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Astron. Astrophys. 351, 869-882 (1999)


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A statistical study of nearby galaxies

I. NIR growth curves and optical-to-NIR colors as a function of type, luminosity and inclination

Michel Fioc 1,2 and Brigitte Rocca-Volmerange 2,3

1 NASA/Goddard Space Flight Center, code 685, Greenbelt, MD 20771, USA
2 Institut d'Astrophysique de Paris, CNRS, 98 bis Bd Arago, 75014 Paris, France
3 Institut d'Astrophysique Spatiale, Bât. 121, Université Paris XI, 91405 Orsay, France

Received 23 April 1999 / Accepted 6 September 1999

Abstract

Growth curves of the near-infrared (NIR) magnitude as a function of the aperture have been built and used to derive NIR total magnitudes from aperture data taken from the literature. By cross-correlating with optical and redshift data, absolute magnitudes and optical-to-NIR colors have been computed for some 1000 galaxies of different types. Significant color gradients are observed, underlining that small aperture colors may lead to a biased picture of the stellar populations of galaxies.

A statistical analysis, using various estimators taking into account the intrinsic scatter, has been performed to establish relations between the colors, the morphological type, the inclination or the shape, and the intrinsic luminosity.

The combination of the optical and the NIR should obviously improve our understanding of the evolution of galaxies. Despite the intrinsic scatter, especially among star-forming galaxies, optical-to-NIR colors show a very well defined sequence with type, blueing by 1.35 mag from ellipticals to irregulars. The colors of spiral galaxies strongly redden with increasing inclination and put new constraints on the modeling of the extinction. No such effect is observed for lenticular galaxies. We also find that rounder ellipticals tend to be redder.

A color-absolute magnitude relation is observed inside each type, with a slope significantly steeper for early and intermediate spirals than for ellipticals or late spirals. This stresses the importance of considering both the mass and the type to study the star formation history of galaxies.

Key words: galaxies: evolution – galaxies: fundamental parameters – galaxies: photometry – galaxies: statistics – infrared: galaxies – ISM: dust, extinction

Send offprint requests to: Michel Fioc

Correspondence to: fioc@zardoz.gsfc.nasa.gov

© European Southern Observatory (ESO) 1999

Online publication: November 16, 1999

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