The power spectrum of the flux distribution in the Lyman-alpha forest of a Large sample of UVES QSO Absorption Spectra (LUQAS)

The flux power spectra of the Lyman-alpha forest from a sample of 27 QSOs taken with the high resolution echelle spectrograph UVES on VLT are presented. We find a similar fluctuation amplitude at the peak of the ``3D'' flux power spectrum at k ~ 0.03 (km/sec)^(-1) as the study by Croft et al. (2002), in the same redshift range. The amplitude of the flux power spectrum increases with decreasing redshift if corrected for the increase in the mean flux level as expected if the evolution of the flux power spectrum is sensitive to the gravitational growth of matter density fluctuations. This is in agreement with the findings of McDonald et al. (2000) at larger redshift. The logarithmic slope of the "3D" flux power spectrum, P_F(k), at large scales k < 0.03 (km/sec)^(-1), is 1.4 +- 0.3, i.e. 0.3 shallower than that found by Croft et al. (2002) but consistent within the errors.Comment: 18 pages, 9 PS figures, 6 tables. Note that the k-values of the 1D flux power spectrum had been erroneously shifted by half a bin size (in log k) in the previous version. All the other results are unaffected. New tables can be found at http://www.ast.cam.ac.uk/~rtnigm/luqas.ht

The effect of (strong) discrete absorption systems on the Lyman α forest flux power spectrum

We demonstrate that the Lyman alpha forest flux power spectrum of 'randomized' quasi-stellar object (QSO) absorption spectra is comparable in shape and amplitude to the flux power spectrum of the original observed spectra. In the randomized spectra a random shift in wave-length has been added to the observed absorption lines as identified and fitted with VPFIT. At 0.03 s km(-1) 15 contribute at large scales, k < 0.03 s km(-1). We further show that a fraction of &GSIM; 15 per cent of the mean flux decrement is contributed by strong absorbers at z &GSIM; 2.1. Analysis of the flux power spectrum which use numerical simulations with too few strong absorption systems calibrated with the observed mean flux may underestimate the inferred rms fluctuation amplitude and the slope of the initial dark matter power spectrum

The UVES Spectral Quasar Absorption Database (SQUAD) Data Release 1: The first 10 million seconds

We present the first data release (DR1) of the UVES Spectral Quasar Absorption Database (SQUAD), comprising 467 fully reduced, continuum-fitted high-resolution quasar spectra from the Ultraviolet and Visual Echelle Spectrograph (UVES) on the European Southern Observatory's Very Large Telescope. The quasars have redshifts $z=0$-5, and a total exposure time of 10 million seconds provides continuum-to-noise ratios of 4-342 (median 20) per 2.5-km/s pixel at 5500 \AA. The SQUAD spectra are fully reproducible from the raw, archival UVES exposures with open-source software, including our UVES_popler tool for combining multiple extracted echelle exposures which we document here. All processing steps are completely transparent and can be improved upon or modified for specific applications. A primary goal of SQUAD is to enable statistical studies of large quasar and absorber samples, and we provide tools and basic information to assist three broad scientific uses: studies of damped Lyman-$\alpha$ systems (DLAs), absorption-line surveys and time-variable absorption lines. For example, we provide a catalogue of 155 DLAs whose Lyman-$\alpha$ lines are covered by the DR1 spectra, 18 of which are reported for the first time. The HI column densities of these new DLAs are measured from the DR1 spectra. DR1 is publicly available and includes all reduced data and information to reproduce the final spectra.Comment: 21 pages, 18 figures. Accepted by MNRAS. All final quasar spectra, reduced contributing exposures, and supplementary material available via https://github.com/MTMurphy77/UVES_SQUAD_DR

An improved measurement of the flux distribution of the Ly\u3b1 forest in QSO absorption spectra: the effect of continuum fitting, metal contamination and noise properties

We have performed an extensive Voigt profile analysis of the neutral hydrogen (HI) and metal absorption present in a sample of 18 high resolution, high signal-to-noise QSO spectra observed with VLT/UVES. We use this analysis to separate the metal contribution from the HI absorption and present an improved measurement of the flux probability distribution function (PDF) due to HI absorption alone at = 2.07, 2.52, and 2.94. The flux PDF is sensitive to the continuum fit in the normalised flux range 0.8 < F < 1.0 and to metal absorption at 0.2 < F < 0.8. Our new measurements of the flux PDF due to HI absorption alone are systematically lower at 0.2 < F < 0.8 by up to 30% compared to the widely used measurement of McDonald et al. (2000), based on a significantly smaller sample of Keck/HIRES data. This discrepancy is probably due to a combination of our improved removal of the metal absorption and cosmic variance, since variations in the flux PDF between different lines-of-sight are large. The HI effective optical depth at 1.7 < z < 4 is best fit with a single power law, (0.0023 +-0.0007) (1+z)^(3.65 +- 0.21), in good agreement with previous measurements from comparable data. As also found previously, the effect of noise on the flux distribution is not significant in high resolution, high signal-to-noise data

