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We present a catalogue of 3405 X-ray sources from the ROSAT All Sky Survey (RASS) Bright Source Catalogue which fall within the area covered by the 6dF Galaxy Survey (6dFGS). The catalogue is count-rate limited at 0.05 cts s−1 in the X-ray and covers the area of sky with and . The RASS–6dFGS sample was one of the additional target catalogues of the 6dFGS and as a result we obtained optical spectra for 2224 (65 per cent) RASS sources. Of these, 1715 (77 per cent) have reliable redshifts with a median redshift of (excluding the Galactic sources). For the optically bright sources in the observed sample, over 90 per cent have reliable redshifts. The catalogue mainly comprises quasi-stellar objects (QSOs) and active galaxies but also includes 238 Galactic sources. Of the sources with reliable redshifts the majority are type 1 active galactic nuclei (AGN, 69 per cent), while 12 per cent are type 2 AGN, 6 per cent absorption-line galaxies and 13 per cent are stars. We also identify a small number of optically faint, very low redshift, compact objects which fall outside the general trend in the plane. The RASS–6dFGS catalogue complements a number of Northern hemisphere samples, particularly the ROSAT Bright Source Catalogue–NRAO VLA Sky Survey (RBSC–NVSS) sample ( Bauer et al. 2000 ), and furthermore, in the same region of sky reveals an additional 561 sources that were not identified as part of that sample. We detect 918 sources (27 per cent) of the RASS–6dFGS sample in the radio using either the 1.4 GHz NVSS or the 843 MHz Sydney University Molonglo Sky Survey (SUMSS) catalogues and find that the detection rate changes with redshift. At redshifts larger than 1 virtually all of these sources have radio counterparts and with a median flux density of 1.15 Jy, they are much stronger than the median flux density of 28.6 mJy for the full sample. We attribute this to the fact that the X-ray flux of these objects is being boosted by a jet component, possibly Doppler boosted, that is only present in radio-loud AGN. The RASS–6dFGS sample provides a large set of homogeneous optical spectra ideal for future studies of X-ray emitting AGN. [ABSTRACT FROM AUTHOR]

We present the quasi-stellar object (QSO) luminosity function (LF) of the completed 2dF–SDSS LRG and QSO (2SLAQ) survey, based on QSOs photometrically selected from Sloan Digital Sky Survey (SDSS) imaging data and then observed spectroscopically using the 2dF instrument on the Anglo-Australian Telescope. We analyse 10 637 QSOs in the redshift range to a g-band flux limit of 21.85 (extinction-corrected) and an absolute continuum magnitude of . This sample covers an area of 191.9 deg2. The binned QSO LF agrees with that of the brighter SDSS main QSO sample, but extends mag fainter, clearly showing the flattening of the LF towards faint absolute magnitudes. 2SLAQ finds an excess of QSOs compared to the 2dF QSO Redshift Survey at , as found previously by Richards et al. The LF is consistent with other previous, much smaller, samples produced to the depth of 2SLAQ. By combining the 2SLAQ and SDSS QSO samples, we produce a QSO LF with an unprecedented combination of precision and dynamic range. With this we are able to accurately constrain both the bright and faint ends of the QSO LF. While the overall trends seen in the evolution of the QSO LF appear similar to pure luminosity evolution, the data show very significant departures from such a model. Most notably we see clear evidence that the number density of faint QSOs peaks at lower redshift than bright QSOs: QSOs with have space densities which peak at , while QSOs at peak at . By fitting simple LF models in narrow intervals, we find that this downsizing is significant at the 99.98 per cent level. We show that LF models which follow the pure luminosity evolution form [i.e. ], but with a redshift-dependent bright-end slope and an additional density evolution term, , provide a much improved fit to the data. The bright-end slope, α, steepens from at to at . This steepening is significant at the 99.9 per cent level. We find a decline in from to 2.5 which is significant at the 94 per cent level. [ABSTRACT FROM AUTHOR]

We present the final spectroscopic QSO catalogue from the 2dF-SDSS LRG (luminous red galaxy) and QSO (2SLAQ) survey. This is a deep, (extinction corrected), sample aimed at probing in detail the faint end of the broad line active galactic nuclei luminosity distribution at . The candidate QSOs were selected from SDSS photometry and observed spectroscopically with the 2dF spectrograph on the Anglo-Australian Telescope. This sample covers an area of 191.9 deg2 and contains new spectra of 16 326 objects, of which 8764 are QSOs and 7623 are newly discovered [the remainder were previously identified by the 2dF QSO Redshift Survey (2QZ) and SDSS]. The full QSO sample (including objects previously observed in the SDSS and 2QZ surveys) contains 12 702 QSOs. The new 2SLAQ spectroscopic data set also contains 2343 Galactic stars, including 362 white dwarfs, and 2924 narrow emission-line galaxies with a median redshift of . We present detailed completeness estimates for the survey, based on modelling of QSO colours, including host-galaxy contributions. This calculation shows that at QSO colours are significantly affected by the presence of a host galaxy up to redshift in the SDSS ugriz bands. In particular, we see a significant reddening of the objects in towards the fainter g-band magnitudes. This reddening is consistent with the QSO host galaxies being dominated by a stellar population of age at least 2–3 Gyr. The full catalogue, including completeness estimates, is available on-line at . [ABSTRACT FROM AUTHOR]

We have used the Two-Degree Field (2dF) instrument on the Anglo-Australian Telescope (AAT) to obtain redshifts of a sample of and quasars selected from Sloan Digital Sky Survey (SDSS) imaging. These data are part of a larger joint programme between the SDSS and 2dF communities to obtain spectra of faint quasars and luminous red galaxies, namely the 2dF–SDSS LRG and QSO (2SLAQ) Survey. We describe the quasar selection algorithm and present the resulting number counts and luminosity function of 5645 quasars in 105.7 deg2. The bright-end number counts and luminosity functions agree well with determinations from the 2dF QSO Redshift Survey (2QZ) data to. However, at the faint end, the 2SLAQ number counts and luminosity functions are steeper (i.e. require more faint quasars) than the final 2QZ results from Croom et al., but are consistent with the preliminary 2QZ results from Boyle et al. Using the functional form adopted for the 2QZ analysis (a double power law with pure luminosity evolution characterized by a second-order polynomial in redshift), we find a faint-end slope of if we allow all of the parameters to vary, and if we allow only the faint-end slope and normalization to vary (holding all other parameters equal to the final 2QZ values). Over the magnitude range covered by the 2SLAQ survey, our maximum-likelihood fit to the data yields 32 per cent more quasars than the final 2QZ parametrization, but is not inconsistent with other deep surveys for quasars. The 2SLAQ data exhibit no well-defined‘break’ in the number counts or luminosity function, but do clearly flatten with increasing magnitude. Finally, we find that the shape of the quasar luminosity function derived from 2SLAQ is in good agreement with that derived from Type I quasars found in hard X-ray surveys. [ABSTRACT FROM AUTHOR]