Protostars and Planets VI, Heidelberg, July 15-20, 2013
Poster 1B082
Signatures of Dynamical Collapse during High-Mass Star Formation
Smith, Rowan (ZAH/ITA University of Heidelberg)
Shetty, Rahul (ZAH/ITA University of Heidelberg)
Beuther, Henrik (MPIA Heidelberg)
Klessen, Ralf (ZAH/ITA University of Heidelberg)
Bonnell, Ian (University of St. Andrews)
Abstract:
Observations of atomic or molecular lines can provide important information about the physical state
of star forming regions. In order to investigate the line profiles from dynamical collapsing massive star
forming regions (MSFRs), we model the emission from hydrodynamic simulations of a collapsing cloud
in the absence of outflows. By performing radiative transfer calculations, we compute the optically
thick HCO+ and optically thin N2H+ line profiles from two collapsing regions at different epochs. Due
to large-scale collapse, the MSFRs have large velocity gradients, reaching up to 20 km/s/pc across
the central core. The optically thin lines typically contain multiple velocity components resulting
from the superposition of numerous density peaks along the line-of-sight. The optically thick lines are
only marginally shifted to the blue side of the optically thin line profiles, and frequently do not have
a central depression in their profiles due to self-absorption. As the regions evolve the lines become
brighter and the optically thick lines become broader. The lower order HCO+ (1-0) transitions are
better indicators of collapse than the higher order (4-3) transitions. We also investigate how the beam
sizes affect profile shapes. Smaller beams lead to brighter and narrower lines that are more skewed to
the blue in HCO+ relative to the true core velocity, but show multiple components in N2H+. High
resolution observations (e.g. with ALMA) can test these predictions and provide insights into the
nature of MSFRs.
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