Large-scale clustering of Lyman alpha emission intensity from SDSS/BOSS

International audienceWe present a tentative detection of the large-scale structure of Ly alpha emission in the Universe at redshifts z = 2-3.5 by measuring the cross-correlation of Ly alpha surface brightness with quasars in Sloan Digital Sky Survey/Baryon Oscillation Spectroscopic Survey. We use amillion spectra targeting luminous red galaxies at z \textless 0.8, after subtracting a best-fitting model galaxy spectrum from each one, as an estimate of the high-redshift Ly alpha surface brightness. The quasar-Ly alpha emission cross-correlation is detected on scales 1 similar to 15 h(-1) Mpc, with shape consistent with a Lambda CDM model with Omega(m) = 0.30(-0.07)(+0.10). The predicted amplitude of this cross-correlation is proportional to the product of the mean Ly alpha surface brightness, \textlessmu(alpha)\textgreater, the amplitude of mass fluctuations and the quasar and Ly alpha emission bias factors. We infer \textlessmu(alpha)\textgreater (b(alpha)/3) = (3.9 +/- 0.9) x 10(-21) erg s(-1) cm(-2) angstrom(-1) arcsec(-2), where b(alpha) is the Ly alpha emission bias. If star-forming galaxies dominate this emission, we find rho(SFR) = (0.28 +/- 0.07)(3/b(alpha)) yr(-1) Mpc(-3). For b(alpha) = 3, this value is similar to 30 times larger than previous estimates from individually detected Ly alpha emitters, but consistent with the total rho(SFR) derived from dust-corrected, continuum UV galaxy surveys, if most of the Ly alpha photons from these galaxies avoid dust absorption and are reemitted after diffusing in large gas haloes. Heating of intergalactic gas by He II photoionization from quasar radiation or jets may alternatively explain the detected correlation, and cooling radiation from gas in galactic haloes may also contribute. We also detect redshift space anisotropy of the quasar-Ly alpha emission cross-correlation, finding evidence at the 3.0 sigma level that it is radially elongated, which may be explained by radiative-transfer effects. Our measurements represent the first application of the intensity mapping technique to optical observations