Possible evidence for an inverted temperature-density relation in the intergalactic medium from the flux distribution of the Lyman-alpha forest

We compare the improved measurement of the Lya forest flux probability distribution at 1.7<z<3.2 presented by Kim et al. (2007) to a large set of hydrodynamical simulations of the Lya forest with different cosmological parameters and thermal histories. The simulations are in good agreement with the observational data if the temperature-density relation for the low density intergalactic medium (IGM), T=T_0 Delta^{gamma-1}, is either close to isothermal or inverted (gamma<1). Our results suggest that the voids in the IGM may be significantly hotter and the thermal state of the low density IGM may be substantially more complex than is usually assumed at these redshifts. We discuss radiative transfer effects which alter the spectral shape of ionising radiation during the epoch of HeII reionisation as a possible physical mechanism for achieving an inverted temperature-density relation at z~3.Comment: 16 pages, 6 figures, accepted for publication in MNRAS following minor revision. The accepted version includes an expanded discussion of the flux power spectru

Geometrical Effects of Baryon Density Inhomogeneities on Primordial Nucleosynthesis

We discuss effects of fluctuation geometry on primordial nucleosynthesis. For the first time we consider condensed cylinder and cylindrical-shell fluctuation geometries in addition to condensed spheres and spherical shells. We find that a cylindrical shell geometry allows for an appreciably higher baryonic contribution to be the closure density (\Omega_b h_{50}^2 \la 0.2) than that allowed in spherical inhomogeneous or standard homogeneous big bang models. This result, which is contrary to some other recent studies, is due to both geometry and recently revised estimates of the uncertainties in the observationally inferred primordial light-element abundances. We also find that inhomogeneous primordial nucleosynthesis in the cylindrical shell geometry can lead to significant Be and B production. In particular, a primordial beryllium abundance as high as [Be] = 12 + log(Be/H) $\approx -3$ is possible while still satisfying all of the light-element abundance constraints.Comment: Latex, 20 pages + 11 figures(not included). Entire ps file with embedded figures available via anonymous ftp at ftp://genova.mtk.nao.ac.jp/pub/prepri/bbgeomet.ps.g

A new measurement of the intergalactic temperature at z∼2.55 − 2.95

We present two measurements of the temperature-density relationship (TDR) of the intergalactic medium (IGM) in the redshift range 2.55 < z < 2.95 using a sample of 13 high-quality quasar spectra and high resolution numerical simulations of the IGM. Our approach is based on fitting the neutral hydrogen column density NHI and the Doppler parameter b of the absorption lines in the Lyα forest. The first measurement is obtained using a novel Bayesian scheme which takes into account the statistical correlations between the parameters characterising the lower cut-off of the b − NHI distribution and the power-law parameters T0 and γ describing the TDR. This approach yields T0/103 K = 15.6 ± 4.4 and γ = 1.45 ± 0.17 independent of the assumed pressure smoothing of the small scale density field. In order to explore the information contained in the overall b − NHI distribution rather than only the lower cut-off, we obtain a second measurement based on a similar Bayesian analysis of the median Doppler parameter for separate column-density ranges of the absorbers. In this case we obtain T0/103 K = 14.6 ± 3.7 and γ = 1.37 ± 0.17 in good agreement with the first measurement. Our Bayesian analysis reveals strong anti-correlations between the inferred T0 and γ for both methods as well as an anti-correlation of the inferred T0 and the pressure smoothing length for the second method, suggesting that the measurement accuracy can in the latter case be substantially increased if independent constraints on the smoothing are obtained. Our results are in good agreement with other recent measurements of the thermal state of the IGM probing similar (over-)density ranges

The kinetic temperature in a damped Lyman-alpha absorption system in Q2206-199 - an example of the warm neutral medium

By comparing the widths of absorption lines from OI, SiII and FeII in the redshift z=2.076 single-component damped Lyman alpha absorption system in the spectrum of Q2206-199 we establish that these absorption lines arise in Warm Neutral Medium gas at ~12000 +/- 3000K. This is consistent with thermal equilibrium model estimates of ~ 8000K for the Warm Neutral Medium in galaxies, but not with the presence of a significant cold component. It is also consistent with, but not required by, the absence of CII* fine structure absorption in this system. Some possible implications concerning abundance estimates in narrow-line WNM absorbers are discussed.Comment: 9 pages, 3 figures. MNRAS accepte