High Redshift Quasars and Star Formation in the Early Universe

In order to derive information on the star formation history in the early universe we observed 6 high-redshift (z=3.4) quasars in the near-infrared to measure the relative iron and \mgii emission strengths. A detailed comparison of the resulting spectra with those of low-redshift quasars show essentially the same FeII/MgII emission ratios and very similar continuum and line spectral properties, indicating a lack of evolution of the relative iron to magnesium abundance of the gas since z=3.4 in bright quasars. On the basis of current chemical evolution scenarios of galaxies, where magnesium is produced in massive stars ending in type II SNe, while iron is formed predominantly in SNe of type Ia with a delay of ~1 Gyr and assuming as cosmological parameters H_o = 72 km/s Mpc, Omega_M = 0.3, and Omega_Lambda = 0.7$, we conclude that major star formation activity in the host galaxies of our z=3.4 quasars must have started already at an epoch corresponding to z_f ~= 10, when the age of the universe was less than 0.5 Gyrs.Comment: 29 pages, 5 figures, ApJ in pres

Effets des précipitations acides sur les écosystèmes aquatiques au Canada: Situation actuelle et future

Cet article représente une évaluation de l'état actuel et des tendances observées dans les écosystèmes lacustres, ainsi que de leur état futur probable lorsque les réductions d'émissions requises dans le cadre de l'Entente Canada-États-Unis sur la qualité de l'air auront été effectives. Outre une synthèse des faits saillants de ce dossier pour l'ensemble du Canada, le présent article s'appuie aussi sur l'ensemble des données physico-chimiques récentes (8874 échantillons) observées sur 2779 lacs de l'est canadien, ainsi que celles recueillies (1012 échantillons) sur 252 lacs de l'ouest canadien depuis 1985. Des données biologiques (poissons, benthos, zooplancton et oiseaux aquatiques) ont également été inventoriées pour identifier l'ampleur des dommages biologiques.Les nombreux lacs ayant subi une acidification anthropique récente sont situés pour la plupart dans l'est du Canada où les dépôts de SO- sont élevés. La sensibilité des sols influence également leur distribution spatiale. Durant la période s'échelonnant de 1981 à 1994, seulement 33% des 202 lacs faisant l'objet d'un suivi temporel dans l'est du Canada ont montré une amélioration significative de leur acidité (réduction) en réponse à la baisse des dépôts de SO- (11% des lacs ont subi une hausse d'acidité et 56% n'ont montré aucun changement). Plus de la moitié des lacs ayant récupéré se situent à proximité de Sudbury en Ontario. Plusieurs processus biogéochimiques sont responsables du retard dans la réversibilité de l'acidification. Pour cette raison, la récupération biologique a été très faible dans l'est canadien, exception faite de la région immédiate de Sudbury.Trois scénarios d'émissions ont été considérés: scénario 1: niveaux d'émission canadiens et américains de 1985; scénario 2: émissions canadiennes de 1994 et émissions américaines de 1990 ; scénario 3: réductions d'émissions américaines et canadiennes complétées. Ces scénarios de réductions d'émissions, qui ont été utilisés comme données d'entrée à des modèles stationnaires simulant la chimie des eaux de surface et qui ont été appliqués à cinq grandes zones lacustres du l'est canadien, suggèrent que la proportion de lacs "endommagés" (définis comme étant des lacs de pH<6) diminuera conséquemment aux réductions d'émissions américaines et canadiennes. De 11 à 49% des lacs acidifiés le resteront après l'ensemble des réductions prévues (scénario 3). Le Québec et l'Ontario, qui reçoivent actuellement les plus fortes retombées acides, bénéficieront le plus des réductions. Les gains environnementaux seront plus faibles dans l'est et dans l'ouest du Canada. De plus faibles dépôts acides et une contribution naturelle à l'acidité pourraient expliquer cette moins grande récupération.Il est maintenant reconnu que le pH est le principal facteur d'influence de la diversité spécifique du poisson, bien que d'autres facteurs comme la morphométrie du lac, l'altitude et les concentrations de COD soient aussi en partie responsables. Une réduction des dommages biologiques (i.e.baisse des disparitions de populations de poisson) serait donc possible, mais cette amélioration ne surviendra qu'après la hausse du pH des eaux de surface. L'importance relative des gains au plan biologique suivra une évolution similaire à celui des aspects chimiques. Des dommages significatifs aux écosystèmes lacustres subsisteront néanmoins après réalisation de l'ensemble des réductions d'émissions. Des pertes de populations de poissons devraient subsister dans 6% (Sudbury) à 15% (Kejimkujik) des lacs. Compte tenu du grand nombre de lacs situés dans le sud-est canadien, les pourcentages précédents impliquent que les ressources piscicoles perdues pourraient être très élevées. La restauration des communautés piscicoles devra passer dans bien des cas par un ré-enpoissonnement. De nouveaux programmes de contrôle visant des réductions supplémentaires d'émissions seront dès lors nécessaires pour protéger correctement les écosystèmes sensibles.This paper is an assessment of the current status and trends of Canadian lake systems, and their likely status after the effect of the emission controls required by the Canada/US Air Quality Agreement is fully realized. Many anthropogenically acidified lakes presently occur in that part of eastern Canada where SO- deposition is elevated. Terrain sensitivity also influences their spatial distribution. From 1981 to 1994, only 33% of 202 lakes monitored across eastern Canada showed a statistically significant improvement (reduction) in acidity in response to reduced SO- deposition (11% had increasing acidity and 56% showed no change). Over half of the improving lakes are near Sudbury, Ontario. Several biogeochemical processes are delaying de-acidification. As a result, there has been little biological recovery in eastern waters, except near Sudbury. Steady-state water chemistry modelling suggests that the proportion of "damaged" lakes (defined as having pH <6) will decline in response to both the Canadian and US emission controls. Reductions in biological damage (e.g. fewer lost fish populations) are expected also, but they will lag behind chemical improvement. Significant damage to aquatic ecosystems will remain after all chemical and biological improvements are realized. Further controls will be needed to protect sensitive ecosystems

