3,182 research outputs found
Obscuring Active Galactic Nuclei with Nuclear Starburst Disks
We assess the potential of nuclear starburst disks to obscure the
Seyfert-like AGN that dominate the hard X-ray background at z~1. Over 1200
starburst disk models, based on the theory developed by Thompson et al., are
calculated for five input parameters: the black hole mass, the radial size of
the starburst disk, the dust-to-gas ratio, the efficiency of angular momentum
transport in the disk, and the gas fraction at the outer disk radius. We find
that a large dust-to-gas ratio, a relatively small starburst disk, a
significant gas mass fraction, and efficient angular momentum transport are all
important to produce a starburst disk that can potentially obscure an AGN. The
typical maximum star-formation rate in the disks is ~10 solar masses per year.
Assuming no mass-loss due to outflows, the starburst disks feed gas onto the
black hole at rates sufficient to produce hard X-ray luminosities of
10^{43}-10^{44} erg s^{-1}. The starburst disks themselves should be detectable
at mid-infrared and radio wavelengths; at z=0.8, the predicted fluxes are ~1
mJy at 24microns and ~10-30 microJy at 1.4GHz. Thus, we predict a large
fraction of radio/X-ray matches in future deep radio surveys. The starburst
disks should be easily distinguished from AGN in future 100microns surveys by
Herschel with expected fluxes of ~5 mJy. Any AGN-obscuring starbursts will be
associated with hot dust, independent of AGN heating, resulting in observable
signatures for separating galactic and nuclear star-formation. Finally, because
of the competition between gas and star-formation, nuclear starbursts will be
associated with lower-luminosity AGN. Thus, this phenomenon is a natural
explanation for the observed decrease in the fraction of obscured AGN with
luminosity.Comment: 13 pages, 12 figures, 3 in color; accepted by Ap
Topological defects and misfit strain in magnetic stripe domains of lateral multilayers with perpendicular magnetic anisotropy
Stripe domains are studied in perpendicular magnetic anisotropy films
nanostructured with a periodic thickness modulation that induces the lateral
modulation of both stripe periods and inplane magnetization. The resulting
system is the 2D equivalent of a strained superlattice with properties
controlled by interfacial misfit strain within the magnetic stripe structure
and shape anisotropy. This allows us to observe, experimentally for the first
time, the continuous structural transformation of a grain boundary in this 2D
magnetic crystal in the whole angular range. The magnetization reversal process
can be tailored through the effect of misfit strain due to the coupling between
disclinations in the magnetic stripe pattern and domain walls in the in-plane
magnetization configuration
Associations between motor proficiency and motor creativity amongst 5-6-year-old children from deprived areas of North West England
Participation in physical activity (PA) is essential for the promotion of physical and mental health outcomes, but children in the UK are not meeting the recommended amounts of PA. Existing literature has linked children’s levels of physical activity to the development of motor competence. Two important components of motor competence are motor proficiency and motor creativity, however limited research has examined their prevalence and relationship in deprived young children. The aim of this study was to examine associations between motor proficiency and motor creativity, as well as to explore gender and age effects on these variables in children aged 5 to 6 years old from areas of high deprivation. This cross-sectional study was realised from the baseline data obtained from a larger project called SAMPLE-PE. A total of 360 children aged 5 to 6 years were recruited, however many children had some missing data and had to be removed from the study. The final sample included 221 children from deprived areas (low SES). The Test of Gross Motor Development (TGMD-3) was used to qualitatively assesses gross motor proficiency in locomotor and ball skills; the test of Stability Skills, was used to measure the stability skill component of motor proficiency. To assess motor creativity the Divergent Movement Ability test (DMA) was used. Associations between motor proficiency and motor creativity were explored using the Pearson’s correlation (bivariate correlations) and the multilevel mixed linear regression. Children’s motor proficiency and motor creativity scores demonstrated a positive but weak relationship. Age was positively related to motor proficiency, indicating that older children demonstrated higher levels of motor proficiency; conversely, age was not associated with total motor creativity. Gender was not associated with total motor proficiency nor total motor creativity. However, gender was associated with all motor proficiency subtests, girls outperformed boys in locomotor and stability skills whereas boys demonstrated higher performance at ball skills. Gender was also associated to motor creativity object control subtest, where boys performed better than girls. The main finding revealed positive but weak associations between motor creativity and motor proficiency. This suggests that these two constructs develop by different means and strategies and are influenced by different biological, psychological and environmental factors. These results suggest that longitudinal research is needed to better understand the nature of the associations between motor creativity and motor proficiency, as well as to understand how motor creativity develops over time and between genders. Future research is needed on the influence of socioeconomic status on the relationship between motor creativity and motor proficiency
An accretion disc model for quasar optical variability
Some different correlations between optical-UV variability and other quasar
properties, such as luminosity, black hole mass and rest-frame wavelength, were
discovered. The positive correlation between optical-UV variability amplitude
and black hole mass was first found by Wold et al., and this was confirmed by
Wilhite et al. We suggest that the accretion disk model can explain these
correlations, provided the optical-UV variability is triggered by the change of
accretion rate. The disk temperature of accretion discs decreases with
increasing black hole mass, which leads to systematical spectral shape
difference with black hole mass even if the black hole is accreting at the same
rate m_dot (m_dot = M_dot / M_dotEdd). The observed positive correlation
between optical-UV variability and black hole mass can be well reproduced by
our model calculations, if the mean accretion rate m_dot0 ~ 0.1 with variation
of m_delta ~ 0.4 - 0.5 m_dot0. We also found that the observed correlations of
optical-UV variability amplitude with luminosity or rest-frame wavelength can
be qualitatively explained by this accretion disc model.Comment: 4 pages, 4 figures, accepted for publication in MNRAS Letter
The optical-ultraviolet continuum of Seyfert 2 galaxies
This paper aims to understand the continuum of Seyfert 2 galaxies. By fitting
the single galaxies in the sample of Heckman et al. (1995) with composite
models (shock+ photoionization from the active center), we show that five main
components characterize the SED of the continuum. Shocks play an important role
since they produce a high temperature zone where soft X-rays are emitted.
