Surface photometry of edge-on spiral galaxies. II - The distribution of light and colour in the disk and spheroid of NGC 891.
We present three-colour surface photometry of the edge-on spiral galaxy NGC 891. We apply the locally isothermal, truncated exponential disk model of Paper I to the disk of NGC 891 and subtract it from the observed brightness distribution to reveal the halo population. We then find the following results: 1. The disk of NGC 891 is fitted satisfactorily by the model and has the feature that the colour index is constant throughout. Its colours indicate old disk population. 2. The spheroidal component is fiattened at large distances from the centre, and appears in the z-profiles as a "thick disk" (Burstein, 1979). The gravitational field of the disk is sufficient to account for this. 3. The spheroid shows a colour distribution indicating a halo population with a radial gradient of heavy element abundance and a range in abundances similar to that of the globular clusters in our Galaxy. This indicates that the "thick disk" is really population II deformed by the gravitational field of the disk. 4. There is no detectable difference between the shapes of the isophotes and isochromes in the spheroid.
Astronomy and Astrophysics
- Pub Date:
- February 1981