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Register a new userDiscovery of Two Galaxies Deeply Embedded in the Great Attractor Wall
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We report on the discovery of two spiral galaxies located behind the southern Milky Way, within the least explored region of the Great Attractor. They lie at 317, -0.5 deg galactic, where obscuration from Milky Way stars and dust exceeds 13 to 15 mag of visual extinction. The galaxies were the most prominent of a set identified using mid-infrared images of the low-latitude (|b| < 1 deg) Spitzer Legacy program GLIMPSE. Follow-up HI radio observations reveal that both galaxies have redshifts that place them squarely in the Norma Wall of galaxies, which appears to extend diagonally across the Galactic Plane from Norma in the south to Centaurus & Vela in the north. We report on the near-infrared, mid-infrared and radio properties of these newly discovered galaxies, and discuss their context in the larger view of the Great Attractor. The work presented here demonstrates that mid-infrared surveys open up a new window to study galaxies in the Zone of Avoidance.
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Dust and stars in the plane of the Milky Way create a Zone of Avoidance in the extragalactic sky. Galaxies are distributed in gigantic labyrinth formations, filaments and great walls with occasional dense clusters. They can be traced all over the sky, except where the dust within our own galaxy becomes too thick - leaving about 25% of the extragalactic sky unaccounted for. Our Galaxy is a natural barrier which constrains the studies of large-scale structures in the Universe, the peculiar motion of our Local Group of galaxies and other streaming motions (cosmic flows) which are important for understanding formation processes in the Early Universe and for cosmological models. Only in recent years have astronomers developed the techniques to peer through the disk and uncover the galaxy distribution in the Zone of Avoidance. I present the various observational multi-wavelength procedures (optical, far infrared, near infrared, radio and X-ray) that are currently being pursued to map the galaxy distribution behind our Milky Way. Particular emphasis is given to discoveries in the Great Attractor region -- a from streaming motions predicted huge overdensity centered behind the Galactic Plane. The recently unveiled massive rich cluster A3627 seems to constitute the previously unidentified core of the Great Attractor.
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.
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.
We present the results of the study of the substructure and galaxy content of ten rich clusters of galaxies in three different superclusters of the Sloan Great Wall. We determine the substructure in clusters using the Mclust package from the R statistical environment and analyse their galaxy content. We analyse the distribution of the peculiar velocities of galaxies in clusters and calculate the peculiar velocity of the first ranked galaxy. We show that clusters in our sample have more than one component; in some clusters different components also have different galaxy content. We find that in some clusters with substructure the peculiar velocities of the first ranked galaxies are large. All clusters in our sample host luminous red galaxies. They can be found both in the central areas of clusters as well as in the outskirts, some of them have large peculiar velocities. About 1/3 of red galaxies in clusters are spirals. The scatter of colours of red ellipticals is in most clusters larger than that of red spirals. The presence of substructure in rich clusters, signs of possible mergers and infall, as well as the large peculiar velocities of the first ranked galaxies suggest that the clusters in our sample are not yet virialized. We present merger trees of dark matter haloes in an N-body simulation to demonstrate the formation of present-day dark matter haloes via multiple mergers during their evolution. In simulated dark matter haloes we find a substructure similar to that in observed clusters.
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