J/ApJ/626/887 HI clouds in Southern Galactic Plane Survey (Kavars+, 2005)
"Missing link" clouds in the Southern Galactic Plane Survey.
Kavars D.W., Dickey J.M., McClure-Griffiths N.M., Gaensler B.M., Green A.J.
<Astrophys. J., 626, 887-899 (2005)>
=2005ApJ...626..887K 2005ApJ...626..887K
ADC_Keywords: Molecular clouds ; H I data ; Radio lines
Keywords: Galaxy: structure - ISM: atoms - ISM: clouds - radio lines: ISM
Abstract:
We present an automated routine to search for HI self-absorption
features within the Southern Galactic Plane Survey (SGPS). The data
were taken with the Australia Telescope Compact Array (ATCA) and the
Parkes Radio Telescope and encompass 3°x105° of sky in the
Galactic plane. We apply our routine to this entire region and derive
spin temperatures and column densities for 70 of the larger HISA
complexes, finding spin temperatures ranging from 6 to 41K with HI
number densities of a few cm-3. These "missing link" clouds fill in
the spin temperature and density gaps between dense molecular clouds
and diffuse atomic clouds. We compare the HI emission with 12CO
emission and find that 60% of detected HI self-absorption is
correlated in space and in velocity with a molecular counterpart. This
is potentially due to a molecular/atomic gas transition. We also
compare HI self-absorption with Galactic spiral arms and discuss the
possibility of using it as a spiral arm tracer.
Description:
The SGPS is one of three large sky surveys that image HI line
emission and 21cm continuum in the plane of the Galaxy. The other two
surveys are the CGPS and the VGPS. Together, the three make up the
International Galactic Plane Survey (IGPS). The SGPS combines
interferometer data from the Australia Telescope Compact Array (ATCA)
and single-dish data from the Parkes 64m telescope. It maps the
region of 253°≤l≤358° and -1.3°≤b≤+1.3° with an angular
resolution of 2';, a channel spacing of 0.82km/s, and an rms
brightness sensitivity per channel of 24K, depending on the brightness
of the HI emission (McClure-Griffiths, 2001, Ph.D. thesis, Univ.
Minnesota). The SGPS data are divided into cubes of 5°x2.6°
centered on b=0° and longitudes that are multiples of 5°. A
further description of the data is detailed in McClure-Griffiths et
al. (2005ApJS..158..178M 2005ApJS..158..178M).
SGPS HI images are available at
http://www.atnf.csiro.au/research/HI/sgps/queryForm.html .
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 54 70 Computed Properties for 70 HISA Features
--------------------------------------------------------------------------------
See also:
J/MNRAS/201/495 : HI Survey of Southern Galactic Plane (Strong+ 1982)
http://www.atnf.csiro.au/research/HI/common : SGPS Home Page
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- [KDM2005] Sequential number
4- 8 F5.1 deg GLON Galactic longitude
10- 13 F4.1 deg GLAT Galactic latitude
15- 20 F6.2 km/s RV Radial velocity (1)
22 A1 --- l_Dist Upper limit flag on distance estimate
23- 26 F4.1 kpc Dist Near kinematic distance
28- 32 F5.1 pc d Linear size of the cloud
34- 35 I2 K TS(1) Spin temperature for τ=1
37- 38 I2 K TS(inf) Spin temperature for τ=∞
40- 43 F4.1 km/s Dnu Equivalent width of the line
45- 48 F4.1 10+19cm-2 NHI HI column density
50- 54 F5.3 cm-3 nHI HI lower limit density value
--------------------------------------------------------------------------------
Note (1): For those clouds with negative radial velocities it is assumed
that they are on the near side of the tangent point with an
optical depth of 1.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 25-Aug-2006