325 research outputs found
Multicolour Optical Imaging of IR-Warm Seyfert Galaxies. I. Introduction and Sample Selection
The standard AGN unification models attempt to explain the diversity of
observed AGN types by a few fundamental parameters, where orientation effects
play a paramount role. Whether other factors, such as the evolutionary stage
and the host galaxy properties are equally important parameters for the AGN
diversity, is a key issue that we are addressing with the present data. Our
sample of IR-selected Seyfert galaxies is based on the important discovery that
their integrated IR spectrum contains an AGN signature. This being an almost
isotropic property, our sample is much less affected by orientation/obscuration
effects compared to most Seyfert samples. It therefore provides a test-bed for
the orientation-dependent models of Seyferts, involving dusty tori. We have
obtained multi-colour broad and narrow band imaging for a sample of mid-IR
``warm'' Seyferts and for a control sample of mid-IR ``cold'' galaxies. In the
present paper we describe the sample selection and briefly discuss their IR
properties. We then give an overview of the data collected and present
broad-band images for all our objects. Finally, we summarize the main issues
that will be addressed with these data in a series of forthcoming papers.Comment: 18 pages including 3 figures and 5 tables (tables 1,4,5 are included
as independent files
COLA II - Radio and Spectroscopic Diagnostics of Nuclear Activity in Galaxies
We present optical spectroscopic observations of 93 galaxies taken from the
infra-red selected COLA (Compact Objects in Low Power AGN) sample. The sample
spans the range of far-IR luminosities from normal galaxies to LIRGs. Of the
galaxies observed, 78 (84%) exhibit emission lines. Using a theoretically-based
optical emission-line scheme we classify 15% of the emission-line galaxies as
Seyferts, 77% as starbursts, and the rest are either borderline AGN/starburst
or show ambiguous characteristics. We find little evidence for an increase in
the fraction of AGN in the sample as a function of far-IR luminosity but our
sample covers only a small range in infrared luminosity and thus a weak trend
may be masked. As a whole the Seyfert galaxies exhibit a small, but
significant, radio excess on the radio-FIR correlation compared to the galaxies
classified as starbursts. Compact (<0.05'') radio cores are detected in 55% of
the Seyfert galaxies, and these galaxies exhibit a significantly larger radio
excess than the Seyfert galaxies in which cores were not detected. Our results
indicate that there may be two distinct populations of Seyferts,
``radio-excess'' Seyferts, which exhibit extended radio structures and compact
radio cores, and ``radio-quiet'' Seyferts, in which the majority of the radio
emission can be attributed to star-formation in the host galaxy. No significant
difference is seen between the IR and optical spectroscopic properties of
Seyferts with and without radio cores. (Abridged)Comment: 24 pages, 4 figures, 6 tables. Accepted for publication in ApJ,
February 200
BATSE Observations of the Piccinotti Sample of AGN
BATSE Earth occultation data have been used to search for emission in the
20-100 keV band from all sources in the Piccinotti sample, which represents to
date the only complete 2-10 keV survey of the extragalactic sky down to a
limiting flux of 3.1 x 10^(-11) erg cm^(-2)$ s^(-1). Nearly four years of
observations have been analyzed to reach a 5sigma sensitivity level of about
7.8x 10^(-11) erg cm^(-2) s^(-1) in the band considered. Of the 36 sources in
the sample, 14 have been detected above 5sigma confidence level while marginal
detection (3<sigma<5) can be claimed for 13 sources; for 9 objects 2sigma upper
limits are reported. Comparison of BATSE results with data at higher energies
is used to estimate the robustness of our data analysis: while the detection
level of each source is reliable, the flux measurement maybe overestimated in
some sources by as much as 35%, probably due to incomplete data cleaning.
