7,026 research outputs found
Hydrogen Two-Photon Continuum Emission from the Horseshoe Filament in NGC 1275
Far ultraviolet emission has been detected from a knot of Halpha emission in
the Horseshoe filament, far out in the NGC 1275 nebula. The flux detected
relative to the brightness of the Halpha line in the same spatial region is
very close to that expected from Hydrogen two-photon continuum emission in the
particle heating model of Ferland et al. (2009) if reddening internal to the
filaments is taken into account. We find no need to invoke other sources of far
ultraviolet emission such as hot stars or emission lines from CIV in
intermediate temperature gas to explain these data.Comment: 9 pages, 8 figures. Accepted for publication in MNRA
How males can gain by harming their mates: Sexual conflict, seminal toxins, and the cost of mating
We suggest that damaging mating tactics, such as physical aggression, the evolution of genital barbs and spines, and the transfer of seminal toxins may serve as a general means by which males can induce females to avoid or to delay remating. Provided that cumulative damage has an accelerating impact on fitness, a female who has already been harmed by previous partner(s) may do best to refrain from remating to avoid suffering still further damage. Consequently, a male can gain through the imposition of mating costs, even though this may reduce female fitness because by doing so he minimizes the chances that his mate will copulate again. We develop a game theoretical model of this possibility, focusing on toxin transfer as an illustrative example. We show that toxicity as a means of inhibiting remating is phenotypically stable over a broad range of conditions (although, under some circumstances, it may be necessary to invoke other selective pressures to account for the initial evolution of toxicity). The model predicts that toxin transfer should be more common (and involve greater levels of toxicity) in species with greater last-male mating advantage; it is also most likely where the poison inflicts strongly accelerating, dose-dependent costs on females
ASCA and ROSAT observations of nearby cluster cooling flows
We present a detailed analysis of the X-ray properties of the cooling flows
in a sample of nearby, X-ray bright clusters of galaxies using high-quality
ASCA spectra and ROSAT X-ray images. We demonstrate the need for multiphase
models to consistently explain the spectral and imaging X-ray data for the
clusters. The mass deposition rates of the cooling flows, independently
determined from the ASCA spectra and ROSAT images, exhibit reasonable
agreement. We confirm the presence of intrinsic X-ray absorption in the
clusters using a variety of spectral models. We also report detections of
extended m infrared emission, spatially coincident with the cooling
flows, in several of the systems studied. The observed infrared fluxes and flux
limits are in good agreement with the predicted values due to reprocessed X-ray
emission from the cooling flows. We present precise measurements of the
abundances of iron, magnesium, silicon and sulphur in the central regions of
the Virgo and Centaurus clusters. Our results firmly favour models in which a
high mass fraction (70-80 per cent) of the iron in the X-ray gas in these
regions is due to Type Ia supernovae. Finally, we present a series of methods
which may be used to measure the ages of cooling flows from the X-ray data. The
results for the present sample of clusters indicate ages of between 2.5 and 7
Gyr. If the ages of cooling flows are primarily set by subcluster merger
events, then our results suggest that in the largest clusters, mergers with
subclusters with masses of approximately 30 per cent of the final cluster mass
are likely to disrupt cooling flows.Comment: Final version. MNRAS, in press. 36 pages, 9 figs, 14 tables in MNRAS
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Collisional excitation of [C II], [O I] and CO in Massive Galaxies
Many massive galaxies at the centres of relaxed galaxy clusters and groups
have vast reservoirs of cool (~10,000 K) and cold (~100 K) gas. In many low
redshift brightest group and cluster galaxies this gas is lifted into the hot
ISM in filamentary structures, which are long lived and are typically not
forming stars. Two important questions are how far do these reservoirs cool and
if cold gas is abundant what is the cause of the low star formation efficiency?
Heating and excitation of the filaments from collisions and mixing of hot
particles in the surrounding X-ray gas describes well the optical and near
infra-red line ratios observed in the filaments. In this paper we examine the
theoretical properties of dense, cold clouds emitting in the far infra-red and
submillimeter through the bright lines of [C II]157 \mu m , [O I]63 \mu m and
CO, exposed to these energetic ionising particles. While some emission lines
may be optically thick we find this is not sufficient to model the emission
line ratios. Models where the filaments are supported by thermal pressure
support alone also cannot account for the cold gas line ratios but a very
modest additional pressure support, either from turbulence or magnetic fields
can fit the observed [O I]/[C II] line ratios by decreasing the density of the
gas. This may also help stabilise the filaments against collapse leading to the
low rates of star formation. Finally we make predictions for the line ratios
expected from cold gas under these conditions and present diagnostic diagrams
for comparison with further observations. We provide our code as an Appendix.Comment: 17 pages, submitted to MNRA
Concordant cues in faces and voices: testing the backup signal hypothesis
Information from faces and voices combines to provide multimodal signals about a person. Faces and voices may offer redundant, overlapping (backup signals), or complementary information (multiple messages). This article reports two experiments which investigated the extent to which faces and voices deliver concordant information about dimensions of fitness and quality. In Experiment 1, participants rated faces and voices on scales for masculinity/femininity, age, health, height, and weight. The results showed that people make similar judgments from faces and voices, with particularly strong correlations for masculinity/femininity, health, and height. If, as these results suggest, faces and voices constitute backup signals for various dimensions, it is hypothetically possible that people would be able to accurately match novel faces and voices for identity. However, previous investigations into novel face–voice matching offer contradictory results. In Experiment 2, participants saw a face and heard a voice and were required to decide whether the face and voice belonged to the same person. Matching accuracy was significantly above chance level, suggesting that judgments made independently from faces and voices are sufficiently similar that people can match the two. Both sets of results were analyzed using multilevel modeling and are interpreted as being consistent with the backup signal hypothesis
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