4,916 research outputs found
Gas entropy in a representative sample of nearby X-ray galaxy clusters (REXCESS): relationship to gas mass fraction
No full textWe examine the radial entropy distribution and its scaling using 31 nearby galaxy clusters from the representative XMM-Newton cluster structure survey (REXCESS), a sample in the temperature range 2-9 keV selected in X-ray luminosity only, with no bias toward any particular morphological type. The entropy profiles are robustly measured at least out to R1000 in all systems and out to R500 in thirteen systems. Compared to theoretical expectations from non-radiative cosmological simulations, the observed distributions show a radial and mass-dependent excess entropy, such that the excess is greater and extends to larger radii in lower mass systems. At R500, the mass dependence and entropy excess are both negligible within the large observational and theoretical uncertainties. Mirroring this behaviour, the scaling of gas entropy is shallower than self-similar in the inner regions, but steepens with radius, becoming consistent with self-similar at R500. There is a large dispersion in scaled entropy in the inner regions, apparently linked to the presence of cool cores and dynamical activity; at larger radii the dispersion decreases by approximately a factor of two to 30 per cent, and the dichotomy between subsamples disappears. There are two peaks in the distribution of both inner slope and, after parameterising the profiles with a power law plus constant model, in central entropy K0. However, we are unable to distinguish between a bimodal or a left-skewed distribution of K0 with the present data. The distribution of outer slopes is unimodal with a median value of 0.98, and there is a clear correlation of outer slope with temperature. Renormalising the dimensionless entropy profiles by the gas mass fraction profile fgas (<R), leads to a remarkable reduction in the scatter, implying that gas mass fraction variations with radius and mass are the cause of the observed entropy structural and scaling properties. The results are consistent with the picture of a cluster population in which entropy modification is centrally concentrated and extends to larger radii at lower mass, leading to both a radial and a mass-dependence in the gas mass fraction, but which is increasingly self-similar at large radius. The observed normalisation, however, would suggest entropy modification at least up to R1000, and even beyond, in all but the most massive systems. We discuss a tentative scenario to explain the observed behaviour of the entropy and gas mass fraction in the REXCESS sample, in which a combination of extra heating and merger mixing maintains an elevated central entropy level in the majority of the population, and a smaller fraction of systems is able to develop a cool core. <br/
Extramural -- 1944-1953 -- Correspondence, Military Service, Dengue -- letter, 1944-07-12
No full textLetter from Bower, Albert G. to Paul, John R. dated 1944-07-12.Sabin Collection Fair Use Policy</a
On the evolutionary status of early-type galaxies in clusters at z~0.2 - I. The Fundamental Plane
No full textWe investigate a spectroscopic sample of 48 early-type (E+S0) galaxies in the rich cluster Abell 2390 (z=0.23) and 48 E+S0 galaxies from a previously published survey of Abell 2218 (z=0.18). The A2390 spectra are based on Multi Object Spectroscopy with MOSCA at the Calar Alto 3.5-m, complemented by ground-based and HST F555W and F814W observations. Our investigation spans a broad range in luminosity (-20.5>M_r>-23.0) and a wide FOV of 1.5x1.5 Mpc^2. Since the A2218 and A2390 samples are very similar, we can combine them and analyse a total of 96 E+S0 galaxies at z~0.2. We construct the Faber-Jackson relation (FJR) for all E+S0s and detect a modest luminosity evolution. The average offset from the local FJR in Gunn r-band is (DeltaM_r)=0.32+-0.22^m. Less-massive galaxies show a trend for a larger evolution than more-massive galaxies. HST/WFPC2 surface brightness profile fits were used to derive structural parameters. For 34 E+S0 galaxies which enter the Fundamental Plane (FP) we deduce a mild evolution in Gunn r with a zero-point offset of 0.10+-0.06, corresponding to 0.31+-0.18^m. Elliptical and lenticular galaxies are uniformly distributed along the FP with a similar scatter of 0.1 dex. We find little evidence for differences between the populations of ellipticals and S0s. Lenticulars induce on average a larger evolution of 0.44+-0.18^m than ellipticals with 0.02+-0.21^m. The M/L ratios at z=0.2 are offset by (Deltalog(M/L_r))=-0.12+-0.06 dex compared to those of Coma. Our results can be reconciled with a passive evolution of the stellar populations and a high formation redshift for the bulk of the stars in E+S0 galaxies. However, our findings are also consistent with the hierarchical formation picture for rich clusters. [abridged
Implications of pollination by food and sexual deception for pollinator specificity, fruit set, population genetics and conservation of Caladenia (Orchidaceae)
No full text© CSIRO 2009Caladenia is very unusual in that it contains species that attract pollinators by two different strategies, food and sexual deception. Among the sexually deceptive species, baiting for pollinators has shown that within populations orchid species are typically pollinated by a single species of thynnine wasp. However, some wasp species can be pollinators of more than one species of orchid usually when their ranges do not overlap. There is a trend for closely related orchids to exploit wasps from the same genus, with different lineages of orchids often pollinated by different genera. Very little is known about pollination of food-deceptive Caladenia species, although it is evident they attract a suite of generalist food-seeking insects. Food-deceptive species have a higher pollination rate than do sexually deceptive species. Studies of population genetics and pollen movements are few, although they suggest a pattern of fine-scale genetic structuring within populations, owing to predominantly restricted seed dispersal and low genetic differentiation among populations as a consequence of rare long-distance seed-dispersal events. Both evolutionary and ecological research of Caladenia will greatly benefit from a better understanding of the insect species involved in pollination, their ecological requirements and the ecological and genetic consequences of food and sexual deception.Ryan D. Phillips, Renate Faast, Colin C. Bower, Graham R. Brown and Rod Peakal
