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Description
Hot ionized gas is important in the baryon cycle of galaxies and may contribute the majority of their “missing baryons”. Up till now, most semi-analytic models of galaxy formation have paid little attention to the hot gaseous haloes and their X-ray emission. In this paper, we adopt the one-dimensional model from Sharma et al. instead of the isothermal sphere in L-Galaxies semi-analytic models to describe the radial distribution of hot gas. The hot gas halo can be divided into two parts according to the ratio of local thermal instability time scale and the free-fall time scale: a cool core with $t_{TI}/t_{ff} = 10$ and a stable region in outer halo with $t_{TI}/t_{ff} > 10$. We update the prescriptions of gas cooling, feedback and gas stripping based on the new hot gas profiles, and then successfully reproduce several X-ray observational results, like the radial profiles of hot gas density, and the scaling relations of $L_X$ and $T_X$. We find: (1) Flatter density profiles in the halo centers produce more accurate X-ray emission than the isothermal sphere; (2) Cool core regions prone to precipitation have higher $T_{gas}$ than $T_{vir}$, and a higher ratio of $T_X/T_{vir}$ in smaller haloes leads to a steeper slope in $L_X − T_X$ relation; (3) The ionized gas in unbounded reservoir and low temperature intergalactic gas in low mass haloes could be the main components for the halo “missing baryons”. Our model outputs can predict the observations of hot gas in nearby universe and mock the surveys of the baryon budgets by future X-ray telescopes.
