Unravelling the Mysteries of the Leo Ring: An Absorption Line Study of an Unusual Gas Cloud

Since the 1980's discovery of the large (2x10^9 Msun) intergalactic cloud known as the Leo Ring, this object has been the center of a lively debate about its origin. Determining the origin of this object is still important as we develop a deeper understanding of the accretion and feedback processes that shape galaxy evolution. We present HST/COS observations of three sightlines near the Ring, two of which penetrate the high column density neutral hydrogen gas visible in 21 cm observations of the object. These observations provide the first direct measurement of the metallicity of the gas in the Ring, an important clue to its origins. Our best estimate of the metallicity of the ring is ~10% Zsun, higher than expected for primordial gas but lower than expected from an interaction. We discuss possible modifications to the interaction and primordial gas scenarios that would be consistent with this metallicity measurement.Comment: 11 pages, 7 figures, accepted Ap

Évaluation d'un système de mesure des pertes de contaminants agricoles par ruissellement et drainage souterrain en régions froides

Cette note technique présente un système automatique de mesure des pertes de polluants agricoles par ruissellement et drainage souterrain pouvant opérer durant la période estivale et la fonte nivale. Le système de mesure du ruissellement est composé d'une trappe à sédiments, d'un déversoir en V et d'un système automatique de mesure du débit et de contrôle de l'échantillonnage. Le système de mesure du drainage souterrain consiste en un auget à bascule, relié à un compteur d'impulsions, et un partiteur de débit. Ces systèmes ont été utilisés sur neuf parcelles expérimentales pour mesurer les masses de contaminants agricoles perdues par ruissellement et drainage souterrain. La hauteur totale de ruissellement durant les deux années (4,6 mm an-1) a été faible comparée au drainage (227 mm an-1). Soixante-seize pourcent du ruissellement annuel s'est produit durant la fonte des neiges. Les principaux avantages de ce système sont de pouvoir mesurer simultanément les volumes et les débits de ruissellement tout en prélevant des échantillons d'eau.This technical note presents an automatic measurement system for measuring losses of agricultural pollutants in surface runoff and subsurface drainage outflow. This system can be operated during rainfall events and snowmelt periods. The runoff system was composed of a sediment trap, a V-notch weir and an automatic system for flow measurement and sampling. The subsurface drainage system consisted of a tipping bucket, connected to a pulse counter, and a sampling unit. This system was used on nine experimental plots for the measurement of pollutant losses by surface runoff and subsurface drainage. The total depth of surface runoff measured was low for the two years of measurement (4.6 mm y-1) compared to subsurface drainage (227 mm y-1). Seventy six percent of the annual surface runoff occurred during the snowmelt period. The principal advantage of this system is to measure runoff volume and flow while taking water samples

Antonio Gramsci’s impact on critical pedagogy

This paper provides an account of Antonio Gramsci’s impact on the area of critical pedagogy. It indicates the Gramscian influence on the thinking of major exponents of the field. It foregrounds Gramsci's ideas and then indicates how they have been taken up by a selection of critical pedagogy exponents who were chosen on the strength of their identification and engagement with Gramsci's ideas, some of them even having written entire essays on Gramsci. The essay concludes with a discussion concerning an aspect of Gramsci's concerns, the question of powerful knowledge, which, in the present author's view, provides a formidable challenge to critical pedagogues.peer-reviewe

Metallicity and Ionization in High Velocity Cloud Complex C

We analyze HST and FUSE ultraviolet spectroscopic data for eleven sight lines passing through the infalling high velocity cloud (HVC) Complex C. These sight lines pass through regions with HI column densities ranging from N(HI) = 10^(18.1) to 10^(20.1). From [OI/HI] abundances, we find that Complex C metallicities range from 0.09 to 0.29 Z_solar, with a column density weighted mean of 0.13 Z_solar. Nitrogen (NI) is underabundant by factors of (0.01-0.07) (N/H)_solar, significantly less than oxygen relative to solar abundances. This pattern suggests nucleosynthetic enrichment by Type II SNe, consistent with an origin in the Galactic fountain or infalling gas produced in winds from Local Group galaxies. The range of metallicity and its possible (2 sigma) dependence on N(HI) could indicate some mixing of primordial material with enriched gas from the Milky Way, but the mixing mechanism is unclear. We also investigate the significant highly ionized component of Complex C, detected in CIV, SiIV, and OVI, but not in NV. High-ion column density ratios show little variance and are consistent with shock ionization or ionization at interfaces between Complex C and a hotter surrounding medium. Evidence for the former mechanism is seen in the Mrk 876 line profiles, where the offset in line centroids between low and high ions suggests a decelerating bowshock.Comment: Submitted to Ap