4,072 research outputs found
The Properties of Radio Galaxies and the Effect of Environment in Large Scale Structures at
In this study we investigate 89 radio galaxies that are
spectroscopically-confirmed to be members of five large scale structures in the
redshift range of . Based on a two-stage classification
scheme, the radio galaxies are classified into three sub-classes: active
galactic nucleus (AGN), hybrid, and star-forming galaxy (SFG). We study the
properties of the three radio sub-classes and their global and local
environmental preferences. We find AGN hosts are the most massive population
and exhibit quiescence in their star-formation activity. The SFG population has
a comparable stellar mass to those hosting a radio AGN but are unequivocally
powered by star formation. Hybrids, though selected as an intermediate
population in our classification scheme, were found in almost all analyses to
be a unique type of radio galaxies rather than a mixture of AGN and SFGs. They
are dominated by a high-excitation radio galaxy (HERG) population. We discuss
environmental effects and scenarios for each sub-class. AGN tend to be
preferentially located in locally dense environments and in the cores of
clusters/groups, with these preferences persisting when comparing to galaxies
of similar colour and stellar mass, suggesting that their activity may be
ignited in the cluster/group virialized core regions. Conversely, SFGs exhibit
a strong preference for intermediate-density global environments, suggesting
that dusty starbursting activity in LSSs is largely driven by galaxy-galaxy
interactions and merging.Comment: 28 pages, 10 figures, accepted to MNRA
Two New Gravitationally Lensed Double Quasars from the Sloan Digital Sky Survey
We report the discoveries of the two-image gravitationally lensed quasars,
SDSS J0746+4403 and SDSS J1406+6126, selected from the Sloan Digital Sky Survey
(SDSS). SDSS J0746+4403, which will be included in our lens sample for
statistics and cosmology, has a source redshift of z_s=2.00, an estimated lens
redshift of z_l~0.3, and an image separation of 1.08". SDSS J1406+6126 has a
source redshift of z_s=2.13, a spectroscopically measured lens redshift of
z_l=0.27, and an image separation of 1.98". We find that the two quasar images
of SDSS J1406+6126 have different intervening MgII absorption strengths, which
are suggestive of large variations of absorbers on kpc scales. The positions
and fluxes of both the lensed quasar systems are easily reproduced by simple
mass models with reasonable parameter values. These objects bring to 18 the
number of lensed quasars that have been discovered from the SDSS data.Comment: 25 pages, 6 figures, The Astronomical Journal accepte
Entanglement between Demand and Supply in Markets with Bandwagon Goods
Whenever customers' choices (e.g. to buy or not a given good) depend on
others choices (cases coined 'positive externalities' or 'bandwagon effect' in
the economic literature), the demand may be multiply valued: for a same posted
price, there is either a small number of buyers, or a large one -- in which
case one says that the customers coordinate. This leads to a dilemma for the
seller: should he sell at a high price, targeting a small number of buyers, or
at low price targeting a large number of buyers? In this paper we show that the
interaction between demand and supply is even more complex than expected,
leading to what we call the curse of coordination: the pricing strategy for the
seller which aimed at maximizing his profit corresponds to posting a price
which, not only assumes that the customers will coordinate, but also lies very
near the critical price value at which such high demand no more exists. This is
obtained by the detailed mathematical analysis of a particular model formally
related to the Random Field Ising Model and to a model introduced in social
sciences by T C Schelling in the 70's.Comment: Updated version, accepted for publication, Journal of Statistical
Physics, online Dec 201
SDSS J115517.35+634622.0: A Newly Discovered Gravitationally Lensed Quasar
We report the discovery of SDSSJ115517.35+634622.0, a previously unknown
gravitationally lensed quasar. The lens system exhibits two images of a quasar, with an image separation of 1{\farcs}832 \pm 0.007 . Near-IR
imaging of the system reveals the presence of the lensing galaxy between the
two quasar images. Based on absorption features seen in the Sloan Digital Sky
Survey (SDSS) spectrum, we determine a lens galaxy redshift of .
