Bibcode
DOI
Kormendy, John; Cornell, Mark E.; Block, David L.; Knapen, Johan H.; Allard, Emma L.
Bibliographical reference
The Astrophysical Journal, Volume 642, Issue 2, pp. 765-774.
Advertised on:
5
2006
Journal
Citations
33
Refereed citations
27
Description
We present Ks-band surface photometry of NGC 7690 (Hubble
type Sab) and NGC 4593 (SBb). We find that, in both galaxies, a major
part of the ``bulge'' is as flat as the disk and has approximately the
same color as the inner disk. In other words, the ``bulges'' of these
galaxies have disklike properties. We conclude that these are examples
of ``pseudobulges,'' that is, products of secular dynamical evolution.
Nonaxisymmetries such as bars and oval disks transport disk gas toward
the center. There star formation builds dense stellar components that
look like-and often are mistaken for-merger-built bulges, but that were
constructed slowly out of disk material. These pseudobulges can most
easily be recognized when, as in the present galaxies, they retain
disklike properties. NGC 7690 and NGC 4593 therefore contribute to the
growing evidence that secular processes help to shape galaxies. NGC 4593
contains a nuclear ring of dust that is morphologically similar to
nuclear rings of star formation that are seen in many barred and oval
galaxies. The nuclear dust ring is connected to nearly radial dust lanes
in the galaxy's bar. Such dust lanes are a signature of gas inflow. We
suggest that gas is currently accumulating in the dust ring and
hypothesize that the gas ring will starburst in the future. The
observations of NGC 4593 therefore suggest that major starburst events
that contribute to pseudobulge growth can be episodic.
Based on observations made with the Anglo-Australian Telescope.
Based in part on observations made with the NASA/ESA Hubble Space
Telescope, obtained from the Data Archive at the Space Telescope Science
Institute (STScI). STScI is operated by the Association of Universities
for Research in Astronomy, Inc., under NASA contract NAS5-26555. The
observations of NGC 7690 are associated with program IDs 7331 (NICMOS:
M. Stiavelli) and 6359 (WFPC2: M. Stiavelli). The observations of NGC
4593 are associated with program IDs 7330 (NICMOS: J. Mulchaey), and
5479 (WFPC2: M. Malkan).