1,019 research outputs found
The CMB Dipole and Circular Galaxy Distribution
The validity of Hubble's law defies the determination of the center of the
big bang expansion, even if it exists. Every point in the expanding universe
looks like the center from which the rest of the universe flies away. In this
article, the author shows that the distribution of apparently circular galaxies
is not uniform in the sky and that there exists a special direction in the
universe in our neighborhood. The data is consistent with the assumption that
the tidal force due to the mass distribution around the universe center causes
the deformation of galactic shapes depending on its orientation and location
relative to the center and our galaxy. Moreover, the cmb dipole data can also
be associated with the center of the universe expansion, if the cmb dipole at
the center of our supercluster is assumed to be due to Hubble flow. The
location of the center is estimated from the cmb dipole data. The direction to
the center from both sets of data is consistent and the distance to the center
is computed from the cmb dipole data.Comment: 9 pages, 3 figures (10 figure captions), 1 tabl
Modeling Non-Circular Motions in Disk Galaxies: Application to NGC 2976
We present a new procedure to fit non-axisymmetric flow patterns to 2-D
velocity maps of spiral galaxies. We concentrate on flows caused by bar-like or
oval distortions to the total potential that may arise either from a
non-axially symmetric halo or a bar in the luminous disk. We apply our method
to high-quality CO and Halpha data for the nearby, low-mass spiral NGC 2976
previously obtained by Simon et al., and find that a bar-like model fits the
data at least as well as their model with large radial flows. We find
supporting evidence for the existence of a bar in the baryonic disk. Our model
suggests that the azimuthally averaged central attraction in the inner part of
this galaxy is larger than estimated by these authors. It is likely that the
disk is also more massive, which will limit the increase to the allowed dark
halo density. Allowance for bar-like distortions in other galaxies may either
increase or decrease the estimated central attraction.Comment: 12 pages, 6 figures, accepted for publication in ApJ. v2: minor
changes to match proofs. For version with high-resolution figures, see
http://www.physics.rutgers.edu/~spekkens/papers/noncirc.pd
The radio source B 1834+620: A double-double radio galaxy with interesting properties
We present a study of the peculiar radio galaxy B 1834+620. It is
characterised by the presence of a 420-kpc large edge-brightened radio source
which is situated within, and well aligned with, a larger (1.66 Mpc) radio
source. Both sources apparently originate in the same host galaxy, which has a
R_s-magnitude of 19.7 and a redshift of 0.5194, as determined from the strong
emission-lines in the spectrum. We have determined the rotation measures
towards this source, as well as the radio spectral energy distribution of its
components. The radio spectrum of the large outer source is steeper than that
of the smaller inner source. The radio core has a spectrum that peaks at a
frequency of a few GHz. The rotation measures towards the four main components
are quite similar, within rad m of 58 rad m. They are
probably largely galactic in origin. We have used the presence of a bright
hotspot in the northern outer lobe to constrain the advance velocity of the
inner radio lobes to the range between 0.19c and 0.29c, depending on the
orientation of the source. This corresponds to an age of this structure in the
range between 2.6 and 5.8 Myr. We estimate a density of the ambient medium of
the inner lobes of \la 1.6 \times 10^{-30} gr\,cm (particle density
\la 8 \times 10^{-7} cm). A low ambient density is further supported
by the discrepancy between the large optical emission-line luminosity of the
host galaxy and the relatively low radio power of the inner lobes.Comment: Accepted for publication in MNRA
The story of Kintu and his sons: naming, ethnic identity formation and power in the precolonial Great Lakes Region of East Africa
This essay investigates the historical background of ethnic disunity in today’s Western Uganda as part of the Great Lakes Region of East Africa. In general, there are two opposing views with respect to the existence of ethnicity in precolonial times. On the one hand, social scientists state that the existence of ethnic groups is an invention of the joint work of colonial administrators and professional ethnologists. On the other hand, several scholars argue that ethnicity is an ancient phenomenon predating colonial times. In the past decades, the study into the ancient history of the Great Lakes Region has made great progress. The interdisciplinary approach of historical linguistics, history and anthropology revealed a fascinating and complex history of languages and cultures. However, the history of the different peoples who spoke these languages and built up these cultures is much less known, in particular about how they interacted with each other and how they judged socio-cultural differences. For example, what names they gave each other. This essay tries to give an impetus for further interdisciplinary research about the existence of ethnicity in precolonial times. Identity formation within and between groups is related to power structures in societies. Therefore, investigating ethnicity in precolonial times has to be carried out in the context of developing power structures. ASC – Publicaties niet-programma gebonde
Self-Consistent Response of a Galactic Disk to an Elliptical Perturbation Halo Potential
We calculate the self-consistent response of an axisymmetric galactic disk
perturbed by an elliptical halo potential of harmonic number m = 2, and obtain
the net disk ellipticity. Such a potential is commonly expected to arise due to
a galactic tidal encounter and also during the galaxy formation process. The
self-gravitational potential corresponding to the self-consistent,
non-axisymmetric density response of the disk is obtained by inversion of
Poisson equation for a thin disk. This response potential is shown to oppose
the perturbation potential, because physically the disk self-gravity resists
the imposed potential. This results in a reduction in the net ellipticity of
the perturbation halo potential in the disk plane. The reduction factor
denoting this decrease is independent of the strength of the perturbation
potential, and has a typical minimum value of 0.75 - 0.9 for a wide range of
galaxy parameters. The reduction is negligible at all radii for higher
harmonics (m > or = 3) of the halo potential. (abridged).Comment: 26 pages (LaTex- aastex style), 3 .eps figures. To appear in the
Astrophysical Journal, Vol. 542, Oct. 20, 200
Self-consistent massive disks in triaxial dark matter halos
Galactic disks in triaxial dark matter halos become deformed by the
elliptical potential in the plane of the disk in such a way as to counteract
the halo ellipticity. We develop a technique to calculate the equilibrium
configuration of such a disk in the combined disk-halo potential, which is
based on the method of Jog (2000) but accounts for the radial variation in both
the halo potential and the disk ellipticity. This crucial ingredient results in
qualitatively different behavior of the disk: the disk circularizes the
potential at small radii, even for a reasonably low disk mass. This effect has
important implications for proposals to reconcile cuspy halo density profiles
with low surface brightness galaxy rotation curves using halo triaxiality. The
disk ellipticities in our models are consistent with observational estimates
based on two-dimensional velocity fields and isophotal axis ratios.Comment: ApJ, in pres
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