VLT spectropolarimetry of two powerful radio galaxies at z~1.4: UV continuum, emission-line properties and the nature of high-redshift dust

(Abridged) Deep VLT spectropolarimetric observations are presented for two powerful radio galaxies, 0850-206 and 1303+091. These observations cover the rest-frame wavelength range ~ 1450 - 3750 A. New radio observations and continuum images of the same sources are also presented. These galaxies are the first two observed from a complete sample of nine radio sources with redshifts in the range 1.3 < z < 1.5 (selected from the equatorial sample of powerful radio sources of Best, Rottgering & Lehnert), as part of a project aimed to investigate the multi-component nature of the UV continuum in radio galaxies and any variations of the continuum properties with the radio source age. The larger radio source of the two, 0850-206, presents a high continuum fractional polarization, averaging 17% across the observed wavelength range and reaching 24% at rest-frame wavelengths of <2000 A. The smaller radio source, 1303+091, shows a lower continuum polarization, averaging 8% and rising to 11% for rest-frame wavelengths >3000 A. For both galaxies, the position angle of the electric vector is generally constant with wavelength and within ~15 degrees of perpendicular to the radio axis. Both their total flux spectra and polarized flux spectra reveal the 2200 A dust feature, and comparison with dust scattering models suggests that the composition of the dust in these galaxies is similar to that of Galactic dust. In 0850-206, scattered quasar radiation dominates the UV continuum emission, with the nebular continuum accounting for no more than ~22% and no requirement for any additional emission component such as emission from young stars. By contrast, in 1303+091, unpolarized radiation could be a major constituent of the UV continuum emission, with starlight accounting for up to ~50% and the nebular continuum accounting for ~11%.Comment: 20 pages, including 14 figures. MNRAS accepte

Outflows and shocks in compact radio sources

We report some key results from the optical emission line study of a complete sample of compact radio sources. We find strong evidence for jet-driven outflows in the circum-nuclear emission line gas namely: 1) highly broadened and blueshifted emission line components (up to 2000 km/s), 2) shock ionised gas (broader, shifted components), 3) consistency in the scales of the emission line gas and the radio source and 4) trends between the maximum outflow velocity and radio source size (and orientation). Full details can be found in Holt (2005).Comment: 4 pages, 4 figures, to be published in Astronomische Nachrichten (proceedings of the Granada workshop on High Redshift Radio Galaxies

Shocks, illumination cones and intrinsic gas structures in the extreme radio galaxy 3C265

We present deep, narrow-band and continuum images of the powerful z=0.811 radio galaxy 3C265, taken with the TTF on the WHT, together with detailed long-slit spectroscopic observations along the axis defined by the UV/optical emission elongation. The deep images reveal the existence of cones in the ionization structure within ~7 arcsec (58 kpc) of the nucleus, where the emission-line structure is not closely aligned with the radio axis. This indicates that anisotropic illumination from the central AGN dominates on a small scale. At larger distances (>10 arcsec) from the nucleus, low-ionization emission gas is closely aligned with the radio axis, suggesting that jet-cloud interactions may be the dominant mechanism in the line-emitting gas on a larger scale. Moreover, the presence of a high-velocity cloud at 2.5 arcsec from the nucleus, close to the radio axis, indicates that even close to the nucleus jet-induced shocks have an important kinematic effect. While on a large scale the low-ionization emission-line structures are aligned with the radio axis, on a smaller scale, where AGN-photoionization dominates, the highest surface brightness structure is aligned with the closest companion galaxy. This suggest that much of the emission-line structure reflects the intrinsic gas distribution, rather than the ionization pattern imprinted by the radio jets or by AGN illumination. Overall, our results underline the need for a variety of mechanisms to explain the properties of the extended emission-line gas of radio galaxies (abridged).Comment: 12 pages, including 6 figures, MNRAS in pres

Ionized outflows in luminous type 2 AGNs at z < 0.6: no evidence for significant impact on the host galaxies

We investigate the presence of extended ionized outflows in 18 luminous type 2 AGNs (11 quasars and 7 high-luminosity Seyfert 2s) at 0.3 <z< 0.6 based on VLT-FORS2 spectroscopy. We infer typical lower limits on the radial sizes of the outflows Ro several × 100 pc and upper limits Ro 1–2 kpc. Our results are inconsistent with related studies which suggest that large scale (Ro ∼ several-15 kpc) are ubiquitous in QSO2. We study the possible causes of discrepancy and propose that seeing smearing is the cause of the large inferred sizes. The implications in our understanding of the feedback phenomenon are important since the mass Mo (through the density), mass injection M˙ o and energy injection E˙ o rates of the outflows become highly uncertain. One conclusion seems unavoidable: Mo, M˙ o and E˙ o are modest or low compared with previous estimations. We obtain typically Mo (0.4–22) × 106 M (median 1.1 × 106 M) assuming n = 1000 cm−3. These are ∼102–104 times lower than values reported in the literature. Even under the most favourable assumptions, we obtain M˙ o 10 M yr−1 in general, 100–1000 times lower than claimed in related studies. Although the uncertainties are large, it is probable that these are lower than typical star-forming rates. In conclusion, no evidence is found supporting that typical outflows can affect the interstellar medium of the host galaxies across spatial scales 1–2 kpc