Angular Momentum of the N2H+ Cores in the Orion A Cloud

TL;DR

This study measures the angular momentum of N2H+ cores in Orion A, revealing their rotational properties and comparing them to cold dark cloud cores, with implications for core formation and cloud dynamics.

Contribution

It provides the first detailed measurement of core angular momentum in Orion A and compares it to cold dark cloud cores, highlighting differences and similarities in rotational energy.

Findings

Core velocity gradients range from 0.5 to 7.8 km/s/pc.

Specific angular momentum J/M tends to be larger than in cold dark clouds.

Rotational energy ratio beta is about 10^{-2.3}, similar to cold dark cores.

Abstract

We have analyzed the angular momentum of the molecular cloud cores in the Orion A giant molecular cloud observed in the N2H+ J = 1-0 line with the Nobeyama 45 m radio telescope. We have measured the velocity gradient using position velocity diagrams passing through core centers, and made sinusoidal fitting against the position angle. 27 out of 34 N2H+ cores allowed us to measure the velocity gradient without serious confusion. The derived velocity gradient ranges from 0.5 to 7.8 km/s/pc. We marginally found that the specific angular momentum J/M (against the core radius R) of the Orion N2H+ cores tends to be systematically larger than that of molecular cloud cores in cold dark clouds obtained by Goodman et al., in the J/M-R relation. The ratio beta of rotational to gravitational energy is derived to be beta = 10^{-2.3+/-0.7}, and is similar to that obtained for cold dark cloud cores in a consistent definition. The large-scale rotation of the integral-shaped filament of the Orion A giant molecular cloud does not likely govern the core rotation at smaller scales.