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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.