Constraining the cosmic UV background at z>3 with MUSE Lyman-α emission observations

Abstract

The intensity of the Cosmic UV background (UVB), coming from all sources of ionising photons such as star-forming galaxies and quasars, determines the thermal evolution and ionization state of the intergalactic medium (IGM) and is, therefore, a critical ingredient for models of cosmic structure formation. Most of the previous estimates are based on the comparison between observed and simulated Lyman-$\alpha$ forest. We present the results of an independent method to constrain the product of the UVB photoionisation rate and the covering fraction of Lyman limit systems (LLSs) by searching for the fluorescent Lyman-$\alpha$ emission produced by self-shielded clouds. Because the expected surface brightness is well below current sensitivity limits for direct imaging, we developed a new method based on three-dimensional stacking of the IGM around Lyman-$\alpha$ emitting galaxies (LAEs) between 2.9<z<6.6 using deep MUSE observations. Combining our results with covering fractions of LLSs obtained from mock cubes extracted from the EAGLE simulation, we obtain new and independent constraints on the UVB at z>3 that are consistent with previous measurements, with a preference for relatively low UVB intensities at z=3, and which suggest a non-monotonic decrease of $\Gamma$HI with increasing redshift between 3<z<5. This could suggest a possible tension between some UVB models and current observations which however require deeper and wider observations in Lyman-$\alpha$ emission and absorption to be confirmed. Assuming instead a value of UVB from current models, our results constrain the covering fraction of LLSs at 3<z<4.5 to be less than 25% within 150kpc from LAEs.

19 pages, 17 figures, accepted on MNRAS

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• (Re)Solving Reionization with Lyα: How Bright Lyα Emitters account for the $z\approx 2-8$ Cosmic Ionizing Background
• MUSE Analysis of Gas around Galaxies (MAGG) -- IV: The gaseous environment of $z\sim$ 3-4 Lyman-alpha emitting galaxies
• Inferring the Thermal History of the Intergalactic Medium from the Properties of the Hydrogen and Helium Lyman-alpha Forest
• Surface Brightness Profile of Lyman-$\alpha$ Halos out to 320 kpc in HETDEX
• The space density of ultra-luminous QSOs at the end of reionization epoch by the QUBRICS Survey and the AGN contribution to the hydrogen ionizing background
• Median Surface Brightness Profiles of Lyman-$\alpha$ Haloes in the MUSE Extremely Deep Field
• Probing the Diffuse Lyman-alpha Emission on Cosmological Scales: Lyα Emission Intensity Mapping Using the Complete SDSS-IV eBOSS Survey
• Revealing the Nature of a Lyman-$\alpha$ Halo in a Strongly Lensed Interacting System at $z=2.92$
• Eddington accreting Black Holes in the Epoch of Reionization
• Spatially-resolved Spectroscopic Analysis of Ly$\alpha$ Haloes: Radial Evolution of the Ly$\alpha$ Line Profile out to 60 kpc
• Probing Large Scale Ionizing Background Fluctuation with Lyman $\alpha$ Forest and Galaxy Cross-correlation at z=2.4
• Probing the cosmic web in Ly$\alpha$ emission over large scales: an Intensity Mapping forecast for DECaLS/BASS and DESI