We show that in the optical-UV range, the slope of the NLR emission
reproduces the observed values, and may be the main component of the
featureless continuum. The presence of star forming regions cannot be excluded
in the circumnuclear region of various Seyfert galaxies. An attempt is made to
find their fingerprints in the observed AGN spectra. Finally, it is
demonstrated that multi-cloud models are necessary to interpret the spectra of
single objects, even in the global investigation of a sample of galaxies.Comment: 26 pages, LaTeX (including 5 Tables) + 17 PostScript figures. To
appear in "The Astrophysical Journal
The Electron Scattering Region in Seyfert Nuclei
The electron scattering region (ESR) is one of important ingredients in
Seyfert nuclei because it makes possible to observe the hidden broad line
region (hereafter HBLR) in some type 2 Seyfert nuclei (hereafter S2s). However,
little is known about its physical and geometrical properties. Using the number
ratio of S2s with and without HBLR, we investigate statistically where the ESR
is in Seyfert nuclei. Our analysis suggests that the ESR is located at radius
between 0.01 pc and 0.1 pc from the central engine. We also
discuss a possible origin of the ESR briefly.Comment: 5 pages and 1 figure. The Astrophysical Journal (Letters), in pres
Catabolism of raw and cooked green pepper (Capsicum annuum) (poly)phenolic compounds after simulated gastrointestinal digestion and fecal fermentation.
A total of 21 (poly)phenolic compounds (free and bound) were quantified in raw, olive oil fried, sunflower oil fried and griddled green pepper before and after a simulated gastrointestinal digestion. Flavonoids, particularly quercetin rhamnoside, were the main compounds. The bioaccessibility of (poly)phenolic compounds after gastrointestinal digestion was higher in cooked (>82%) than in raw (48%) samples, showing a positive effect of heat treatment on the release of (poly)phenols from the vegetal matrix. Additionally, a faecal fermentation was carried out for 24h. A time-dependent microbial metabolic activity was observed, which resulted firstly (<5h) in the hydrolysis of flavonoid glycosides and then in the formation of 3 catabolites, namely 3,4-dihydroxybenzoic acid, dihydrocaffeic acid and 3-(3′-hydroxyphenyl)propionic acid, this being by far the most abundant. Catabolic pathways for colonic microbial degradation of flavonoids and hydroxycinnamic acids have been proposed. Griddled pepper showed the highest amount of (poly)phenols both after gastrointestinal digestion and colonic fermentation
Predicting spectral features in galaxy spectra from broad-band photometry
We explore the prospects of predicting emission line features present in
galaxy spectra given broad-band photometry alone. There is a general consent
that colours, and spectral features, most notably the 4000 A break, can predict
many properties of galaxies, including star formation rates and hence they
could infer some of the line properties. We argue that these techniques have
great prospects in helping us understand line emission in extragalactic objects
and might speed up future galaxy redshift surveys if they are to target
emission line objects only. We use two independent methods, Artifical Neural
Neworks (based on the ANNz code) and Locally Weighted Regression (LWR), to
retrieve correlations present in the colour N-dimensional space and to predict
the equivalent widths present in the corresponding spectra. We also investigate
how well it is possible to separate galaxies with and without lines from broad
band photometry only. We find, unsurprisingly, that recombination lines can be
well predicted by galaxy colours. However, among collisional lines some can and
some cannot be predicted well from galaxy colours alone, without any further
redshift information. We also use our techniques to estimate how much
information contained in spectral diagnostic diagrams can be recovered from
broad-band photometry alone. We find that it is possible to classify AGN and
star formation objects relatively well using colours only. We suggest that this
technique could be used to considerably improve redshift surveys such as the
upcoming FMOS survey and the planned WFMOS survey.Comment: 10 pages 7 figures summitted to MNRA
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