COLORS, LINE STRENGTHS AND STELLAR KINEMATICS OF NGC-2663 AND NGC-5018

Results of the analysis of broad-band optical images and long-slit spectra of the two elliptical galaxies NGC 2663 and 5018 are presented. Line-strength profiles of Mg-2, Fe-5270 and Fe-5335 have been derived for both galaxies, together with rotational velocity and velocity dispersion curves at three and four position angles (PAs) for NGC 2663 and 5018, respectively. The measurements extend to about 1.8 effective radii for NGC 2663, and to about 3 effective radii for NGC 5018. Axisymmetric dynamical models with distribution function f = f(E, J(z)) (i.e. depending only on the energy E and the angular momentum along the symmetry axis J(z)) have been fitted to the kinematic profiles of both galaxies, to derive information about the intrinsic shapes of the luminous galaxies and the sizes and shapes of possible dark haloes. In agreement with what has been found for other ellipticals: (i) [Fe] versus Mg-2 shows, within both galaxies, a steeper slope than that shown by galactic nuclei, and (ii) the slope is approximately equal in the two galaxies and constant within each galaxy (over the whole radial range, to approximate to 2R(e)). A shift is observed between the two galaxies, implying different [Mg/Fe] abundance ratios. In NGC 2663, the derived [Mg/Fe] abundance ratio is (as is normally found in ellipticals) larger than solar; its colour [d(B - R)/dlog r= - 0.08] and Mg-2 (dMg(2)/dlog r= -0.06) gradients are consistent with each other and with a change in metallicity only. The galaxy shows a hint of counter-rotation within the innermost 20 arcsec and minor axis rotation. Any oblate or prolate model fitting its kinematics along any two position angles fails to fit the third position angle available, the discrepancy with the data being a systematic shift. Most probably, this galaxy is a triaxial object (observed V-rot/sigma approximate to 0.15 with epsilon approximate to 0.3, anisotropy parameter delta greater than or equal to 0.2-0.3); alternatively it might be prolate but always with an anisotropic velocity dispersion tensor. In NGC 5018, an almost flat velocity dispersion profile is observed out to the last measured point. Assuming that the galaxy is an axisymmetric rotator, such a flat a profile can be reproduced at a confidence level greater than or similar to 5 sigma only if a very massive dark matter halo surrounds the luminous component (M(D) approximate to 6 M(lum)) (B - R) colour gradient is observed in NGC 5018 [d(B - R)/dlog r= - 0.13], despite its shallow Mg-2 gradient (dMg(2)/dlog r= - 0.04). Although the whole galaxy is blue, its central (B - R) colour and the observed patchy structure in the (B - R) colour map suggest a considerable amount of extinction in its central regions. If the dust follows the Galactic extinction law, at 1550 Angstrom one could even expect approximate to 2 mag of extinction. This might hide a younger stellar population diluting the Mg-2 line strength, and might explain the lack of UV flux reported by other authors. The dilution of Mg-2 would also explain the solar [Mg/Fe] abundance ratio.