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We present a new, uniform analysis of the H  i transmitted flux (F) and H  i column density (⁠|$N_{\mathrm{H\,{\small I}}}$|⁠) distribution in the low-density IGM as a function of redshift z for 0 <  z  < 3.6 using 55 HST /COS FUV (Δ z  = 7.2 at z  < 0.5), five HST /STIS + COS NUV (Δ z  = 1.3 at z  ∼ 1) and 24 VLT/UVES, and Keck/HIRES (Δ z  = 11.6 at 1.7 <  z  < 3.6) AGN spectra. We performed a consistent, uniform Voigt profile analysis to combine spectra taken with different instruments, to reduce systematics and to remove metal-line contamination. We confirm previously known conclusions on firmer quantitative grounds in particular by improving the measurements at z  ∼ 1. Two flux statistics at 0 <  F  < 1, the mean H  i flux and the flux probability distribution function (PDF), show that considerable evolution occurs from z  = 3.6 to z  = 1.5, after which it slows down to become effectively stable for z  < 0.5. However, there are large sightline variations. For the H  i column density distribution function (CDDF, f  ∝  |$N_{\rm H\,{\small I}}^{-\beta }$|⁠) at |$\log (N_{\mathrm{H\,{\small I}}}/1\, {\mathrm{cm}^{-2}})$|  ∈ [13.5, 16.0], β increases as z decreases from β = 1.60 at z  ∼ 3.4 to β = 1.82 at z ∼ 0.1. The CDDF shape at lower redshifts can be reproduced by a small amount of clockwise rotation of a higher- z CDDF with a slightly larger CDDF normalization. The absorption line number per z (d n /d z) shows a similar evolutionary break at z ∼ 1.5 as seen in the flux statistics. High- |$N_{\mathrm{H\,{\small I}}}$| absorbers evolve more rapidly than low- |$N_{\mathrm{H\,{\small I}}}$| absorbers to decrease in number or cross-section with time. The individual d n /d z shows a large scatter at a given z. The scatter increases towards lower z , possibly caused by a stronger clustering at lower z. [ABSTRACT FROM AUTHOR]

The gravitational potential ϕ = GM / Rc 2 at the surface of the white dwarf G191−B2B is 10 000 times stronger than that at the Earth's surface. Numerous photospheric absorption features are detected, making this a suitable environment to test theories in which the fundamental constants depend on gravity. We have measured the fine-structure constant, α, at the white dwarf surface, used a newly calibrated Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph spectrum of G191−B2B, two new independent sets of laboratory Fe  v wavelengths, and new atomic calculations of the sensitivity parameters that quantify Fe  v wavelength dependency on α. The two results obtained are: Δα/α0 = (6.36 ± 0.35stat ± 1.84sys) × 10−5 and Δα/α0 = (4.21 ± 0.48stat ± 2.25sys) × 10−5. The measurements hint that the fine-structure constant increases slightly in the presence of strong gravitational fields. A comprehensive search for systematic errors is summarized, including possible effects from line misidentifications, line blending, stratification of the white dwarf atmosphere, the quadratic Zeeman effect and electric field effects, photospheric velocity flows, long-range wavelength distortions in the HST spectrum, and variations in the relative Fe isotopic abundances. None fully account for the observed deviation but the systematic uncertainties are heavily dominated by laboratory wavelength measurement precision. [ABSTRACT FROM AUTHOR]

For around 100 yr, hydrogen spectral modelling has been based on Voigt profile fitting. The semiclassical Voigt profile is based on a two-level atom approximation. Whilst the Voigt profile is excellent for many circumstances, the accuracy is insufficient for very high column density damped Lyman-α absorption systems. We have adapted the quantum-mechanical Kramers–Heisenberg model to include thermal broadening, producing a new profile, the KHT profile. Interactions involving multiple discrete atomic levels and continuum terms, not accounted for in the Voigt model, generate asymmetries in the Lyman line wings. If not modelled, this can lead to significant systematics in parameter estimation when modelling real data. There are important ramifications in particular for measurements of the primordial deuterium abundance. However, the KHT model is complicated. We therefore present a simplified formulation based on Taylor series expansions and look-up tables, quantifying the impact of the approximations made. The KHT profile has been implemented within the widely used vpfit code. [ABSTRACT FROM AUTHOR]

At low densities, the standard ionization history of the intergalactic medium (IGM) predicts a decreasing temperature of the IGM with decreasing density once hydrogen (and helium) reionization is complete. Heating the high-redshift, low-density IGM above the temperature expected from photoheating is difficult, and previous claims of high/rising temperatures in lowdensity regions of the Universe based on the probability density function (PDF) of the opacity in Ly α forest data at 2 < z < 4 have been met with considerable scepticism, particularly since they appear to be in tension with other constraints on the temperature-density relation (TDR). We utilize here an ultrahigh signal-to-noise spectrum of the Quasi-stellar object HE0940-1050 and a novel technique to study the low opacity part of the PDF. We show that there is indeed evidence (at 90 per cent confidence level) that a significant volume fraction of the underdense regions at z ~ 3 has temperatures as high or higher than those at densities comparable to the mean and above. We further demonstrate that this conclusion is nevertheless consistent with measurements of a slope of the TDR in overdense regions that imply a decreasing temperature with decreasing density, as expected if photoheating of ionized hydrogen is the dominant heating process.We briefly discuss implications of our findings for the need to invoke either spatial temperature fluctuations, as expected during helium reionization, or additional processes that heat a significant volume fraction of the low-density IGM. [ABSTRACT FROM AUTHOR]

