Bastien Aracil

Limits on the time variation of the electromagnetic fine-structure constant in the low energy limit from absorption lines in the spectra of distant quasars.

We present the results of a detailed many-multiplet analysis performed on a new sample of Mg ii systems observed in high quality quasar spectra obtained using the Very Large Telescope. The weighted mean value of the variation in alpha derived from our analysis over the redshift range 0.4</=z</=2.3 is Deltaalpha/alpha=(-0.06+/-0.06)x10(-5). The median redshift of our sample (z approximately 1.55) corresponds to a look-back time of 9.7 Gyr in the most favored cosmological model today. This gives a 3sigma limit, -2.5 x 10(-16)</=(Deltaalpha/alphaDeltat)</=+1.2 x 10(-16) yr(-1), for the time variation of alpha, that forms the strongest constraint obtained based on high redshift quasar absorption line systems.

Probing the cosmological variation of the fine-structure constant: Results based on VLT-UVES sample ?

Development of fundamental physics relies on the constancy of various fundamental quantities such as the fine- structure constant. Detecting or constraining the possible time variations of these fundamental physical quantities is an im- portant step toward a complete understanding of basic physics. High-quality absorption lines seen in the spectra of distant QSOs allow one to probe time variations of several of these quantities. Here we present the results from a detailed many- multiplet analysis, to detect the possible variation of the fine-structure constant, performed using high signal-to-noise ratio, (∼70 per pixel), high spectral resolution (R ≥ 45 000) observations of 23 Mg  systems detected toward 18 QSOs in the redshift range 0.4 ≤ z ≤ 2.3 obtained using UVES at the VLT. We validate our procedure and define the selection criteria that will avoid possible systematics using a detailed analysis of a simulated data set. The spectra of Mg  doublets and Fe  multiplets are generated considering variations in α and specifications identical to that of our UVES spectra. We show that our Voigt profile fitting code recovers the variation in α very accurately when we use single component systems and multiple-component systems that are not heavily blended. Spurious detections are frequently seen when we use heavily blended systems or systems with very weak lines. Thus we avoided these system while analysing the UVES data. To make the analysis transparent and accessible to the community for critical scrutiny, all the steps involved in the analysis are presented in detail. The weighted mean value of the variation in α obtained from our analysis over the redshift range 0.4 ≤ z ≤ 2. 3i s∆α/α = (−0.06 ± 0.06) × 10 −5 . The median redshift of our sample is 1.55 and corresponds to a look-back time of 9.7 Gyr in the most favored cosmological model today. The 3σ upper limit on the time variation of α is −2.5 × 10 −16 yr −1 ≤ (∆α/α∆t) ≤ +1.2 × 10 −16 yr −1 . To our knowledge this is the strongest constraint from quasar absorption line studies to till date.

The sizes and kinematic structure of absorption systems towards the lensed quasar APM08279+5255

We have obtained spatially resolved spectra of the z em = 3.911 triply imaged QSO APM08279+5255 using the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope (HST). We study the line of sight equivalent width (EW) differences and velocity shear of high and low ionization absorbers (including a damped Lyman alpha [DLA] system identified in a spatially unresolved ground based spectrum) in the three lines of sight. The combination of a particularly rich spectrum and three sight-lines allow us to study 27 intervening absorption systems over a redshift range 1.1 80%) over kpc scales. A minimum radius for strong (EW > 0.3 A) Mg II systems of >1.4 h -1 70 kpc is inferred from absorption coincidences in all lines of sight. For weak Mg II absorbers (EW < 0.3 A), a maximum likelihood analysis indicates a most probable coherence scale of 2.0 h -1 70 kpc for a uniform spherical geometry, with 95% confidence limits ranging between 1.5 and 4.4 h -1 70 kpc. The weak Mg II absorbers may therefore represent a distinct population of smaller galaxies compared with the strong Mg II systems which we know to be associated with luminous galaxies whose halos extend over tens of kpc. Alternatively, the weak systems may reside in the outer parts of larger galaxies, where their filling factor may be lower. By cross-correlating spectra along different lines of sight, we infer shear velocities of typically less than 20 km s -1 for both high and low ionization absorbers. Finally, for systems with weak absorption that can be confidently converted to column densities, we find constant N(C IV)/N(Si IV) across the three lines of sight. Similarly, the [Al/Fe] ratios in the z abs = 2.974 DLA are consistent with solar relative abundances over a transverse distance of ∼0.35 h -1 70 kpc.

