Gaussian Decomposition of {\lambda}21-cm Interstellar HI profiles
  Following an established protocol of science, that results must be
reproducible, we examine the Gaussian fits to Galactic 21-cm emission profiles
obtained by two seemingly complementary methods: the semi-automated approach
based on the method used by Verschuur (2004) and the automated technique of
Nidever et al. (2008). Both methods use data from the Leiden/Argentine/Bonn
all-sky survey. The appeal of an automated routine is great, if for no other
reason than the time saved over semi-automated fits. The pitfalls, however, are
often unanticipated, and the most important aspect of any algorithm is the
reproducibility of the results. The comparisons led to the identification of
four problems with the Nidever et al. (2008) analysis: (1) different methods of
calculating the reduced chi-squared measuring the goodness of fit; (2) an
ultra-broad component found bridging the gap between low and intermediate
velocity gas; (3) the lack of an imposed spatial coherence allowing different
components to appear and disappear in profiles separated by a fraction of a
beam width; and (4) multiple, fundamentally different solutions for the
profiles at both the North and South Galactic Poles. A two-step method would
improve the algorithm, where an automated fit is followed by a
quality-assurance, visual inspection. Confirming evidence emerges from this
study of a pervasive component with a line width of order 34 km/s, which may be
explained by the Critical Ionization Velocity (CIV) of helium. Since the
Nidever et al. (2008) paper contains the only result in the refereed literature
that contradicts the CIV model, it is important to understand the flaws in the
analysis that let to this contradiction.
