Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21533206k&link_type=abstract
American Astronomical Society, AAS Meeting #215, #332.06; Bulletin of the American Astronomical Society, Vol. 42, p.431
Astronomy and Astrophysics
Astronomy
Scientific paper
Highly ionized species such as C IV, N V, and O VI, are commonly observed in diffuse gas in various places in the universe. One possible mechanism for producing high ions is turbulent mixing of warm/cool gas with hot gas. By using hydrodynamic simulations with radiative cooling and non-equilibrium ionization (NEI) calculations, we investigate the physical properties of turbulent mixing layers. We focus on the production of high ions and the ratios between the column densities of different ions, because column density ratios are most commonly compared with observations. Our simulations reveal that the mixed region separates into a tepid zone containing radiatively cooled, C IV-rich gas and a hotter zone which is rich in C IV, N V, and O VI. Although collisional ionization equilibrium (CIE) calculations are convenient and frequently used approximations, our NEI calculations produce more high ions but similar ion ratios when compared with CIE predictions. Mixing occurs faster than ionization or recombination, making the mixed gas a better source of C IV, N V, and O VI in NEI simulations than in CIE simulations. In addition, the gas radiatively cools faster than the ions recombine, which also yields larger numbers of C IV, N V, and O VI ions in NEI simulations. We simulate various initial configurations and find that the column densities and ion ratios calculated from NEI are not affected significantly as long as mixing is efficient. However, our simulation with a higher temperature (three million degrees K) hot gas produces larger N(C IV)/N(N V) and N(O VI)/N(N V) ratios than our reference simulation (million degrees K). We find that the results of our simulations are valid in the range of simulation scales from distance/time = 10 pc/8 Myr to 100 pc/80 Myr.
Kwak Kyujin
Shelton Robin L.
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