Kinematics of galaxies in compact groups

Studying the B-band Tully-Fischer relation^{*, **}

¹ Departamento de Astronomia, Instituto de Astronomia, Geofísica e Ciências Atmosféricas da USP, Rua do Matão 1226, Cidade Universitária, 05508-090 São Paulo, Brazil e-mail: storres@astro.iag.usp.br
² Laboratoire d'Astrophysique de Marseille, OAMP, Université de Provence & CNRS, 38 rue F. Joliot-Curie, 13388 Marseille Cedex 13, France
³ Laboratório de Astrofísica Teórica e Observacional, Universidade Estadual de Santa Cruz, Ilheus, Brazil
⁴ Laboratoire d'Astrophysique de Toulouse-Tarbes, Université de Toulouse & CNRS, 14 avenue Edouard Belin, 31400 Toulouse, France
⁵ Laboratoire d'Astrophysique Expérimentale (LAE), Observatoire du Mont Mégantic, and Département de Physique, Université de Montréal, CP 6128, Succ. Centre-Ville, H3C 3J7, Montréal, QC, Canada
⁶ Observatoire d'Astrophysique de l'Université de Ouagadougou (UFR/SEA), 03 BP 7021 Ouagadougou 03, Burkina Faso
⁷ GEPI, Observatoire de Paris, Paris University Denis Diderot & CNRS, 5 place Jules Janssen, Meudon, France

Received: 18 December 2009
Accepted: 26 February 2010

Abstract

We obtained new Fabry-Perot data cubes and derived velocity fields, monochromatic, and velocity dispersion maps for 28 galaxies in the Hickson compact groups 37, 40, 47, 49, 54, 56, 68, 79, and 93. We also derived rotation curves for 9 of the studied galaxies, 6 of which are strongly asymmetric. Combining these new data with previously published 2D kinematic maps of compact group galaxies, we investigated the differences between the kinematic and morphological position angles for a sample of 46 galaxies. We find that one third of the unbarred compact group galaxies have position angle misalignments between the stellar and gaseous components. This and the asymmetric rotation curves are clear signatures of kinematic perturbations, probably because of interactions among compact group galaxies. A comparison between the B-band Tully-Fisher relation for compact group galaxies and for the GHASP field-galaxy sample shows that, despite the high fraction of compact group galaxies with asymmetric rotation curves, these lay on the TF relation defined by galaxies in less dense environments, although with more scatter. This agrees with previous results, but now confirmed for a larger sample of 41 galaxies. We confirm the tendency for compact group galaxies at the low-mass end of the Tully-Fisher relation (HCG 49b, 89d, 96c, 96d, and 100c) to have either a magnitude that is too bright for its mass (suggesting brightening by star formation) and/or a low maximum rotational velocity for its luminosity (suggesting tidal stripping). These galaxies are outside the Tully Fisher relation at the 1σ level, even when the minimum acceptable values of inclinations are used to compute their maximum velocities. Including such galaxies with v < 100 km s^-1 in the determination of the zero point and slope of the compact group B-band Tully-Fisher relation would strongly change the fit, making it different from the relation for field galaxies, which has to be kept in mind when studying scaling relations of interacting galaxies, especially at high redshifts.