494 research outputs found
A Survey for HO Megamasers in Active Galactic Nuclei -- II. A Comparison of Detected and Undetected Galaxies
A survey for H2O megamaser emission from 354 active galaxies has resulted in
the detection of 10 new sources, making 16 known altogether. The galaxies
surveyed include a distance-limited sample (covering Seyferts and LINERs with
recession velocities < 7000 km s^{-1}) and a magnitude-limited sample (covering
Seyferts and LINERs with m(B) <= 14.5). In order to determine whether the
H2O-detected galaxies are "typical" AGN or have special properties which
facilitate the production of powerful masers, we have accumulated a database of
physical, morphological, and spectroscopic properties of the observed galaxies.
The most significant finding is that H2O megamasers are detected only in
Seyfert 2 and LINER galaxies, not Seyfert 1s. Implications for this finding are
discussed. LINERs are detected at a similar rate to Seyfert 2s, constituting a
strong argument that at least some nuclear LINERs are AGN rather than
starbursts, since starbursts have not been detected as H2O megamasers. We
preferentially detect H2O emission from the nearer galaxies and from those
which are apparently brighter at mid- and far-infrared and centimeter radio
wavelengths. There is also a possible trend for the H2O-detected galaxies to be
more intrinsically luminous in nuclear 6 cm radio emission than the undetected
ones, though these data are incomplete. We find evidence that Seyfert 2s with
very high (N(H) > 10^{24} cm^{-2}) X-ray absorbing columns of gas are more
often detected as H2O maser emitters than Seyfert 2s with lower columns. It may
be that the probability of detecting H2O maser emission in Seyfert galaxies
increases with increasing column of cool gas to the nucleus, from Seyfert 1s
through NLXGs to Seyfert 2s.Comment: 19 pages, 35 figures, 3 of the tables are contained in separate LaTeX
files: Table 1-a, 1-b, and 3. Also, figure captions are contained in a
separate file which must be compiled with plain TeX, not LaTe
Impact of HCV testing and treatment on HCV transmission among men who have sex with men and who inject drugs in San Francisco: A modelling analysis
Gastrointestinal helminth infection improves insulin sensitivity, decreases systemic inflammation, and alters the composition of gut microbiota in distinct mouse models of Type 2 diabetes
Type 2 diabetes (T2D) is a major health problem and is considered one of the top 10 diseases leading to death globally. T2D has been widely associated with systemic and local inflammatory responses and with alterations in the gut microbiota. Microorganisms, including parasitic worms and gut microbes have exquisitely co-evolved with their hosts to establish an immunological interaction that is essential for the formation and maintenance of a balanced immune system, including suppression of excessive inflammation. Herein we show that both prophylactic and therapeutic infection of mice with the parasitic hookworm-like nematode, Nippostrongylus brasiliensis, significantly reduced fasting blood glucose, oral glucose tolerance and body weight gain in two different diet-induced mouse models of T2D. Helminth infection was associated with elevated type 2 immune responses including increased eosinophil numbers in the mesenteric lymph nodes, liver and adipose tissues, as well as increased expression of IL-4 and alternatively activated macrophage marker genes in adipose tissue, liver and gut. N. brasiliensis infection was also associated with significant compositional changes in the gut microbiota at both the phylum and order levels. Our findings show that N. brasiliensis infection drives changes in local and systemic immune cell populations, and that these changes are associated with a reduction in systemic and local inflammation and compositional changes in the gut microbiota which cumulatively might be responsible for the improved insulin sensitivity observed in infected mice. Our findings indicate that carefully controlled therapeutic hookworm infection in humans could be a novel approach for treating metabolic syndrome and thereby preventing T2D
The Spitzer Extragalactic Representative Volume Survey (SERVS): The Environments of High-z SDSS Quasi-Stellar-Objects
This paper presents a study of the environments of SDSS Quasi-Stellar-Objects
(QSOs) in the Spitzer Extragalactic Representative Volume Survey (SERVS). We
concentrate on the high-redshift QSOs as these have not been studied in large
numbers with data of this depth before. We use the IRAC 3.6-4.5{\mu}m colour of
objects and ancillary r-band data to filter out as much foreground
contamination as possible. This technique allows us to find a significant (>
