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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 (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:
FileName Lrecl Records Explanations
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
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
Bytes Format Units Label Explanations
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)
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.
Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
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)
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.
History: From electronic version of the journal
(End) Prepared by Tiphaine Pouvreau [CDS] 28-Sep-2017
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