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F. J. Carrera X. Barcons A. C. Fabian G. Hasinger K. O. Mason R. G. McMahon J. P. D. Mittaz & M. J. Page 《Monthly notices of the Royal Astronomical Society》1998,299(1):229-236
A total of 235 active galactic nuclei (AGN) from two different soft X-ray surveys [the ROSAT Deep Survey (DRS) and the ROSAT International X-ray Optical Survey (RIXOS)] with redshifts between 0 and 3.5 are used to study the clustering of X-ray selected AGN and its evolution. A 2σ significant detection of clustering of such objects is found on scales < 40–80 h −1 Mpc in the RIXOS sample, while no clustering is detected on any scales in the DRS sample. Assuming a single power-law model for the spatial correlation function (SCF), quantitative limits on the AGN clustering have been obtained: a comoving correlation length 1.5 ≲ r 0 ≲ 3.3 h −1 Mpc is implied for comoving evolution, while 1.9 ≲ r 0 ≲ 4.8 for stable clustering and 2.2 ≲ r 0 ≲ 5.5 for linear evolution. These values are consistent with the correlation lengths and evolutions obtained for galaxy samples, but imply smaller amplitude or faster evolution than recent ultraviolet and optically selected AGN samples. We also constrain the ratio of bias parameters between X-ray selected AGN and IRAS galaxies to be ≲ 1.7 on scales ≲ 10 h −1 Mpc, a somewhat smaller value than is inferred from local large-scale dynamical studies. 相似文献
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M. J. Page J. P. D. Mittaz F. J. Carrera 《Monthly notices of the Royal Astronomical Society》2000,318(4):1073-1085
We present a catalogue of 147 serendipitous X-ray sources selected to have hard spectra ( α <0.5) from a survey of 188 ROSAT fields. Such sources must be the dominant contributors to the X-ray background at faint fluxes. We have used Monte Carlo simulations to verify that our technique is very efficient at selecting hard sources: the survey has 10 times as much effective area for hard sources as it has for soft sources above a 0.5–2 keV flux level of 10−14 erg cm−2 s−1 . The distribution of best-fitting spectral slopes of the hard sources suggests that a typical ROSAT hard source in our survey has a spectral slope α ∼0. The hard sources have a steep number flux relation (d N /d S ∝ S − γ with a best-fitting value of γ =2.72±0.12) and make up about 15 per cent of all 0.5–2 keV sources with S >10−14 erg cm−2 s−1 . If their N ( S ) continues to fainter fluxes, the hard sources will comprise ∼40 per cent of sources with 5×10−15 < S <10−14 erg cm−2 s−1 . The population of hard sources can therefore account for the harder average spectra of ROSAT sources with S <10−14 erg cm−2 s−1 . They probably make a strong contribution to the X-ray background at faint fluxes and could be the solution to the X-ray background spectral paradox. 相似文献
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K. O. Mason F. J. Carrera G. Hasinger H. Andernach A. Aragon-Salamanca X. Barcons R. Bower W. N. Brandt G. Branduardi-Raymont J. Burgos-Martín F. Cabrera-Guerra R. Carballo F. Castander R. S. Ellis J. I. González-Serrano E. Martínez-González J. M. Martín-Mirones R. G. McMahon J. P. D. Mittaz K. L. Nicholson M. J. Page I. Pérez-Fournon E. M. Puchnarewicz E. Romero-Colmenero A. D. Schwope B. Vila M. G. Watson D. Wonnacott 《Monthly notices of the Royal Astronomical Society》2000,311(3):456-484