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

• Published in: Monthly notices of the Royal Astronomical Society 2015-02, Vol.447 (2), p.1826-1833
• Main Authors: Zapata, Luis A., Palau, Aina, Galván-Madrid, Roberto, Rodríguez, Luis F., Garay, Guido, Moran, James M., Franco-Hernández, Ramiro
• Format: Article
• Language: English
• Subjects: Arrays; Astronomy; Continuums; Discs; Disks; Luminosity; Molecules; Orientation; Protostars; Radio telescopes; Star & galaxy formation
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stu2527

We present high angular resolution (∼0.3 arcsec) 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 arcsec), 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 (E k  ≲ 300 K) are present in both millimeter continuum sources, and show a south-east–north-west velocity gradient of 7 km s− 1 over 3 arcsec (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 (E k  ≳ 500 K) are tracing a rotating structure elongated perpendicular to the orientation of the thermal jet, which we interpret as a candidate disc surrounding IRAS 16547−4247. The dynamical mass corresponding to the velocity gradient of the candidate to disc is about 20 M⊙, which is consistent with the bolometric luminosity of IRAS 16547−4247.