From star‐forming spirals to passive spheroids: integral field spectroscopy of E+A galaxies
No full textWe present three‐dimensional spectroscopy of 11 E+A galaxies at z = 0.06–0.12. These galaxies were selected for their strong Hδ absorption but weak (or non‐existent) [O ii ] λ3727 and Hα emission. This selection suggests that a recent burst of star formation was triggered but subsequently abruptly ended. We probe the spatial and spectral properties of both the young (≲1 Gyr) and old (≳few Gyr) stellar populations. Using the Hδ equivalent widths we estimate that the burst masses must have been at least 10 per cent by mass ( M burst ≳ 10 10 M ⊙ ), which is also consistent with the star formation history inferred from the broad‐band spectral energy distributions. On average the A stars cover ∼33 per cent of the galaxy image, extending over 2–15 kpc 2 , indicating that the characteristic E+A signature is a property of the galaxy as a whole and not due to a heterogeneous mixture of populations. In approximately half of the sample, we find that the A stars, nebular emission and continuum emission are not co‐located, suggesting that the newest stars are forming in a different place than those that formed ≲1 Gyr ago, and that recent star formation has occurred in regions distinct from the oldest stellar populations. At least 10 of the galaxies (91 per cent) have dynamics that class them as ‘fast rotators’ with magnitudes, v /σ, λ R and bulge‐to‐total (B/T) ratio comparable to local, representative ellipticals and S0s. We also find a correlation between the spatial extent of the A stars and the dynamical state of the galaxy such that the fastest rotators tend to have the most compact A star populations, providing new constraints on models that aim to explain the transformation of later type galaxies into early types. Finally, we show that there are no obvious differences between the line extents and kinematics of E+A galaxies detected in the radio (active galactic nucleus, AGN) compared to non‐radio sources, suggesting that AGN feedback does not play a dramatic role in defining their properties, and/or that its effects are short.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90164/1/j.1365-2966.2011.20082.x.pd
The early-type galaxy population in Abell 2218
No full text(Abridged) We present morphological, photometric, kinematic and line-strength data of 48 early-type members of the rich cluster Abell 2218 at z=0.18. This sample is both larger and spans a wider galaxy luminosity range, down to M*_B+1, than previous studies. We compare A2218 with similar samples drawn from local clusters to identify evolutionary changes between the samples which have occured over the last 3Gyrs. The overall picture is one of little or no evolution in nearly all galaxy parameters. Zeropoint offsets in the Faber--Jackson, Mg_b-sigma and Fundamental Plane relations are all consistent with passively evolving stellar populations. The slopes of these relations have not changed significantly. We do however find a significant spread in the estimated luminosity-weighted ages of the stellar populations in the galaxies, based on line diagnostic diagrams. This age spread is seen in both the disky early-type galaxies (S0) and also the ellipticals. We observe both ellipticals with a strong contribution from a young stellar population and lenticulars dominated by old stellar populations. On average, we find no evidence for systematic differences between the populations of ellipticals and lenticulars. This points to a common formation epoch for the bulk of the stars in most of the early-type galaxies in A2218. This result can be reconciled with the claims of rapid morphological evolution in distant clusters if the suggested transformation from spirals to lenticulars does not involve significant new star formation
The Evolutionary Status of Early-type Galaxies in Abell 2390
No full textWe explore the evolution of the early-type galaxy population in the rich cluster Abell 2390 at z=0.23. For this purpose, we have obtained spectroscopic data of 51 elliptical and lenticular galaxies with MOSCA at the 3.5 m telescope on Calar Alto Observatory. As our investigation spans both a broad range in luminosity (-22.
Extramural -- 1944-1953 -- Correspondence, Military Service, Dengue -- letter, 1944-07-18
No full textLetter from Paul, John R. to Bower, Albert G. dated 1944-07-18.Sabin Collection Fair Use Policy</a
The baryonic and dark matter properties of high-redshift gravitationally lensed disc galaxies
No full textWe present a detailed study of the structural properties of four gravitationally lensed disc galaxies at z = 1. Modelling the rotation curves on sub-kpc scales, we derive the values for the disc mass, the reference dark matter density and core radius, and the angular momentum per unit mass. The derived models suggest that the rotation curve profile and amplitude are best fitted with a dark matter component similar to those of local spiral galaxies. The stellar component also has a similar length-scale, but with substantially smaller masses than similarly luminous disc galaxies in the local Universe. Comparing the average dark matter density inside the optical radius, we find that the disc galaxies at z = 1 have larger densities (by up to a factor of ~7) than similar disc galaxies in the local Universe. Furthermore, the angular momentum per unit mass versus reference velocity is well matched to the local relation, suggesting that the angular momentum of the disc remains constant between high redshifts and the present day. Though statistically limited, these observations point towards a spirals' formation scenario in which stellar discs are slowly grown by the accretion of angular momentum conserving material
Improving outcomes for the treatment of Anal Squamous Cell Carcinoma and Anal Intraepithelial Neoplasia
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