526 research outputs found
The quest for dark matter in dwarf spheroidal galaxies with the Cherenkov Telescope Array
Dwarf spheroidal galaxies are among the best environments that can be studied
with Cherenkov telescopes for indirect searches of -ray signals coming
from dark matter self-interaction (annihilation or decay), due to their
proximity and negligible background emission. We present new determinations of
the dark-matter amount - i.e. the astrophysical factors and - in
dwarf-galaxy halos obtained through the MCMC Jeans analysis of their brightness
and kinematic data. Such factors are of great importance to test the
performances of the next-generation -ray instruments such as the
Cherenkov Telescope Array in detecting dark-matter signals from astronomical
environments, or constraining the limits to dark-matter physics parameters
(particle mass and lifetime, annihilation cross section).Comment: 4 pages, 2 figures, 1 table, proceedings of the "RICAP-18 - 7th Roma
International Conference on Astroparticle Physics" held on 2018 Sep 04-07 at
Universit\`a di "Roma Tre", Via V. Volterra 62, I-00182 Roma, Italy (to
appear on EPJ Web of Conferences
"Zombie" or active? An alternative explanation to the properties of star-forming galaxies at high redshift
Star-forming galaxies at high redshift show anomalous values of infrared
excess, which can be described only by extremizing the existing relations
between the shape of their ultraviolet continuum emission and their
infrared-to-ultraviolet luminosity ratio, or by constructing \textit{ad-hoc}
models of star formation and dust distribution. We present an alternative
explanation, based on unveiled AGN activity, to the existence of such galaxies.
In fact, the presence of a weak AGN configures as a natural scenario in order
to explain the observed spectral properties of such high- objects in terms
of a continuum slope distribution rather than altered infrared excesses, due to
the different shape of the AGN continuum emission with respect to quiescent
galaxies. To this aim, we directly compare the infrared-to-ultraviolet
properties of high-redshift galaxies to those of known categories of AGN
(quasars and Seyferts). We also infer the characteristics of their possible
X-ray emission. We find a strong similarity between the spectral shapes and
luminosity ratios of AGN with the corresponding properties of such galaxies. In
addition, we derive expected X-ray fluxes that are compatible with energetics
from AGN activity. We conclude that a moderate AGN contribution to the UV
emission of such high- objects is a valid alternative to explain their
spectral properties. Even the presence of an active nucleus in each source
would not violate the expected quasar statistics. Furthermore, we suggest that
the observed similarities between anomalous star-forming galaxies and quasars
may provide a benchmark for future theoretical and observational studies on the
galaxy population in the early Universe.Comment: 13 pages, 7 figures, 4 tables, accepted for publication in A&
CIV and CIII] reverberation mapping of the luminous quasar PG 1247+267
So far the masses of about 50 active galactic nuclei have been measured
through the reverberation mapping technique (RM). Most measurements have been
performed for objects of moderate luminosity and redshift, based on H,
which is also used to calibrate the scaling relation which allows single-epoch
(SE) mass determination based on AGN luminosity and the width of different
emission lines. The SE mass obtained from CIV line shows a
large spread around mean values, due to complex structure and gas dynamics of
the relevant emission region. Direct RM measures of CIV exist for only 6 AGNs
of low luminosity and redshift, and only one luminous quasar (Kaspi et al
2007). We have collected since 2003 photometric and spectroscopic observations
of PG1247+267, the most luminous quasar ever analyzed for RM. We provide light
curves for the continuum and for CIV and
CIII], and measures of the reverberation time lags based on the
SPEAR method (Zu et al. 2011). The sizes of the line emission regions are in a
ratio , similar to the case of Seyfert galaxies,
indicating for the first time a similar ionization stratification in a luminous
quasar and low luminosity nuclei. Due to relatively small broad line region
size and relatively narrow line widths, we estimate a small mass and an
anomalously high Eddington ratio. We discuss the possibility that either the
shape of the emission region or an amplification of the luminosity caused by
gravitational lensing may be in part responsible of the result.Comment: 10 pagese, 6 figures, 3 tables, Accepted for publication in Ap
A multi-epoch spectroscopic study of the BAL quasar APM 08279+5255: I. C IV absorption variability
Broad Absorption Lines indicate gas outflows with velocities from thousands
km/s to about 0.2 the speed of light, which may be present in all quasars and
may play a major role in the evolution of the host galaxy. The variability of
absorption patterns can provide informations on changes of the density and
velocity distributions of the absorbing gas and its ionization status. We
collected 23 photometrical and spectro-photometrical observations at the 1.82m
Telescope of the Asiago Observatory since 2003, plus other 5 spectra from the
literature. We analysed the evolution in time of the equivalent width of the
broad absorption feature and two narrow absorption systems, the correlation
among them and with the R band magnitude. We performed a structure function
analysis of the equivalent width variations. We present an unprecedented
monitoring of a broad absorption line quasar based on 28 epochs in 14 years.
