Surface photometry of spiral galaxies. I - Theoretical color variation and surface brightness across spiral arms
Abstract
A method for the construction of color variations and surface brightness across a galactic spiral arm, using the concepts and results of the density-wave theory, is developed. The color variation measured by the index Q varies with the ratio of the light of young stars to that of the old stars, the initial mass function, and the pattern speed. The fact that the variation of brightness and color across a spiral arm is relatively smooth and symmetrical and not sharp as in the galactic shock picture is due to the smearing-out effects of star formation inside a cloud in the regions behind the galactic shock, and the tendency of new stars to fall back to small galactocentric distances after their formation because of their lower angular velocity at birth. Both effects arise naturally in the context of the density-wave theory.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 1981
- DOI:
- 10.1086/158610
- Bibcode:
- 1981ApJ...243..432Y
- Keywords:
-
- Astronomical Photometry;
- Brightness;
- Color;
- Galactic Structure;
- Spiral Galaxies;
- Density Wave Model;
- Graphs (Charts);
- Milky Way Galaxy;
- Probability Distribution Functions;
- Astrophysics