Extreme-infrared (800{mu}m) polarimetry of the M17-SW molecular cloud with the JCMT.
J. P. Vallée, P. Bastien;
AaA, 1996, 313, 255
ABSTRACT:Extreme-infrared (800{mu}m) linear polarization observations have been obtained at
the JCMT on Mauna Kea in Hawaii, toward the elongated molecular cloud
M17-SW located at a distance of 2.2kpc.
The six strongest dust peaks in total
continuum intensity were observed.
From the total intensity continuum
observations, we find that the typical dust peaks in M17-SW have a mean size of 0.24pc, a
mean density of 3.7x10^5^cm^-3^, and a mean mass of 245M_{sun}_.
From the
polarimetric observations, we measure a mean polarized E-vector amplitude of
2.0+/-0.3%, and we find that the mean E-vector position angle at extreme IR
wavelengths is at PA=169+/-19deg.
This mean E-vector PA is mostly parallel to the
cloud elongation, which is at PA=158+/-10deg follows that the mean magnetic
field vector is at PA=79+/-19deg, implying that the cloud's magnetic field
is mostly perpendicular to the cloud's elongation.
We have grouped the
theoretical models for the magnetic fields in molecular clouds into eleven
`magnetic classes', according to the shape and the scale of the magnetic field
involved.
Comparisons are made between the predictions from these 11 classes and the JCMT
observations for the B-vectors in the cloud M17-SW.
Nine of the 11 magnetic classes
are unlikey to pertain to M17-SW.
The other two magnetic classes are: the
class with a 1-dimensional cloud collapse along the localized magnetic
field lines; and the class with the magnetic field vectors in the cloud being
parallel to the surrounding magnetic field.
These results suggest that a
proper distance scale for the magnetic field involved is of the order of 10pc to
100pc outside the cloud (larger than the cloud size), and of the order of 1pc to
10pc inside the cloud M17-SW (larger than the clump sizes of 0.2pc).
Two
scenarios for the origin of the dust peaks in M17-SW are examined.
The
`sequential star formation' scenario is supported, and our polarization data and
other data cast doubts on the `radially expanding shell' scenario for
M17-SW.
KEYWORDS: radio continuum: ism, linear polarization, ism: individual: m17-sw, magnetic fields
PERSOKEY:polarisation, submillimeter, molecular clouds, jcmt, magnetic field, ,
CODE: vallee96