Mon. Not. R. Astron. Soc. 362, 127–166 (2005) doi:10.1111/j.1365-2966.2005.09274.x GHASP: an Hα kinematic survey of spiral and irregular galaxies – IV. 44 new velocity fields. Extension, shape and asymmetry of Hα rotation curves , O. Garrido,1 2 M. Marcelin,2 P. Amram,2 C. Balkowski,1 J. L. Gach2 and J. Boulesteix2 1Observatoire de Paris, section Meudon, GEPI, CNRS UMR 8111, Universite Paris 7, 5 Place Jules Janssen, 92195 Meudon, France 2 Observatoire Astronomique de Marseille Provence, Laboratoire d’Astrophysique de Marseille, 2 Place Le Verrier, 13248 Marseille Cedex 04 France Downloaded from https://academic.oup.com/mnras/article/362/1/127/1339746 by guest on 30 September 2021 Accepted 2005 June 3. Received 2005 May 26; in original form 2004 August 24 ABSTRACT We present Fabry–Perot observations obtained in the frame of the GHASP survey (Gassendi HAlpha survey of SPirals). We have derived the Hα map, the velocity field and the rotation curve for a new set of 44 galaxies. The data presented in this paper are combined with the data published in the three previous papers providing a total number of 85 of the 96 galaxies observed up to now. This sample of kinematical data has been divided into two groups: isolated (ISO) and softly interacting (SOFT) galaxies. In this paper, the extension of the Hα discs, the shape of the rotation curves, the kinematical asymmetry and the Tully–Fisher relation have been investigated for both ISO and SOFT galaxies. The Hα extension is roughly proportional to R25 for ISO as well as for SOFT galaxies. The smallest extensions of the ionized disc are found for ISO galaxies. The inner slope of the rotation curves is found to be correlated with the central concentration of light more clearly than with the type or the kinematical asymmetry, for ISO as well as for SOFT galaxies. The outer slope of the rotation curves increases with the type and with the kinematical asymmetry for ISO galaxies but shows no special trend for SOFT galaxies. No decreasing rotation curve is found for SOFT galaxies. The asymmetry of the rotation curves is correlated with the morphological type, the luminosity, the (B − V ) colour and the maximal rotational velocity of galaxies. Our results show that the brightest, the most massive and the reddest galaxies, which are fast rotators, are the least asymmetric, meaning that they are the most efficient with which to average the mass distribution on the whole disc. Asymmetry in the rotation curves seems to be linked with local star formation, betraying disturbances of the gravitational potential. The Tully–Fisher relation has a smaller slope for ISO than for SOFT galaxies. Keywords: catalogues – galaxies: dwarf – galaxies: interactions – galaxies: irregular – galax- ies: kinematics and dynamics – galaxies: spiral. cal and photometric axes are confused. GHASP galaxies were first 1 INTRODUCTION chosen to cover the ‘galaxy mass–galaxy morphological type’ plane This paper is the fourth of a series presenting and analysing the for a large range of luminosity (−15 Mb −22) and morpholog- observational data obtained in the frame of the GHASP survey ical types (from Sa to irregular). We estimate that a total sample of (acronym for Gassendi Hα survey of SPirals). This survey consists about 200 galaxies is necessary (see Garrido et al. 2002) to cover in mapping the distribution of the ionized hydrogen of field galaxies the whole ‘MB–type’ plane. Furthermore, they were chosen in low- using a scanning Fabry–Perot interferometer at the 1.93-m telescope density environments, excluding cluster, group or pair galaxies. This of the Observatoire de Haute-Provence (OHP). High-resolution 2D survey will provide a homogeneous reference sample at z = 0of velocity fields (with a sampling about 5 km s−1 in velocity and 3 2D Hα velocity fields (the largest by now after that of Schommer arcsec in spatial resolution) in the Hα line of hydrogen are derived. et al. 1993, which concerns cluster galaxies in the southern hemi- Velocity fields enable us to deduce rotation curves in a more robust sphere) and will allow us to study the mass distribution all along the way than slit spectra, which most often assume that both kinemati- Hubble sequence for various luminosities, the evolution of galaxies when comparing 2D kinematics of distant galaxies (Flores et al. 2004) with nearby ones, the environmental effects and the inner E-mail: [email protected] kinematics with the help of simulations. C 2005 RAS 128 O. Garrido et al. The search for links between the shape of rotation curves (RCs) and physical properties of galaxies has been the subject of many studies. Tully & Fisher (1977) have shown that both luminosity and maximal velocity are tightly linked. Rubin et al. (1985) then showed that in fact the maximal rotational velocity is linked both with the