The Pittsburgh Sloan Digital Sky Survey MgII Quasar Absorption-Line Survey Catalog

We present a catalog of intervening MgII quasar absorption-line systems in the redshift interval 0.36 <= z <= 2.28. The catalog was built from Sloan Digital Sky Survey Data Release Four (SDSS DR4) quasar spectra. Currently, the catalog contains > 17,000 measured MgII doublets. We also present data on the ~44,600 quasar spectra which were searched to construct the catalog, including redshift and magnitude information, continuum-normalized spectra, and corresponding arrays of redshift-dependent minimum rest equivalent widths detectable at our confidence threshold. The catalog is available on the web. A careful second search of 500 random spectra indicated that, for every 100 spectra searched, approximately one significant MgII system was accidentally rejected. Current plans to expand the catalog beyond DR4 quasars are discussed. Many MgII absorbers are known to be associated with galaxies. Therefore, the combination of large size and well understood statistics makes this catalog ideal for precision studies of the low-ionization and neutral gas regions associated with galaxies at low to moderate redshift. An analysis of the statistics of MgII absorbers using this catalog will be presented in a subsequent paper.Comment: AJ, in pres

Ineficiencia en la Distribución de Energía Eléctrica: Una Aplicación de las Funciones de Distancia Estocástica

Este documento evalúa el desempeño de las empresas distribuidoras de energía durante el periodo 1999-2003, utilizando la metodología de funciones de distancia estocástica, la cual a través de la estimación de las desviaciones de una función ideal de producción, permite medir los niveles de eficiencia técnica de las diferentes empresas. Los resultados indican que existen diferencias significativas en el desempeño de las empresas, sugiriendo que se podrían obtener importantes ganancias en términos de eficiencia técnica si las empresas operaran o se acercaran a los niveles de operación de las más eficientes. Estas ganancias se podrían expresar en el ahorro de recursos, la calidad del servicio y/o en menores niveles de tarifas a los usuarios finales. También se encontró que el desempeño de las empresas distribuidoras de energía puede verse afectado por factores fuera del control de las firmas, tales como las condiciones geográficas, el número de usuarios atendidos y la densidad poblacional. En particular, se encuentra que empresas con un entorno más favorable en términos de densidad poblacional y/o de los niveles de consumo de los usuarios se ven favorecidas cuando dichas variables afectan directamente la tecnología de producción. Por otra parte, se observa que las empresas públicas registran un mejor desempeño cuando las variables ambientales afectan directamente la eficiencia y no la función de producción. Estos resultados sugieren que las empresas privadas se podrían estar beneficiando de condiciones de entorno más favorables, teniendo en cuenta que estas, en promedio atienden áreas de más alta densidad poblacional y usuarios de consumos más altos.

Mg II Absorption Systems in SDSS QSO Spectra

We present the results of a MgII absorption-line survey using QSO spectra from the SDSS EDR. Over 1,300 doublets with rest equivalent widths greater than 0.3\AA and redshifts $0.366 \le z \le 2.269$ were identified and measured. We find that the $\lambda2796$ rest equivalent width ($W_0^{\lambda2796}$) distribution is described very well by an exponential function $\partial N/\partial W_0^{\lambda2796} = \frac{N^*}{W^*} e^{-\frac{W_0}{W^*}}$, with $N^*=1.187\pm0.052$ and $W^*=0.702\pm0.017$\AA. Previously reported power law fits drastically over-predict the number of strong lines. Extrapolating our exponential fit under-predicts the number of $W_0 \le 0.3$\AA systems, indicating a transition in $dN/dW_0$ near $W_0 \simeq 0.3$\AA. A combination of two exponentials reproduces the observed distribution well, suggesting that MgII absorbers are the superposition of at least two physically distinct populations of absorbing clouds. We also derive a new redshift parameterization for the number density of $W_0^{\lambda2796} \ge 0.3$\AA lines: $N^*=1.001\pm0.132(1+z)^{0.226\pm0.170}$ and $W^*=0.443\pm0.032(1+z)^{0.634\pm 0.097}$\AA. We find that the distribution steepens with decreasing redshift, with $W^*$ decreasing from $0.80\pm0.04$\AA at $z=1.6$ to $0.59\pm0.02$\AA at $z=0.7$. The incidence of moderately strong MgII $\lambda2796$ lines does not show evidence for evolution with redshift. However, lines stronger than $\approx 2$\AA show a decrease relative to the no-evolution prediction with decreasing redshift for $z \lesssim 1$. The evolution is stronger for increasingly stronger lines. Since $W_0$ in saturated absorption lines is an indicator of the velocity spread of the absorbing clouds, we interpret this as an evolution in the kinematic properties of galaxies from moderate to low z.Comment: 50 pages, 26 figures, accepted for publication in Ap

Narrowband imaging of Escaping Lyman-Continuum Emission in the SSA22 Field

We present the results of an ultradeep, narrowband imaging survey for Lyman-continuum (LyC) emission at z~3 in the SSA22a field. We employ a custom narrowband filter centered at 3640A (NB3640), which probes the LyC region for galaxies at z>3.06. We also analyze new and archival NB4980 imaging tuned to the wavelength of the Lya emission line at z=3.09, and archival broadband B, V, and R images of the non-ionizing UV continuum. Our NB3640 images contain 26 z>3.06 Lyman Break Galaxies (LBGs) as well as a set of 130 Lya emitters (LAEs), identified by their excess NB4980 flux relative to the BV continuum. Six LBGs and 28 LAEs are detected in the NB3640 image. LBGs appear to span a range of NB3640-R colors, while LAEs appear bimodal in their NB3640-R properties. We estimate average UV to LyC flux density ratios, corrected for foreground contamination and intergalactic medium absorption, finding <F_{UV}/F_{LyC}>^{LBG} = 11.3^{+10.3}_{-5.4}, which implies a LBG LyC escape fraction f_{esc}^{LyC} ~ 0.1, and <F_{UV}/F_{LyC}>^{LAE} = 2.2^{+0.9}_{-0.6}. The strikingly blue LAE flux density ratios defy interpretation in terms of standard stellar population models. Assuming <F_{UV}/F_{LyC}>^{LBG} applies down to L=0.1L*, we estimate a galaxy contribution to the intergalactic hydrogen ionization rate that is consistent with independent estimates based on the Lya forest opacity at z~3. If we assume that <F_{UV}/F_{LyC}>^{LAE} holds at the faintest luminosities, the galaxy contribution significantly exceeds that inferred from the Lya forest. Further follow-up study of these faint LAEs is crucial, given the potentially important contribution similar objects make to the process of reionization. (Abridged)Comment: 30 pages, 15 figures; Accepted for publication by Ap