ALMA discovery of a dual dense probably rotating outflow from a massive young stellar object G18.88MME

Abstract

ABSTRACT We report the discovery of a very dense jet-like fast molecular outflow surrounded by a wide-angle wind in a massive young stellar object (MYSO) G18.88MME (stellar mass ∼8 M⊙) powering an extended green object G18.89−0.47. Four cores MM1–4 are identified in the Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm continuum map (resolution ${\sim} 0.8\, \mathrm { arcsec}$) towards G18.88MME, and are seen at the centre of the emission structure (extent ∼0.3 pc × 0.2 pc) detected in the ALMA map. G18.88MME is embedded in the core MM1 (mass ∼13–18 M⊙), where no radio continuum emission is detected. The molecular outflow centred at MM1 is investigated in the SiO(5–4), HC3N(24–23) and 13CO(2–1) lines. The detection of HC3N in the outflow is rare in MYSOs and indicates its very high density. The position–velocity diagrams display a fast narrow outflow (extent ∼28 000 AU) and a slower wide-angle more extended outflow towards MM1, and both of these components show a transverse velocity gradient indicative of a possible rotation. All these observed features together make G18.88MME as a unique object for studying the unification of the jet-driven and wind-driven scenarios of molecular outflows in MYSOs.