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Issue A&A Volume 374, Number 1, July IV 2001 Page(s) 83 - 91 Section Extragalactic astronomy DOI 10.1051/0004-6361:20010691

A&A 374, 83-91 (2001)
DOI: 10.1051/0004-6361:20010691

The visible environment of galaxies with counterrotation

D. Bettoni¹, G. Galletta² and F. Prada<sup>3

1</sup>  Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
²  Dipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 2, 35122 Padova, Italy
³  Centro Astronómico Hispano-Alemán, Apartado 511, 04080 Almería, Spain

(Received 6 February 2001 / Accepted 23 April 2001)

Abstract
In this paper we present a statistical study of the environments of 49 galaxies in which there is gas- or stellar-counterrotation. The number of possible companions in the field (to apparent magnitude 22), their size and concentration were considered. All the statistical parameters were analysed by means of Kolgomorov-Smirnov tests, using a control sample of 43 galaxies without counterrotation. From our data, no significant differences between the counter-rotating and control samples appear. This is different to Seyfert or radio-loud galaxies which lie in environments with a higher density of companions. On the contrary, if a weak tendency exists, for galaxies with gas counterrotation only, it is discovered in regions of space where the large scale density of galaxies is smaller. Our results tend to disprove the hypothesis that counterrotation and polar rings derive from a recent interaction with a small satellite or a galaxy of similar size. To a first approximation, they seem to follow the idea that all galaxies are born through a merger process of smaller objects occurring very early in their life, or that they derive from a continuous, non-traumatic infall of gas that formed stars later. Whatever the special machinery is which produces counterrotation or polar rings instead of a co-planar, co-rotating distribution of gas and stars, it seems not to be connected to the present galaxy density of their environments.

Key words: galaxies: evolution -- galaxies: formation -- galaxies: interactions -- galaxies: peculiar

Offprint request: G. Galletta, galletta@pd.astro.it

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© ESO 2001

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