21,969 research outputs found
Discovery of Counter-Rotating Gas in the Galaxies NGC1596 and NGC3203 and the Incidence of Gas Counter-Rotation in S0 Galaxies
We have identified two new galaxies with gas counter-rotation (NGC1596 and
NGC3203) and have confirmed similar behaviour in another one (NGC128), this
using results from separate studies of the ionized-gas and stellar kinematics
of a well-defined sample of 30 edge-on disc galaxies. Gas counter-rotators thus
represent 10+/-5% of our sample, but the fraction climbs to 21+/-11% when only
lenticular (S0) galaxies are considered and to 27+/-13% for S0s with detected
ionized-gas only. Those fractions are consistent with but slightly higher than
previous studies. A compilation from well-defined studies of S0s in the
literature yields fractions of 15+/-4% and 23+/-5%, respectively. Although
mainly based on circumstantial evidence, we argue that the counter-rotating gas
originates primarily from minor mergers and tidally-induced transfer of
material from nearby objects. Assuming isotropic accretion, twice those
fractions of objects must have undergone similar processes, underlining the
importance of (minor) accretion for galaxy evolution. Applications of gas
counter-rotators to barred galaxy dynamics are also discussed.Comment: 8 pages, including 1 table and 2 figures. Accepted for publication in
MNRAS. Version with full resolution figures available at
http://www-astro.physics.ox.ac.uk/~bureau/pub_list.htm
The Chandra Fornax Survey - I: The Cluster Environment
We present the first results of a deep Chandra survey of the inner 1 degree
of the Fornax cluster of galaxies. Ten 50 ksec pointings were obtained in a
mosaic centered on the giant elliptical galaxy NGC 1399 at the nominal cluster
center. Emission and temperature maps of Fornax are presented, and an initial
study of 771 detected X-ray point sources is made. Regions as small as 100pc
are resolved. The intra-cluster gas in Fornax exhibits a highly asymmetric
morphology and temperature structure, dominated by a 180 kpc extended ``plume''
of low surface brightness, cool, ~1 keV) gas to the North-East of NGC 1399 with
a sharper edge to the South West. The elliptical galaxy NGC 1404 also exhibits
a cool halo of X-ray gas within the cluster, with a highly sharpened leading
edge as it presumably falls into the cluster, and a cometary-like tail. We
estimate that some ~200-400 point sources are physically associated with
Fornax. Confirming earlier works, we find that the globular cluster population
in NGC 1399 is highly X-ray active, extending to globulars which may in fact be
intra-cluster systems. We have also found a remarkable correlation between the
location of giant and dwarf cluster galaxies and the presence of X-ray
counterparts, such that systems inhabiting regions of low gas density are more
likely to show X-ray activity. Not only does this correlate with the asymmetry
of the intra-cluster gas but also with the axis joining the center of Fornax to
an infalling group 1 Mpc to the South-West. We suggest that Fornax may be
experiencing an intergalactic ``headwind'' due to motion relative to the
surrounding large-scale structure.Comment: 35 pages, 15 figures, submitted to ApJ. Most figures not included
owing to severe compression degradation - we strongly recommend downloading
the full resolution paper from
http://www.astro.columbia.edu/~caleb/ms_highres.pdf (1.9Mb
Size matters: the value of small populations for wintering waterbirds
Protecting systematically selected areas of land is a major step towards biodiversity conservation worldwide. Indeed, the identification and designation of protected areas more often than not forms a core component of both national and international conservation policies. In this paper we provide an overview of those Special Protection Areas and Ramsar Sites that have been classified in Great Britain as of 1998/99 for a selection of wintering waterbird species, using bird count data from the Wetland Bird Survey.
