1,749 research outputs found
Properties of the integrated spectrum of serendipitous 2XMM catalogue sources
Our analysis is aimed at characterizing the properties of the integrated
spectrum of active galactic nuclei (AGNs) such as the ubiquity of the Fe
K{\alpha} emission in AGNs and the dependence of the spectral parameters on the
X-ray luminosity and redshift. We selected 2646 point sources from the 2XMM
catalogue at high galactic latitude (|BII| > 25 degrees) and with the sum of
EPIC-PN and EPIC-MOS 0.2-12 keV counts greater than 1000. Redshifts were
obtained for 916 sources from the NED. The final sample consists of 507 AGN.
Individual source spectra have been summed in the observed frame to compute the
integrated spectra in different redshift and luminosity bins over the range
0<z<5. Detailed analysis of these spectra has been performed. We find that the
narrow Fe K{\alpha} line at 6.4 keV is significantly detected up to z=1. The
line equivalent width decreases with increasing X-ray luminosity in the 2-10
keV band (''IT effect''). The anti-correlation is characterized by the relation
log(EWFe) = (1.66 +/- 0.09) + (-0.43 +/- 0.07) log(LX,44), where EWFe is the
rest frame equivalent width of the neutral iron K{\alpha} line in eV and LX,44
is the 2-10 keV X-ray luminosity in units of 10^{44} erg s^{-1}. The equivalent
width is nearly independent of redshift up to z ~ 0.8 with an average value of
101+/-40 (rms dispersion) eV in the luminosity range 43.5<= logLX <= 44.5. Our
analysis also confirmed the hardening of the spectral indices at low
luminosities implying a dependence of obscuration on luminosity. We confirm
that the neutral narrow Fe K{\alpha} line is an almost ubiquitous feature of
AGNs. We find compelling evidence for the ''IT effect'' over a redshift
interval larger than probed in any previous study. We detect no evolution of
the average rest frame equivalent width of the Fe K{\alpha} line with redshift.Comment: 10 pages, 7 figures, 2 Tables. A&A in pres
Two-Face(s): ionized and neutral gas winds in the local Universe
We present a comprehensive study of the Na I 5890, 5895 (Na I D)
resonant lines in the Sloan Digital Sky Survey (SDSS, DR7) spectroscopic sample
to look for neutral gas outflows in the local galaxies. Individual galaxy
spectra are stacked in bins of M and SFR to investigate the dependence
of galactic wind occurrence and velocity as a function of the galaxy position
in the SFR- plane. In massive galaxies at the high SFR tail we find
evidence of a significant blue-shifted Na I D absorption, which we interpret as
evidence of neutral outflowing gas. The occurrence of the blue-shifted
absorption is observed at the same significance for purely SF galaxies, AGN and
composite systems at fixed SFR. In all classes of objects the blue-shift is the
largest and the Na I D equivalent width the smallest for face-on galaxies while
the absorption feature is at the systemic velocity for edge-on systems. This
indicates that the neutral outflow is mostly perpendicular or biconical with
respect to the galactic disk. We also compare the kinematics of the neutral gas
with the ionized gas phase as traced by the [OIII]5007, H,
[NII] and [NII] emission lines. Differently for the
neutral gas phase, all the emission lines show evidence of perturbed kinematics
only in galaxies with a significant level of nuclear activity and, they are
independent from the disk inclination. In conclusion, we find that, in the
local Universe, galactic winds show two faces which are related to two
different ejection mechanisms, namely the neutral outflowing gas phase related
to the SF activity along the galaxy disk and the ionized phase related to the
AGN feedback. In both the neutral and ionized gas phases, the observed wind
velocities suggest that the outflowing gas remains bound to the galaxy with no
definitive effect on the gas reservoir.Comment: Accepted to A&A, 13 pages, 9 figure
Rest-frame stacking of 2XMM catalog sources : Properties of the Fe Kalpha line
The aim of this work is to characterize the average Fe K emission properties
of active galactic nuclei (AGNs) in the source rest-frame. We selected a sample
of 248 AGNs from the 2XMM catalog, covering a wide redshift range 0 < z < 5 and
with the EPIC-PN net 2-10 keV rest-frame counts >=200 and power law photon
indices in the range 1.5-2.2. We employed two fully independent rest-frame
stacking procedures to compute the mean Fe K profile. The counting statistics
for the integrated spectrum is comparable to the one available for the best
studied local Seyferts. To identify the artifacts possibly introduced by the
stacking procedure, we have carried out simulations. We report that the average
Fe K line profile in our sample is best represented by a combination of a
narrow and a broad line. The equivalent widths of the narrow and broad
(parametrized with a diskline) components are ~30 eV and ~100 eV, respectively.
