X-ray properties of K-selected galaxies at 0.5<z<2.0: Investigating trends with stellar mass, redshift and spectral type

We examine how the total X-ray luminosity correlates with stellar mass, stellar population, and redshift for a K-band limited sample of ~3500 galaxies at 0.5<z<2.0 from the NEWFIRM Medium Band Survey in the COSMOS field. The galaxy sample is divided into 32 different galaxy types, based on similarities between the spectral energy distributions. For each galaxy type, we further divide the sample into bins of redshift and stellar mass, and perform an X-ray stacking analysis using the Chandra COSMOS (C-COSMOS) data. We find that full band X-ray luminosity is primarily increasing with stellar mass, and at similar mass and spectral type is higher at larger redshifts. When comparing at the same stellar mass, we find that the X-ray luminosity is slightly higher for younger galaxies (i.e., weaker 4000\AA breaks), but the scatter in this relation is large. We compare the observed X-ray luminosities to those expected from low and high mass X-ray binaries (XRBs). For blue galaxies, XRBs can almost fully account for the observed emission, while for older galaxies with larger 4000\AA breaks, active galactic nuclei (AGN) or hot gas dominate the measured X-ray flux. After correcting for XRBs, the X-ray luminosity is still slightly higher in younger galaxies, although this correlation is not significant. AGN appear to be a larger component of galaxy X-ray luminosity at earlier times, as the hardness ratio increases with redshift. Together with the slight increase in X-ray luminosity this may indicate more obscured AGNs or higher accretion rates at earlier times.Comment: 9 pages, 9 figures, ApJ accepte

A selective chromogenic plate, YECA, for the detection of pathogenic Yersinia enterocolitica: specificity, sensibility and capacity to detect pathogenic Y. enterocolitica from pig tonsils

A new selective chromogenic plate, YECA, was tested for its specificity, sensitivity and accuracy to detect pathogenic Y. enterocolitica from pig tonsils. We tested a panel of 26 bacterial strains on YECA and compared it to PCA, CIN and YeCM media. Detection of pathogenic Y. enterocolitica was carried out on 50 pig tonsils collected in one slaughterhouse. Enrichment was done in PSB and ITC broths. Streaking on YECA and CIN was done in direct, after 24H incubation of ITC, after 48H incubation of PSB and ITC. All the plates were incubated at 30°C during 24 hours. Presence of typical colonies on CIN and YECA was checked and isolates were biotyped

Exploring the Nature of the Energy Barriers on the Mechanism of the Zirconocene-Catalyzed Ethylene Polymerization: A Quantitative Study from Reaction Force Analysis

Ethylene polymerization mediated by methyl-bis(cyclopentadienyl)-zirconium or zirconocene catalyst, [ZrCp₂CH₃]⁺, is one of the most popular catalytic reaction for polyethylene production. Rationalizing the major effects that control the polymer growth result in a challenge for computational studies. Through quantum chemical calculations, we characterized the zirconocene ethylene polymerization reaction mechanism: chain initiation (I; first ethylene insertion) [ZrCp₂CH₂CH₂CH₃]⁺, chain propagation (P; from second (P₁) to ninth (P₉) ethylene insertion) [ZrCp₂ (CH₂)₂₀CH₃]⁺, and chain termination processes (T; β-hydrogen elimination from P₅ or P₉) [ZrHCp₂ (H₂C═CH(CH₂)₁₈CH₃]⁺ are analyzed through the potential energy surface (PES) and reaction force analysis (RFA). The RFA approach involves pulling out the portion of an activation barrier that corresponds to distorting reactants into the geometries they adopt in a transition state structure until it reaches the structural relaxation toward the equilibrium geometry of the product. Because the interactions between the zirconocene and the ethylene molecule are influenced by a combination of several kinds of steric and electronic effects, it is indispensable to understanding these interactions in order to rationalize and predict in a quantitative manner the reaction barrier heights and the concomitant polymer growth. In the present work, we employ a simple procedure within the framework of the RFA and the density functional steric energy decomposition analysis (EDA) approach to quantitatively separate the different types of interactions; steric (ΔE_s), electrostatic (ΔE_e), and quantum (ΔE_q) effects in order to predict the impact of each factor on the course of the polymerization process as well as for the polymer control and design

The Evolution of the Fractions of Quiescent and Star-forming Galaxies as a Function of Stellar Mass Since z=3: Increasing Importance of Massive, Dusty Star-forming Galaxies in the Early Universe

