Detecting cold gas at intermediate redshifts: GMRT survey using Mg II systems

Intervening HI 21-cm absorption systems at z > 1.0 are very rare and only 4 confirmed detections have been reported in the literature. Despite their scarcity, they provide interesting and unique insights into the physical conditions in the interstellar medium of high-z galaxies. Moreover, they can provide independent constraints on the variation of fundamental constants. We report 3 new detections based on our ongoing Giant Metrewave Radio Telescope (GMRT) survey for 21-cm absorbers at 1.10< z_abs< 1.45 from candidate damped Lyman_alpha systems. The 21-cm lines are narrow for the z_abs = 1.3710 system towards SDSS J0108-0037 and z_abs = 1.1726 system toward SDSS J2358-1020. Based on line full-width at half maximum, the kinetic temperatures are <= 5200 K and <=800 K, respectively. The 21-cm absorption profile of the third system, z_abs =1.1908 system towards SDSS J0804+3012, is shallow, broad and complex, extending up to 100 km/s. The centroids of the 21-cm lines are found to be shifted with respect to the corresponding centroids of the metal lines derived from SDSS spectra. This may mean that the 21-cm absorption is not associated with the strongest metal line component.Comment: 13 pages with 5 figures. Accepted for publication in ApJ

Radiative Transfer Effects during Photoheating of the Intergalactic Medium

The thermal history of the intergalactic medium (IGM) after reionization is to a large extent determined by photoheating. Here we demonstrate that calculations of the photoheating rate which neglect radiative transfer effects substantially underestimate the energy input during and after reionization. The neglect of radiative transfer effects results in temperatures of the IGM which are too low by a factor of two after HeII reionization. We briefly discuss implications for the absorption properties of the IGM and the distribution of baryons in shallow potential wells.Comment: 4 pages, 2 figures, submitted to ApJ

Dosage du carbone organique dissous dans les eaux douces naturelles. Intérêt, Principe, Mise en Oeuvre et Précautions Opératoires

International audienceCe mémoire présente un travail de validation du dosage du carbone organique dissous(COD) et du carbone inorganique (CI) contenus dans les eaux douces naturelles développé surl'analyseur Shimadzu©, modèle TOC 5050A.Les limites de détection calculées pour cet analyseur avec un catalyseur de sensibilitédite normale sont de 0.31 ppm pour le COD et de 0.10 ppm pour le CI, respectivement. Leslimites de quantification sont logiquement plus élevées: 0.41 ppm (COD) et 0.13 ppm (CI).Ces résultats permettent de conclure que le catalyseur dit de "sensibilité normale" qui équipeen routine cet analyseur est adapté à l'analyse de la plupart des eaux douces naturelles.Les tests d'étalonnage effectués ont montré que l'appareil Shimadzu© TOC 5050A étaittrès stable dans le temps, les dérives constatées étant inférieures à 5%. De ce fait, uneprocédure allégée d'étalonnage comprenant l'injection d'un seul point de gamme en début dechaque série d'échantillons suffit à garantir une bonne justesse des résultats, même si celle-ciest difficile à quantifier du fait de l'absence de solutions standard certifiées.Les trois méthodes susceptibles d'être mises en oeuvre par l'analyseur Shimadzu©, TOC5050A (COD = CT – CI; NPOC, NPIW) ont été testées. Seules la méthode COD = CT – CIpermet de doser la totalité du compartiment "matière organique dissoute" des eaux doucesnaturelles. Les deux autres ne permettent pas d'appréhender les molécules les plus volatiles,les écarts entre valeurs "vraies" et valeurs "mesurées" pouvant aller jusqu'à 25%.Des expériences visant à tester les modalités de préparation et de conservation deséchantillons ont également été effectuées. Les résultats montrent que pour des eaux peuchargées en matière organique (COD 5%) entre valeurs mesurées et valeurs vraies. Dans ce cas,l'opérateur soucieux de produire des résultats justes sera conduit à filtrer les eaux directementsur le terrain et à réduire au maximum l'intervalle de temps entre le prélèvement et l'analyse

The Population of Weak Mg II Absorbers I. A Survey of 26 QSO HIRES/Keck Spectra

We present a search for "weak" MgII absorbers [those with W_r(2796) < 0.3 A in the HIRES/Keck spectra of 26 QSOs. We found 30, of which 23 are newly discovered. The spectra are 80% complete to W_r(2796) = 0.02 A and have a cumulative redshift path of ~17.2 for the redshift range 0.4 < z < 1.4. The number of absorbers per unit redshift, dN/dz, is seen to increase as the equivalent width threshold is decreased; we obtained dN/dz = 1.74+/-0.10 for our 0.02 <= W_r(2796) < 0.3 A sample. The equivalent width distribution follows a power law with slope -1.0; there is no turnover down to W_r(2796) = 0.02 A at = 0.9. Weak absorbers comprise at least 65% of the total MgII absorption population, which outnumbers Lyman limit systems (LLS) by a factor of 3.8+/-1.1; the majority of weak MgII absorbers must arise in sub-LLS environments. Tentatively, we predict that ~5% of the Lyman-alpha forest clouds with W_r(1215) > 0.1 A will have detectable MgII absorption to W_r,min(2796) = 0.02 A and that this is primarily a high-metallicity selection effect (Z/Z_sun] > -1). This implies that MgII absorbing structures figure prominently as tracers of sub-LLS environments where gas has been processed by stars. We compare the number density of W_r(2796) > 0.02 A absorbers with that of both high and low surface brightness galaxies and find a fiducial absorber size of 35h^-1 to 63h^-1 kpc, depending upon the assumed galaxy population and their absorption properties. The individual absorbing "clouds" have W_r(2796) <= 0.15 A and their narrow (often unresolved) line widths imply temperatures of ~25,000 K. We measured W_r(1548) from CIV in FOS/HST archival spectra and, based upon comparisons with FeII, found a range of ionization conditions (low, high, and multi-phase) in absorbers selected by weak MgII.Comment: Accepted Version: 43 pages, PostScript figures embedded; accepted to ApJ; updated version includes analysis of CIV absorptio

