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تسجيل مستخدم جديدLarge-scale clustering of Lyman-alpha emission intensity from SDSS/BOSS
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(Abridged) We detect the large-scale structure of Lya emission in the Universe at redshifts z=2-3.5 by measuring the cross-correlation of Lya surface brightness with quasars in SDSS/BOSS. We use a million spectra targeting Luminous Red Galaxies at z<0.8, after subtracting a best fit model galaxy spectrum from each one, as an estimate of the high-redshift Lya surface brightness. The quasar-Lya emission cross-correlation we detect has a shape consistent with a LambdaCDM model with Omega_M =0.30^+0.10-0.07. The predicted amplitude of this cross-correlation is proportional to the product of the mean Lya surface brightness, <mu_alpha>, the amplitude of mass fluctuations, and the quasar and Lya emission bias factors. Using known values, we infer <mu_alpha>(b_alpha/3) = (3.9 +/- 0.9) x 10^-21 erg/s cm^-2 A^-1 arcsec^-2, where b_alpha is the Lya emission bias factor. If the dominant sources of Lya emission are star forming galaxies, we infer rho_SFR = (0.28 +/- 0.07) (3/b_alpha) /yr/Mpc^3 at z=2-3.5. For b_alpha=3, this value is a factor of 21-35 above previous estimates from individually detected Lya emitters, although consistent with the total rho_SFR derived from dust-corrected, continuum UV surveys. 97% of the Lya emission in the Universe at these redshifts is therefore undetected in previous surveys of Lya emitters. Our measurement is much greater than seen from stacking analyses of faint halos surrounding previously detected Lya emitters, but we speculate that it arises from similar Lya halos surrounding all luminous star-forming galaxies. We also detect redshift space anisotropy of the quasar-Lya emission cross-correlation, finding evidence at the 3.0 sigma level that it is radially elongated, consistent with distortions caused by radiative-transfer effects (Zheng et al. (2011)). Our measurements represent the first application of the intensity mapping technique to optical observations.
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We investigate the large-scale structure of Lyman-alpha emission intensity in the Universe at redshifts z=2-3.5 using cross-correlation techniques. Our Lya emission samples are spectra of BOSS Luminous Red Galaxies from Data Release 12 with the best
fit model galaxies subtracted. We cross-correlate the residual flux in these spectra with BOSS quasars, and detect a positive signal on scales 1-15 Mpc/h. We identify and remove a source of contamination not previously accounted for, due to the effects of quasar clustering on cross-fibre light. Corrected, our quasar-Lya emission cross-correlation is 50 % lower than that seen by Croft et al. for DR10, but still significant. Because only 3% of space is within 15 Mpc/h of a quasar, the result does not fully explore the global large-scale structure of Lya emission. To do this, we cross-correlate with the Lya forest. We find no signal in this case. The 95% upper limit on the global Lya mean surface brightness from Lya emission-Lya forest cross-correlation is mu < 1.2x10^-22 erg/s/cm^2/A/arcsec^2 This null result rules out the scenario where the observed quasar-Lya emission cross-correlation is primarily due to the large scale structure of star forming galaxies, Taken in combination, our results suggest that Lya emitting galaxies contribute, but quasars dominate within 15 Mpc/h. A simple model for Lya emission from quasars based on hydrodynamic simulations reproduces both the observed forest-Lya emission and quasar-Lya emission signals. The latter is also consistent with extrapolation of observations of fluorescent emission from smaller scales r < 1 Mpc.
General relativistic effects have long been predicted to subtly influence the observed large-scale structure of the universe. The current generation of galaxy redshift surveys have reached a size where detection of such effects is becoming feasible.
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