We investigate the prospects of extending observations of high redshift QSOs from the current z \sim 7 to z > 8 by means of a very wide-area near-infrared slitless spectroscopic survey , considering as an example the planned survey with the European Space Agency ’ s Euclid telescope ( scheduled for a 2019 launch ) .
For any QSOs at z > 8.06 the strong Lyman- \alpha line will enter the wavelength range of the Euclid near-infrared spectrometer and imaging photometer ( NISP ) .
We perform a detailed simulation of Euclid -NISP slitless spectroscopy ( with the parameters of the wide survey ) in an artificial field containing QSO spectra at all redshifts up to z = 12 and to a faint limit H = 22.5 .
QSO spectra are represented with a template based on an SDSS composite spectrum , with the added effects of absorption from neutral hydrogen in the intergalactic medium .

The spectra extracted from the simulation are analysed with an automated redshift finder , and a detection rate estimated as a function of H magnitude and redshift ( defined as the proportion of spectra with both correct redshift measurements and classifications ) .
We show that , as expected , spectroscopic identification of QSOs would reach deeper limits for the redshift ranges where either H \alpha ( 0.67 < z < 2.05 ) or Lyman- \alpha ( z > 8.06 ) is visible .
Furthermore , if photometrically-selected z > 8 spectra can be re-examined and re-fitted to minimize the effects of spectral contamination , the QSO detection rate in the Lyman- \alpha window will be increased by an estimated \sim 60 \% and will then be better here than at any other redshift , with an effective limit H \simeq 21.5 .

With an extrapolated rate of QSO evolution , we predict the Euclid wide ( 15000 deg ^ { 2 } ) spectroscopic survey will identify and measure spectroscopic redshifts for a total of 20–35 QSOs at z > 8.06 ( reduced slightly to 19–33 if we apply a small correction for missed weak-lined QSOs ) .
However , for a model with a faster rate of evolution , this prediction goes down to 4 or 5 .
In any event , the survey will give important constraints on the evolution of QSO at z > 8 and therefore the formation of the first super-massive black holes .
The z > 8.06 detections would be very luminous objects ( with M _ { B } = -26 to -28 ) and many would also be detectable by the proposed Wide Field X-ray Telescope .