A Fully Bidirectional Optical Network With Latency Monitoring Capability for the Distribution of Timing-Trigger and Control Signals in High-Energy Physics Experiments

The present paper discusses recent advances on a Passive Optical Network inspired Timing-Trigger and Control scheme for the future upgrade of the TTC system installed in the LHC experiments' and more specifically the currently known as TTCex to TTCrx link. The timing PON is implemented with commercially available FPGAs and 1-Gigabit Ethernet PON transceivers and provides a fixed latency gigabit downlink that can carry level-1 trigger accept decisions and commands as well as an upstream link for feedback from the front-end electronics

K-band Spectroscopy of Clusters in NGC 4038/4039

Integral field spectroscopy in the K-band (1.9-2.4um) was performed on four IR-bright star clusters and the two nuclei in NGC 4038/4039 (``The Antennae''). Two of the clusters are located in the overlap region of the two galaxies, and together comprise ~25% of the total 15um and ~10% of the total 4.8 GHz emission from this pair of merging galaxies. The other two clusters, each of them spatially resolved into two components, are located in the northern galaxy, one in the western and one in the eastern loop of blue clusters. Comparing our analysis of Brgamma, CO band-heads, He I (2.058um), Halpha (from archival HST data), and V-K colors with stellar population synthesis models indicates that the clusters are extincted (A_V ~ 0.7 - 4.3 mags) and young, displaying a significant age spread (4-13 Myrs). The starbursts in the nuclei are much older (65 Myrs), with the nucleus of NGC 4038 displaying a region of recent star formation northward of its K-band peak. Using our derived age estimates and assuming the parameters of the IMF (Salpeter slope, upper mass cut-off of 100 M_sun, Miller-Scalo between 1 M_sun and 0.1 M_sun), we find that the clusters have masses between 0.5 and 5 * 10^6M_sun.Comment: 10 pages, 3 figures, ApJ accepte

On the transverse mode of an atom laser

The transverse mode of an atom laser beam that is outcoupled from a Bose-Einstein condensate is investigated and is found to be strongly determined by the mean--field interaction of the laser beam with the condensate. Since for repulsive interactions the geometry of the coupling scheme resembles an interferometer in momentum space, the beam is found show filamentation. Observation of this effect would prove the transverse coherence of an atom laser beam.Comment: 4 pages, 4 figure

