%0 Generic %1 gray2017effect %A Gray, William J. %A Scannapieco, Evan %D 2017 %K emission lines nebular turbulence %T The Effect of Turbulence on Nebular Emission Line Ratios %U http://arxiv.org/abs/1710.01312 %X Motivated by the observed differences in the nebular emission of nearby and high-redshift galaxies, we carry out a set of direct numerical simulations of turbulent astrophysical media exposed to a UV background. The simulations assume a metallicity of $Z/Z_ødot$=0.5 and explicitly track ionization, recombination, charge transfer, and ion-by-ion radiative cooling for several astrophysically important elements. Each model is run to a global steady state that depends on the ionization parameter $U$, and the one-dimensional turbulent velocity dispersion, $\sigma_1D$, and the turbulent driving scale. We carry out a suite of models with a T=42,000K blackbody spectrum, $n_e$ = 100 cm$^-3$ and $\sigma_1D$ ranging between 0.7 to 42 km s$^-1,$ corresponding to turbulent Mach numbers varying between 0.05 and 2.6. We report our results as several nebular diagnostic diagrams and compare them to observations of star-forming galaxies at a redshift of $z\approx$2.5, whose higher surface densities may also lead to more turbulent interstellar media. We find that subsonic, transsonic turbulence, and turbulence driven on scales of 1 parsec or greater, have little or no effect on the line ratios. Supersonic, small-scale turbulence, on the other hand, generally increases the computed line emission. In fact with a driving scale $0.1$ pc, a moderate amount of turbulence, $\sigma_1D$=21-28 km s$^-1,$ can reproduce many of the differences between high and low redshift observations without resorting to harder spectral shapes.

@misc{gray2017effect, abstract = {Motivated by the observed differences in the nebular emission of nearby and high-redshift galaxies, we carry out a set of direct numerical simulations of turbulent astrophysical media exposed to a UV background. The simulations assume a metallicity of $Z/Z_{\odot}$=0.5 and explicitly track ionization, recombination, charge transfer, and ion-by-ion radiative cooling for several astrophysically important elements. Each model is run to a global steady state that depends on the ionization parameter $U$, and the one-dimensional turbulent velocity dispersion, $\sigma_{\rm 1D}$, and the turbulent driving scale. We carry out a suite of models with a T=42,000K blackbody spectrum, $n_e$ = 100 cm$^{-3}$ and $\sigma_{\rm 1D}$ ranging between 0.7 to 42 km s$^{-1},$ corresponding to turbulent Mach numbers varying between 0.05 and 2.6. We report our results as several nebular diagnostic diagrams and compare them to observations of star-forming galaxies at a redshift of $z\approx$2.5, whose higher surface densities may also lead to more turbulent interstellar media. We find that subsonic, transsonic turbulence, and turbulence driven on scales of 1 parsec or greater, have little or no effect on the line ratios. Supersonic, small-scale turbulence, on the other hand, generally increases the computed line emission. In fact with a driving scale $\approx 0.1$ pc, a moderate amount of turbulence, $\sigma_{\rm 1D}$=21-28 km s$^{-1},$ can reproduce many of the differences between high and low redshift observations without resorting to harder spectral shapes.}, added-at = {2017-10-05T09:59:59.000+0200}, author = {Gray, William J. and Scannapieco, Evan}, biburl = {https://www.bibsonomy.org/bibtex/2109d0a9412df1a4fbfeb19dc178bf572/miki}, description = {[1710.01312] The Effect of Turbulence on Nebular Emission Line Ratios}, interhash = {688330ee1651a11b8fec3c31d590cbaf}, intrahash = {109d0a9412df1a4fbfeb19dc178bf572}, keywords = {emission lines nebular turbulence}, note = {cite arxiv:1710.01312Comment: 18 pages, 9 figures, accepted to ApJ, comments welcome}, timestamp = {2017-10-05T09:59:59.000+0200}, title = {The Effect of Turbulence on Nebular Emission Line Ratios}, url = {http://arxiv.org/abs/1710.01312}, year = 2017 }