http://arxiv.org/abs/1701.07129
We have carried out synthetic observations of interstellar atomic hydrogen at 21cm wavelength by utilizing the theoretical results of magnetohydrodynamical numerical simulations of the inhomogeneous turbulent interstellar medium which includes both CNM and WNM (Inoue & Inutsuka 2012). We used the ultraviolet absorption measurements of H2 in the local interstellar space in order to constrain the model parameters. We find the following: (1) The WHI-NHI scatter plot shows a systematic change depending on Ts, (2) the contribution of H2 in the WHI-NHI plot is minor, indicating that “CO-free H2” is not important, (3) the HI optical depth measured by absorption toward a radio continuum point source is significantly smaller than the optical depth derived from HI emission observed with large beams, because the covering factor of high HI optical-depth (tauHI > 0.5) regions is significantly small, ~30%, as compared with that of low HI optical-depth regions, ~70%. It is also found that the WHI-tau353 (dust optical depth at 353GHz) plot is better explained if dust evolution expressed as $N_{\text{H$\;$I}}+2N_\mathrm{H2}\propto \tau_{353}^{1/1.3}$ is taken into account. HI column density derived by emission-absorption Heiles & Troland (2003a) is systematically smaller by a factor of ~1.7 than that corrected for the optically thick HI and for the dust evolution as is consistent with Fukui et al. (2014, 2015). The total mass of HI in the local interstellar space is accurately estimated to be 1.7-times the optically thin case by the latter method.
Y. Fukui, T. Hayakawa, T. Inoue, et. al.
Thu, 26 Jan 17
47/68
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