The shape of broad absorption feature shows a relative stability, while its
equivalent width slowly declines until it sharply increases during 2011. In the
same time the R magnitude stays almost constant until it sharply increases
during 2011. The equivalent width of the narrow absorption redwards of the
systemic redshift only shows a decline. The broad absorption behaviour suggests
changes of the ionisation status as the main cause of variability. We show for
the first time a correlation of this variability with the R band flux. The
different behaviour of the narrow absorption system might be due to
recombination time delay. The structure function of the absorption variability
has a slope comparable with typical optical variability of quasars. This is
consistent with variations of the 200 A ionising flux originating in the inner
part of the accretion disk.Comment: 10 pages, 8 figures, to appear on Astronomy & Astrophysic
Celiac Disease, Inflammation and Oxidative Damage: A Nutrigenetic Approach
Celiac disease (CD), a common heritable chronic inflammatory condition of the small intestine caused by permanent intolerance to gluten/gliadin (prolamin), is characterized by a complex interplay between genetic and environmental factors. Developments in proteomics have provided an important contribution to the understanding of the biochemical and immunological aspects of the disease and the mechanisms involved in toxicity of prolamins. It has been demonstrated that some gliadin peptides resistant to complete proteolytic digestion may directly affect intestinal cell structure and functions by modulating gene expression and oxidative stress. In recent years, the creation of the two research fields Nutrigenomics and Nutrigenetics, has enabled the elucidation of some interactions between diet, nutrients and genes. Various dietary components including long chain ω-3 fatty acids, plant flavonoids, and carotenoids have been demonstrated to modulate oxidative stress, gene expression and production of inflammatory mediators. Therefore their adoption could preserve intestinal barrier integrity, play a protective role against toxicity of gliadin peptides and have a role in nutritional therapy of celiac disease
Extinction curve template for intrinsically reddened quasars
We analyze the near-infrared to UV data of 16 quasars with redshifts ranging
from 0.71 2.13 to investigate dust extinction properties. The
sample presented in this work is obtained from the High Quasar (HAQ)
survey. The quasar candidates were selected from the Sloan Digital Sky Survey
(SDSS) and the UKIRT Infrared Deep Sky Survey (UKIDSS), and follow-up
spectroscopy was carried out at the Nordic Optical Telescope (NOT) and the New
Technology Telescope (NTT). To study dust extinction curves intrinsic to the
quasars, from the HAQ survey we selected 16 cases where the Small Magellanic
Cloud (SMC) law could not provide a good solution to the spectral energy
distributions (SEDs). We derived the extinction curves using Fitzpatrick &
Massa 1986 (FM) law by comparing the observed SEDs to the combined quasar
template from Vanden Berk et al. 2001 and Glikman et al. 2006. The derived
extinction, , ranges from 0.2-1.0 mag. All the individual extinction
curves of our quasars are steeper (-2.7) than that of the SMC, with a
weighted mean value of . We derive an `average quasar extinction
curve' for our sample by fitting SEDs simultaneously by using the weighted mean
values of the FM law parameters and a varying . The entire sample is well
fit with a single best-fit value of . The `average quasar
extinction curve' deviates from the steepest Milky Way and SMC extinction
curves at a confidence level . Such steep extinction curves
suggest a significant population of silicates to produce small dust grains.
