Temperature profiles of hot gas in early-type galaxies

Using the data products of the Chandra Galaxy Atlas (Kim et al.), we have investigated the radial profiles of the hot gas temperature in 60 early-type galaxies (ETGs). Considering the characteristic temperature and radius of the peak, dip, and break (when scaled by the gas temperature and virial radius of each galaxy), we propose a universal temperature profile of the hot halo in ETGs. In this scheme, the hot gas temperature peaks at RMAX = 35 ± 25 kpc (or ∼0.04 RVIR) and declines both inward and outward. The temperature dips (or breaks) at RMIN (or RBREAK) = 3–5 kpc (or ∼0.006 RVIR). The mean slope between RMIN (RBREAK) and RMAX is 0.3 ± 0.1. Allowing for selection effects and observational limits, we find that the universal temperature profile can describe the temperature profiles of 72 per cent (possibly up to 82 per cent) of our ETG sample. The remaining ETGs (18 per cent) with irregular or monotonically declining profiles do not fit the universal profile and require another explanation. The temperature gradient inside RMIN (RBREAK) varies widely, indicating different degrees of additional heating at small radii. Investigating the nature of the hot core (HC with a negative gradient inside RMIN), we find that HC is most clearly visible in small galaxies. Searching for potential clues associated with stellar, active galactic nucleus (AGN) feedback, and gravitational heating, we find that HC may be related to recent star formation. But we see no clear evidence that AGN feedback and gravitational heating play any significant role for HC.