We present detailed spatially resolved measurements of the thermodynamic properties of the X-ray emitting gas in the inner regions of the five nearest , X-ray and optically brightest , and most X-ray morphologically relaxed giant elliptical galaxies known .
Beyond the innermost region at r \gtrsim 1 kpc , and out to r \sim 6 kpc , the density , pressure , entropy , and cooling time distributions for the X-ray emitting gas follow remarkably similar , simple , power-law like distributions .
Notably , the entropy profiles follow a form K \propto r ^ { \alpha } , with an index \alpha = 0.92 -1.07 .
The cumulative hot X-ray emitting gas mass profiles and the gas-mass to stellar-light ratios of all five galaxies are also similar .
Overall the observed similarity of the thermodynamic profiles in this radial range argues that , in these systems , relativistic jets heat the gas at a similar rate averaged over time scales longer than the cooling time t _ { cool } \gtrsim 10 ^ { 8 } yr .
These jets are powered by accretion from the hot gas , or material entrained within it , onto the central super-massive black hole .
This jet heating creates an energy balance where heating and cooling are in equilibrium , keeping the hot galactic atmospheres in a ‘ steady-state ’ .
Within r \lesssim 1 kpc , this similarity breaks down : the observed entropy profiles show well resolved flattening and the values differ from system to system substantially .
The accretion rate onto the black hole and the AGN activity , heating the interstellar medium , must therefore vary significantly on time scales shorter than t _ { cool } = 10 ^ { 7 } – 10 ^ { 8 } yr .