High-resolution ammonia mapping of the very young protostellar core Chamaeleon-MMS1

摘要

Cha-MMS1 was mapped in the NH_3(1,1) line and the 1.2 cm continuum using theAustralia Telescope Compact Array, ATCA. The angular resolution of the ATCAobservations is 7'' (~ 1000 AU), and the velocity resolution is 50 m s^{-1}.The core was also mapped with the 64-m Parkes telesope in the NH_3(1,1) and(2,2) lines. Observations from Herschel Space Observatory and Spitzer Spacetelescope were used to help interpretation. A compact high column density corewith a steep velocity gradient is detected in ammonia, with a fractionalammonia abundance compatible with determinations towards other dense cores. Thedirection of the velocity gradient agrees with previous single-dishobservations, and the overall velocity distribution can be interpreted asrotation. The rotation axis goes through the position of a compact far-infraredsource detected by Spitzer and Herschel. The specific angular momentum of thecore is typical for protostellar envelopes. A string of 1.2 cm continuumsources is tentatively detected near the rotation axis. The ammonia spectrasuggest the presence of warm embedded gas in its vicinity. An hourglass-shapedstructure is seen in ammonia at the cloud's average LSR velocity, also alignedwith the rotation axis. Although this structure resembles a pair of outflowlobes the ammonia spectra show no indications of shocked gas. The observedammonia structure mainly delineates the inner envelope around the centralsource. The velocity gradient is likely to originate in the angular momentum ofthe contracting core, although influence of the outflow from the neighbouringyoung star IRS4 is possibly visible on one side of the core. The tentativecontinuum detection and the indications of a warm background component near therotation axis suggest that the core contains a deeply embedded outflow whichmay have been missed in previous single-dish CO surveys owing to beam dilution.