R. F. Carswell

Indications of a spatial variation of the fine structure constant.

We previously reported Keck telescope observations suggesting a smaller value of the fine structure constant α at high redshift. New Very Large Telescope (VLT) data, probing a different direction in the Universe, shows an inverse evolution; α increases at high redshift. Although the pattern could be due to as yet undetected systematic effects, with the systematics as presently understood the combined data set fits a spatial dipole, significant at the 4.2 σ level, in the direction right ascension 17.5 ± 0.9 h, declination -58 ± 9 deg. The independent VLT and Keck samples give consistent dipole directions and amplitudes, as do high and low redshift samples. A search for systematics, using observations duplicated at both telescopes, reveals none so far which emulate this result.

Galactic winds in the intergalactic medium

We have performed hydrodynamical simulations to investigate the effects of galactic winds on the high-redshift (z = 3) universe. Strong winds suppress the formation of low-mass galaxies significantly, and the metals carried by them produce C IV absorption lines with properties in reasonable agreement with observations. The winds have little effect on the statistics of the H I-absorption lines, because the hot gas bubbles blown by the winds fill only a small fraction of the volume and because they tend to escape into the voids, thereby leaving the filaments that produce these lines intact. Subject headings: cosmology: observations — cosmology: theory — galaxies: formation — intergalactic medium — quasars: absorption lines

An improved measurement of the flux distribution of the Lyα 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 (H i) and metal absorption present in a sample of 18 high-resolution, high signal-to-noise ratio quasi-stellar object (QSO) spectra observed with the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph. We use this analysis to separate the metal contribution from the H absorption and present an improved measurement of the flux probability distribution function (PDF) due to H i absorption alone at (z) = 2.07,2.52 and 2.94. The flux PDF is sensitive to the continuum fit in the normalized 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 H i absorption alone are systematically lower at 0.2 < F < 0.8 by up to 30 per cent compared to the widely used measurement of McDonald et al., based on a significantly smaller sample of Keck High Resolution Echelle Spectrometer 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 H effective optical depth τ eff Ht at 1.7 < z < 4 is best fit with a single power law, τ eff HI = (0.0023 ± 0.0007)(1 + z) 365±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 ratio data.

The physical properties of the Lyα forest at z > 1.5★

Combining a new, increased data set of eight quasi-stellar objects (QSOs) covering the Lyα forest at redshifts 1.5 < z < 3.6 from VLT/UVES observations with previously published results, we have investigated the properties of the Lyα forest at 1.5 < z <4. With the six QSOs covering the Lyα forest at 1.5 < z < 2.5, we have extended previous studies in this redshift range. In particular, we have concentrated on the evolution of the line number density and the clustering of the Lyα forest at z≤ 2.5, where the Lyα forest starts to show some inhomogeneity from sightline to sightline. We have fitted Voigt profiles to the Lyα absorption lines as in previous studies, and have, for two QSOs with zem∼ 2.4, fitted Lyα and higher order of Lyman lines down to 3050 A simultaneously. This latter approach has been taken in order to study the Lyβ forest at z∼ 2.2 and the higher H i column density Lyα forest in the Lyβ forest region. For a given NH I range, the Lyα forest at 1.5 1014 cm−2, there is a variation in the line number density from sightline to sightline at z < 2.5. This variation is stronger for higher column density systems, probably due to more gravitationally evolved structures at lower z. The mean H i opacity is at 1.5 < z < 4. HST observations show evidence for slower evolution of at z < 1. For NH i= 1012.5–15 cm−2, the differential column density distribution function, f(NH i), can be best fitted by f(NH I∝NH i−β with β≈ 1.5 for 1.5 < z < 4. When combined with HST observations, the exponent β increases as z decreases at 0 < z < 4 for NH i= 1013–17 cm−2. The correlation strength of the step optical depth correlation function shows the strong evolution from 〈z〉= 3.3 to 〈z〉= 2.1, although there is a large scatter along different sightlines. The analyses of the Lyβ forest at z∼ 2.2 are, in general, in good agreement with those of the Lyα forest.

Possible evidence for an inverted temperature–density relation in the intergalactic medium from the flux distribution of the Lyα forest

We compare the improved measurement of the Lya forest flux probability distribution at 1.7 < z < 3.2 presented by Kim et al. 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 Δ γ-1 , is either close to isothermal or inverted (y < 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 ionizing radiation during the epoch of He II reionization as a possible physical mechanism for achieving an inverted temperature-density relation at z ≃ 3.

