The Keck+Magellan Survey for Lyman Limit Absorption I: The Frequency Distribution of Super Lyman Limit Systems

We present the results of a survey for super Lyman limit systems (SLLS; defined to be absorbers with 19.0 <= log(NHI) <= 20.3 cm^-2) from a large sample of high resolution spectra acquired using the Keck and Magellan telescopes. Specifically, we present 47 new SLLS from 113 QSO sightlines. We focus on the neutral hydrogen frequency distribution f(N,X) of the SLLS and its moments, and compare these results with the Lyman-alpha forest and the damped Lyman alpha systems (DLA; absorbers with log(NHI) >= 20.3 cm^-2). We find that that f(N,X) of the SLLS can be reasonably described with a power-law of index alpha = -1.43^{+0.15}_{-0.16} or alpha = -1.19^{+0.20}_{-0.21} depending on whether we set the lower N(HI) bound for the analysis at 10^{19.0} cm^-2 or 10^{19.3}$ cm^-2, respectively. The results indicate a flattening in the slope of f(N,X) between the SLLS and DLA. We find little evidence for redshift evolution in the shape of f(N,X) for the SLLS over the redshift range of the sample 1.68 < z < 4.47 and only tentative evidence for evolution in the zeroth moment of f(N,X), the line density l_lls(X). We introduce the observable distribution function O(N,X) and its moment, which elucidates comparisons of HI absorbers from the Lyman-alpha through to the DLA. We find that a simple three parameter function can fit O(N,X) over the range 17.0 <= log(NHI) <=22.0. We use these results to predict that f(N,X) must show two additional inflections below the SLLS regime to match the observed f(N,X) distribution of the Lyman-alpha forest. Finally, we demonstrate that SLLS contribute a minor fraction (~15%) of the universe's hydrogen atoms and, therefore, an even small fraction of the mass in predominantly neutral gas.Comment: 15 pages, 10 figures, accepted to the Astrophysical Journal. Revision includes updated reference

Optical properties and spatial distribution of MgII absorbers from SDSS image stacking

We present a statistical analysis of the photometric properties and spatial distribution of more than 2,800 MgII absorbers with 0.37<z<1 and rest equivalent width W_0(\lambda2796)>0.8\AA detected in SDSS quasar spectra. Using an improved image stacking technique, we measure the cross-correlation between MgII gas and light (in the g, r, i and z-bands) from 10 to 200 kpc and infer the light-weighted impact parameter distribution of MgII absorbers. Such a quantity is well described by a power-law with an index that strongly depends on W_0, ranging from ~-1 for W_0~ 1.5\AA. At redshift 0.37<z<0.55, we find the average luminosity enclosed within 100 kpc around MgII absorbers to be M_g=-20.65+-0.11 mag, which is ~0.5 L_g*. The global luminosity-weighted colors are typical of present-day intermediate type galaxies. However, while the light of weaker absorbers originates mostly from red passive galaxies, stronger systems display the colors of blue star-forming galaxies. Based on these observations, we argue that the origin of strong MgII absorber systems might be better explained by models of metal-enriched gas outflows from star-forming/bursting galaxies. Our analysis does not show any redshift dependence for both impact parameter and rest-frame colors up to z=1. However, we do observe a brightening of the absorbers related light at high redshift (~50% from z~0.4 to 1). We argue that MgII absorbers are a phenomenon typical of a given evolutionary phase that more massive galaxies experience earlier than less massive ones, in a downsizing fashion. (abridged)Comment: ApJ in press, 28 pages, 16 figures, using emulateapj. Only typo corrections wrt the original submission (v1

Big Line Bundles over Arithmetic Varieties

We prove a Hilbert-Samuel type result of arithmetic big line bundles in Arakelov geometry, which is an analogue of a classical theorem of Siu. An application of this result gives equidistribution of small points over algebraic dynamical systems, following the work of Szpiro-Ullmo-Zhang. We also generalize Chambert-Loir's non-archimedean equidistribution

The Blue Straggler population in the globular cluster M53 (NGC5024): a combined HST, LBT, CFHT study

