DETECTION OF A LUMINOUS HOT X-RAY CORONA AROUND THE MASSIVE SPIRAL GALAXY NGC 266

The presence of luminous hot X-ray coronae in the dark matter halos of massive spiral galaxies is a basic prediction of galaxy formation models. However, observational evidence for such coronae is very scarce, with the first few examples having only been detected recently. In this paper, we study the large-scale diffuse X-ray emission associated with the massive spiral galaxy NGC 266. Using ROSAT and Chandra X-ray observations we argue that the diffuse emission extends at least similar to 70 kpc, whereas the bulk of the stellar light is confined to within similar to 25 kpc. Based on X-ray hardness ratios, we find that most of the diffuse emission is released at energies less than or similar to 1.2 keV, which indicates that this emission originates from hot X-ray gas. Adopting a realistic gas temperature and metallicity, we derive that in the (0.05-0.15)r(200) region (where r(200) is the virial radius) the bolometric X-ray luminosity of the hot gas is (4.3 +/- 0.8) x 10(40) erg s(-1) and the gas mass is (9.1 +/- 0.9) x 10(9) M-circle dot. These values are comparable to those observed for the two other well-studied X-ray coronae in spiral galaxies, suggesting that the physical properties of such coronae are similar. This detection offers an excellent opportunity for comparison of observations with detailed galaxy formation simulations.