Structure and stability in TMC-1: analysis of NH${}_3$ molecular line and Herschel continuum data

Abstract

We observed high S/N, high velocity resolution NH${}_3$(1,1) and (2,2) emission on an extended map in TMC-1, a filamentary cloud in a nearby quiescent star forming area. By fitting multiple hyperfine-split line profiles to the NH${}_3$(1,1) spectra we derived the velocity distribution of the line components and calculated gas parameters on several positions. Herschel SPIRE continuum observations were reduced and used to calculate the physical parameters of the Planck Galactic Cold Clumps in the region. The Herschel-based column density map of TMC-1 shows a main ridge with two local maxima and a separated peak to the south-west. H${}_2$-column densities and dust temperatures are in the range of 0.5-3.3 $\times$ 10${}^{22}$ cm${}^{-2}$ and 10.5-12 K, respectively. NH${}_3$-column densities are 2.8-14.2 $\times$ 10${}^{14}$ cm${}^{-2}$ and and H${}_2$-volume densities are 0.4-2.8 $\times$ 10${}^4$ cm${}^{-3}$. Kinetic temperatures are typically very low with a minimum of 9 K, and a maximum of 13.7 K was found at the Class I protostar IRAS 04381+2540. The kinetic temperatures vary similarly as the dust temperatures in spite of the fact that densities are lower than the critical density for coupling between the gas and dust phase. The k-means clustering method separated four sub-filaments in TMC-1 in the position-velocity-column density parameter space. They have masses of 32.5, 19.6, 28.9 and 45.9 M${}_{\odot }$, low turbulent velocity dispersion (0.13-0.2 kms${}^{-1}$) and they are close to gravitational equilibrium. We label them TMC-1F1 through F4. TMC-1F1, TMC-1F2 and TMC-1F4 are very elongated, dense and cold. TMC-1F3 is a little less elongated and somewhat warmer, probably heated by IRAS 04381+2540 that is embedded in it. TMC-1F3 is $\approx$ 0.1 pc behind TMC1-F1. Because of its structure, TMC-1 is a good target to test filament evolution scenarios.

17 pages, 9 figures; accepted for publication in A&A

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