A Virialized Filamentary Infrared Dark Cloud

TL;DR

This study investigates whether a filamentary Infrared Dark Cloud (IRDC) is in virial equilibrium by analyzing mass and velocity data, finding it consistent with equilibrium without needing magnetic support.

Contribution

The paper provides improved mass measurements and demonstrates that the IRDC G035.39-00.33 is in virial equilibrium, refining previous super-virial assessments.

Findings

IRDC G035.39-00.33 is consistent with virial equilibrium.

Mass measurements were improved using combined NIR & MIR extinction maps.

The equilibrium does not require magnetic support.

Abstract

The initial conditions of massive star and star cluster formation are expected to be cold, dense and high column density regions of the interstellar medium, which can reveal themselves via near, mid and even far-infrared absorption as Infrared Dark Clouds (IRDCs). Elucidating the dynamical state of IRDCs thus constrains theoretical models of these complex processes. In particular, it is important to assess whether IRDCs have reached virial equilibrium, where the internal pressure balances that due to the self-gravitating weight of the cloud plus the pressure of the external environmental. We study this question for the filamentary IRDC G035.39-00.33 by deriving mass from combined NIR & MIR extinction maps and velocity dispersion from C18O (1-0) & (2-1) line emission. In contrast to our previous moderately super-virial results based on 13CO emission and MIR-only extinction mapping, with improved mass measurements we now find that the filament is consistent with being in virial equilibrium, at least in its central parsec-wide region where ~1000 M_Sun snakes along several parsecs. This equilibrium state does not require large-scale net support or confinement by magnetic fields.