We measure the large-scale cross-correlation of quasars with the Ly \alpha forest absorption in redshift space , using \sim 60000 quasar spectra from Data Release 9 ( DR9 ) of the Baryon Oscillation Spectroscopic Survey ( BOSS ) .
The cross-correlation is detected over a wide range of scales , up to comoving separations r of 80 h ^ { -1 } { Mpc } .
For r > 15 h ^ { -1 } { Mpc } , we show that the cross-correlation is well fitted by the linear theory prediction for the mean overdensity around a quasar host halo in the standard \Lambda CDM model , with the redshift distortions indicative of gravitational evolution detected at high confidence .
Using previous determinations of the Ly \alpha forest bias factor obtained from the Ly \alpha autocorrelation , we infer the quasar bias factor to be b _ { q } = 3.64 ^ { +0.13 } _ { -0.15 } at a mean redshift z = 2.38 , in agreement with previous measurements from the quasar auto-correlation .
We also obtain a new estimate of the Ly \alpha forest redshift distortion factor , \beta _ { F } = 1.1 \pm 0.15 , slightly larger than but consistent with the previous measurement from the Ly \alpha forest autocorrelation .
The simple linear model we use fails at separations r < 15 h ^ { -1 } { Mpc } , and we show that this may reasonably be due to the enhanced ionization due to radiation from the quasars .
We also provide the expected correction that the mass overdensity around the quasar implies for measurements of the ionizing radiation background from the line-of-sight proximity effect .