The performance of this network of sites is remarkable, particularly in comparison with published analyses of networks elsewhere in the world. Nevertheless, the current site-based approach, whilst having the great benefit of simplicity, is deliberately biased towards aggregating species at the expense of the more dispersed distribution species. To ensure that the network continues successfully to protect nationally and internationally important waterbird populations, efforts now need to concentrate on the derivation of species-specific representation targets and, in particular, the ways in which these can be incorporated into the site selection process. Although these analyses concern the performance of protected areas for waterbirds in Great Britain, the results have wide-ranging importance for conservation planning in general and the design of protected area networks
Molecular Gas Properties of the Giant Molecular Cloud Complexes in the Arms and Inter-arms of the Spiral Galaxy NGC 6946
Combining observations of multiple CO lines with radiative transfer modeling
is a very powerful tool to investigate the physical properties of the molecular
gas in galaxies. Using new observations as well as literature data, we provide
the most complete CO ladders ever generated for eight star-forming regions in
the spiral arms and inter-arms of the spiral galaxy NGC 6946, with observations
of the CO(1-0), CO(2-1), CO(3-2), CO(4-3), CO(6-5), 13CO(1-0) and 13CO(2-1)
transitions. For each region, we use the large velocity gradient assumption to
derive beam-averaged molecular gas physical properties, namely the gas kinetic
temperature (T_K), H2 number volume density n(H2) and CO number column density
N(CO). Two complementary approaches are used to compare the observations with
the model predictions: chi-square minimisation and likelihood. The physical
conditions derived vary greatly from one region to the next: T_K=10-250 K,
n(H2)=10^2.3-10^7.0 cm^-3 and N(CO)=10^15.0-10^19.3 cm^-2. The spectral line
energy distribution (SLED) of some of these extranuclear regions indicates a
star-formation activity that is more intense than that at the centre of our own
Milky Way. The molecular gas in regions with a large SLED turnover transition
(J_max>4) is hot but tenuous with a high CO column density, while that in
regions with a low SLED turnover transition (J_max<=4) is cold but dense with a
low CO column density. We finally discuss and find some correlations between
the physical properties of the molecular gas in each region and the presence of
young stellar population indicators (supernova remnants, HII regions, HI holes,
etc.)Comment: 23 pages, 11 figures, MNRAS, Accepte
A black-hole mass measurement from molecular gas kinematics in NGC4526
The masses of the supermassive black-holes found in galaxy bulges are
correlated with a multitude of galaxy properties, leading to suggestions that
galaxies and black-holes may evolve together. The number of reliably measured
black-hole masses is small, and the number of methods for measuring them is
limited, holding back attempts to understand this co-evolution. Directly
measuring black-hole masses is currently possible with stellar kinematics (in
early-type galaxies), ionised-gas kinematics (in some spiral and early-type
galaxies) and in rare objects which have central maser emission. Here we report
that by modelling the effect of a black-hole on the kinematics of molecular gas
it is possible to fit interferometric observations of CO emission and thereby
accurately estimate black hole masses. We study the dynamics of the gas in the
early-type galaxy NGC4526, and obtain a best fit which requires the presence of
a central dark-object of 4.5(+4.2-3.0)x10^8 Msun (3 sigma confidence limit).
