Probing the Diffuse Lyman-alpha Emission on Cosmological Scales: Lyα Emission Intensity Mapping Using the Complete SDSS-IV eBOSS Survey

Abstract

Based on the Sloan Digital Sky Survey Data Release 16, we have detected the large-scale structure of Ly$\alpha$ emission in the Universe at redshifts $z=2$--3.5 by cross-correlating quasar positions and Ly$\alpha$ emission imprinted in the residual spectra of luminous red galaxies. We apply an analytical model to fit the corresponding Ly$\alpha$ surface brightness profile and multipoles of the redshift-space quasar-Ly$\alpha$ emission cross-correlation function. The model suggests an average cosmic Ly$\alpha$ luminosity density of $6.6_{-3.1}^{+3.3}\times 10^{40}\mathrm{erg}{\mathrm{s}}^{-1}\mathrm{cMp}{\mathrm{c}}^{-3}$, a $\sim 2\sigma$ detection with a median value about 8--9 times those estimated from deep narrowband surveys of Ly$\alpha$ emitters at similar redshifts. Although the low signal-to-noise ratio prevents us from a significant detection of the Ly$\alpha$ forest-Ly$\alpha$ emission cross-correlation, the measurement is consistent with the prediction of our best-fit model from quasar-Ly$\alpha$ emission cross-correlation within current uncertainties. We rule out the scenario that these Ly$\alpha$ photons mainly originate from quasars. We find that Ly$\alpha$ emission from star-forming galaxies, including contributions from that concentrated around the galaxy centers and that in the diffuse Ly$\alpha$ emitting halos, is able to explain the bulk of the the Ly$\alpha$ luminosity density inferred from our measurements. Ongoing and future surveys can further improve the measurements and advance our understanding of the cosmic Ly$\alpha$ emission field.

Accepted for Publication in ApJS; 21 pages, 15 figures, 2 tables

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