A high-resolution study of the Hydra A cluster with Chandra: Comparison ofthe core mass distribution with theoretical predictions and evidence for feedback in the cooling flow

The cooling flow cluster Hydra A was observed during the orbital activation and the Chandra Observatory. While the X-ray image of the cluster exhibits complex structure in the central region as reported in McNamara et al., th e large-scale X-ray morphology of the cluster is fairly smooth. A spectrosc opic analysis of the ACIS data shows that the gas temperature in Hydra A in creases outward, reaches a maximum temperature of 4 keV at 200 kpc, and the n decreases slightly at larger radii. The, distribution of heavy elements i s nonuniform, with a factor of 2 increase in the Fe and Si abundances withi n the central 100 kpc. Beyond the central 100 kpc the Si-to-Fe abundance ra tio is twice solar, while the Si-to-Fe ratio of the central excess is consi stent with the solar value. One of the more surprising results is the lack of spectroscopic evidence for multiphase gas within the bulk of the cooling flow. Beyond the central 30 kpc, the ACIS spectra are adequately fitted wi th a single-temperature model. The addition of a cooling flow component doe s not significantly improve the fit. Only within the central 30 kpc (where the cooling time is less than 1 Gyr) is there spectroscopic evidence for mu ltiphase gas. However, the spectroscopic mass deposition rate is more than a factor of 10 less than the morphologically derived mass accretion rate at 30 kpc. We propose that the cooling flow region is convectively unstable o wing to heating by the central radio source, which significantly reduces th e net accretion rate. In addition, we show that the mass distribution withi n the central 30-200 kpc region scales as rho (d) proportional to r(-1.3), intermediate between an NFW and a Moore proffle, but with a best-fit NFW co ncentration parameter (c(NFW) = 12) approximately 3 times greater than that found in numerical simulations. However, given the limited photon statisti cs, we cannot rule out the presence of a flat-density core with a core radi us less than 30 kpc.