John J. Tobin, Lee Hartmann, Edwin A. Bergin, Hsin-Fang Chiang, Leslie W. Looney, Claire J. Chandler, Sebastien Maret, Fabian Heitsch
We present an interferometric kinematic study of morphologically complex
protostellar envelopes based on observations of the dense gas tracers N2H+ and
NH3. The strong asymmetric nature of most envelopes in our sample leads us to
question the common interpretation of velocity gradients as rotation, given the
possibility of projection effects in the observed velocities. Several
"idealized" sources with well-ordered velocity fields and envelope structures
are now analyzed in more detail. We compare the interferometric data to
position-velocity diagrams of kinematic models for spherical rotating collapse
and filamentary rotating collapse. For this purpose, we developed a filamentary
parametrization of the rotating collapse model to explore the effects of
geometric projection on the observed velocity structures. We find that most
envelopes in our sample have PV structures that can be reproduced by an
infalling filamentary envelope projected at different angles within the plane
of the sky. The infalling filament produces velocity shifts across the envelope
that can mimic rotation, especially when viewed at single-dish resolutions and
the axisymmetric rotating collapse model does not uniquely describe any
dataset. Furthermore, if the velocities are assumed to reflect rotation, then
the inferred centrifugal radii are quite large in most cases, indicating
significant fragmentation potential or more likely another component to the
line-center velocity. We conclude that ordered velocity gradients cannot be
interpreted as rotation alone when envelopes are non-axisymmetric and that
projected infall velocities likely dominate the velocity field on scales larger
than 1000 AU.
View original:
http://arxiv.org/abs/1201.2174
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