1,234 research outputs found
Perception of Disease Risk and Vulnerability as a Function of Proximity to National Park Boundaries in East Africa
Studies suggest households closest to parks and protected areas (PAs) are more likely to sustain park-related losses, but the relationship between human sickness and PAs has not been fully explored. Existing literature primarily focuses on human-wildlife conflicts (i.e. crop raiding) and the potential for zoonotic disease spillover and emergence at the human-livestock-wildlife interface at PA boundaries. Understanding local perceptions of disease risk and vulnerability is essential for assessing human health relative to conservation areas. This understanding will promote better-informed consideration of human health impacts in decision making for conservation. Data from surveys taken at 301 households around Kibale National Park (KNP), an important conservation area, were used to identify risk perception and factors influencing perceived disease risk and vulnerability. Human sickness was the most frequently cited worry by respondents (88%) and malaria was the most frequently cited illness (80.1 %). Those living closer to PAs may be at greater risk for park-related harm and cited more frequent cases of malaria and non-malarial fever. The perception of high risk for human sickness is pervasive across the region independent of household distance to the park and actual disease risk
Halo and Relic Sources in Clusters of Galaxies
New images of 7 radio halos and relics, obtained with the Very Large Array at
20 or 90 cm, are presented here. The existence of a cluster-wide radio halo in
the clusters A 665 and CL 0016+16 is confirmed. Both these clusters share the
properties of the other clusters with radio halos, i.e. are luminous in X-rays,
have high temperature, and show recent merger processes. No diffuse sources are
detected in a sample of clusters showing at least a tailed radio galaxy within
300 kpc from the cluster center, indicating that the connection between tailed
radio galaxies and halos is not relevant. For these clusters we give limits to
the surface brightness and to the angular size of possible undetected diffuse
sources.Comment: 16 Figures in separated files. A large ps file with figures
(gg-aug00.ps.gz) in the text is avaialble at
ftp://terra.bo.cnr.it/papers/journals New Astronomy Vol. 5, p.335, in pres
Multifrequency VLA radio observations of the X-ray cavity cluster of galaxies RBS797: evidence of differently oriented jets
We report on the peculiar activity of the radio source located at the center
of the cooling flow cluster RBS797 (z=0.35), the first distant cluster in which
two pronounced X-ray cavities have been discovered. New multifrequency (1.4,
4.8, and 8.4 GHz) observations obtained with the Very Large Array clearly
reveal the presence of radio emission on three different scales showing
orientation in different directions, all of which indicates that RBS797
represents a very peculiar case. The lowest resolution images show large-scale
radio emission characterized by amorphous morphology and a steep spectrum,
extended on a scale of hundreds of kpc. On a scale of tens of kpc, there is
evidence of 1.4 GHz radio emission elongated in the northeast-southwest
direction exactly towards the holes detected in X-rays. The highest resolution
image shows the details of the innermost 4.8 GHz radio jets on a kpc scale;
they are remarkably oriented in a direction that is perpendicular to that of
the extended structure detected at a lower resolution. We therefore find
evidence of a strong interaction between the central radio source and the
intra-cluster medium in RBS797. We suggest a scenario in which the 1.4 GHz
emission filling the X-ray cavities consists of buoyant bubbles of radio
emitting plasma that are created by twin jets in the past and whose expansion
has displaced the thermal gas that was formerly in the X-ray holes, whereas the
two jets visible at 4.8 GHz are related to the present nuclear activity that
has restarted at a different position angle from the original outburst that
created the outer radio lobes. The total radio luminosity is ~ 10^42 erg/s,
corresponding to a factor of a few thousand times less than the estimated
cooling luminosity.Comment: 9 pages, 4 figures, accepted for publication in Astronomy &
Astrophysics; replaced with revised version corrected for language editin
Radio Halo and Relic Candidates from the NRAO VLA Sky Survey
We present the first results of the search of new halo and relic candidates
in the NRAO VLA Sky Survey. We have inspected a sample of 205 clusters from the
X-ray-brightest Abell-type clusters presented by Ebeling et al (1996), and
found 29 candidates. Out of them, 11 clusters are already known from the
literature to contain a diffuse cluster-wide source, while in 18 clusters this
is the first indication of the existence of this type of sources. We classify
these sources as halos or relics according to their location in the cluster
center or periphery, respectively. We find that the occurrence of cluster halos
and relics is higher in clusters with high X-ray luminosity and high
temperature. We also confirm the correlation between the absence of a cooling
flow and the presence of a radio halo at the cluster center.Comment: 25 Pages, 4 Figures included in the text, Figures 3a to 3g in
separated files. New Astronomy in pres
Diffuse radio emission from the Intracluster medium
An important aspect of the radio emission from galaxy clusters is represented
by the diffuse radio sources associated with the intracluster medium: radio
halos, relics and mini-halos. The radio halos and relics are indicators of
cluster mergers, whereas mini-halos are detected at the center of cooling core
clusters. SKA will dramatically improve the knowledge of these sources, thanks
to the detection of new objects, and to detailed studies of their spectra and
polarized emission. SKA will also provide the opportunity to investigate the
presence of halos produced by radiation scattered by a powerful radio galaxy at
the cluster centers.Comment: 8 pages, 6 figures, to appear in: "Science with the Square Kilometer
Array", eds. C. Carilli & S. Rawlings, New Astronomy Reviews, (Elsevier,
Amsterdam
Comparative analysis of the diffuse radio emission in the galaxy clusters A1835, A2029, and Ophiuchus
We recently performed a study of a sample of relaxed, cooling core galaxy
clusters with deep Very Large Array observations at 1.4 GHz. We find that in
the central regions of A1835, A2029, and Ophiuchus the dominant radio galaxy is
surrounded by a diffuse low-brightness radio emission that takes the form of a
mini-halo. Here we present the results of the analysis of the extended diffuse
radio emission in these mini-halos. In order to investigate the morphological
properties of the diffuse radio emission in clusters of galaxies we propose to
fit their azimuthally averaged brightness profile with an exponential,
obtaining the central brightness and the e-folding radius from which the radio
emissivity can be calculated. We investigate the radio properties of the
mini-halos in A1835, A2029, and Ophiuchus in comparison with the radio
properties of a representative sample of mini-halos and halos already known in
the literature. We find that radio halos can have quite different length-scales
but their emissivity is remarkably similar from one halo to the other. In
contrast, mini-halos span a wide range of radio emissivity. Some of them, like
the Perseus mini-halos, are characterized by a radio emissivity which is more
than 100 times greater than that of radio halos. On the other hand, the new
mini-halos in cooling core clusters analyzed in this work, namely A2029,
Ophiuchus, and A1835, have a radio emissivity which is much more typical of
halos in merging clusters rather than similar to that of the other mini-halos
previously known.Comment: 17 pages, 11 figures, A&A in press. For a version with high quality
figures, see http://erg.ca.astro.it/preprints/mini_halo_2
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