3.…”

“…Shimonishi et al (2016b) have claimed a hot core detection toward the LMC young stellar object (YSO) ST11 based on the derived physical conditions and the presence of simple molecules connected to hot gas chemistry (e.g., SO 2 and its isotopologues). Neither methanol or COMs were detected.…”

Diverse Nuclear Star-forming Activities in the Heart of NGC 253 Resolved with 10-pc-scale ALMA Images

“…To resolve the chemical diversity of molecular clouds, or namely, to discern their evolutionary stages of star-formation with a high time resolution, the spatially-resolved spectroscopy at clump scales (or smaller) is highly necessary (e.g., Suzuki et al 1992;Sakai et al 2010;Sakai et al 2012). Its importance is in fact demonstrated by the recent observations of ST11, a high-mass young stellar object (YSO) in the Large Magellanic Cloud (LMC), yielding the first extragalactic detection of a hot molecular core, one of the early phases of the massive star-formation process (Shimonishi et al 2016).…”

“…Here, in order to interpret the environment of Clump 1 described above, we propose a hypothesis that Clump 1 is a giant hot core cluster, which is a several-parsec-scale aggregate of hot molecular cores (Kobulnicky & Johnson 2001) where high-mass star-formation takes place. Hot molecular cores are defined with the following characteristics: small source size (≤ 0.1 pc), high density (≥ 10 6 cm −3 ), and warm gas and dust temperatures (≥ 100 K) (Kurtz et al 2000;van der Tak et al 2003;Shimonishi et al 2016). Owing to the lack of angular resolution of conventional radio telescopes, the observational studies of hot molecular cores were limited to Galactic sources, until Shimonishi et al (2016) detected the first extragalactic hot core in the LMC with ALMA.…”

“…Hot molecular cores are defined with the following characteristics: small source size (≤ 0.1 pc), high density (≥ 10 6 cm −3 ), and warm gas and dust temperatures (≥ 100 K) (Kurtz et al 2000;van der Tak et al 2003;Shimonishi et al 2016). Owing to the lack of angular resolution of conventional radio telescopes, the observational studies of hot molecular cores were limited to Galactic sources, until Shimonishi et al (2016) detected the first extragalactic hot core in the LMC with ALMA. The results of our analysis, which suggest the existence of the hot molecular gases and the chemically rich environment in Clump 1, are consistent with the hypothesis.…”