With next generation mm-interferometers (e.g. ALMA) these observations could be
reproduced in galaxies out to 75 megaparsecs in less the 5 hours of observing
time. The use of molecular gas as a kinematic tracer should thus allow one to
estimate black-hole masses in hundreds of galaxies in the local universe, many
more than accessible with current techniques.Comment: To appear in Nature online on 30/01/2013. 3 Pages, 2 Figures (plus
two pages of supplementary information
ISM chemistry in metal rich environments: molecular tracers of metallicity
In this paper we use observations of molecular tracers in metal rich and
alpha-enhanced galaxies to study the effect of abundance changes on molecular
chemistry. We selected a sample of metal rich spiral and star bursting objects
from the literature, and present here new data for a sample of early-type
galaxies (ETGs). We conducted the first survey of CS and methanol emission in
ETGs, detecting 7 objects in CS, and 5 in methanol emission. We find evidence
to support the hypothesis that CS is a better tracer of dense star-forming gas
than HCN. We suggest that the methanol emission in these sources is driven by
dust mantle destruction due to ionisation from high mass star formation, but
cannot rule out shocks dominating in some sources. The derived source averaged
CS/methanol column densities and rotation temperatures are similar to those
found in normal spiral and starburst galaxies, suggesting dense clouds are
little affected by the differences between galaxy types. Finally we used the
total column density ratios for our galaxy samples to show for the first time
that some molecular tracers do seem to show systematic variations that appear
to correlate with metallicity, and that these variations roughly match those
predicted by chemical models. Using this fact, the chemical models of Bayet et
al. (2012b), and assumptions about the optical depth we are able to roughly
predict the metallicity of our spiral and ETG sample, with a scatter of ~0.3
dex. We provide the community with linear approximations to the relationship
between the HCN and CS column density ratio and metallicity. Further study will
clearly be required to determine if this, or any, molecular tracer can be used
to robustly determine gas-phase metallically, but that a relationship exists at
all suggests that in the future it may be possible to calibrate a metallicity
indicator for the molecular interstellar medium (abridged).Comment: 14 pages, 9 figures. MNRAS, accepte
Gap Probabilities for Edge Intervals in Finite Gaussian and Jacobi Unitary Matrix Ensembles
The probabilities for gaps in the eigenvalue spectrum of the finite dimension
random matrix Hermite and Jacobi unitary ensembles on some
single and disconnected double intervals are found. These are cases where a
reflection symmetry exists and the probability factors into two other related
probabilities, defined on single intervals. Our investigation uses the system
of partial differential equations arising from the Fredholm determinant
expression for the gap probability and the differential-recurrence equations
satisfied by Hermite and Jacobi orthogonal polynomials. In our study we find
second and third order nonlinear ordinary differential equations defining the
probabilities in the general case. For N=1 and N=2 the probabilities and
thus the solution of the equations are given explicitly. An asymptotic
expansion for large gap size is obtained from the equation in the Hermite case,
and also studied is the scaling at the edge of the Hermite spectrum as , and the Jacobi to Hermite limit; these last two studies make
correspondence to other cases reported here or known previously. Moreover, the
differential equation arising in the Hermite ensemble is solved in terms of an
explicit rational function of a {Painlev\'e-V} transcendent and its derivative,
and an analogous solution is provided in the two Jacobi cases but this time
involving a {Painlev\'e-VI} transcendent.Comment: 32 pages, Latex2
Rate effects on layering of a confined linear alkane
We perform drainage experiments of a linear alkane fluid (n-hexadecane) down
to molecular thicknesses, and focus on the role played by the confinement rate.
We show that molecular layering is strongly influenced by the velocity at which
the confining walls are approached: under high enough shear rates, the confined
medium behaves as a structureless liquid of enhanced viscosity for film
thickness below 10 nm. Our results also lead us to conclude that a
rapidly confined film can be quenched in a metastable disordered state, which
might be related with recent intriguing results on the shear properties of
confined films produced at different rates [Zhu and Granick, Phys. Rev. Lett.
{\bf 93}, 096101 (2004)]
Learning subversion in the business school: An ‘improbable’ encounter
Entrepreneurs develop activities that aim to challenge the status quo, break rules and subvert systems. How can such a thing be taught/learnt in a business school? This article contributes to current debates within entrepreneurship studies that seek to address the subversive nature of entrepreneurial activity. It presents an ethnographic case study of an entrepreneurship course that attempts to re-define the teaching and learning boundaries of subversive activities in a leading European business school. Drawing on the theory of Bakhtin, which has thus far been overlooked in entrepreneurship studies, we unpick the potentiality of art practices in the learning and experiencing of the subversive dimension of entrepreneurship. We employ the concept of ‘dialogical pedagogy’ in order to address calls for more ‘relationally experienced’ approaches to management learning that foreground the conflicts, emotional strains and uncertainties that are embedded in the fabric of entrepreneurial practice. We show how ‘subversive dialogues’ are enacted between students and teachers as they engage in the learning process, and we discuss implications for critical entrepreneurship teaching in an increasingly commoditized education environment
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