1,871 research outputs found
Star Formation-Regulated Growth of Black Holes in Protogalactic Spheroids
The observed relation between central black hole mass and spheroid velocity
dispersion is interpreted in terms of a self-regulation model that incorporates
a viscous Keplerian accretion disk to feed the black hole, embedded in a
massive, self-gravitating star forming disk that eventually populates the
spheroid. The model leads to a constant ratio between black hole mass and
spheroid mass which is equal to the inverse of the critical Reynolds number for
the onset of turbulence in the accretion disk surrounding the central black
hole. Applying the fundamental plane correlation for spheroids, we find that
the black hole mass has a power-law dependence on the spheroid velocity
dispersion with a slope in the range of 4-5. We explain the larger scatter in
the Magorrian relation with respect to the black hole mass-spheroid velocity
dispersion relationship as a result of secular evolution of the spheroid that
primarily affects its luminosity and to a much lesser extent its velocity
dispersion.Comment: 12 pages, no figures, submitted to ApJ Letter
Out-of-plane thermopower of strongly correlated layered systems: an application to Bi_2(Sr,La)_2CaCu_2O_{8+\delta}
We calculate the out-of-plane thermopower in a quasi-two dimensional system,
and argue that this quantity is an effective probe of the asymmetry of the
single-particle spectral function. We find that the temperature and doping
dependence of the out-of-plane thermopower in Bi_2(Sr,La)_2CaCu_2O_{8+\delta}
single crystals is broadly consistent with the behavior of the spectral
function determined from ARPES and tunneling experiments. We also investigate
the relationship between out-of-plane thermopower and entropy in a quasi-two
dimensional material. We present experimental evidence that at moderate
temperatures, there is a qualitative correspondence between the out-of-plane
thermopower in Bi_2(Sr,La)_2CaCu_2O_{8+\delta}, and the entropy obtained from
specific heat measurements. Finally, we argue that the derivative of the
entropy with respect to particle number may be the more appropriate quantity to
compare with the thermopower, rather than the entropy per particle.Comment: 11 pages, 5 figures. v2: substantially rewritten, including a more
detailed analysis of the relationship between thermopower and entrop
Towards a Comprehensive Fueling-Controlled Theory on the Growth of Massive Black Holes and Host Spheroids
We study the relation between nuclear massive black holes and their host
spheroid gravitational potential. Using AMR numerical simulations, we analyze
how gas is transported in the nuclear (central kpc) regions of galaxies. We
study the gas fueling onto the inner accretion disk (sub-pc scale) and the star
formation in a massive nuclear disk like those generally found in
proto-spheroids (ULIRGs, SCUBA Galaxies). These sub-pc resolution simulation of
gas fueling that is mainly depleted by star formation naturally satisfy the
`M_BH - $M_virial' relation, with a scatter considerably less than the observed
one. We found a generalized version of Kennicutt-Schmidt Law for starbursts is
satisfied, in which the total gas depletion rate (dot{M}_gas = dot{M}_BH +
dot{M}_SF) is the one that scales as M_gas/t_orbital. We also found that the
`M_BH - sigma' relation is a byproduct of the `M_BH - M_virial' relation in the
fueling controlled scenario.Comment: 12 pages, figures, submited to ApJ, email: [email protected]
A cross-correlation of WMAP and ROSAT
We cross-correlate the recent CMB WMAP 1 year data with the diffuse soft
X-ray background map of ROSAT. We look for common signatures due to galaxy
clusters (SZ effect in CMB, bremsstrahlung in X-rays) by cross-correlating the
two maps in real and in Fourier space. We do not find any significant
correlation and we explore the different reasons for this lack of correlation.
The most likely candidates are the possibility that we live in a low universe () and/or systematic effects in the data
especially in the diffuse X-ray maps which may suffer from significant cluster
signal subtraction during the point source removal process.Comment: To appear in New Astronomy Reviews, Proceedings of the CMBNET
Meeting, 20-21 February, 2003, Oxford, U
Tidal Destruction of The First Dark Microhalos
We point out that the usual self-similarity in cold dark matter models is
broken by encounters with individual normal galactic stars on sub-pc scale.
Tidal heating and stripping must have redefined the density and velocity
structures of the population of the Earth-mass dark matter halos, which are
likely to have been the first bound structures to form in the Universe. The
disruption rate depends strongly on {\it galaxy types} and the orbital
distribution of the microhalos; in the Milky Way, stochastic radial orbits are
destroyed first by stars in the triaxial bulge, microhalos on non-planar
retrograde orbits with large pericenters and/or apocenters survive the longest.
