23,242 research outputs found
Tracing Quasar Narrow-Line Regions Across Redshift: A Library of High S/N Optical Spectra
In a single optical spectrum, the quasar narrow-line region (NLR) reveals low
density, photoionized gas in the host galaxy interstellar medium, while the
immediate vicinity of the central engine generates the accretion disk continuum
and broad emission lines. To isolate these two components, we construct a
library of high S/N optical composite spectra created from the Sloan Digital
Sky Survey (SDSS-DR7). We divide the sample into bins of continuum luminosity
and Hbeta FWHM that are used to construct median composites at different
redshift steps up to 0.75. We measure the luminosities of the narrow-emission
lines [NeV]3427, [NeIII]3870, [OIII]5007, and [OII]3728 with ionization
potentials (IPs) of 97, 40, 35, and 13.6 eV respectively. The high IP lines'
luminosities show no evidence of increase with redshift consistent with no
evolution in the AGN SED or the host galaxy ISM illuminated by the continuum.
In contrast, we find that the [OII] line becomes stronger at higher redshifts,
and we interpret this as a consequence of enhanced star formation contributing
to the [OII] emission in host galaxies at higher redshifts. The SFRs estimated
from the [OII] luminosities show a flatter increase with z than non-AGN
galaxies given our assumed AGN contribution to the [OII] luminosity. Finally,
we confirm an inverse correlation between the strength of the FeII4570 complex
and both the [OIII] EW (though not the luminosity) and the width of the Hbeta
line as known from the eigenvector 1 correlations.Comment: 17 pages, colour figures, accepted for publication in MNRA
Discharge coefficients for thick-plate orifices
Investigation enables more accurate prediction of coolant flows within internally cooled turbine blades and vanes. The data is applicable for predicting flows in complex flow passages
An outside-inside view of exclusive practice within an inclusive mainstream school
This article is a reflection on a sabbatical experience in a mainstream school where an inclusive ethos underpinned the curriculum and environmental approaches for all children. The period as Acting Head teacher raised some challenges for me in reconciling inclusion for all children and the exclusive nature of some professional and physical spaces available to the community of adults working in the school. It has highlighted some development opportunities for the senior management of the school and its governing body
A 100 micro Kelvin bolometer system for SIRTF
Progress toward a prototype of 100 mK bolometric detection system for the Space Infrared Telescope Facility (SIRTF) is described. Two adiabatic demagnetization refrigerators (ADR's) were constructed and used to investigate the capabilities necessary for orbital operation. The first, a laboratory ADR, demonstrated a hold time at 0.1 K of over 12 hours, with temperature stability approx. 3 micro-K RMS achieved by controlling the magnetic field. A durable salt pill and an efficient support system have been demonstrated. A second ADR, the SIRTF flight prototype, has been built and will be flown on a balloon. Techniques for magnetic shielding, low heat leak current leads, and a mechanical heat switch are being developed in this ADR. Plans for construction of 100 mK bolometers are discussed. Three important cosmological investigations which will be carried out by these longest wavelength SIRTF detectors are described
QCD Sum Rule Analysis of Heavy Quarkonium Hybrids
We have studied the charmonium and bottomonium hybrid states with various
quantum numbers in QCD sum rules. At leading order in , the
two-point correlation functions have been calculated up to dimension six
including the tri-gluon condensate and four-quark condensate. After performing
the QCD sum rule analysis, we have confirmed that the dimension six condensates
can stabilize the hybrid sum rules and allow the reliable mass predictions. We
have updated the mass spectra of the charmonium and bottomonium hybrid states
and identified that the negative-parity states with form the lightest hybrid supermultiplet while the positive-parity
states with belong to a heavier hybrid
supermultiplet.Comment: 7 pages, 1 figures. Some minor edits have been made. Presentation at
the DPF 2013 Meeting of the American Physical Society Division of Particles
and Fields, Santa Cruz, California, August 13-17, 201