The warm-hot intergalactic medium at z ∼ 2.2: Metal enrichment and ionization source

Results are presented for our search for warm-hot gas towards the quasar Q 0329 385. We identify ten Ovi systems of which two are within 5000 km s 1 of zem and a third one should be of intrinsic origin. The seven remaining systems have Hi column densities 10 13:7 N(Hi) 10 15:6 cm 2 . At least1/3 of the individual Ovi sub-systems have temperatures T < 1 10 5 K and cannot originate in collisionally ionized gas. Photoionization by a hard UV background field reproduces well the ionic ratios for metallicities in the range 10 2:5 10 0:5 solar, with possibly sub-solar N/C relative abundance. For (O=C)= 0, the sizes inferred for the Ovi clouds are in some cases larger than the maximum extent implied by the Hubble flow. This constraint is fulfilled assuming a moderate overabundance of oxygen relative to carbon. For a soft UV ionizing spectrum, an overabundance of O/C is required, (O=C) 0:0 1:3. For a hard(soft) U spectrum and (O=C)= 0(1), the Ovi regions have overdensities= 10 40.

The correlation of the Lyman α forest in close pairs and groups of high-redshift quasars: clustering of matter on scales of 1–5 Mpc

We study the clustering of matter in the intergalactic medium from the Lyman a forests seen in the spectra of pairs or groups of z ∼ 2 quasars observed with FORS2 and UVES at the VLT-UT2 Kueyen ESO telescope. The sample consists of five pairs with separation of 0.6, 1, 2.1, 2.6 and 4.4 arcmin and a group of four quasars with separations from 2 up to 10 arcmin. This unprecedented data set allows us to measure the transverse flux correlation function for a range of angular scales. Correlations are clearly detectable at separations smaller than 3 arcmin. The shape and correlation length of the transverse correlation function on these scales are in good agreement with those expected from absorption by the photoionized warm intergalactic medium associated with the filamentary and sheet-like structures predicted in cold dark matter-like models for structure formation. At larger separation no significant correlation is detected. Assuming that the absorbing structures are randomly orientated with respect to the line of sight, the comparison of transverse and longitudinal correlation lengths constrains the cosmological parameters (as a modified version of the Alcock & Paczynski test). The present sample is too small to have significant constraints. Using N-body simulations, we investigate the possibility of constraining Ω A from future larger samples of quasistellar object pairs with similar separations. The observation of a sample of 30 pairs at 2, 4.5 and 7.5 arcmin should constrain the value of Ω A at ′15 per cent (2σ level). We also use the observed spectra of the group of four quasars to search for underdense regions in the intergalactic medium. We find a quasi-spherical structure of reduced absorption with radius 12.5 h - 1 Mpc, which we identify as an underdense region.

The Lyα forest around high‐redshift galaxies

Motivated by the relative lack of neutral hydrogen around Lyman Break Galaxies deduced from recent observations, we investigate the properties of the Lyalpha forest around high redshift galaxies. The study is based on improved numerical SPH simulations implementing, in addition to standard processes, a new scheme for multiphase and outflow physics description. Although on large scales our simulations reproduce a number of statistical properties of the IGM (because of the small filling factor of shock-heated gas), they underpredict the Lyalpha optical depth decrease inside 1 Mpc/h of the galaxies by a factor of ~2. We interpret this result as due to the combined effect of infall occurring along the filaments, which prevents efficient halo gas clearing by the outflow, and the insufficient increase of (collisional) hydrogen ionization produced by the temperature increase inside the hot, outflow-carved bubble. Unless an observational selection bias is present, we speculate that local photoionization could be the only viable explanation to solve the puzzle.

