J/ApJ/582/756 Velocities of HII regions (Kolpak+, 2003)
Resolving the kinematic ambiguity toward galactic H II regions.
Kolpak M.A., Jackson J.M., Bania T.M., Clemens D.P., Dickey J.M.
<Astrophys. J. 582, 756 (2003)>
=2003ApJ...582..756K 2003ApJ...582..756K
ADC_Keywords: H II regions ; Radial velocities ; Radio lines
Keywords: Galaxy: general - Galaxy: structure - H II regions - ISM: atoms -
radio lines: ISM - techniques: spectroscopic
Abstract:
Kinematic distance determinations in the inner Galaxy are hampered by
the near-far kinematic distance ambiguity. Here we resolve the
ambiguity for 49 HII region complexes with known recombination-line
velocities in the first Galactic quadrant. We measured the 21cm HI
absorption spectrum toward each source with the Very Large Array in
the C array. The maximum velocity of HI absorption was used to
discriminate between the near and far kinematic distances. The number
ratio of far to near sources, ∼3, can be entirely explained as a
geometrical effect. The kinematic distances that we derive are
compared with previous determinations for the same sources. Although
our distance determinations are largely in agreement with previous
measurements, there are 22 discrepancies that we discuss. Using our
distance determinations, we create a face-on Galactic map of the HII
region complexes and compare it with a kinematically derived profile
of the distribution of CO-traced molecular hydrogen. The HII region
complexes delineate the large-scale features seen in the molecular
gas. The 5kpc molecular ring and the Sagittarius spiral arm are
clearly evident, and a few HII region complexes lie in the Perseus
arm.
Description:
The data presented here were collected in 2000 March and April using
the NRAO VLA in the C-array configuration in the L band. The
correlator was configured to have a total bandwidth of 1.6MHz, 128
channels, and 12.2kHz/channel, corresponding to a velocity resolution
of 2.6km/s/channel.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 65 51 HII region complexes
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See also:
VII/50 : CO Radial Velocities Toward Galactic H II Regions (Blitz+ 1982)
J/A+A/397/213 : Galactic HII regions (Paladini+, 2003)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- [KJB2003] Source name based on Galactic coordinates (1)
14 A1 --- n_[KJB2003] [a] a: sources form the initial target list
16- 17 I2 h RAh Right ascension (J2000.0)
19- 20 I2 min RAm Right ascension (J2000.0)
22- 25 F4.1 s RAs Right ascension (J2000.0)
27 A1 --- DE- Declination sign (J2000.0)
28- 29 I2 deg DEd Declination (J2000.0)
31- 32 I2 arcmin DEm Declination (J2000.0)
34- 37 F4.1 arcsec DEs Declination (J2000.0)
39- 43 F5.1 km/s RV HII region complex recombination-line
velocity
45- 47 I3 km/s Vtang HII region complex tangential-point velocity
49- 52 I4 km/s Vabs Maximum velocity of HI absorption
54 A1 --- KDA [NFT?] Kinematic Distance Ambiguity
resolution (2)
56- 59 F4.1 kpc Dist ? Distance
61- 63 F3.1 kpc e_Dist ? rms uncertainty on Dist
65 A1 --- q_KDA [AB] Quality assignment for our resolution of
the KDA
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Note (1): Two sources, G23.900+0.068 and G31.243-0.110, are listed twice
because Lockman, 1989, Cat. VIII/58, reports two
recombination-line velocity components toward each of these sources.
Note (2): Our determination of whether the sources are at the
near kinematic distance (N), the far kinematic distance (F),
the tangent point (T), or undetermined (?)
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History:
From electronic version of the journal
(End) James Marcout, Patricia Bauer [CDS] 26-Mar-2003