We used a proper combination of multiband high-resolution and wide field multi-wavelength observations collected at three different telescopes (HST, LBT and CFHT) to probe Blue Straggler Star (BSS) populations in the globular cluster M53. Almost 200 BSS have been identified over the entire cluster extension. The radial distribution of these stars has been found to be bimodal (similarly to that of several other clusters) with a prominent dip at ~60'' (~2 r_c) from the cluster center. This value turns out to be a factor of two smaller than the radius of avoidance (r_avoid, the radius within which all the stars of ~1.2 M_sun have sunk to the core because of dynamical friction effects in an Hubble time). While in most of the clusters with a bimodal BSS radial distribution, r_avoid has been found to be located in the region of the observed minimum, this is the second case (after NGC6388) where this discrepancy is noted. This evidence suggests that in a few clusters the dynamical friction seems to be somehow less efficient than expected. We have also used this data base to construct the radial star density profile of the cluster: this is the most extended and accurate radial profile ever published for this cluster, including detailed star counts in the very inner region. The star density profile is reproduced by a standard King Model with an extended core (~25'') and a modest value of the concentration parameter (c=1.58). A deviation from the model is noted in the most external region of the cluster (at r>6.5' from the center). This feature needs to be further investigated in order to address the possible presence of a tidal tail in this cluster.Comment: 25 pages, 9 figures, accepted for publication on Ap

Probabilistic analysis of the upwind scheme for transport

We provide a probabilistic analysis of the upwind scheme for multi-dimensional transport equations. We associate a Markov chain with the numerical scheme and then obtain a backward representation formula of Kolmogorov type for the numerical solution. We then understand that the error induced by the scheme is governed by the fluctuations of the Markov chain around the characteristics of the flow. We show, in various situations, that the fluctuations are of diffusive type. As a by-product, we prove that the scheme is of order 1/2 for an initial datum in BV and of order 1/2-a, for all a>0, for a Lipschitz continuous initial datum. Our analysis provides a new interpretation of the numerical diffusion phenomenon

Non-Equilibrium Quantum Fields in the Large N Expansion

An effective action technique for the time evolution of a closed system consisting of one or more mean fields interacting with their quantum fluctuations is presented. By marrying large $N$ expansion methods to the Schwinger-Keldysh closed time path (CTP) formulation of the quantum effective action, causality of the resulting equations of motion is ensured and a systematic, energy conserving and gauge invariant expansion about the quasi-classical mean field(s) in powers of $1/N$ developed. The general method is exposed in two specific examples, $O(N)$ symmetric scalar \l\F^4 theory and Quantum Electrodynamics (QED) with $N$ fermion fields. The \l\F^4 case is well suited to the numerical study of the real time dynamics of phase transitions characterized by a scalar order parameter. In QED the technique may be used to study the quantum non-equilibrium effects of pair creation in strong electric fields and the scattering and transport processes in a relativistic $e^+e^-$ plasma. A simple renormalization scheme that makes practical the numerical solution of the equations of motion of these and other field theories is described.Comment: 43 pages, LA-UR-94-783 (PRD, in press), uuencoded PostScrip

Non variability of intervening absorbers observed in the UVES spectra of the "naked-eye" GRB080319

The aim of this paper is to investigate the properties of the intervening absorbers lying along the line of sight of Gamma-Ray Burst (GRB) 080319B through the analysis of its optical absorption features. To this purpose, we analyze a multi-epoch, high resolution spectroscopic observations (R=40000, corresponding to 7.5 km/s) of the optical afterglow of GRB080319B (z=0.937), taken with UVES at the VLT. Thanks to the rapid response mode (RRM), we observed the afterglow just 8m:30s after the GRB onset when the magnitude was R ~ 12. This allowed us to obtain the best signal-to-noise, high resolution spectrum of a GRB afterglow ever (S/N per resolution element ~ 50). Two further RRM and target of opportunity observations were obtained starting 1.0 and 2.4 hours after the event, respectively. Four MgII absorption systems lying along the line of sight to the afterglow have been detected in the redshift range 0.5 < z < 0.8, most of them showing a complex structure featuring several components. Absorptions due to FeII, MgI and MnII are also present; they appear in four, two and one intervening absorbers, respectively. One out of four systems show a MgII2796 rest frame equivalent width larger than 1A. This confirms the excess of strong MgII absorbers compared to quasars, with dn/dz = 0.9, ~ 4 times larger than the one observed along quasar lines of sight. In addition, the analysis of multi-epoch, high-resolution spectra allowed us to exclude a significant variability in the column density of the single components of each absorber. Combining this result with estimates of the size of the emitting region, we can reject the hypothesis that the difference between GRB and QSO MgII absorbers is due to a different size of the emitting regions.Comment: 10 pages, 15 ps figures, submitted to MNRA

