J/ApJ/754/62 HRDS III. HII region kinematic distances (Anderson+, 2012)
The Green Bank Telescope H II Region Discovery Survey.
III. Kinematic distances.
Anderson L.D., Bania T.M., Balser D.S., Rood R.T.
<Astrophys. J., 754, 62 (2012)>
=2012ApJ...754...62A 2012ApJ...754...62A
ADC_Keywords: H II regions ; Radio lines ; Surveys ; Stars, distances
Keywords: H II regions; ISM: molecules; radio lines: ISM; stars: formation
Abstract:
Using the H I emission/absorption method, we resolve the kinematic
distance ambiguity and derive distances for 149 of 182 (82%) H II
regions discovered by the Green Bank Telescope H II Region Discovery
Survey (GBT HRDS). The HRDS is an X-band (9 GHz, 3 cm) GBT survey of
448 previously unknown H II regions in radio recombination line and
radio continuum emission. Here, we focus on HRDS sources from
67°≥ℓ≥18°, where kinematic distances are more reliable.
The 25 HRDS sources in this zone that have negative recombination line
velocities are unambiguously beyond the orbit of the Sun, up to 20kpc
distant. They are the most distant H II regions yet discovered. We
find that 61% of HRDS sources are located at the far distance, 31% at
the tangent-point distance, and only 7% at the near distance. "Bubble"
H II regions are not preferentially located at the near distance (as
was assumed previously) but average 10 kpc from the Sun. The HRDS
nebulae, when combined with a large sample of H II regions with
previously known distances, show evidence of spiral structure in two
circular arc segments of mean Galactocentric radii of 4.25 and 6.0kpc.
We perform a thorough uncertainty analysis to analyze the effect of
using different rotation curves, streaming motions, and a change to
the solar circular rotation speed. The median distance uncertainty for
our sample of H II regions is only 0.5 kpc, or 5%. This is
significantly less than the median difference between the near and far
kinematic distances, 6 kpc. The basic Galactic structure results are
unchanged after considering these sources of uncertainty.
Description:
Here, we resolve the kinematic distance ambiguity (KDA) for 149 HRDS
sources using the HI emission/absorption (HI E/A) method (Kuchar & Bania
1994ApJ...436..117K 1994ApJ...436..117K; Kolpak et al. 2003, Cat. J/ApJ/582/75;
Anderson & Bania 2009, Cat. J/ApJ/690/706; Urquhart et al. 2012,
Cat. J/MNRAS/420/1656) and data from the VLA Galactic Plane Survey
(VGPS; Stil et al. 2006AJ....132.1158S 2006AJ....132.1158S).
The VGPS is a survey of 21cm HI emission that extends from
67.5°≥l≥17.9° at a spatial resolution of 1' and a spectral
resolution of 1.56km/s. In addition to the spectral line data, the
VGPS provides 1' resolution 21 cm continuum maps from spectral
channels with no line emission.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 76 182 HRDS (HII Region Discovery Survey)
kinematic distances
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See also:
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/MNRAS/420/1656 : RMS compact HII regions distances (Urquhart+, 2012)
J/ApJ/738/27 : Galactic HII regions RRL and continuum data (Balser+, 2011)
J/A+A/532/A127 : Inner Galaxy HII regions (Du+, 2011)
J/ApJS/195/14 : The Bolocam Galactic Plane Survey V. (Schlingman+, 2011)
J/ApJS/194/32 : The HII Region Discovery Survey (HRDS). II. (Anderson+, 2011)
J/ApJ/723/492 : GRS molecular clouds physical properties (Roman-Duval+, 2010)
J/ApJS/182/131 : Molecular clouds and clumps in the GRS (Rathborne+, 2009)
J/ApJ/690/706 : Distances of Galactic HII regions (Anderson+, 2009)
J/A+A/470/161 : UBV photometry of HII regions exciting stars (Russeil+, 2007)
J/ApJ/649/759 : Bubbles in the galactic disk (Churchwell+, 2006)
J/ApJ/626/195 : HI self-absorption (HISA) survey in the CGPS (Gibson+, 2005)
J/ApJS/154/553 : Inner galaxy massive star formation regions (Sewilo+, 2004)
J/ApJ/587/714 : H2CO and Halpha observations of UC HII (Watson+, 2003)
J/ApJ/582/756 : Velocities of HII regions (Kolpak+, 2003)
J/ApJS/138/63 : H2CO and Halpha observations of UC HII (Araya+, 2002)
http://www.cv.nrao.edu/hrds/ : HRDS home page
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- HRDS Source name (GLLL.lll+B.bbb)
16- 21 F6.3 deg GLON Galactic longitude
23- 28 F6.3 deg GLAT Galactic latitude
30- 34 F5.1 km/s VLSR [-76/112] Local Standard of Rest velocity
from Paper II (Cat. J/ApJS/194/32)
36- 38 I3 km/s Vabs ? Maximum velocity of detected HI absorption
40- 44 F5.1 km/s VTP Tangent point velocity
46- 48 F3.1 kpc Dnear [0/8]? Near distance
50- 53 F4.1 kpc Dfar [3/20] Far distance
55 A1 --- N/F [FNT] Kinematic distance ambiguity resolution
(F:Far, N:Near or T:Tangent)
57 A1 --- QF [A-C] Quality Factor (A: most confident
KDA determination) (1)
59- 62 F4.1 kpc Dist [3.4/19.7]? Derived heliocentric distance
64- 66 F3.1 kpc e_Dist [0/1.6]? Uncertainty in Dist
68- 71 F4.1 kpc RGal [3/15] Galactocentric radius
73- 76 I4 pc Zdist [-150/250]? Distance from Galactic plane
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Note (1): We assign for each source a quality factor (QF) based on our
confidence that the kinematic distance ambiguity (KDA) was resolved
correctly. This qualitative factor takes into account the number of
absorption signals detected, the strength of said signals, the
distance from the source to the tangent point, and the morphological
agreement between the absorption and the radio continuum emission from
the source. As Anderson & Bania (2009, Cat. J/ApJ/690/706) did, the
QF can have a value of "A" or "B" for sources with resolved KDAs, or
"C" for sources too faint for a KDA resolution. Sources for which we
assign the tangent-point distance have no QF.
See section 3 for further explanations.
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History:
From electronic version of the journal
References:
Bania et al. Paper I. 2010ApJ...718L.106B 2010ApJ...718L.106B
Anderson et al. Paper II. 2011ApJS..194...32A 2011ApJS..194...32A Cat. J/ApJS/194/32
Wenger et al. Paper IV. 2013ApJ...764...34W 2013ApJ...764...34W Cat. J/ApJ/764/34
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 03-Mar-2014