IS THE STANDARD ELLIPTIC NGC-3379 A TRIAXIAL DISK GALAXY

The two-dimensional B-band surface brightness distribution of NGC 3379, derived in a previous study by combining CCD exposures and deep Schmidt plates, is used to investigate whether this well-known elliptical galaxy, a standard for its morphological class, contains a small disk. It is assumed that the bulge of the SO NGC 3115 is the photometric prototype for this class of galaxian components. The minor-axis light profile of NGC 3115, which is almost uncontaminated by its edge-on disk, is scaled and subtracted from both the major and minor axis profiles of NGC 3379. The residuals are well fitted by an exponential disk, with a deprojected central surface brightness mu-B(c)(0) = 21.56 +/- 0.20 obtained from fitting the two axes. The fact that this value, which is not built into our fitting procedure, is identical to those of all disks (e.g., work of van der Kruit) gives some support to our interpretation. With a distance of 9.8 Mpc, the parameters of the disk are scale length 1.4 kpc (= 30".2), luminosity 2 x 10(9) L. (m(B) = 12.16 +/- 0.33), and bulge-to-disk ratio 8 +/- 2.8. If the analogy with NGC 3115 is pushed to say that the two galaxies also have the same geometrical shape, then from the photometry alone one can determine their axial ratios to be b/a = 0.9 +/- 0.1 and c/a = 0.5 +/- 0.1 in the inner (r/r(e) < 0.4) region, and b/a = 0.75 +/- 0.1 and c/a = 0.5 +/- 0.1 in the outer region. In other words, the model common to both NGC 3379 and NGC 3115 is found to be almost oblate close to the center and triaxial further out. The implications of the presence of disks in elliptical galaxies for their formation histories are briefly commented on.