Exploring the Spectrum of Heavy Quarkonium Hybrids with QCD Sum Rules
QCD Laplace sum rules are used to calculate heavy quarkonium (charmonium and
bottomonium) hybrid masses in several distinct channels. Previous
studies of heavy quarkonium hybrids did not include the effects of
dimension-six condensates, leading to unstable sum rules and unreliable mass
predictions in some channels. We have updated these sum rules to include
dimension-six condensates, providing new mass predictions for the spectra of
heavy quarkonium hybrids. We confirm the finding of other approaches that the
negative-parity states form the lightest hybrid
supermultiplet and the positive-parity
states are members of a heavier supermultiplet. Our results disfavor a pure
charmonium hybrid interpretation of the , in agreement with previous
work.Comment: Presented by RTK at the Theory Canada 9 Conference, held at Wilfrid
Laurier University in June 2014. Submitted for the conference proceedings to
be published in the Canadian Journal of Physics. 5 pages, 1 figure. Version
2: reference added, typo correcte
The Obscured Fraction of AGN in the XMM-COSMOS Survey: A Spectral Energy Distribution Perspective
The fraction of AGN luminosity obscured by dust and re-emitted in the mid-IR
is critical for understanding AGN evolution, unification, and parsec-scale AGN
physics. For unobscured (Type-1) AGN, where we have a direct view of the
accretion disk, the dust covering factor can be measured by computing the ratio
of re-processed mid-IR emission to intrinsic nuclear bolometric luminosity. We
use this technique to estimate the obscured AGN fraction as a function of
luminosity and redshift for 513 Type-1 AGN from the XMM-COSMOS survey. The
re-processed and intrinsic luminosities are computed by fitting the 18-band
COSMOS photometry with a custom SED-fitting code, which jointly models emission
from: hot-dust in the AGN torus, the accretion disk, and the host-galaxy. We
find a relatively shallow decrease of the luminosity ratio as a function of
Lbol, which we interpret as a corresponding decrease in the obscured fraction.
In the context of the receding torus model, where dust sublimation reduces the
covering factor of more luminous AGN, our measurements require a torus height
which increases with luminosity as h ~ Lbol^{0.3-0.4}. Our obscured
fraction-luminosity relation agrees with determinations from SDSS censuses of
Type-1 and Type-2 quasars, and favors a torus optically thin to mid-IR
radiation. We find a much weaker dependence of obscured fraction on 2-10 keV
luminosity than previous determinations from X-ray surveys, and argue that
X-ray surveys miss a significant population of highly obscured Compton-thick
AGN. Our analysis shows no clear evidence for evolution of obscured fraction
with redshift.Comment: 33 pages, 24 figures, ApJ accepte
The dust emission of high-redshift quasars
The detection of powerful near-infrared emission in high redshift (z>5)
quasars demonstrates that very hot dust is present close to the active nucleus
also in the very early universe. A number of high-redshift objects even show
significant excess emission in the rest frame NIR over more local AGN spectral
energy distribution (SED) templates. In order to test if this is a result of
the very high luminosities and redshifts, we construct mean SEDs from the
latest SDSS quasar catalogue in combination with MIR data from the WISE
preliminary data release for several redshift and luminosity bins. Comparing
these mean SEDs with a large sample of z>5 quasars we could not identify any
significant trends of the NIR spectral slope with luminosity or redshift in the
regime 2.5 < z < 6 and 10^45 < nuL_nu(1350AA) < 10^47 erg/s. In addition to the
NIR regime, our combined Herschel and Spitzer photometry provides full infrared
SED coverage of the same sample of z>5 quasars. These observations reveal
strong FIR emission (L_FIR > 10^13 L_sun) in seven objects, possibly indicating
star-formation rates of several thousand solar masses per year. The FIR excess
emission has unusally high temperatures (T ~ 65 K) which is in contrast to the
temperature typically expected from studies at lower redshift (T ~ 45 K). These
objects are currently being investigated in more detail.Comment: 6 pages, 3 figures, to appear in the proceedings to "The Central
Kiloparsec in Galactic Nuclei (AHAR2011)", Journal of Physics: Conference
Series (JPCS), IOP Publishin
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