J/AJ/132/242        H II absorption regions at 74MHz         (Nord+, 2006)
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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
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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{deg}>l>-15{deg}, -5{deg}<b<5{deg} 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:
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 FileName   Lrecl  Records   Explanations
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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
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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{deg}
 (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{deg}
 (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{deg}
 (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{deg}
 (1Jy/beam=1490K). The rms at the center of the field is 0.6Jy/beam.
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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
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  Bytes Format Units   Label     Explanations
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  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
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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.
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Byte-by-byte Description of file: table6.dat
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  Bytes Format Units   Label    Explanations
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  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 3{sigma} upper limit of the
                                integrated cosmic ray electron brightness
                                temperature of the column behind the HII region
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Note (1): 7000K used when the electron temperature isn't available.
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History:
    From electronic version of the journal
    27-Oct-2007: Insert into VizieR
    05-Mar-2019: Gname corrected (wrong declination latitude signs)

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(End)                  Greg Schwarz [AAS], Patricia Vannier [CDS]    31-Aug-2007