On the X-ray emission of the low-mass galaxy groups
  It is shown that the low-mass groups obey the $L_{x}\sim\sigma_v^{4}$ law deduced for galaxy clusters. The impression of the more shallow slope of the $L_x-\sigma_{v}$ correlation for groups is created not by enhanced X-ray emission, but by underestimation of the radial velocity dispersion of some groups. 
H. M. Tovmassian and O. Yam (INAOE, Mexico), H. Tiersch (Sternwarte   Konigsleiten, Germany)