luminosity and the morphological type. Persic, Salucci & Stel (1991) noted that both the shape of the RCs and luminosity are linked, and derived a universal rotation curve (1996) which mainly depends on the luminosity. However, Verheijen (1997) and Sofue et al. (1999) showed that the URC is not able to reproduce systematically the inner and outer parts of their RCs. Galaxies mainly belong to large-scale aggregations (Vettolani, de Souza & Chincarini 1986) providing environments of different den- Downloaded from https://academic.oup.com/mnras/article/362/1/127/1339746 by guest on 30 September 2021 sity. The environment is responsible for the morphological evolution of galaxies through dynamical modifications (Moore, Lake & Katz 1998; Dubinski 1999) resulting in a morphological–density relation (Dressler et al. 1997). But it is possible to find galaxies in low-density Figure 1. Histogram of the 96 GHASP galaxies according to the isolation environments which have not suffered from recent interactions and criterion. which have therefore evolved in a secular way for the last billion years. A great number of studies based on large samples of RCs (e.g. gramme and only a few pairs or groups of galaxies have been ob- Rubin, Waterman & Kenney 1999; Marquez et al. 2002; Dale & served. The degree of isolation of the GHASP galaxies has been Uson 2003; Varela et al. 2004; Vogt et al. 2004a,b,c) concerns the accurately estimated using the logarithmic ratio f between external gravitational effects on the shape of the RCs. But, in order to discrim- and internal forces (equation 1) defined from numerical simulations inate a secular from an external origin for any dynamical peculiar- (Athanassoula 1984): ity, it is necessary to investigate deeply all the possible relationships F R M between kinematical properties and fundamental quantities which f =log external = 3 log + log C (1) F b M characterize isolated and non-isolated galaxies. For this purpose, internal G we have clearly defined in Section 2.1 the degree of interaction for where R is the radius of the galaxy, b the impact parameter, MC the each galaxy, differentiating the isolated galaxies from the galaxies mass of the companion and MG the mass of the galaxy. subjected to faint interactions or strong interactions. The results of simulation works (Varelaet al. 2004, and references In this paper, we mainly discuss the 1D properties extracted therein) show that if, for a given galaxy, f −2 then the galaxy from the 1D derived rotation curves. The 2D information is only has not been affected by gravitational interaction for at least 2 × used to derive kinematically determined position angles of the ma- 109 yr. In this case, the galaxy can be considered as isolated. jor axis and inclinations. Galaxies experiencing strong interactions Varela et al. (2004) have redefined this parameter replacing the have been excluded from this analysis since they are not numerous estimation of the masses by the luminosity, and the impact parameter enough. In forthcoming papers, the impact of the environment (in b by the projected distance between a galaxy and its companion. The alow-density environment) on the kinematical properties of nearby expression for f then becomes galaxies will be investigated together with a detailed analysis of the R velocity fields. f = 3 log + 0.4(m − m ) (2) D G C The goal of this article is to evaluate the kinematical properties p of a sample of 85 galaxies divided into two groups: undisturbed where R is the radius measured along the major axis of the galaxy, and softly interacting. Studying all the links between parameters Dp the projected distance in the plane of the sky between the galaxy reflecting the dynamical state of a galaxy will help us to have a and the companion, and mG and mC, respectively, are the apparent better understanding of the evolution of galaxies. In this paper, we magnitudes of the galaxy and the companion. present a new set of 44 velocity fields providing 43 RCs. Including We computed the f values, from equation (2), for the GHASP the previous papers, the GHASP survey now totals reduced Fabry– galaxies, using the ALADIN, NED and HyperLEDA data bases. Perot data for 96 galaxies, uniformly covering the ‘magnitude–type’ The values of f are given in Table B1 (see Appendix B). For each plane (Fig. 1). In Section 2, the properties of the sample and the galaxy, the investigation of the companions has been made within analysis of the isolation criterion are described. In Section 3, we a radius of 20 times the diameter of the considered galaxy (which describe the data reduction processing. In Section 4, we analyse the is the criterion used by Karachentseva 1973) and in the range of kinematical properties of the sample. More precisely, we study the ±700 km s−1 around the systemic velocity of the galaxy.