Global Jet Watch

Abstract:

We have imaged the X-ray binary SS 433 with unprecedented Fourier plane coverage at 6 cm using simultaneously the Very Long Baseline Array (VLBA), MERLIN, and the Very Large Array and also at 20 cm using the VLBA. At both wavelengths we have securely detected smooth, low surface brightness emission having the appearance of a "ruff" or collar attached perpendicularly to the well-studied knotty jets in this system and extending over at least a few hundred AU. We interpret this smooth emission as a windlike outflow from the binary and discuss its implications for the present evolutionary stage of this system. © 2001. The American Astronomical Society. All rights reserved.

Abstract:

We present a deep image of the optically powerful quasar E1821+643 at 18 cm made with the Very Large Array. This image reveals radio emission, over 280 h-1 kpc in extent, elongated way beyond the quasar's host galaxy. Its radio structure has decreasing surface brightness with increasing distance from the bright core, characteristic of FR I sources. Its radio luminosity at 5 GHz falls in the classification for "radio-quiet" quasars (it is only 1023.9 W Hz-1 sr-1). Its radio luminosity at 151 MHz (which is 1025.3 W Hz-1 sr-1) is at the transition luminosity observed to separate FR I and FR II structures. Hitherto, no optically powerful quasar had been found to have a conventional FR I radio structure. For searches at low frequency, this is unsurprising given current sensitivity and plausible radio spectral indices for radio-quiet quasars. We demonstrate the inevitability of the extent of any FR I radio structures being seriously underestimated by existing targeted follow-up observations of other optically selected quasars, which are typically short exposures of z > 0.3 objects, and we discuss the implications for the purported radio bimodality in quasars. The nature of the inner arcsecond-scale jet in E1821+643, together with its large-scale radio structure, suggest that the jet axis in this quasar is precessing (cf. Galactic jet sources such as SS 433). A possible explanation for this is that its central engine is a binary whose black holes have yet to coalesce. The ubiquity of precession in radio-quiet quasars, perhaps as a means of reducing the observable radio luminosity expected in highly accreting systems, remains to be established. © 2001. The American Astronomical Society. All rights reserved.

Abstract:

At least half the radio galaxies at z > 1 in the 7C Redshift Survey have extremely red colours (R - K > 5), consistent with stellar populations which formed at high redshift (z greater than or similar to 5). We discuss the implications of this for the evolution of massive galaxies in general and for the fraction of near-IR-selected EROs which host AGN, a result which is now being tested by deep, hard X-ray surveys. The conclusion is that many massive galaxies undergo at least two active phases: one at z similar to 5 when the black hole and stellar bulge formed and another at z similar to 1 - 2 when activity is triggered by an event such as an interaction or merger.

Abstract:

Using a new radio sample, 6C* designed to find radio galaxies at z > 4 along with the complete 3CRR and 6CE sample we extend the radio galaxy K - z relation to z - 4.5. The 6C* K - z data significantly improve delineation of the K - z relation for radio galaxies at high redshift (z > 2). Accounting for non-stellar contamination, and for correlations between radio luminosity and estimates of stellar mass, we find little support for previous claims that the underlying scatter in the stellar luminosity of radio galaxies increases significantly at z > 2. This indicates that we are not probing into the formation epoch until at least z greater than or similar to 3.

Abstract:

We present RIJHK imaging of seven radio galaxies from the 7C Redshift Survey (7CRS) which lack strong emission lines and we use these data to investigate their spectral energy distributions (SEDs) with models which constrain their redshifts. Six of these seven galaxies have extremely red colours (R-K>5.5) and we find that almost all of them lie in the redshift range 1L*) galaxies which formed the bulk of their stars several Gyr earlier, that is at epochs corresponding to redshifts z>5. If a similar fraction of all z~1.5 radio galaxies are old, then extrapolation of the radio luminosity function shows that, depending on the radio source lifetimes, between 10-100% of the near-IR selected extremely red object (ERO) population undergo a radio outburst at epochs corresponding to 15 and these objects probably undergo at least two periods of AGN activity: one at high redshift during which the black hole forms and another one at an epoch corresponding to z~1.5.