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Astron. Astrophys. 344, 421-432 (1999)

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Effects of interaction on the properties of spiral galaxies

II. Isolated galaxies: The zero point *

I. Márquez 1 and M. Moles **  2,3

1 Instituto de Astrofísica de Andalucía (C.S.I.C.), Apdo. 3004, E-18080 Granada, Spain
2 Instituto de Matemáticas y Física Fundamental (C.S.I.C.), C/Serrano 123, E-28006 Madrid, Spain
3 Observatorio Astronómico Nacional, Madrid, Spain

Received 9 November 1998 / Accepted 18 January 1999


We analyse the properties of a sample of 22 bright isolated spiral galaxies on the basis of Johnson B,V,I images and optical rotation curves. The fraction of early morphological types in our sample of isolated galaxies (or in other samples of non-interacting spiral galaxies) appears to be smaller than in samples including interacting systems. The overall morphological aspect is regular and symmetric, but all the galaxies present non-axisymmetric components in the form of bars or rings. We find that the color indices become bluer towards the outer parts and that their central values are well correlated with the total colors. The properties of the bulges span a larger range than those of the disks, that thus are more alike between them. None of the galaxies shows a truncated, type II disk profile. It is found that the relation between surface brightness and size for the bulges, the Kormendy relation, is tighter when only isolated galaxies are considered. We find a similar relation for the disk parameters with an unprecedented low scatter.

A Principal Component Analysis of the measured parameters shows that 2 eigenvectors suffice to explain more than 95 [FORMULA] of the total variance. These are, as found for other samples including spiral galaxies in different environmental situations, a scale parameter given by the mass or, equivalently, the luminosity or the size; and a form parameter given by the bulge to disk luminosity ratio, B/D, or, equivalently, by the gradient of the solid-body rotation region of the rotation curve, the G-parameter. We report here a tight correlation between G and B/D for our sample of isolated spirals that could be used as a new distance indicator.

Key words: galaxies: fundamental parameters – galaxies: interactions – galaxies: kinematics and dynamics – galaxies: photometry – galaxies: spiral – galaxies: structure

* Based on data obtained at the 1.5m telescope of the Estación de Observación de Calar Alto, Instituto Geográfico Nacional, which is jointly operated by the Instituto Geográfico Nacional and the Consejo Superior de Investigaciones Científicas through the Instituto de Astrofísica de Andalucía
** Visiting Astronomer, German-Spanish Astronomical Center, Calar Alto, operated by the Max-Planck-Institut für Astronomie jointly with the Spanish National Commission for Astronomy

Send offprint requests to: I. Márquez (isabel@iaa.es)

© European Southern Observatory (ESO) 1999

Online publication: March 18, 1999