Perseus Pisces Research Articles

Density distribution of matter on 75-Mpc scales derived by the POTENT method from the bulk motions of RFGC galaxies

The data on the peculiar velocities of 1493 RFGC flat spiral galaxies processed using the POTENT method allowed the density distribution of matter, including dark matter, on 75-Mpc scales to be reconstructed. Well-known attractors (the Great Attractor, the Perseus—Pisces and Coma superclusters) and voids are separated from the distribution. In general, the density distribution is close to that of IRAS galaxies, suggesting that the luminous-to-dark matter density ratio is constant. The masses of the main attractors were estimated.

Kinematics of the local universe

The matter distribution around the Perseus-Pisces (PP) supercluster is studied by comparing peculiar velocities given by the Kinematics of the local universe (KLUN) galaxy sample to those predicted by Tolman-Bondi (TB) models. To restrict the TB solutions we first solve the mass of the densest part of PP. This part is identified as a sphere at , Mpc having a radius of Mpc. This sphere surrounds the main part of the PP ridge and four most prominent clusters of the region. Using virial-like mass estimators we calculate the cluster masses and obtain the upper and lower limits for the mass inside the Mpc sphere: -. This corresponds to a mass overdensity , or -. Mass to light ratios of the clusters are 200 -600 , giving mass density ratio -0.3, if the value of is assumed to be representative elsewhere in the universe. We estimate a radial density distribution around the PP core using two toy models and a smoothed density distribution observed for IRAS galaxies. The cosmological density parameters and the PP mass are free parameters in the TB calculations. The KLUN velocities, obtained by Tully-Fisher relation and the normalized distance method, are adjusted by the Local Group (LG) infall velocity towards PP. Comparison of the TB velocities to KLUN data points indicates that the infall velocity km s-1. Allowing MPP to vary within the limits given above we get constraints for the value of ; -0.4 are prefered to the more extreme values, or 1. A choice of either or 0 do not cause any significant changes in the results. The validity of the TB model in complex environments is studied with an N-body simulation. There we see that the radially averaged velocity fields around simulated clusters are compatible with the corresponding TB velocities. This confirms the applicability of the TB model around large galaxy concentrations, providing that smoothed density and radially averaged velocity fields are used.

Loose groups of galaxies in the Perseus–Pisces survey

We present a large catalog 1 of loose groups of galaxies in the Southern Galactic Hemisphere, selected from the Perseus{Pisces redshift Survey (PPS). Particular care is taken in order to obtain group samples as ho- mogeneous as possible to previously published catalogs. All our catalogs contain about 200 groups, signicantly more than in most previous studies where group samples were obtained from galaxy data sets of comparable qual- ity to (but smaller extent than) PPS. Groups are iden- tied with the adaptive Friends{Of{Friends (FOF) algo- rithm of Huchra & Geller (1982), with suitable normal- izations D0 =0 :231 h 1 Mpc and V0 = 350 km s 1 at cz0 = 1000 km s 1 . The luminosity function (LF) normal- ization =0 :02 h 3 Mpc 3 appropriate for PPS yields a number density threshold n=n 180 for the adopted D0, instead of n=n 80 used in previous studies of other samples. However, the customary choice of D0 obtained (through the LF) from a xed mass overdensity= = 80, well motivated in theory, suers from important observa- tional uncertainties and sample{to{sample variations of the LF normalization, and from major uncertainties in the relation between galaxy densityn and mass density .W e discuss how to self{consistently match FOF parameters among dierent galaxy samples. We then separately vary several FOF and sample parameters, and discuss their ef- fect on group properties. Loose groups in PPS nicely trace the large scale structure (LSS) in the parent galaxy sam- ple. The group properties vary little with dierent redshift corrections, redshift cut{o, and galaxy LF, but are rather sensitive to the adopted links D0 and V0. More precisely, the typical group size (velocity dispersion) is linearly re-

On the Cosmic Rotation Axis

Recently, Nodland and Ralston reported to have discovered a cosmic axis. We argue that their axis is supported by an earlier independent observation on the spin axes of galaxies in the Perseus–Pisces supercluster and explainable within the framework of Gödel's cosmology.

Galaxy clusters in the Perseus-Pisces region -- II. The peculiar velocity 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)

Are the Perseus--Pisces chain and the Pavo--Indus wall connected?

A significant empty region was found between the southern Pavo- Indus (PI) wall and the northern Perseus-Pisces (PP) chain. This survey tests the reality of this void which may simply reflect previous poor sampling of the galaxies in this region. Redshifts for a magnitude selected sample of 379 galaxies were obtained covering the four UKST/SERC survey fields with Bt <= 17.0. All redshifts were obtained with the FLAIR multi-object spectroscopy system on the 1.2 m U.K. Schmidt Telescope at Siding Spring, Australia. Two highly significant density enhancements were found in the galaxy distribution at 133 Mpc and 200 Mpc (Ho=75 km/s/Mpc). We claim that no connexion exists between PP and PI. However, a southern extension of PP was detected and makes the total length of this chain of more than 150 Mpc.

