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981.
The 2dF Galaxy Redshift Survey: the bias of galaxies and the density of the Universe 总被引:1,自引:0,他引:1
Licia Verde Alan F. Heavens Will J. Percival Sabino Matarrese Carlton M. Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Matthew Colless Chris Collins Warrick Couch Gavin Dalton Roberto De Propris Simon P. Driver George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Steve Maddox Darren Madgwick Peder Norberg John A. Peacock Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2002,335(2):432-440
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Antonio Chrysostomou Rachel Curran David Aitken Tim Jenness Chris Davis 《Astrophysics and Space Science》2003,287(1-4):161-164
We report on early results of magnetic field measurements towards a sample of young stellar objects. The results show a variety of field configurations, some of which can be explained by conventional models, while others cannot. We find that the field in some cases is curved over large scales and influenced by the gas kinematics in the local environment. This implies that, at these scales at least, the magnetic field plays a passive rôle in the star formation process. 相似文献
984.
Roberto De Propris Warrick J. Couch Matthew Colless Gavin B. Dalton Chris Collins Carlton M. Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Nicholas Cross Kathryn Deeley Simon P. Driver George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Steve Maddox Darren Madgwick Stephen Moody Peder Norberg John A. Peacock Will Percival Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2002,329(1):87-101
We have carried out a study of known clusters within the 2dF Galaxy Redshift Survey (2dFGRS) observed areas and have identified 431 Abell, 173 APM and 343 EDCC clusters. Precise redshifts, velocity dispersions and new centroids have been measured for the majority of these objects, and this information is used to study the completeness of these catalogues, the level of contamination from foreground and background structures along the cluster's line of sight, the space density of the clusters as a function of redshift, and their velocity dispersion distributions. We find that the Abell and EDCC catalogues are contaminated at the level of about 10 per cent, whereas the APM catalogue suffers only 5 per cent contamination. If we use the original catalogue centroids, the level of contamination rises to approximately 15 per cent for the Abell and EDCC catalogues, showing that the presence of foreground and background groups may alter the richness of clusters in these catalogues. There is a deficiency of clusters at that may correspond to a large underdensity in the Southern hemisphere. From the cumulative distribution of velocity dispersions for these clusters, we derive a space density of clusters of This result is used to constrain models for structure formation; our data favour low-density cosmologies, subject to the usual assumptions concerning the shape and normalization of the power spectrum. 相似文献
985.
We present deep near-infrared images, taken with the Subaru Telescope, of the region around the z =1.08 radio source 3C 356 which show it to be associated with a poor cluster of galaxies. We discuss evidence that this cluster comprises two subclusters traced by the two galaxies previously proposed as identifications for 3C 356, which both seem to harbour active galactic nuclei, and which have the disturbed morphologies expected if they underwent an interpenetrating collision at the time the radio jets were triggered. We explain the high luminosity and temperature of the diffuse X-ray emission from this system as the result of shock heating of intracluster gas by the merger of two galaxy groups. Taken together with the results on other well-studied powerful radio sources, we suggest that the key ingredient for triggering a powerful radio source, at least at epochs corresponding to z ∼1 , is a galaxy–galaxy interaction which can be orchestrated by the merger of their parent subclusters. This provides an explanation for the rapid decline in the number density of powerful radio sources since z ∼1 . We argue that attempts to use distant radio-selected clusters to trace the formation and evolution of the general cluster population must address ways in which X-ray properties can be influenced by the radio source, both directly, by mechanisms such as inverse Compton scattering, and indirectly, by the fact that the radio source may be preferentially triggered at a specific time during the formation of the cluster. 相似文献
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Is the soft excess in active galactic nuclei real? 总被引:1,自引:0,他引:1
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990.