Open AccessThe small‐scale structure in interstellar H i : a resolvable puzzle
Author(s) -
Deshpande Avinash A.
Publication year - 2000
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2000.03631.x
Subject(s) - physics , astrophysics , galaxy , pulsar , interstellar medium , scale (ratio) , astronomy , power law , very long baseline interferometry , statistics , quantum mechanics , mathematics
During the past decade or so, measurements of Galactic H i 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 H i distribution with densities n H i ∼10 4 –10 5 cm −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 H i 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 H i and other species in the Galaxy.