The lens is rather unusual in that one of the quasar images is only
0{\farcs}22\pm0{\farcs}07 () from the center of the
lens galaxy and photometric modeling indicates that this image is significantly
brighter than predicted by a SIS model. This system was discovered in the
course of an ongoing search for strongly lensed quasars in the dataset from the
SDSS.Comment: 18 pages, 6 figures. Accepted for publication in A
The FIRST Bright Quasar Survey. II. 60 Nights and 1200 Spectra Later
We have used the VLA FIRST survey and the APM catalog of the POSS-I plates as
the basis for constructing a new radio-selected sample of optically bright
quasars. This is the first radio-selected sample that is competitive in size
with current optically selected quasar surveys. Using only two basic criteria,
radio-optical positional coincidence and optical morphology, quasars and BL
Lacs can be identified with 60% selection efficiency; the efficiency increases
to 70% for objects fainter than magnitude 17. We show that a more sophisticated
selection scheme can predict with better than 85% reliability which candidates
will turn out to be quasars.
This paper presents the second installment of the FIRST Bright Quasar Survey
with a catalog of 636 quasars distributed over 2682 square degrees. The quasar
sample is characterized and all spectra are displayed. The FBQS detects both
radio-loud and radio-quiet quasars out to a redshift z>3. We find a large
population of objects of intermediate radio-loudness; there is no evidence in
our sample for a bimodal distribution of radio characteristics. The sample
includes ~29 broad absorption line quasars, both high and low ionization, and a
number of new objects with remarkable optical spectra.Comment: 41 pages plus 39 gifs which contain all quasar spectra. Accepted for
publication in the Astrophysical Journal Supplement Serie
Actinopolyspora algeriensis sp. nov., a novel halophilic actinomycete isolated from a Saharan soil
A halophilic actinomycete strain designated H19T, was isolated from a Saharan soil in the Bamendil region (Ouargla province, South Algeria) and was characterized taxonomically by using a polyphasic approach. The morphological and chemotaxonomic characteristics of the
strain were consistent with those of members of the genus
Actinopolyspora, and 16S rRNA gene sequence analysis confirmed that strain H19T was a novel species of the genus
Actinopolyspora. DNAâDNA hybridization value between strain H19T and the nearest Actinopolyspora species, A. halophila, was clearly below the 70 % threshold. The genotypic and phenotypic data showed that the organism represents a novel species of the genus Actinopolyspora for which the name Actinopolyspora algeriensis sp. nov. is proposed, with the type strain H19T (= DSM 45476T = CCUG 62415T)
Quasar Absorption Lines as a Function of Quasar Orientation Measures
We present high resolution radio data at 3.5 and 20 cm from the VLA in the A
configuration for 144 quasars with known CIV absorption line properties. Using
these measurements, we compare and contrast a number of quasar orientation
indicators. These quantities are used to study the velocity distribution of CIV
absorption lines as a function of quasar orientation measures. That there is an
excess of narrow, high-velocity CIV absorbers in flat-spectrum quasars as
compared to steep-spectrum quasars is confirmed. Orientation indicators that
are not based upon spectral indices (e.g. R_V and the core-to-lobe ratio) do
not show the same effect. These seemingly contradictory results may be
reconciled if the absorber distribution is not strictly a function of
orientation, but rather a function of intrinsic radio properties that may or
may not be good orientation indicators.Comment: 34 pages, 7 figures, 3 tables, ApJ in pres
Discovery of Two Gravitationally Lensed Quasars with Image Separations of 3 Arcseconds from the Sloan Digital Sky Survey
We report the discovery of two doubly-imaged quasars, SDSS
J100128.61+502756.9 and SDSS J120629.65+433217.6, at redshifts of 1.838 and
1.789 and with image separations of 2.86'' and 2.90'', respectively. The
objects were selected as lens candidates from the Sloan Digital Sky Survey
(SDSS). Based on the identical nature of the spectra of the two quasars in each
pair and the identification of the lens galaxies, we conclude that the objects
are gravitational lenses. The lenses are complicated; in both systems there are
several galaxies in the fields very close to the quasars, in addition to the
lens galaxies themselves. The lens modeling implies that these nearby galaxies
contribute significantly to the lens potentials. On larger scales, we have
detected an enhancement in the galaxy density near SDSS J100128.61+502756.9.
The number of lenses with image separation of ~3'' in the SDSS already exceeds
the prediction of simple theoretical models based on the standard
Lambda-dominated cosmology and observed velocity function of galaxies.Comment: 24 pages, 9 figures, accepted for publication in Ap
PACIFIC NORTHWEST CYBER SUMMIT
On March 26, 2013, the Snohomish County Public Utility District (PUD) and the U.S. Department of Energyâs (DOEâs) Pacific Northwest National Laboratory (PNNL) jointly hosted the Pacific Northwest Cyber Summit with the DOEâs Office of Electricity Delivery and Energy Reliability, the White House, Washington State congressional delegation, Washington State National Guard, and regional energy companies
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