J/ApJS/91/1        Lyman-Alpha forest near 34 QSOs      (Bechtold 1994)
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The Lyman-Alpha forest near 34 quasi-stellar objects with z > 2.6.
   Bechtold J.
   <Astrophys. J. Suppl. Ser., 91, 1 (1994)>
   =1994ApJS...91....1B
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ADC_Keywords: QSOs ; Spectra, optical
Keywords: quasars: absorption lines

Abstract:
    Moderate-resolution spectra of 34 high-redshift QSOs were obtained at
    the Multiple Mirror Telescope and Palomar 5m Telescope in order to
    study the properties of the Ly{alpha} forest absorption lines with
    z_abs_~z_em_. For z_abs_<<z_em_, the evolution of the number of lines
    per unit redshift, dN/dz, is well described by the form (1+z)gamma,
    with gamma=1.89+/-0.28 for lines with rest equivalent width greater
    than 0.32{AA}. For lines stronger than 0.16{AA}, gamma=1.32+/-0.24.
    These results imply slower evolution in the mean free path for
    absorption for the clouds than previously thought. When this sample is
    combined with HST results for low redshift (Bahcall et al. 1993), a
    single gamma is an acceptable fit to the data, with gamma=1.26+/-0.13
    for z_abs_=0-4.1, although and inflection at z~1.5 may be present. In
    the high- redshift sample, there is a significant trend of decreasing
    gamma with decreasing equivalent width limit, or, alternatively, a
    change in equivalent width distribution with redshift. There is no
    significant curvature in the log (dN/dz) versus log(1+z) relation for
    the strong lines, but some steepening of gamma at z~2.5 for the weak
    ones. While these findings for the weak lines are highly significant
    in a statistical sense, they may result from some subtle line-blending
    problem, rather than a real physical process. The lines with
    z_abs_~z_em_ are significantly depleted. The strength of the deficit
    of lines depends weakly on QSO Lyman limit luminosity, but not
    redshift. The strength of the deficit also depends on the rest
    equivalent width of the lines, with weak lines showing a relatively
    weaker effect. These findings support previous suggestions that the
    "proximity effect" results from enhanced photoionization by the QSO's
    EUV radiation, rather than some property of the QSO or intergalactic
    medium which evolves with redshift. The simple photoionization model
    of Bajtlik, Duncan, & Ostriker describes the data well. If the
    ionizing background at the Lyman limit, Jnu_, is assumed to be
    constant with redshift for 1.6<z<4.1, and writing
    J_nu_=J_-21_x10^-21^ergs/cm^2^/s/Hz/sr, then J_-21_~3. This value is
    formally consistent with previous results, although about a factor of
    3 larger. Hence, the factor by which QSOs fail to provide the EUV
    background at high redshifts (at least in this simple picture), is
    also increased. If the redshift dependence of Jnu_ is parameterized as
    Jnu_ is proportional to (1+z)^j^, then j is not well constrained owing
    to the small redshift interval sampled, and acceptable fits are
    obtained for -7<j<4. Additions to the simple model and the resulting
    uncertainties in these estimates of Jnu_ are discussed. One serious
    uncertainty is the neutral fraction of the clouds. If the clouds are
    nearly neutral, then Jnu_ must be implausibly low, J_-21_~0.01 in
    order to account for the proximity effect observed in this sample. In
    addition, if the systemic redshifts of the QSOs are systematically
    underestimated, then J_-21_ may be up to a factor of ~3 smaller. Given
    these uncertainties, the J_-21_ at z~3 derived from the proximity
    effect is in reasonable agreement with the expected contribution of
    luminous QSOs.

Description:
    Moderate-resolution spectra of 33 QSOs are presented.

File Summary:
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 FileName      Lrecl  Records   Explanations
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ReadMe            80        .   This file
qsos.dat          47       33   List of QSOs
sp/*              .        33   Individual spectra
ew/*              .        33   Individual equivalent width files
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Byte-by-byte Description of file: qsos.dat
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   Bytes Format Units   Label     Explanations
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   1-  2  I2    h       RAh       Right ascension (J2000)
   4-  5  I2    min     RAm       Right ascension (J2000)
   7- 10  F4.1  s       RAs       Right ascension (J2000)
      12  A1    ---     DE-       Declination sign (J2000)
  13- 14  I2    deg     DEd       Declination (J2000)
  16- 17  I2    arcmin  DEm       Declination (J2000)
  19- 20  I2    arcsec  DEs       Declination (J2000)
  24- 32  A9    ---     Name      QSO name (QHHMM+DDd)
  35- 47  A13   ---     FileName  Name of the spectrum file in subdirectory sp
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Byte-by-byte Description of file: sp/*
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   Bytes Format Units   Label     Explanations
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   5- 11  F7.2  0.1nm   Lambda    Wavelength
  15- 25  F11.5 ct      Counts    Counts
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History:
    From http://lithops.as.arizona.edu/~jill/QuasarSpectra/MMT/QSOplots

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(End)                                   Francois Ochsenbein [CDS]    27-Dec-2002