The Perseus Arm

The Perseus arm has been studied in multiple wavelengths before; however, this is the first time where we attempt to characterize the whole arm in H-alpha emission. It is the easier of the two principal arms to study because most of it is outside of the solar circle and on the same side of the Milky Way as the sun.

Fig. 2: This is an image made by Thomas Dame from the Harvard-Smithsonian Center for Astrophysics showing an artist's conception of the Milky Way Galaxy, with the spiral arms we have evidence for overlaid.

In the above image, the Perseus arm is overlaid with a dark blue line, near the bottom of the image. As seen, it starts at the opposite end of the galactic bar as the Scutum-Centaurus arm (overlaid in light blue) and wraps almost all the way around the galaxy. L.M. Haffner et. al. (Haffner, L. M., et. al. 1999, ApJ, 523, 223) studied a small chunk of the Perseus arm in H-alpha emission. The part they looked at was l=123°-164°, b=-6°- -35°. In contrast, we took H-alpha data from l=0°-360° degrees and b=±30°, a full sky strip.

The next page depicts this region of the sky we used as well as similar regions in other wavelengths in the form of LV Diagrams.

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