2,105 research outputs found
The evolution of the spatially-resolved metal abundance in galaxy clusters up to z=1.4
We present the combined analysis of the metal content of 83 objects in the
redshift range 0.09-1.39, and spatially-resolved in the 3 bins (0-0.15,
0.15-0.4, >0.4) R500, as obtained with similar analysis using XMM-Newton data
in Leccardi & Molendi (2008) and Baldi et al. (2012). We use the pseudo-entropy
ratio to separate the Cool-Core (CC) cluster population, where the central gas
density tends to be relatively higher, cooler and more metal rich, from the
Non-Cool-Core systems. The average, redshift-independent, metal abundance
measured in the 3 radial bins decrease moving outwards, with a mean metallicity
in the core that is even 3 (two) times higher than the value of 0.16 times the
solar abundance in Anders & Grevesse (1989) estimated at r>0.4 R500 in CC (NCC)
objects. We find that the values of the emission-weighted metallicity are
well-fitted by the relation at given radius. A
significant scatter, intrinsic to the observed distribution and of the order of
0.05-0.15, is observed below 0.4 R500. The nominal best-fit value of
is significantly different from zero in the inner cluster regions () and in CC clusters only. These results are confirmed also with a
bootstrap analysis, which provides a still significant negative evolution in
the core of CC systems (P>99.9 per cent). No redshift-evolution is observed
when regions above the core (r > 0.15 R500) are considered. A reasonable good
fit of both the radial and redshift dependence is provided from the functional
form , with in CC clusters
and for NCC systems. Our results
represent the most extensive study of the spatially-resolved metal distribution
in the cluster plasma as function of redshift.Comment: 5 pages. Research Note accepted for publication in A&
X-ray reprocessing in Seyfert Galaxies: simultaneous XMM-Newton/BeppoSAX observations
We selected a sample of eight bright unobscured (at least at the iron line
energy) Seyfert Galaxies observed simultaneously by XMM-Newton and BeppoSAX,
taking advantage of the complementary characteristics of the two missions. The
main results of our analysis can be summarized as follows: narrow neutral iron
lines are confirmed to be an ubiquitous component in Seyfert spectra; none of
the analyzed sources shows unambiguously a broad relativistic iron line; all
the sources of our sample (with a single exception) show the presence of a
Compton reflection component; emission lines from ionized iron are observed in
some sources; peculiar weak features around 5-6 keV (possibly arising from
rotating spots on the accretion disk) are detected in two sources. The scenario
emerging from these results strongly requires some corrections for the
classical model of reprocessing from the accretion disk. As for materials
farther away from the Black Hole, our results represent a positive test for the
Unification Model, suggesting the presence of the torus in (almost) all
sources, even if unobscured.Comment: Accepted for publication in A&
Evolution in the iron abundance of the ICM
We present a Chandra analysis of the X-ray spectra of 56 clusters of galaxies
at , which cover a temperature range of keV. Our analysis
is aimed at measuring the iron abundance in the ICM out to the highest redshift
probed to date. We find that the emission-weighted iron abundance measured
within in clusters below 5 keV is, on average, a factor of
higher than in hotter clusters, following , which confirms the trend seen in local samples. We made use of
combined spectral analysis performed over five redshift bins at
to estimate the average emission weighted iron abundance. We find a constant
average iron abundance as a function of redshift,
but only for clusters at . The emission-weighted iron abundance is
significantly higher () in the redshift range
, approaching the value measured locally in the inner radii for a mix of cool-core and non cool-core clusters in the
redshift range . The decrease in with can be
parametrized by a power law of the form . The observed
evolution implies that the average iron content of the ICM at the present epoch
is a factor of larger than at . We confirm that the ICM is
already significantly enriched () at a look-back time
of 9 Gyr. Our data provide significant constraints on the time scales and
physical processes that drive the chemical enrichment of the ICM.Comment: 4 pages, 4 figures, to appear in the Proceedings of "The Extreme
Universe in the Suzaku Era", Dicember 2006, Kyoto (Japan
A Comparison of Performances of Different Feature Selection Methods applied to Biomedical Data
Migraine is a debilitating disease whose causes are not yet completely explained. Near-InfraRed Spectroscopy (NIRS) is a non-invasive technology commonly used for the assessment of the cerebral autoregulation during active stimuli.
Feature Selection (FS) allows dimensionality reduction of multivariate datasets, highlighting the most informative variables and deleting redundant and irrelevant information. Rough Set Theory (RST) is one of the most used tool for FS, enables to manage incomplete and imperfect knowledge without any assumption about data model.
