EDP Sciences

Vol. 618
In section 6. Interstellar and circumstellar matter

Properties of cold and warm HI gas phases derived from a Gaussian decomposition of HI4PI data

by P.M.W. Kalberla and U. Haud A&A 618, A58


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The neutral ISM, traced by 21 cm emission, is now available for the whole sky over a vast range of velocities. This paper presents a dynamical separaton of the components with velocity widths (FWHM) extending to about 60 km/s. The separation is automatically performed using Gaussian profiles that have a range of widths to distinguish along each sight line among about 7.9 million lines of sight assuming the individual components (up to eight per line of sight) are from individual clouds. The authors present comparisons of derived properties for the components, such as column densities, filling factors, and antenna temperatures with infrared dust temperatures, and filling fractions. The filling factors are also separated in centroid velocity intervals. For example, -8 < vLSR 8 km/s has about 41% LNM.34% WNM, and 25% CNM and the authors find that the first two are distinct and imbedded within the WNM. Another interesting result of this study is the separation of a very high FWHM component, referred to by the authors as the XNM, which may also contain largescale power-law tails and remains an open question.