Astrophys. J., 860, 33-33 (2018/June-2)
Synthetic observations of 21 cm H I line profiles from inhomogeneous turbulent interstellar H I gas with magnetic fields.
FUKUI Y., HAYAKAWA T., INOUE T., TORII K., OKAMOTO R., TACHIHARA K., ONISHI T. and HAYASHI K.
Abstract (from CDS):
We carried out synthetic observations of interstellar atomic hydrogen at 21 cm wavelength by utilizing the magnetohydrodynamic numerical simulations of the inhomogeneous turbulent interstellar medium. The cold neutral medium (CNM) shows a significantly clumpy distribution with a small volume filling factor of 3.5%, whereas the warm neutral medium (WNM) has a distinctly different and smooth distribution with a large filling factor of 96.5%. In projection on the sky, the CNM exhibits a highly filamentary distribution with a subparsec width, whereas the WNM shows a smooth, extended distribution. In the H I optical depth, the CNM is dominant and the contribution of the WNM is negligibly small. The CNM has an area covering factor of 30% in projection, while the WNM has a covering factor of 70%. This means that the emission-absorption measurements toward radio continuum compact sources tend to sample the WNM with a probability of 70%, yielding a smaller H I optical depth and a smaller H I column density than those of the bulk H I gas. The emission-absorption measurements, which are significantly affected by the small-scale large fluctuations of the CNM properties, are not suitable for characterizing the bulk H I gas. Larger-beam emission measurements that are able to fully sample the H I gas will provide a better tool for that purpose, if a reliable proxy for hydrogen column density, possibly dust optical depth and gamma rays, is available. The present results provide a step toward precise measurements of the interstellar hydrogen with ∼10% accuracy. This will be crucial in interstellar physics, including identification of the proton-proton interaction in gamma-ray supernova remnants.
© 2018. The American Astronomical Society. All rights reserved.
ISM: atoms - ISM: clouds - radio lines: ISM
Table 6: 3C33-1, 3C33-2, 3C75-1, 3C75-2, 3C98-1, 3C98-2, 3C225a, 3C225b are 3C33S, CTA10, Cul 0255+05A, Cul 0255+05B, Cul 0356+10B, Cul 0356+10A, Cul 0939+14B, and 3C 225B respectively.
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