Edge on spiral galaxies in which we are almost exactly in the plane of the galaxy possess a unique visual appearance. This 9.8 magnitude Sc spiral, reveals a web work of dark obscuring lanes across the central region, nearly hidden by this extensive dust shroud. This galaxy is called the "Whale" because of its asymmetrical shape, and the companion galaxy (the Pup) which is gravitationally bound to 4631 is NGC4627, a 12.5 magnitude warped elliptical type, is seen just below the core to the left. NGC4631 is engulfed in star forming activity. A yellow population is visible in the nuclear region, with faintly bluish arms studded with OB associations. The tawny color of the companion, is because it is the prototype for metal poor ellipticals.
The color presented here is based on the landmark Wray Atlas, in which an extensive study was done on this object to define the color indexes of the galaxies components. The G2 star calibrated RGB images used for this image match very closely with the B-V indices, with a secondary confirmation coming from the correct pink coloration of the large HII regions in the equatorial region, which are the result of the combined light of Halpha and OIII components.
Instrument: 12.5" f/5 Home made Newtonian CCD Camera: SBIG ST7E Exposure: LRGB = 90:20:20:40 (RGB Binned 2x2) Filters: RGB Tricolor Location: Payson, Arizona Elevation: 5150 ft. Sky: Seeing 5/10, Transparency 2/10 Outside Temperature: 50 F CCD Temperature: -15F Processing: Maxim DL, Photoshop, PW Pro.