1,104 research outputs found
The Asiago-ESO/RASS QSO Survey II. The Southern Sample
This is the second paper of a series describing the Asiago-ESO/RASS QSO
survey, a project aimed at the construction of an all-sky statistically
well-defined sample of very bright QSOs (B_J < 15). Such a survey is required
to remove the present uncertainties about the properties of the local QSO
population and constitutes an homogeneous database for detailed evolutionary
studies of AGN. We present here the complete Southern Sample, which comprises
243 bright (12.60 < B_J < 15.13) QSO candidates at high galactic latitudes
(|b_{gal}| > 30^{\circ}). The area covered by the survey is 5660 sq. deg.
Spectroscopy for the 137 still unidentified objects has been obtained. The
total number of AGN turns out to be 111, 63 of which are new identifications.
The properties of the selection are discussed. The completeness and the success
rate for this survey at the final stage are 63% and 46%, respectively.Comment: 36 pages Latex, with 15 PostScript figures. Accepted for publication
in Astronomical Journa
The dusty environment of Quasars. Far-IR properties of Optical Quasars
We present the ISO far-IR photometry of a complete sub-sample of optically
selected bright quasars belonging to two complete surveys selected through
multicolour (U,B,V,R,I) techniques. The ISOPHOT camera on board of the ISO
Satellite was used to target these quasars at wavelengths of 7.3, 11.5, 60, 100
and 160 micron. Almost two thirds of the objects were detected at least in one
ISOPHOT band. The detection rate is independent of the source redshift, very
likely due to the negative K-correction of the far-IR thermal emission. More
than a half of the optically selected QSOs show significant emission between 4
and 100 micron in the quasar rest-frame. These fluxes have a very likely
thermal origin, although in a few objects an additional contribution from a
non-thermal component is plausible in the long wavelength bands. In a
colour-colour diagram these objects span a wide range of properties from
AGN-dominated to ULIRG-like. The far-IR composite spectrum of the quasar
population presents a broad far-IR bump between 10 and 30 micron and a sharp
drop at wavelengths greater than 100 micron in the quasar restframe. The amount
of energy emitted in the far-IR, is on average a few times larger than that
emitted in the blue and the ratio L(FIR)/L(B) increases with the bolometric
luminosity. Objects with fainter blue magnitudes have larger ratios between the
far-IR (wavelengths > 60 micron) fluxes and the blue band flux, which is
attributed to extinction by dust around the central source. No relation between
the blue absolute magnitude and the dust colour temperature is seen, suggesting
that the dominant source of FIR energy could be linked to a concurrent
starburst rather than to gravitational energy produced by the central engine.Comment: Astronomical Journal, in pres
Topological Analysis of Emerging Bipole Clusters Producing Violent Solar Events
During the rising phase of Solar Cycle 24 tremendous activity occurred on the
Sun with fast and compact emergence of magnetic flux leading to bursts of
flares (C to M and even X-class). We investigate the violent events occurring
in the cluster of two active regions (ARs), NOAA numbers 11121 and 11123,
observed in November 2010 with instruments onboard the {\it Solar Dynamics
Observatory} and from Earth. Within one day the total magnetic flux increased
by with the emergence of new groups of bipoles in AR 11123. From all the
events on 11 November, we study, in particular, the ones starting at around
07:16 UT in GOES soft X-ray data and the brightenings preceding them. A
magnetic-field topological analysis indicates the presence of null points,
associated separatrices and quasi-separatrix layers (QSLs) where magnetic
reconnection is prone to occur. The presence of null points is confirmed by a
linear and a non-linear force-free magnetic-field model. Their locations and
general characteristics are similar in both modelling approaches, which
supports their robustness. However, in order to explain the full extension of
the analysed event brightenings, which are not restricted to the photospheric
traces of the null separatrices, we compute the locations of QSLs. Based on
this more complete topological analysis, we propose a scenario to explain the
origin of a low-energy event preceding a filament eruption, which is
accompanied by a two-ribbon flare, and a consecutive confined flare in AR
11123. The results of our topology computation can also explain the locations
of flare ribbons in two other events, one preceding and one following the ones
at 07:16 UT. Finally, this study provides further examples where flare-ribbon
locations can be explained when compared to QSLs and only, partially, when
using separatrices.Comment: 42 pages, 15 figure
Cosmic Dynamics in the Chameleon Cosmology
We study in this paper chameleon cosmology applied to
Friedmann-Robertson-Walker space, which gives rise to the equation of state
(EoS) parameter larger than -1 in the past and less than -1 today, satisfying
current observations. We also study cosmological constraints on the model using
the time evolution of the cosmological redshift of distant sources which
directly probes the expansion history of the universe. Due to the evolution of
the universe's expansion rate, the model independent Cosmological Redshift
Drift (CRD)test is expected to experience a small, systematic drift as a
function of time. The model is supported by the observational data obtained
from the test.Comment: 16 pages, 9 figure
The power spectrum of the flux distribution in the Lyman-alpha forest of a Large sample of UVES QSO Absorption Spectra (LUQAS)
The flux power spectra of the Lyman-alpha forest from a sample of 27 QSOs
taken with the high resolution echelle spectrograph UVES on VLT are presented.
