275 research outputs found
Testing quantised inertia on galactic scales
Galaxies and galaxy clusters have rotational velocities apparently too fast
to allow them to be gravitationally bound by their visible matter. This has
been attributed to the presence of invisible (dark) matter, but so far this has
not been directly detected. Here, it is shown that a new model that modifies
inertial mass by assuming it is caused by Unruh radiation, which is subject to
a Hubble-scale (Theta) Casimir effect predicts the rotational velocity (v) to
be: v^4=2GMc^2/Theta (the Tully-Fisher relation) where G is the gravitational
constant, M is the baryonic mass and c is the speed of light. The model
predicts the outer rotational velocity of dwarf and disk galaxies, and galaxy
clusters, within error bars, without dark matter or adjustable parameters, and
makes a prediction that local accelerations should remain above 2c^2/Theta at a
galaxy's edge.Comment: 7 pages, 1 figure. Accepted for publication in Astrophysics and Space
Science on 27/7/201
Intrinsic Redshifts and the Tully-Fisher Distance Scale
The Tully-Fisher relationship (TFR) has been shown to have a relatively small
observed scatter of ~ +/-0.35 mag implying an intrinsic scatter < +/-0.30 mag.
However, when the TFR is calibrated from distances derived from the Hubble
relation for field galaxies scatter is consistently found to be +/-0.64 to
+/-0.84 mag. This significantly larger scatter requires that intrinsic TFR
scatter is actually much larger than +/-0.30 mag, that field galaxies have an
intrinsic TFR scatter much larger than cluster spirals, or that field galaxies
have a velocity dispersion relative to the Hubble flow in excess of 1000 km
s-1. Each of these potential explanations faces difficulties contradicted by
available data and the results of previous studies. An alternative explanation
is that the measured redshifts of galaxies are composed of a cosmological
redshift component predicted from the value of the Hubble Constant and a
superimposed intrinsic redshift component previously identified in other
studies. This intrinsic redshift component may exceed 5000 km s-1 in individual
galaxies. In this alternative scenario a possible value for the Hubble Constant
is 55-60 km s-1 Mpc-1.Comment: 15 pages, Astrophysics&Space Science - Accepted for publicatio
Understanding Galaxy Formation and Evolution
The old dream of integrating into one the study of micro and macrocosmos is
now a reality. Cosmology, astrophysics, and particle physics intersect in a
scenario (but still not a theory) of cosmic structure formation and evolution
called Lambda Cold Dark Matter (LCDM) model. This scenario emerged mainly to
explain the origin of galaxies. In these lecture notes, I first present a
review of the main galaxy properties, highlighting the questions that any
theory of galaxy formation should explain. Then, the cosmological framework and
the main aspects of primordial perturbation generation and evolution are
pedagogically detached. Next, I focus on the ``dark side'' of galaxy formation,
presenting a review on LCDM halo assembling and properties, and on the main
candidates for non-baryonic dark matter. It is shown how the nature of
elemental particles can influence on the features of galaxies and their
systems. Finally, the complex processes of baryon dissipation inside the
non-linearly evolving CDM halos, formation of disks and spheroids, and
transformation of gas into stars are briefly described, remarking on the
possibility of a few driving factors and parameters able to explain the main
body of galaxy properties. A summary and a discussion of some of the issues and
open problems of the LCDM paradigm are given in the final part of these notes.Comment: 50 pages, 10 low-resolution figures (for normal-resolution, DOWNLOAD
THE PAPER (PDF, 1.9 Mb) FROM http://www.astroscu.unam.mx/~avila/avila.pdf).
Lectures given at the IV Mexican School of Astrophysics, July 18-25, 2005
(submitted to the Editors on March 15, 2006
Observations of the High Redshift Universe
(Abridged) In these lectures aimed for non-specialists, I review progress in
understanding how galaxies form and evolve. Both the star formation history and
assembly of stellar mass can be empirically traced from redshifts z~6 to the
present, but how the various distant populations inter-relate and how stellar
assembly is regulated by feedback and environmental processes remains unclear.
I also discuss how these studies are being extended to locate and characterize
the earlier sources beyond z~6. Did early star-forming galaxies contribute
significantly to the reionization process and over what period did this occur?
Neither theory nor observations are well-developed in this frontier topic but
the first results presented here provide important guidance on how we will use
more powerful future facilities.Comment: To appear in `First Light in Universe', Saas-Fee Advanced Course 36,
Swiss Soc. Astrophys. Astron. in press. 115 pages, 64 figures (see
http://www.astro.caltech.edu/~rse/saas-fee.pdf for hi-res figs.) For lecture
ppt files see
http://obswww.unige.ch/saas-fee/preannouncement/course_pres/overview_f.htm
Astronomical Distance Determination in the Space Age: Secondary Distance Indicators
The formal division of the distance indicators into primary and secondary leads to difficulties in description of methods which can actually be used in two ways: with, and without the support of the other methods for scaling. Thus instead of concentrating on the scaling requirement we concentrate on all methods of distance determination to extragalactic sources which are designated, at least formally, to use for individual sources. Among those, the Supernovae Ia is clearly the leader due to its enormous success in determination of the expansion rate of the Universe. However, new methods are rapidly developing, and there is also a progress in more traditional methods. We give a general overview of the methods but we mostly concentrate on the most recent developments in each field, and future expectations. © 2018, The Author(s)
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