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Register a new userSuperclusters of galaxies from the 2dF redshift survey. II. Comparison with simulations
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We investigate properties of superclusters of galaxies found on the basis of the 2dF Galaxy Redshift Survey, and compare them with properties of superclusters from the Millennium Simulation. We study the dependence of various characteristics of superclusters on their distance from the observer, on their total luminosity, and on their multiplicity. The multiplicity is defined by the number of Density Field (DF) clusters in superclusters. Using the multiplicity we divide superclusters into four richness classes: poor, medium, rich and extremely rich. We show that superclusters are asymmetrical and have multi-branching filamentary structure, with the degree of asymmetry and filamentarity being higher for the more luminous and richer superclusters. The comparison of real superclusters with Millennium superclusters shows that most properties of simulated superclusters agree very well with real data, the main differences being in the luminosity and multiplicity distributions.
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We use the 2dF Galaxy Redshift Survey data to compile catalogues of superclusters for the Northern and Southern regions of the 2dFGRS, altogether 543 superclusters at redshifts 0.009 < z < 0.2. We analyse methods of compiling supercluster catalogues and use results of the Millennium Simulation to investigate possible selection effects and errors. We find that the most effective method is the density field method using smoothing with an Epanechnikov kernel of radius 8 Mpc/h. We derive positions of the highest luminosity density peaks and find the most luminous cluster in the vicinity of the peak, this cluster is considered as the main cluster and its brightest galaxy the main galaxy of the supercluster. In catalogues we give equatorial coordinates and distances of superclusters as determined by positions of their main clusters. We also calculate the expected total luminosities of the superclusters.
UGC 8584 was selected by a computer program as having a number of quasars around it that obeyed the Karlsson periodicity in its reference frame. On closer examination 9 of the nearest 10 quasars turned out to be extremely close to the predicted values. Also it turned out that UGC 8584 was a disturbed triple galaxy and a strong triple radio source as well as being a strong millimeter and infrared source. Evidence for present ejection velocities of $z_v sim .01$ for the associated quasars is present and some pairing of ejections is noted. A new and important result emerges from this sample of galaxy/quasar families, namely that rings and shells of galaxies and quasars tend to surround galaxies which have active nuclei. Test cases suggest obscuration of the background around these galaxies out to about 20 or beyond. Because incidents of strong reddening are not observed, obscuring particles are suggested to be large compared to optical wavelengths. In principle, material ejected with the quasars could be of sizes of gravel or larger.
We present a clustering analysis of QSOs over the redshift range z=0.3-2.9. We use a sample of 10558 QSOs taken from the preliminary catalogue of the 2dF QSO Redshift Survey (2QZ). The two-point redshift-space correlation function of QSOs is shown to follow a power law on scales s~1-35h-1Mpc. Fitting a power law to QSO clustering averaged over the redshift interval 0.3<z<2.9 we find s_0=3.99+0.28-0.34h-1Mpc and gamma=1.58+0.10-0.09 for an Einstein-de Sitter cosmology (EdS). With Omega_0=0.3 and lambda_0=0.7 the power law extends to s~60h-1Mpc with a best fit of s_0=5.69+0.42-0.50h-1Mpc and gamma=1.56+0.10-0.09. These values, measured at a mean redshift of z=1.49, are comparable to the clustering of local optically selected galaxies. We measure the evolution of QSO clustering as a function of redshift. For an EdS cosmology there is no evolution in comoving coordinates over the redshift range of the 2QZ. For Omega_0=0.3 and lambda_0=0.7 QSO clustering shows a marginal increase at high redshift. Although the clustering of QSOs is measured on large scales where linear theory should apply, the evolution of QSO clustering does not follow the linear theory predictions for growth via gravitational instability (rejected at the >99 per cent confidence level). A redshift dependent bias is required to reconcile QSO clustering observations with theory. A simple biasing model, in which QSOs have cosmologically long lifetimes (or alternatively form in peaks above a constant threshold in the density field) is acceptable in an EdS cosmology, but is only marginally acceptable if Omega_0=0.3 and lambda_0=0.7. Biasing models which assume QSOs form over a range in redshift, based on the Press-Schechter formalism are approximately consistent with QSO clustering evolution (abridged).
The clustering properties of local, S_{1.4 GHz} > 1 mJy, radio sources are investigated for a sample of 820 objects drawn from the joint use of the FIRST and 2dF Galaxy Redshift surveys. To this aim, we present 271 new bj < 19.45 spectroscopic counterparts of FIRST radio sources to be added to those already introduced in Magliocchetti et al. (2002). The two-point correlation function for the local radio population is found to be entirely consistent with estimates obtained for the whole sample of 2dFGRS galaxies. We estimate the parameters of the real-space correlation function xi(r)=(r/r_0)^{-gamma}, r_0=6.7^{+0.9}_{-1.1} Mpc and gamma=1.6pm 0.1, where h=0.7 is assumed. Different results are instead obtained if we only consider sources that present signatures of AGN activity in their spectra. These objects are shown to be very strongly correlated, with r_0=10.9^{+1.0}_{-1.2} Mpc and gamma=2pm 0.1, a steeper slope than has been claimed in other recent works. No difference is found in the clustering properties of radio-AGNs of different radio luminosity. These results show that AGN-fuelled sources reside in dark matter halos more massive than sim 10^{13.4} M_{sun}},higher the corresponding figure for radio-quiet QSOs. This value can be converted into a minimum black hole mass associated with radio-loud, AGN-fuelled objects of M_{BH}^{min}sim 10^9 M_{sun}. The above results then suggest -at least for relatively faint radio objects -the existence of a threshold black hole mass associated with the onset of significant radio activity such as that of radio-loud AGNs; however, once the activity is triggered, there appears to be no evidence for a connection between black hole mass and level of radio output. (abridged)
The 2dF Galaxy Redshift Survey (2dFGRS) has produced a three-dimensional map of the distribution of 221,000 galaxies covering 5% of the sky and reaching out to a redshift z=0.3. This is first map of the large-scale structure in the local Universe to probe a statistically representative volume, and provides direct evidence that the large-scale structure of the Universe grew through gravitational instability. Measurements of the correlation function and power spectrum of the galaxy distribution have provided precise measurements of the mean mass density of the Universe and the relative contributions of cold dark matter, baryons, and neutrinos. The survey has produced the first measurements of the galaxy bias parameter and its variation with galaxy luminosity and type. Joint analysis of the 2dFGRS and cosmic microwave background power spectra gives independent new estimates for the Hubble constant and the vacuum energy density, and constrains the equation of state of the vacuum.
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