Outsider's view of the galaxy: Photometric parameters, scale lengths, and absolute magnitudes of the spheroidal and disk components of our galaxy
A two-component model of the Galaxy consisting of (I) an R/sup 1/4/ spheroid of effective radius r/sup I//sub e/=2.67 kpc (for r/sub 0/=8.0 kpc) and peak brightness ..mu../sup I//sub B/(0) =15.11 mag arcsec/sup -2/, and (II) an exponential disk of effective radius r/sup II//sub e/=5.98 kpc and (assumed) peak brightness ..mu../sup II//sub B/(0) =21.65 (after Freeman) is shown to be consistent with the galactic disk brightness inferred from star counts and to give a good representation of new observations of the brightness distribution in the bulge along galactic meridian 0/sup degree/. An ellipsoidal model of the spheroid with a/sup I//sub e/=3.45 kpc and c/a=0.6 is also considered with little change in most results; averages from the two cases are adopted. For an outside observer the face-on total absolute magnitude of the Galaxy (with allowance for uniform internal extinction of total optical depth A/sub B/=0.4 mag) is M/sup 0//sub T/(B) =-20.08 or L/sub T/(B) =1.6 x 10/sup 10/L/sub sun/, of which half is emitted within the effective radius r/sub e/=5.1 kpc. The fraction K/sub I/=L/sup I//L/sub T/=0.34 +- 0.04 contributed by the spheroidal component is in close agreement with corresponding values for several Sbc (T=4) galaxies. The calculated standard face-on isophotal diameter of the Galaxy at the ..mu../sub B/=25.0 level, D/sub 0/=23.0 kpc is in close agreement with three independent estimates (21.4--23.4) from statistical relations for spiral galaxies. The luminosity index ..lambda..= (T+L)/10 of the Galaxy derived by three independent methods is ..lambda..=0.71 +- 0.03, implying a luminosity class L=3 +- 1 (LC=II), if T=4 +- 0.5. The mean intrinsic color (corrected for extinction) of the spheroidal component derived from the observations is /sub I/=0.65 +- 0.05; that of the disk stellar population derived from local luminosity functions is /sub II/=0.40 (after Holmberg, transformed to B,V system).
- Research Organization:
- Department of Astronomy and McDonald Observatory, The University of Texas, Austin, Texas 78712
- OSTI ID:
- 6734906
- Journal Information:
- Astron. J.; (United States), Vol. 83:10
- Country of Publication:
- United States
- Language:
- English
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