A tight correlation between the enclosed gravitational mass and hot gas
  mass in galaxy clusters at intermediate radii
  Many studies point out that there exists some tight correlations between dark
matter and baryonic matter at different radii in galaxies. However, similar
tight correlations can only be found in galaxy clusters for large radii. Here
we report extremely tight correlations between the gravitational mass $M_{\rm
grav}$ and hot gas mass $M_{\rm gas}$ in galaxy clusters at the hot gas core
radius $r_c$ and at $2r_c$ (i.e. $M_{\rm grav}(r_c)$ vs $M_{\rm gas}(r_c)$ and
$M_{\rm grav}(2r_c)$ vs $M_{\rm gas}(2r_c)$). By using the X-ray data of 64
large galaxy clusters with different sizes and masses, we find that the
correlations can be described by a single relation $\log(M_{\rm
grav}/M_{\odot})=(0.74 \pm 0.02) \log(M_{\rm gas}/M_{\odot})+(4.47 \pm 0.23)$
for a wide range of hot gas mass ($10^{11}M_{\odot}-10^{14}M_{\odot}$). The
corresponding correlation coefficient and scatter are 0.97 and 0.10 dex
respectively. This would be the first tight correlation with very small scatter
between the enclosed gravitational mass and hot gas mass for galaxy clusters
within intermediate radii ($\sim 100-1000$ kpc) and it provides a new kind of
observational evidence to support the universality of correlation between dark
matter and baryons.
