The structure of galactic HI in directions of low total column density
F. J. Lockman, K. Jahoda, D. McCammon;
ApJ, 1986, 302, 432
ABSTRACT:A detailed 21 cm study of areas of that have the smallest known amount of HI in the northern sky was performed.
These observations
were corrected for stray radiation.
The region of main interest, around
alpha = 10(h)45(m), delta = 57 deg 20 arcmin, has a minimum N(HI) of 4.5 x 10 to
the 19th power/sq cm.
Spectra taken at 21 arcmin resolution over a field 4 x
3 deg in this direction show up to four HI line components.
Two, near 0 and
-50 km/s, are ubiquitous.
There is also a narrow component at -10 km/s
attributable to a diffuse cloud covering half of the field, and scattered patches of
HI at v -100 km/s the low and intermediate velocity components have a broad
line width and are so smoothly distributed across the region that it is
unlikely that they contain significant unresolved angular structure.
Eight
other low column density directions were also observed.
Their spectra
typically have several components, but the total column density is always 7 x 10 to
the 19th power/sq cm and changes smoothly along a 2 deg strip.
Half of the
directions show narrow lines arising from weak diffuse HI clouds that contain 0.5
to 3.0 x 10 to the 19th power/sq cm.
KEYWORDS: hydrogen, interstellar gas, milky way galaxy, neutral gases, northern sky, astronomical spectroscopy, clouds, particle density (concentration), space observations (from earth)
PERSOKEY:milky way, ,
CODE: lockman86a