12,055 research outputs found
Clustering of the Diffuse Infrared Light from the COBE DIRBE maps. III. Power spectrum analysis and excess isotropic component of fluctuations
The cosmic infrared background (CIB) radiation is the cosmic repository for
energy release throughout the history of the universe. Using the all-sky data
from the COBE DIRBE instrument at wavelengths 1.25 - 100 mic we attempt to
measure the CIB fluctuations. In the near-IR, foreground emission is dominated
by small scale structure due to stars in the Galaxy. There we find a strong
correlation between the amplitude of the fluctuations and Galactic latitude
after removing bright foreground stars. Using data outside the Galactic plane
() and away from the center () we extrapolate
the amplitude of the fluctuations to cosec. We find a positive intercept
of nW/m2/sr at 1.25, 2.2,3.5 and 4.9 mic
respectively, where the errors are the range of 92% confidence limits. For
color subtracted maps between band 1 and 2 we find the isotropic part of the
fluctuations at nW/m2/sr. Based on detailed numerical and
analytic models, this residual is not likely to originate from the Galaxy, our
clipping algorithm, or instrumental noise. We demonstrate that the residuals
from the fit used in the extrapolation are distributed isotropically and
suggest that this extra variance may result from structure in the CIB. For
2\deg< \theta < 15^\deg, a power-spectrum analysis yields firm upper limits
of (\theta/5^\deg) \times\delta F_{\rm rms} (\theta) < 6, 2.5, 0.8, 0.5
nW/m2/sr at 1.25, 2.2, 3.5 and 4.9 mic respectively. From 10-100 mic, the upper
limits <1 nW/m2/sr.Comment: Ap.J., in press. 69 pages including 24 fig
Band structures of rare gas solids within the GW approximation
Band structures for solid rare gases (Ne, Ar) have been calculated using the
GW approximation. All electron and pseudopotential ab initio calculations were
performed using Gaussian orbital basis sets and the dependence of particle-hole
gaps and electron affinities on basis set and treatment of core electrons is
investigated. All electron GW calculations have a smaller particle-hole gap
than pseudopotential GW calculations by up to 0.2 eV. Quasiparticle electron
and hole excitation energies, valence band widths and electron affinities are
generally in very good agreement with those derived from optical absorption and
photoemission measurements.Comment: 7 pages 1 figur
Correlated Anisotropies in the Cosmic Far-Infrared Background Detected by MIPS/Spitzer: Constraint on the Bias
We report the detection of correlated anisotropies in the Cosmic Far-Infrared
Background at 160 microns. We measure the power spectrum in the Spitzer/SWIRE
Lockman Hole field. It reveals unambiguously a strong excess above cirrus and
Poisson contributions, at spatial scales between 5 and 30 arcminutes,
interpreted as the signature of infrared galaxy clustering. Using our model of
infrared galaxy evolution we derive a linear bias b=1.74 \pm 0.16. It is a
factor 2 higher than the bias measured for the local IRAS galaxies. Our model
indicates that galaxies dominating the 160 microns correlated anisotropies are
at z~1. This implies that infrared galaxies at high redshifts are biased
tracers of mass, unlike in the local Universe.Comment: ApJ Letters, in pres
The Power Spectrum of the PSC Redshift Survey
We measure the redshift-space power spectrum P(k) for the recently completed
IRAS Point Source Catalogue (PSC) redshift survey, which contains 14500
galaxies over 84% of the sky with 60 micron flux >= 0.6 Jansky. Comparison with
simulations shows that our estimated errors on P(k) are realistic, and that
systematic errors due to the finite survey volume are small for wavenumbers k
>~ 0.03 h Mpc^-1. At large scales our power spectrum is intermediate between
those of the earlier QDOT and 1.2 Jansky surveys, but with considerably smaller
error bars; it falls slightly more steeply to smaller scales. We have fitted
families of CDM-like models using the Peacock-Dodds formula for non-linear
evolution; the results are somewhat sensitive to the assumed small-scale
velocity dispersion \sigma_V. Assuming a realistic \sigma_V \approx 300 km/s
yields a shape parameter \Gamma ~ 0.25 and normalisation b \sigma_8 ~ 0.75; if
\sigma_V is as high as 600 km/s then \Gamma = 0.5 is only marginally excluded.
There is little evidence for any `preferred scale' in the power spectrum or
non-Gaussian behaviour in the distribution of large-scale power.Comment: Latex, uses mn.sty, 14 pages including 11 Postscript figures.
