4,197 research outputs found
Some characterizations of the spherical harmonics coefficients for isotropic random fields
In this paper we provide some simple characterizations for the spherical
harmonics coefficients of an isotropic random field on the sphere. The main
result is a characterization of isotropic gaussian fields through independence
of the coefficients of their development in spherical harmonics.Comment: 9 pages. Submitted June 200
Recent star formation in nearby 3CR radio-galaxies from UV HST observations
We analyzed HST images of 31 nearby (z <~ 0.1) 3CR radio-galaxies. We
compared their UV and optical images to detect evidence of recent star
formation. Six objects were excluded because they are highly nucleated or had
very low UV count rates. After subtracting the emission from their nuclei
and/or jets, 12 of the remaining 25 objects, presenting an UV/optical colors
NUV - r < 5.4, are potential star-forming candidates. Considering the
contamination from other AGN-related processes (UV emission lines, nebular
continuum, and scattered nuclear light), there are 6 remaining star-forming
"blue" galaxies.
We then divide the radio galaxies, on the basis of the radio morphology,
radio power, and diagnostic optical line ratios, into low and high excitation
galaxies, LEG and HEG. While there is no correlation between the FR type (or
radio power) and color, the FR type is clearly related to the spectroscopic
type. In fact, all HEG (with one possible exception) show morphological
evidence of recent star formation in UV compact knots, extended over 5-20 kpc.
Conversely, there is only 1 "blue" LEG out of 19, including in this class also
FR I galaxies.
The picture that emerges, considering color, UV, optical, and dust
morphology, is that only in HEG recent star formation is associated with these
relatively powerful AGN, which are most likely triggered by a recent, major,
wet merger. Conversely, in LEG galaxies the fraction of actively star-forming
objects is not enhanced with respect to quiescent galaxies. The AGN activity in
these sources can be probably self-sustained by their hot interstellar medium.Comment: Accepted for publication in A&
Subsampling needlet coefficients on the sphere
In a recent paper, we analyzed the properties of a new kind of spherical
wavelets (called needlets) for statistical inference procedures on spherical
random fields; the investigation was mainly motivated by applications to
cosmological data. In the present work, we exploit the asymptotic uncorrelation
of random needlet coefficients at fixed angular distances to construct
subsampling statistics evaluated on Voronoi cells on the sphere. We illustrate
how such statistics can be used for isotropy tests and for bootstrap estimation
of nuisance parameters, even when a single realization of the spherical random
field is observed. The asymptotic theory is developed in detail in the high
resolution sense.Comment: Published in at http://dx.doi.org/10.3150/08-BEJ164 the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
Asymptotics for spherical needlets
We investigate invariant random fields on the sphere using a new type of
spherical wavelets, called needlets. These are compactly supported in frequency
and enjoy excellent localization properties in real space, with
quasi-exponentially decaying tails. We show that, for random fields on the
sphere, the needlet coefficients are asymptotically uncorrelated for any fixed
angular distance. This property is used to derive CLT and functional CLT
convergence results for polynomial functionals of the needlet coefficients:
here the asymptotic theory is considered in the high-frequency sense. Our
proposals emerge from strong empirical motivations, especially in connection
with the analysis of cosmological data sets.Comment: Published in at http://dx.doi.org/10.1214/08-AOS601 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
FR0CAT: a FIRST catalog of FR0 radio galaxies
With the aim of exploring the properties of the class of FR0 radio galaxies,
we selected a sample of 108 compact radio sources, called FR0CAT, by combining
observations from the NVSS, FIRST, and SDSS surveys. The catalog includes
sources with z, with a radio size 5 kpc, and with an
optical spectrum characteristic of low-excitation galaxies. Their 1.4-GHz radio
luminosities range erg/s. The
FR0CAT hosts are mostly (86%) luminous () red
early-type galaxies with black hole masses : similar to the hosts of FRI radio galaxies, but they are on
average a factor 1.6 less massive. The number density of FR0CAT sources
is 5 times higher than that of FRIs, and thus they represent the dominant
population of radio sources in the local Universe. Different scenarios are
considered to account for the smaller sizes and larger abundance of FR0s with
respect to FRIs. An age-size scenario that considers FR0s as young radio
galaxies that will all eventually evolve into extended radio sources cannot be
reconciled with the large space density of FR0s. However, the radio activity
recurrence, with the duration of the active phase covering a wide range of
values and with short active periods strongly favored with respect to longer
ones, might account for their large density number. Alternatively, the jet
properties of FR0s might be intrinsically different from those of the FRIs, the
former class having lower bulk Lorentz factors, possibly due to lower black
hole spins. Our study indicates that FR0s and FRI/IIs can be interpreted as two
extremes of a continuous population of radio sources that is characterized by a
broad distribution of sizes and luminosities of their extended radio emission,
but shares a single class of host galaxies.Comment: 11 pages, 6 figures, accepted for publication on A&
FRICAT: A FIRST catalog of FRI radio galaxies
We built a catalog of 219 FRI radio galaxies (FRIs), called FRICAT, selected
from a published sample and obtained by combining observations from the NVSS,
FIRST, and SDSS surveys. We included in the catalog the sources with an
edge-darkened radio morphology, redshift , and extending (at the
sensitivity of the FIRST images) to a radius larger than 30 kpc from the
center of the host. We also selected an additional sample (sFRICAT) of 14
smaller (10 30 kpc) FRIs, limiting to . The hosts of the FRICAT
sources are all luminous (), red early-type
galaxies with black hole masses in the range ; the spectroscopic classification based on the optical
emission line ratios indicates that they are all low excitation galaxies.
