Quasar composite made from bright QSOs

However, combinations of various QSO samples obtained at different times and with different instruments so as to expand a composite and to cover a wider rest frame wavelength region may create systematic effects, and the contribution from QSO hosts may contaminate the composite.

We have constructed a composite spectrum from luminous blue QSOs at 1<z<2.1 selected from the Sloan Digital Sky Survey (SDSS). The observations with X-shooter simultaneously cover ultraviolet (UV) to near-infrared (NIR) light, which ensures that the composite spectrum covers the full rest-frame range from Ly{beta} to 11350{AA} without any significant host contamination. Assuming a power-law continuum for the composite we find a spectral slope of {alpha}{lambda}=1.70+/-0.01, which is steeper than previously found in the literature.