19,775 research outputs found
Diffuse light and galaxy interactions in the core of nearby clusters
The kinematics of the diffuse light in the densest regions of the nearby
clusters can be unmasked using the planetary nebulae (PNs) as probes of the
stellar motions. The position-velocity diagrams around the brightest cluster
galaxies (BCGs) identify the relative contributions from the outer halos and
the intracluster light (ICL), defined as the light radiated by the stars
floating in the cluster potential. The kinematics of the ICL can then be used
to asses the dynamical status of the nearby cluster cores and to infer their
formation histories. The cores of the Virgo and Coma are observed to be far
from equilibrium, with mergers currently on-going, while the ICL properties in
the Fornax and Hydra clusters show the presence of sub-components being
accreted in their cores, but superposed to an otherwise relaxed population of
stars. Finally the comparison of the observed ICL properties with those
predicted from Lambda-CDM simulations indicates a qualitative agreement and
provides insights on the ICL formation. Both observations and simulations
indicate that BCG halos and ICL are physically distinct components, with the
``hotter" ICL dominating at large radial distances from the BCGs halos as the
latter become progressively fainter.Comment: 14 pages, 5 figures. Invited review to appear in the proceedings of
"Galaxies and their masks" eds. Block, D.L., Freeman, K.C. and Puerari, I.,
2010, Springer (New York
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Medieval property investors, ca. 1300-1500
This paper utilises a dataset of freehold land and property transactions from medieval England to highlight the growing commercialisation of the economy. By drawing on the legal records we are able to demonstrate that the medieval real estate market provided the opportunity for investors to profit. Careful analysis of the data provides evidence of group purchases, multiple transactions and investors buying outside of their own locality. The identification of these âinvestorsâ and their buying behaviours, set within the context of the English medieval economy, contributes to the early commercialisation debate
Compact Stellar Systems around NGC 1399
We have obtained spectroscopic redshifts of colour-selected point sources in
four wide area VLT-FLAMES fields around the Fornax Cluster giant elliptical
galaxy NGC 1399, identifying as cluster members 30 previously unknown faint
(-10.5<M_g'<-8.8) compact stellar systems (CSS), and improving redshift
accuracy for 23 previously catalogued CSS.
By amalgamating our results with CSS from previous 2dF observations and
excluding CSS dynamically associated with prominent (non-dwarf) galaxies
surrounding NGC 1399, we have isolated 80 `unbound' systems that are either
part of NGC 1399's globular cluster (GC) system or intracluster GCs. For these
unbound systems, we find (i) they are mostly located off the main stellar locus
in colour-colour space; (ii) their projected distribution about NGC 1399 is
anisotropic, following the Fornax Cluster galaxy distribution, and there is
weak evidence for group rotation about NGC 1399; (iii) their
completeness-adjusted radial surface density profile has a slope similar to
that of NGC 1399's inner GC system; (iv) their mean heliocentric recessional
velocity is between that of NGC 1399's inner GCs and that of the surrounding
dwarf galaxies, but their velocity dispersion is significantly lower; (v)
bright CSS (M_V<-11) are slightly redder than the fainter systems, suggesting
they have higher metallicity; (vi) CSS show no significant trend in
colour index with radial distance from NGC 1399.Comment: 13 pages (including supplementary table), 13 figures, 5 tables.
Accepted for publication in MNRA
AGN-Induced Cavities in NGC 1399 and NGC 4649
We present an analysis of archival Chandra and VLA observations of the E0
galaxy NGC 1399 and the E2 galaxy NGC 4649 in which we investigate cavities in
the surrounding X-ray emitting medium caused by the central AGN. We calculate
the jet power required for the AGN to evacuate these cavities and find values
of ~8x10^{41} erg/s and ~14x10^{41} erg/s for the lobes of NGC 1399 and
~7x10^{41} erg/s and ~6x10^{41} erg/s for those of NGC 4649. We also calculate
the k/f values for each cavity, where k is the ratio of the total particle
energy to that of electrons radiating in the range of 10 MHz to 10 GHz, and f
is the volume filling factor of the plasma in the cavity. We find that the
values of k/f for the lobes of NGC 1399 are ~93 and ~190, and those of the
lobes of NGC 4649 are ~15000 and ~12000. We conclude that the assumed spectrum
describes the electron distribution in the lobes of NGC 1399 reasonably well,
and that there are few entrained particles. For NGC 4649, either there are many
entrained particles or the model spectrum does not accurately describe the
population of electrons.Comment: 8 pages, 2 figures, accepted for publication in MNRA
Human Vulnerability to Climatic Dry Periods in the Prehistoric U.S. Southwest
