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ESO 13/08 - Associated Images

13 May 2008
For Immediate Release

A Molecular Thermometer for the Distant Universe

First accurate measurement of the temperature of the cosmic background at an early epoch

Well-hidden galaxies can be discovered through the imprint their interstellar gas leave on the spectrum of an even more remote quasar. Interstellar clouds of gas in galaxies, located between the quasars and us on the same line of sight, absorb parts of the light emitted by the quasars. The resulting spectrum consequently presents dark 'valleys' that can be attributed to well-known elements and possibly molecules. In this schematic representation, the VLT observes (D) the features associated with three systems, located at different distances (A, B, and C), and whose light is therefore shifted by different amounts. The quasar, which acts as a beacon, is the bright object at the left of the image.

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Spectrum of a very distant quasar on which the footprints from a galaxy located almost 11 billion light-years away are seen. Various bands of carbon monoxide (CO), as well as bands of normal and deuterated molecular hydrogen (H₂, HD) were identified by the astronomers. The different intensities of the CO bands allow the astronomers to infer the temperature of the Cosmic Background Radiation at this very remote epoch. The spectrum was obtained with UVES on ESO's VLT. It is the result of more than 8 hours of observations.

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