2,902 research outputs found
The Book of Leviticus
The book of Leviticus: critical edition of the Hebrew text printed in colors exhibiting the composite structure of the book / with notes by S.R. Driver ; assisted by H.A. White.https://scholar.csl.edu/ebooks/1017/thumbnail.jp
A log-quadratic relation for predicting supermassive black hole masses from the host bulge Sersic index
We reinvestigate the correlation between black hole mass and bulge
concentration. With an increased galaxy sample, updated estimates of galaxy
distances, black hole masses, and Sersic indices `n' - a measure of
concentration - we perform a least-squares regression analysis to obtain a
relation suitable for the purpose of predicting black hole masses in other
galaxies. In addition to the linear relation, log(M_bh) = 7.81(+/-0.08) +
2.69(+/-0.28)[log(n/3)] with epsilon_(intrin)=0.31 dex, we investigated the
possibility of a higher order M_bh-n relation, finding the second order term in
the best-fitting quadratic relation to be inconsistent with a value of zero at
greater than the 99.99% confidence level. The optimal relation is given by
log(M_bh) = 7.98(+/-0.09) + 3.70(+/-0.46)[log(n/3)] -
3.10(+/-0.84)[log(n/3)]^2, with epsilon_(intrin)=0.18 dex and a total absolute
scatter of 0.31 dex. Extrapolating the quadratic relation, it predicts black
holes with masses of ~10^3 M_sun in n=0.5 dwarf elliptical galaxies, compared
to ~10^5 M_sun from the linear relation, and an upper bound on the largest
black hole masses in the local universe, equal to 1.2^{+2.6}_{-0.4}x10^9
M_sun}. In addition, we show that the nuclear star clusters at the centers of
low-luminosity elliptical galaxies follow an extrapolation of the same
quadratic relation. Moreover, we speculate that the merger of two such
nucleated galaxies, accompanied by the merger and runaway collision of their
central star clusters, may result in the late-time formation of some
supermassive black holes. Finally, we predict the existence of, and provide
equations for, a relation between M_bh and the central surface brightness of
the host bulge
The Luminosity Function of Low-Redshift Abell Galaxy Clusters
We present the results from a survey of 57 low-redshift Abell galaxy clusters
to study the radial dependence of the luminosity function (LF). The dynamical
radius of each cluster, r200, was estimated from the photometric measurement of
cluster richness, Bgc. The shape of the LFs are found to correlate with radius
such that the faint-end slope, alpha, is generally steeper on the cluster
outskirts. The sum of two Schechter functions provides a more adequate fit to
the composite LFs than a single Schechter function. LFs based on the selection
of red and blue galaxies are bimodal in appearance. The red LFs are generally
flat for -22 < M_Rc < -18, with a radius-dependent steepening of alpha for M_Rc
> -18. The blue LFs contain a larger contribution from faint galaxies than the
red LFs. The blue LFs have a rising faint-end component (alpha ~ -1.7) for M_Rc
> -21, with a weaker dependence on radius than the red LFs. The dispersion of
M* was determined to be 0.31 mag, which is comparable to the median measurement
uncertainty of 0.38 mag. This suggests that the bright-end of the LF is
universal in shape at the 0.3 mag level. We find that M* is not correlated with
cluster richness when using a common dynamical radius. Also, we find that M* is
weakly correlated with BM-type such that later BM-type clusters have a brighter
M*. A correlation between M* and radius was found for the red and blue galaxies
such that M* fades towards the cluster center.Comment: Accepted for publication in ApJ, 16 pages, 4 tables, 24 figure
The Properties of Poor Groups of Galaxies: III. The Galaxy Luminosity Function
We obtain R-band photometry for galaxies in six nearby poor groups for which
we have spectroscopic data, including 328 new galaxy velocities. For the five
groups with luminous X-ray halos, the composite group galaxy luminosity
function (GLF) is fit adequately by a Schechter function with Mstar = -21.6 +/-
0.4 + 5log h and alpha = -1.3 +/- 0.1. We also find that (1) the ratio of
dwarfs to giants is significantly larger for the five groups with luminous
X-ray halos than for the one marginally X-ray detected group, (2) the composite
GLF for the luminous X-ray groups is consistent in shape with that for rich
clusters, (3) the composite group GLF rises more steeply at the faint end than
that of the field, (4) the shape difference between the field and composite
group GLF's results mostly from the population of non-emission line galaxies,
whose dwarf-to-giant ratio is larger in the denser group environment than in
the field, and (5) the non-emission line dwarfs are more concentrated about the
group center than the non-emission line giants. This last result indicates that
the dwarfs and giants occupy different orbits (i.e., have not mixed completely)
and suggests that the populations formed at a different times. Our results show
that the shape of the GLF varies with environment and that this variation is
due primarily to an increase in the dwarf-to-giant ratio of quiescent galaxies
in higher density regions, at least up to the densities characteristic of X-ray
luminous poor groups. This behavior suggests that, in some environments, dwarfs
are more biased than giants with respect to dark matter. This trend conflicts
with the prediction of standard biased galaxy formation models. (Abridged)Comment: 36 pages, AASLaTeX with 8 figures. Table 1 also available at
http://atropos.as.arizona.edu/aiz/papers/all_grp_lf_ascii.dat.final . To
appear in Ap
Populating Stellar Orbits Inside a Rotating, Gaseous Bar
In an effort to better understand the formation and evolution of barred
galaxies, we have examined the properties of equatorial orbits in the effective
potential of one model of a rapidly rotating, steady-state gas-dynamical bar
that has been constructed via a self-consistent hydrodynamical simulation.