The final microhalo distribution in the {\it solar neighborhood} is better
described as a superposition of filamentry microstreams rather than as a set of
discrete spherical clumps in an otherwise homogeneous medium. We discuss its
important consequences to our detections of microhalos by direct recoil signal
and indirect annihilation signal.Comment: 13 pages, 3 figures, Astrophysical Journal, accepte
Reionization Constraints on the Contribution of Primordial Compact Objects to Dark Matter
Many lines of evidence suggest that nonbaryonic dark matter constitutes
roughly 30% of the critical closure density, but the composition of this dark
matter is unknown. One class of candidates for the dark matter is compact
objects formed in the early universe, with typical masses M between 0.1 and 1
solar masses to correspond to the mass scale of objects found with microlensing
observing projects. Specific candidates of this type include black holes formed
at the epoch of the QCD phase transition, quark stars, and boson stars. Here we
show that accretion onto these objects produces substantial ionization in the
early universe, with an optical depth to Thomson scattering out to z=1100 of
approximately tau=2-4 [f_CO\epsilon_{-1}(M/Msun)]^{1/2} (H_0/65)^{-1}, where
\epsilon_{-1} is the accretion efficiency \epsilon\equiv L/{\dot M}c^2 divided
by 0.1 and f_CO is the fraction of matter in the compact objects. The current
upper limit to the scattering optical depth, based on the anisotropy of the
microwave background, is approximately 0.4. Therefore, if accretion onto these
objects is relatively efficient, they cannot be the main component of
nonbaryonic dark matter.Comment: 12 pages including one figure, uses aaspp4, submitted to Ap
Which Law Applies to the Afghan Conflict?
Soviet armed forces have been directly engaged in combat in Afghanistan for more than 8 years. The level of international protest, sanctions and media coverage diminished after the initial outcry over the large-scale Soviet intervention in December 1979. With the conclusion in many diplomatic and professional quarters that the Soviet presence in Afghanistan would be of long duration, the focus of international disapproval shifted from the question whether the Soviet presence in Afghanistan was lawful or not to whether Soviet conduct in Afghanistan was lawful or not: fromjus ad bellum to jus in bello
Secondary CMB anisotropies in a universe reionized in patches
In a universe reionized in patches, the Doppler effect from Thomson
scattering off free electrons generates secondary cosmic microwave background
(CMB) anisotropies. For a simple model with small patches and late
reionization, we analytically calculate the anisotropy power spectrum. Patchy
reionization can, in principle, be the main source of anisotropies on arcminute
scales. On larger angular scales, its contribution to the CMB power spectrum is
a small fraction of the primary signal and is only barely detectable in the
power spectrum with even an ideal, i.e. cosmic variance limited, experiment and
an extreme model of reionization. Consequently patchy reionization is unlikely
to affect cosmological parameter estimation from the acoustic peaks in the CMB.
Its detection on small angles would help determine the ionization history of
the universe, in particular the typical size of the ionized region and the
duration of the reionization process.Comment: 7 pages, 2 figures, submitted to Ap
Evaluational adjectives
This paper demarcates a theoretically interesting class of "evaluational adjectives." This class includes predicates expressing various kinds of normative and epistemic evaluation, such as predicates of personal taste, aesthetic adjectives, moral adjectives, and epistemic adjectives, among others. Evaluational adjectives are distinguished, empirically, in exhibiting phenomena such as discourse-oriented use, felicitous embedding under the attitude verb `find', and sorites-susceptibility in the comparative form. A unified degree-based semantics is developed: What distinguishes evaluational adjectives, semantically, is that they denote context-dependent measure functions ("evaluational perspectives")—context-dependent mappings to degrees of taste, beauty, probability, etc., depending on the adjective. This perspective-sensitivity characterizing the class of evaluational adjectives cannot be assimilated to vagueness, sensitivity to an experiencer argument, or multidimensionality; and it cannot be demarcated in terms of pretheoretic notions of subjectivity, common in the literature. I propose that certain diagnostics for "subjective" expressions be analyzed instead in terms of a precisely specified kind of discourse-oriented use of context-sensitive language. I close by applying the account to `find x PRED' ascriptions
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