Astronomy and Astrophysics, volume 293, 20-43 (1995/1-1)
The internal structure of disky elliptical galaxies.
SCORZA C. and BENDER R.
Abstract (from CDS):
The structure of seven disky ellipticals, one bulge-dominated S0 (NGC 3115) and one boxy elliptical with a disky core (NGC 5322) has been investigated on the basis of two-component decomposition techniques applied to photometric and kinematic data. We find that both disky isophotes and the observed asymmetric velocity line profiles of these objects can consistently be interpreted within simple disk + bulge models. Stellar disks in disky ellipticals appear to have on average smaller scale lengths and higher surface brightnesses than disks in S0 and Sa galaxies. The disk-to-bulge ratios of the objects investigated here range from 0.03 to 0.28. The surface brightness profiles of the disks are in most cases intermediate between exponential and r1/4 profiles. In all disky ellipticals bulges and disks have parallel angular momenta. This demonstrates that stellar disks in disky ellipticals are not the result of late accretion or merger events but are likely to be primordial (in the same sense as are disks in S0's). The anisotropy parameter of the bulges appears to be correlated with their mean surface brightness. Bulges of higher surface brightness are rotationally flattened, while those of lower surface brightness show considerable anisotropy ((v/σ)*≃0.3). In NGC 4660, the object with the highest disk-to-bulge ratio, we detect evidence for a bar with a radius of 1kpc. In NGC 3115, we find that the nuclear disk may contribute up to 50% of the light on the major axis at about 1arcsec. This study supports the hypothesis that disky ellipticals form a continuity in disk-to-bulge ratio and kinematic properties with S0 galaxies.
galaxies: elliptical and lenticular, photometry, structure