4-{\sigma}) over-density of galaxies around QSOs in a redshift bin centred on z
~ 2.0 and a (> 2-{\sigma}) over-density of galaxies around QSOs in a redshift
bin centred on z ~ 3.3. We compare our findings to the predictions of a
semi-analytic galaxy formation model, based on the {\Lambda}CDM millennium
simulation, and find for both redshift bins that the model predictions match
well the source-density we have measured from the SERVS data.Comment: 13 pages, 12 figures, Accepted by Ap
A powerful intervention: general practitioners' use of sickness certification in depression
<b>Background</b> Depression is frequently cited as the reason for sickness absence, and it is estimated that sickness certificates are issued in one third of consultations for depression. Previous research has considered GP views of sickness certification but not specifically in relation to depression. This study aimed to explore GPs views of sickness certification in relation to depression.<p></p>
<b>Methods</b> A purposive sample of GP practices across Scotland was selected to reflect variations in levels of incapacity claimants and antidepressant prescribing. Qualitative interviews were carried out between 2008 and 2009.<p></p>
<b>Results</b> A total of 30 GPs were interviewed. A number of common themes emerged including the perceived importance of GP advocacy on behalf of their patients, the tensions between stakeholders involved in the sickness certification system, the need to respond flexibly to patients who present with depression and the therapeutic nature of time away from work as well as the benefits of work. GPs reported that most patients with depression returned to work after a short period of absence and that it was often difficult to predict which patients would struggle to return to work.<p></p>
<b>Conclusions</b>
GPs reported that dealing with sickness certification and depression presents distinct challenges. Sickness certificates are often viewed as powerful interventions, the effectiveness of time away from work for those with depression should be subject to robust enquiry
The environments of z~1 Active Galactic Nuclei at 3.6um
We present an analysis of a large sample of AGN environments at z~1 using
stacked Spitzer data at 3.6um. The sample contains type-1 and type-2 AGN in the
form of quasars and radio galaxies, and spans a large range in both optical and
radio luminosity. We find, on average, that 2 to 3 massive galaxies containing
a substantial evolved stellar population lie within a 200-300 kpc radius of the
AGN, constituting a >8-sigma excess relative to the field. Secondly, we find
evidence for the environmental source density to increase with the radio
luminosity of AGN, but not with black-hole mass. This is shown first by
dividing the AGN into their classical AGN types, where we see more significant
over-densities in the fields of the radio-loud AGN. If instead we dispense with
the classical AGN definitions, we find that the source over-density as a
function of radio luminosity for all our AGN exhibits a positive correlation.
One interpretation of this result is that the Mpc-scale environment is in some
way influencing the radio emission that we observe from AGN. This could be
explained by the confinement of radio jets in dense environments leading to
enhanced radio emission or, alternatively, may be linked to more rapid
black-hole spin brought on by galaxy mergers.Comment: 13 pages, 12 figures, accepted by MNRA
Gas and Star Formation in the Circinus Galaxy
We present a detailed study of the Circinus Galaxy, investigating its star
formation, dust and gas properties both in the inner and outer disk. To achieve
this, we obtained high-resolution Spitzer mid-infrared images with the IRAC
(3.6, 5.8, 4.5, 8.0 micron) and MIPS (24 and 70 micron) instruments and
sensitive HI data from the Australia Telescope Compact Array (ATCA) and the
64-m Parkes telescope. These were supplemented by CO maps from the Swedish-ESO
Submillimetre Telescope (SEST). Because Circinus is hidden behind the Galactic
Plane, we demonstrate the careful removal of foreground stars as well as large-
and small-scale Galactic emission from the Spitzer images. We derive a visual
extinction of Av = 2.1 mag from the Spectral Energy Distribution of the
Circinus Galaxy and total stellar and gas masses of 9.5 x 10^{10} Msun and 9 x
10^9 Msun, respectively. Using various wavelength calibrations, we find
obscured global star formation rates between 3 and 8 Msun yr^{-1}. Star forming
regions in the inner spiral arms of Circinus, which are rich in HI, are
beautifully unveiled in the Spitzer 8 micron image. The latter is dominated by
polycyclic aromatic hydrocarbon (PAH) emission from heated interstellar dust.
