J/AJ/132/242 H II absorption regions at 74MHz (Nord+, 2006)
74 MHz discrete H II absorption regions toward the inner galaxy. Nord M.E., Henning P.A., Rand R.J., Lazio T.J.W., Kassim N.E. <Astron. J., 132, 242-252 (2006)> =2006AJ....132..242N
ADC_Keywords: H II regions ; Effective temperatures Keywords: cosmic rays - H II regions - ISM: magnetic fields - radio continuum: general Abstract: In this work we present 74MHz observations in the region 26°>l>-15°, -5°<b<5° report the detection of 92 absorption features associated with known HII regions; and derive the brightness temperature of the Galactic cosmic-ray electron synchrotron emission emanating from the column behind these regions. For the 42 HII regions with known distances, the average emissivity of the column behind the HII region is derived. The 74MHz emissivity values range between 0.3 and 1.0K/pc for a model assuming uniform distribution of emissivity. Methods for using this type of data to model the three-dimensional distribution of cosmic-ray emissivity and the possibility of using this method to break the HII region kinematic distance degeneracy are discussed. Description: Observations presented here were performed with the Naval Research Laboratory (NRL) NRAO 74/330MHz system on the VLA in the most compact configurations, which permit the optimal balance between surface brightness sensitivity and resolution for detecting the greatest number of HII absorption features. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 92 36 *HII Regions in the Field of G21.5-0.5 table3.dat 92 22 *HII Regions in the Field of G11.2-0.3 table4.dat 92 32 *HII Regions in the Field of the Galactic Center table5.dat 92 8 *HII Regions in the Field of G349.7+0.2 table6.dat 30 134 HII region non-detections
Note on table2.dat: The field is centered on 17 45 40.0, -29 00 27.9 (J2000.0). The resolution element is 17.41'x6.67', and the position angle is 5° (1Jy/beam=537K). The rms at the center of the field is 0.8Jy/beam. Note on table3.dat: The field is centered on 18 11 30.6, -19 25 16.0 (J2000.0). The resolution element is 6.67'x5.67', and the position angle is -10° (1Jy/beam=1650K). The rms at the center of the field is 0.7Jy/beam. Note on table4.dat: The field is centered on 17 45 40.0, -29 00 27.9 (J2000.0). The resolution element is 17.41'x6.67', and the position angle is 5° (1Jy/beam=537K). The rms at the center of the field is 0.8Jy/beam. Note on table5.dat: The field is centered on 17 18 02.7, -37 26 13.0 (J2000.0). The resolution element is 8.33'x5.00', and the position angle is 10° (1Jy/beam=1490K). The rms at the center of the field is 0.6Jy/beam.
See also: VII/20 : Catalogue of HII Regions (Sharpless 1959) J/A+AS/131/319 : HII regions catalogue (Petit+ 1998) J/A+A/397/213 : Galactic HII regions (Paladini+, 2003) Byte-by-byte Description of file: table2.dat table3.dat table4.dat table5.dat
Bytes Format Units Label Explanations
1- 4 I4 --- [PBD2003] Paladini et al. (2003, cat. J/A+A/397/213) catalog number 6- 15 A10 --- Gname Name, based on Galactic position. 17- 18 I2 h RAh Right ascension (J2000) 20- 21 I2 min RAm Right ascension (J2000) 23- 26 F4.1 s RAs Right ascension (J2000) 28 A1 --- DE- Declination sign (J2000) 29- 30 I2 deg DEd Declination (J2000) 32- 33 I2 arcmin DEm Declination (J2000) 35- 36 I2 arcsec DEs Declination (J2000) 38- 42 F5.1 Jy Int Observed intensity at 74MHz, in Jy/beam. 44- 48 F5.3 Jy e_Int rms uncertainty on Int 50- 54 F5.1 10+3K Tobs Sky brightness temperature derived from the measured intensity 56- 58 F3.1 10+3K e_Tobs rms uncertainty on Tobs 60- 63 F4.1 10+3K Tgb Integrated cosmic-ray electron brightness temperature of the column behind the HII region 64 A1 --- n_Tgb [a] Note on Tgb (1) 66- 68 F3.1 10+3K e_Tgb rms uncertainty on Tgb 70- 73 F4.1 10+3K Te Electron temperature of the HII region 75- 77 F3.1 10+3K e_Te rms uncertainty on Te 79- 82 F4.1 kpc Dist ?=- Distance from the Sun to the HII region 84- 87 F4.2 K/pc Emi ?=- Emissivity of the column behind the HII region using the assumptions of Sect. 5. 89- 92 F4.2 K/pc e_Emi ? rms uncertainty on Emi
Note (1): the electron temperature of this HII region was unavailable, so a value of 7000±2000K was used in the calculation of the background brightness temperature.
Byte-by-byte Description of file: table6.dat
Bytes Format Units Label Explanations
1- 4 I4 --- [PBD2003] Paladini et al. (2003, cat. J/A+A/397/213) catalog number 6- 15 A10 --- Gname Name, based on Galactic position. 17- 20 F4.1 kpc Dist Geocentric distance 22- 25 F4.1 10+3K Te ? Electron temperature (1) 27- 30 F4.1 10+3K Tgb Nondetection 3σ upper limit of the integrated cosmic ray electron brightness temperature of the column behind the HII region
Note (1): 7000K used when the electron temperature isn't available.
History: From electronic version of the journal
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 31-Aug-2007
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