We find a similar fluctuation amplitude at the peak of the ``3D'' flux power
spectrum at k ~ 0.03 (km/sec)^(-1) as the study by Croft et al. (2002), in the
same redshift range. The amplitude of the flux power spectrum increases with
decreasing redshift if corrected for the increase in the mean flux level as
expected if the evolution of the flux power spectrum is sensitive to the
gravitational growth of matter density fluctuations. This is in agreement with
the findings of McDonald et al. (2000) at larger redshift. The logarithmic
slope of the "3D" flux power spectrum, P_F(k), at large scales k < 0.03
(km/sec)^(-1), is 1.4 +- 0.3, i.e. 0.3 shallower than that found by Croft et
al. (2002) but consistent within the errors.Comment: 18 pages, 9 PS figures, 6 tables. Note that the k-values of the 1D
flux power spectrum had been erroneously shifted by half a bin size (in log
k) in the previous version. All the other results are unaffected. New tables
can be found at http://www.ast.cam.ac.uk/~rtnigm/luqas.ht
The Asiago-ESO/RASS QSO Survey. I.The Catalog and the Local QSO Luminosity Function
This paper presents the first results of a survey for bright quasars (V <
14.5 and R30.
The photometric database is derived from the GSC and USNO catalogs. Quasars are
identified on the basis of their X-ray emission measured in the ROSAT All Sky
Survey. The surface density of quasars brighter than 15.5 mag turns out to be
, about 3 times higher than that estimated by
the PG survey. The quasar optical Luminosity Function (LF) at is computed and shown to be consistent with a Luminosity Dependent
Luminosity Evolution of the type derived by La Franca and Cristiani (1997) in
the range . The predictions of semi-analytical models of
hierarchical structure formation agree remarkably well with the present
observations.Comment: 54 pages Latex, with 7 PostScript figures. Some minor changes.
Astronomical Journal, in pres
On Magnetic Interlayer Coupling and Proximity Effect in a LaCaMnO(10 nm)/YBaCuO(10 nm) Superlattice
We present a study of interlayer coupling and proximity effects in a
LaCaMnO(10 nm)/YBaCuO(10 nm) superlattice.
Using element-sensitive x-ray probes, the magnetic state of Mn can be probed
without seeing the strong diamagnetism of the superconductor, which makes this
approach ideal to study changes in the magnetic properties across the
superconducting transition. By a combined experiment using {\it in situ}
transport measurements during polarized soft x-ray measurements, we were able
to see no noticeable influence of the superconducting state on the magnetic
properties and no evidence for magnetic coupling across a 10 nm YBCO layer.Comment: 4 pages, submitted to Applied Physics Letter
NICMOS Observations of Low-Redshift Quasar Host Galaxies
We have obtained Near-Infrared Camera and Multi-Object Spectrometer images of
16 radio quiet quasars observed as part of a project to investigate the
``luminosity/host-mass limit.'' The limit results were presented in McLeod,
Rieke, & Storrie-Lombardi (1999). In this paper, we present the images
themselves, along with 1- and 2-dimensional analyses of the host galaxy
properties. We find that our model-independent 1D technique is reliable for use
on ground-based data at low redshifts; that many radio-quiet quasars live in
deVaucouleurs-law hosts, although some of the techniques used to determine host
type are questionable; that complex structure is found in many of the hosts,
but that there are some hosts that are very smooth and symmetric; and that the
nuclei radiate at ~2-20% of the Eddington rate based on the assumption that all
galaxies have central black holes with a constant mass fraction of 0.6%.
Despite targeting hard-to-resolve hosts, we have failed to find any that imply
super-Eddington accretion rates.Comment: To appear in ApJ, 28 pages including degraded figures. Download the
paper with full-resolutio figures from
http://www.astro.wellesley.edu/kmcleod/mm.p
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