Galactic bulges from Hubble Space Telescope near-infrared camera multi-object spectrometer observations: the lack of r 1/4 bulges

摘要

We use Hubble Space Telescope (HST) near-infrared imaging to explore the shapes of the surface brightness profiles of bulges of S0-Sbc galaxies at high resolution. Modeling extends to the outer bulge via bulge-disk decompositions of combined HST-ground-based profiles. Compact, central unresolved components similar to those reported by others are found in ~84% of the sample. We also detect a moderate frequency (~34%) of nuclear components with exponential profiles that may be disks or bars. Adopting the Sérsic r1/n functional form for the bulge, none of the bulges have an r 1/4 behavior; derived Sérsic shape indices are (n) = 1.7 ± 0.7, For the same sample, fits to near-infrared ground-based profiles yield Sérsic indices up to n = 4-6. The high n of ground-based profiles are the result of nuclear point sources blending with the extended light of the bulge because of seeing. The low Sérsic indices are not expected from violent relaxation in mergers.