J/ApJ/810/42 Hydrogen RRL parameters of H II regions (Anderson+, 2015)
Untangling the recombination line emission from H II regions with multiple
velocity components.
Anderson L.D., Hough L.A., Wenger T.V., Bania T.M., Balser D.S.
<Astrophys. J., 810, 42 (2015)>
=2015ApJ...810...42A 2015ApJ...810...42A (SIMBAD/NED BibCode)
ADC_Keywords: H II regions ; Radio lines ; Infrared sources
Keywords: Galaxy: structure - HII regions - infrared: ISM - stars: formation
Abstract:
H II regions are the ionized spheres surrounding high-mass stars. They
are ideal targets for tracing Galactic structure because they are
predominantly found in spiral arms and have high luminosities at
infrared and radio wavelengths. In the Green Bank Telescope H II Region
Discovery Survey (GBT HRDS), we found that >30% of first Galactic
quadrant H II regions have multiple hydrogen radio recombination line
(RRL) velocities, which makes determining their Galactic locations and
physical properties impossible. Here we make additional GBT RRL
observations to determine the discrete H II region velocity for all
117 multiple-velocity sources within 18°<l<65°. The
multiple-velocity sources are concentrated in the zone 22°<l<32°,
coinciding with the largest regions of massive star formation, which
implies that the diffuse emission is caused by leaked ionizing
photons. We combine our observations with analyses of the electron
temperature, molecular gas, and carbon recombination lines to
determine the source velocities for 103 discrete H II regions (88% of
the sample). With the source velocities known, we resolve the
kinematic distance ambiguity for 47 regions, and thus determine their
heliocentric distances.
Description:
We used the GBT 100 m telescope to observe RRLs in a sample of
multiple RRL velocity H II regions from 2011 December through 2013 April.
Our spectral line observational setup was identical to that of the
HRDS (described in Anderson et al. 2011, J/ApJS/194/32). Our
observations made total-power position-switched 6 minutes. On-target
and 6 minutes. Off-target integrations at X-band (9 GHz; 3 cm),
hereafter called "pairs". The on- and off-target integrations followed
the same path on the sky, and we observed a single pair for each
position. We simultaneously observed the H 87 α to H 93 α
transitions. We began each observation by measuring a source of known
position and intensity in order to obtain pointing and focus
corrections. We made no corrections for atmospheric effects.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 131 53 On-target Hydrogen RRL Parameters of Literature
H II Regions
table2.dat 131 225 Off-target Hydrogen RRL Parameters for the Full
Sample
table4.dat 63 103 H II Region Velocities and Distances
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See also:
J/ApJ/653/1226 : Physical properties of galactic HII regions (Quireza+, 2006)
J/ApJS/165/338 : Radio recombination lines in HII regions (Quireza+, 2006)
J/ApJ/690/706 : Distances of Galactic HII regions (Anderson+, 2009)
J/ApJS/181/255 : CO in Galactic HII regions (Anderson+, 2009)
J/ApJ/738/27 : Galactic HII regions RRL and continuum data (Balser+, 2011)
J/ApJS/194/32 : The HII Region Discovery Survey (HRDS). II. (Anderson+, 2011)
J/ApJ/754/62 : HRDS III. HII region kinematic distances (Anderson+, 2012)
J/ApJS/212/1 : The WISE catalog of Galactic HII regions (Anderson+, 2014)
Byte-by-byte Description of file: table1.dat table2.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- Source Source name (GLLL.lll+B.bbb) (only in table1)
15 A1 --- n_Source [abc ] Note on Source (only in table1) (1)
17- 22 F6.3 deg GLON Galactic longitude
24- 29 F6.3 deg GLAT Galactic latitude
31- 34 F4.1 arcmin Sep ? Separation (2)
36- 40 F5.1 mK TL Derived radio recombination line (RRL) peak
antenna temperature
42- 44 F3.1 mK e_TL Uncertainty in TL
46- 50 F5.1 km/s VLSR Local Standard of Rest velocity
52- 54 F3.1 km/s e_VLSR Uncertainty in VLSR
56- 59 F4.1 km/s DeltaV Line FWHM
61- 63 F3.1 km/s e_DeltaV Uncertainty in DeltaV
65- 67 F3.1 mK rms rms noise
69-131 A63 --- Region Multiple-velocity H II region(s) that use this
off-target position in our subsequent analyses
(GLLL.lll+BB.bbb) (only in table2)
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Note (1): When multiple RRL components are detected, we follow our usual
convention and append "a" to the source name of the strongest
component, "b" to the source name of the next strongest component,
etc.
Note (2): From the nominal centroid position of the nearest multiple-velocity
H II region.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Source Source name (GLLL.lll+BB.bbb)
17- 21 F5.1 km/s VLSR Local Standard of Rest velocity
23- 25 F3.1 kpc DN ? Near kinematic distance
27- 30 F4.1 kpc DF Far kinematic distance
32- 34 F3.1 kpc DTP Tangent point kinematic distance
36 A1 --- KDAR [FNT-] Kinematic distance ambiguity resolution
(F:Far, N:Near or T:Tangent) (1)
38 A1 --- QF [ABC-] Quality factor for the KDAR (2)
40- 43 F4.1 kpc Rgal Galactocentric radius
45- 48 F4.1 kpc Dist ? Heliocentric distance
50- 52 I3 pc Z ? Height above the plane
54- 63 A10 --- Crit Criteria used to determine the H II region
velocity (3)
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Note (1): Using H I absorption, in the same manner as Anderson & Bania
(2009, J/ApJ/690/706) and Anderson et al. (2012, J/ApJ/754/62).
Note (2): We assign each KDAR a quality factor based on our qualitative
assessment of our confidence in the KDAR.
Quality factor as follows:
A = Very certain;
B = Less certain;
C = We cannot resolve the KDAR.
Note (3): Criteria as follows:
1 = Only one on-target velocity component was detected (literature sources
only);
2 = One on-target velocity component has a negative LSR velocity;
3a = The intensity of one off-target line component is at least 50 mK less
than that of the on-target position;
3b = The intensity of one off-target line component is between 20 and 50 mK
less than that of the on-target position (the former being the more
reliable criterion);
4a = The electron temperature derived from only one line component is within
the reasonable range, for high quality sources;
4b = The electron temperature derived from only one line component is within
the reasonable range, for low quality sources;
5a = Anderson et al. (2009, J/ApJS/181/255) find CO emission matching the
source morphology at only at one velocity (their quality factors of "A"
or "B");
5b = Dense molecular gas, compiled in the WISE catalog of Galactic H II
regions (Anderson et al. 2014, J/ApJS/212/1), is only found at one
velocity;
6 = A carbon RRL is found at only one of the RRL velocities.
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History:
From electronic version of the journal
(End) Prepared by Tiphaine Pouvreau [CDS] 28-Sep-2017