X-ray Spectra of Circumgalactic Medium Around Star-Forming Galaxies:
  Connecting Simulations to Observations
  The hot component of the circum-galactic medium (CGM) around star forming
galaxies is detected as diffuse X-ray emission. The X-ray spectra from the CGM
depend on the temperature and metallicity of the emitting plasma, providing
important information about the feeding and feedback of the galaxy. The
observed spectra are commonly fitted using simple 1-Temperature (1-T) or 2-T
models. However, the actual temperature distribution of the gas can be complex
because of the interaction between galactic outflows and halo gas. Here we
demonstrate this by analysing 3-D hydrodynamical simulations of the CGM with a
realistic outflow model. We investigate the physical properties of the
simulated hot CGM, which shows a broad distribution in density, temperature,
and metallicity. By constructing and fitting the simulated spectra, we show
that, while the 1-T and 2-T models are able to fit the synthesized spectra
reasonably well, the inferred temperature(s) does not bear much physical
meaning. Instead, we propose a log-normal distribution as a more physical
model. The log-normal model better fits the simulated spectra while reproducing
the gas temperature distribution. We also show that when the star formation
rate is high, the spectra inside the bi-conical outflows are distinct from that
outside, as outflows are generally hotter and more metal-enriched. Finally, we
produce mock spectra for future missions with the eV-level spectral resolution,
such as Athena, Lynx, HUBS and XRISM.
