1,552 research outputs found
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 EnergÃa Eléctrica: Una Aplicación de las Funciones de Distancia Estocástica
Este documento evalúa el desempeño de las empresas distribuidoras de energÃa durante el periodo 1999-2003, utilizando la metodologÃa 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 podrÃan 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 podrÃan 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 energÃa 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 tecnologÃa 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 podrÃan 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 were identified and measured. We
find that the rest equivalent width ()
distribution is described very well by an exponential function , with
and \AA. Previously reported power law
fits drastically over-predict the number of strong lines. Extrapolating our
exponential fit under-predicts the number of \AA systems,
indicating a transition in near \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 \AA lines:
and \AA. We find that the distribution steepens with decreasing redshift,
with decreasing from \AA at to \AA at
. The incidence of moderately strong MgII lines does not
show evidence for evolution with redshift. However, lines stronger than
\AA show a decrease relative to the no-evolution prediction with
decreasing redshift for . The evolution is stronger for
increasingly stronger lines. Since 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
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