9,939 research outputs found
Resurrection of Traditional Luminosity Evolution Models to Explain Faint Field Galaxies
We explore the nature of the evolution of faint field galaxies by assuming
that the local luminosity function is not well defined. We use a non-negative
least squares technique to derive a near optimal set of local luminosity
functions for different spectral types of galaxies by fitting to the observed
optical and near-infrared counts, B-R colors, and redshift distributions for
galaxies with 15 < B < 27. We report here the results of using only traditional
luminosity evolution (ie. the photometric evolution of stars in a galaxy over
time given reasonable assumptions of the form of the star formation history for
various galaxy types), and simple galaxy reddening and find excellent fits to
the observed data to B = 27. We conclude that models more exotic than
traditional luminosity evolution are not yet required to explain existing faint
field galaxy data and thus the need for contributions by mergers or new
populations of galaxies is at least 5x less than previously estimated.Comment: 9 pages + 1 table + 4 figures; uuencoded tar compressed postscript;
to be published in The Astrohysical Journal Letter
Delay-rate tradeoff for ergodic interference alignment in the Gaussian case
In interference alignment, users sharing a wireless channel are each able to
achieve data rates of up to half of the non-interfering channel capacity, no
matter the number of users. In an ergodic setting, this is achieved by pairing
complementary channel realizations in order to amplify signals and cancel
interference. However, this scheme has the possibility for large delays in
decoding message symbols. We show that delay can be mitigated by using outputs
from potentially more than two channel realizations, although data rate may be
reduced. We further demonstrate the tradeoff between rate and delay via a
time-sharing strategy. Our analysis considers Gaussian channels; an extension
to finite field channels is also possible.Comment: 7 pages, 2 figures, presented at 48th Allerton Conference on
Communication Control and Computing, 2010. Includes appendix detailing Markov
chain analysi
A deep redshift survey of field galaxies. Comments on the reality of the Butcher-Oemler effect
A spectroscopic survey of over 400 field galaxies has been completed in three fields for which we have deep UBVI photographic photometry. The galaxies typically range from B=20 to 22 and possess redshifts z from 0.1 to 0.5 that are often quite spiky in distribution. Little, if any, luminosity evolution is observed up to redshifts z approx 0.5. By such redshifts, however, an unexpectedly large fraction of luminous galaxies has very blue intrinsic colors that suggest extensive star formation; in contrast, the reddest galaxies still have colors that match those of present-day ellipticals
Exact Zeros of the Partition Function for a Continuum System with Double Gaussian Peaks
We calculate the exact zeros of the partition function for a continuum system
where the probability distribution for the order parameter is given by two
asymmetric Gaussian peaks. When the positions of the two peaks coincide, the
two separate loci of zeros which used to give first-order transition touch each
other, with density of zeros vanishing at the contact point on the positive
real axis. Instead of the second-order transition of Ehrenfast classification
as one might naively expect, one finds a critical behavior in this limit.Comment: 13 pages, 6 figures, revtex, minor changes in fig.2, to be published
in Physical Review
Resonant x-ray scattering study on multiferroic BiMnO3
Resonant x-ray scattering is performed near the Mn K-absorption edge for an
epitaxial thin film of BiMnO3. The azimuthal angle dependence of the resonant
(003) peak (in monoclinic indices) is measured with different photon
polarizations; for the channel a 3-fold symmetric oscillation
is observed in the intensity variation, while the scattering
intensity remains constant. These features are accounted for in terms of the
peculiar ordering of the manganese 3d orbitals in BiMnO3. It is demonstrated
that the resonant peak persists up to 770 K with an anomaly around 440 K; these
high and low temperatures coincide with the structural transition temperatures,
seen in bulk, with and without a symmetry change, respectively. A possible
relationship of the orbital order with the ferroelectricity of the system is
discussed.Comment: 14 pages, 4 figure
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