Spiral galaxy M99 = NGC 4254


This color-composite CCD image shows the bright, attractive spiral galaxy M99 (NGC 4254) in Virgo. This galaxy is an advertisement for how asymmetric spiral galaxies can be for no obvious reason; the single strong arm on the west side stands in contrast to the multiple arms on the other side of the disk. It has no especially close neighbors in the Virgo cluster, so tidal distortion is not a very attarctive explanation. There may be several interesting questions here- how does a galaxy become asymmetric, is the asymmetry only a function of the gas distribution driving star formation, and how long can such a structure remain without being smeared out by the galaxy's dynamics? Even for a galaxy of such late Hubble type, one can see a strong color contrast between the bulge and arms.

This color composite is from B and R images (with synthetic V) taken during twilight with a Tektronix 2048x2048 CCD at the 2.1-meter telescope of Kitt Peak National Observatory, by Bill Keel and Lisa Frattare. North is at the top and east to the left, for direct comparison with a chart or eyepiece view. The image has been block-averaged by a factor of 2 for this presentation, which uses a logarithmic intensity transformation to preserve information across a wide dynamic range, and further averaged 2x as shown above (click to see it in full size). The field is 9.3 arcminutes on a side.


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