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arXiv · 1805.03206

The spectral and environment properties of $z\sim2.0-2.5$ quasar pairs

Elisabeta Lusso·Michele Fumagalli·Marc Rafelski·Marcel Neeleman·Jason X. Prochaska·Joseph F. Hennawi·John M. O'Meara·Tom Theuns
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Abstract

We present the first results from our survey of intervening and proximate Lyman limit systems (LLSs) at $z$$\sim$2.0-2.5 using the Wide Field Camera 3 on-board the Hubble Space Telescope. The quasars in our sample are projected pairs with proper transverse separations $R_\perp$$\leq$150 kpc and line of sight velocity separations $\lesssim$11,000 km/s. We construct a stacked ultraviolet (rest-frame wavelengths 700-2000Å) spectrum of pairs corrected for the intervening Lyman forest and Lyman continuum absorption. The observed spectral composite presents a moderate flux excess for the most prominent broad emission lines, a $\sim$30% decrease in flux at $λ$=800-900Å compared to a stack of brighter quasars not in pairs at similar redshifts, and lower values of the mean free path of the HI ionizing radiation for pairs ($λ_{\rm mfp}^{912}=140.7\pm20.2~h_{70}^{-1}$Mpc) compared to single quasars ($λ_{\rm mfp}^{912}=213.8\pm28~h_{70}^{-1}$Mpc) at the average redshift $z\simeq2.44$. From the modelling of LLS absorption in these pairs, we find a higher ($\sim$20%) incidence of proximate LLSs with $\log N_{\rm HI}\geq17.2$ at $δv$$<$5,000 km/s compared to single quasars ($\sim$6%). These two rates are different at the 5$σ$ level. Moreover, we find that optically-thick absorbers are equally shared between foreground and background quasars. Based on these pieces of evidence, we conclude that there is a moderate excess of gas absorbing Lyman continuum photons in our closely-projected quasar pairs compared to single quasars. We argue that this gas arises mostly within large-scale structures or partially neutral regions inside the dark matter haloes where these close pairs reside.

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Elisabeta Lusso, Michele Fumagalli, Marc Rafelski, Marcel Neeleman, Jason X. Prochaska, Joseph F. Hennawi, John M. O'Meara, Tom Theuns. 2018-06-06. The spectral and environment properties of $z\sim2.0-2.5$ quasar pairs. https://doi.org/10.3847/1538-4357%2Faac514

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