177 research outputs found
Bounds on the mass and abundance of dark compact objects and black holes in dwarf spheroidal galaxy halos
We establish new dynamical constraints on the mass and abundance of compact
objects in the halo of dwarf spheroidal galaxies. In order to preserve
kinematically cold the second peak of the Ursa Minor dwarf spheroidal (UMi
dSph) against gravitational scattering, we place upper limits on the density of
compact objects as a function of their assumed mass. The mass of the dark
matter constituents cannot be larger than 1000 solar masses at a halo density
in UMi's core of 0.35 solar masses/pc^3. This constraint rules out a scenario
in which dark halo cores are formed by two-body relaxation processes. Our
bounds on the fraction of dark matter in compact objects with masses >3000
solar masses improve those based on dynamical arguments in the Galactic halo.
In particular, objects with masses solar masses can comprise no
more than a halo mass fraction . Better determinations of the
velocity dispersion of old overdense regions in dSphs may result in more
stringent constraints on the mass of halo objects. For illustration, if the
preliminary value of 0.5 km/s for the secondary peak of UMi is confirmed,
compact objects with masses above solar masses could be excluded
from comprising all its dark matter halo.Comment: 6 pages, 2 figures, accepted for publication in ApJ Letter
Pulmonary rehabilitation in chronic obstructive pulmonary disease: Outcomes in a 12 week programme
The thickness of HI in galactic discs under MOND: theory and application to the Galaxy
The outskirts of galaxies are a very good laboratory for testing the nature
of the gravitational field at low accelerations. By assuming that the neutral
hydrogen gas is in hydrostatic equilibrium in the gravitational potential of
the host galaxy, the observed flaring of the gas layer can be used to test
modified gravities. For the first time we construct a simple framework to
derive the scaleheight of the neutral hydrogen gas disc in the MOND scenario
and apply this to the Milky Way. It is shown that using a constant gas velocity
dispersion of ~9 km/s, MOND is able to give a very good fit to the observed HI
flaring beyond a galactocentric distance of 17 kpc up to the last measured
point (~40 kpc). Between 10 and 16 kpc, however, the observed scaleheight is
about 40% more than what MOND predicts for the standard interpolating function
and 70% for the form suggested by Famaey & Binney. Given the uncertainties in
the non-thermal pressure support by cosmic rays and magnetic fields, MOND seems
to be a plausible alternative to dark matter in explaining the Milky Way
flaring. Studying the flaring of extended HI discs in external edge-on galaxies
may be a promising approach to assess the viability of MOND.Comment: 13 pages, 4 figure
The orbital poles of Milky Way satellite galaxies: a rotationally supported disc-of-satellites
Available proper motion measurements of Milky Way (MW) satellite galaxies are
used to calculate their orbital poles and projected uncertainties. These are
compared to a set of recent cold dark-matter (CDM) simulations, tailored
specifically to solve the MW satellite problem. We show that the CDM satellite
orbital poles are fully consistent with being drawn from a random distribution,
while the MW satellite orbital poles indicate that the disc-of-satellites of
the Milky Way is rotationally supported. Furthermore, the bootstrapping
analysis of the spatial distribution of theoretical CDM satellites also shows
that they are consistent with being randomly drawn. The theoretical CDM
satellite population thus shows a significantly different orbital and spatial
distribution than the MW satellites, most probably indicating that the majority
of the latter are of tidal origin rather than being DM dominated
sub-structures. A statistic is presented that can be used to test a possible
correlation of satellite galaxy orbits with their spatial distribution.Comment: Accepted for publication in Ap
Distant star clusters of the Milky Way in MOND
We determine the mean velocity dispersion of six Galactic outer halo globular
clusters, AM 1, Eridanus, Pal 3, Pal 4, Pal 15, and Arp 2 in the weak
acceleration regime to test classical vs. modified Newtonian dynamics (MOND).
Owing to the non-linearity of MOND's Poisson equation, beyond tidal effects,
the internal dynamics of clusters is affected by the external field in which
they are immersed. For the studied clusters, particle accelerations are much
lower than the critical acceleration a_0 of MOND, but the motion of stars is
neither dominated by internal accelerations (a_i >> a_e) nor external
accelerations (a_e >> a_i). We use the N-body code N-MODY in our analysis,
which is a particle-mesh-based code with a numerical MOND potential solver
developed by Ciotti, Londrillo, and Nipoti (2006) to derive the line-of-sight
velocity dispersion by adding the external field effect. We show that Newtonian
dynamics predicts a low-velocity dispersion for each cluster, while in modified
Newtonian dynamics the velocity dispersion is much higher. We calculate the
minimum number of measured stars necessary to distinguish between Newtonian
gravity and MOND with the Kolmogorov-Smirnov test. We also show that for most
clusters it is necessary to measure the velocities of between 30 to 80 stars to
distinguish between both cases. Therefore the observational measurement of the
line-of-sight velocity dispersion of these clusters will provide a test for
MOND.Comment: A&A, accepted, LaTeX, 8 pages, 4 figure
Milky Way potentials in CDM and MOND. Is the Large Magellanic Cloud on a bound orbit?