Automatic alignment of surgical videos using kinematic data

Over the past one hundred years, the classic teaching methodology of "see one, do one, teach one" has governed the surgical education systems worldwide. With the advent of Operation Room 2.0, recording video, kinematic and many other types of data during the surgery became an easy task, thus allowing artificial intelligence systems to be deployed and used in surgical and medical practice. Recently, surgical videos has been shown to provide a structure for peer coaching enabling novice trainees to learn from experienced surgeons by replaying those videos. However, the high inter-operator variability in surgical gesture duration and execution renders learning from comparing novice to expert surgical videos a very difficult task. In this paper, we propose a novel technique to align multiple videos based on the alignment of their corresponding kinematic multivariate time series data. By leveraging the Dynamic Time Warping measure, our algorithm synchronizes a set of videos in order to show the same gesture being performed at different speed. We believe that the proposed approach is a valuable addition to the existing learning tools for surgery.Comment: Accepted at AIME 201

ON THE COARSE GEOMETRY OF JAMES SPACES

International audienceIn this note we prove that the Kalton interlaced graphs do not equi-coarsely embed into the James space J nor into its dual J *. It is a particular case of a more general result on the non equi-coarse embeddability of the Kalton graphs into quasi-reflexive spaces with a special asymptotic stucture. This allows us to exhibit a coarse invariant for Banach spaces, namely the non equi-coarse embeddability of this family of graphs, which is very close to but different from the celebrated property Q of Kalton. We conclude with a remark on the coarse geometry of the James tree space J T and of its predual

Probing the BLR in AGNs using time variability of associated absorption line

It is know that most of the clouds producing associated absorption in the spectra of AGNs and quasars do not completely cover the background source (continuum + broad emission line region, BLR). We note that the covering factor derived for the absorption is the fraction of photons occulted by the absorbing clouds, and is not necessarily the same as the fractional area covered. We show that the variability in absorption lines can be produced by the changes in the covering factor caused by the variation in the continuum and the finite light travel time across the BLR. We discuss how such a variability can be distinguished from the variability caused by other effects and how one can use the variability in the covering factor to probe the BLR.Comment: 12 pages, latex(aaspp4.sty), 2 figures, (To appear in ApJ

The Statistics of Density Peaks and the Column Density Distribution of the Lyman-Alpha Forest

We develop a method to calculate the column density distribution of the Lyman-alpha forest for column densities in the range $10^{12.5} - 10^{14.5} cm^{-2}$. The Zel'dovich approximation, with appropriate smoothing, is used to compute the density and peculiar velocity fields. The effect of the latter on absorption profiles is discussed and it is shown to have little effect on the column density distribution. An approximation is introduced in which the column density distribution is related to a statistic of density peaks (involving its height and first and second derivatives along the line of sight) in real space. We show that the slope of the column density distribution is determined by the temperature-density relation as well as the power spectrum on scales $2 h Mpc^{-1} < k < 20 h Mpc^{-1}$. An expression relating the three is given. We find very good agreement between the column density distribution obtained by applying the Voigt-profile-fitting technique to the output of a full hydrodynamic simulation and that obtained using our approximate method for a test model. This formalism then is applied to study a group of CDM as well as CHDM models. We show that the amplitude of the column density distribution depends on the combination of parameters $(\Omega_b h^2)^2 T_0^{-0.7} J_{HI}^{-1}$, which is not well-constrained by independent observations. The slope of the distribution, on the other hand, can be used to distinguish between different models: those with a smaller amplitude and a steeper slope of the power spectrum on small scales give rise to steeper distributions, for the range of column densities we study. Comparison with high resolution Keck data is made.Comment: match accepted version; discussion added: the effect of the shape of the power spectrum on the slope of the column density distributio

The Cross-correlation of MgII Absorption and Galaxies in BOSS

We present a measurement of the cross-correlation of MgII absorption and massive galaxies, using the DR11 main galaxy sample of the Baryon Oscillation Spectroscopic Survey of SDSS-III (CMASS galaxies), and the DR7 quasar spectra of SDSS-II. The cross-correlation is measured by stacking quasar absorption spectra shifted to the redshift of galaxies that are within a certain impact parameter bin of the quasar, after dividing by a quasar continuum model. This results in an average MgII equivalent width as a function of impact parameter from a galaxy, ranging from 50 kpc to more than 10 Mpc in proper units, which includes all MgII absorbers. We show that special care needs to be taken to use an unbiased quasar continuum estimator, to avoid systematic errors in the measurement of the mean stacked MgII equivalent width. The measured cross-correlation follows the expected shape of the galaxy correlation function, although measurement errors are large. We use the cross-correlation amplitude to derive the bias factor of MgII absorbers, finding bMgII = 2.33 \pm? 0.19, where the error accounts only for the statistical uncertainty in measuring the mean equivalent width. This bias factor is larger than that obtained in previous studies and may be affected by modeling uncertainties that we discuss, but if correct it suggests that MgII absorbers at redshift z \simeq 0:5 are spatially distributed on large scales similarly to the CMASS galaxies in BOSS. Keywords: galaxies: haloes, galaxies: formation, quasars: absorption lines, large-scale structure of universeComment: Accepted for publication to MNRAS. Accepted 2014 December 12. Received 2014 November 29; in original form 2014 February