(Abridged) This is the second in a series of three papers which present and interpret basic observational data on the 6C* 151-MHz radio sample: a low-frequency selected sample which exploits ...filtering criteria based on radio properties (steep spectral index and small angular size) to find radio sources at redshift z > 4 within a 0.133sr patch of sky. We present results of a programme of optical spectroscopy which has yielded redshifts in the range 0.5 < z < 4.4 for the 29 sources in the sample, all but six of which are secure. We find that the fil tering criteria used for 6C* are very effective in excluding the low-redshift, low-luminosity radio sources: the median redshift of 6C* is z~1.9 compared to z~1.1 for a complete sample matched in 151-MHz flux density. By combining the emission-line dataset for the 6C* radio sources with those for the 3CRR, 6CE and 7CRS samples we establish that z > 1.75 radio galaxies follow a rough proportionality between Lyalpha- and 151 MHz-luminosity which, like similar correlations seen in samples of lower-redshift radio sources, are indicative of a primary link between the power in the source of the photoionising photons (most likely a hidden quasar nucleus) and the power carried by the radio jets. We argue that radio sources modify their environments and that the range of emission-line properties seen is determined more by the range of source age than by the range in ambient environment. This is in accord with the idea that all high-redshift, high-luminosity radio sources are triggered in similar environments, presumably recently collapsed massive structures.
In a companion paper (Paper I: Jones et al. 1996) we report the discovery of
a cosmic microwave background decrement, indicative of a distant cluster with
mass ~10^{15} solar masses, towards the ...quasar pair PC1643+4631A&B
(z=3.79,3.83, separation 198''). To search for the cluster responsible, we have
obtained R-, J- and K-band images of the field and have also carried out
optical spectroscopy of selected objects in it. No such cluster is evident in
these images. Assuming the cluster causing the decrement is similar to massive
clusters already known, our magnitude limits imply that it must lie about or
beyond z=1. This provides independent support for the X-ray-based distance
argument of Paper I. The cluster must gravitationally lens objects behind it;
for a cluster z around 1-2, the Einstein-ring radius for sources at z ~= 3.8 is
~ 100''. Simple modelling, producing simultaneously the S-Z effect and the
lensing, shows that the source positions of quasars A and B lie within ~10'' of
each other and may indeed be coincident. The two quasar spectra are found to be
remarkably similar apart from their one-percent redshift difference. Assuming A
and B are images of a single quasar, we present a possible explanation of this
difference.
Using complete samples of steep-spectrum quasars, we present evidence for a correlation between radio and optical luminosity which is not caused by selection effects, nor caused by an orientation ...dependence (such as relativistic beaming), nor a byproduct of cosmic evolution. We argue that this rules out models of jet formation in which there are no parameters in common with the production of the optical continuum. This is arguably the most direct evidence to date for a close link between accretion onto a black hole and the fuelling of relativistic jets. The correlation also provides a natural explanation for the presence of aligned optical/radio structures in only the most radio luminous high-redshift galaxies.
In a companion paper (Paper I: Jones et al. 1996) we report the discovery of a cosmic microwave background decrement, indicative of a distant cluster with mass ~10^{15} solar masses, towards the ...quasar pair PC1643+4631A&B (z=3.79,3.83, separation 198''). To search for the cluster responsible, we have obtained R-, J- and K-band images of the field and have also carried out optical spectroscopy of selected objects in it. No such cluster is evident in these images. Assuming the cluster causing the decrement is similar to massive clusters already known, our magnitude limits imply that it must lie about or beyond z=1. This provides independent support for the X-ray-based distance argument of Paper I. The cluster must gravitationally lens objects behind it; for a cluster z around 1-2, the Einstein-ring radius for sources at z ~= 3.8 is ~ 100''. Simple modelling, producing simultaneously the S-Z effect and the lensing, shows that the source positions of quasars A and B lie within ~10'' of each other and may indeed be coincident. The two quasar spectra are found to be remarkably similar apart from their one-percent redshift difference. Assuming A and B are images of a single quasar, we present a possible explanation of this difference.
The 50 Best Inventions Grossman, Lev; Brock-Abraham, Cleo; Carbone, Nick ...
Time (Chicago, Ill.),
11/2011, Letnik:
178, Številka:
21
Magazine Article
Grossman et al talk about year's most inspired ideas, innovations and revolutions, from the microscopic to the stratospheric. Recent scholarship on innovation, such as Steven Johnson's Where Good ...Ideas Come From, suggests that most inventions are the result of slow-burning collaborative efforts hatched in academic labs and corporate R&D departments rather than in some isolated genius's garage. One day someone like Steve Jobs will take it as raw material to be tamed and refined and turned into something that will change the world.
Reviews of Books Rawlings, Helen; Rohland de Langbehn, Regula; Helena Chinchilla, Rosa ...
Bulletin of Spanish Studies,
20/1/1/, Letnik:
85, Številka:
1
Book Review
