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 NGC266 .
Using ROSAT and Chandra X-ray observations we argue that the diffuse emission extends to at least \sim 70 kpc , whereas the bulk of the stellar light is confined to within \sim 25 kpc .
Based on X-ray hardness ratios , we find that most of the diffuse emission is released at energies \lesssim 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 \pm 0.8 ) \times 10 ^ { 40 } { erg s ^ { -1 } } and the gas mass is ( 9.1 \pm 0.9 ) \times 10 ^ { 9 } { M _ { \odot } } .
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 .