Using the UltraVISTA DR1 and 3D-HST catalogs, we construct a stellar-mass-complete sample, unique for its combination of surveyed volume and depth, to study the evolution of the fractions of quiescent galaxies, moderately unobscured star-forming galaxies, and dusty star-forming galaxies as a function of stellar mass over the redshift interval $0.2 \le z \le 3.0$. We show that the role of dusty star-forming galaxies within the overall galaxy population becomes more important with increasing stellar mass, and grows rapidly with increasing redshift. Specifically, dusty star-forming galaxies dominate the galaxy population with $\log{(M_{\rm star}/M_{\odot})} \gtrsim 10.3$ at $z\gtrsim2$. The ratio of dusty and non-dusty star-forming galaxies as a function of stellar mass changes little with redshift. Dusty star-forming galaxies dominate the star-forming population at $\log{(M_{\rm star}/M_{\odot})} \gtrsim 10.0-10.5$, being a factor of $\sim$3-5 more common, while unobscured star-forming galaxies dominate at $\log{(M_{\rm star}/M_{\odot})} \lesssim 10$. At $\log{(M_{\rm star}/M_{\odot})} > 10.5$, red galaxies dominate the galaxy population at all redshift $z<3$, either because they are quiescent (at late times) or dusty star-forming (in the early universe).Comment: 7 pages, 4 figures, 1 table. Accepted by Astrophysical Journal Letters after minor revisio

Paul Ginestier: Anouilh; París, Seghers, 1969, 191 p., 16 x 13 cm.

Fil: Labbé, Liliana E.. Universidad Nacional de Cuy

Études littéraires, Quebec, Les Presses de L'Université Laval, volume I, N° 1, avril 1968, 157 p., 15 x 23 cm.

Fil: Labbé, Liliana E.. Universidad Nacional de Cuy

R. M. Albéres. Michel Butor. Editions Universitaires. París. 1964. 124 p., 17 x 11 cm.

Fil: Labbé, Liliana E. . Universidad Nacional de Cuyo. Facultad de Filosofía y Letra

Ages of massive galaxies at 0.5<z<2.00.5 < z < 2.0 from 3D-HST rest-frame optical spectroscopy

We present low-resolution near-infrared stacked spectra from the 3D-HST survey up to $z=2.0$ and fit them with commonly used stellar population synthesis models: BC03 (Bruzual & Charlot, 2003), FSPS10 (Flexible Stellar Population Synthesis, Conroy & Gunn 2010), and FSPS-C3K (Conroy, Kurucz, Cargile, Castelli, in prep). The accuracy of the grism redshifts allows the unambiguous detection of many emission and absorption features, and thus a first systematic exploration of the rest-frame optical spectra of galaxies up to $z=2$. We select massive galaxies ($\rm log(M_{*} / M_{\odot}) > 10.8$), we divide them into quiescent and star-forming via a rest-frame color-color technique, and we median-stack the samples in 3 redshift bins between $z=0.5$ and $z=2.0$. We find that stellar population models fit the observations well at wavelengths below $\rm 6500 \AA$ rest-frame, but show systematic residuals at redder wavelengths. The FSPS-C3K model generally provides the best fits (evaluated with a $\chi^2_{red}$ statistics) for quiescent galaxies, while BC03 performs the best for star-forming galaxies. The stellar ages of quiescent galaxies implied by the models, assuming solar metallicity, vary from 4 Gyr at $z \sim 0.75$ to 1.5 Gyr at $z \sim 1.75$, with an uncertainty of a factor of 2 caused by the unknown metallicity. On average the stellar ages are half the age of the Universe at these redshifts. We show that the inferred evolution of ages of quiescent galaxies is in agreement with fundamental plane measurements, assuming an 8 Gyr age for local galaxies. For star-forming galaxies the inferred ages depend strongly on the stellar population model and the shape of the assumed star-formation history.Comment: 13 pages, 15 figures, accepted for publication in Ap

The Age Spread of Quiescent Galaxies with the NEWFIRM Medium-band Survey: Identification of the Oldest Galaxies out to z~2

With a complete, mass-selected sample of quiescent galaxies from the NEWFIRM Medium-Band Survey (NMBS), we study the stellar populations of the oldest and most massive galaxies (>10^11 Msun) to high redshift. The sample includes 570 quiescent galaxies selected based on their extinction-corrected U-V colors out to z=2.2, with accurate photometric redshifts, sigma_z/(1+z)~2%, and rest-frame colors, sigma_U-V~0.06 mag. We measure an increase in the intrinsic scatter of the rest-frame U-V colors of quiescent galaxies with redshift. This scatter in color arises from the spread in ages of the quiescent galaxies, where we see both relatively quiescent red, old galaxies and quiescent blue, younger galaxies towards higher redshift. The trends between color and age are consistent with the observed composite rest-frame spectral energy distributions (SEDs) of these galaxies. The composite SEDs of the reddest and bluest quiescent galaxies are fundamentally different, with remarkably well-defined 4000A- and Balmer-breaks, respectively. Some of the quiescent galaxies may be up to 4 times older than the average age- and up to the age of the universe, if the assumption of solar metallicity is correct. By matching the scatter predicted by models that include growth of the red sequence by the transformation of blue galaxies to the observed intrinsic scatter, the data indicate that most early-type galaxies formed their stars at high redshift with a burst of star formation prior to migrating to the red sequence. The observed U-V color evolution with redshift is weaker than passive evolution predicts; possible mechanisms to slow the color evolution include increasing amounts of dust in quiescent galaxies towards higher redshift, red mergers at z<1, and a frosting of relatively young stars from star formation at later times.Comment: 20 pages, 20 figures, accepted for publication in Ap