179 research outputs found
The extremely asymmetric radio structure of the z=3.1 radio galaxy B3 J2330+3927
We report on 1.7 and 5.0 GHz observations of the z=3.087 radio galaxy B3
J2330+3927, using the Very Long Baseline Array (VLBA), and archival 1.4 and 8.4
GHz Very Large Array (VLA) data. Our VLBA data identify a compact, flat
spectrum (\alpha_{1.7 GHz}^{5 GHz} = -0.2 +/- 0.1; S_\nu ~ \nu^\alpha) radio
component as the core. The VLA images show that the fraction of core emission
is very large (f_c \approx 0.5 at 8.4 GHz), and reveal a previously undetected,
very faint counterjet, implying a radio lobe flux density ratio R >= 11 and a
radio lobe distance ratio Q \approx 1.9. Those values are much more common in
quasars than in radio galaxies, but the optical/near-IR spectra show a clear
type II AGN for B3 J2330+3927, confirming that it is indeed a radio galaxy.
Unlike all other radio galaxies, the bright Ly-\alpha emitting gas is located
towards the furthest radio arm. We argue against environmental and relativistic
beaming effects being the cause of the observed asymmetry, and suggest this
source has intrinsically asymmetric radio jets. If this is the case, B3
J2330+3927 is the first example of such a source at high redshift, and seems to
be difficult to reconcile with the unified model, which explains the
differences between quasars and radio galaxies as being due to orientation
effects.Comment: 6 pages, 3 figures, to appear as a Letter to MNRA
CO Emission from z>3 Radio Galaxies
We report on the detection of the CO(4-3) line with the IRAM Plateau de Bure
Interferometer in two z>3 radio galaxies, doubling the number of successful
detections in such objects. A comparison of the CO and Ly-alpha velocity
profiles indicates that in at least half of the cases, the CO is coincident in
velocity with associated HI absorption seen against the Ly-alpha emission. This
strongly suggests that the CO and HI originate from the same gas reservoir, and
could explain the observed redshift differences between the optical narrow
emission lines and the CO. The CO emission traces a mass of H_2 100-1000 times
larger than the HI and HII mass traced by Ly-alpha, providing sufficient gas to
supply the massive starbursts suggested by their strong thermal dust emission.Comment: 6 Pages, including 3 PostScript figures. To appear in the proceedings
of the conference "Radio Galaxies: Past, present and future", Leiden, 11-15
Nov 2002, eds. M. Jarvis et a
Spectropolarimetry of PKS 0040-005 and the Orientation of Broad Absorption Line Quasars
We have used the Very Large Telescope (VLT) to obtain spectropolarimetry of
the radio-loud, double-lobed broad absorption line (BAL) quasar PKS 0040-005.
We find that the optical continuum of PKS 0040-005 is intrinsically polarized
at 0.7% with an electric vector position angle nearly parallel to that of the
large-scale radio axis. This result is naturally explained in terms of an
equatorial scattering region seen at a small inclination, building a strong
case that the BAL outflow is not equatorial. In conjunction with other recent
results concerning radio-loud BAL quasars, the era of simply characterizing
these sources as ``edge-on'' is over.Comment: 5 Pages, including 2 PostScript figures. Accepted for publication in
MNRAS letter
A Sample of 669 Ultra Steep Spectrum Radio Sources to Find High Redshift Radio Galaxies
Since radio sources with Ultra Steep Spectra (USS; alpha <~ -1.30; S ~
nu^alpha) are efficient tracers of high redshift radio galaxies (HzRGs), we
have defined three samples of such USS sources using the recently completed
WENSS, TEXAS, MRC, NVSS and PMN radio-surveys. Our combined sample contains 669
sources with S_1400 > 10 mJy and covers virtually the entire sky outside the
Galactic plane (|b|>15). For our 2 largest samples, covering declination > -35,
we selected only sources with angular sizes Theta < 1'. For 410 sources, we
present radio-maps with 0.3" to ~5" resolution from VLA and ATCA observations
or from the FIRST survey, which allows the optical identification of these
radio sources. We find that the spectral index distribution of 143,000 sources
from the WENSS and NVSS consists of a steep spectrum galaxy and a flat spectrum
quasar population, with the relative contribution of flat spectrum sources
doubling from S_1400 >0.1 Jy to S_1400 >2.5 Jy. The identification fraction of
our USS sources on the POSS (R <~ 20) is as low as 15%, independent of spectral
index alpha < -1.30. We further show that 85% of the USS sources that can be
identified with an X-ray source are probably contained in galaxy clusters, and
that alpha < -1.6 sources are excellent Galactic pulsar candidates, because the
percentage of these sources is four times higher in the Galactic plane. Our
sample has been constructed to start an intensive campaign to obtain a large
sample of high redshift objects (z>3) that is selected in a way that does not
suffer from dust extinction or any other optical bias [abridged].Comment: 28 Pages, 12 PostScript figures. Accepted for publication in
Astronomy & Astrophysics Supplements. Appendices B, C & D available on
http://www.strw.LeidenUniv.nl/~debreuck/paper
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