4,920 research outputs found
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
The HST view of the innermost narrow line region
We analyze the properties of the innermost narrow line region in a sample of
low-luminosity AGN. We select 33 LINERs (bona fide AGN) and Seyfert galaxies
from the optical spectroscopic Palomar survey observed by HST/STIS. We find
that in LINERs the [NII] and [OI] lines are broader than the [SII] line and
that the [NII]/[SII] flux ratio increases when moving from ground-based to HST
spectra. This effect is more pronounced considering the wings of the lines. Our
interpretation is that, as a result of superior HST spatial resolution, we
isolate a compact region of dense ionized gas in LINERs, located at a typical
distance of about 3 pc and with a gas density of about 10-10 cm,
which we identify with the outer portion of the intermediate line region (ILR).
Instead, we do not observe these kinds of effects in Seyferts; this may be the
result of a stronger dilution from the NLR emission, since the HST slit maps a
larger region in these sources. Alternatively, we argue that the innermost,
higher density component of the ILR is only present in Seyferts, while it is
truncated at larger radii because of the presence of the circumnuclear torus.
The ILR is only visible in its entirety in LINERs because the obscuring torus
is not present in these sources.Comment: 11 pages, 9 figures, A&A in pres
Characterizing dark interactions with the halo mass accretion history and structural properties
We study the halo mass accretion history (MAH) and its correlation with the
internal structural properties in coupled dark energy cosmologies (cDE). To
accurately predict all the non-linear effects caused by dark interactions, we
use the COupled Dark Energy Cosmological Simulations (CoDECS). We measure the
halo concentration at z=0 and the number of substructures above a mass
resolution threshold for each halo. Tracing the halo merging history trees back
in time, following the mass of the main halo, we develope a MAH model that
accurately reproduces the halo growth in term of M_{200} in the {\Lambda}CDM
Universe; we then compare the MAH in different cosmological scenarios. For cDE
models with a weak constant coupling, our MAH model can reproduce the
simulation results, within 10% of accuracy, by suitably rescaling the
normalization of the linear matter power spectrum at z=0, {\sigma}_8. However,
this is not the case for more complex scenarios, like the "bouncing" cDE model,
for which the numerical analysis shows a rapid growth of haloes at high
redshifts, that cannot be reproduced by simply rescaling the value of
{\sigma}_8. Moreover, at fixed value of {\sigma}_8, cold dark matter (CDM)
haloes in these cDE scenarios tend to be more concentrated and have a larger
amount of substructures with respect to {\Lambda}CDM predictions. Finally, we
present an accurate model that relates the halo concentration to the time at
which it assembles half or 4% of its mass. Combining this with our MAH model,
we show how halo concentrations change while varying only {\sigma}_8 in a
{\Lambda}CDM Universe, at fixed halo mass.Comment: 18 pages, 14 figures, accepted for publication in MNRA
New flaring of an ultraluminous X-ray source in NGC 1365
We have studied a highly variable ultraluminous X-ray source (ULX) in the
Fornax galaxy NGC 1365, with a series of 12 Chandra and XMM-Newton observations
between 2002 and 2006. In 2006 April, the source peaked at a luminosity ~ 3 x
10^{40} erg/s in the 0.3-10 keV band (similar to the maximum luminosity found
by ASCA in 1995), and declined on an e-folding timescale ~ 3 days. The X-ray
spectrum is always dominated by a broad power-law-like component. When the
source is seen at X-ray luminosities ~ 10^{40} erg/s, an additional soft
thermal component (which we interpret as emission from the accretion disk)
contributes ~ 1/4 of the X-ray flux; when the luminosity is higher, ~ 3 x
10^{40} erg/s, the thermal component is not detected and must contribute < 10%
of the flux. At the beginning of the decline, ionized absorption is detected
around 0.5-2 keV; it is a possible signature of a massive outflow. The
power-law is always hard, with a photon index Gamma ~ 1.7 (and even flatter at
times), as is generally the case with bright ULXs. We speculate that this
source and perhaps most other bright ULXs are in a high/hard state: as the
accretion rate increases well above the Eddington limit, more and more power is
extracted from the inner region of the inflow through non-radiative channels,
and is used to power a Comptonizing corona, jet or wind. The observed thermal
component comes from the standard outer disk; the transition radius between
outer standard disk and Comptonizing inner region moves further out and to
lower disk temperatures as the accretion rate increases. This produces the
observed appearance of a large, cool disk. Based on X-ray luminosity and
spectral arguments, we suggest that this accreting black hole has a likely mass
~ 50-150 Msun (even without accounting for possible beaming).Comment: 14 pages, to appear in MNRA
WATCAT: a tale of wide-angle tailed radio galaxies
We present a catalog of 47 wide-angle tailed radio galaxies (WATs), the
WATCAT; these galaxies were selected by combining observations from the
National Radio Astronomy Observatory/Very Large Array Sky Survey (NVSS), the
Faint Images of the Radio Sky at Twenty-Centimeters (FIRST), and the Sloan
Digital Sky Survey (SDSS), and mainly built including a radio morphological
classification. We included in the catalog only radio sources showing two-sided
jets with two clear "warmspots" (i.e., jet knots as bright as 20% of the
nucleus) lying on the opposite side of the radio core, and having classical
extended emission resembling a plume beyond them. The catalog is limited to
redshifts z 0.15, and lists only sources with radio emission extended
beyond 30 kpc from the host galaxy. We found that host galaxies of WATCAT
sources are all luminous (-20.5 Mr -23.7), red early-type
galaxies with black hole masses in the range M M. The spectroscopic classification indicates that they
are all low-excitation galaxies (LEGs). Comparing WAT multifrequency properties
with those of FRI and FRII radio galaxies at the same redshifts, we conclude
that WATs show multifrequency properties remarkably similar to FRI radio
galaxies, having radio power of typical FRIIs
Deciphering the large-scale environment of radio galaxies in the local Universe: where do they born, grow and die?