Comparison of BATSE fluxes with X-ray fluxes, obtained in the 2-10 keV range
and averaged over years, indicates that a canonical power law of photon index
1.7 gives a good description of the broad band spectra of bright AGNs and that
spectral breaks preferentially occur above 100 keV.Comment: 18 pages, 1 figure. Accepted for publication on Apj
Task shifting and integration of HIV care into primary care in South Africa: The development and content of the streamlining tasks and roles to expand treatment and care for HIV (STRETCH) intervention
Background: Task shifting and the integration of human immunodeficiency virus (HIV) care into primary care services have been identified as possible strategies for improving access to antiretroviral treatment (ART). This paper describes the development and content of an intervention involving these two strategies, as part of the Streamlining Tasks and Roles to Expand Treatment and Care for HIV (STRETCH) pragmatic randomised controlled trial. Methods: Developing the intervention: The intervention was developed following discussions with senior management, clinicians, and clinic staff. These discussions revealed that the establishment of separate antiretroviral treatment services for HIV had resulted in problems in accessing care due to the large number of patients at ART clinics. The intervention developed therefore combined the shifting from doctors to nurses of prescriptions of antiretrovirals (ARVs) for uncomplicated patients and the stepwise integration of HIV care into primary care services. Results: Components of the intervention: The intervention consisted of regulatory changes, training, and guidelines to support nurse ART prescription, local management teams, an implementation toolkit, and a flexible, phased introduction. Nurse supervisors were equipped to train intervention clinic nurses in ART prescription using outreach education and an integrated primary care guideline. Management teams were set up and a STRETCH coordinator was appointed to oversee the implementation process. Discussion: Three important processes were used in developing and implementing this intervention: active participation of clinic staff and local and provincial management, educational outreach to train nurses in intervention sites, and an external facilitator to support all stages of the intervention rollout
The AGN nature of 11 out of 12 Swift/RXTE unidentified sources through optical and X-ray spectroscopy
The Swift Burst Alert Telescope (BAT) is performing a high Galactic latitude
survey in the 14-195 keV band at a flux limit of ~10^{-11} erg cm^{-2} s^{-1},
leading to the discovery of new high energy sources, most of which have not so
far been properly classified. A similar work has also been performed with the
RXTE slew survey leading to the discovery of 68 sources detected above 8 keV,
many of which are still unclassified. Follow-up observations with the Swift
X-ray Telescope (XRT) provide, for many of these objects, source localization
with a positional accuracy of few arcsec, thus allowing the search for optical
counterparts to be more efficient and reliable. We present the results of
optical/X-ray follow-up studies of 11 Swift BAT detections and one AGN detected
in the RXTE Slew Survey, aimed at identifying their counterparts and at
assessing their nature. These data allowed, for the first time, the optical
classification of 8 objects and a distance determination for 3 of them. For
another object, a more refined optical classification than that available in
the literature is also provided. For the remaining sources, optical
spectroscopy provides a characterization of the source near in time to the
X-ray measurement. The sample consists of 6 Seyfert 2 galaxies, 5 Seyferts of
intermediate type 1.2-1.8, and one object of Galactic nature - an Intermediate
Polar (i.e., magnetic) Cataclysmic Variable. Out of the 11 AGNs, 8 (~70%)
including 2 Seyferts of type 1.2 and 1.5, are absorbed with NH > 10^{22}
cm^{-2}. Up to 3 objects could be Compton thick (i.e. NH > 1.5 x 10^{24}
cm^{-2}), but only in one case (Swift J0609.1-8636) does all the observational
evidence strongly suggests this possibility.Comment: 50 pages, including 16 figures and 7 tables. Accepted for publication
in Ap
Vertical heat flux and lateral mass transport in nonlinear internal waves
Author Posting. © American Geophysical Union, 2010. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 37 (2010): L08601, doi:10.1029/2010GL042715.Comprehensive observations of velocity, density, and turbulent dissipation permit quantification of the nonlinear internal wave (NLIW) contribution to vertical heat flux and lateral mass transport over New Jersey's shelf. The effect of NLIWs on the shelf heat budget was significant. On average, heat flux in NLIWs was 10 times larger than background at the pycnocline depth. NLIWs were present at midshelf <10% of the time, yet we estimate that they contributed roughly one−half the heat flux across the pycnocline during the observation period, which was characterized by weak to moderate winds. Lateral transport distances due to the leading 3 waves in NLIW packets were typically inline equation(100 m) but ranged several kilometers. The month-averaged daily onshore transport (per unit alongshelf dimension) by NLIWs is estimated as 0.3 m2s−1. This is comparable to a weak downwelling wind, but sustained over an entire month.This work was funded by the Office of Naval Research
Multimorbidity, control and treatment of noncommunicable diseases among primary healthcare attenders in the Western Cape, South Africa