We compute the Milky Way potential in different cold dark matter (CDM) based
models, and compare these with the modified Newtonian dynamics (MOND)
framework. We calculate the axis ratio of the potential in various models, and
find that isopotentials are less spherical in MOND than in CDM potentials. As
an application of these models, we predict the escape velocity as a function of
the position in the Galaxy. This could be useful in comparing with future data
from planned or already-underway kinematic surveys (RAVE, SDSS, SEGUE, SIM,
GAIA or the hypervelocity stars survey). In addition, the predicted escape
velocity is compared with the recently measured high proper motion velocity of
the Large Magellanic Cloud (LMC). To bind the LMC to the Galaxy in a MOND
model, while still being compatible with the RAVE-measured local escape speed
at the Sun's position, we show that an external field modulus of less than
is needed.Comment: Accepted for publication in MNRAS, 13 pages, 7 figures, 3 table
Semi-Analytical Models for the Formation of Disk Galaxies II. Dark Matter versus Modified Newtonian Dynamics
We present detailed semi-analytical models for the formation of disk galaxies
both in a Universe dominated by dark matter (DM), and in one for which the
force law is given by modified Newtonian dynamics (MOND). We tune the models to
fit the observed near-infrared Tully-Fisher (TF) relation, and compare numerous
predictions of the resulting models with observations. The DM and MOND models
are almost indistinguishable. They both yield gas mass fractions and dynamical
mass-to-light ratios which are in good agreement with observations. Both models
reproduce the narrow relation between global mass-to-light ratio and central
surface brightness, and reveal a characteristic acceleration, contrary to
claims that these relations are not predicted by DM models. Both models require
SN feedback in order to reproduce the lack of high surface brightness dwarf
galaxies. However, the introduction of feedback to the MOND models steepens the
TF relation and increases the scatter, making MOND only marginally consistent
with observations. The most serious problem for the DM models is their
prediction of steep central rotation curves. However, the DM rotation curves
are only slightly steeper than those of MOND, and are only marginally
inconsistent with the poor resolution data on LSB galaxies.Comment: 26 pages, 11 figures. Accepted for publication in Ap
Two component dark matter
We explain the PAMELA positron excess and the PPB-BETS/ATIC e+ + e- data
using a simple two component dark matter model (2DM). The two particle species
in the dark matter sector are assumed to be in thermal equilibrium in the early
universe. While one particle is stable and is the present day dark matter, the
second one is metastable and decays after the universe is 10^-8 s old. In this
model it is simple to accommodate the large boost factors required to explain
the PAMELA positron excess without the need for large spikes in the local dark
matter density. We provide the constraints on the parameters of the model and
comment on possible signals at future colliders.Comment: 6 pages, 2 figures, discussion clarified and extende
Cloning of cDNA and chromosomal location of genes encoding the three types of subunits of the wheat tetrameric inhibitor of insect a-amylase
We have characterized three cDNA clones corresponding to proteins CM1, CM3 and CM16, which represent the three types of subunits of the wheat tetrameric inhibitor of insect -amylases. The deduced amino acid sequences of the mature polypeptides are homologous to those of the dimeric and monomeric -amylase inhibitors and of the trypsin inhibitors. The mature polypeptides are preceded by typical signal peptides. Southern blot analysis of appropriate aneuploids, using the cloned cDNAs as probes, has revealed the location of genes for subunits of the CM3 and of the CM16 type within a few kb of each other in chromosomes 4A, 4B and 4D, and those for the CM1 type of subunit in chromosomes 7A, 7B and 7D. Known subunits of the tetrameric inhibitor corresponding to genes from the B and D genomes have been previously characterized. No proteins of this class have been found to be encoded by the A genome in hexaploid wheat (genomes AA, BB, DD) or in diploid wheats (AA) and no anti -amylase activity has been detected in the latter, so that the A-genome genes must be either silent (pseudogenes) or expressed at a much lower level
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The Met Office Global Coupled model 2.0 (GC2) configuration
The latest coupled configuration of the Met Office Unified Model (Global Coupled configuration 2, GC2) is presented. This paper documents the model components which make up the configuration (although the scientific description of these components is detailed elsewhere) and provides a description of the coupling between the components. The performance of GC2 in terms of its systematic errors is assessed using a variety of diagnostic techniques. The configuration is intended to be used by the Met Office and collaborating institutes across a range of timescales, with the seasonal forecast system (GloSea5) and climate projection system (HadGEM) being the initial users. In this paper GC2 is compared against the model currently used operationally in those two systems. Overall GC2 is shown to be an improvement on the configurations used currently, particularly in terms of modes of variability (e.g. mid-latitude and tropical cyclone intensities, the Madden–Julian Oscillation and El Niño Southern Oscillation). A number of outstanding errors are identified with the most significant being a considerable warm bias over the Southern Ocean and a dry precipitation bias in the Indian and West African summer monsoons. Research to address these is ongoing
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