The [CII] 158 um Line Deficit in Ultraluminous Infrared Galaxies Revisited

We present a study of the [CII] 157.74 um fine-structure line in a sample of 15 ultraluminous infrared (IR) galaxies (L_IR>10^12 Lsun; ULIRGs) using the Long Wavelength Spectrometer (LWS) on the Infrared Space Observatory (ISO). We confirm the observed order of magnitude deficit (compared to normal and starburst galaxies) in the strength of the [CII] line relative to the far-IR dust continuum emission found in our initial report (Luhman et al. 1998), but here with a sample that is twice as large. This result suggests that the deficit is a general phenomenon affecting 4/5 ULIRGs. We present an analysis using observations of generally acknowledged photodissociation region (PDR) tracers ([CII], [OI] 63 and 145 um, and FIR continuum emission), which suggests that a high UV flux G_o incident on a moderate density n PDR could explain the deficit. However, comparisons with other ULIRG observations, including CO (1-0), [CI] (1-0), and 6.2 um polycyclic aromatic hydrocarbon (PAH) emission, suggest that high G_o/n PDRs alone cannot produce a self-consistent solution that is compatible with all of the observations. We propose that non-PDR contributions to the FIR continuum can explain the apparent [CII] deficiency. Here, unusually high G_o and/or n physical conditions in ULIRGs as compared to those in normal and starburst galaxies are not required to explain the [CII] deficit. Dust-bounded photoionization regions, which generate much of the FIR emission but do not contribute significant [CII] emission, offer one possible physical origin for this additional non-PDR component. Such environments may also contribute to the observed suppression of FIR fine-structure emission from ionized gas and PAHs, as well as the warmer FIR colors found in ULIRGs. The implications for observations at higher redshifts are also revisited.Comment: to be published in The Astrophysical Journal, 58 page

Analyzing Collective Motion with Machine Learning and Topology

We use topological data analysis and machine learning to study a seminal model of collective motion in biology [D'Orsogna et al., Phys. Rev. Lett. 96 (2006)]. This model describes agents interacting nonlinearly via attractive-repulsive social forces and gives rise to collective behaviors such as flocking and milling. To classify the emergent collective motion in a large library of numerical simulations and to recover model parameters from the simulation data, we apply machine learning techniques to two different types of input. First, we input time series of order parameters traditionally used in studies of collective motion. Second, we input measures based in topology that summarize the time-varying persistent homology of simulation data over multiple scales. This topological approach does not require prior knowledge of the expected patterns. For both unsupervised and supervised machine learning methods, the topological approach outperforms the one that is based on traditional order parameters.Comment: Published in Chaos 29, 123125 (2019), DOI: 10.1063/1.512549

V1647 Orionis: One Year into Quiescence

We present new optical, near-IR, and mid-IR observations of the young eruptive variable star V1647 Orionis that went into outburst in late 2004 for approximately two years. Our observations were taken one year after the star had faded to its pre-outburst optical brightness and show that V1647Ori is still actively accreting circumstellar material. We compare and contrast these data with existing observations of the source from both pre-outburst and outburst phases. From near-IR spectroscopy we identify photospheric absorption features for the first time that allow us to constrain the classification of the young star itself. Our best fit spectral type is M0+-2 sub-classes with a visual extinction of 19+-2 magnitudes and a K-band veiling of rK~1.5+-0.2. We estimate that V1647Ori has a quiescent bolometric luminosity of ~9.5Lsun and a mass accretion rate of ~1.10^-6Msun yr^-1. Our derived mass and age, from comparison with evolutionary models, are 0.8+-0.2 Msun and ~0.5Myrs, respectively. The presence towards the star of shock excited optical [S II] and [Fe II] emission as well as near-IR H2 and [Fe II] emission perhaps suggests that a new Herbig-Haro flow is becoming visible close to the star.Comment: 22 pages, 19 Figures, accepted AJ 13 October 200