A Virialized Filamentary Infrared Dark Cloud
  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.
