We have used narrow emission‐line data from the new 7C Redshift Survey to investigate correlations between the narrow‐line luminosities and the radio properties of radio galaxies and steep‐spectrum quasars. The 7C Redshift Survey is a low‐frequency (151 MHz) selected sample with a flux density limit about 25 times fainter than the 3CRR sample. By combining these samples, we can for the first time distinguish whether the correlations present are controlled by 151‐MHz radio luminosity L151 or redshift z. We find unequivocal evidence that the dominant effect is a strong positive correlation between narrow‐line luminosity LNLR and L151, of the form . Correlations of LNLR with redshift or radio properties, such as linear size or 151‐MHz (rest frame) spectral index, are either much weaker or absent. We use simple assumptions to estimate the total bulk kinetic power Q of the jets in FR II radio sources, and confirm the underlying proportionality between jet power and narrow‐line luminosity first discussed by Rawlings & Saunders. We make the assumption that the main energy input to the narrow‐line region is photoionization by the quasar accretion disc, and relate Q to the disc luminosity, Qphot. We find that 0.05≲QQphot≲1, so that the jet power is within about an order of magnitude of the accretion disc luminosity. Values of QQphot∼1 require the volume filling factor η of the synchrotron‐emitting material to be of the order of unity, and in addition require one or more of the following: (i) an important contribution to the energy budget from protons; (ii) a large reservoir of mildly relativistic electrons; and (iii) a substantial departure from the minimum‐energy condition in the lobe material. The most powerful radio sources are accreting at rates close to the Eddington limit of supermassive black holes (MBH≳109 M⊙), whilst lower power sources are accreting at sub‐Eddington rates.

We present discovery imaging and spectroscopy for nine new z ∼ 6 quasars found in the Canada-France Highz Quasar Survey (CFHQS) bringing the total number of CFHQS quasars to 19. By combining the CFHQS with the more luminous SDSS sample we are able to derive the quasar luminosity function from a sample of 40 quasars at redshifts 5.74 < z < 6.42. Our binned luminosity function shows a slightly lower normalisation and flatter slope than found in previous work. The binned data also suggest a break in the luminosity function at M 1450 ≈ −25. A double power law maximum likelihood fit to the data is consistent with the binned results. The luminosity function is strongly constrained (1 σ uncertainty < 0.1 dex) over the range −27.5 < M 1450 < −24.7. The best-fit parameters are Φ(M * 1450 ) = 1.14 × 10 −8 Mpc −3 mag −1 , break magnitude M * 1450 = −25.13 and bright end slope β = −2.81. However the covariance between β and M * 1450 prevents strong constraints being placed on either parameter. For a break magnitude in the range −26 < M * 1450 < −24 we find −3.8 < β < −2.3 at 95% confidence. We calculate the z = 6 quasar intergalactic ionizing flux and show it is between 20 and 100 times lower than that necessary for reionization. Finally, we use the luminosity function to predict how many higher redshift quasars may be discovered in future near-IR imaging surveys.

We present first results of a study aimed to constrain the star formation rate and dust content of galaxies at z≈2. We use a sample of BzK-selected star-forming galaxies, drawn from the COSMOS survey, to perform a stacking analysis of their 1.4 GHz radio continuum as a function of different stellar population properties, after removing AGN contaminants from the sample. Dust unbiased star formation rates are derived from radio fluxes assuming the local radio-IR correlation. The main results of this work are: i) specific star formation rates are constant over about 1 dex in stellar mass and up to the highest stellar mass probed; ii) the dust attenuation is a strong function of galaxy stellar mass with more massive galaxies being more obscured than lower mass objects; iii) a single value of the UV extinction applied to all galaxies would lead to grossly underestimate the SFR in massive galaxies; iv) correcting the observed UV luminosities for dust attenuation based on the Calzetti recipe provide results in very good agreement with the radio derived ones; v) the mean specific star formation rate of our sample steadily decreases by a factor of ∼ 4 with decreasing redshift from z = 2.3 to 1.4 and a factor of ∼ 40 down the local Universe.These empirical SFRs would cause galaxies to dramatically overgrow in mass if maintained all the way to low redshifts, we suggest that this does not happen because star formation is progressively quenched, likely starting from the most massive galaxies.

We present discovery observations of a quasar in the Canada-France High-z Quasar Survey (CFHQS) at redshift z = 6.44. We also use near-IR spectroscopy of nine CFHQS quasars at z ∼ 6 to determine black hole masses. These are compared with similar estimates for more luminous Sloan Digital Sky Survey (SDSS) quasars to investigate the relationship between black hole mass and quasar luminosity. We find a strong correlation between Mg ii FWHM and UV luminosity and that most quasars at this early epoch are accreting close to the Eddington limit. Thus these quasars appear to be in an early stage of their life cycle where they are building up their black hole mass exponentially. Combining these results with the quasar luminosity function, we derive the black hole mass function at z = 6. Our black hole mass function is ∼ 10 4 times lower than at z = 0 and substantially below estimates from previous studies. The main uncertainties which could increase the black hole mass function are a larger population of obscured quasars at high-redshift than is observed at low-redshift and/or a low quasar duty cycle at z = 6. In comparison, the global stellar mass function is only ∼ 10 2 times lower at z = 6 than at z = 0. The difference between the black hole and stellar mass function evolution is due to either rapid early star formation which is not limited by radiation pressure as is the case for black hole growth or inefficient black hole seeding. Our work predicts that the black hole mass -stellar mass relation for a volume-limited sample of galaxies declines rapidly at very high redshift. This is in contrast to the observed increase at 4 < z < 6 from the local relation if one just studies the most massive black holes.

We describe the inter-dependence of four properties of classical double radio sources -spectral index, linear size, luminosity and redshift -from an extensive study based on spectroscopicallyidentified complete samples. We use these relationships to discuss aspects of strategies for searching for radio galaxies at extreme redshifts, in the context of possible capabilities of the new generation of proposed radio telescopes.