We also discuss the results of more complex fits and the implications of the
adopted continuum modeling on the broad line parameters and its detection
significance.Comment: 13 pages, 13 figures, Accepted for publication in A&
Physical activity programs for balance and fall prevention in elderly: A systematic review
BACKGROUND:
Due to demographic changes the world's population is progressively ageing. The physiological decay of the elderly adult may lead to a reduction in the ability to balance and an increased risk of falls becoming an important issue among the elderly. In order to counteract the decay in the ability to balance, physical activity has been proven to be effective. The aim of this study is to systematically review the scientific literature in order to identify physical activity programs able to increase balance in the elderly.
METHODS:
This review is based on the data from Medline-NLM, Pubmed, ScienceDirect, and SPORTDiscuss and includes randomized control trials that have analyzed balance and physical activity in healthy elderly over 65 years of age during the last decade. A final number of 8 manuscripts were included in the qualitative synthesis, which comprised 200 elderly with a mean age of 75.1 ± 4.4 years. The sample size of the studies varied from 9 to 61 and the intervention periods from 8 to 32 weeks.
RESULTS:
Eight articles were considered eligible and included in the quantitative synthesis. The articles investigated the effects of resistance and aerobic exercise, balance training, T-bow© and wobble board training, aerobic step and stability ball training, adapted physical activity and Wii Fit training on balance outcomes. Balance measures of the studies showed improvements between 16% and 42% compared to baseline assessments.
CONCLUSIONS:
Balance is a multifactorial quality that can be effectively increased by different exercise training means. It is fundamental to promote physical activity in the aging adult, being that a negative effect on balance performance has been seen in the no-intervention control groups
The high-redshift Universe with the International X-ray Observatory
We discuss some of the main open issues related to the light-up and evolution
of the first accreting sources powering high redshift luminous quasars. We
discuss the perspectives of future deep X-ray surveys with the International
X-ray Observatory and possible synergies with the Wide Field X-ray Telescope.Comment: 6 pages, 6 figures. Proceedings of "The Wide Field X-ray Telescope
Workshop", held in Bologna, Italy, Nov. 25-26 2009. To appear in Memorie
della Societ\`a Astronomica Italiana 2010 (arXiv:1010.5889
Biomasse da praterie seminaturali come fonte di energia: un fuoco di paglia?
Biomass from seminatural grasslands as energy source: flash in the pan? - The aim of the study is to evaluate the potentiality of four seminatural herbaceous communities (grasslands of Arrhenatherion, Nardo-Agrostion tenuis, Bromion erecti and Polygono-Trisetion alliances) in the Prealpine Lombardy. We quantified the biomass production (stubble height 5 cm), the main bioenergetic features, such as ash, carbon, hydrogen and nitrogen content, and the Higher Heating Value. Biomass values vary greatly, with means between 513 (Arrhenatherion) to 227 g m-2 (Bromion erecti). The mean ash content ranges between 4.3-7.7% and mean HHV from 18.3 to 19.6 MJ kg-1. The mean energy per unit area varies between 4.5-9.5 MJ m-2.We suggest that the management of seminatural grasslands could provide biomass suitable for bioenergy production instead of common energy crops and at the same time promote conservation of habitats and their biodiversity, mostly in protected areas
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