STAR-FORMATION HISTORY OF EARLY-TYPE GALAXIES IN LOW-DENSITY ENVIRONMENT II - KINEMATICS

The present paper is a companion of two others dedicated one to the me asurement of the line-strength indices (Longhetti et al. 1997a) and th e second to trace back the star formation history of a sample of early -type galaxies by comparing observed indices to the predictions of new spectro-photometric models (Longhetti et al. 1997b). The sample of 51 early-type galaxies in low density environments is composed of two su b-sets of galaxies: 21 shell galaxies from the Malin & Carter (1983) c atalogue tone of which shows double nucleous and has been considered a s two separate objects) and 30 members of isolated interacting pairs f rom the Reduzzi & Rampazzo (1995) catalogue. Most of the objects show fine structures. The paper collects nuclear kinematic data together wi th the velocity and velocity dispersion curves of the stellar and gase ous components as a function of the distance from the galaxies centres . The galaxies heliocentric systemic velocity compares within -1 +/- 3 2 km s(-1) with RC3 data, while their central velocity dispersion comp ares within 9+/-9 km s(-1), 10+/-27 km s(-1) and 2+/-33 km s(-1) with Gonzalez (1993), Davies et al. (1987) and Carter et al. (1988) respect ively. The detailed comparison between our velocity and velocity dispe rsion curves and those from several authors is discussed. 9 out of 22 shell galaxies nuclei show emission lines, 4 of which, using data in t he literature, have line ratios char acteristic of LINERs. 10 members of pairs out of 30 show emission lines. RR 331a has a Seyfert like nuc leus, while for the remaining galaxies the ([O III] lambda 5007)/H bet a ratio is characteristic of low ionization regions. In a small fracti on of the objects the emission component is detectable outside the cen tral value. None of the objects in the sample shows counter-rotation o f the gaseous versus the stellar component. The two components appear associated, although, in two cases there is evidence that gas and star s lie on different planes. This latter phenomenon could be associated to accretion events. Emission lines in the central part of the RR 331a show a secondary component in the emission lines profile. E 2400100 h as two nuclei embedded in the main body of the galaxy. The U-shape pro file of the stellar velocity profile shows the ongoing interaction of the two nuclei. V/sigma profile of shell galaxies is, finally, discuss ed in relation to the hypothesis of the accretion/merging origin of th ese galaxies.