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Register a new userThe Motions of Clusters of Galaxies and the Dipoles of the Peculiar Velocity Field
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Riccardo Giovanelli
Publication date
1998
fields
Physics
and research's language is
English
Authors
R. Giovanelli
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In preceding papers of this series, TF relations for galaxies in 24 clusters with radial velocities between 1000 and 9200 km/s (SCI sample) were obtained, a Tully-Fisher (TF) template relation was constructed and mean offsets of each cluster with respect to the template obtained. Here, an estimate of the line-of-sight peculiar velocities of the clusters and their associated errors are given. It is found that cluster peculiar velocities in the Cosmic Microwave Background reference frame do not exceed 600 k/ms and that their distribution has a line-of-sight dispersion of 300 k/ms, suggesting a more quiescent cluster peculiar velocity field than previously reported. When measured in a reference frame in which the Local Group is at rest, the set of clusters at cz > 3000 km/s exhibits a dipole moment in agreement with that of the CMB, both in amplitude and apex direction. It is estimated that the bulk flow of a sphere of 6000 km/s radius in the CMB reference frame is between 140 and 320 km/s. These results are in agreement with those obtained from an independent sample of field galaxies (Giovanelli et al. 1998; see astro-ph/9807274)
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The Tully-Fisher (Tully and Fisher 1977; TF) relation is applied to obtain peculiar velocities of field spirals galaxies and to calculate dipoles of the peculiar velocity field to cz ~ 8000 km/s. The field galaxy sample is spatially co-extensive with and completely independent on a cluster sample, for which dipole characteristics are given in a separate paper. Dipoles of the peculiar velocity field are obtained separately by applying (i) an inverse version of the TF relation and selecting galaxies by redshift windowing and (ii) a direct TF relation, with velocities corrected for the inhomogeneous Malmquist bias, and windowing galaxies by TF distance. The two determinations agree, as they do with the cluster sample. When measured in a reference frame in which the Local Group is at rest, the dipole moment of field galaxies farther than ~4000 km/s is in substantial agreement, both in amplitude and direction, with that exhibited by the Cosmic Microwave Background radiation field.
We analyze in detail the peculiar velocity field traced by 56 clusters within 120 h^-1 Mpc in the Streaming Motions of Abell Clusters (SMAC) sample. The bulk flow of the SMAC sample is 687 +- 203 km/s, toward l = 260 +- 13, b = 0 +- 11. We discuss possible systematic errors and show that no systematic effect is larger than half of the random error. The flow does not drop off significantly with depth, which suggests that it is generated by structures on large scales. In particular, a Great Attractor as originally proposed by Lynden-Bell et al. cannot be responsible for the SMAC bulk flow. The SMAC data suggest infall into an attractor at the location of the Shapley Concentration, but the detection is marginal (at the 90% confidence level). We find that distant attractors in addition to the Shapley Concentration are required to explain the SMAC bulk flow. A comparison with peculiar velocities predicted from the IRAS PSCz redshift survey shows good agreement with a best fit value of Beta_I = Omega^0.6/b_I = 0.39 +- 0.17. However, the PSCz density field is not sufficient to acount for all of the SMAC bulk motion. We also detect, at the 98% confidence level, a residual bulk flow of 372 +- 127 km/s toward l = 273, b = 6 which must be generated by sources not included in the PSCz catalogue, that is, either beyond 200 h^-1 Mpc, in the Zone of Avoidance or in superclusters undersampled by IRAS. Finally, we compare the SMAC bulk flow with other recent measurements. We suggest that a bulk flow of 225 km/s toward l = 300, b = 10 at depths greater than 60 h^-1 Mpc is consistent with all peculiar velocity surveys, when allowance is made for sparse sampling effects. (abridged)
We present results of a new study of peculiar motions of 7 clusters in the Perseus-Pisces (PP) region, using the Fundamental Plane as a distance indicator. The sample is calibrated by reference to 9 additional clusters with data from the literature. Careful attention is paid to the matching of spectroscopic and photometric data from several sources. For six clusters in the PP supercluster no significant peculiar motions are detected. For these clusters we derive a bulk motion of 60 +/- 220 km/s, in the CMB frame, directed towards the Local Group. This non-detection is in marginal conflict with previous Tully-Fisher studies. Two clusters in the background of the supercluster exhibit significant negative peculiar velocities, characteristic of backside infall into PP. A bulk-flow fit to all 16 clusters reveals a statistically insignificant motion of 430 +/- 280 km/s towards l=265, b=26 (CMB frame). Comparison with the velocity field predicted from the IRAS 1.2Jy survey yields beta = 1.0 +/- 0.5. We find no evidence for residual bulk motions generated by mass concentrations beyond the limiting depth of the IRAS density field.
We have measured the mean peculiar motions of 103 early-type galaxies in 7 clusters in the Perseus-Pisces (PP) ridge or PP background, and a further 249 such galaxies in 9 calibrating clusters from the literature, using the inverse Fundamental Plane relation. This relation is found to have a distance error of 20% per galaxy. None of the 6 clusters in the PP ridge has a significant motion with respect to the CMB frame, but the PP background cluster J8 shows marginal evidence of `backside infall into the PP supercluster. The full 16 cluster sample has a mean CMB-frame bulk motion of 420 +/- 280 km/s, towards l=262, b=-25. This result is consistent both with no bulk motion in the CMB frame and with the ~350 km/s bulk motion found by Courteau et al. It is inconsistent at the 98% confidence level with the ~700 km/s bulk flow found by Lauer & Postman (LP). The PP ridge clusters are found to have a small and statistically insignificant mean radial motion with respect to the CMB frame: -60 +/- 220 km/s. A comparison between our cluster peculiar velocities and the predicted peculiar velocities from the IRAS 1.2 Jy density field, smoothed on a 500 km/s scale, yields beta_I = Omega^0.6/b_I = 0.95 +/- 0.48, consistent with previous results. We find agreement between our peculiar motions and published Tully-Fisher results for the same clusters. The disagreement between the 11 clusters common to our sample and that of LP, based on BCGs, is statistically significant at the >~ 99.7% confidence level indicating that the errors of one or both of these data sets are underestimated. When the BCG distances corrected for the X-ray luminosity of the host cluster are used, the disagreement is reduced to the ~94% confidence level. (Abridged)
We have made measurements of the Sunyaev-Zeldovich (SZ) effect in six galaxy clusters at z > 0.2 using the Sunyaev-Zeldovich Infrared Experiment (SuZIE II) in three frequency bands between 150 and 350 GHz. Simultaneous multi-frequency measurements have been used to distinguish between thermal and kinematic components of the SZ effect, and to significantly reduce the effects of variations in atmospheric emission which can otherwise dominate the noise. We have set limits to the peculiar velocities of each cluster with respect to the Hubble flow, and have used the cluster sample to set a 95% confidence limit of < 1410 km/s to the bulk flow of the intermediate-redshift universe in the direction of the CMB dipole. This is the first time that SZ measurements have been used to constrain bulk flows. We show that systematic uncertainties in peculiar velocity determinations from the SZ effect are likely to be dominated by submillimeter point sources and we discuss the level of this contamination.
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