The small-scale structure in interstellar Hi: a resolvable puzzle
A. A. Deshpande;
MNRAS, 2000, 317, 199
ABSTRACT:During the past decade or so, measurements of Galactic Hi absorption using VLBI against extragalactic sources, as well as multi-epoch
observations in pulsar directions, have detected small-scale transverse
variations corresponding to tens of au at the distance of the absorbing
matter.
Hitherto these measurements have been interpreted as small-scale structure in
the Hi distribution with densities
nHi~104-105cm-3, orders of magnitude greater than those of the pc-scale
structure.
Naturally, it is difficult to imagine how such structures could exist in
equilibrium with other components of the ISM.
In this paper we show that structure
on all scales contributes to the differences on neighbouring lines of
sight, and that the observed differences can be accounted for by a natural
extension of the distribution of irregularities in the distribution of Hi
opacities at larger scales, using a single power law.
This, in our opinion,
should put an end to the decades-long puzzle of the so-called small-scale
structure in Hi and other species in the Galaxy.
KEYWORDS: pulsars: general, ism: clouds, ism: molecules, ism: structure, radio lines: ism
PERSOKEY:h_i, ,
CODE: deshpande2000a