206 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
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
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
Radio jet interactions in the radio galaxy PKS 2152-699
We present radio observations of the radio galaxy PKS 2152-699 obtained with
the Australia Telescope Compact Array (ATCA). The much higher resolution and
s/n of the new radio maps reveals the presence of a bright radio component
about 10 arcsec NE of the nucleus. This lies close to the highly ionized cloud
previously studied in the optical and here shown in a broadband red snapshot
image with the HST PC2. It suggests that PKS 2152-699 may be a jet/cloud
interaction similar to 3C277.3. This could cause the change in the position
angle (of ~20 deg) of the radio emission from the inner to the outer regions.
On the large scale, the source has Fanaroff & Riley type II morphology although
the presence of the two hot-spots in the centres of the lobes is unusual. The
northern lobe shows a particularly relaxed structure while the southern one has
an edge-brightened, arc-like structure.Comment: 7 pages, 5 encapsulated figures, 1 JPEG figure, accepted for MNRA
VIMOS-VLT spectroscopy of the giant Ly-alpha nebulae associated with three z~2.5 radio galaxies
The morphological and spectroscopic properties of the giant (>60 kpc)
Ly-alpha nebulae associated with three radio galaxies at z~2.5 (MRC 1558-003,
MRC 2025-218 and MRC 0140-257) have been investigated using integral field
spectroscopic data obtained with VIMOS on VLT.
The morphologies are varied. The nebula of one source has a centrally peaked,
rounded appearance. In the other two objects, it consists of two spatial
components. The three nebulae are aligned with the radio axis within <30 deg.
The total Ly-alpha luminosities are in the range (0.3-3.4) x 1e44 erg s-1. The
Ly-alpha spectral profile shows strong variation through the nebulae, with FWHM
values in the range ~400-1500 km s-1 and velocity shifts V~120-600 km s-1.
We present an infall model which can explain successfully most Ly-alpha
morphological and spectroscopic properties of the nebula associated with MRC
1558-003. This adds further support to our previous conclusion that the
_quiescent_ giant nebulae associated with this and other high redshift powerful
radio galaxies are in infall. A problem for this model is the difficulty to
reproduce the large Ly-alpha FWHM values.
We have discovered a giant (~85 kpc) Ly-alpha nebula associated with the
radio galaxy MRC 0140-257 at z=2.64. It shows strikingly relaxed kinematics
(FWHM2) radio galaxies.Comment: 14 pages, 13 figures. Accepted for publication in MNRA
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