  We demonstrate that individual elliptical galaxies and clusters of galaxies
form a continuous X-ray luminosity---velocity dispersion (LX-sigma) relation.
Our samples of 280 clusters and 57 galaxies have LX ~ sigma^4.4 and LX ~
sigma^10, respectively. This unified LX - sigma relation spans 8 orders of
magnitude in LX and is fully consistent with the observed and theoretical
luminosity---temperature scaling laws. Our results support the notion that
galaxies and clusters of galaxies are the luminous tracers of similar dark
matter halos.
