1420 MHz Continuum Emission (left) - Atomic Hydrogen
Line Emission (right)
Prior to undertaking the full Canadian Galactic Plane Survey project, The University of Calgary Radio Astronomy Laboratory, in collaboration with the Dominion Radio Astronomy Observatory, undertook a pilot project to test the feasibility of the project and to trouble-shoot the observing and data processing methodology. The pilot project consists of observations of 10 overlapping synthesis field in the direction of the W3, W4, W5 and HB3 regions of the second quadrant of the Galaxy. The DRAO atomic hydrogen observations have a resolution of 1' and fully sample spatial structures down to that limit. In addition to the HI line data, the DRAO synthesis telescope provides simultaneous continuum data at 1420 MHz (both total intensity and polarization) and 408 MHz (total intensity only).
The 1420 MHz continuum mosaiced image of the region is shown at left above. At right above is a mosaic of one channel of the atomic hydrogen emission data cube. The spectral line channel shows very distinct large scale structures. Some are clearly related to the objects visible in the continuum, and some are not. On the eastern edge of the image there is a void in the HI emission. The boundaries of the void closely match the extent of the ionized gas of W5. The intense bridge of HI emission just to the west of the void delineates the region between the western edge of W5 and the eastern edge of W4. A bright filament of HI emission extends from near western edge of W4 upward to the northeast and off the top of the map. This filament extends in the same direction as the ionized "streamer" that emanates from the eastern edge of W4 and may represent outflow of atomic gas from the disk to the halo. On the northwest part of the image, there are several clumps of HI and a filamentary arc. The clumps accurately match the morphology the western edge of the HB3 supernova remnant and probably represent swept up atomic gas. The arc is a precise continuation of the faint continuum arc that rises from the northern edge of HB3.
For a detailed description of the pilot project refer to:
Normandeau, M., Taylor, A.R. and Dewdney, P.E., 1997, Astrophysical Journal Supplementary Series, 108, 279.
FITS files of the data are available via ftp.
Click on the the thumbnail for a full sized image [183689 bytes]
This figure shows three maps from the DRAO Pilot Project, along with a complementary image from the FCRAO CO (1-0) survey. The images are 8 degrees by 6 degrees in size. All have identical scale and very nearly the same angular resolution of 1 arc minute. The multiple images show several gaseous components of the ISM (ionized gas, relativistic plasma, neutral atomic gas, and molecular gas) and highlight how the different states of the ISM matter are distinct but interdependent.
At the upper left is the 21-cm continuum image.. The display levels have been set to emphasize the spatial extent of the high intensity emission from ionized gas in the W3/W4/W5 star formation complex. The synchrotron radiation from the large shell of the supernova remnant HB3 is visible to the right of W3. The intense emission from W3 itself is saturated in the display. The large filamentray loop of W4 occupies the center of the image. The faint continuum wisp extended from the upper left of W4 may represent the ionized wall of the newly discovered Perseus Chimney (figure at upper right). W5 occupies the left part of the picture.
The images at top and bottom on the right hand side are two of the DRAO atomic hydrogen spectral line mosaics. These two images are taken from data cube planes that are separated by about 18 km/s in the velocity dimension. In both cases the gas giving rise to the emission is thought to come from the Perseus arm region of the Galaxy that also contains the ionized and relativistic gas seen in the continuum image. At upper right the void and ``rabbit ears'' of the Perseus chimney are evident in the top central part of the image. The other emission in the images has been saturated to enhance the contrast around the chimney. The HI image at lower right shows the highly disturbed state of the ISM in this region. This is almost certainly related to the star formation activity.
At the lower left is the FCRAO image of the molecular (CO) emission from this same region. The molecular cloud complexes associated with W3 and W5 are clearly visible. Interestingly, there is no large molecular cloud associated with W4, only small, kinematically disturbed cloudlets. This observations reinforces the idea suggested by the presence of the chimney associated with W4, that W4 has largely dispersed the nascent cloud and the ISM conditions from which its young stars formed.
On each of the CO and HI spectral line images a contour has been plotted to demarcate the edge of the region of high brightness continuum emission. The bottom end of the Perseus Chimney is seen to merge precisly with the upper portion of the ionized gas in W4.
The DRAO observations were carried out by Magdalen Normandeau for her Ph.D. thesis. For more information about the pilot project and/or the Canadian Galactic Plane Survey project contact Russ Taylor.
"Cosmic Chimney" Press Release (May 24/95)