420 research outputs found
WFPC2 LRF Imaging of Emission Line Nebulae in 3CR Radio Galaxies
We present HST/WFPC2 Linear Ramp Filter images of high surface brightness
emission lines (either [OII], [OIII], or H-alpha+[NII]) in 80 3CR radio
sources. We overlay the emission line images on high resolution VLA radio
images (eight of which are new reductions of archival data) in order to examine
the spatial relationship between the optical and radio emission. We confirm
that the radio and optical emission line structures are consistent with weak
alignment at low redshift (z < 0.6) except in the Compact Steep Spectrum (CSS)
radio galaxies where both the radio source and the emission line nebulae are on
galactic scales and strong alignment is seen at all redshifts. There are weak
trends for the aligned emission line nebulae to be more luminous, and for the
emission line nebula size to increase with redshift and/or radio power. The
combination of these results suggests that there is a limited but real capacity
for the radio source to influence the properties of the emission line nebulae
at these low redshifts (z < 0.6). Our results are consistent with previous
suggestions that both mechanical and radiant energy are responsible for
generating alignment between the radio source and emission line gas.Comment: 80 pages, 54 figures. Accepted for publication in ApJ
Extended X-ray emission in radio galaxies: the peculiar case of 3C 305
Extended X-ray structures are common in Active Galactic Nuclei (AGNs). Here
we present the first case of a Compact Steep Spectrum (CSS) radio galaxy, 3C
305, in which the X-ray radiation appears to be associated with the optical
emission line region, dominated by the [O III]5007. On the basis of a
morphological study, performed using the comparison between the X-rays, the
optical and the radio band, we argue that the high energy emission has a
thermal nature and it is not directly linked to the radio jet and hotspots of
this source. Finally, we discuss the origin of the extended X-ray structure
connected with the optical emission line region following two different
interpretations: as due to the interaction between matter outflows and
shock-heated environment gas, or as due to gas photoionized by nuclear
emission.Comment: 5 pages, 2 figures, Accepted for publication in The ApJL Comments:
references and affilitations correcte
High Frequency Peakers: young radio sources or flaring blazars?
We present new, simultaneous, multifrequency observations of 45 out of the 55
candidate High Frequency Peakers (HFP) selected by Dallacasa et al. (2000),
carried out 3 to 4 years after a first set of observations. Our sub-sample
consists of 10 galaxies, 28 stellar objects (``quasars'') and 7 unidentified
sources. Both sets of observations are sensitive enough to allow the detection
of variability at the 10% level or lower. While galaxies do not show
significant variability, most quasars do. Seven of them no longer show the
convex spectrum which is the defining property of Gigahertz Peaked Spectrum
(GPS)/HFP sources and are interpreted as blazars caught by Dallacasa et al.
(2000) during a flare, when a highly self-absorbed component dominated the
emission. In general, the variability properties (amplitude, timescales,
correlation between peak luminosity and peak frequency of the flaring
component) of the quasar sub-sample resemble those of blazars. We thus conclude
that most HFP candidates identified with quasars may well be flaring blazars.Comment: 20 pages, 18 figures, accepted for publication in Astronomy &
Astrophysic
Observations of HI Absorbing Gas in Compact Radio Sources at Cosmological Redshifts
We present an overview of the occurrence and properties of atomic gas
associated with compact radio sources at redshifts up to z=0.85. Searches for
HI 21cm absorption were made with the Westerbork Synthesis Radio Telescope at
UHF-high frequencies (725-1200 MHz). Detections were obtained for 19 of the 57
sources with usable spectra (33%). We have found a large range in line depths,
from tau=0.16 to tau<=0.001. There is a substantial variety of line profiles,
including Gaussians of less than 10km/s, to more typically 150km/s, as well as
irregular and multi-peaked absorption profiles, sometimes spanning several
hundred km/s. Assuming uniform coverage of the entire radio source, we obtain
column depths of atomic gas between 1e19 and 3.3e21(Tsp/100K)(1/f)cm^(-2).
