De Vaucouleurs Atlas Type: Sb sp
Telescope: WIYN 3.5-m
North up , East left
Field Dimensions: 6.7 x 6.7 arcminutes
RC3 Type: SA:(s?)b sp
RSA Type: Sb
Surface Brightness Range Displayed: 17.5-26.0 mag per square arcsec
Absolute Blue Magnitude: -22.1
De Vaucouleurs Atlas Description:
Only the inner part of this famous edge-on spiral is covered in our Atlas image, but the quality of the image is very high. NGC 4565 is an exceptional edge-on spiral with a significant bulge and a very extended disk. The Sb classification is based mainly on this apparent bulge-to-disk ratio, and also on the general patchiness of the disk. Although de Vaucouleurs suspected the galaxy is nonbarred and of the (s) variety, we cannot be certain of either just by looking at the image. The most striking feature of the galaxy is its strong planar dust lane. The galaxy is not exactly edge-on, because the nucleus peers out of the dust layer just south of the lane.
The B-V color index map shows the interesting feature that the dust lane is not as red in its midsection as it is near its edge. Also, the dust lane seems hardly red at all, in spite of an obviously large amount of extinction. Witt, Thronson, and Capuano (1992) note that broadband colors are not always correlated with the amount of extinction. There will be some compensation for reddening due to scattering that can almost neutralize the broadband colors. The fraction of stars only lightly obscured is also important. In NGC 4565 , we may be seeing some of these effects in the color of its dust lane. Also, if the dust layer does not extend all the way to the edge of a disk, then there may be some disk light in front of the dust layer to reduce the reddening. The Atlas images are from Howk and Savage (1999), who studied the vertical distribution of dust in NGC 4565 .
NGC 4565 has been the subject of numerous studies, in particular of its vertical light distribution (e.g., van der Kruit and Searle 1981; Naslund and Jorsater 1997).