Properties of starless and prestellar cores in Taurus revealed by Herschel SPIRE/PACS imaging

Abstract

The density and temperature structures of dense cores in the L1495 cloud of the Taurus star-forming region are investigated using Herschel Spectral and Photometric Imaging Receiver and Photodetector Array Camera and Spectrometer images in the 70, 160, 250, 350 and 500 μm continuum bands. A sample consisting of 20 cores, selected using spectral and spatial criteria, is analysed using a new maximum likelihood technique, COREFIT, which takes full account of the instrumental point spread functions. We obtain central dust temperatures, T0, in the range 6–12 K and find that, in the majority of cases, the radial density falloff at large radial distances is consistent with the asymptotic r−2 variation expected for Bonnor–Ebert spheres. Two of our cores exhibit a significantly steeper falloff, however, and since both appear to be gravitationally unstable, such behaviour may have implications for collapse models. We find a strong negative correlation between T0 and peak column density, as expected if the dust is heated predominantly by the interstellar radiation field. At the temperatures we estimate for the core centres, carbon-bearing molecules freeze out as ice mantles on dust grains, and this behaviour is supported here by the lack of correspondence between our estimated core locations and the previously published positions of H13CO+ peaks. On this basis, our observations suggest a sublimation-zone radius typically ∼104 au. Comparison with previously published N2H+ data at 8400 au resolution, however, shows no evidence for N2H+ depletion at that resolution.