198 research outputs found
An optical spectroscopic survey of the 3CR sample of radio galaxies with z<0.3. III. Completing the sample
We present optical nuclear spectra for nine 3CR radio sources obtained with
the Telescopio Nazionale Galileo, that complete our spectroscopic observations
of the sample up to redshifts 0.3. We measure emission line luminosities
and ratios, and derive a spectroscopic classification for these sources.Comment: Accepted for publication in A&A. We provide as additional material
two tables presenting the main data for the whole sample, combining the
results presented here with those of Paper I and Paper I
An optical spectroscopic survey of the 3CR sample of radio galaxies with z<0.3. IV. Discovery of the new spectroscopic class of relic radio galaxies
From an optical spectroscopic survey of 3CR radio galaxies with z<0.3, we
discovered a new spectroscopic class of powerful radio-loud AGN. The defining
characteristics of these galaxies are that compared with radio galaxies of
similar radio luminosity they have: a [O III]\Hb ratio of ~0.5, indicative of
an extremely low level of gas excitation; a large deficit of [O III] emission
and radio core power. We interpret these objects as relic AGN, i.e. sources
that experienced a large drop in their level of nuclear activity, causing a
decrease in their nuclear and line luminosity. This class opens a novel
approach to investigating lifetimes and duty cycles of AGN.Comment: Accepted for publication in A&
The fast matched filter for gravitational-wave data analysis: Characteristics and applications
We report on the application of a matched filter to the data of two-mode resonant gravitational-wave antennas for the detection of burst signals, with reference to data obtained by direct acquisition, i.e. without going through
lock-in amplifiers, sampled at relatively high speed. After a review of the basic model of resonant detectors, that includes a discussion of the signal and of the noise, we
present a detailed mathematical derivation of the optimum filter matched to an input burst. We then analyze and discuss the performance of the matched filter as regards
both the improvement of the signal-to-noise ratio and the observation bandwidth, also considering the adaptive realization of the filter, based on the actual spectrum of
the noise as estimated from the data. The discussion that follows is centered on various aspects concerning the practical application of the matched filter as well as
the loss of performance due both to uncertainties on the parameters used for building the filter and to various discretization effects, both in the time and frequency domains. Finally, we consider some experimental results obtained by applying the matched filter to the data of the Explorer detector, also providing a comparison with what we obtained by applying an optimum filter to data processed
by lock-in amplifiers, sampled at lower speed
Exploring the spectroscopic properties of relic radiogalaxies
From an optical spectroscopic survey of 3CR radiogalaxies (RGs) with z < 0.3, we discovered three objects characterized by an extremely low level of gas excitation and a large deficit of line emission with respect to RGs of similar radio luminosity. We interpreted these objects as relic active galactic nuclei (AGN), i.e., sources observed after a large drop in their nuclear activity. We here present new spectroscopic observations for these three galaxies and for a group of "candidate" relics. None of the candidates can be convincingly confirmed. From the new data for the three relics, we estimate the density of the line-emitting gas. This enables us to explore the temporal evolution of the line ratios after the AGN "death". The characteristic timescale is the light-crossing time of the emission-line region, a few ~103 years, too short to correspond to a substantial population of relic RGs. Additional mechanisms of gas ionization, such as "relic shocks" from their past high power phase or stellar sources, should also be considered to account for the spectroscopic properties of the relic RGs. Relic RGs appear to be a mixed bag of sources in different phases of evolution, including AGN recently (~104 years ago) quenched, galaxies that have been inactive for at least ~106 years, and objects caught during the transition from a powerful RG to a low power FR I source
Extended soft X-ray emission in 3CR radio galaxies at z < 0.3: High Excitation and Broad Line Galaxies
We analyze Chandra observations of diffuse soft X-ray emission associated
with a complete sample of 3CR radio galaxies at z < 0.3. In this paper we focus
on the properties of the spectroscopic sub-classes of high excitation galaxies
(HEGs) and broad line objects (BLOs). Among the 33 HEGs we detect extended (or
possibly extended) emission in about 40% of the sources; the fraction is even
higher (8/10) restricting the analysis to the objects with exposure times
larger than 10 ks. In the 18 BLOs, extended emission is seen only in 2 objects;
this lower detection rate can be ascribed to the presence of their bright X-ray
nuclei that easily outshine any genuine diffuse emission.
