J/ApJ/690/706 Distances of Galactic HII regions (Anderson+, 2009)
Resolution of the distance ambiguity for Galactic H II regions.
Anderson L.D., Bania T.M.
<Astrophys. J., 690, 706-719 (2009)>
=2009ApJ...690..706A 2009ApJ...690..706A
ADC_Keywords: H II regions ; Radio lines ; H I data
Keywords: H II regions - ISM: molecules - radio lines: ISM - stars: formation
Abstract:
We resolve the kinematic distance ambiguity for 266 inner Galaxy HII
regions out of a sample of 291 using existing HI and 13CO sky
surveys. Our sample contains all HII regions with measured radio
recombination line emission over the extent of the 13CO Boston
University-Five College Radio Astronomy Observatory Galactic Ring
Survey (18<l<55° and |b|<1) and contains ultra compact (UC),
compact, and diffuse HII regions. We use two methods for resolving the
distance ambiguity for each HII region: HI emission/absorption (HI
E/A) and HI self-absorption (HI SA).
Description:
Our sample of 291 HII regions is that of Paper I (Anderson et al.
2009ApJS..181..255A 2009ApJS..181..255A).
For the HI SA analysis we use both the HI surveys and the Boston
University-Five College Radio Astronomy Observatory (BU-FCRAO) 13CO
Galactic Ring Survey data (GRS; Jackson et al. 2006ApJS..163..145J 2006ApJS..163..145J
available at http://www.bu.edu/galacticring).
For the HI E/A analysis we use data from the VLA 21cm HI Galactic
Plane Survey (VGPS; Stil et al. 2006AJ....132.1158S 2006AJ....132.1158S) and the Southern
Galactic Plane Survey (SGPS; McClure-Griffiths et al.
2005ApJS..158..178M 2005ApJS..158..178M).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 47 291 HII region kinematic parameters
table2.dat 40 291 HII region kinematic distances
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See also:
V/112 : Catalog of Star-Forming Regions in the Galaxy (Avedisova, 2002)
VIII/58 : A Survey of Radio H II Regions in the Northern Sky (Lockman+ 1989)
VII/50 : CO Radial Velocities Toward Galactic H II Regions (Blitz+ 1982)
J/ApJS/181/255 : CO in galactic HII regions (Anderson+, 2009)
J/ApJ/626/887 : HI clouds in Southern Galactic Plane Survey (Kavars+, 2005)
J/A+A/397/133 : Star-forming complexes in the Galaxy (Russeil+, 2003)
J/ApJS/140/331 : High-velocity HI observations at 21cm (Lockman+, 2002)
http://www.bu.edu/galacticring : Galactic Ring Survey (GRS) home page
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 12 A12 --- Name Source name, based on galactic position (1)
14- 18 F5.2 deg GLON Galactic longitude
20- 24 F5.2 deg GLAT Galactic latitude
26- 30 F5.1 km/s VLSR Radio recombination line LSR velocity (2)
32- 34 F3.1 kpc Rgal Galactrocentric radius (3)
36- 38 F3.1 kpc Dnear The near distance
40- 43 F4.1 kpc Dfar The far distance
45- 47 F3.1 kpc Dtp The tangent point distance
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Note (1): There are 25 lines of sight with multiple radio recombination
line velocities. The source names for these HII regions are denoted
with an extra "a" or "b".
Note (2): Typical measurement errors are 2km/s (see data compiled in
Anderson et al. 2009ApJS..181..255A 2009ApJS..181..255A). This error is insignificant
compared to uncertainties in the rotation curve model, which may be 10km/s.
Note (3): All kinematic distances calculated using the rotation curve of
McClure-Griffiths & Dickey (2007ApJ...671..427M 2007ApJ...671..427M).
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 12 A12 --- Name Source name
14- 16 I3 km/s Vabs ? Maximum velocity of HI absorption
18 A1 --- Abs? [N/Y] HI absorption detected within 10km/s of
radio recombination line velocity
20 A1 --- KDA1 [NFT] Near/Far kinematics distance ambiguity
(KDA) resolution for Emission/Absorption
method
21 A1 --- f_KDA1 [*] Ambiguity on KDA1 (4)
23 A1 --- q_KDA1 [A/B] Confidence parameter for KDA1 (A for
high confidence or B for low) (5)
25 A1 --- KDA2 [NF] Near/Far KDA resolution for
Self-Absorption method
26 A1 --- f_KDA2 [*] Ambiguity on KDA2 (4)
28 A1 --- q_KDA2 [A/B] Confidence parameter for KDA2 (A for
high confidence or B for low) (5)
30- 33 F4.1 kpc Dist ? Distance from the sun (6)
35- 40 F6.1 pc Z ? Height above the Galactic plane
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Note (4): For sources whose HIE/A and HISA kinematics distance ambiguity
(KDA) resolutions disagree, the KDA resolution that we adopt is marked
with an asterisk.
Note (5): We assign to each source a confidence parameter in order to
indicate the likelihood that the HI SA feature is an artifact of noise
or of background fluctuations. This qualitative parameter indicates
our confidence that the HI SA kinematics distance ambiguity (KDA)
resolution is correct. For "A" sources at the near distance, the HI
absorption signal is strong, unambiguous, and at the same velocity as
the 13CO emission line. For "A" sources at the far distance, the HI
at the velocity of the 13CO emission line is smooth and shows no
fluctuations that could be interpreted as weak absorption. The
reliability of the KDA resolution for "B" quality sources is less
certain due to a fluctuating HI spectrum or weak 13CO emission.
Note (6): Kinematic distances calculated using the rotation curve of
McClure-Griffiths & Dickey (2007ApJ...671..427M 2007ApJ...671..427M).
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History:
From electronic version of the journal
References:
Anderson et al. Paper I. 2009ApJS..181..255A 2009ApJS..181..255A Cat. J/ApJS/181/255
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 16-Feb-2011