Friday, July 8, 2011

The Most Distant Galaxy Super Cluster

Galaxies are usually found as members of clusters. Rich clusters can have thousands of members and poor clusters may have only dozens of galaxies. The clustering of galaxies is an important constraint on cosmological models and the degree of clustering in the Universe today is related to the anisotropies in the matter distribution of the early universe. Margaret Geller and colleagues at Princeton University have mapped a portion of the Universe and attempts are currently being made to characterize the degree of galaxy-clustering using correlation functions.

The Most Distant Galaxy Cluster

What are the largest "gravitationally" bound objects in the universe? That would be galaxy super clusters. We live in the outskirts of the nearest one, the Virgo Super cluster, even though it's centered 55 million light years away. Look farther and the universe is riddled with them, connected by streamers and walls of galaxies like an endless cobwebby foam. These streamers and walls are the largest structures of any kind that exist.
The wider you look beyond that, the cosmic foam simply becomes more uniform. By contrast, the universe was extremely smooth and "structureless" when it emerged from the Big Bang.

Clumping began with small pieces having the masses of dwarf galaxies or less. These clumps gathered to form galaxies of increasingly large size. When did galaxies themselves start clustering? Well, nobody know, but a group led by Peter Capak (Caltech) has just pushed back the envelope. Using deep exposures at many wavelengths, Capak and his colleagues found a group of gravitationally bound mini-galaxies at redshift 5.3, when the universe was only 1.1 billion years old.
The previous record-holding early clusters were between redshifts 4 and 5. The cluster, named COSMOS-AzTEC3, has about 12 galaxies bright enough to be detectable. All are much smaller than our Milky Way, like other early galaxies,and are bursting with star formation. One already harbors a black hole with an estimated 30 million solar masses.

It's likely that since the era in which we see them, these galaxies have fallen together and merged to form a single galaxy much like our own. Meanwhile, other astronomers announced a galaxy likely to be at a redshift of 10.3, corresponding to 500 million years after the Big Bang. This is the highest redshift yet found.

The circled red smudges, in the constellation Sextans, are members of a cluster of young mini-galaxies seen in the early universe 1.1 billion years after the Big Bang. Since then they have probably fallen together to form a large galaxy like our Milky Way.

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