X-ray emission and internal kinematics in early-type galaxies -- I. Observations

Long slit spectroscopic data for 7 early-type galaxies with X-ray emissionhave been analyzed to derive velocity dispersion and radial velocity profiles.Major axis rotation curves out to $R\sim R_e$ are presented. Adding these newdata to those available in the literature, we have built a sample of early-typegalaxies with detected X-ray emission and known kinematics (central velocitydispersion $\sigma_0$ and maximum rotational velocity $v_r$). Using this samplewe investigate from an observational point of view the role of rotation andflattening on the X-ray emission, particularly with regard to the X-rayunderluminosity of flat systems. The trend between the X-ray to optical ratio$L_X/L_B$, a measure of the hot gas content of the galaxies, and $v_r/\sigma_0$is L-shaped, with the X-ray brightest objects confined at $v_r/\sigma_0 <0.4$,both for Es and S0s. Neither for low or intermediate, nor for high $L_X/L_B$,there is any clear correlation between X-ray emission and rotationalproperties. The trend between $L_X/L_B$ and the ellipticity $\epsilon$ is alsoL-shaped: there are no high $L_X/L_B$ objects with high $\epsilon$. Theexistence of a relation between $v_r/\sigma_0$ and $\epsilon$ makes itdifficult to assess whether rotation or flattening is at the basis of thetrends found. Our observational findings are finally discussed in connectionwith the effects that rotation and flattening are predicted to have in thecooling flow and in the wind/outflow/inflow scenarios.Comment: 10 pages, plain tex, plus 7 .ps figures and tex-macro mn.tex -- accepted by MNRAS (main journal