Spatially resolved STIS spectra of the gravitationally lensed broad absorption line quasar APM08279+5255: the nature of component C and evidence for microlensing

While gravitationally lensed quasars are expected to display an odd number of images, invariably systems are observed with an even number of quasars. For this, lensing galaxies must have very small core radii; this provides strong demagnification of one of the images. High-resolution imaging of the gravitationally lensed broad absorption line (BAL) quasar, APM08279+5255, reveals three point-like images. As these images possess similar colours, it has been suggested that each represents a lensed image. Here, spatially resolved spectra of the individual components, obtained with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST), are presented, clearly revealing that each is an image of the quasar. This confirms that APM08279+5255 represents the first example of an odd-image gravitationally lensed system. The implications for the properties of the lensing galaxy are discussed. It is also found that the individual images possess spectral differences indicative of the influence of gravitational microlensing in this system.

The Clustering of Intergalactic Metals

We measure the spatial clustering of metals in the intergalactic medium (IGM) from z = 1.7 to 3.0, as traced by 643 C IV and 104 Si IV N ≥ 1012 cm-2 absorption systems in 19 high signal-to-noise ratio (40-80) and high-resolution (R = 45,000) quasar spectra. The number densities and two-point correlation functions of both these species are largely constant with redshift, suggesting that the bulk of metal ejection occurred at z ≥ 3. However, at z ≤ 1.9, some additional signature appears in the C IV correlation function at 500 km s-1, associated with four strong and peculiar systems. At all redshifts, the C IV and Si IV correlation functions exhibit a steep rise at large separations and a flatter profile at small separations, with an elbow occurring at ~150 km s-1. We show that these properties are consistent with metals confined within bubbles with a typical radius Rs about sources of mass ≥Ms, and we use numerical simulations to derive best-fit values of Rs ~ 2 comoving Mpc and Ms ~ 5 × 1011 M☉ at z = 3. This does not exclude the possiblity that metals could have been produced at higher redshifts in smaller, but equally rare, objects. At the level of detection of this survey, IGM enrichment is likely to be incomplete and inhomogeneous, with a filling factor of ~10%.

A new measurement of zinc metallicity in a DLA at z∼3.35

Abstract We present chemical abundance measurements in the zabs=3.35045 Damped Lyman-α (DLA) system observed in the UVES spectrum of the BAL quasar BR 1117-1329 . We measure a neutral hydrogen column density N(HI)=6.9±1.7×1020 atoms cm−2 and derive mean abundances relative to solar: [Si/H]=−1.26±0.13, [Fe/H]=−1.51±0.13, [Ni/H]=−1.57±0.13, [Cr/H]=−1.36±0.13, [Zn/H]=−1.18±0.13, [Al/H]>−1.25, [O/H]>−1.25 and [N/H] 3. The iron to zinc and chromium to zinc ratios, [Fe/Zn]=−0.33±0.05 and [Cr/Zn]=−0.18±0.05 demonstrate that the absorber has a low dust content. The nitrogen ratio [N/Si]

Probing the variation of the fine-structure constant using QSO absorption lines

Search for the time variation of the fundamental constants is motivated by various unification theories. Here we present constraints on the variation of the fine-structure constant α≡ 2 / ħc) obtained using UVES/VLT samples of QSO absorption systems. We find w = (-0.06 ± 0.06) × 10 -5 using 23 Mg II systems and the many-multiplet (MM) method. Well selected 15 Si IV systems provide w = (0.15 ± 0.43) ×10 -5 . Absence of detectable variation in α is also confirmed by our new very high resolution (R ~ 100,000) observation of z abs = 1.1508 toward HE 0515-4414 using HARPS on the ESO 3.6m telescope.