111 research outputs found
Ground State Energy of the One-Dimensional Discrete Random Schr\"{o}dinger Operator with Bernoulli Potential
In this paper, we show the that the ground state energy of the one
dimensional Discrete Random Schroedinger Operator with Bernoulli Potential is
controlled asymptotically as the system size N goes to infinity by the random
variable \ell_N, the length the longest consecutive sequence of sites on the
lattice with potential equal to zero. Specifically, we will show that for
almost every realization of the potential the ground state energy behaves
asymptotically as in the sense that the ratio of
the quantities goes to one
Radio-optically selected clusters of galaxies. I. The radiogalaxy sample
In order to study the status and the possible evolution of clusters of
galaxies at intermediate redshifts (z ~ 0.1 - 0.3), as well as their spatial
correlation and relationship with the local environment, we built a sample of
candidate groups and clusters of galaxies using radiogalaxies as tracers of
dense environments. This technique - complementary to purely optical or X-ray
cluster selection methods - represents an interesting tool for the selection of
clusters in a wide range of richness, so to make it possible to study the
global properties of groups and clusters of galaxies, such as their
morphological content, dynamical status and number density, as well as the
effect of the environment on the radio emission phenomena. In this paper we
describe the compilation of a catalogue of 16000 radio sources in the region of
the South Galactic Pole extracted from the publicly available NRAO VLA Sky
Survey maps, and the optical identification procedure with galaxies brighter
than b_J=20.0 in the EDSGC Catalogue. The radiogalaxy sample, valuable for the
study of radio source populations down to low flux levels, consists of 1288
identifications and has been used to detect candidate groups and clusters
associated to NVSS radio sources. In a companion paper we will discuss the
cluster detection method, the cluster sample as well as first spectroscopic
results.Comment: 15 pages, 6 Postscript and 1 GIF figures. Accepted for publication in
A&
Assembly of Advanced Materials into 3D Functional Structures by Methods Inspired by Origami and Kirigami: A Review
Origami and kirigami, the ancient techniques for making paper works of art, also provide inspiration for routes to structural platforms in engineering applications, including foldable solar panels, retractable roofs, deployable sunshields, and many others. Recent work demonstrates the utility of the methods of origami/kirigami and conceptually related schemes in cutting, folding, and buckling in the construction of devices for emerging classes of technologies, with examples in mechanical/optical metamaterials, stretchable/conformable electronics, micro/nanoscale biosensors, and large‐amplitude actuators. Specific notable progress is in the deployment of functional materials such as single‐crystal silicon, shape memory polymers, energy‐storage materials, and graphene into elaborate 3D micro and nanoscale architectures. This review highlights some of the most important developments in this field, with a focus on routes to assembly that apply across a range of length scales and with advanced materials of relevance to practical applications.113Ysciescopu
Radio-optically selected clusters of galaxies. II. The cluster sample
We present a sample of 171 candidate groups and clusters of galaxies at
intermediate redshift over an area of ~550 square degrees at the South Galactic
Pole selected by using optically identified radio sources from the NRAO VLA Sky
Survey as tracers of dense environment. Out of these 171 candidates, 76 have a
counterpart in the literature while 95 of them are previously unknown clusters.
This paper presents the cluster selection technique, based on the search of
excesses in the optical surface density of galaxies near identified
radiogalaxies, and the first spectroscopic results aimed to confirm the
presence of a cluster. Spectroscopy for 11 candidates led to the detection of 9
clusters at redshift in the range 0.13 - 0.3, with estimated velocity
dispersions ranging from values typical of clusters to those of galaxy groups.
These results show that this technique represents a powerful tool for the
selection of homogeneous samples of intermediate redshift clusters over a wide
range of richness.Comment: 13 pages, 3 Postscript and 2 GIF figures. Accepted for publication in
A&
FIRST-based survey of Compact Steep Spectrum sources I. MERLIN images of arc-second scale objects
Compact Steep Spectrum (CSS) sources are powerful extragalactic radio sources
with angular dimensions of the order of a few arcseconds or less. Such a
compactness is apparently linked to the youth of these objects. The majority of
CSSs investigated so far have been known since the early 1980s. This paper is
the first in a series where we report the results of an observational campaign
targeted on a completely new sample of CSSs which are significantly weaker than
those investigated before. The ultimate goal of that campaign is to find out
how ``weak'' CSSs compare to ``strong'', classical ones, especially with regard
to the morphologies. Here we present an analysis of morphological and physical
properties of five relatively large sources based on MERLIN observations at 1.6
and 5 GHz.Comment: 8 pages, 7 figures, A&A in pres
Structure of the Accretion Flow in Broad-Line Radio Galaxies: The Case of 3C390.3
We present XMM and Suzaku observations of the Broad-Line Radio Galaxy (BLRG)
3C390.3. The Fe Ka line has a width FWHM ~ 8,800 km/s, consistent within a
factor two with the width of the double-peaked H_alpha line, suggesting an
origin from the Broad Line Region. The data show for the first time a weak,
broad bump extending from 5 to 7 keV. When fitted with a Gaussian, its centroid
energy is 6.6 keV in the source's rest-frame with FWHM of 43,000 km/s and EW of
50 eV; its most likely interpretation is emission from He-like Fe (Fe XXV),
suggesting the presence of an ionized medium in the inner regions of 3C390.3.
