Deep Surface Photometry of NGC 891

Senior Thesis Project, Oberlin College, 1996

Stellar Populations in Edge-On Galaxies From Deep CCD Surface Photometry. II. One-Dimensional Fits of NGC 891
Heather L. Morrison, Eric D. Miller, Paul Harding, Daniel R. Stinebring, and Todd A. Boroson, 1997, The Astronomical Journal, 113, 2061

This is a false-color image of the edge-on spiral galaxy NGC 891. The color levels, shown on a scale corresponding to the log of the brightness, show the presence of a variety of components to this galaxy. The bulge (brightest yellow) can be seen in the center of the galaxy; it appears to have "boxy" isophotes, hinting at the presence of a central bar. The dust lane can clearly be seen running through the bulge and thin disk (orange). The red region is the thick disk; the diamond shape of the thick disk isophotes indicate a scale height that is constant with radial distance from the galactic center. One theory holds that thick disks are created by heating from satellite accretion. However, numerical models show that such accretion events tend to cause flaring in the thick disk, leading to a radially-varying scale height. The apparent lack of flaring of NGC 891's thick disk could be preliminary evidence against such a theory.

From this image alone, it is difficult to determine whether NGC 891 has a faint massive halo component. Two-dimensional modeling will provide a better perspective on that issue.