We studied the physical properties of the intracluster medium in the virialization region of a sample of 320 clusters ( 0.056 < z < 1.24 , kT \mathrel { \hbox { \hbox to 0.0 pt { \hbox { \lower 4.0 pt \hbox { $ \sim$ } } } \hbox { $ > $ } } } 3 keV ) in the Chandra archive .
With the emission measure profiles from this large sample , the typical gas density , gas slope and gas fraction can be constrained out to and beyond R _ { 200 } .
We observe a steepening of the density profiles beyond R _ { 500 } with \beta \sim 0.68 at R _ { 500 } and \beta \sim 1 at R _ { 200 } and beyond .
By tracking the direction of the cosmic filaments approximately with the ICM eccentricity , we report that galaxy clusters deviate from spherical symmetry , with only small differences between relaxed and disturbed systems .
We also did not find evolution of the gas density with redshift , confirming its self-similar evolution .
The value of the baryon fraction reaches the cosmic value at R _ { 200 } : however , systematics due to non-thermal pressure support and clumpiness might enhance the measured gas fraction , leading to an actual deficit of the baryon budget with respect to the primordial value .
This study has important implications for understanding the ICM physics in the outskirts .