Moreover, another possibility could be that the large dust grains may have been
destroyed by the activity of the nearby active galactic nuclei (AGN), resulting
in steep extinction curves.Comment: 8 pages, 4 figures, 1 tabl
The rest-frame UV-to-optical spectroscopy of APM 08279+5255 - BAL classification and black hole mass estimates
We present the analysis of the rest-frame optical-to-UV spectrum of APM
08279+5255, a well-known lensed broad absorption line (BAL) quasar at . The spectroscopic data are taken with the optical DOLoRes and near-IR
NICS instruments at TNG, and include the previously unexplored range between C
III] 1910 and [O III] 4959,5007. We investigate the
possible presence of multiple BALs by computing "balnicity" and absorption
indexes (i.e. BI, BI and AI) for the transitions Si IV 1400, C IV
1549, Al III 1860 and Mg II 2800. No clear evidence
for the presence of absorption features is found in addition to the already
known, prominent BAL associated to C IV, which supports a high-ionization BAL
classification for APM 08279+5255. We also study the properties of the [O III],
H and Mg II emission lines. We find that [O III] is intrinsically weak
(), as it is typically found in
luminous quasars with a strongly blueshifted C IV emission line (2500 km
s for APM 08279+5255). We compute the single-epoch black hole mass based
on Mg II and H broad emission lines, finding M, with the magnification factor that can
vary between 4 and 100 according to CO and rest-frame UV-to-mid-IR imaging
respectively. Using a Mg II equivalent width (EW)-to-Eddington ratio relation,
the EW \AA\ measured for APM 08279+5255 translates into an
Eddington ratio of 0.4, which is more consistent with . This
magnification factor also provides a value of that is consistent
with recent reverberation-mapping measurements derived from C IV and Si IV.Comment: 10 pages, 4 figures, 4 tables, accepted for publication in A&
Serendipitous discovery of a projected pair of QSOs separated by 4.5 arcsec on the sky
We present the serendipitous discovery of a projected pair of quasi-stellar
objects (QSOs) with an angular separation of arcsec. The
redshifts of the two QSOs are widely different: one, our programme target, is a
QSO with a spectrum consistent with being a narrow line Seyfert 1 AGN at
. For this target we detect Lyman-, \ion{C}{4}, and
\ion{C}{3]}. The other QSO, which by chance was included on the spectroscopic
slit, is a Type 1 QSO at a redshift of , for which we detect
\ion{C}{4}, \ion{C}{3]} and \ion{Mg}{2}. We compare this system to previously
detected projected QSO pairs and find that only about a dozen previously known
pairs have smaller angular separation.Comment: 4 pages, 3 figures. Accepted for publication in A
The High A(V) Quasar Survey: Reddened quasi-stellar objects selected from optical/near-infrared photometry - II
Quasi-stellar objects (QSOs) whose spectral energy distributions (SEDs) are
reddened by dust either in their host galaxies or in intervening absorber
galaxies are to a large degree missed by optical color selection criteria like
the one used by the Sloan Digital Sky Survey (SDSS). To overcome this bias
against red QSOs, we employ a combined optical and near-infrared color
selection. In this paper, we present a spectroscopic follow-up campaign of a
sample of red candidate QSOs which were selected from the SDSS and the UKIRT
Infrared Deep Sky Survey (UKIDSS). The spectroscopic data and SDSS/UKIDSS
photometry are supplemented by mid-infrared photometry from the Wide-field
Infrared Survey Explorer. In our sample of 159 candidates, 154 (97%) are
confirmed to be QSOs. We use a statistical algorithm to identify sightlines
with plausible intervening absorption systems and identify nine such cases
assuming dust in the absorber similar to Large Magellanic Cloud sightlines. We
find absorption systems toward 30 QSOs, 2 of which are consistent with the
best-fit absorber redshift from the statistical modeling. Furthermore, we
observe a broad range in SED properties of the QSOs as probed by the rest-frame
2 {\mu}m flux. We find QSOs with a strong excess as well as QSOs with a large
deficit at rest-frame 2 {\mu}m relative to a QSO template. Potential solutions
to these discrepancies are discussed. Overall, our study demonstrates the high
efficiency of the optical/near-infrared selection of red QSOs.Comment: 64 pages, 18 figures, 16 pages of tables. Accepted to ApJ
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