297 research outputs found
Cu(II) Complexes of the Oximes of 2-Hydroxy-5-methyl-acetophenone, -propiophenone & -butyrophenone
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Extragalactic sources with asymmetric radio structure I. Observations of 17 sources
We present total-intensity and linear-polarization observations with the Very Large Array (VLA) at λ6 and 2 cm of 17 sources, almost all of which were suspected to have extended emission only on one side of the nucleus. Five of them are still one-sided, three appear unresolved, while seven have radio lobes on both sides of the nucleus. The outer components in the double-lobed sources, however, have significantly different surface brightness or are very asymmetrically located with respect to the nucleus
Cosmological Studies with Radio Galaxies and Supernovae
Physical sizes of extended radio galaxies can be employed as a cosmological
"standard ruler", using a previously developed method. Eleven new radio
galaxies are added to our previous sample of nineteen sources, forming a sample
of thirty objects with redshifts between 0 and 1.8. This sample of radio
galaxies are used to obtain the best fit cosmological parameters in a
quintessence model in a spatially flat universe, a cosmological constant model
that allows for non-zero space curvature, and a rolling scalar field model in a
spatially flat universe. Results obtained with radio galaxies are compared with
those obtained with different supernova samples, and with combined radio galaxy
and supernova samples. Results obtained with different samples are consistent,
suggesting that neither method is seriously affected by systematic errors. Best
fit radio galaxy and supernovae model parameters determined in the different
cosmological models are nearly identical, and are used to determine
dimensionless coordinate distances to supernovae and radio galaxies, and
distance moduli to the radio galaxies. The distance moduli to the radio
galaxies can be combined with supernovae samples to increase the number of
sources, particularly high-redshift sources, in the samples. The constraints
obtained here with the combined radio galaxy plus supernovae data set in the
rolling scalar field model are quite strong. The best fit parameter values
suggest a value of omega is less than about 0.35, and the model parameter alpha
is close to zero; that is, a cosmological constant provides a good description
of the data. We also obtain new constraints on the physics of engines that
power the large-scale radio emission.Comment: 32 pages. Accepted for publication in the Astrophysical Journa
Optical Nuclei of Radio-loud AGN and the Fanaroff-Riley Divide
We investigate the nature of the point-like optical ``cores'' that have been
found in the centres of the host galaxies of a majority of radio galaxies by
the Hubble Space Telescope. We examine the evidence that these optical cores
are relativistically beamed, and look for differences in the behaviour of the
cores found in radio galaxies of the two Fanaroff-Riley types. We also attempt
to relate this behaviour to the properties of the optical nuclei in their
highly beamed counterparts (the BL Lac objects and radio-loud quasars) as
hypothesized by the simple Unified Scheme. Simple model-fitting of the data
suggests that the emission may be coming from a non-thermal relativistic jet.
It is also suggestive that the contribution from an accretion disk is not
significant for the FRI objects and for the narrow-line radio galaxies of FRII
type, while it may be significant for the Broad-line objects, and consistent
with the idea that the FRII optical cores seem to suffer from extinction due to
an obscuring torus while the FRI optical cores do not. These results are in
agreement with the Unified Scheme for radio-loud AGNs.Comment: 16 pages including 7 figures and 6 tables, v3: Accepted for
publication in A&
CSSs in a sample of B2 radio sources of intermediate strength
We present radio observations of 19 candidate compact steep-spectrum (CSS)
objects selected from a well-defined, complete sample of 52 B2 radio sources of
intermediate strength. These observations were made with the VLA A-array at
4.835 GHz. The radio structures of the entire sample are summarised and the
brightness asymmetries within the compact sources are compared with those of
the more extended ones, as well as with those in the 3CRR sample and the CSSs
from the B3-VLA sample. About 25 per cent of the CSS sources exhibit large
brightness asymmetries, with a flux density ratio for the opposing lobes of
5, possibly due to interaction of the jets with infalling material. The
corresponding percentage for the larger-sized objects is only about 5 per cent.
We also investigate possible dependence of the flux density asymmetry of the
lobes on redshift, since this might be affected by more interactions and
mergers in the past. No such dependence is found. A few individual objects of
interest are discussed in the paper.Comment: 10 pages, 7 figures, 2 tables; accepted for publication in Astronomy
and Astrophysic
VLA Observations of a New Population of Blazars
We present the first deep VLA radio images of flat-spectrum radio quasars
(FSRQ) with multiwavelength emission properties similar to those of BL Lacs
with synchrotron X-rays. Our observations of twenty-five of these sources show
that their radio morphologies are similar to those of other radio quasars.