Sources in the FRICAT are then indistinguishable from the FRIs belonging to the
Third Cambridge Catalogue of Radio Sources (3C) on the basis of their optical
properties. Conversely, while the 3C-FRIs show a strong positive trend between
radio and [OIII] emission line luminosity, these two quantities are unrelated
in the FRICAT sources; at a given line luminosity, they show radio luminosities
spanning about two orders of magnitude and extending to much lower ratios
between radio and line power than 3C-FRIs. Our main conclusion is that the
3C-FRIs just represent the tip of the iceberg of a much larger and diverse
population of FRIs.Comment: 34 pages, 8 figures, 1 table, 1 appendix,accepted for publication in
A&A, pre-proof versio
High-resolution VLA observations of FR0 radio galaxies: properties and nature of compact radio sources
We present the results of Karl G. Jansky Very Large Array (VLA) observations
to study the properties of FR0 radio galaxies, the compact radio sources
associated with early-type galaxies which represent the bulk of the local
radio-loud AGN population. We obtained A-array observations at 1.5, 4.5, and
7.5 GHz for 18 FR0s from the FR0CAT sample: these are sources at ,
unresolved in the FIRST images and spectroscopically classified as low
excitation galaxies (LEG). Although we reach an angular resolution of 0.3
arcsec, the majority of the 18 FR0s is still unresolved. Only four objects show
extended emission. Six have steep radio spectra, 11 are flat cores, while one
shows an inverted spectrum. We find that 1) the ratio between core and total
emission in FR0s is 30 times higher than in FRI and 2) FR0s share the
same properties with FRIs from the nuclear and host point of view. FR0s differ
from FRIs only for the paucity of extended radio emission. Different scenarios
were investigated: 1) the possibility that all FR0s are young sources
eventually evolving into extended sources is ruled out by the distribution of
radio sizes; 2) similarly, a time-dependent scenario, where a variation of
accretion or jet launching prevents the formation of large-scales radio
structures, appears to be rather implausible due to the large abundance of
sub-kpc objects 3) a scenario in which FR0s are produced by mildly relativistic
jets is consistent with the data but requires observations of a larger sample
to be properly tested.Comment: accepted for publication on MNRAS (12 pages, 8 figures
On the characterization of isotropic Gaussian fields on homogeneous spaces of compact groups
Let T be a random field invariant under the action of a compact group G We
give conditions ensuring that independence of the random Fourier coefficients
is equivalent to Gaussianity. As a consequence, in general it is not possible
to simulate a non-Gaussian invariant random field through its Fourier expansion
using independent coefficients
Discovery of a FR0 radio galaxy emitting at -ray energies
We present supporting evidence for the first association of a Fermi source,
3FGLJ1330.0-3818, with the FR0 radio galaxy Tol1326-379. FR0s represent the
majority of the local radio loud AGN population but their nature is still
unclear. They share the same properties of FRIs from the point of view of the
nuclear and host properties, but they show a large deficit of extended radio
emission. Here we show that FR0s can emit photons at very high energies.
Tol1326-379 has a GeV luminosity of erg
s, typical of FRIs, but with a steeper -ray spectrum
(). This could be related to the intrinsic jet properties
but also to a different viewing angle.Comment: 7 pages, 5 figures , accepted for publication on MNRA
The Literacy of America's College Students
Measures the literacy of 1,827 graduating college and university students from eighty institutions. Looks at the ability to perform prose tasks such as read and use texts; search and comprehend forms; and conduct quantitative, computational tasks
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