522 research outputs found
Spectroscopic Confirmation of a Radio-Selected Galaxy Overdensity at z=1.11
We report the discovery of a galaxy overdensity at z=1.11 associated with the
z=1.110 high-redshift radio galaxy MG0442+0202. The group, CL0442+0202, was
found in a near-infrared survey of z>1 radio galaxies undertaken to identify
spatially-coincident regions with a high density of objects red in I-K' color,
typical of z>1 elliptical galaxies. Spectroscopic observations from the Keck
telescope reveal five galaxies within 35" of MG0442+0202 at 1.10<z<1.11. These
member galaxies have broad-band colors and optical spectra consistent with
passively-evolving elliptical galaxies formed at high redshift. A 45ks Chandra
X-Ray Observatory observation detects the radio galaxy and four point sources
within 15" of the radio galaxy, corresponding to a surface density two orders
of magnitude higher than average for X-ray sources at these flux levels,
S(0.5-2keV) > 5e-16 erg/cm2/s. One of these point sources is identified with a
radio-quiet, typeII quasar at z=1.863, akin to sources recently reported in
deep Chandra surveys. The limit on an extended hot intracluster medium in the
Chandra data is S(1-6keV) < 1.9e-15 erg/cm2/s (3-sigma, 30" radius aperture).
Though the X-ray observations do not confirm the existence of a massive, bound
cluster at z>1, the success of the optical/near-infrared targeting of
early-type systems near the radio galaxy validates searches using radio
galaxies as beacons for high-redshift large-scale structure. We interpret
CL0442+0202 to be a massive cluster in the process of formation.Comment: 23 pages, 7 figure
Discovery of a Color-Selected Quasar at z=5.50
We present observations of RD J030117+002025, a quasar at z=5.50 discovered
from deep, multi-color, ground-based observations covering 74 square arcmin.
This is the most distant quasar or AGN currently known. The object was targeted
as an R-band dropout, with R(AB)>26.3 (3-sigma limit in a 3 arcsec diameter
region), I(AB)=23.8, and z(AB)=23.4. The Keck/LRIS spectrum shows broad
Lyman-alpha/NV emission and sharp absorption decrements from the
highly-redshifted hydrogen forests. The fractional continuum depression due to
the Lyman-alpha forest is D(A)=0.90. RD J030117+002025 is the least luminous,
high-redshift quasar known (M(B)~-22.7).Comment: 9 pages, 2 figures; to appear in the The Astrophysical Journal
Letter
Proximal business intelligence on the semantic web
This is the post-print version of this article. The official version can be accessed from the link below - Copyright @ 2010 Springer.Ubiquitous information systems (UBIS) extend current Information System thinking to explicitly differentiate technology between devices and software components with relation to people and process. Adapting business data and management information to support specific user actions in context is an ongoing topic of research. Approaches typically focus on providing mechanisms to
improve specific information access and transcoding but not on how the information
can be accessed in a mobile, dynamic and ad-hoc manner. Although web ontology has been used to facilitate the loading of data warehouses, less research has been carried out on ontology based mobile reporting. This paper explores how business data can be modeled and accessed using the web ontology
language and then re-used to provide the invisibility of pervasive access; uncovering
more effective architectural models for adaptive information system strategies of this type. This exploratory work is guided in part by a vision of business intelligence that is highly distributed, mobile and fluid, adapting to sensory understanding of the underlying environment in which it operates. A proof-of concept mobile and ambient data access architecture is developed in order to further test the viability of such an approach. The paper concludes with an ontology engineering framework for systems of this type – named UBIS-ONTO
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Sequestering the Gravitino: Neutralino Dark Matter in Gauge Mediation
