The JCMT Legacy Survey of the Gould Belt: a molecular line study of the Ophiuchus molecular cloud

Abstract

CO, ${}^{13}$CO and C${}^{18}$O $J$ = 3--2 observations are presented of the Ophiuchus molecular cloud. The ${}^{13}$CO and C${}^{18}$O emission is dominated by the Oph A clump, and the Oph B1, B2, C, E, F and J regions. The optically thin(ner) C${}^{18}$O line is used as a column density tracer, from which the gravitational binding energy is estimated to be $4.5\times 10^{39}$ J (2282 $M_{\odot }$ km${}^2$ s${}^{-2}$). The turbulent kinetic energy is $6.3\times 10^{38}$ J (320 $M_{\odot }$ km${}^2$ s${}^{-2}$), or 7 times less than this, and therefore the Oph cloud as a whole is gravitationally bound. Thirty protostars were searched for high velocity gas, with eight showing outflows, and twenty more having evidence of high velocity gas along their lines-of-sight. The total outflow kinetic energy is $1.3\times 10^{38}$ J (67 $M_{\odot }$ km${}^2$ s${}^{-2}$), corresponding to 21$\%$ 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 $\sim$ 0.01--0.05 pc, virial masses $\sim$ 0.1--12 $M_{\odot }$, luminosities $\sim$ 0.001--0.1 K~km s${}^{-1}$ pc${}^{-2}$, and excitation temperatures $\sim$ 10--50K. These are consistent with the standard GMC based size-line width relationships, showing that the scaling laws extend down to size scales of hundredths of a parsec, and to sub solar-mass condensations. There is however no compelling evidence that the majority of clumplets are undergoing free-fall collapse, nor that they are pressure confined.

MNRAS in press 1 November 2014 - 29 pages