610 research outputs found
On fixed points of Poisson shot noise transforms
Distributional fixed points of a Poisson shot noise transform (for
nonnegative, nonincreasing response functions bounded by 1) are characterized.
The tail behavior of fixed points is described. Typically they have either
exponential moments or their tails are proportional to a power function, with
exponent greater than -1. The uniqueness of fixed points is also discussed.
Finally, it is proved that in most cases fixed points are absolutely
continuous, apart from the possible atom at zero
A new factorization property of the selfdecomposable probability measures
We prove that the convolution of a selfdecomposable distribution with its
background driving law is again selfdecomposable if and only if the background
driving law is s-selfdecomposable. We will refer to this as the factorization
property of a selfdecomposable distribution; let L^f denote the set of all
these distributions. The algebraic structure and various characterizations of
L^f are studied. Some examples are discussed, the most interesting one being
given by the Levy stochastic area integral. A nested family of subclasses
L^f_n, n\ge 0, (or a filtration) of the class L^f is given.Comment: Published at http://dx.doi.org/10.1214/009117904000000225 in the
Annals of Probability (http://www.imstat.org/aop/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Toughening of BIS maleimide resins: Synthesis and characterization of maleimide terminated poly(arylene ether) oligomers and polymers
Amine functional poly(arylene ether) sulfones were previously reported. Herein, the chemistry was extended to amorphous poly(arylene ether) ketones because of their higher fracture toughness values, relative to the polysulfones. It was demonstrated that the amino functional oligomers undergo a self-crosslinking reaction at temperatures above about 220 C. This produces an insoluble, but ductile network that has excellent resistance. A ketamine structure hypothesis was proposed and verified using solid state magic angle NMR. In most cases, the water generated upon ketamine formation is too low to produce porosity and solid networks are obtained. The stability of the ketamine networks towards hydrolysis is excellent. The chemistry was further demonstrated to be able to crosslink preformed nonfunctional poly(arylene ether) ketones if a difunctional amine was utilized. This concept has the possibility of greatly improving the creep resistance of thermoplastics. Also, a new technique was developed for converting the amine functional oligomers cleanly into maleimide structures. This method involves reacting maleic anhydride with monomeric aminophenols in the presence of solvent mixtures
The Large Area Radio Galaxy Evolution Spectroscopic Survey (LARGESS): survey design, data catalogue and GAMA/WiggleZ spectroscopy
© 2016 The Authors. We present the Large Area Radio Galaxy Evolution Spectroscopic Survey (LARGESS), a spectroscopic catalogue of radio sources designed to include the full range of radio AGN populations out to redshift z ~ 0.8. The catalogue covers ~800 deg 2 of sky, and provides optical identifications for 19 179 radio sources from the 1.4 GHz Faint Images of the Radio Sky at Twenty-cm (FIRST) survey down to an optical magnitude limit of i mod < 20.5 in Sloan Digital Sky Survey (SDSS) images. Both galaxies and point-like objects are included, and no colour cuts are applied. In collaboration with the WiggleZ and Galaxy And Mass Assembly (GAMA) spectroscopic survey teams, we have obtained new spectra for over 5000 objects in the LARGESS sample. Combining these new spectra with data from earlier surveys provides spectroscopic data for 12 329 radio sources in the survey area, of which 10 856 have reliable redshifts. 85 per cent of the LARGESS spectroscopic sample are radio AGN (median redshift z = 0.44), and 15 per cent are nearby star-forming galaxies (median z = 0.08). Low-excitation radio galaxies (LERGs) comprise the majority (83 per cent) of LARGESS radio AGN at z < 0.8, with 12 per cent being high-excitation radio galaxies (HERGs) and 5 per cent radioloud QSOs. Unlike the more homogeneous LERG and QSO sub-populations, HERGs are a heterogeneous class of objects with relatively blue optical colours and a wide dispersion in mid-infrared colours. This is consistent with a picture in which most HERGs are hosted by galaxies with recent or ongoing star formation as well as a classical accretion disc
Luminous K-band Selected Quasars from UKIDSS