The broad-band 0.5-100 keV continuum is well described by a single power law
with photon index Gamma=1.6 and cutoff energy 157 keV, plus cold reflection
with strength R=0.5. In addition, ionized reflection is required to account for
the 6.6 keV bump in the broad-band continuum, yielding an ionization parameter
xi ~ 2700 ergs cm s^-1; the inner radius of the ionized reflector is
constrained to be larger than 20 r_G, although this result depends on the
assumed emissivity profile of the disk. If true, we argue that the lack of
broad Fe K emission from within 20 r_G indicates that the innermost regions of
the disk in 3C390.3 are obscured and/or poorly illuminated. While the SED of
3C390.3 is generally dominated by accretion-related continuum, during accretion
low states the jet can significantly contribute in the optical to X-ray bands
via synchrotron self-Compton emission. (Abridged)Comment: 7 figures, 5 tables, accepted for publication in Ap
Dust in 3CR radio galaxies: On the FR1-FR2 difference
We compare three 3CR samples of 11 FR1 galaxies, 17 FR2 galaxies and 18
lobe-dominated quasars contained in the ISO Data Archive. In contrast to the
powerful FR2 galaxies with edge-brightened lobes, the low radio power FR1
galaxies in our sample do not exhibit any high MIR or FIR dust luminosity,
which is typical for a buried, intrinsically more luminous AGN. This
consolidates the fact already inferred from optical studies that their AGNs
have only a relatively low luminosity. Also the FR1 galaxies show a high
FIR/MIR luminosity ratio, compared to quasars, suggesting that their FIR
luminosity is substantially powered by the interstellar radiation field (ISRF)
of the giant elliptical hosts. Finally, we discuss the FR1-FR2 morphological
dichotomy. FR1 galaxies do not have more interstellar matter (ISM) than FR2s as
traced -- on the large scale -- by the cool FIR emitting dust and -- in the
nuclear region -- by the warm MIR emitting dust. Due to the lack of central gas
we suggest that the black holes of our FR1 galaxies are fed at a lower
accretion rate than those of the FR2 galaxies.Comment: 4 pages 3 figures Letter accepted by A&
Episodic Star Formation Coupled to Reignition of Radio Activity in 3C 236
We present Hubble Space Telescope UV and optical imaging of the radio galaxy
3C 236, whose relic 4 Mpc radio jet lobes and inner 2 kpc CSS radio source are
evidence of multiple epochs of AGN activity. Our data confirm the presence of
four bright knots of FUV emission in an arc along the edge of the inner
circumnuclear dust disk in the galaxy's nucleus, as well as FUV emission
cospatial with the nucleus itself. We interpret these to be sites of recent or
ongoing star formation. We present photometry of these knots, as well as an
estimate for the internal extinction in the source using the Balmer decrement
from SDSS spectroscopy. We estimate the ages of the knots by comparing our
extinction-corrected photometry with stellar population synthesis models. We
find the four knots cospatial with the dusty disk to be young, of order 10^7 yr
old. The FUV emission in the nucleus is likely due to an episode of star
formation triggered ~10^9 yr ago. We argue that the young 10^7 yr old knots
stem from an episode of star formation that was roughly coeval with the event
resulting in reignition of radio activity, creating the CSS source. The 10^9 yr
old stars in the nucleus may be associated with the previous epoch of activity
that generated the 4 Mpc relic source, before it was cut off by exhaustion or
interruption. The ages of the knots, considered in context with the disturbed
morphology of the nuclear dust and the double-double morphology of the "old"
and "young" radio sources, present evidence for an episodic AGN/starburst
connection. We suggest that the AGN fuel supply was interrupted for ~10^7 yr
due to a minor merger event and has now been restored, and the resultant
non-steady flow of gas toward the nucleus is likely responsible for both the
new episode of infall-induced star formation and also the multiple epochs of
radio activity.Comment: 15 pages, 7 figures. Accepted for publication in ApJ
Starbursts and the triggering of the activity in nearby powerful radio galaxies
We present high quality long-slit spectra for three nearby powerful radio
galaxies 3C293, 3C305, PKS1345+12. These were taken with the aim of
characterising the young stellar populations (YSP), and thereby investigating
the evolution of the host galaxies, as well as the events that triggered the
activity. Isochrone spectral synthesis modelling of the wide wavelength
coverage spectra of nuclear and off-nuclear continuum-emitting regions have
been used to estimate the ages, masses and luminosities of the YSP component,
taking full account of reddening effects and potential contamination by
activity-related components. We find that the YSP make a substantial
contribution to the continuum flux in the off-nuclear regions on a radial scale
of 1 - 20kpc in all three objects. Moreover, in two objects we find evidence
for reddened post-starburst stellar populations in the near-nuclear regions of
the host galaxies. The YSP are relatively old (0.1- 2Gyr), massive and make up
a large proportion (~1 - 50%) of the total stellar mass in the regions of
galaxies sampled by the observations. Overall, these results are consistent
with the idea that AGN activity in some radio galaxies is triggered by major
gas-rich mergers. Therefore, these radio galaxies form part of the subset of
early-type galaxies that is evolving most rapidly in the local universe.
Intriguingly, the results also suggest that the radio jets are triggered
relatively late in the merger sequence, and that there is an evolutionary link
between radio galaxies and luminous/ultra-luminous infrared galaxies.Comment: 17 pages, 13 figures, accepted for publication in MNRA
- …