Projected density from within the disc



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Projected density from within the disc

It is possible to ``observe'' the model from any arbitrary angle to deduce quantities to be compared with observations. Figure 2 shows contours of ``surface brightness'' towards the inner galaxy from the point marked in the last frame. The particles were projected into a raster of bins and weighted by the inverse square of their distance from the observer, except those closer than half the distance to the centre were discarded. The viewing angle is 30 to the bar major axis; if this angle is increased, the bulge acquires too much of a peanut shape to be consistent with the extinction corrected COBE image (Weiland et al., this meeting), while if it is reduced, the asymmetry between the two sides becomes more pronounced. The distance from the centre was chosen in order that the box-like feature in the third contour down from the peak subtends an angle of approximately 10. (Equating this distance to 8 kpc and setting the velocity unit at 300 km/s, then the time unit of the simulation is 4.33 Myr and the total mass is .) The resemblance to the Weiland et al. COBE photometry is quite striking, although the asymmetry in the extent of the bar between the near and far sides is perhaps too strong.

 
Figure 3: The line-of-sight components (full drawn) and perpendicular components (dashed) over a range of longitudes at fixed latitude. All particles within 2 kpc of the galactic centre distance contribute equally and data from above and below the plane combined to improve statistics. The bottom pair of curves are for , higher pairs are for values increasing by 2 and offset vertically by 100 km/s each time for clarity.



Peter Teuben
Wed Feb 8 15:23:27 EST 1995