How young galaxies can grow gently

Galaxies often collide and then merge to form larger systems.

Washington: Galaxies often collide and then merge to form larger systems and this process is certainly an important growth mechanism. However, an additional way has been proposed so that they grow in a gentler manner.

A European team of astronomers has used ESO``s Very Large Telescope to test that young galaxies can also grow by sucking in cool streams of the hydrogen and helium gas that filled the early Universe and forming new stars from this primitive material.

Young galaxies could perhaps also grow in two different ways — by merging with other galaxies or by accreting material.

"The new results from the VLT are the first direct evidence that the accretion of pristine gas really happened and was enough to fuel vigorous star formation and the growth of massive galaxies in the young Universe," said team leader, Giovanni Cresci (Osservatorio Astrofisico di Arcetri).

The selected galaxies were very regular, smoothly rotating discs, similar to the Milky Way, and they were seen about two billion years after the Big Bang.

When Cresci``s team mapped their selected distant galaxies, they saw that in all three cases there was a patch of the galaxy, close to the centre, with fewer heavy elements, but hosting vigorously forming stars, suggesting that the material to fuel the star formation was coming from the surrounding pristine gas that is low in heavy elements.

"This study has only been possible because of the outstanding performance of the SINFONI instrument on the VLT. It has opened a new window for studying the chemical properties of very distant galaxies. SINFONI provides information not only in two spatial dimensions, but also in a third, spectral dimension, which allows us to see the internal motions inside galaxies and study the chemical composition of the interstellar gas,” Cresci concluded.


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