248 research outputs found
Infrared imaging of WENSS radio sources
We have performed deep imaging in the IR J- and K-bands for three sub-samples
of radio sources extracted from the Westerbork Northern Sky Survey, a large
low-frequency radio survey containing Ultra Steep Spectrum (USS), Gigahertz
Peaked Spectrum (GPS) and Flat Spectrum (FS) sources. We present the results of
these IR observations, carried out with the ARcetri Near Infrared CAmera
(ARNICA) at the Nordic Optical Telescope (NOT), providing photometric and
morphologic information on high redshift radio galaxies and quasars. We find
that the radio galaxies contained in our sample do not show the pronounced
radio/IR alignment claimed for 3CR sources. IR photometric measurements of the
gravitational lens system 1600+434 are also presented.Comment: 8 pages, 54 Postscript figures, to be published in Astronomy and
Astrophysics, Supplement Serie
Jet-gas interactions in z~2.5 radio galaxies: evolution of the ultraviolet line and continuum emission with radio morphology
We present an investigation into the nature of the jet-gas interactions in a
sample of 10 radio galaxies at 2.3<z<2.9 using deep spectroscopy of the UV line
and continuum emission obtained at Keck II and the Very Large Telescope.
Kinematically perturbed gas, which we have shown to be within the radio
structure in previous publications, is always blueshifted with respect to the
kinematically quiescent gas, is usually spatially extended, and is usually
detected on both sides of the nucleus. In the three objects from this sample
for which we are able to measure line ratios for both the perturbed and
quiescent gases, we suggest that the former has a lower ionization state than
the latter.
We propose that the perturbed gas is part of a jet-induced outflow, with dust
obscuring the outflowing gas that lies on the far side of the object. The
spatial extent of the blueshifted perturbed gas, typically ~35 kpc, implies
that the dust is spatially extended at least on similar spatial scales.
We also find interesting interrelationships between UV line, UV continuum and
radio continuum properties of this sample.Comment: Accepted for publication in MNRA
Deep spectroscopy of the FUV-optical emission lines from a sample of radio galaxies at z~2.5: metallicity and ionization
We present long-slit NIR spectra, obtained using the ISAAC instrument at the
Very Large Telescope, for nine radio galaxies at z~2.5. One-dimensional spectra
have been extracted and cross calibrated with optical spectra from the
literature to produce line spectra spanning a rest wavelength of ~1200-7000 A.
We have also produced a composite of the rest-frame UV-optical line fluxes of
powerful, z~2.5 radio galaxies. We have investigated the relative strengths of
Ly-alpha, H-beta, H-alpha, HeII 1640 and HeII 4687, and we find that Av can
vary significantly from object to object. In addition, we identify new line
ratios to calculate electron temperature: [NeV] 1575/[NeV] 3426, [NeIV]
1602/[NeIV] 2423, OIII] 1663/[OIII] 5008 and [OII] 2471/[OII]3728. We model the
emission line spectra and conclude they are best explained by
AGN-photoionization with the ionization parameter U varying between objects.
Single slab photoionization models are unable to reproduce the high- and the
low-ionization lines simultaneously: this may be alleviated either by combining
two or more single slab photoionization models with different U, or by using
mixed-medium models such as those of Binette, Wilson & Storchi-Bergmann (1996).
On the basis of NV/NIV] and NIV]/CIV we argue that shocks make a fractional
contribution to the ionization of the EELR. We find that in the EELR of z~2
radio galaxies the N/H abundance ratio is close to its solar value. We conclude
that N/H and metallicity do not vary by more than a factor of two in our
sample. This is consistent with the idea that massive ellipticals are assembled
very early in the history of the universe, and then evolve relatively passively
up to the present day.Comment: Accepted for publication by MNRA
What is 3C 324?
We report ground based and HST observations of the z=1.206 radio galaxy 3C
324, a prototypical example of the radio-optical ``alignment effect.'' While
infrared images shows a simple, round object reminiscent of a giant elliptical
galaxy, the HST images reveal a spectacular, linear chain of UV-bright
subcomponents closely aligned with the radio axis. In light of the available
data, we consider various scenarios to explain the properties of 3C 324, as
well as evidence for the presence of dust which may obscure the central active
nucleus and scatter its light to produce the polarized, aligned continuum seen
in the rest-frame UV.Comment: 9 pages, uuencoded gzipped postscript. To appear in ``Galaxies in the
Young Universe,'' ed. H. Hippelein, Springer Verlag. Revised version
(hopefully) corrects postscript error which garbled the last pag
Interpreting the kinematics of the extended gas in distant radiogalaxies from 8-10m telescope spectra
The nature of the extreme kinematics in the extended gas of distant radio
galaxies (z>0.7) is still an open question. With the advent of the 8-10 m
telescope generation and the development of NIR arrays we are in the position
for the first time to develop a more detailed study by using lines other than
Lya and [OII]3727 depending on redshift. In this paper we review the main
sources of uncertainty in the interpretation of the emission line kinematics:
the presence of several kinematic components, Lya absorption by neutral
gas/dust and the contribution of scattered light to some of the lines. As an
example, several kinematic components can produce apparent, false rotation
curves. We propose methods to solve these uncertainties. We propose to extend
the methods applied to low redshift radio galaxies to investigate the nature of
the kinematics in distant radio galaxies: by means of the spectral
decomposition of the strong optical emission lines (redshifted into the NIR) we
can isolate the different kinematic components and study the emission line
ratios for the individual components. If shocks are responsible for the extreme
kinematics, we should be able to isolate a kinematic component (the shocked
gas) with large FWHM (>900 km/s), low ionization level [OIII]5007/Hb~2-4 and
weak HeII4686/Hb<0.07, together with a narrow component (~few hundred km/s)
with higher ionization level and strong HeII emission (HeII/Hb~0.5)Comment: 11 pages, 6 Figures, to be published in A&A Supplement Serie
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