2,819 research outputs found
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
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&
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
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
LeMMINGs III. The e-MERLIN legacy survey of the Palomar sample: exploring the origin of nuclear radio emission in active and inactive galaxies through the [O III] - radio connection
What determines the nuclear radio emission in local galaxies? To address this question, we combine optical [O III] line emission, robust black hole (BH) mass estimates, and high-resolution e-MERLIN 1.5-GHz data, from the LeMMINGs survey, of a statistically complete sample of 280 nearby optically active (LINER and Seyfert) and inactive [H II and absorption line galaxies (ALGs)] galaxies. Using [O III] luminosity (L[O III]) as a proxy for the accretion power, local galaxies follow distinct sequences in the optical-radio planes of BH activity, which suggest different origins of the nuclear radio emission for the optical classes. The 1.5-GHz radio luminosity of their parsec-scale cores (Lcore) is found to scale with BH mass (Mbh) and [O III] luminosity. Below Mbh ~ 10^(6.5) Msun, stellar processes from non-jetted H II galaxies dominate with Lcore \propto Mbh^(0.62\pm0.33) and Lcore \propto L[O III]^(0.79\pm0.30). Above Mbh ~ 10^(6.5) Msun, accretion-driven processes dominate with Lcore \propto Mbh^(1.5-1.65) and Lcore \propto L[O III]^(0.99-1.31) for active galaxies: radio-quiet/loud LINERs, Seyferts, and jetted H II galaxies always display (although low) signatures of radio-emitting BH activity, with L1.5GHz > 10^(19.8) W Hz^(-1) and Mbh > 10^7 Msun, on a broad range of Eddington-scaled accretion rates (mdot). Radio-quiet and radio-loud LINERs are powered by low-mdot discs launching sub-relativistic and relativistic jets, respectively. Low-power slow jets and disc/corona winds from moderately high to high-mdot discs account for the compact and edge-brightened jets of Seyferts, respectively. Jetted H II galaxies may host weakly active BHs. Fuel-starved BHs and recurrent activity account for ALG properties. In conclusion, specific accretion-ejection states of active BHs determine the radio production and the optical classification of local active galaxies
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&
Hard - X-rays selected Active Galactic Nuclei. I. A radio view at high-frequencies
A thorough study of radio emission in Active Galactic Nuclei (AGN) is of
fundamental importance to understand the physical mechanisms responsible for
the emission and the interplay between accretion and ejection processes. High
frequency radio observations can target the nuclear contribution of smaller
emitting regions and are less affected by absorption. We present JVLA 22 and 45
GHz observations of 16 nearby (0.003z0.3) hard - X-rays selected AGN
at the (sub)-kpc scale with tens uJy beam sensitivity. We detected 15/16
sources, with flux densities ranging from hundreds uJy beam to tens Jy
(specific luminosities from 10 to 10 at
22 GHz). All detected sources host a compact core, with 8 being core-dominated
at either frequencies, the others exhibiting also extended structures. Spectral
indices range from steep to flat/inverted. We interpret this evidence as either
due to a core+jet system (6/15), a core accompanied by surrounding star
formation (1/15), to a jet oriented close to the line of sight (3/15), to
emission from a corona or the base of a jet (1/15), although there might be
degeneracies between different processes. Four sources require more data to
shed light on their nature. We conclude that, at these frequencies, extended,
optically-thin components are present together with the flat-spectrum core. The
relation is roughly followed, indicating a possible
contribution to radio emission from a hot corona. A weakly significant
correlation between radio core (22 and 45 GHz) and X-rays luminosities is
discussed in the light of an accretion-ejection framework.Comment: Accepted for publication on MNRA
Jets in FR0 radio galaxies
The local radio-loud AGN population is dominated by compact sources named
FR0s. These sources show features, for example the host type, the mass of the
supermassive black hole (SMBH), and the multi-band nuclear characteristics,
that are similar to those of FRI radio galaxies. However, in the radio band,
while FR0 and FRI share the same nuclear properties, the kiloparsec-scale
diffuse component dominant in FRI is missing in FR0s. With this project we
would like to study the parsec-scale structure in FR0s in comparison with that
of FRI sources. To this end we observed 18 FR0 galaxies with the VLBA at 1.5
and 5 GHz and/or with the EVN at 1.7 GHz and produced detailed images at
milliarcsec resolution of their nuclear emission to study the jet and core
structure. All sources have been detected but one. Four sources are unresolved,
even in these high-resolution images; jets have been detected in all other
sources. We derived the distribution of the jet-to-counter-jet ratio of FR0s
and found that it is significantly different from that of FRIs, suggesting
different jet bulk speed velocities. Combining the present data with published
data of FR0 with VLBI observations, we derive that the radio structure of FR0
galaxies shows strong evidence that parsec-scale jets in FR0 sources are mildly
relativistic with a bulk velocity on the order of 0.5c or less. A jet structure
with a thin inner relativistic spine surrounded by a low-velocity sheath could
be in agreement with the SMBH and jet launch region properties.Comment: 12 pages, 16 figures Accepted for the publication in Astronomy and
Astrophysic
Cosmic degeneracies III: N-body simulations of Interacting Dark Energy with non-Gaussian initial conditions
We perform for the first time N-body simulations of interacting dark energy assuming non-Gaussian initial conditions, with the aim of investigating possible degeneracies of these two theoretically independent phenomena in different observational probes. We focus on the large-scale matter distribution, as well as on the statistical and structural properties of collapsed haloes and cosmic voids. On very large scales, we show that it is possible to choose the interaction and non-Gaussian parameters such that their effects on the halo power spectrum cancel, and the power spectrum is indistinguishable from a \u39b cold dark matter (\u2060\u39bCDM) model. On small scales, measurements of the non-linear matter power spectrum, halo-matter bias, halo and subhalo mass function, and cosmic void number function validate the degeneracy determined on large scales. However, the internal structural properties of haloes and cosmic voids, namely halo concentration\u2013mass relation and void density profile, are very different from those measured in the \u39bCDM model, thereby breaking the degeneracy. In practice, the values of fNL required to cancel the effect of interaction are already ruled by observations. Our results show in principle that the combination of large- and small-scale probes is needed to constrain interacting dark energy and primordial non-Gaussianity separately
- …