167 research outputs found
Radio imaging of core-dominated high redshift quasars
VLA imaging at kiloparsec-scale resolution of sixteen core-dominated
radio-loud QSOs is presented. Many objects appear to display variable radio
emission and their radio morphologies are significantly smaller than those of
steep-spectrum quasars, consistent with these objects being observed at sight
lines close to their (relativistic, 4-7) jet axes. The
usefulness of the radio source orientation indicator R_V, being defined as
ratio of radio core and rest frame optical V-band luminosity, is confirmed.Comment: 11 pages, 11 postscript figures, uses aa.cls 4.03 for LaTeX2e To
appear in Astronomy and Astrophysic
1245+676 - a CSO/GPS source being an extreme case of a double-double structure
AGN with the so-called `double-double' radio structure have been interpreted
as restarted AGN where the inner structure is a manifestation of a new phase of
activity which happened to begin before the outer radio lobes resulting from
the previous one had faded completely. The radio galaxy 1245+676 is an extreme
example of such a double-double object - its outer structure, measuring 970
h^{-1} kpc, is five orders of magnitude larger than the 9.6 h^{-1} pc inner
one. We present a series of VLBI observations of the core of 1245+676 which
appears to be a compact symmetric object (CSO). We have detected the motion of
the CSO's lobes, measured its velocity, and inferred the kinematic age of that
structure.Comment: A contribution to The Third Workshop on Compact Steep Spectrum and
GHz-Peaked Spectrum Radio Sources, Kerastari, Greece May 28-31, 2002.
Refereed and accepted by Publications of the Astronomical Society of
Australia. 4 pages. Final version copyedited by PASA Edito
Nature of 60 micron emission in 3C47, 3C207 and 3C334
We try to explain the unusually high far-infrared emission seen by IRAS in
the double-lobed radio-loud quasars 3C47, 3C207 and 3C334. High resolution
cm--mm observations were carried out to determine their radio core spectra,
which are subsequently extrapolated to the far-infrared in order to determine
the strength of the synchrotron far-infrared emission. The extrapolated flux
densities being considerably lower than the observed values, a significant
nonthermal far-infrared component is unlikely in the case of 3C47 and 3C334.
However, this component could be responsible for the far-infrared brightness of
3C207. Our analysis demonstrates that nonthermal emission cannot readily
account for the difference between quasars and radio galaxies in the amount of
their far-infrared luminosity. On the other hand, a significant role for this
mechanism is likely; full sampling of the mm-submm spectral energy
distributions is needed to address the issue quantitatively.Comment: 7 pages, incl. 3 figures; accepted for publication in A&
3C 220.3: a radio galaxy lensing a submillimeter galaxy
Herschel Space Observatory photometry and extensive multiwavelength followup
have revealed that the powerful radio galaxy 3C 220.3 at z=0.685 acts as a
gravitational lens for a background submillimeter galaxy (SMG) at z=2.221. At
an observed wavelength of 1mm, the SMG is lensed into three distinct images. In
the observed near infrared, these images are connected by an arc of 1.8" radius
forming an Einstein half-ring centered near the radio galaxy. In visible light,
only the arc is apparent. 3C 220.3 is the only known instance of strong
galaxy-scale lensing by a powerful radio galaxy not located in a galaxy cluster
and therefore it offers the potential to probe the dark matter content of the
radio galaxy host. Lens modeling rejects a single lens, but two lenses centered
on the radio galaxy host A and a companion B, separated by 1.5", provide a fit
consistent with all data and reveal faint candidates for the predicted fourth
and fifth images. The model does not require an extended common dark matter
halo, consistent with the absence of extended bright X-ray emission on our
Chandra image. The projected dark matter fractions within the Einstein radii of
A (1.02") and B (0.61") are about 0.4 +/- 0.3 and 0.55 +/- 0.3. The mass to
i-band light ratios of A and B, M/L ~ 8 +/- 4 Msun/Lsun, appear comparable to
those of radio-quiet lensing galaxies at the same redshift in the CASTLES, LSD,
and SL2S samples. The lensed SMG is extremely bright with observed f(250um) =
440mJy owing to a magnification factor mu~10. The SMG spectrum shows luminous,
narrow CIV 154.9nm emission, revealing that the SMG houses a hidden quasar in
addition to a violent starburst. Multicolor image reconstruction of the SMG
indicates a bipolar morphology of the emitted ultraviolet (UV) light suggestive
of cones through which UV light escapes a dust-enshrouded nucleus.Comment: 17 pages, 14 Figures, accepted for publication in Ap
The Radio Properties of Composite LINER/HII Galaxies
Arcsec-resolution VLA observations -- newly obtained as well as published --
of 40 nearby galaxies are discussed, completing a study of the radio properties
of a magnitude-limited sample of nearby galaxies of the composite LINER/HII
type. Our results reveal an overall detection rate of at least 25% AGN
candidates among these composite sources. The general properties of these AGN
candidates, as compared to non-AGN composite sources and HII galaxies, are
discussed.Comment: Accepted for publication in ApJ
The Nature of Composite LINER/HII Galaxies, As Revealed from High-Resolution VLA Observations
A sample of 37 nearby galaxies displaying composite LINER/HII and pure HII
spectra was observed with the VLA in an investigation of the nature of their
weak radio emission. The resulting radio contour maps overlaid on optical
galaxy images are presented here, together with an extensive literature list
and discussion of the individual galaxies. Radio morphological data permit
assessment of the ``classical AGN'' contribution to the global activity
observed in these ``transition'' LINER galaxies. One in five of the latter
objects display clear AGN characteristics: these occur exclusively in
bulge-dominated hosts.Comment: 31 pages, 27 figures, accepted by ApJ
The Far-Infrared Surveyor (FIS) for AKARI
The Far-Infrared Surveyor (FIS) is one of two focal plane instruments on the
AKARI satellite. FIS has four photometric bands at 65, 90, 140, and 160 um, and
uses two kinds of array detectors. The FIS arrays and optics are designed to
sweep the sky with high spatial resolution and redundancy. The actual scan
width is more than eight arcmin, and the pixel pitch is matches the diffraction
limit of the telescope. Derived point spread functions (PSFs) from observations
of asteroids are similar to the optical model. Significant excesses, however,
are clearly seen around tails of the PSFs, whose contributions are about 30% of
the total power. All FIS functions are operating well in orbit, and its
performance meets the laboratory characterizations, except for the two longer
wavelength bands, which are not performing as well as characterized.
Furthermore, the FIS has a spectroscopic capability using a Fourier transform
spectrometer (FTS). Because the FTS takes advantage of the optics and detectors
of the photometer, it can simultaneously make a spectral map. This paper
summarizes the in-flight technical and operational performance of the FIS.Comment: 23 pages, 10 figures, and 2 tables. Accepted for publication in the
AKARI special issue of the Publications of the Astronomical Society of Japa
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