A very close correspondence between the soft X-ray and optical line
morphology emerges. We also find that the ratio between [O III] and extended
soft X-ray luminosity is confined within a factor of 2 around a median value of
5. Both results are similar to what is seen in Seyfert galaxies.
We discuss different processes that could explain the soft X-ray emission and
conclude that the photoionization of extended gas, coincident with the narrow
line region, is the favored mechanism.Comment: 15 pages, 11 figures. Accepted for publication on A&
Herschel-ATLAS: The angular correlation function of submillimetre galaxies at high and low redshift
Original article can be found at: http://www.aanda.org/ Copyright The European Southern ObservatoryWe present measurements of the angular correlation function of galaxies selected from the first field of the H-ATLAS survey. Careful removal of the background from galactic cirrus is essential, and currently dominates the uncertainty in our measurements. For our 250 ÎŒm-selected sample we detect no significant clustering, consistent with the expectation that the 250 ÎŒm-selected sources are mostly normal galaxies at z 1. For our 350 ÎŒm and 500 ÎŒm-selected samples we detect relatively strong clustering with correlation amplitudes A of 0.2 and 1.2 at 1', but with relatively large uncertainties. For samples which preferentially select high redshift galaxies at z~2â3 we detect significant strong clustering, leading to an estimate of r0 ~ 7â11 h-1 Mpc. The slope of our clustering measurements is very steep, ÎŽ ~ 2. The measurements are consistent with the idea that sub-mm sources consist of a low redshift population of normal galaxies and a high redshift population of highly clustered star-bursting galaxies.Peer reviewe
A search for debris disks in the Herschel-ATLAS
Original article can be found at: http://www.aanda.org/ Copyright The European Southern Observatory (ESO)Aims. We aim to demonstrate that the Herschel-ATLAS (H-ATLAS) is suitable for a blind and unbiased survey for debris disks by identifying candidate debris disks associated with main sequence stars in the initial science demonstration field of the survey. We show that H-ATLAS reveals a population of far-infrared/sub-mm sources that are associated with stars or star-like objects on the SDSS main-sequence locus. We validate our approach by comparing the properties of the most likely candidate disks to those of the known population. Methods. We use a photometric selection technique to identify main sequence stars in the SDSS DR7 catalogue and a Bayesian Likelihood Ratio method to identify H-ATLAS catalogue sources associated with these main sequence stars. Following this photometric selection we apply distance cuts to identify the most likely candidate debris disks and rule out the presence of contaminating galaxies using UKIDSS LAS K-band images. Results. We identify 78 H-ATLAS sources associated with SDSS point sources on the main-sequence locus, of which two are the most likely debris disk candidates: H-ATLAS J090315.8 and H-ATLAS J090240.2. We show that they are plausible candidates by comparing their properties to the known population of debris disks. Our initial results indicate that bright debris disks are rare, with only 2 candidates identified in a search sample of 851 stars. We also show that H-ATLAS can derive useful upper limits for debris disks associated with Hipparcos stars in the field and outline the future prospects for our debris disk search programme.Peer reviewe
The Nature of the Near-IR Core Source in 3C 433
We report the analysis of near-infrared imaging, polarimetric and
spectroscopic observations of the powerful radio galaxy 3C433, obtained with
the HST and UKIRT telescopes. The high spatial resolution of HST allows us to
study the near-nuclear regions of the galaxy (<1 kpc). In line with previous
observations, we find that 3C433 has an unresolved core source that is detected
in all near-IR bands, but dominates over the host galaxy emission at 2.05 um.
Our analysis reveals: (1) the presence of a dust lane aligned close to
perpendicular (PA=70\pm5\degr) to the inner radio jet axis
(PA=-12\pm2\degr); (2) a steep slope to the near-IR SED (;
F); (3) an apparent lack of broad permitted
emission lines at near-IR wavelengths, in particular the absence of a broad
Pa emission line; and (4) high intrinsic polarization for the
unresolved core nuclear source ( per cent), with an E-vector
perpendicular (PA=83.0\pm 2.3\degr) to the inner radio jet. Using five
independent techniques we determine an extinction to the compact core source in
the range 3<A_V<67 mag. An analysis of the long wavelength SED rules out a
synchrotron origin for the high near-IR polarization of the compact core
source. Therefore, scattering and dichroic extinction are plausible polarizing
mechanisms, although in both of these cases the broad permitted lines from the
AGN are required to have a width >10^4 km/s (FWHM) to escape detection in our
near-IR spectrum. Dichroic extinction is the most likely polarization mechanism
because it is consistent with the various available extinction estimates. In
this case, a highly ordered, coherent toroidal magnetic field must be present
in the obscuring structure close to the nucleus.Comment: 12 pages, 5 figures, accepted for publication in MNRA
Testing Black Hole Jet Scaling Relations in Low Luminosity AGN
We present the results of the analysis of a sample of 17 low-luminosity (L_x
< 1e42 erg/s), radio loud AGNs in massive galaxies. The sample is extracted
from the SDSS database and it spans uniformly a wide range in optical [OIII]
emission line and radio luminosity, but within a narrow redshift range (0.05 <
z < 0.11) and a narrow super massive black hole mass range (~ 1e8 M_sun). For
these sources we measured core X-ray emission with the Chandra X-ray telescope
and radio emission with the VLA. Our main goal is to establish which emission
component, if any, can be regarded as the most reliable accretion/jet-power
estimator at these regimes. In order to do so, we studied the correlation
between emission line properties, radio luminosity, radio spectral slopes and
X-ray luminosity, as well as more complex multi-variate relations involving
black hole mass, such as the fundamental plane of black hole activity. We find
that 15 out of 17 sources of our sample can be classified as Low-Excitation
Galaxies (LEG) and their observed properties suggest X-ray and radio emission
to originate from the jet basis. We also find that X-ray emission does not
appear to be affected by nuclear obscuration and can be used as a reliable
jet-power estimator. More generally, X-ray, radio and optical emission appear
to be related, although no tight correlation is found. In accordance with a
number of recent studies of this class of objects these findings may be
explained by a lack of cold (molecular) gaseous structures in the innermost
region of these massive galaxies.Comment: 11 pages, 6 figures, published in MNRA
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