In this work, we investigate the abundance and distribution of metals in the intergalactic medium (IGM) at 〈z〉 ≃ 2.8 through the analysis of an ultra-high signal-to-noise ratio UVES spectrum of the quasar HE0940-1050. In the CIV forest, our deep spectrum is sensitive at 3σ to lines with column density down to log NCIV ≃ 11.4 and in 60 per cent of the considered redshift range down to ≃11.1. In our sample, all H I lines with log NHI ≥ 14.8 show an associated C IV absorption. In the range 14.0 ≤ log NHI < 14.8, 43 per cent of H I lines has an associated C IV absorption. At log NHI < 14.0, the detection rates drop to <10 per cent, possibly due to our sensitivity limits and not to an actual variation of the gas abundance properties. In the range log NHI ≥ 14, we observe a fraction of H I lines with detected C IV a factor of 2 larger than the fraction of H I lines lying in the circumgalactic medium (CGM) of relatively bright Lyman-break galaxies hosted by dark matter haloes with 〈M〉 ~ 1012 M☉. The comparison of our results with the output of a grid of photoionization models and of two cosmological simulations implies that the volume filling factor of the IGM gas enriched to a metallicity logZ/Z☉≳-3log⁡Z/Z☉≳-3 should be of the order of ~10-13 per cent. In conclusion, our results favour a scenario in which metals are found also outside the CGM of bright star-forming galaxies, possibly due to pollution by lower mass objects and/or to an early enrichment by the first sources. [ABSTRACT FROM AUTHOR]

This paper presents a self-consistent model for the evolution of gas produced in the debris disc of β Pictoris. Our model proposes that atomic carbon and oxygen are created from the photodissociation of CO, which is itself released from volatile-rich bodies in the debris disc due to grain-grain collisions or photodesorption. While the CO lasts less than one orbit, the atomic gas evolves by viscous spreading resulting in an accretion disc inside the parent belt and a decretion disc outside. The temperature, ionization fraction and population levels of carbon and oxygen are followed with the photodissociation region model CLOUDY, which is coupled to a dynamical viscous a model. We present new gas observations of β Pic, of C I observed with Atacama Pathfinder EXperiment and OI observed with Herschel, and show that these along with published CII and CO observations can all be explained with this new model. Our model requires a viscosity α > 0.1, similar to that found in sufficiently ionized discs of other astronomical objects; we propose that the magnetorotational instability is at play in this highly ionized and dilute medium. This new model can be tested from its predictions for high-resolution ALMA observations of C I. We also constrain the water content of the planetesimals in β Pic. The scenario proposed here might be at play in all debris discs and this model could be used more generally on all discs with C, O or CO detections. [ABSTRACT FROM AUTHOR]

From the Voigt profile fitting analysis of 183 intervening CIVCIV systems at 1.7 < z < 3.3 in 23 high-quality UVES/VLT and HIRES/Keck QSO spectra, we find that a majority of CIVCIV systems (~75 per cent) display a well-characterized scaling relation between integrated column densities of HIHI and CIVCIV with a negligible redshift evolution, when column densities of all the HIHI and CIVCIV components are integrated within a given ±150?km?s-1 range centred at the CIVCIV flux minimum. The integrated CIVCIV column density NCIV,sys increases with NHI,sys at logNHI,sys∈[14,16] and logNCIV,sys∈[11.8,14.0], then becomes almost independent of NHI,sys at logNHI,sys=16, with a large scatter: at logNHI,sys∈[14,22], logNCIV,sys=[C1/logNHI,sys+C2]+C3, with C1 = -1.90 ± 0.55, C2 = -14.11 ± 0.19 and C3 = 14.76 ± 0.17, respectively. The steep (flat) part is dominated by SiIVSiIV-free (SiIVSiIV-enriched) CIVCIV systems. Extrapolating the NHI,sys-NCIV,sys relation implies that most absorbers with logNHI≤14 are virtually CIVCIV-free. The NHI,sys-NCIV,sys relation does not hold for individual components, clumps or the integrated velocity range less than ±100?km?s-1. This is expected if the line-of-sight extent of CIVCIV is smaller than HIHI and NCIV,sys decreases more rapidly than NHI,sys at the larger impact parameter, regardless of the location of the HIHI+CIVCIV gas in intergalactic medium filaments or in intervening galactic haloes. [ABSTRACT FROM AUTHOR]

We present the Voigt profile analysis of 132 intervening CIV+CIII components associated with optically thinHI absorbers at 2.1= 1.0 ± 0.3 with a negligible redshift evolution. For 54 CIV components tied (aligned) with HI at logNHI [12.2, 16.0] and logNCIV [11.8, 13.8], the gas temperature Tb estimated from absorption line widths is well approximated to a Gaussian peaking at log Tb ~ 4.4 ± 0.3 for log Tb [3.5, 5.5], with a negligible non-thermal contribution. For 32 of 54 tied HI+CIV pairs, also tied with CIII at logNCIII [11.7, 13.8], we ran both photoionization equilibrium (PIE) and non-PIE (using a fixed temperature Tb) CLOUDY models for the Haardt-Madau QSOs+galaxies 2012 UV background. We find evidence of bimodality in observed and derived physical properties. High-metallicity branch absorbers have a carbon abundance [C/H]temp =-1.0, a line-of-sight length Ltemp = 20 kpc and a total (neutral and ionized) hydrogen volume density log nH,temp [-4.5, -3.3] and log Tb [3.9, 4.5]. Low-metallicity branch absorbers have [C/H]temp = -1.0, Ltemp [20, 480] kpc and log nH,temp [-5.2, -4.3] and log Tb ∼ 4.5. High-metallicity branch absorbers seem to be originated from extended discs, inner haloes or outflowing gas of intervening galaxies, while low-metallicity absorbers are produced by galactic haloes or the surrounding intergalactic medium filament. [ABSTRACT FROM AUTHOR]