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
105
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'.
Related projects
Kinematic, Structural and Composition Studies of the Interstellar and Intergalactic Media
The basic objective of the broject is to investigate the evolution of galaxies by deepening our understanding of the interaction between the insterstellar medium and the stars.The main technique which we use is the two-dimensional kinematic study of whole galaxies observed using our instrument:GHaFaS, a Fabry-Perot interferometer on the William
Prof.
John E. Beckman