Photometric study of a sample of southern binary galaxies

Free access article

Issue		A&A Volume 457, Number 2, October II 2006


Page(s)		405 - 424
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20054442

A&A 457, 405-424 (2006)
DOI: 10.1051/0004-6361:20054442

Photometric study of a sample of southern binary galaxies

T. C. Couto da Silva¹ and R. E. de Souza²

¹ Departamento de Física - ICET, UFMT, Av. Fernando Correa s/n, Cuiabá, MT, Brazil
e-mail: tcsp@terra.com.br
² Instituto de Astronomia, Geofísica e Ciências Atmosféricas - USP C.Postal 9638, 01065 - 970 São Paulo, Brazil
e-mail: ronaldo@astro.iag.usp.br

(Received 30 October 2005 / Accepted 31 March 2006)

Abstract
Aims.This work exhibits the basic optical photometric data for a sample of 50 probable southern binary galaxies. Our sample covers a broad range of pair separations, stages of interaction, and morphologies. From the initial list of selected pairs, using spectroscopic data from the literature and our own data, we conclude that $84\%$ of these systems are true binary galaxies.
Methods.We present residual and asymmetric maps, R major semi-axis profiles of surface brightness, ellipticity, position-angle, harmonic Fourier coefficients of third and fourth order (b₃ and b₄) for 50 probable pairs, and B-R color maps for 47 of these pairs. For most galaxies, we present the profiles in two different ways, aiming to verify the influence of random errors on them.
Results. We note that random errors in position-angle profiles are at least $2^\circ$ , but a more significant result must take into account a variation larger than $11^\circ$ for this distribution. Barred galaxies usually show a typical behavior in ellipticity and position-angle profiles: these profiles display variations when changing from a bar to a disk region. In some cases, the variations also occur along the bar. Some galaxies show distribution profiles that are common for their morphological type, and the interaction signature is only evidenced by their residual maps. Bars are usually redder and rings are bluer, when compared with the galaxy outskirts.
Conclusions.Our data indicates that there is a connection between interaction strength and morphological distortions in binary galaxies. If we consider the projected separation of a pair as an indication of interaction strength, distortions such as displaced centers, anomalous shapes of spiral arms, and twistings of external regions are easily detected in some close pairs, although not all components of close pairs show this behavior. Our data suggests that besides interaction, other parameters, like orbital geometry and internal properties of galaxies, can stimulate binary galaxies' peculiarities.

Key words: galaxies: interactions -- galaxies: photometry

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