Mon. Not. R. Astron. Soc., 446, 4039-4077 (2015/February-1)
Composite bulges: the coexistence of classical bulges and discy pseudo-bulges in S0 and spiral galaxies.
ERWIN P., SAGLIA R.P., FABRICIUS M., THOMAS J., NOWAK N., RUSLI S., BENDER R., VEGA BELTRAN J.C. and BECKMAN J.E.
Abstract (from CDS):
We present an analysis of nine S0-Sb galaxies which have (photometric) bulges consisting of two distinct components. The outer component is a flattened, kinematically cool, disc-like structure: a `discy pseudo-bulge'. Embedded inside is a rounder, kinematically hot spheroidal structure: a `classical bulge'. This indicates that pseudo-bulges and classical bulges are not mutually exclusive phenomena: some galaxies have both. The discy pseudo-bulges almost always consist of an exponential disc (scalelengths = 125-870 pc, mean size ∼ 440 pc) with one or more disc-related subcomponents: nuclear rings, nuclear bars, and/or spiral arms. They constitute 11-59 percent of the galaxy stellar mass (mean PB/T = 0.33), with stellar masses ∼ 7x109-9x1010 M☉. The classical-bulge components have Sérsic indices of 0.9-2.2, effective radii of 25-430 pc and stellar masses of 5x108-3x1010 M☉; they are usually <10 percent of the galaxy's stellar mass (mean B/T = 0.06). The classical bulges do show rotation, but are clearly kinematically hotter than the discy pseudo-bulges. Dynamical modelling of three systems indicates that velocity dispersions are isotropic in the classical bulges and equatorially biased in the discy pseudo-bulges. In the mass-radius and mass-stellar mass density planes, classical-bulge components follow sequences defined by ellipticals and (larger) classical bulges. Discy pseudo-bulges also fall on this sequence; they are more compact than large-scale discs of similar mass. Although some classical bulges are quite compact, they are as a class clearly distinct from nuclear star clusters in both size and mass; in at least two galaxies they coexist with nuclear clusters. Since almost all the galaxies in this study are barred, they probably also host boxy/peanut-shaped bulges (vertically thickened inner parts of bars). NGC 3368 shows isophotal evidence for such a zone just outside its discy pseudo-bulge, making it a clear case of a galaxy with all three types of `bulge'.
© 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society (2014)
galaxies: bulges - galaxies: elliptical and lenticular, cD - galaxies: evolution - galaxies: kinematics and dynamics - galaxies: spiral - galaxies: structure
VizieR on-line data:
<Available at CDS (J/MNRAS/446/4039): galaxy.dat tableb2.dat>
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