The role played by the large-scale environment on the nuclear activity of
radio galaxies (RGs), is still not completely understood. Accretion mode, jet
power and galaxy evolution are connected with their large-scale environment
from tens to hundreds of kpc. Here we present a detailed, statistical, analysis
of the large-scale environment for two samples of RGs up to redshifts
=0.15. The main advantages of our study, with respect to those
already present in the literature, are due to the extremely homogeneous
selection criteria of catalogs adopted to perform our investigation. This is
also coupled with the use of several clustering algorithms. We performed a
direct search of galaxy-rich environments around RGs using them as beacon. To
perform this study we also developed a new method that does not appear to
suffer by a strong dependence as other algorithms. We conclude
that, despite their radio morphological (FR\,I FR\,II) and/or their
optical (HERG LERG) classification, RGs in the local Universe tend to live
in galaxy-rich large-scale environments having similar characteristics and
richness. We highlight that the fraction of FR\,Is-LERG, inhabiting galaxy rich
environments, appears larger than that of FR\,IIs-LERG. We also found that 5
out of 7 FR\,II-HERGs, with 0.11, lie in groups/clusters of
galaxies. However, we recognize that, despite the high level of completeness of
our catalogs, when restricting to the local Universe, the low number of HERGs
(10\% of the total FR\,IIs investigated) prevent us to make a strong
statistical conclusion about this source class.Comment: 21 pages, 25 figures, accepted for publication on the Astrophysical
Journal Supplement Series - pre-proof versio
LEDAkem: a post-quantum key encapsulation mechanism based on QC-LDPC codes
This work presents a new code-based key encapsulation mechanism (KEM) called
LEDAkem. It is built on the Niederreiter cryptosystem and relies on
quasi-cyclic low-density parity-check codes as secret codes, providing high
decoding speeds and compact keypairs. LEDAkem uses ephemeral keys to foil known
statistical attacks, and takes advantage of a new decoding algorithm that
provides faster decoding than the classical bit-flipping decoder commonly
adopted in this kind of systems. The main attacks against LEDAkem are
investigated, taking into account quantum speedups. Some instances of LEDAkem
are designed to achieve different security levels against classical and quantum
computers. Some performance figures obtained through an efficient C99
implementation of LEDAkem are provided.Comment: 21 pages, 3 table
Emission lines in early-type galaxies: active nuclei or stars?
We selected 27244 nearby, red, giant early-type galaxies (RGEs) from the
Sloan Digital Sky Survey (SDSS). In a large fraction (53%) of their spectra the
[O III] emission line is detected, with an equivalent width (EW) distribution
strongly clustered around ~0.75 A. The vast majority of those RGEs for which it
is possible to derive emission line ratios (amounting to about half of the
sample) show values characteristic of LINERs. The close connection between
emission lines and stellar continuum points to stellar processes as the most
likely source of the bulk of the ionizing photons in RGEs, rather than active
nuclei. In particular, the observed EW and optical line ratios are consistent
with the predictions of models in which the photoionization comes from to hot
evolved stars. Shocks driven by supernovae or stellar ejecta might also
contribute to the ionization budget. A minority, ~4%, of the galaxies show
emission lines with an equivalent that is width a factor of ~2 greater than the
sample median. Only among them are Seyfert-like spectra found. Furthermore, 40%
of this subgroup have a radio counterpart, compared to ~6% of the rest of the
sample. These characteristics argue in favor of an AGN origin for their
emission lines. Emission lines diagnostic diagrams do not reveal a distinction
between the AGN subset and the other members of the sample, and consequently
they are not a useful tool for establishing the dominant source of the ionizing
photons, which is better predicted by the EW of the emission lines.Comment: Accepted for publication in A&
Disentangling dark sector models using weak lensing statistics
We perform multi-plane ray-tracing using the GLAMER gravitational lensing
code within high-resolution light-cones extracted from the CoDECS simulations:
a suite of cosmological runs featuring a coupling between Dark Energy and Cold
Dark Matter. We show that the presence of the coupling is evident not only in
the redshift evolution of the normalisation of the convergence power spectrum,
but also in differences in non-linear structure formation with respect to
{\Lambda}CDM. Using a tomographic approach under the assumption of a
{\Lambda}CDM cosmology, we demonstrate that weak lensing measurements would
result in a {\sigma}8 value that changes with the source redshift if the true
underlying cosmology is a coupled Dark Energy one. This provides a generic null
test for these types of models. We also find that different models of coupled
Dark Energy can show either an enhanced or a suppressed correlation between
convergence maps with differing source redshifts as compared to {\Lambda}CDM.
This would provide a direct way to discriminate between different possible
realisations of the coupled Dark Energy scenario. Finally, we discuss the
impact of the coupling on several lensing observables for different source
redshifts and angular scales with realistic source redshift distributions for
current ground-based and future space-based lensing surveys.Comment: 17 pag. and 14 fig. replaced to match the accepted version (increased
the number of light-cone realisations
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