This study involved a total of 80 subjects, divided in 3 groups: 15 healthy subjects taken as controls, 14 women suffered from migraine without aura and 51 women from migraine with aura. We apply three different methods of FS based on RST to a set of 26 parameters extracted from NIRS signals recorded in the subjects during breath-holding (BH) and hyperventilation (HYP). We compare the extracted subsets of features in the subjects’ classification by means of Artificial Neural Networks. The results show good performance for all subsets, with a percentage of correct classification above the 90%
Tracing the evolution in the iron content of the ICM
We present a Chandra analysis of the X-ray spectra of 56 clusters of galaxies
at z>0.3, which cover a temperature range of 3>kT>15 keV. Our analysis is aimed
at measuring the iron abundance in the ICM out to the highest redshift probed
to date. We find that the emission-weighted iron abundance measured within
(0.15-0.3)R_vir in clusters below 5 keV is, on average, a factor of ~2 higher
than in hotter clusters, following Z(T)~0.88T^-(0.47)Z_o, which confirms the
trend seen in local samples. We made use of combined spectral analysis
performed over five redshift bins at 0.3>z>1.3 to estimate the average emission
weighted iron abundance. We find a constant average iron abundance Z_Fe~0.25Z_o
as a function of redshift, but only for clusters at z>0.5. The
emission-weighted iron abundance is significantly higher (Z_Fe~0.4Z_o) in the
redshift range z~0.3-0.5, approaching the value measured locally in the inner
0.15R_vir radii for a mix of cool-core and non cool-core clusters in the
redshift range 0.1<z<0.3. The decrease in Z_Fe with redshift can be
parametrized by a power law of the form ~(1+z)^(-1.25). The observed evolution
implies that the average iron content of the ICM at the present epoch is a
factor of ~2 larger than at z=1.2. We confirm that the ICM is already
significantly enriched (Z_Fe~0.25Z_o) at a look-back time of 9 Gyr. Our data
provide significant constraints on the time scales and physical processes that
drive the chemical enrichment of the ICM.Comment: 6 pages, 6 figures, to appear in the Proceedings of "Heating vs.
Cooling in Galaxies and Clusters of Galaxies", August 2006, Garching
(Germany
The outer regions of galaxy clusters: Chandra constraints on the X-ray surface brightness
(Abridged version) We study the properties of the X-ray surface brightness
profiles in a sample of galaxy clusters that were observed with Chandra and
have emission detectable with a signal-to-noise ratio higher than 2 at a radius
beyond R500 ~ 0.7 R200. Our study aims to measure the slopes of the X-ray
surface brightness and of the gas density profiles in the outskirts of massive
clusters. These constraints are compared to similar results obtained from
observations and numerical simulations of the temperature and dark matter
density profiles with the intention of presenting a consistent picture of the
outer regions of galaxy clusters. We extract the surface brightness profiles
Sb(r) of 52 X-ray luminous galaxy clusters at z>0.3 from X-ray exposures
obtained with Chandra. We estimate R200 using both a beta-model that reproduces
Sb(r) and scaling relations from the literature. The two methods converge to
comparable values. We determine the radius, R_S2N, at which the signal-to-noise
ratio is larger than 2 and select the objects in the sample that satisfy the
criterion R_S2N/R200 > 0.7. For the eleven selected objects, we model with a
power-law the behaviour of Sb(r). We measure a consistent steepening of the
Sb(r) profile moving outward from 0.4 R200, where an average slope of -3.6
(sigma=0.8) is estimated. At R200, we evaluate a slope of -4.3 (sigma=0.9) that
implies a slope in the gas density profile of -2.6 and a predicted mean value
of the surface brightness in the 0.5-2 band of 2e-12 erg/s/cm2/deg2. Combined
with estimates of the outer slope of the gas temperature profile and
expectations about the dark matter distribution, these measurements allow us to
describe properly how X-ray luminous clusters behave out to the virial radius.Comment: 7 pages. A&A in press. Minor revisions to match published version:
added references, corrected typo
An X-ray view of Mrk 705: A borderline narrow-line Seyfert 1 galaxy
Mrk 705 exhibits optical properties of both narrow- and broad-line Seyfert 1
galaxies. We examine the X-ray properties of this borderline object utilising
proprietary and public data from Chandra, ASCA, ROSAT and RXTE, spanning more
than twelve years. Though long-term flux variability from the pointed
observations appears rather modest (about 3 times), we do find examples of rare
large amplitude outbursts in the RXTE monitoring data. There is very little
evidence of long-term spectral variability as the low- and high-energy spectra
appear constant with time. A 6.4 keV emission line is detected in the ASCA
spectra of Mrk 705, but not during the later, higher flux state Chandra
observation. However, the upper limit on the equivalent width of a line in the
Chandra spectrum is consistent with a constant-flux emission line and a
brighter continuum, suggesting that the line is emitted from distant material
such as the putative torus. Overall, the X-ray properties of Mrk 705 appear
typical of BLS1 activity.Comment: 7 pages, 7 figures. Accepted for publication in A&A (Research Note
Electron effective masses of Scx Al1- x N and Alx Ga1- x N from first-principles calculations of unfolded band structure
The electron effective masses of Sc x Al 1 - xN and Al x Ga 1 - xN, two of the most promising wide bandgap materials for power and RF electronic applications, have been calculated using the predictions of the density functional theory (DFT). More specifically, the unfolding technique has been adopted to extract the effective band structure of the two alloys under investigation. It has been found that the AlGaN effective masses m - approximately follow the Vegard law. On the contrary, due to the larger amount of disorder inside the crystal, the ScAlN shows a non-monotonic change of m - as a function of the Sc concentration, which requires the DFT calculations to be consistently performed for an accurate prediction. The ScAlN effective masses as a function of Sc content have been reported in the range 0 ≤ x ≤ 0.25 for the first time
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