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Session 21 -- Diffuse Galactic Emission


Bregman, J.N, Rosen, A. (U. Mich.)

In order to investigate the effect of energy injection rate on the structure and kinematics in the interstellar medium, we have completed two-dimensional simulations with a hydrodynamical code that simulates the interaction of gas and stars in the interstellar medium. Each of our simulations, which include star formation, mass loss, heating from stellar winds and supernovae, and radiative cooling, naturally recreates a multiphase medium with filaments of cold dense gas surrounding low-density warm and hot gas. The main variable in this set of simulations is the heating rate, and we have also varied whether the heating comes from stellar winds or supernovae. We simulate the vertical extent of a galaxy up to $\pm$ 15 kpc, and 2 kpc in a dimension perpendicular to that (rotational effects are not included). We analyze the cold, warm and hot phases of gas for scale heights and volume filling factors for each of the three energy injection rates, which differ by factors of four between each of the low, moderate (Galactic), and high rates. The moderate energy injection rate scales up to 8 $\times$ 10$^{41}$ erg s$^{-1}$ for a disk of 16 kpc radius, which is roughly the Galactic value, and does best at reproducing the scale heights and volume filling factors in the Galaxy. For example, the volume filling factors near the midplane are 0.15, 0.25, and 0.60 for the cold, warm, and hot gas, respectively. We obtain kinematic information from position-velocity plots and other related H I emission plots ($<$ N $>$ (v)). Also, we show the latitude dependence of H I for some positions within bubbles of hot, low-density gas, and we calculate the X-ray flux as well as the integrated X-ray flux at a number of distances from the same position. We can compare these with slices in latitude from H I and X-ray all-sky surveys, and show the relative contribution to the XRB of a local bubble. With the inclusion of X-ray absorption by cold and warm gas, we can calculate the frequency for and typical absorption of shadowing events.

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