XMM-Newton and Chandra Observations of the Galaxy Group NGC 5044. I. Evidence for Limited Multiphase Hot Gas

Using new XMM and Chandra observations, we present an analysis of the temperature structure of the hot gas within a radius of 100 kpc of the bright nearby galaxy group NGC 5044. A spectral deprojection analysis of data extracted from circular annuli reveals that a two-temperature model (2T) of the hot gas is favored over single-phase or cooling flow ( = 4.5 ± 0.2 M☉ yr-1) models within the central ~30 kpc. Alternatively, the data can be fitted equally well if the temperature within each spherical shell varies continuously from ~Th to Tc ~ Th/2, but no lower. The high spatial resolution of the Chandra data allows us to determine that the temperature excursion Th → Tc required in each shell exceeds the temperature range between the boundaries of the same shell in the best-fitting single-phase model. This is strong evidence for a multiphase gas having a limited temperature range. We do not find any evidence that azimuthal temperature variations within each annulus on the sky can account for the range in temperatures within each shell. We provide a detailed investigation of the systematic errors on the derived spectral models considering the effects of calibration, plasma codes, bandwidth, variable NH, and background rate. We find that the RGS gratings and the EPIC and ACIS CCDs give fully consistent results when the same models are fitted over the same energy ranges for each instrument. The cooler component of the 2T model has a temperature (Tc ~ 0.7 keV) similar to the kinetic temperature of the stars. The hot phase has a temperature (Th ~ 1.4 keV) characteristic of the virial temperature of the ~1013 M☉ halo expected in the NGC 5044 group. However, in view of the morphological disturbances and X-ray holes visible in the Chandra image within R ≈ 10 kpc, bubbles of gas heated to ~Th in this region may be formed by intermittent AGN feedback. Some additional heating at larger radii may be associated with the evolution of the cold front near R ~ 50 kpc, as suggested by the sharp edge in the EPIC images.