Issue |
A&A
Volume 423, Number 3, September I 2004
|
|
---|---|---|
Page(s) | 849 - 859 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20035804 | |
Published online | 12 August 2004 |
Spiral galaxies observed in the near-infrared K band *,**,***
I. Data analysis and structural parameters
1
European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany e-mail: pgrosbol@eso.org
2
Research Center for Astronomy, Academy of Athens, Anagnostopoulou 14, 10673 Athens, Greece
3
European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago 19, Chile
Received:
4
December
2003
Accepted:
3
April
2004
Deep surface photometry in the K band was obtained for 54 normal spiral galaxies, with the aim of quantifying the percentage of
faint bars and studying the morphology of spiral arms. The sample was
chosen to cover a wider range of morphological types while inclination
angles and distances were limited to allow a detailed investigation of
the internal structure of their disks and future observations and
studies of the disk kinematics.
An additional constraint for a well defined subsample was
that no bar structure was seen on images in the visual bands.
Accurate sky projection parameters were determined from the K maps
comparing several different methods. The surface brightness
distribution was decomposed into axisymmetric components while bars and
spiral structures were analyzed using Fourier techniques.
Bulges were best represented by a Sérsic law with
an index in the typical range of 1-2. The central surface brightness
of the exponential disk and bulge-to-disk ratio only showed weak
correlation with Hubble type. Indications of a central point source
were found in many of the galaxies. An additional central, steep,
exponential disk improved the fit for more than 80% of the galaxies
suggesting that many of the bulges are oblate.
Bars down to the detection level at a relative amplitude of 3% were
detected in 26 of 30 galaxies in a subsample classified as ordinary
SA spirals. This would correspond to only 5% of all spiral
galaxies being non-barred at this level. In several cases, bars are
significantly offset compared to the starting points of the main
spiral pattern which indicates that bar and spiral have different
pattern speeds. A small fraction (~10%) of the sample has
complex central structures consisting of several sets of bars, arcs or
spirals.
A majority of the galaxies (~60%) displays a two-armed,
grand-design spiral pattern in their inner parts which often breaks
up into multiple arms in their outer regions. Phase shifts between
the inner and outer patterns suggest in some cases that they belong to
different spiral modes. The pitch angles of the main two-armed
symmetric spiral pattern in the galaxies have a typical range of
5-30°. The sample shows a lack of strong, tight spirals which
could indicate that such patterns are damped by non-linear,
dynamical effects due to their high radial force perturbations.
Key words: galaxies: photometry / galaxies: spiral / galaxies: structure / galaxies: fundamental parameters / infrared: galaxies
Based on observations collected at the European Southern Observatory, La Silla, Chile; programs: ESO 63.N-0343, 65.N-0287, 66.N-0257.
© ESO, 2004
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