Super-Solar Super Lyman Limit Systems

We present abundance measurements for two super Lyman Limit systems (SLLS; quasar absorption line systems with 10^19 cm^-2 < N_HI < 10^20.3 cm^-2) selected from a set of metal-strong absorbers in the Sloan Digital Sky Survey quasar database. After applying estimate corrections for photoionization effects, we derive gas-phase metallicities of [M/H]=+0.7 +/- 0.2 dex for the SLLS at z=1.7749 toward SDSS0927+5621 and [M/H]=+0.05 +/- 0.1 dex for the SLLS at z=1.7678 toward SDSS0953+5230. The former exhibits among the highest gas metallicity of any astrophysical environment and its total metal surface density exceeds that of nearly every known damped Lya system. The properties of these absorbers -- high metallicity and large velocity width (> 300 km/s) -- resemble those of gas observed in absorption in the spectra of bright, star-forming galaxies at high redshift. We discuss the metal mass density of the SLLS based on these observations and our ongoing SLLS survey and argue that a conservative estimate to the total metal budget at z=2 is greater than 15% of the total, suggesting that the metal-rich LLS may represent the dominant metal reservoir in the young universe.Comment: 6 pages, 2 figures. Submitted to ApJL; Revised June 22, 200

The Role of Sub-damped Lyman-alpha Absorbers in the Cosmic Evolution of Metals

Observations of low mean metallicity of damped Lyman-alpha (DLA) quasar absorbers at all redshifts studied appear to contradict the predictions for the global mean interstellar metallicity in galaxies from cosmic chemical evolution models. On the other hand, a number of metal-rich sub-DLA systems have been identified recently, and the fraction of metal-rich sub-DLAs appears to be considerably larger than that of metal-rich DLAs, especially at z < 1.5. In view of this, here we investigate the evolution of metallicity in sub-DLAs. We find that the mean Zn metallicity of the observed sub-DLAs may be higher than that of the observed DLAs, especially at low redshifts, reaching a near-solar level at z <~ 1. This trend does not appear to be an artifact of sample selection, the use of Zn, the use of N_{HI}-weighting, or observational sensitivity. While a bias against very low metallicity could be present in the sub-DLA sample in some situations, this cannot explain the difference between the DLA and sub-DLA metallicities at low z. The primary reason for the difference between the DLAs and sub-DLAs appears to be the dearth of metal-rich DLAs. We estimate the sub-DLA contribution to the total metal budget using measures of their metallicity and comoving gas density. These calculations suggest that at z <~ 1, the contribution of sub-DLAs to the total metal budget may be several times that of DLAs. At higher redshifts also, there are indications that the sub-DLAs may contribute significantly to the cosmic metal budget.Comment: 9 pages, 2 figures, Accepted for Publication in the Astrophysical Journa

Low percentage of clinically relevant pistachio nut and mango co-sensitisation in cashew nut sensitised children

Background: Cashew nut, pistachio nut and mango belong to the Anacardiaceae family and are botanically related. Therefore, cashew nut sensitised children are frequently advised to eliminate cashew nuts and pistachio nuts from their diet. The ‘Improvement of Diagnostic mEthods for ALlergy assessment (IDEAL trial number NTR3572) study showed that cashew nut sensitised children were co-sensitised to pistachio nut in 98% of cases and to mango in 21% of cases. The aim of this follow-up study to IDEAL is to assess the clinical relevance of co-sensitisation to pistachio nut and mango in cashew nut sensitised children. Methods: Children were recruited from the study: ‘Improvement of Diagnostic mEthods for ALlergy assessment (IDEAL trial number NTR3572). Inclusion criterion for the IDEAL study was sensitization to cashew nut as demonstrated by either SPT or sIgE, and a clinical history of reactions to cashew nuts or no previous (known) exposure. Sensitized children who were tolerant to cashew nuts were excluded. Inclusion criterion for this IDEAL follow-up study was co-sensitization to pistachio nut, regardless the result of the DBPCFC with cashew nut. In this follow-up study a double-blind placebo-controlled food challenge with pistachio nut and an open food challenge with mango were performed. Results: Twenty-nine children (mean age of 11.6 years, 62% male) were included. Pistachio nut sensitisation was clinically relevant in only 34% of cashew-sensitised children and only 31% of cashew challenge positive children. None of the children was challenge positive to mango. Conclusion: Although co-sensitisation between cashew nut and pistachio nut was observed in 98%, pistachio nut sensitisation was only clinically relevant in 34% of the children. Therefore, a challenge test with pistachio nut is recommended in children with cashew nut and pistachio nut sensitisation.</p