Accepted by MNRA
Experiments with a Malkus-Lorenz water wheel: Chaos and Synchronization
We describe a simple experimental implementation of the Malkus-Lorenz water
wheel. We demonstrate that both chaotic and periodic behavior is found as wheel
parameters are changed in agreement with predictions from the Lorenz model. We
furthermore show that when the measured angular velocity of our water wheel is
used as an input signal to a computer model implementing the Lorenz equations,
high quality chaos synchronization of the model and the water wheel is
achieved. This indicates that the Lorenz equations provide a good description
of the water wheel dynamics.Comment: 12 pages, 7 figures. The following article has been accepted by the
American Journal of Physics. After it is published, it will be found at
http://scitation.aip.org/ajp
Anisotropic domain walls
We find an anisotropic, non-supersymmetric generalization of the extreme
supersymmetric domain walls of simple non-dilatonic supergravity theory. As
opposed to the isotropic non- and ultra-extreme domain walls, the anisotropic
non-extreme wall has the \emph{same} spatial topology as the extreme wall. The
solution has naked singularities which vanish in the extreme limit. Since the
Hawking temperature on the two sides is different, the generic solution is
unstable to Hawking decay.Comment: 11 pages, LaTeX, 3 PostScript figures, uses amstex and epsfi
Mid-Infrared Emission from E+A Galaxies in the Coma Cluster
We have used ISO to observe at 12m seven E+A galaxies plus an additional
emission line galaxy, all in the Coma cluster. E+A galaxies lacking narrow
emission lines have 2.2m to 12m flux density ratios or limits similar
to old stellar populations (typical of early-type galaxies). Only galaxies with
emission lines have enhanced 12m flux density. Excess 12m emission is
therefore correlated with the presence of on-going star formation or an active
galactic nucleus (AGN).
By comparing the current star formation rates with previous rates estimated
from the Balmer absorption features, we divide the galaxies into two groups:
those for which star formation has declined significantly following a dramatic
peak 1 Gyr ago; and those with a significant level of ongoing star
formation or/and an AGN. There is no strong difference in the spatial
distribution on the sky between these two groups. However, the first group has
systemic velocities above the mean cluster value and the second group below
that value. This suggests that the two groups differ kinematically.
Based on surveys of the Coma cluster in the radio, the IRAS sources, and
galaxies detected in H emission, we sum the far infrared luminosity
function of galaxies in the cluster. We find that star formation in late type
galaxies is probably the dominant component of the Coma cluster far infrared
luminosity. The presence of significant emission from intracluster dust is not
yet firmly established. The member galaxies also account for most of the far
infrared output from nearby rich clusters in general.Comment: AAS Latex, accepted for publication in Ap
Derivation of the quantum probability law from minimal non-demolition measurement
One more derivation of the quantum probability rule is presented in order to
shed more light on the versatile aspects of this fundamental law. It is shown
that the change of state in minimal quantum non-demolition measurement, also
known as ideal measurement, implies the probability law in a simple way.
Namely, the very requirement of minimal change of state, put in proper
mathematical form, gives the well known Lueders formula, which contains the
probability rule.Comment: 8 page
Complementarity and Scientific Rationality
Bohr's interpretation of quantum mechanics has been criticized as incoherent
and opportunistic, and based on doubtful philosophical premises. If so Bohr's
influence, in the pre-war period of 1927-1939, is the harder to explain, and
the acceptance of his approach to quantum mechanics over de Broglie's had no
reasonable foundation. But Bohr's interpretation changed little from the time
of its first appearance, and stood independent of any philosophical
presuppositions. The principle of complementarity is itself best read as a
conjecture of unusually wide scope, on the nature and future course of
explanations in the sciences (and not only the physical sciences). If it must
be judged a failure today, it is not because of any internal inconsistency.Comment: 29 page
Optical Imaging of Very Luminous Infrared Galaxy Systems: Photometric Properties and Late Evolution
A sample of 19 low redshift (0.03z0.07) very luminous infrared galaxy
(VLIRG: L[8-1000 m] ) systems (30
galaxies) has been imaged in , , and . These objects cover a
luminosity range that is key to linking the most luminous infrared galaxies
with the population of galaxies at large. We have obtained photometry for all
of these VLIRG systems, the individual galaxies (when detached), and their
nuclei, and the relative behavior of these classes has been studied in optical
color-magnitude diagrams. The photometric properties of the sample are also
compared with previously studied samples of ULIRGs. The mean observed
photometric properties of VLIRG and ULIRG samples, considered as a whole, are
indistinguishable at optical wavelengths. This suggests that not only ULIRG,
but also the more numerous population of VLIRGs, have similar rest-frame
optical photometric properties as the submillimeter galaxies (SMG), reinforcing
the connection between low-{\it z} LIRGs -- high-{\it z} SMGs. When the nuclei
of the {\it young} and {\it old} interacting systems are considered separately,
some differences between the VLIRG and the ULIRG samples are found. In
particular, the old VLIRGs are less luminous and redder than old ULIRG systems.
If confirmed with larger samples, this behavior suggests that the late-stage
evolution is different for VLIRGs and ULIRGs. Specifically, as suggested from
spectroscopic data, the present photometric observations support the idea that
the activity during the late phases of VLIRG evolution is dominated by
starbursts, while a higher proportion of ULIRGs could evolve into a QSO type of
object.Comment: 27 pages, 5 figures (degraded to reduce space). Figures 1 and 2 are
multiple page figures (i.e. Fig 1a,b and Fig2a-g
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