2,656 research outputs found
PKS 1004+13: A High-Inclination, Highly-Absorbed Radio-Loud QSO -- The First Radio-Loud BAL QSO at Low Redshift?
The existence of BAL outflows in only radio-quiet QSOs was thought to be an
important clue to mass ejection and the radio-loud - radio-quiet dichotomy.
Recently a few radio-loud BAL QSOs have been discovered at high redshift. We
present evidence that PKS 1004+13 is a radio-loud BAL QSO. It would be the
first known at low-redshift (z = 0.24), and one of the most radio luminous. For
PKS 1004+13, there appear to be broad absorption troughs of O VI, N V, Si IV,
and C IV, indicating high-ionization outflows up to about 10,000 km/s. There
are also two strong, broad (~500 km/s), high-ionization, associated absorption
systems that show partial covering of the continuum source. The strong UV
absorption we have detected suggests that the extreme soft-X-ray weakness of
PKS 1004+13 is primarily the result of absorption. The large radio-lobe
dominance indicates BAL and associated gas at high inclinations to the central
engine axis, perhaps in a line-of-sight that passes through an accretion disk
wind.Comment: To appear in Ap.J. Letters, 1999 (June or July); 4 pages, 5 figure
Emission lines and optical continuum in low-luminosity radio galaxies
We present spectroscopic observations of a complete sub-sample of 13
low-luminosity radio galaxies selected from the 2Jy sample. The underlying
continuum in these sources is carefully modelled in order to make a much-needed
comparison between the emission line and continuum properties of FRIs with
those of other classes of radio sources. We find that 5 galaxies in the sample
show a measurable UV excess: 2 of the these sources are BL Lacs and in the
remaining 3 galaxies we argue that the most likely contributor to the UV excess
is a young stellar component. Excluding the BL Lacs, we therefore find that
\~30% of the sample show evidence for young stars, which is similar to the
results obtained for higher luminosity samples. We compare our results with
far-infrared measurements in order to investigate the far-infrared-starburst
link. The nature of the optical-radio correlations is investigated in light of
this new available data and, in contrast to previous studies, we find that the
FRI sources follow the correlations with a similar slope to that found for the
FRIIs. Finally, we compare the luminosity of the emission lines in the FRI and
BL Lac sources and find a significant difference in the [OIII] line
luminosities of the two groups. Our results are discussed in the context of the
unified schemes.Comment: 18 pages, 31 figures, MNRAS in press, (all enquiries to Clive
Tadhunter ([email protected])
The Optical Polarization and Warm Absorber in IRAS 17020+4544
We report the detection of ionized absorption in the ASCA spectrum of the
narrow-line Seyfert 1 galaxy IRAS 17020+4544. Subsequent optical
spectropolarimetry revealed high polarization increasing from 3% in the red to
5% in the blue, indicating electron or dust scattering as a likely origin. The
broad emission line H is somewhat less polarized than the continuum,
supporting a location of the polarizing material within the AGN. The Balmer
line decrement and reddened optical spectrum support the presence of a dusty
warm absorber in this object.
We compared the broad band optical polarization and ionized X-ray absorption
of a collection of Seyfert 1 and 1.5 galaxies, excluding classes of objects
that are likely to have significant neutral X-ray absorption. Warm absorber
objects are generally more likely to have high optical polarization than
objects with no detected ionized absorption. This result lends additional
support to the idea that the warm absorber is associated with dust and implies
either that dust transmission is responsible for at least part of the
polarization or that the polarization is revealed because of the dimming of the
optical spectrum. Spectropolarimetry of Seyfert 1s generally locates the
scattering material inside the narrow-line region and often close to or within
the broad line region, consistent with estimates of the location of the dusty
warm absorber.Comment: 11 pages using (AASTeX) aaspp4.sty and 3 Postscript figures. Accepted
for publication in Astrophysical Journal Letter
HI absorption in radio galaxies: effect of orientation or interstellar medium?
A search for HI absorption has been made in 23 radio galaxies using the ATCA,
the VLA and the WSRT. In five galaxies HI absorption was detected. We
investigate how the detection rate is distributed among galaxies with different
radio and optical properties. Among the Fanaroff-Riley (FR) type I radio
galaxies, only one object (10% of total) was detected. The HI absorption in
these objects is likely to come from a nuclear disk, as found for other
galaxies of this type. The low detection rate is consistent with the hypothesis
(as suggested by optical and X-ray data) that the ``standard'' pc scale,
geometrically thick torus is not required in low-luminosity radio galaxies. In
the case of FR type-II powerful radio galaxies, no HI absorption has been
detected in broad line radio galaxies, while three out of four narrow-line
radio galaxies have been detected (the one non-detection having quite a high
upper limit). All these are compact or small radio galaxies. To first order
this is consistent with the predictions of the unified schemes, assuming that
the HI absorption is due to an obscuring torus. However, the indications of
this being the only cause of the absorption are not very strong. In particular,
we find that in two of the three detected objects that the HI is blueshifted
compared to the systemic velocity. In the third galaxy (PKS 1549-79) two
redshift systems (from the optical lines) are found. The uncertainty in the
systemic velocity derived from optical lines is discussed. Finally, we find a
tendency for radio galaxies with a strong component of young stellar population
and far-IR emission to show HI absorption. The overall richer ISM that is
likely to be present in these galaxies may be a factor in producing the
absorption
Near-IR spectroscopy of PKS1549-79: a proto-quasar revealed?
We present a near-IR spectrum of the nearby radio galaxy PKS1549-79 (z=0153).
These data were taken with the aim of testing the idea that this object
contains a quasar nucleus that is moderately extinguished, despite evidence
that its radio jet points close to our line-of-sight. We detect broad Paschen
Alpha emission (FWHM ~1745 km/s), relatively bright continuum emission, and a
continuum slope consistent with a reddened quasar spectrum (3.1 < Av < 7.3),
all emitted by an unresolved point source. Therefore we conclude that we have,
indeed, detected a hidden quasar nucleus in PKS1549-79. Combined with previous
results, these observations are consistent with the idea that PKS1549-79 is a
young radio source in which the cocoon of debric left over from the triggering
events has not yet been swept aside by circumnuclear outflows.Comment: 6 pages, 4 figures, accepted for publication in MNRA
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