A 12CO (J = 1 → 0) study towards the Ara OB1 region

Abstract

Intermediate angular resolution (HPBW = 8′.7) carbon monoxide (<SUP>12</SUP>CO J = 1 → 0) line observations towards the OB association Ara OB1 are reported. The molecular line observations cover an area of 2°.75 × 3°.00, and disclose a rich and complex distribution of the molecular line emission. The molecular features likely to be associated with the OB-association Ara OB1 span the velocity range from -28 to -20 km s<SUP>-1</SUP>. The most negative radial velocities are observed along NGC 6188 (≡Rim nebula). This nebula marks the interface between the HII region RCW 108 and the highly absorbing molecular material located westwards of the ionised region. The dominant CO structures, labeled E and F, have a radial velocity of about -23.5 and -21.8 km s<SUP>-1</SUP>, respectively. The former harbours a bright optical knot, the infrared cluster RCW-108 and the strong IRAS source 16362-4845. IRAS point sources are also seen in projection onto <SUP>12</SUP>CO concentrations F and H. This may indicate that the star forming process is a widespread phenomenon in this molecular complex. Extended continuum emission, having a high degree of spatial correlation with both the infrared and molecular emission, is observed in the region. We believe that this emission, thermal in nature, arises from the ionised surface layers of the molecular complex. The ionising agents are the high mass stars of NGC6193, the nucleus of Ara OB1. The total amount of molecular gas related to Ara OB1 is about ∼1.4×10<SUP>4</SUP> M⊙.