Bibcode
Erwin, P.; Saglia, Roberto P.; Fabricius, Maximilian; Thomas, Jens; Nowak, Nina; Rusli, Stephanie; Bender, Ralf; Vega Beltrán, J. C.; Beckman, J. E.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 446, Issue 4, p.4039-4077
Advertised on:
2
2015
Citations
111
Refereed citations
104
Description
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 per cent of the galaxy
stellar mass (mean PB/T = 0.33), with stellar masses ˜7 ×
109-9 × 1010 M⊙. The
classical-bulge components have Sérsic indices of 0.9-2.2,
effective radii of 25-430 pc and stellar masses of 5 ×
108-3 × 1010 M⊙; they are
usually <10 per cent 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'.
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