UVES Investigates the Environment of a Very Remote Galaxy

Surplus of Intergalactic Material May Be Young Supercluster

Observations with ESO`s Very Large Telescope (VLT) have enabled an international group of astronomers to study in unprecedented detail the surroundings of a very remote galaxy, almost 12 billion light-years distant. The corresponding light travel time means that it is seen at a moment only about 3 billion years after the Big Bang.

This galaxy is designated MS 1512-cB58 and is the brightest known at such a large distance and such an early time. This is due to a lucky circumstance: a massive cluster of galaxies (MS 1512+36) is located about halfway along the line-of-sight, at a distance of about 7 billion light-years, and acts as a gravitational “magnifying glass”. Thanks to this lensing effect, the image of MS1512-cB58 appears 50 times brighter.

Nevertheless, the apparent brightness is still as faint as magnitude 20.6 (i.e., nearly 1 million times fainter than what can be perceived with the unaided eye). Moreover, MS 1512-cB58 is located 36deg north of the celestial equator and never rises more than 29deg above the horizon at Paranal. It was therefore a great challenge to secure the present observational data with the UVES high-dispersion spectrograph on the 8.2-m VLT KUEYEN telescope.

The extremely detailed UVES-spectrum of MS 1512-cB58 displays numerous signatures (absorption lines) of intergalactic gas clouds along the line-of-sight. Some of the clouds are quite close to the galaxy and the astronomers have therefore been able to investigate the distribution of matter in its immediate surroundings.

They found an excess of material near MS 1512-cB58, possible evidence of a young supercluster of galaxies, already at this very early epoch. The new observations thus provide an invaluable contribution to current studies of the birth and evolution of structures in the early Universe.

This is the first time this kind of observation has ever been done of a galaxy at such a large distance. All previous studies were based on much more luminous quasars (QSOs – extremely active galaxy nuclei). However, any investigation of the intergalactic matter around a quasar is complicated by the strong radiation and consequently, high ionization of the gas by the QSO itself, rendering an unbiased assessment of the gas distribution impossible.

The full text of this ESO Press Release, with three photos and all weblinks, is available at: www.eso.org/outreach/press-rel/pr-2002/pr-03-02.html