Spiral Galaxies and the Peculiar Velocity Field

We report results of a redshift-independent distance measurement survey that extends to all sky and out to a redshift of approximately 7500 km s−1. Tully–Fisher (TF) distances for a homogeneous sample of 1600 late spiral galaxies are used to analyze the peculiar velocity field. We find large peculiar velocities in the neighborhood of superclusters, such as Perseus–Pisces (PP) and Hydra–Centaurus, but the main clusters embedded in those regions appear to be virtually at rest in the CMB reference frame. We find no compelling evidence for large-scale bulk flows, whereby the Local Group, Hydra–Cen and PP would share a motion of several hundred km s−1with respect to the CMB. Denser sampling in the PP region allows a clear detection of infall and backflow motions, which can be used to map the mass distribution in the supercluster and to obtain an estimate of the cosmological density parameter.

Correlation Functions from the Perseus-Pisces Redshift Survey

The three- and four-point correlation functions are evaluated from the Perseus Pisces galaxy redshift sample. Former results on the two-point function ξ are also reviewed. In the range of distances from 1 h -1 Mpc to 10 h -1 Mpc, three- and four-point functions do not agree with the expressions of the hierarchical clustering model. On the contrary they are steeper and can be fitted by adding terms with a higher power of ξ. Such results from a redshift catalog partially modifies the picture of the large-scale matter distribution obtained from early two-dimensional samples. The relation among these results, biased models of galaxy formation, and observed velocity fields is discussed

Optical galaxies within 8000 km s-1 -I. The density field

The density field of optical galaxies to a depth of 8000 km s–1 over 67 per cent of the sky is determined using the UGC and ESO catalogues. The reconstruction method compensates for the varying completeness of the redshift data and for the galaxies that are not selected in the catalogues. The optical density field is dominated by supercluster complexes with dimensions in excess of 6000 km s–1. The most prominent of these are Perseus–Pisces and Centaurus–Hydra–Virgo–Pavo. The same complexes are seen in maps of IRAS galaxies, but the contrast of the optical maps is higher by a factor of 1.35 ± 0.16 when measured in 2500 km s–1 cells. By comparing the overdensity of galaxies in the Virgo supercluster to Virgo infall and assuming that mass follows light, we obtain |$\Omega =0.20_{-0.15}^{+0.30}$| . The ‘Great Attractor Region’ covered by Dressler's Supergalactic Plane Survey is overdense to 6000 km s–1, well beyond the Cen 30 cluster. However, unless there is a massive supercluster hidden in the zone of avoidance, this region is not sufficiently overdense for it to be identified with the Great Attractor inferred from |${D}_{n} - \sigma$| and Tully–Fisher peculiar velocities. Furthermore, within the Centaurus–Hydra–Virgo–Pavo complex, the density field peaks close to the Cen 30 cluster, which suggests that large-scale streaming motions may be better described by a weak 200 ± 150 km s–1 infall centred near Cen 30, plus a bulk dipole motion of 400 ± 150 km s–1 in the CMB frame.

TULLY-FISHER DISTANCES AND MOTIONS IN THE NORTHERN SKY

ABSTRACT This dissertation consists of a study of large-scale velocity deviations in a uniformly expanding universe. At the onset of this work, galaxy motions in the northern hemisphere, contrary to the impressive sky coverage in the south, were still very poorly mapped. To improve on this situation, we identified a well-defined sample of 380 northern Sb-Sc UGC spirals with a magnitude cutoff of mB=15.5. Distances are estimated using the Tully-Fisher relation but with rotation velocities measured from long-slit spectra in lieu of 21 cm delta-V's. Surface-brightness profiles and total magnitudes are extracted for 820 r-band images, and (H-alpha +[N II]) rotation curves, fluxes, and rotation profiles are measured from 450 red spectra. The galaxy magnitudes are accurate internally to ±0.022 mag and the delta-V's agree internally to ± 12 km s-1. A tight linear correlation of optical versus radio velocity widths with a scatter of 24 km s-1 is also derived. The redshift distribution peaks at 5400 km s-1, with a tail extending out to 15,000 km s-1. We find evidence for large-scale motions near the concentration of Perseus-Pisces (PP), but identify a vast region of unperturbed, quiet Hubble flow (QHF) perpendicular to PP. The peculiar velocity (PV) data are corrected for uniform-density Malmquist bias when they are analyzed in estimated distance space; an empirical correction for selection effects mainly due to magnitude cutoff is derived from the QHF region and applied to the PV's in redshift space. Both analyses are consistent in showing the PP supercluster as streaming in bulk towards the Local Group at 392 ± 79 km s-1 (with respect to the microwave background rest frame). The cause for such motion remains undetermined, but it is most certainly not due to one single object. Gravitational collapse within PP is detected, but the statistical error is large. While we have not calculated a formal bulk motion for the whole volume of space bounded by the Great Attractor and PP, it appears, from simple considerations, that a reasonable streaming solution will have a net amplitude of 450 ± 100 km s-1 in the general direction of l=310 degrees, b=+20 degrees. We show that the Rubin-Ford effect (using Schechter's non-diameter-corrected solution) is perfectly consistent with our estimated rough bulk streaming. However, comparison of our measured PV's with radial-velocity reconstructions using IRAS galaxies shows conflicting results at PP which remain, at present, unresolved. An emerging picture of large-scale velocity fields shows the main infall regions to be correlated with the observed clumpiness of luminous matter. This provides support in favor of models based on the gravitational instability picture. Our data, combined with published PV surveys, provide strong support for the existence of low-amplitude perturbations in the universe on scales not yet probed by current samples (> 120 h-1 Mpc). The implications of cosmic bulk motions with such large coherence lengths pose a serious challenge for models of generation of structure in the universe.

Evading the zone of avoidance

Evading the zone of avoidance