73,898 research outputs found
What fraction of the density fluctuations in the Perseus cluster core is due to gas sloshing rather than AGN feedback?
Deep Chandra observations of the core of the Perseus cluster show a plethora
of complex structure. It has been found that when the observed density
fluctuations in the intracluster medium are converted into constraints on AGN
induced turbulence, the resulting turbulent heating rates are sufficient to
balance cooling locally throughout the central 220kpc. However while the
signatures of AGN feedback (inflated bubbles) dominate the central 60kpc in
X-ray images, beyond this radius the intracluster medium is increasingly shaped
by the effects of gas sloshing, which can also produce subtle variations in
X-ray surface brightness. We use mock Chandra observations of gas sloshing
simulations to investigate what fraction of the observed density fluctuations
in the core of the Perseus galaxy cluster may originate from sloshing rather
than AGN induced feedback. Outside 60kpc, we find that the observed level of
the density fluctuations is broadly consistent with being produced by sloshing
alone. If this is the case, AGN-generated turbulence is likely to be
insufficient in combating cooling outside 60kpc.Comment: 9 pages, 5 figures, accepted for publication in MNRA
Control of common scab without the use of water
The most effective way to control common scab is by irrigating a potato crop at tuber initiation. With the introduction of legislation such as the Water Framework Directive this will become increasingly difficult. In this field experiment, we assessed the potential of a number of non-water measures for controlling this disease. Common scab on daughter tubers at harvest was reduced by applying rapeseed meal at 1 t ha-1 to the beds and then incorporating it into the soil, and adding a mixture of Trichoderma viride isolates into the furrow at planting. None of these treatments was as effective as using water
Large scale gas sloshing out to half the virial radius in the strongest cool core REXCESS galaxy cluster, RXJ2014.8-2430
We search the cool core galaxy clusters in the REXCESS sample for evidence of
large scale gas sloshing, and find clear evidence for sloshing in
RXJ2014.8-2430, the strongest cool core cluster in the REXCESS cluster sample.
The residuals of the surface brightness distribution from the azimuthal average
for RXJ2014 show a prominent swirling excess feature extending out to an abrupt
surface brightness discontinuity at 800 kpc from the cluster core (half the
virial radius) to the south, which the XMM-Newton observations confirm to be
cold, low entropy gas. The gas temperature is significantly higher outside this
southern surface brightness discontinuity, indicating that this is a cold front
800 kpc from the cluster core. Chandra observations of the central 200 kpc show
two clear younger cold fronts on opposite sides of the cluster. The scenario
appears qualitatively consistent with simulations of gas sloshing due to minor
mergers which raise cold, low entropy gas from the core to higher radius,
resulting in a swirling distribution of opposing cold fronts at increasing
radii. However the scale of the observed sloshing is much larger than that
which has been simulated at present, and is similar to the large scale sloshing
recently observed in the Perseus cluster and Abell 2142.Comment: 5 pages, 5 figures. Accepted for publication in MNRA
An XMM-Newton view of the merging activity in the Centaurus cluster
We report the results of XMM-Newton observations of the regions around the
core of the Centaurus cluster where evidence for merging activity between the
subgroup Cen 45 and the main Centaurus cluster has previously been observed
using ASCA and ROSAT data. We confirm the ASCA findings of a temperature excess
surrounding Cen 45. We find that this temperature excess can be explained using
simple shock heating given the large line of sight velocity difference between
Cen 45 and the surrounding main Centaurus cluster. We find that there is a
statistically significant excess in metallicity around Cen 45, showing that Cen
45 has managed to retain its gas as it has interacted with the main Centaurus
cluster. There is a pressure excess to the east in the direction of the merger,
and there is also an entropy excess around the central galaxy of Cen 45. The
metallicity between 50-100 kpc to the north of NGC 4696 is higher than to the
south, which may be the result of the asymmetric distribution of metals due to
previous sloshing of the core, or which may be associated with the filamentary
structure we detect between NGC 4696 and NGC 4696B.Comment: 11 pages, 12 figures. Accepted for publication in MNRA
