Mid-J CO observations of Perseus B1-East 5: evidence for turbulent dissipation via low-velocity shocks

TL;DR

This study uses Herschel observations of CO transitions in Perseus B1-East 5 to provide evidence that turbulence dissipates through low-velocity shocks, heating the gas and contributing to the cloud's energy balance.

Contribution

It presents new CO J=5-4 and 6-5 observations combined with archival data, demonstrating shock heating as a mechanism for turbulent energy dissipation in a molecular cloud.

Findings

Detection of warm gas component via excess CO 6-5 emission

Evidence of low-velocity shocks with a small volume filling factor

Estimated turbulent energy dissipation rate and timescale

Abstract

Giant molecular clouds contain supersonic turbulence and magnetohydrodynamic simulations predict that this turbulence should decay rapidly. Such turbulent dissipation has the potential to create a warm (T ~100 K) gas component within a molecular cloud. We present observations of the CO J = 5-4 and 6-5 transitions, taken with the Herschel Space Observatory, towards the Perseus B1-East 5 region. We combine these new observations with archival measurements of lower rotational transitions and fit photodissociation region models to the data. We show that Perseus B1-E5 has an anomalously large CO J = 6-5 integrated intensity, consistent with a warm gas component existing within the region. This excess emission is consistent with predictions for shock heating due to the dissipation of turbulence in low velocity shocks with the shocks having a volume filling factor of 0.15 per cent. We find that B1-E has a turbulent energy dissipation rate of 3.5 x 10$^{32}$ erg / s and a dissipation time-scale that is only a factor of 3 larger than the flow crossing time-scale.