Chandra survey of nearby highly inclined disc galaxies – II. Correlation analysis of galactic coronal properties

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Abstract
X-ray observations provide a key tool for exploring the properties of galactic coronae and their formation processes. In an earlier paper, we have presented a Chandra data analysis of the coronae of 53 nearby highly inclined disc galaxies. Here we study the correlation of the X-ray measurements of the coronae with other galaxy properties and compare the results with those obtained for elliptical galaxies. A good correlation is present between the coronal luminosity (LX) and the star formation rate (SFR). But we find a better correlation between LX and the total supernova (SN) mechanical energy input rate (ĖSN), including the expected contribution from both core collapsed (CC) and Type Ia SNe. The X-ray radiation efficiency (η ≡ LX/ĖSN) of the coronae has a mean value of ∼0.4 per cent with an rms of 0.50 ± 0.06 dex. η further correlates with MTF/M* (MTF is the total baryon mass measured from the rotation velocity and the Tully–Fisher relation, and M* is the stellar mass measured from the K-band luminosity) and the CC SN rate surface density [FSN(CC), in units of SN yr−1 kpc−2], which can be characterized as η =(0.41-0.12+0.13 per cent) MTF/M* and η =(1.4 ± 0.5 per cent)FSN(CC)-(0.29 ± 0.11). These correlations reflect the roles played by the gravitational mass and energetic feedback concentrations of the galaxies in determining their X-ray radiation efficiency. The characteristic temperature (TX) of the coronal gas shows little dependence on the total or specific SFR, the cold gas content or LX. The coronae of disc galaxies tend to be more X-ray luminous, hotter and lower in the Fe/O abundance ratio than those of elliptical ones of similar masses. Early-type non-starburst disc galaxies tend to be more Fe-rich, while starburst ones have a roughly constant abundance ratio of Fe/O ∼ 0.36 ± 0.12 solar. Our results are consistent with the coronal gas being mainly provided by stellar feedback in a galaxy stellar mass range of ∼108.7−11 M⊙. In addition, processes such as charge exchange at cool/hot gas interfaces, as well as various other environmental effects, are also needed to explain the diversity of the observed coronal X-ray properties.
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