There is evidence for significant gas motions, but in contrast to earlier
results at low redshift, there are many sources in which the HI velocity is
substantially negative (up to v=-1420km/s) with respect to the optical
redshift, suggesting that in these sources the atomic gas, rather than falling
into the centre, may be be flowing out, interacting with the jets, or rotating
around the nucleus.Comment: 10 pages, accepted for publication in A&
Evidence for Ordered Magnetic Fields in the Quasar Environment
At a distance of 20 pc from the purported supermassive black hole powering
quasars, temperatures and densities are inferred from optical observations to
be ~10**4 K and ~10**4 cm**-3. Here we present Very Long Baseline
Interferometry radio observations revealing organized magnetic fields on the
parsec scale in the hot plasma surrounding the quasar OQ172 (1442+101). These
magnetic fields rotate the plane of polarization of the radio emission coming
from the core and inner jet of the quasar. The derived rotation measure (RM) is
40,000 rad m**-2 in the rest frame of the quasar. Only 10 mas (a projected
distance of 68 pc) from the nucleus the jet absolute values of RM fall to less
than 100 rad m**-2.Comment: in press at ApJ Letters, 12 page LaTeX document includes 4 postscript
figure
Vitamin D status and the risk of type 2 diabetes: the Melbourne Collaborative Cohort Study
Aims: Inverse associations between vitamin D status and risk of type 2 diabetes observed in epidemiological studies could be biased by confounding and reverse causality. We investigated the prospective association between vitamin D status and type 2 diabetes and the possible role of reverse causality. Methods: We conducted a case-cohort study within the Melbourne Collaborative Cohort Study (MCCS), including a random sample of 628 participants who developed diabetes and a sex-stratified random sample of the cohort (n=1,884). Concentration of 25-hydroxyvitamin D (25(OH)D) was measured using liquid chromatography-tandem mass spectrometry in samples collected at recruitment. Logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for the risk of type 2 diabetes for quartiles of 25(OH)D relative to the lowest quartile and per 25 nmol/L increase in 25(OH)D, adjusting for confounding variables. Results: The ORs for the highest versus lowest 25(OH)D quartile and per 25 nmol/L increase in 25(OH)D were 0.60 (95% CI: 0.44, 0.81) and 0.76 (95% CI: 0.63, 0.92; p=0.004), respectively. In participants who reported being in good/very good/excellent health approximately four years after recruitment, ORs for the highest versus lowest 25(OH)D quartile and per 25 nmol/L increase in 25(OH)D were 0.46 (95% CI: 0.29, 0.72) and 0.71 (95% CI: 0.56, 0.89; p=0.003), respectively. Conclusions: In this sample of middle-aged Australians, vitamin D status was inversely associated with the risk of type 2 diabetes, and this association did not appear to be explained by reverse causality
The MURALES survey. I. A dual AGN in the radio galaxy 3C459?
We observed the FRII radio galaxy 3C459 (z=0.22) with the MUSE spectrograph
at the Very Large Telescope (VLT) as part of the MURALES project (a MUse RAdio
Loud Emission line Snapshot survey). We detected diffuse nuclear emission and a
filamentary ionized gas structure forming a one-sided, triangular-shaped region
extending out to 80 kpc. The central emission line region is dominated by
two compact knots of similar flux: the first (N1) cospatial with the radio core
and the (N2) second located 1.2" (5.3 kpc) to the SE. The two regions differ
dramatically from the point of view of velocity (with an offset of ~400 km/s),
line widths, and line ratios. This suggests that we are observing a dual AGN
system formed by a radio loud AGN and type 2 QSO companion, which is the result
of the recent merger that also produced its disturbed host morphology. The
alternative possibility that N2 is just a bright emission line knot resulting
from, for example, a jet-cloud interaction, is disfavored because of 1) the
presence of a high ionization bicone whose apex is located at N2; 2) the
observed narrow line widths; 3) its line luminosity (~10^42 erg s-1) typical of
luminous QSOs; and 4) its location, which is offset from the jet path. The
putative secondary AGN must be highly obscured, since we do not detect any
emission in the Chandra and infrared Hubble Space Telescope images.Comment: 6 pages, 6 figures, A&A in pres
ISO observations of a sample of Compact Steep Spectrum and GHz Peaked Spectrum Radio Galaxies
We present results from observations obtained with ISOPHOT, on board the ISO
satellite, of a representative sample of seventeen CSS/GPS radio galaxies and
of a control sample of sixteen extended radio galaxies spanning similar ranges
in redshift (0.2 = 10^26 W/Hz).
The observations have been performed at lambda = 60, 90, 174 and 200 microns.
Seven of the CSS/GPS sources have detections >= 3 sigma at one or more
wavelengths, one of which is detected at >= 5 sigma. By co-adding the data we
have obtained average flux densities at the four wavelengths. We found no
evidence that the FIR luminosities of the CSS/GPS sources are significantly
different from those of the extended objects and therefore there is not any
support for CSS/GPS sources being objects "frustrated" by an abnormally dense
ambient medium. The two samples were then combined, providing FIR information
on a new sample of radio galaxies at intermediate redshifts. We compare this
information with what previously known from IRAS and discuss the average
properties of radio galaxies in the redshift range 0.2 - 0.8. The FIR emission
cannot be accounted for by extrapolation of the synchrotron radio spectrum and
we attribute it to thermal dust emission. The average FIR luminosity is >=
6*10^11 L_sun. Over the observed frequency range the infrared spectrum can be
described by a power law with spectral index alpha >~1.0 +/- 0.2. Assuming the
emission to be due to dust, a range of temperatures is required, from >=80 K to
\~25 K. The dust masses required to explain the FIR emission range from 5*10^5
M_sun for the hotter component up to 2*10^8 M_sun for the colder one.
(abridged)Comment: Astronomy & Astrophysics, in press, 16 pages, 2 Figure
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