J/ApJS/91/1 Lyman-Alpha forest near 34 QSOs (Bechtold 1994)
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 1994ApJS...91....1B
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 Lyα forest absorption lines with
zabs∼zem. For zabs≪zem, 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 0.32Å. For lines stronger than 0.16Å, 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 zabs=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
zabs∼zem 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
Jnu=J-21x10-21ergs/cm2/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
(End) Francois Ochsenbein [CDS] 27-Dec-2002