ar X iv : a st ro - p h / 05 01 52 1 v 1 2 4 Ja n 20 05 XMM - Newton Observations of High Redshift Quasars

We report on our XMM observations of the high redshift quasars BR 2237–0607 (z=4.558) and BR 0351–1034 (z=4.351), together with 14 other z> 4 objects found in the XMM public archive. Contrary to former reports, we do not find high redshift radio-loud quasars to be more absorbed than their radio-quiet counterparts. We find that the optical to X-ray spectral index αox is correlated with the luminosity density at 2500Å, but does not show a correlation with redshift. The mean 2-10 keV power-law slope of the 9 high redshift radio-quiet quasars in our sample for which a spectral analysis can be performed is αX=1.23±0.48, similar to αX=1.19 found from the ASCA observations of low redshift Narrow-Line Seyfert 1 galaxies (NLS1s), and significantly different from αX=0.78 found for low redshift Broad-Line Seyfert galaxies. While the optical/UV spectra of low to high redshift quasars look remarkably similar, we find a first indication of a difference in their X-ray spectrum. The steep X-ray spectral index suggests high Eddington ratios L/LEdd. These observations give credence to the hypothesis of Mathur (2000) that NLS1s are low luminosity cousins of high redshift quasars, both likely to be in their early evolutionary stage. Subject headings: galaxies: active quasars:general quasars: individual (BR 2237–0607, BR0351–1034)