%0 Generic %1 bialy2017hitoh2 %A Bialy, Shmuel %A Burkhart, Blakesley %A Sternberg, Amiel %D 2017 %K H2 HI formation medium turbulent %T The HI-to-H2 Transition in a Turbulent Medium %U http://arxiv.org/abs/1703.08549 %X We study the effect of density fluctuations induced by turbulence on the HI/H$_2$ structure in photodissociation regions (PDRs) both analytically and numerically. We perform magnetohydrodynamic numerical simulations for both subsonic and supersonic turbulent gas and chemical HI/H$_2$ balance calculations. We derive atomic-to-molecular density profiles and the HI column density probability density function (PDF). We find that while the HI/H$_2$ density profiles are strongly perturbed in turbulent gas, the mean HI column density is well approximated by the uniform-density analytic formula of Sternberg et al. (2014). The important effect of supersonic density fluctuations is to produce a wide HI column density PDF which depends on (a) the radiation intensity to mean density ratio, (b) the sonic Mach number and (c) the turbulence decorrelation scale, or driving scale. We derive an analytic model for the HI PDF and demonstrate how our model, combined with 21 cm observations, can be used to constrain the Mach number and driving scale of turbulent gas. We test our model using observations of HI in the Perseus GMC. We find that the narrow observed HI PDF may imply small scale decorrelation, pointing to the potential importance of subcloud-scale turbulence driving in Perseus.

@misc{bialy2017hitoh2, abstract = {We study the effect of density fluctuations induced by turbulence on the HI/H$_2$ structure in photodissociation regions (PDRs) both analytically and numerically. We perform magnetohydrodynamic numerical simulations for both subsonic and supersonic turbulent gas and chemical HI/H$_2$ balance calculations. We derive atomic-to-molecular density profiles and the HI column density probability density function (PDF). We find that while the HI/H$_2$ density profiles are strongly perturbed in turbulent gas, the mean HI column density is well approximated by the uniform-density analytic formula of Sternberg et al. (2014). The important effect of supersonic density fluctuations is to produce a wide HI column density PDF which depends on (a) the radiation intensity to mean density ratio, (b) the sonic Mach number and (c) the turbulence decorrelation scale, or driving scale. We derive an analytic model for the HI PDF and demonstrate how our model, combined with 21 cm observations, can be used to constrain the Mach number and driving scale of turbulent gas. We test our model using observations of HI in the Perseus GMC. We find that the narrow observed HI PDF may imply small scale decorrelation, pointing to the potential importance of subcloud-scale turbulence driving in Perseus.}, added-at = {2017-03-28T09:55:06.000+0200}, author = {Bialy, Shmuel and Burkhart, Blakesley and Sternberg, Amiel}, biburl = {https://www.bibsonomy.org/bibtex/24f6f16caa76c369fd0b3372025ec8e6c/miki}, description = {[1703.08549] The HI-to-H2 Transition in a Turbulent Medium}, interhash = {8a3b9b8a8c4ec31b8c0df3cc5a7328d4}, intrahash = {4f6f16caa76c369fd0b3372025ec8e6c}, keywords = {H2 HI formation medium turbulent}, note = {cite arxiv:1703.08549Comment: 12 pages, 10 figures. ApJ submitted. Comments are welcome}, timestamp = {2017-03-28T09:55:06.000+0200}, title = {The HI-to-H2 Transition in a Turbulent Medium}, url = {http://arxiv.org/abs/1703.08549}, year = 2017 }