In conventional models of gauge-mediated supersymmetry breaking, the lightest supersymmetric particle (LSP) is invariably the gravitino. However, if the supersymmetry breaking sector is strongly coupled, conformal sequestering may raise the mass of the gravitino relative to the remaining soft supersymmetry-breaking masses. In this letter, we demonstrate that such conformal dynamics in gauge-mediated theories may give rise to satisfactory neutralino dark matter while simultaneously solving the flavor and {mu}/B{mu} problems
Clustering of red galaxies around the z=1.53 quasar 3C270.1
In the paradigm of hierarchical galaxy formation, luminous radio galaxies
mark mass assembly peaks that should contain clusters of galaxies. Observations
of the z=1.53 quasar 3C270.1 with the Spitzer Space Telescope at 3.6-24 micron
and with the 6.5-m MMT in the z'- and Y-bands allow detection of potential
cluster members via photometric redshifts. Compared with nearby control fields,
there is an excess of 11 extremely red objects (EROs) at 1.33 < z_phot < 1.73,
consistent with a proto-cluster around the quasar. The spectral energy
distributions (SEDs) of 3/4 of the EROs are better fitted with passive
elliptical galaxies than withdust-reddened starbursts, and of four sources
well-detected on an archival HST snapshot image, all have undisturbed
morphologies. However, one ERO, not covered by the HST image, is a double
source with 0.8" separation on the z' image and a marginal (2sigma) 24 micron
detection indicating a dust-enshrouded starburst. The EROs are more luminous
than L* (H = -23.6 AB mag at z=1.5).Comment: 12 pages, 7 figures, accepted by Ap
A New Population of High-z, Dusty Lyα Emitters and Blobs Discovered by WISE: Feedback Caught in the Act?
By combining data from the NASA Wide-field Infrared Survey Explorer (WISE) mission with optical spectroscopy from the W. M. Keck telescope, we discover a mid-IR color criterion that yields a 78% success rate in identifying rare, typically radio-quiet, 1.6 ≾ z ≾ 4.6 dusty Lyα emitters (LAEs). Of these, at least 37% have emission extended on scales of 30-100 kpc and are considered Lyα "blobs" (LABs). The objects have a surface density of only ~0.1 deg^(–2), making them rare enough that they have been largely missed in deep, small area surveys. We measured spectroscopic redshifts for 92 of these galaxies, and find that the LAEs (LABs) have a median redshift of 2.3 (2.5). The WISE photometry coupled with data from Herschel (Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA) reveals that these galaxies are in the Hyper Luminous IR galaxy regime (L IR ≳ 10^(13)-10^(14) L_☉) and have warm colors. They are typically more luminous and warmer than other dusty, z ~ 2 populations such as submillimeter-selected galaxies and dust-obscured galaxies. These traits are commonly associated with the dust being illuminated by intense active galactic nucleus activity. We hypothesize that the combination of spatially extended Lyα, large amounts of warm IR-luminous dust, and rarity (implying a short-lived phase) can be explained if the galaxies are undergoing brief, intense "feedback" transforming them from an extreme dusty starburst/QSO into a mature galaxy
Mid-infrared Selection of Active Galactic Nuclei with the Wide-Field Infrared Survey Explorer. I. Characterizing WISE-selected Active Galactic Nuclei in COSMOS
The Wide-field Infrared Survey Explorer (WISE) is an extremely capable and efficient black hole finder. We present a simple mid-infrared color criterion, W1 – W2 ≥ 0.8 (i.e., [3.4]–[4.6] ≥0.8, Vega), which identifies 61.9 ± 5.4 active galactic nucleus (AGN) candidates per deg^2 to a depth of W2 ~ 15.0. This implies a much larger census of luminous AGNs than found by typical wide-area surveys, attributable to the fact that mid-infrared selection identifies both unobscured (type 1) and obscured (type 2) AGNs. Optical and soft X-ray surveys alone are highly biased toward only unobscured AGNs, while this simple WISE selection likely identifies even heavily obscured, Compton-thick AGNs. Using deep, public data in the COSMOS field, we explore the properties of WISE-selected AGN candidates. At the mid-infrared depth considered, 160 μJy at 4.6 μm, this simple criterion identifies 78% of Spitzer mid-infrared AGN candidates according to the criteria of Stern et al. and the reliability is 95%. We explore the demographics, multiwavelength properties and redshift distribution of WISE-selected AGN candidates in the COSMOS field
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