The James Clerk Maxwell telescope Legacy Survey of the Gould Belt: a molecular line study of the Ophiuchus molecular cloud

Abstract

CO, 13CO, and C18O J = 3-2 observations are presented of the Ophiuchus molecular cloud. The 13CO and C18O emission is dominated by the Oph A clump, and the Oph B1, B2, C, E, F, and J regions. The optically thin(ner) C18O line is used as a column density tracer, from which the gravitational binding energy is estimated to be 4.5 × 1039 J (2282 M&sun; km2 s-2). The turbulent kinetic energy is 6.3 × 1038 J (320 M&sun; km2 s-2), or seven times less than this, and therefore the Oph cloud as a whole is gravitationally bound. 30 protostars were searched for high-velocity gas, with 8 showing outflows, and 20 more having evidence of high-velocity gas along their lines of sight. The total outflow kinetic energy is 1.3 × 1038 J (67 M&sun; km2 s-2), corresponding to 21 per cent of the cloud's turbulent kinetic energy. Although turbulent injection by outflows is significant, but does not appear to be the dominant source of turbulence in the cloud. 105 dense molecular clumplets were identified, which had radii ˜0.01-0.05 pc, virial masses ˜0.1-12 M&sun;, luminosities ˜0.001-0.1 K km s-1 pc-2, and excitation temperatures ˜10-50 K. These are consistent with the standard Giant Molecular Cloud (GMC) based size-linewidth relationships, showing that the scaling laws extend down to size scales of hundredths of a parsec, and to subsolar-mass condensations. There is however no compelling evidence that the majority of clumplets are undergoing free-fall collapse, nor that they are pressure confined.