Using a ``Restriction Hypothesis'' to determine initial conditions, we find
that a significant fraction of orbits in this potential are quasi-ergodic and
that regular orbits have a ``bowtie'' shape in contrast to the more typical x1
orbits. This bowtie orbit should give a boxy-peanut shape to such systems.Comment: Accepted for publication in The Astrophysical Journal; 29 pages, 29
gif figure
Can the Future Influence the Present?
One widely accepted model of classical electrodynamics assumes that a moving charged particle produces both retarded and advanced fields. This formulation first appeared at least 75 years ago. It was popularized in the 1940\u27s by work of Wheeler and Feynman. But the most fundamental question associated with the model has remained unanswered: When (if ever) does the two-body problem have a unique solution? The present paper gives an answer in one special case. Imagine two identical charged particles alone in the universe moving symmetrically along the x axis. One is at x(t) and the other is at âx(t). Their motion is then governed by a system of functional differential equations involving both retarded and advanced arguments. This system together with the Newtonian initial data x(0)=x0\u3e0 and xâČ(0)=0 has a unique solution for all time provided x0 is sufficiently large. Perhaps the existence and uniqueness proof given for this special case will pave the way for more general results on this curious two-body problem
Argumentation in school science : Breaking the tradition of authoritative exposition through a pedagogy that promotes discussion and reasoning
The value of argumentation in science education has become internationally recognised and has been the subject of many research studies in recent years. Successful introduction of argumentation activities in learning contexts involves extending teaching goals beyond the understanding of facts and concepts, to include an emphasis on cognitive and metacognitive processes, epistemic criteria and reasoning. The authors focus on the difficulties inherent in shifting a tradition of teaching from one dominated by authoritative exposition to one that is more dialogic, involving small-group discussion based on tasks that stimulate argumentation. The paper builds on previous research on enhancing the quality of argument in school science, to focus on how argumentation activities have been designed, with appropriate strategies, resources and modelling, for pedagogical purposes. The paper analyses design frameworks, their contexts and lesson plans, to evaluate their potential for enhancing reasoning through foregrounding the processes of argumentation. Examples of classroom dialogue where teachers adopt the frameworks/plans are analysed to show how argumentation processes are scaffolded. The analysis shows that several layers of interpretation are needed and these layers need to be aligned for successful implementation. The analysis serves to highlight the potential and limitations of the design frameworks
Time separation as a hidden variable to the Copenhagen school of quantum mechanics
The Bohr radius is a space-like separation between the proton and electron in
the hydrogen atom. According to the Copenhagen school of quantum mechanics, the
proton is sitting in the absolute Lorentz frame. If this hydrogen atom is
observed from a different Lorentz frame, there is a time-like separation
linearly mixed with the Bohr radius. Indeed, the time-separation is one of the
essential variables in high-energy hadronic physics where the hadron is a bound
state of the quarks, while thoroughly hidden in the present form of quantum
mechanics. It will be concluded that this variable is hidden in Feynman's rest
of the universe. It is noted first that Feynman's Lorentz-invariant
differential equation for the bound-state quarks has a set of solutions which
describe all essential features of hadronic physics. These solutions explicitly
depend on the time separation between the quarks. This set also forms the
mathematical basis for two-mode squeezed states in quantum optics, where both
photons are observable, but one of them can be treated a variable hidden in the
rest of the universe. The physics of this two-mode state can then be translated
into the time-separation variable in the quark model. As in the case of the
un-observed photon, the hidden time-separation variable manifests itself as an
increase in entropy and uncertainty.Comment: LaTex 10 pages with 5 figure. Invited paper presented at the
Conference on Advances in Quantum Theory (Vaxjo, Sweden, June 2010), to be
published in one of the AIP Conference Proceedings serie
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