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

Spitzer Observations of High Redshift Radio Galaxies

We present the results of a comprehensive Spitzer survey of 70 radio galaxies across 1<z<5.2. Using IRAC, IRS and MIPS imaging we determine the rest-frame AGN contribution to the stellar emission peak at 1.6um. The stellar luminosities are found to be consistent with that of a giant elliptical with a stellar mass of 10^11-12Msun. The mean stellar mass remains constant at \~10^11.5Msun up to z=3 indicating that the upper end of the mass function is already in place by this redshift. The mid-IR luminosities imply bolometric IR luminosities that would classify all sources as ULIRGs. The mid-IR to radio luminosity generally correlate implying a common origin for these emissions. The ratio is higher than that found for lower redshift, ie z<1, radio galaxies.Comment: 6 pages, 5 figures, to appear in the proceedings of "The Spitzer Science Center 2005 Conference: Infrared Diagnostics of Galaxy Evolution", held in Pasadena, November 200