A large population of metal-rich, compact, intergalactic C iv absorbers – evidence for poor small-scale metal mixing

We carried out a survey for high-metallicity Civ absorbers at redshift z ≈ 2.3 in nine high-quality quasar spectra. Using a novel analysis technique, based on detections of C iv lines and automatically determined upper limits on the column densities of H I, C III, N v and O vi, we find a large (dN/dz > 7) population of photoionized, compact (R ∼ 10 2 pc), metal-rich (Z ≥ Z⊙) Civ clouds with moderate densities (n H ∼ 10 -3.5 cm -3 ), properties that we show are robust with respect to uncertainties in the ionization model. In particular, local sources of ionizing radiation, overabundance of oxygen, departures from ionization equilibrium and collisional ionization would all imply more compact clouds. The clouds are too small to be self-gravitating and pressure confinement is only consistent under special conditions. We argue that the clouds are, in any case, likely to be short-lived and we demonstrate that this implies that the clouds could easily have been responsible for the transport of all metals that end up in the intergalactic medium (IGM). When metal-rich clouds reach pressure equilibrium with the general, photoionized IGM, the heavy elements will still be concentrated in small high-metallicity patches, but they will look like ordinary, low-metallicity absorbers. We conclude that intergalactic metals are poorly mixed on small scales and that nearly all of the IGM, and thus the universe, may therefore be of primordial composition.

H-alpha emission lines in high-redshift quasars

Infrared spectra have been obtained of the H-alpha lines in 18 medium- to high-redshift QSOs and optical spectra taken nearly simultaneously to measure the strong UV line. It is found that the H-alpha line is redshifted by an average of 1000 km/s with respect to the lines from high ionization species such as C IV. Low ionization lines from ions like O I and Mg II are shifted by similar, or slightly smaller, amounts with respect to the high ionization lines. These results are difficult to reconcile with any simple models currently available, including those where dust obscuration is solely responsible for the observed velocity shifts. The similarity between the velocities of H-alpha and Mg II, O I provides some support for models in which the Balmer lines are produced predominantly in a warm H I region, while the Lyman lines arise mainly in a population of optically thin clouds. A velocity separation between the two cloud populations, along with some obscuration, could explain the main features. 25 refs.

Temperature fluctuations in the intergalactic medium

ABSTRA C T The temperature of the low-density intergalactic medium (IGM) is set by the balance between adiabatic cooling resulting from the expansion of the Universe, and photoheating by the ultraviolet (UV) background. We have analysed the Lya forest of 11 high-resolution quasar spectra using wavelets, and find strong evidence of a marked jump in the temperature at the mean density, T0 ,o f 60^ 14 per cent over the redshift interval zaâ3:5; 3:1a, which we attribute to reionization of He II. The jump can be seen in all three of our spectra that straddle redshift 3.3, at a significance of > 99 per cent. Below z , 3:1, our results are consistent with a smooth cooling down of the universe, as expected when adiabatic expansion dominates over photoheating by a UV background from quasi-stellar objects (QSOs) and galaxies. We find no evidence of thermal fluctuations on scales > 5000 km s 21 larger than 50 per cent, which could be detected by our method, suggesting that the IGM follows a reasonably well-defined temperature ‐ density relation. We demonstrate that the mean wavelet amplitude kAl/ 1/T 0, and calibrate the relation with hydrodynamical simulations. We find T 0 > 1:2 £ 10 4 Ka t z > 3:6. Such high temperatures suggest that H I reionization occurred relatively recently.

Stringent null constraint on cosmological evolution of the proton-to-electron mass ratio.

We present a strong constraint on variation of the proton-to-electron mass ratio mu over cosmological time scales using molecular hydrogen transitions in optical quasar spectra. Using high quality spectra of quasars Q0405-443, Q0347-383, and Q0528-250, variation in micro relative to the present day value is limited to Deltamicro/micro=(2.6+/-3.0)x10;{-6}. We reduce systematic errors compared to previous works by substantially improving the spectral wavelength calibration method and by fitting absorption profiles to the forest of hydrogen Lyman alpha transitions surrounding each H2 transition. Our results are consistent with no variation, and inconsistent with a previous approximately 4sigma detection of mu variation involving Q0405-443 and Q0347-383. If the results of this work and those suggesting that alpha may be varying are both correct, then this would tend to disfavor certain grand unification models.

Keck Telescope Constraint on Cosmological Variation of the Proton-to-Electron Mass Ratio

Molecular transitions recently discovered at redshift z(abs) = 2.059 towards the bright background quasar J2123-0050 are analysed to limit cosmological variation in the proton-to-electron mass ratio, mu equivalent to m(p)/m(e). Observed with the Keck telescope, the optical echelle spectrum has the highest resolving power and largest number (86) of H-2 transitions in such analyses so far. Also, (seven) HD transitions are used for the first time to constrain mu-variation. These factors, and an analysis employing the fewest possible free parameters, strongly constrain mus relative deviation from the current laboratory value: delta mu/mu = (+5.6 +/- 5.5(stat) +/- 2.9(sys)) x 10-6, indicating an insignificantly larger mu in the absorber. This is the first Keck result to complement recent null constraints from three systems at z(abs) > 2.5 observed with the Very Large Telescope. The main possible systematic errors stem from wavelength calibration uncertainties. In particular, distortions in the wavelength solution on echelle order scales are estimated to contribute approximately half the total systematic error component, but our estimate is model dependent and may therefore under or overestimate the real effect, if present. To assist future mu-variation analyses of this kind, and other astrophysical studies of H-2 in general, we provide a compilation of the most precise laboratory wavelengths and calculated parameters important for absorption-line work with H-2 transitions redwards of the hydrogen Lyman limit.