Large scatter in X-ray emission among elliptical galaxies: correlations   with mass of host halo
  The enormous range of X-ray luminosities among elliptical galaxies with similar optical luminosities can be attributed to large scatter and systematic variations in the dark halo mass determined from X-ray observations. The mean halo mass decreases sharply with both the X-ray and K-band luminosities. Smaller halos contain less diffuse hot gas and have lower X-ray luminosities. In addition the hot gas in low mass halos is more easily depleted by supernova-driven outflows, further lowering the X-ray luminosity. 
W. G. Mathews, F. Brighenti, A. Faltenbacher, D. A. Buote, P. J.   Humphrey, F. Gastaldello, and L. Zappacosta