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