The Initial Conditions of Clustered Star Formation I: NH3 Observations of Dense Cores in Ophiuchus

TL;DR

This study uses high-resolution NH3 observations to analyze the physical conditions and structure of dense cores in the Ophiuchus star-forming region, revealing variations in gas properties and core structures.

Contribution

It provides detailed NH3 mapping of dense cores in Ophiuchus, highlighting discrepancies between dense gas tracers and submillimeter emission, and characterizing temperature and kinematic differences.

Findings

Significant discrepancies between NH3 and continuum emission at small scales.

Oph B has large, often supersonic line widths; Oph C has narrow, near-thermal lines.

Gas temperatures are higher in Oph B and F (~15 K) than in Oph C (~12 K).

Abstract

We present combined interferometer and single dish telescope data of NH3 (J,K) = (1,1) and (2,2) emission towards the clustered star forming Ophiuchus B, C and F Cores at high spatial resolution (~1200 AU) using the Australia Telescope Compact Array, the Very Large Array, and the Green Bank Telescope. While the large scale features of the NH3 (1,1) integrated intensity appear similar to 850 micron continuum emission maps of the Cores, on 15" (1800 AU) scales we find significant discrepancies between the dense gas tracers in Oph B, but good correspondence in Oph C and F. Using the Clumpfind structure identifying algorithm, we identify 15 NH3 clumps in Oph B, and 3 each in Oph C and F. Only five of the Oph B NH3 clumps are coincident within 30" (3600 AU) of a submillimeter clump. We find v_LSR varies little across any of the Cores, and additionally varies by only ~1.5 km/s between them. The observed NH3 line widths within the Oph B and F Cores are generally large and often mildly supersonic, while Oph C is characterized by narrow line widths which decrease to nearly thermal values. We find several regions of localized narrow line emission (\Delta v < 0.4 km/s), some of which are associated with NH3 clumps. We derive the kinetic temperatures of the gas, and find they are remarkably constant across Oph B and F, with a warmer mean value (T_K = 15 K) than typically found in isolated regions and consistent with previous results in clustered regions. Oph C, however, has a mean T_K = 12 K, decreasing to a minimum T_K = 9.4 K towards the submillimeter continuum peak, similar to previous studies of isolated starless cores. There is no significant difference in temperature towards protostars embedded in the Cores. [Abridged]