Bolocam Survey for 1.1 mm Dust Continuum Emission in the c2d Legacy Clouds. II. Ophiuchus

Abstract

We present a large-scale millimeter continuum map of the Ophiuchus molecular cloud. Nearly 11 deg2, including all of the area in the cloud with AV ≥ 3 mag, was mapped at 1.1 mm with Bolocam on the Caltech Submillimeter Observatory (CSO). By design, the map also covers the region mapped in the infrared with the Spitzer Space Telescope. We detect 44 definite sources, and a few likely sources are also seen along a filament in the eastern streamer. The map indicates that dense cores in Ophiuchus are very clustered and often found in filaments within the cloud. Most sources are round, as measured at the half-power point, but elongated when measured at lower contour levels, suggesting spherical sources lying within filaments. The masses, for an assumed dust temperature of 10 K, range from 0.24 to 3.9 M☉, with a mean value of 0.96 M☉. The total mass in distinct cores is 42 M☉, 0.5%-2% of the total cloud mass, and the total mass above 4 σ is about 80 M☉. The mean densities in the cores are quite high, with an average of 1.6 × 106 cm-3, suggesting short free-fall times. The core mass distribution can be fitted with a power law with slope α = 2.1 ± 0.3 for M > 0.5 M☉, similar to that found in other regions, but slightly shallower than that of some determinations of the local IMF. In agreement with previous studies, our survey shows that dense cores account for a very small fraction of the cloud volume and total mass. They are nearly all confined to regions with AV ≥ 9 mag, a lower threshold than found previously.