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Register a new userAn HI Survey of the Great Attractor Region
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Lister Staveley-Smith
Publication date
2000
fields
Physics
and research's language is
English
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A blind HI survey using the Parkes telescope at |b|<5 deg, 300 deg < l < 332 deg has so far revealed 305 galaxies, most of which were previously unknown. These galaxies are used to map out the distribution of filaments and voids out to 10000 km/s. A preliminary measurement of the galaxy overdensity suggests only a moderate overdensity is present, and that the excess mass (above the background density) is ~2.10^{15}.Omega.M(sun). This is below the mass predicted in POTENT reconstructions of the local velocity field, and implies that the `Great Attractor (GA) is not as massive as these reconstructions indicate, or does not lie hidden in the region investigated.
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ATCA 21 cm HI observations of the rich galaxy cluster ACO 3627 in the Great Attractor region are presented. Three fields of 30 diameter located within one Abell radius of ACO 3627 were observed with a resolution of 15 and an rms noise of sim 1 mJy/beam. Only two galaxies were detected in these fields. We compare their HI distribution to new optical R-band images and discuss their velocity fields. The first galaxy is a gas-rich unperturbed spiral whereas the second shows a peculiar HI distribution. The estimated 3-sigma HI mass limit of our observations is sim 7 x 10^8 M_{odot} for a line width of 150 km s^{-1}. The non-detection of a considerable number of luminous spiral galaxies indicates that the spiral galaxies are HI deficient. The low detection rate is comparable to the HI deficient Coma cluster (Bravo-Alfaro et al. 2000). ACO 3627 is a bright X-ray cluster. We therefore suspect that ram pressure stripping is responsible for the HI deficiency of the bright cluster spirals.
A deep optical galaxy search behind the southern Milky Way and a subsequent redshift survey of the identified obscured galaxies traces clusters and superclusters into the deepest layers of Galactic foreground extinction (A_B <= 3^m - 5^m). In the Great Attractor region, we have identified a low-mass cluster (the Centaurus-Crux cluster) at (l, b, v, sigma) = (305.5deg, +5.5deg, 6214 km/s, 472 km/s) and found that ACO 3627 (the Norma cluster) at (l, b, v, sigma) = (325.3deg, -7.2deg, 4844 km/s, 848 km/s) is the most massive cluster in the Great Attractor region known to date. It is comparable in virial mass, richness and size to the well-known but more distant Coma cluster. The Norma cluster most likely marks the bottom of the potential well of the Great Attractor. It is located at the intersection of two main large-scale structures, the Centaurus Wall and the Norma supercluster. The flow field observed around the Great Attractor probably is caused by the confluence of these two massive structures.
This paper presents the analysis of a deep near-infrared J,H,Ks-imaging survey (37.5 sq deg) aimed at tracing the galaxy distribution of the Great Attractor (GA) in the Zone of Avoidance along the so-called Norma Wall. The resulting galaxy catalog is complete to extinction-corrected magnitudes Ks^o = 14.8 mag for extinctions less than A_K = 1.0 mag and star densities below log N(Ks<14.0) < 4.72. Of the 4360 cataloged galaxies, 99.2% lie in the hereby constrained 89.5% of the survey area. Although the analyzed galaxy distribution reveals no new major galaxy clusters at the GA distance (albeit some more distant ones), the overall number counts and luminosity density indicate a clear and surprisingly smooth overdensity at the GA distance that extends over the whole surveyed region. A mass estimate of the Norma Wall overdensity derived from (a) galaxy number counts and (b) photometric redshift distribution gives a lower value compared to the original prediction by Lynden-Bell et al. 1988 (~14%), but is consistent with more recent independent assessments.
We compare the measured peculiar velocities of 98 local (<150/h Mpc) type Ia supernovae (SNIa) with predictions derived from the PSCz. There is excellent agreement between the two datasets with a best fit beta_I (=Omega_m^0.6/b_I) of 0.55+-0.06. Subsets of the SNIa dataset are further analysed and the above result is found to be robust with respect to culls by distance, host-galaxy extinction and to the reference frame in which the analysis is carried out. We briefly review the peculiar motions in the direction of the Great Attractor. Most clusters in this part of the sky out to a distance of 14,000 km/s, i.e. those closer than the Shapley Concentration, have sizable positive peculiar velocities, i.e. (~ +400 km/s). There are nine local SNIa in the GA direction that are in the foreground of Shapley. All these SNIa have positive peculiar velocities. Hence both the cluster and local SNIa data strongly support the idea of a sizable flow into Shapley.
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