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J/ApJ/524/536   Nearby Ly{alpha} quasar absorbers        (Impey+, 1999)
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A study of Ly{alpha} quasar absorbers in the nearby universe
    Impey C.D., Petry C.E., Flint K.P.
   <Astrophys. J. 524, 536 (1999)>
   =1999ApJ...524..536I
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ADC_Keywords: QSOs ; Spectroscopy
Mission_Name: HST
Keywords: galaxies: halos - intergalactic medium - large-scale structure
          of universe - quasars: absorption lines

Abstract:
    Spectroscopy of 10 quasars obtained with the Goddard High Resolution
    Spectrograph (GHRS) of the Hubble Space Telescope (HST) is presented.
    In the 10 sight lines, we detect 357 absorption lines above a
    significance level of 3{sigma} and 272 lines above a significance
    level of 4.5{sigma}. Automated software is used to detect and identify
    the lines, almost all of which are unresolved at the GHRS G140L
    resolution of 200km/s. After identifying Galactic lines, intervening
    metal lines, and higher order Lyman lines, we are left with 139
    Ly{alpha} absorbers in the redshift range 0<z<0.22 (lines within
    900km/s of geocoronal Ly{alpha} are not selected). These diffuse
    hydrogen absorbers have column densities that are mostly in the range
    10^13^-10^15^cm^-2^ for an assumed Doppler parameter of 30km/s. The
    number density of lines above a rest equivalent width of 0.24{AA},
    dN/dz=38.3{+/-}5.3, agrees well with the measurement from the Quasar
    Absorption-Line Key Project. There is marginal evidence for cosmic
    variance in the number of absorbers detected among the 10 sight lines.

File Summary:
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 FileName      Lrecl  Records   Explanations
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ReadMe            80        .   This file
table2.dat       132      355   Absorption-Line measurements & identifications
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See also:
   VII/23 : A catalogue of absorption lines in QSO spectra
   J/ApJS/77/203 : QSO absorption systems (Junkkarinen+ 1991)
   J/ApJS/97/1 : HST Quasar Absorption Line Key Project. X. (Lockman+ 1995)

Byte-by-byte Description of file: table2.dat
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   Bytes Format Units   Label     Explanations
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   1- 13  A13   ---     Name      QSO name
  15- 18  F4.2  ---     z         QSO redshift
  21- 22  I2    ---     Number    Absorption line number
  25- 31  F7.2  0.1nm   Wave      Observed vacuum heliocentric line
                                   wavelength in Angstroms
  34- 37  F4.2  0.1nm e_Wave      Error in Wave in Angstroms
      39  A1    ---   f_Wave      [h] Flag on Wave (1)
  41- 45  F5.3  0.1nm   EqWidth   Equivalent width in Angstroms
  48- 52  F5.3  0.1nm e_EqWidth   Error in EqWidth in Angstroms
  57- 60  F4.2  0.1nm   FWHM      Full Width Half Maximum in Angstroms (2)
  63- 66  F4.2  0.1nm e_FWHM      Error in the FWHM in Angstroms
  69- 73  F5.2  ---     Chi2      The {Chi}^2^ of the line fit
  79- 83  F5.2  ---     Signif    Significance of the line width (3)
  86- 91  F6.2  ---     SignifL   Significance of the line width (4)
      93  A1    ---   f_SignifL   [i] Flag on SignifL (5)
  95-101  F7.5  ---     zAbsorp   ? Redshift of the absorption system
 103-113  A11   ---     ID        Line identification
     115  A1    ---   f_ID        [*] Indicates excited transitions
     116  A1    ---   n_ID        [fg] Note on ID (6)
 118-121  I4    0.1nm   RWave     ? Rest wavelength of line
     122  A1    ---   f_RWave     [ab] Indicates one of the two strongest
                                   transitions of the N I 1200 angstrom triplet
 127-131  F5.2  0.1nm   DWave     ? Wavelength residual in Angstroms (7)
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Note (1): On wing of damped Ly{alpha}; Wave is very uncertain
Note (2): Lines with a value of 0.80{+/-}0.00 were fit with the FWHM set
          to the minimum allowed value.
Note (3): Significance of the line defined as EqWidth/{sigma}_W_, where
          {sigma}_W_ is the error in the measured equivalent width.
Note (4): Significance of the line defined as EqWidth/{sigma}_lim_, where
          {sigma}_lim_ is the 1{sigma} (observed) limiting equivalent width.
Note (5): Based on a single comparison with a higher resolution
          spectrum of 3C 273, a significant fraction of lines with
          3.0 < SignifL < 4.5 may be false detections.
Note (6):
    f = Alternately identified as Si II 1304 at z = 0.0000 with
        residual 0.45 Angstroms.
    g = Alternately identified as Si II 1190 at z = 0.1419 with
        residual -0.53 Angstroms.
Note (7): Defined as ({lambda}_measured_ - {lambda}_predicted_)
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History:
    From ApJ electronic edition

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(End)                                          Greg Schwarz [AAS]    13-Mar-2000