The nature of the dense core population in the pipe nebula: core and cloud kinematics from C18O observations

TL;DR

This study uses C18O observations to analyze the internal and radial kinematics of 94 dark cloud cores in the Pipe nebula, revealing two main kinematic components and insights into their physical nature and structure.

Contribution

It provides detailed kinematic analysis of cores in the Pipe nebula, identifying two main components and their physical characteristics, which enhances understanding of cloud structure and star formation.

Findings

Most cores are true cloud cores, not filament superpositions.

Two main kinematic components: a narrow filament and a ring-like structure.

Cores in the ring show larger linewidths and motions.

Abstract

We present molecular-line observations of 94 dark cloud cores identified in the Pipe nebula through near-IR extinction mapping. Using the Arizona Radio Observatory 12m telescope, we obtained spectra of these cores in the J=1-0 transition of C18O. We use the measured core parameters, i.e., antenna temperature, linewidth, radial velocity, radius and mass, to explore the internal kinematics of these cores as well as their radial motions through the larger molecular cloud. We find that the vast majority of the dark extinction cores are true cloud cores rather than the superposition of unrelated filaments. While we identify no significant correlations between the core's internal gas motions and the cores' other physical parameters, we identify spatially correlated radial velocity variations that outline two main kinematic components of the cloud. The largest is a 15pc long filament that is surprisingly narrow both in spatial dimensions and in radial velocity. Beginning in the Stem of the Pipe, this filament displays uniformly small C18O linewidths (dv~0.4kms-1) as well as core to core motions only slightly in excess of the gas sound speed. The second component outlines what appears to be part of a large (2pc; 1000 solar mass) ring-like structure. Cores associated with this component display both larger linewidths and core to core motions than in the main cloud. The Pipe Molecular Ring may represent a primordial structure related to the formation of this cloud.