Turbulence measurements from H I absorption spectra

Roy, Nirupam ; Peedikakkandy, Leshma ; Chengalur, Jayaram N. (2008) Turbulence measurements from H I absorption spectra Monthly Notices of the Royal Astronomical Society: Letters, 387 (1). L18-L22. ISSN 1745-3925

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Official URL: http://onlinelibrary.wiley.com/doi/10.1111/j.1745-...

Related URL: http://dx.doi.org/10.1111/j.1745-3933.2008.00473.x

Abstract

We use the millennium Arecibo 21-cm absorption-line survey measurements to examine the issue of the non-thermal contribution to the observed Galactic H I linewidths. If we assume a simple, constant pressure model for the H i in the Galaxy, we find that the non-thermal contribution to the linewidth, vnt scales as v2ntOC/α, for vnt larger than ~0.7 km s−1. Here, l is a derived length-scale and α~0.7 ± 0.1. This is consistent with what one would expect from a turbulent medium with a Kolmogorov scaling. Such a scaling is also predicted by theoretical models and numerical simulations of turbulence in a magnetized medium. For non-thermal linewidths narrower than ~0.7 km s−1, this scaling breaks down, and we find that the likely reason is ambiguities arising from Gaussian decomposition of intrinsically narrow, blended lines. We use the above estimate of the non-thermal contribution to the linewidth to determine corrected H I kinetic temperature. The new limits that we obtain imply that a significantly smaller (~40 per cent as opposed to 60 per cent) fraction of the atomic interstellar medium in our Galaxy is in the warm neutral medium phase.

Item Type:Article
Source:Copyright of this article belongs to John Wiley and Sons.
Keywords:Turbulence; ISM: Atoms; ISM: General; ISM: Kinematics and Dynamics; ISM: Structure; Radio Lines: ISM
ID Code:63575
Deposited On:29 Sep 2011 04:10
Last Modified:29 Sep 2011 04:10

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