Background. South Africa (SA) is facing a heavy burden of non-communicable diseases (NCDs). Few studies address multimorbidity, control and treatment of NCDs in patients attending primary healthcare (PHC) clinics. Objectives. To describe multimorbidity, related risk factors, disease severity and treatment status of patients with four important NCDs attending public sector PHC clinics in two districts in SA. Methods. A cross-sectional sample of patients completed baseline data collection for a randomised controlled trial of a health systems intervention. The study population comprised adults attending PHC clinics in the Eden and Overberg districts of the Western Cape in 2011. Four subgroups of patients were identified: hypertension, diabetes, chronic respiratory disease and depression. A total of 4 393 participants enrolled from 38 clinics completed a baseline structured questionnaire and had measurements taken. Prescription data were recorded. Results. Of participants with hypertension, diabetes, respiratory disease and depression, 80%, 92%, 88% and 80%, respectively, had at least one of the other three conditions. There were low levels of control and treatment: 59% of participants with hypertension had a blood pressure ≥140/90 mmHg, the mean haemoglobin A1c (HbA1c) value in participants with diabetes was 9%, 12% of participants in the depression group were prescribed an antidepressant at a therapeutic dose, and 48% of respiratory participants were prescribed a b2-agonist and 34% an inhaled corticosteroid. Conclusion. Considerable multimorbidity and unmet treatment needs exist among patients with NCDs attending public sector PHC clinics. Improved strategies are required for diagnosing and managing NCDs in this sector
A Comparison of the Intrinsic Shapes of Two Different Types of Dwarf Galaxies: Blues Compact Dwarfs and Dwarf Ellipticals
We measure the apparent shapes for a sample of 62 blue compact dwarf galaxies
(BCDs), and compare them with the apparent shapes for a sample of 80 dwarf
elliptical galaxies (dEs). The BCDs are flatter, on average, than the dEs, but
the difference is only marginally significant. We then use both non-parametric
and parametric techniques to determine possible distributions of intrinsic
shapes for the BCDs. The hypothesis that BCDs are oblate spheroids can be ruled
out with a high confidence level (), but the hypothesis that they are
prolate spheroids cannot be excluded. The apparent shapes of BCDs are totally
consistent with the hypothesis that they are triaxial ellipsoids. If the
intrinsic axis ratios, and , are distributed according to a
Gaussian with means and and standard deviation ,
we find the best-fitting distribution for BCDs has , while that for dEs has . Our results are consistent with the hypothesis that BCDs
have a close evolutionary relation with dEs.Comment: total 23 pages, 9 figures, and 1 Table, submitted to ApJ on Sep 19
1997. Email addresses: [email protected],
[email protected], [email protected],
[email protected], [email protected]
Spinflop transition in dopped antiferromagnets
In this paper we compute the mean field phase diagram of a doped
antiferromagnet, in a magnetic field and with anisotropic exchange. We show
that at zero temperature there is a metamagnetic transition from the
antiferromagnetic configuration along the z direction to a spin-flop state. In
the spin flop phase the system prefers a commensurate magnetic order, at low
doping, whereas at larger doping the incommensurate phase is favorable.
Contrary to the pure Heisenberg case, the spin flop region does not span an
infinite area in the ('Delta',h) plane, where 'Delta' is the exchange
anisotropy and h is the external magnetic field. We characterize the magnetic
and charge-transport properties of the spin-flop phase, computing the magnetic
susceptibility and the Drude weight. This latter quantity presents a sudden
variation as the spin-flop to paramagnet phase transition line is crossed. This
effect could be used as a possible source of large magneto-resistance. Our
findings may have some relevance for doped La_{2-\delta}Sr_{\delta}CuO_4 in a
magnetic field.Comment: 18 pages. accepted for Journal of Physics: Condensed Matte
Average luminosity distance in inhomogeneous universes
The paper studies the correction to the distance modulus induced by
inhomogeneities and averaged over all directions from a given observer. The
inhomogeneities are modeled as mass-compensated voids in random or regular
lattices within Swiss-cheese universes. Void radii below 300 Mpc are
considered, which are supported by current redshift surveys and limited by the
recently observed imprint such voids leave on CMB. The averaging over all
directions, performed by numerical ray tracing, is non-perturbative and
includes the supernovas inside the voids. Voids aligning along a certain
direction produce a cumulative gravitational lensing correction that increases
with their number. Such corrections are destroyed by the averaging over all
directions, even in non-randomized simple cubic void lattices. At low
redshifts, the average correction is not zero but decays with the peculiar
velocities and redshift. Its upper bound is provided by the maximal average
correction which assumes no random cancelations between different voids. It is
described well by a linear perturbation formula and, for the voids considered,
is 20% of the correction corresponding to the maximal peculiar velocity. The
average correction calculated in random and simple cubic void lattices is
severely damped below the predicted maximal one after a single void diameter.
That is traced to cancellations between the corrections from the fronts and
backs of different voids. All that implies that voids cannot imitate the effect
of dark energy unless they have radii and peculiar velocities much larger than
the currently observed. The results obtained allow one to readily predict the
redshift above which the direction-averaged fluctuation in the Hubble diagram
falls below a required precision and suggest a method to extract the background
Hubble constant from low redshift data without the need to correct for peculiar
velocities.Comment: 34 pages, 21 figures, matches the version accepted in JCA
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