We find a good correlation between the 8 micron emission in the arms and
regions of dense HI gas. The (PAH 8 micron) / 24 micron surface brightness
ratio shows significant variations across the disk of Circinus.Comment: 18 pages, 14 figures. All figures have been compressed. Contact
authors for original figures. Accepted by MNRA
The XMM Cluster Survey: Active Galactic Nuclei and Starburst Galaxies in XMMXCS J2215.9-1738 at z=1.46
We use Chandra X-ray and Spitzer infrared observations to explore the AGN and
starburst populations of XMMXCS J2215.9-1738 at z=1.46, one of the most distant
spectroscopically confirmed galaxy clusters known. The high resolution X-ray
imaging reveals that the cluster emission is contaminated by point sources that
were not resolved in XMM observations of the system, and have the effect of
hardening the spectrum, leading to the previously reported temperature for this
system being overestimated. From a joint spectroscopic analysis of the Chandra
and XMM data, the cluster is found to have temperature T=4.1_-0.9^+0.6 keV and
luminosity L_X=(2.92_-0.35^+0.24)x10^44 erg/s extrapolated to a radius of 2
Mpc. As a result of this revised analysis, the cluster is found to lie on the
sigma_v-T relation, but the cluster remains less luminous than would be
expected from self-similar evolution of the local L_X-T relation. Two of the
newly discovered X-ray AGN are cluster members, while a third object, which is
also a prominent 24 micron source, is found to have properties consistent with
it being a high redshift, highly obscured object in the background. We find a
total of eight >5 sigma 24 micron sources associated with cluster members (four
spectroscopically confirmed, and four selected using photometric redshifts),
and one additional 24 micron source with two possible optical/near-IR
counterparts that may be associated with the cluster. Examining the IRAC colors
of these sources, we find one object is likely to be an AGN. Assuming that the
other 24 micron sources are powered by star formation, their infrared
luminosities imply star formation rates ~100 M_sun/yr. We find that three of
these sources are located at projected distances of <250 kpc from the cluster
center, suggesting that a large amount of star formation may be taking place in
the cluster core, in contrast to clusters at low redshift.Comment: Accepted for publication in ApJ, 16 pages, 10 figure
The Atacama Cosmology Telescope: A Measurement of the Thermal Sunyaev-Zel'dovich Effect Using the Skewness of the CMB Temperature Distribution
We present a detection of the unnormalized skewness induced by the
thermal Sunyaev-Zel'dovich (tSZ) effect in filtered Atacama Cosmology Telescope
(ACT) 148 GHz cosmic microwave background temperature maps. Contamination due
to infrared and radio sources is minimized by template subtraction of resolved
sources and by constructing a mask using outlying values in the 218 GHz
(tSZ-null) ACT maps. We measure = -31 +- 6 \mu K^3 (measurement error
only) or +- 14 \mu K^3 (including cosmic variance error) in the filtered ACT
data, a 5-sigma detection. We show that the skewness is a sensitive probe of
sigma_8, and use analytic calculations and tSZ simulations to obtain
cosmological constraints from this measurement. From this signal alone we infer
a value of sigma_8= 0.79 +0.03 -0.03 (68 % C.L.) +0.06 -0.06 (95 % C.L.). Our
results demonstrate that measurements of non-Gaussianity can be a useful method
for characterizing the tSZ effect and extracting the underlying cosmological
information.Comment: 9 pages, 5 figures. Replaced with version accepted by Phys. Rev. D,
with improvements to the likelihood function and the IR source treatment;
only minor changes in the result
Interactions of Candida albicans with host epithelial surfaces
Candida albicans is an opportunistic, fungal pathogen of humans that frequently causes superficial infections
of oral and vaginal mucosal surfaces of debilitated and susceptible individuals. The organism is however,
commonly encountered as a commensal in healthy individuals where it is a component of the normal
microflora. The key determinant in the type of relationship that Candida has with its host is how it interacts
with the epithelial surface it colonises. A delicate balance clearly exists between the potentially damaging
effects of Candida virulence factors and the nature of the immune response elicited by the host. Frequently, it
is changes in host factors that lead to Candida seemingly changing from a commensal to pathogenic existence.
However, given the often reported heterogeneity in morphological and biochemical factors that exist between
Candida species and indeed strains of C. albicans, it may also be the fact that colonising strains differ in the
way they exploit resources to allow persistence at mucosal surfaces and as a consequence this too may affect
the way Candida interacts with epithelial cells. The aim of this review is to provide an overview of some of the
possible interactions that may occur between C. albicans and host epithelial surfaces that may in turn dictate
whether Candida removal, its commensal persistence or infection follows
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