The largest K-band flux-limited sample of luminous quasars to date has been
constructed from the UKIDSS Large Area Survey Early Data Release, covering an
effective area of 12.8 deg^2. Exploiting the K-band excess of all quasars with
respect to foreground stars, including quasars experiencing dust reddening and
objects with non-standard SEDs, a list of targets suitable for spectroscopic
follow-up observations with the AAOmega multi-object spectrograph is
constructed, resulting in more than 200 confirmed AGN. KX-selection
successfully identifies as quasar candidates objects that are excluded from the
SDSS quasar selection algorithm due to their colours being consistent with the
stellar locus in optical colour space (with the space density of the excluded
objects agreeing well with results from existing completeness analyses). Nearly
half of the KX-selected quasars with K<17.0 at z<3 are too faint in the i-band
to have been targeted by the SDSS quasar selection algorithm, revealing a large
population of quasars with red i-K colours. The majority of these objects have
significant amounts of host galaxy light contributing to their K-band
magnitudes, consistent with previous predictions. The remaining objects are
morphologically stellar and have colours consistent with quasars experiencing
SMC-type reddening with 0.10<E(B-V)<0.25. The i-K colour distribution indicates
that <10 per cent of the quasar population is missing from this K-band selected
sample due to dust reddening, and comparisons with simulations strongly favour
an obscured fraction of <20 per cent. (Abridged)Comment: 22 pages, 18 figures, accepted for publication in MNRAS. Resolution
of Figure 2 has been reduced for astro-ph submission. The complete Table 5
can be found at http://www.aip.de/People/nmaddox/KX/catalogue.tx
A Catalog of Spectroscopically Confirmed White Dwarfs from the Sloan Digital Sky Survey Data Release 4
We present a catalog of 9316 spectroscopically confirmed white dwarfs from
the Sloan Digital Sky Survey Data Release 4. We have selected the stars through
photometric cuts and spectroscopic modeling, backed up by a set of visual
inspections. Roughly 6000 of the stars are new discoveries, roughly doubling
the number of spectroscopically confirmed white dwarfs. We analyze the stars by
performing temperature and surface gravity fits to grids of pure hydrogen and
helium atmospheres. Among the rare outliers are a set of presumed helium-core
DA white dwarfs with estimated masses below 0.3 Msun, including two candidates
that may be the lowest masses yet found. We also present a list of 928 hot
subdwarfs.Comment: Accepted by the Astrophysical Journal Supplements, 25 pages, 24
figures, LaTeX. The electronic catalog, as well as diagnostic figures and
links to the spectra, is available at http://das.sdss.org/wdcat/dr4
Discovery of Ultra-Compact Dwarf Galaxies in the Virgo Cluster
We have discovered nine ultra-compact dwarf galaxies (UCDs) in the Virgo
Cluster, extending samples of these objects outside the Fornax Cluster. Using
the 2dF multi-fiber spectrograph on the Anglo-Australian Telescope, the new
Virgo members were found among 1500 color-selected, star-like targets with 16.0
< b_j < 20.2 in a two-degree diameter field centered on M87 (NGC4486). The
newly-found UCDs are comparable to the UCDs in the Fornax Cluster, with sizes
<~ 100 pc, -12.9 < M_B < -10.7, and exhibiting red, absorption-line spectra,
indicative of an older stellar population. The properties of these objects
remain consistent with the tidal threshing model for the origin of UCDs from
the surviving nuclei of nucleated dwarf ellipticals disrupted in the cluster
core, but can also be explained as objects that were formed by mergers of star
clusters created in galaxy interactions. The discovery that UCDs exist in Virgo
shows that this galaxy type is probably a ubiquitous phenomenon in clusters of
galaxies; coupled with their possible origin by tidal threshing, the UCD
population is a potential indicator and probe of the formation history of a
given cluster.
We also describe one additional bright UCD with M_B = -12.0 in the core of
the Fornax Cluster. We find no further UCDs in our Fornax Cluster Spectroscopic
Survey down to b_j = 19.5 in two additional 2dF fields extending as far as 3
degrees from the center of the cluster. All six Fornax bright UCDs identified
with 2dF lie within 0.5 degree (projected distance of 170 kpc) of the central
elliptical galaxy NGC1399.Comment: 26 pages; 12 figures; accepted for publication in the Astronomical
Journa
- …