This movie shows the Stokes Q and U intensity in a field of the Galactic plane (329 < l < 332.5 degrees, 0.5 < b < 3.5 degrees) mapped with the ATCA interferometer as part of our Southern Galactic Plane Survey
There are 18 images in the movie, each one is made by combining the Q and U maps according to :
S(i) = (cos(theta) * Q) + (sin(theta) * U)
where Q and U are maps of the two linear Stokes parameters,
theta = (i-1) * 10 degrees.
Thus the consecutive frames of the movie are consecutive projections of the Stokes Q and U maps on a coordinate axis which rotates 180 degrees from parallel to the Q axis, through the U axis (frame 10) on to be almost parallel to the negative Q axis. Obviously the consecutive frames are not independent, there are only two independent maps, but rotating through this half circle in position angle allows any linearly polarized feature to show up (negative or positive) in one frame or another.
A few interesting features are shown on the sketch above. There are at least two elliptical structures, reminiscent of the "lens" feature discovered by Gray et al. (1998 Nature, 393, 660) in the Canadian Galactic Plane Survey of the Northern Milky Way. There is also a large, roughly round area which is apparently depolarized. This may be associated with the bright continuum source near its center, PK332+01.1. The Stokes I continuum map is shown below, with source identifications superposed.
To watch the movie, it is good to slow down your movie viewer to 50% or less of normal speed, and zoom the frame to two or three times the default size. It also helps to set the viewer to "swing" back and forth from end to end, rather than repeating the frames from the beginning each time. If the Quicktime format version is not accessible to your computer, try the mpeg format version or the sgi format versions.
Below is the Stokes I map of the same field, on the same scale.