However, their range of extended powers is more similar to that of BL Lacertae
objects (BL Lacs) and extends down to the low values typical of FR I radio
galaxies. Five out of our nine lobe-dominated sources have extended radio
powers in the range typical of both FR I and FR II radio galaxies, but their
extended radio structure is clearly FR II-like. Therefore, we have not yet
found a large population of radio quasars hosted by FR Is. Two thirds of our
sources have a core-dominated radio morpholgy and thus X-rays likely dominated
by the jet. We find that their ratios of radio core to total X-ray luminosity
are low and in the regime indicative of synchrotron X-rays. This result shows
that also blazars with strong emission lines can produce jets of high-energy
synchrotron emission and undermines at least in part the ``blazar sequence''
scenario which advocates that particle Compton cooling by an external radiation
field governs the frequency of the synchrotron emission peak.Comment: 26 pages, 33 figures. Accepted for publication in Ap
Parsec-scale Magnetic-Field Structures in HEAO-1 BL Lacs
We present very long baseline interferometry polarization images of an X-ray
selected sample of BL Lacertae objects belonging to the first High Energy
Astronomy Observatory (HEAO-1) and the ROSAT-Green Bank (RGB) surveys. These
are primarily high-energy-peaked BL Lacs (HBLs) and exhibit core-jet radio
morphologies on pc-scales. They show moderately polarized jet components,
similar to those of low-energy-peaked BL Lacs (LBLs). The fractional
polarization in the unresolved cores of the HBLs is, on average, lower than in
the LBLs, while the fractional polarizations in the pc-scale jets of HBLs and
LBLs are comparable. However a difference is observed in the orientation of the
inferred jet magnetic fields -- while LBL jets are well-known to preferentially
exhibit transverse magnetic fields, the HBL jets tend to display longitudinal
magnetic fields. Although a `spine-sheath' jet velocity structure, along with
larger viewing angles for HBLs could produce the observed magnetic field
configuration, differences in other properties of LBLs and HBLs, such as their
total radio power, cannot be fully reconciled with the different-angle scenario
alone. Instead it appears that LBLs and HBLs differ intrinsically, perhaps in
the spin rates of their central black holes.Comment: 41 pages, 21 figures, accepted for publication in MNRA
Extended radio emission in MOJAVE Blazars: Challenges to Unification
We present the results of a study on the 1.4 GHz kpc-scale radio emission in
the complete flux density limited MOJAVE sample, comprising 135 radio-loud
AGNs. While extended emission is detected in the majority of the sources, about
7% of the sources exhibit only radio core emission. Many BL Lacs exhibit
extended radio power and kpc-scale morphology typical of powerful FRII jets,
while a substantial number of quasars possess radio powers intermediate between
FRIs and FRIIs. This poses challenges to the simple radio-loud unified scheme,
which links BL Lacs to FRIs and quasars to FRIIs. We find a significant
correlation between extended radio emission and pc-scale jet speeds: the more
radio powerful sources possess faster jets. This indicates that the 1.4 GHz (or
low frequency) radio emission is indeed related to jet kinetic power. Various
properties such as extended radio power and apparent pc-scale jet speeds vary
smoothly between different blazar subclasses, suggesting that, at least in
terms of radio jet properties, the distinction between quasars and BL Lac
objects, at an emission-line equivalent width of 5 Angstrom is essentially an
arbitrary one. Based on the assumption that the extended radio luminosity is
affected by the kpc-scale environment, we define the ratio of extended radio
power to absolute optical magnitude as a proxy for environmental effects.
Trends with this parameter suggest that the pc-scale jet speeds and the
pc-to-kpc jet misalignments are not affected by the large-scale environment,
but are more likely to depend upon factors intrinsic to the AGN, or its local
pc-scale environment. We suggest that some of the extremely misaligned MOJAVE
blazar jets could be "hybrid" morphology sources, with an FRI jet on one side
and an FRII jet on the other. (Abridged)Comment: 40 pages, 16 figures, accepted for publication in Ap
HST Imaging of the Host Galaxies of High Redshift Radio-Loud Quasars
We present rest-frame UV and Ly-alpha images of spatially-resolved structures
around five high-redshift radio-loud quasars obtained with the WFPC2 camera on
the Hubble Space Telescope. We find that all five quasars are extended and this
"fuzz" contains ~5-40% of the total continuum flux and 15-65% of the Ly-alpha
flux within a radius of about 1.5 arcsec. The rest-frame UV luminosities of the
hosts are log lambda P_lambda = 11.9 to 12.5 solar luminosities (assuming no
internal dust extinction), comparable to the luminous radio galaxies at similar
redshifts and a factor 10 higher than both radio-quiet field galaxies at z~2-3
and the most UV-luminous low redshift starburst galaxies. The Ly-alpha
luminosities of the hosts are (in the log) approximately 44.3-44.9 erg/s which
are also similar to the those of luminous high redshift radio galaxies and
considerably larger than the Ly-alpha luminosities of high redshift field
galaxies. To generate the Ly-alpha luminosities of the hosts would require
roughly a few percent of the total observed ionizing luminosity of the quasar.
We find good alignment between the extended Ly-alpha and the radio sources,
strong evidence for jet-cloud interactions in two cases, again resembling radio
galaxies, and what is possibly the most luminous radio-UV synchrotron jet in
one of the hosts at z=2.110.Comment: 36 pages (latex, aas macros), 3 figures (3 gif and 10 postscript
files), accepted for publication in the the Astrophysical Journal Supplement
Serie
High-redshift radio galaxies from the Molonglo catalogue
We report the result of radio and optical observations of a sample of southern hemisphere radio galaxies, selected from the Molonglo Reference Catalogue. The source were selected to have 408 MHz flux densities greater than 0.9 Jy and low-frequency spectral indices steeper than -0.9 VLA 6 cm maps and optical identifications of 13 sources are presented. All of these sources are indentified with faint galaxies, many of which have extended optical structures with morphologies characteristics od high redshift (Z > 0.8) radio galaxies. Long - slit spectroscopic observation have yielded redshifts for 11 of the galaxies, 5 of which are at Z > 2. The most distant source in the present sample, 0316 - 257, has a redshift of 3.13, while the median redshift for the sample is 1.6. Our result for this subsample suggest that our total sample of 150 sources may contain ~ 40 galaxies with Z > 2. We have imaged four of our galaxies having Z > 2 in the light of Lyα. Three of these have highly extended Lyα emission distributed along their radio axes
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