763,559 research outputs found
Starburst and cirrus models for submillimeter galaxies
We present radiative transfer models for submillimeter galaxies with
spectroscopic redshifts and mid-infrared spectroscopy from Spitzer/IRS and
analyze available Spitzer/MIPS 24, 70 and 160mu data. We use two types of
starburst models, a cirrus model and a model for the emission of an AGN torus
in order to investigate the nature of these objects. We find that for three of
the objects (25%) cirrus emission alone can account for the mid-infrared
spectrum and the MIPS and submillimeter data. For the remaining objects we find
that we need a combination of starburst and cirrus in order to fit
simultaneously the multi--wavelength data.
We find that the typical submillimeter galaxy has comparable luminosity in
the starburst (median L=10^12.5 Lo) and cirrus (median L=10^12.4 Lo)
components. This could arise if the galaxies have been forming stars
continuously for the last 250Myr with the star formation occurring in the last
5Myr being shrouded by high-optical-depth molecular cloud dust, whereas the
rest of the starlight is attenuated by diffuse dust or cirrus with an Av of
about 1mag.Comment: 9 pages, AA accepte
Moving Objects in the Hubble Ultra Deep Field
We identify proper motion objects in the Hubble Ultra Deep Field (UDF) using
the optical data from the original UDF program in 2004 and the near-infrared
data from the 128-orbit UDF 2012 campaign. There are 12 sources brighter than
I=27 mag that display >3sigma significant proper motions. We do not find any
proper motion objects fainter than this magnitude limit. Combining optical and
near-infrared photometry, we model the spectral energy distribution of each
point-source using stellar templates and state-of-the-art white dwarf models.
For I<27 mag, we identify 23 stars with K0-M6 spectral types and two faint blue
objects that are clearly old, thick disk white dwarfs. We measure a thick disk
white dwarf space density of 0.1-1.7 E-3 per cubic parsec from these two
objects. There are no halo white dwarfs in the UDF down to I=27 mag. Combining
the Hubble Deep Field North, South, and the UDF data, we do not see any
evidence for dark matter in the form of faint halo white dwarfs, and the
observed population of white dwarfs can be explained with the standard Galactic
models.Comment: ApJ, in pres
Efficient Regularized Least-Squares Algorithms for Conditional Ranking on Relational Data
In domains like bioinformatics, information retrieval and social network
analysis, one can find learning tasks where the goal consists of inferring a
ranking of objects, conditioned on a particular target object. We present a
general kernel framework for learning conditional rankings from various types
of relational data, where rankings can be conditioned on unseen data objects.
We propose efficient algorithms for conditional ranking by optimizing squared
regression and ranking loss functions. We show theoretically, that learning
with the ranking loss is likely to generalize better than with the regression
loss. Further, we prove that symmetry or reciprocity properties of relations
can be efficiently enforced in the learned models. Experiments on synthetic and
real-world data illustrate that the proposed methods deliver state-of-the-art
performance in terms of predictive power and computational efficiency.
Moreover, we also show empirically that incorporating symmetry or reciprocity
properties can improve the generalization performance
Model-Based Geostatistics the Easy Way
This paper briefly describes geostatistical models for Gaussian and non-Gaussian data and demonstrates the geostatsp and dieasemapping packages for performing inference using these models. Making use of R’s spatial data types, and raster objects in particular, makes spatial analyses using geostatistical models simple and convenient. Examples using real data are shown for Gaussian spatial data, binomially distributed spatial data, a logGaussian Cox process, and an area-level model for case counts
Shape models and physical properties of asteroids
Despite the large amount of high quality data generated in recent space
encounters with asteroids, the majority of our knowledge about these objects
comes from ground based observations. Asteroids travelling in orbits that are
potentially hazardous for the Earth form an especially interesting group to be
studied. In order to predict their orbital evolution, it is necessary to
investigate their physical properties. This paper briefly describes the data
requirements and different techniques used to solve the lightcurve inversion
problem. Although photometry is the most abundant type of observational data,
models of asteroids can be obtained using various data types and techniques. We
describe the potential of radar imaging and stellar occultation timings to be
combined with disk-integrated photometry in order to reveal information about
physical properties of asteroids.Comment: From Assessment and Mitigation of Asteroid Impact Hazards boo
Fast Autocorrelated Context Models for Data Compression
A method is presented to automatically generate context models of data by
calculating the data's autocorrelation function. The largest values of the
autocorrelation function occur at the offsets or lags in the bitstream which
tend to be the most highly correlated to any particular location. These offsets
are ideal for use in predictive coding, such as predictive partial match (PPM)
or context-mixing algorithms for data compression, making such algorithms more
efficient and more general by reducing or eliminating the need for ad-hoc
models based on particular types of data. Instead of using the definition of
the autocorrelation function, which considers the pairwise correlations of data
requiring O(n^2) time, the Weiner-Khinchin theorem is applied, quickly
obtaining the autocorrelation as the inverse Fast Fourier transform of the
data's power spectrum in O(n log n) time, making the technique practical for
the compression of large data objects. The method is shown to produce the
highest levels of performance obtained to date on a lossless image compression
benchmark.Comment: v2 includes bibliograph
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