We constrain the total mass distribution in the cluster A3571 , combining spatially resolved ASCA temperature data with ROSAT imaging data with the assumption that the cluster is in hydrostatic equilibrium .
The total mass within r _ { 500 } ( 1.7 h _ { 50 } ^ { -1 } Mpc ) is M _ { 500 } = 7.8 ^ { +1.4 } _ { -2.2 } \times 10 ^ { 14 } h _ { 50 } ^ { -1 } M _ { \odot } at 90 % confidence , 1.1 times smaller than the isothermal estimate .
The Navarro , Frenk & White “ universal profile ” is a good description of the dark matter density distribution in A3571 .
The gas density profile is shallower than the dark matter profile , scaling as r ^ { -2.1 } at large radii , leading to a monotonically increasing gas mass fraction with radius .
Within r _ { 500 } the gas mass fraction reaches a value of f _ { gas } = 0.19 ^ { +0.06 } _ { -0.03 } h _ { 50 } ^ { -3 / 2 } ( 90 % confidence errors ) .
Assuming that this value of f _ { gas } is a lower limit for the the universal value of the baryon fraction , we estimate the 90 % confidence upper limit of the cosmological matter density to be \Omega _ { m } < 0.4 .