An optical study of stars and dust in the Andromeda galaxy.
Abstract
We have analyzed the light distribution of the nearby spiral M 31, using recently obtained surface photometry in four colours. Three main topics are discussed. First, we study the structure in the outer parts of the disk. Our data confirm previously presented evidence for a significant change in the position angle of the light distribution. probably indicating a warping of the stellar disk. The warping starts at 18 kpc and is in the same direction as the warp in the gas distribution. Second, we discuss the structure and global color distribution of the disk and bulge of M 31. A decomposition of the major and minor axis profiles allows us to separate radial color variations in bulge and disk. No color gradient is found for the bulge light. We show that the apparent flattening of the light profile of the disk noted by de Vaucouleurs can be attributed to the contribution from spiral arms. The disk colors at small radii and the colors of the bulge are typically those of an old, metal-rich stellar population. The disk light, corrected for the contribution of spiral arms, becomes bluer with radius, due to a metal abundance gradient or to a contribution from younger stars inbetween the arms. Finally, we derive the optical extinction law in M 31 from a detailed analysis of the absorption of light in two major dust lanes on the near side of the galaxy. A correlation of the optical extinctions with neutral atomic gas column densities shows that the dust-to-(atomic) hydrogen gas ratio is similar to that in the solar neighborhood, but may well decrease with radius.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- June 1988
- Bibcode:
- 1988A&A...198...61W
- Keywords:
-
- Andromeda Galaxy;
- Astronomical Photometry;
- Cosmic Dust;
- Galactic Structure;
- Interstellar Extinction;
- Interstellar Gas;
- Photographic Plates;
- Astrophysics