Mathematics – Logic
Scientific paper
Oct 1978
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1978apj...225...56s&link_type=abstract
Astrophysical Journal, Part 1, vol. 225, Oct. 1, 1978, p. 56-66. Research supported by the Consejo Nacional de Investigaciones
Mathematics
Logic
51
Astronomical Photometry, Galactic Structure, Halos, Mass To Light Ratios, Spiral Galaxies, Astronomical Photography, Brightness, Electrophotometry, Elliptical Galaxies, Galactic Rotation, Hubble Diagram, Isophotes
Scientific paper
Photographic and photoelectric photometry of three representative edge-on spiral galaxies, NGC 4594 (Sa), NGC 4565 (Sb), and NGC 253 (Sc), shows that each has an extensive faint spheroidal component qualitatively similar to that of an elliptical galaxy. However, their exterior surface brightnesses decline more rapidly, as power laws, with the inverse 2.5 or 3rd power of distance, and the ellipticity tends to decrease with increasing radius. The total spheroidal luminosity is comparable to or greater than the disk luminosity in all cases. Radio and optical rotation curves for two of the galaxies (NGC 4594 and 4565) indicate that the local mass-to-light ratio increases sharply with radius from the square root of 10 in the central regions to 10 to the 2.5 power to 1000 for NGC 4565 at 50 kpc. The integral mass-to-light ratios are probably less than about 0.01. Color information is inconclusive; no clear evidence for a population variation with distance has been found other than the well-known trend toward bluer B-V color due to decreasing metallicity with radius. In the Sc galaxy NGC 253 one can say that any color gradient is small to a distance of about 10 kpc. Most of the mass appears to reside in a component having a very large value of local M/L ratio and, at present, a totally unknown nature.
Bruzual Gustavo A.
George Chiu Liang-Tai
Ostriker Jeremiah P.
Spinrad Hyron
Stone Remington P. S.
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