For refcode 2007MNRAS.376.1227K: Retrieve 73 NED objects in this reference. Please click here for ADS abstract
NED Abstract
Copyright by Royal Astronomical Society.
2007MNRAS.376.1227K
Continuous statistics of the Ly{alpha} forest at 0 < z < 1.6: the mean
flux, flux distribution and autocorrelation from HST FOS spectra
David Kirkman, David Tytler, Dan Lubin and Jane Charlton
Abstract. We measure the amount of absorption in the Ly{alpha} forest at
0 < z < 1.6 in Hubble Space Telescope Faint Object Spectrograph spectra
of 74 quasistellar objects (QSOs). Starting with a 334 QSO sample
compiled by Bechtold et al., we selected 74 QSOs that have the highest
signaltonoise ratio and complete coverage of restframe wavelengths
10701170 Angstrom. We measure the absorption from the flux in each
pixel in units of the unabsorbed continuum level. We mask out regions of
spectra that contain metal lines, or strong Ly{alpha} lines that are
accompanied by other Lyman series line or metals at the same redshift,
leaving Ly{alpha} absorption from the lowdensity intergalactic medium
(IGM). At 0 < z < 1.6 we find that 79 per cent of the absorption is from
the lowdensity IGM, 12 per cent from metals and 9 per cent from the
strong H I lines, nearly identical to the percentages (78, 15 and 7)
that we measured independently at z = 2 from spectra taken with the Kast
spectrograph on the Lick 3m. At z = 1 the lowdensity IGM absorbs 0.037
+/ 0.004 of the flux. The error includes some but not all of the
uncertainty in the continuum level. The remaining part gives relative
errors of approximately 0.21 when we report the mean absorption in eight
independent redshift intervals, and 0.047 when we average over all
redshifts. We find 1.46 times more absorption from the lowdensity IGM
than comes from Ly{alpha} lines that Bechtold et al. listed in the same
spectra. The amount of absorption increases with z and can be fit by a
power law (1 + z)^{alpha}^, with {alpha} = 1.01. If the absorption comes
entirely from lines with fixed rest equivalent width, this result
implies the number density of lines evolves like (1 + z)^0.01^, or no
change in the number of lines per unit redshift, consistent with the
Janknecht et al. results on the distribution of lines. When we include
similar measurements from higher redshifts, we need more degrees of
freedom to fit the amount of absorption at 0 < z < 3.2. A power law with
a break in slope, changing from index 1.5 at low z to 3.0 above z ~ 1.1
is a better but only marginally acceptable fit. We also calculate two
other continuous statistics, the flux probability distribution function
and the flux autocorrelation function that is nonzero out to v ~ 500 km
s^1^ at 0.5 < z < 1.5.
Retrieve 73 NED objects in this reference. Please click here for ADS abstract
