Observations of quasars

Gaia will provide astrometric and photometric observations for about 500,000 quasars (QSOs) to G = 20 mag over the whole sky, 5 times more than the number expected from the Sloan Digital Sky Survey. In the process Gaia will create the first all-sky survey of optically selected Active Galactic Nuclei (AGN) and QSOs.

AGN and QSOs are of prime importance in establishing the relativistic reference frame for the Gaia mission. In addition, the resulting QSO sample will have a profound impact on studies of the large scale structure of the Universe. Gaia also offers the prospect of constraining the value of cosmological parameters from their small angular scale lensing structure.

In Gaia's medium band photometry (MBP) filters, QSO emission lines make strong signatures at specific redshifts. These can be clearly seen in the colour-colour diagram above which shows star and QSO loci (G = 18 mag), where the signatures of the CIII], CIV and Ly-alpha emission lines are visible in the distribution of the blue, green and red objects respectively.

For more information see the Information Sheet on Observations of Quasars.

Image courtesy of Jean-François Claeskens & Alain Smette.

[Published: 13/10/2003]