1,167 research outputs found
Social enterprise as a model for developing Aboriginal lands
AbstractCommon property (communal land) is often viewed negatively with some claiming that communal land ownership and the absence of private property rights more generally have been insurmountable barriers to Indigenous enterprise. This paper provides a brief overview of common property resources and explores how Aboriginal common property is being used by some Aboriginal groups to develop social enterprises that provide benefits to remote communities, the environment and wider Australia. It notes that while some conservation and philanthropic organisations recognise this and have begun to work with and invest in these enterprises, government support often remains risk averse
The impact of spheroid stars for Macho microlensing surveys of the Andromeda Galaxy
The Andromeda Galaxy (M31) is an important test case for a number of
microlensing surveys looking for massive compact halo objects (Machos). A
long-standing theoretical prediction is that the high inclination of the M31
disk should induce an asymmetry in the spatial distribution of M31 Macho
events, whilst the distribution of variable stars and microlensing events in
the M31 disk should be symmetric. We examine the role of stars in the M31
visible spheroid as both lenses and sources to microlensing events. We compute
microlensing event number density maps and estimate pixel-lensing rates and
event durations for three-component models of M31 which are consistent with the
observed rotation curve, surface brightness profile and dynamical mass
estimates. Three extreme models are considered: a massive spheroid model; a
massive disk model; and a massive Macho halo model. An important consequence of
the spheroid is that, even if Machos are absent in M31, an asymmetric spatial
signature is still generally expected from stellar lensing alone. The relative
mass-to-light ratio of the spheroid and disk populations controls which of
these signatures dominates the overall stellar spatial distribution. We find
that the inclusion of the spheroid weakens the M31 Macho spatial asymmetry by
about 20-30% over a disk-only asymmetry for the models considered. We also find
for our models that Machos dominate over most of the far disk provided they
contribute at least ~25% of the halo dark matter density. The presence of the
spheroid also has beneficial consequences for M31 lensing surveys. The stellar
asymmetry is likely to be important in distinguishing between a spheroidal
Macho halo or a highly flattened halo or dark matter dominated disk, since
spatial asymmetries of opposing signs are expected in these cases. (Abridged)Comment: 10 pages. Accepted for publication in MNRA
Microlensing Halo Models with Abundant Brown Dwarfs
All previous attempts to understand the microlensing results towards the
Large Magellanic Cloud (LMC) have assumed homogeneous present day mass
functions (PDMFs) for the lensing populations. Here, we present an
investigation into the microlensing characteristics of haloes with spatially
varying PDMFs and anisotropic velocity dispersion tensors. One attractive
possibility -- suggested by baryonic dark cluster formation in pregalactic and
protogalactic cooling flows -- is that the inner halo is dominated by stellar
mass objects, whereas low mass brown dwarfs become more prevalent on moving
outwards. The contribution to the microlensing rate must be dominated by dark
remnants (of about 0.5 solar masses) to recover the observed timescales of the
microlensing experiments. But, even though stellar remnants control the rate,
they do not dominate the mass of the baryonic halo, and so the well-known
enrichment and mass budget problems are much less severe. Using a simple ansatz
for the spatial variation of the PDMF, models are constructed in which the
contribution of brown dwarfs to the mass of the baryonic halo is 55 % and to
the total halo is 30 %. An unusual property of the models is that they predict
that the average timescale of events towards M31 is shorter than the average
timescale towards the LMC. This is because the longer line of sight towards M31
probes more of the far halo where brown dwarfs are the most common constituent.Comment: 17 pages, 1 figure, in press at The Astrophysical Journal (Letters
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