Constraining gas motions in the Centaurus cluster using X-ray surface brightness fluctuations and metal diffusion
We compare two different methods of constraining the characteristic velocity
and spatial scales of gas motions in the X-ray bright, nearby Centaurus
cluster, using new deep (760ks) Chandra observations. The power spectrum of
excess surface brightness fluctuations in the 0.5-6.0 keV band in a sector to
the west is measured and compared to theoretical expectations for Kolmogorov
index fluctuations. The observed power spectrum is flatter than these
expectations, and the surface brightness fluctuations are around the 8 percent
level on length scales of 2 kpc. We convert the 2D power spectrum of
fluctuations into a 3D power spectrum using the method of Churazov et al., and
then convert this into constraints on the one-component velocity of the gas
motions as a function of their length scale. We find one-component velocities
in the range 100-150 km/s on spatial scales of 4-10 kpc. An independent
constraint on the characteristic velocity and length scales of the gas motions
is then found by considering the diffusion coefficient needed to explain the
distribution of metals in the Centaurus cluster, combined with the need to
balance the rate of gas cooling with the rate of heat dissipated by the gas
motions. We find that these two methods of constraining the velocity and length
scales of the gas motions are in good agreement.Comment: 8 pages, 7 figures. Accepted for publication in MNRA
The effects on health of a publicly funded domestic heating programme: a prospective controlled study
<b>Objective</b>: To assess the effect of a publicly funded domestic heating programme on self-reported health.
<b>Design, setting and participants</b>: A prospective controlled study of 1281 households in Scotland receiving new central heating under a publicly funded initiative, and 1084 comparison households not receiving new heating. The main outcome measures were self-reported diagnosis of asthma, bronchitis, eczema, nasal allergy, heart disease, circulatory problems or high blood pressure; number of primary care encounters and hospital contacts in the past year; and SF-36 Health Survey scores.
<b>Results</b>: Usable data were obtained from 61.4% of 3849 respondents originally recruited. Heating recipients reported higher scores on the SF-36 Physical Functioning scale (difference 2.51; 95% CI 0.67 to 4.37) and General Health scale (difference 2.57; 95% CI 0.90 to 4.34). They were less likely to report having received a first diagnosis of heart disease (OR 0.69; 95% CI 0.52 to 0.91) or high blood pressure (OR 0.77; 95% CI 0.61 to 0.97), but the groups did not differ significantly in use of primary care or hospital services.
<b>Conclusions</b>: Provision of central heating was associated with significant positive effects on general health and physical functioning; however, effect sizes were small. Evidence of a reduced risk of first diagnosis with heart disease or high blood pressure must be interpreted with caution, due to the self-reported nature of the outcomes, the limited time period and the failure to detect any difference in health service use
The JCMT dense gas survey of the Perseus Molecular Cloud
We present the results of a large-scale survey of the very dense gas in the
Perseus molecular cloud using HCO+ and HCN (J = 4 - 3) transitions. We have
used this emission to trace the structure and kinematics of gas found in pre-
and protostellar cores, as well as in outflows. We compare the HCO+/HCN data,
highlighting regions where there is a marked discrepancy in the spectra of the
two emission lines. We use the HCO+ to identify positively protostellar
outflows and their driving sources, and present a statistical analysis of the
outflow properties that we derive from this tracer. We find that the relations
we calculate between the HCO+ outflow driving force and the Menv and Lbol of
the driving source are comparable to those obtained from similar outflow
analyses using 12CO, indicating that the two molecules give reliable estimates
of outflow properties. We also compare the HCO+ and the HCN in the outflows,
and find that the HCN traces only the most energetic outflows, the majority of
which are driven by young Class 0 sources. We analyse the abundances of HCN and
HCO+ in the particular case of the IRAS 2A outflows, and find that the HCN is
much more enhanced than the HCO+ in the outflow lobes. We suggest that this is
indicative of shock-enhancement of HCN along the length of the outflow; this
process is not so evident for HCO+, which is largely confined to the outflow
base.Comment: 25 pages, 14 figures, 9 table
- âŠ