46 research outputs found
The Effect of Helium Sedimentation on Galaxy Cluster Masses and Scaling Relations
Recent theoretical studies predict that the inner regions of galaxy clusters
may have an enhanced helium abundance due to sedimentation over the cluster
lifetime. If sedimentation is not suppressed (e.g., by tangled magnetic
fields), this may significantly affect the cluster mass estimates. We use
Chandra X-ray observations of eight relaxed galaxy clusters to investigate the
upper limits to the effect of helium sedimentation on the measurement of
cluster masses and the best-fit slopes of the Y_X - M_500 and Y_X - M_2500
scaling relations. We calculated gas mass and total mass in two limiting cases:
a uniform, un-enhanced abundance distribution and a radial distribution from
numerical simulations of helium sedimentation on a timescale of 11 Gyrs. The
assumed helium sedimentation model, on average, produces a negligible increase
in the gas mass inferred within large radii (r < r500) (1.3 +/- 1.2 per cent)
and a (10.2 +/- 5.5) per cent mean decrease in the total mass inferred within r
< r500. Significantly stronger effects in the gas mass (10.5 +/- 0.8 per cent)
and total mass (25.1 +/- 1.1 per cent) are seen at small radii owing to a
larger variance in helium abundance in the inner region, r < 0.1 r500. We find
that the slope of the Y_X -M_500 scaling relation is not significantly affected
by helium sedimentation.Comment: 11 pages, accepted for publication in Astronomy and Astrophysic
Heating cooling flows with jets
Active galactic nuclei are clearly heating gas in `cooling flows'. The
effectiveness and spatial distribution of the heating are controversial. We use
three-dimensional simulations on adaptive grids to study the impact on a
cooling flow of weak, subrelativistic jets. The simulations show cavities and
vortex rings as in the observations. The cavities are fast-expanding dynamical
objects rather than buoyant bubbles as previously modelled, but shocks still
remain extremely hard to detect with X-rays. At late times the cavities turn
into overdensities that strongly excite the cluster's g-modes. These modes damp
on a long timescale. Radial mixing is shown to be an important phenomenon, but
the jets weaken the metallicity gradient only very near the centre. The central
entropy density is modestly increased by the jets. We use a novel algorithm to
impose the jets on the simulations.Comment: 16 pages, 15 figures. Accepted for publication in MNRAS. Revised
version taking referee's comments into account, minor changes.
High-resolution version and MPEGs can be found at
http://www.clusterheating.org/papers.ph
An approach to understanding hydrologic connectivity on the hillslope and the implications for nutrient transport
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94780/1/gbc975.pd
Evapotranspiration and Runoff from Large Land Areas: Land Surface Hydrology for Atmospheric General Circulation Models
Evapotranspiration and runoff from large land areas: Land surface hydrology for atmospheric general circulation models
Cabauw Experimental Results from the Project for Intercomparison of Land-Surface Parameterization Schemes
Recommended from our members
Using Similarity Theory to Parameterize Mesoscale Heat Fluxes Generated by Subgrid-Scale Landscape Discontinuities in GCMs
Calculations of river-runoff in the giss GCM - impact of a new land-surface paramatrization and runoff routing model on the hydrology of the Amazon river
This study examines the impact of a new land-surface parameterization and a river routing scheme on the hydrology of the Amazon basin, as depicted by the NASA/Goddard Institute of Space Studies (GISS) global climate model (GCM). The more physically realistic land surface scheme introduces a vegetation canopy resistance and a six-layer soil system. The new routing scheme allows runoff to travel from a river's headwater to its mouth according to topography and other channel characteristics and improves the timing of the peak flow. River runoff is examined near the mouth of the Amazon and for all of its sub-basins. With the new land-surface parameterization, river runoff increases significantly and is consistent with that observed in most basins and at the mouth. The representation of the river hydrology in small basins is not as satisfactory as in larger basins. One positive impact of the new land-surface parameterization is that it produces more realistic evaporation over the Amazon basin, which was too high in the previous version of the GCM. The realistic depiction of evaporation also affects the thermal regime in the lower atmosphere in the Amazon. In fact, the lower evaporation in some portions of the basin reduces the cloudiness, increases the solar radiation reaching the ground, increases the net radiation at the surface, and warms the surface as compared to observations. Further GCM improvement is needed to obtain a better representation of rainfall processes.Pages: 349-36