ALMA reveals a candidate hot and compact disc around the O-type protostar IRAS 16547-4247

Abstract

We present high angular resolution (∼ 0.3′′) submillimeter continuum (0.85 mm) and line observations of the O-type protostar IRAS 16547−4247 carried out with the Atacama Large Millimeter/Submillimeter Array (ALMA). In the 0.85 mm continuum band, the observations revealed two compact sources (with a separation of 2′′), one of them associated with IRAS 16547−4247, and the other one to the west. Both sources are well resolved angularly, revealing a clumpy structure. On the other hand, the line observations revealed a rich variety of molecular species related to both continuum sources. In particular, we found a large number of S-bearing molecules, such as the rare molecule methyl mercaptan (CH3SH). At scales larger than 10,000 AU, molecules (e.g., SO2 or OCS) mostly with low excitation temperatures in the upper states (Ek . 300 K) are present in both millimeter continuum sources, and show a southeast-northwest velocity gradient of 7 km s−1 over 3′′ (165 km s−1 pc−1). We suggest that this gradient probably is produced by the thermal (free-free) jet emerging from this object with a similar orientation at the base. At much smaller scales (about 1000 AU), molecules with high excitation temperatures (Ek & 500 K) are tracing a rotating structure elongated perpendicular to the orientation of the thermal jet, which we interpret as a candidate disk surrounding IRAS 16547−4247. The dynamical mass corresponding to the velocity gradient of the candidate to disk is about 20 M⊙, which is consistent with the bolometric luminosity of IRAS 16547−4247.