abstract: This study investigates the vulnerability of subsistence agriculturalists to food shortfalls associated with dry periods. I approach this effort by evaluating prominent and often implicit conceptual models of vulnerability to dry periods used by archaeologists and other scholars investigating past human adaptations in dry climates. The conceptual models I evaluate rely on an assumption of regional-scale resource marginality and emphasize the contribution of demographic conditions (settlement population levels and watershed population density) and environmental conditions (settlement proximity to perennial rivers and annual precipitation levels) to vulnerability to dry periods. I evaluate the models and the spatial scales they might apply by identifying the extent to which these conditions influenced the relationship between dry-period severity and residential abandonment in central Arizona from A.D. 1200 to 1450. I use this long-term relationship as an indicator of potential vulnerability to dry periods. I use tree-ring precipitation and streamflow reconstructions to identify dry periods. Critically examining the relationship between precipitation conditions and residential abandonment potentially sparked by the risk of food shortfalls due to demographic and environmental conditions is a necessary step toward advancing understanding of the influences of changing climate conditions on human behavior. Results of this study support conceptual models that emphasize the contribution of high watershed population density and watershed-scale population-resource imbalances to relatively high vulnerability to dry periods. Models that emphasize the contribution of: (1) settlement population levels, (2) settlement locations distant from perennial rivers, (3) settlement locations in areas of low average annual precipitation; and (4) settlement-scale population-resource imbalances to relatively high vulnerability to dry periods are, however, not supported. Results also suggest that people living in watersheds with the greatest access to and availability of water were the most vulnerable to dry periods, or at least most likely to move when confronted with dry conditions. Thus, commonly held assumptions of differences in vulnerability due to settlement population levels and inherently water poor conditions are not supported. The assumption of regional-scale resource marginality and widespread vulnerability to dry periods in this region of the U.S. Southwest is also not consistently supported throughout the study area.Dissertation/ThesisPh.D. Anthropology 201
Fornax compact object survey FCOS: On the nature of Ultra Compact Dwarf galaxies
The results of the Fornax Compact Object Survey (FCOS) are presented. The
FCOS aims at investigating the nature of the Ultra Compact Dwarf galaxies
(UCDs) recently discovered in the center of the Fornax cluster (Drinkwater et
al. 2000). 280 unresolved objects in the magnitude space covering UCDs and
bright globular clusters (18<V<21 mag) were observed spectroscopically. 54 new
Fornax members were discovered, plus five of the seven already known UCDs.
Their distribution in radial velocity, colour, magnitude and space was
investigated. It is found that bright compact objects (V<20 or M_V<-11.4 mag),
including the UCDs, have a higher mean velocity than faint compact objects
(V>20 mag) at 96% confidence. The mean velocity of the bright compact objects
is consistent with that of the dwarf galaxy population in Fornax, but
inconsistent with that of NGC 1399's globular cluster system at 93.5%
confidence. The compact objects follow a colour magnitude relation with a slope
very similar to that of normal dEs, but shifted about 0.2 mag redwards. The
magnitude distribution of compact objects shows a fluent transition between
UCDs and GCs with an overpopulation of 8 +/- 4 objects for V<20 mag with
respect to the extrapolation of NGC 1399's GC luminosity function. The spatial
distribution of bright compact objects is in comparison to the faint ones more
extended at 88% confidence. All our findings are consistent with the threshing
scenario (Bekki et al. 2003), suggesting that a substantial fraction of compact
Fornax members brighter than V~20 mag could be created by threshing dE,Ns.
Fainter than V~20 mag, the majority of the objects seem to be genuine GCs. Our
results are also consistent with merged stellar super-clusters (Fellhauer &
Kroupa 2002) as an alternative explanation for the bright compact objects.Comment: 15 pages, 11 figures, accepted for publication in A&
Searching for rotating galaxy clusters in SDSS and 2dFGRS
We present a result of searching for galaxy clusters that show an indication
of global rotation using a spectroscopic sample of galaxies in SDSS and 2dFGRS.
We have determined the member galaxies of 899 Abell clusters covered in SDSS
and 2dFGRS using the redshift and the positional data of galaxies, and have
estimated the ratio of the cluster rotation amplitude to the cluster velocity
dispersion and the velocity gradient across the cluster. We have found 12
tentative rotating clusters that have large ratios of rotation amplitude to
dispersion and large velocity gradients. We have determined the morphological
parameters for 12 tentative rotating clusters using the positional information
of the member galaxies: the ellipticity of the dispersion ellipse is in the
range of 0.080.57, and the position angle of major or minor axis does not
appear to be related to the position angle of rotation axis. We have
investigated the substructures in the sample of tentative rotating clusters,
finding from the Dressler-Shectman plots that the majority (9 out of 12) of
clusters show an evidence of substructure due to the spatially correlated
velocities of galaxies. We have selected six probable rotating clusters (A0954,
A1139, A1399, A2162, A2169, and A2366) that show a single number density peak
around the cluster center with a spatial segregation of the high and low
velocity galaxies. We have found no strong evidences of a recent merging for
the probable rotating clusters: the probable rotating clusters do not deviate
significantly from the relation of the X-ray luminosity and the velocity
dispersion or the virial mass of the clusters, and two probable rotating
clusters (A0954 and A1399) have small values of the peculiar velocities and the
clustercentric distances of the brightest cluster galaxies.Comment: 33 pages, 9 figures. To appear in Ap
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