6,934 research outputs found
Constraining ultra-compact dwarf galaxy formation with galaxy clusters in the local universe
We compare the predictions of a semi-analytic model for ultra-compact dwarf
galaxy (UCD) formation by tidal stripping to the observed properties of
globular clusters (GCs) and UCDs in the Fornax and Virgo clusters. For Fornax
we find the predicted number of stripped nuclei agrees very well with the
excess number of GCsUCDs above the GC luminosity function. GCsUCDs with
masses M are consistent with being entirely formed by tidal
stripping. Stripped nuclei can also account for Virgo UCDs with masses
M where numbers are complete by mass. For both Fornax and
Virgo, the predicted velocity dispersions and radial distributions of stripped
nuclei are consistent with that of UCDs within 50-100 kpc but disagree at
larger distances where dispersions are too high and radial distributions too
extended. Stripped nuclei are predicted to have radially biased anisotropies at
all radii, agreeing with Virgo UCDs at clustercentric distances larger than 50
kpc. However, ongoing disruption is not included in our model which would cause
orbits to become tangentially biased at small radii. We find the predicted
metallicities and central black hole masses of stripped nuclei agree well with
the metallicities and implied black hole masses of UCDs for masses
M. The predicted black hole masses also agree well with that of
M60-UCD1, the first UCD with a confirmed central black hole. These results
suggest that observed GCUCD populations are a combination of genuine GCs and
stripped nuclei, with the contribution of stripped nuclei increasing toward the
high-mass end.Comment: 18 pages, 12 figures, accepted for publication in MNRA
Contribution of stripped nuclear clusters to globular cluster and ultra-compact dwarf galaxy populations
We use the Millennium II cosmological simulation combined with the
semi-analytic galaxy formation model of Guo et al. (2011) to predict the
contribution of galactic nuclei formed by the tidal stripping of nucleated
dwarf galaxies to globular cluster (GC) and ultra-compact dwarf galaxy (UCD)
populations of galaxies. We follow the merger trees of galaxies in clusters
back in time and determine the absolute number and stellar masses of disrupted
galaxies. We assume that at all times nuclei have a distribution in
nucleus-to-galaxy mass and nucleation fraction of galaxies similar to that
observed in the present day universe. Our results show stripped nuclei follow a
mass function in the mass range ,
significantly flatter than found for globular clusters. The contribution of
stripped nuclei will therefore be most important among high-mass GCs and UCDs.
For the Milky Way we predict between 1 and 3 star clusters more massive than
come from tidally disrupted dwarf galaxies, with the most
massive cluster formed having a typical mass of a few times ,
like omega Centauri. For a galaxy cluster with a mass , similar to Fornax, we predict 19 UCDs more massive than
and 9 UCDs more massive than within
a projected distance of 300 kpc come from tidally stripped dwarf galaxies. The
observed number of UCDs are 200 and 23, respectively. We conclude that
most UCDs in galaxy clusters are probably simply the high mass end of the GC
mass function.Comment: 15 pages, 9 figures, accepted for publication in MNRA
On the continuity of the Volterra variational derivative
AbstractWe give a sufficient condition for the continuity of the Volterra variational derivative of a functional with respect to a fixed function. For linear functionals this condition is automatically satisfied, and so the Volterra variational derivative of a linear functional is always continuous
The Gauss–Green theorem and removable sets for PDEs in divergence form
AbstractApplying a very general Gauss–Green theorem established for the generalized Riemann integral, we obtain simple proofs of new results about removable sets of singularities for the Laplace and minimal surface equations. We treat simultaneously singularities with respect to differentiability and continuity
Atmospheric transport and deposition of Indonesian volcanic emissions
International audienceA regional climate model has been used to study the transport and deposition of sulfur (SO2 and SO42-) and PbCl2 emissions from Indonesian volcanoes. The sensitivity of the atmospheric loss of these trace species to meteorological conditions and their solubility was examined. Two experiments were conducted: 1) volcanic sulfur released as primarily SO2 and subject to transport, deposition, and oxidation to SO42-; and 2) PbCl2 released as an infinitely soluble passive tracer subject to only transport and deposition. The first experiment was used to calculate SO2 loss rates from each active Indonesian volcano producing an annual mean loss rate for all volcanoes of 1.1×10-5 s-1, or an e-folding rate of approximately 1 day. SO2 loss rate was found to vary seasonally, be poorly correlated with wind speed, and uncorrelated with temperature or relative humidity. The variability of SO2 loss rates is found to be correlated with the variability of wind speeds, suggesting that it is much more difficult to establish a "typical'' SO2 loss rate for volcanoes that are exposed to changeable winds. Within an average distance of 70 km away from the active Indonesian volcanoes, 53% of SO2 loss is due to conversion to SO42-, 42% due to dry deposition, and 5% due to lateral transport away from the dominant direction of plume travel. The solubility of volcanic emissions in water is shown to influence their atmospheric transport and deposition. High concentrations of PbCl2 are predicted to be deposited near to the volcanoes while volcanic S travels further away until removal from the atmosphere primarily via the wet deposition of H2SO4. The ratio of the concentration of PbCl2 to SO2 is found to exponentially decay at increasing distance from the volcanoes. The more rapid removal of highly soluble species should be considered when observing SO2 in an aged plume and relating this concentration to other volcanic species. An assumption that the ratio between the concentrations of highly soluble volcanic compounds and SO2 within a plume is equal to that observed in fumarolic gases is reasonable at small distances from the volcanic vent, but will result in an underestimation of the emission flux of highly soluble species
- …