Millimetre observations of the IRAS 18162−2048 outflow: evidence for cloud disruption around an intermediate-mass protostar

Abstract

In order to study the morphology and the dynamics of the molecular outflow associated with IRAS 18162−2048, a wide area of ∼95 arcmin 2 around the source has been mapped by means of CO and 13 CO (1‐0) lines, and has been complemented by a map of a smaller region surrounding the high-mass object using the C 18 O (1‐0) and CH3OH (2k‐1k) and (3k‐2k) transitions. The lines profile reveals the presence of several velocity components among which two major line components at 11.9 and 12.8 km s −1 have been detected in all the tracers. Simple morphological and energetic considerations led us to interpret the observations in a relatively straightforward scenario in which the powerful jet ejected by IRAS 18162−2048 sets a big portion of the surrounding molecular cloud into motion. The energy and momentum deposited by the flow break the cloud apart, shifting the northern region to a blue velocity and the southern region to a red velocity, and giving rise to a giant outflow. We calculated the physical parameters of the outflow, which make the IRAS 18162−2048 outflow one of the most massive (M = 570 M� ) and energetic (K > 10 46 erg) known. Despite the intrinsic difficulties in giving a precise value of the age and of the inclination angle of the flow, we used different methods to derive a reliable estimate. Our data show evidence in favour of a small inclination angle (<50 ◦ ) and of a maximum outflow age of ∼10 6 yr. C 18 O and CH3OH trace the dense core surrounding IRAS 18162−2048 and show an elongated emission in the direction perpendicular to the outflow axis. Besides the peak emission associated with the IRAS source, we found another peak at the position RA(B1950) = 18 h 16 m 20. s 2, Dec.(B1950) =− 20 ◦ 49 � 18 �� which coincides with a red near-infrared source. We provided evidence that this second peak may be surrounded by a flattened rotating structure, suggesting that the newly discovered infrared source can be another site of recent star formation in this region. Our analysis suggest that the powerful wind/outflow from the luminous stars within the young cluster embedded in the GGD 27 nebula is tearing apart the parental molecular cloud. IRAS 18162−2048 appears to be in the act of clearing the surrounding material on the verge of becoming an optically revealed young stellar cluster, similar to those associated with Herbig Be stars.