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arXiv · 1808.05605

The Power Spectrum of the Lyman-$α$ Forest at z < 0.5

Vikram Khaire·Michael Walther·Joseph F. Hennawi·Jose Oñorbe·Zarija Lukić·J. Xavier Prochaska·Todd M. Tripp·Joseph N. Burchett·Christian Rodriguez
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Abstract

We present new measurements of the flux power-spectrum P(k) of the $z<0.5$ HI Lyman-$α$ forest spanning scales k ~ 0.001-0.1 s/km. These results were derived from 65 far ultraviolet quasar spectra (resolution R~18000) observed with the Cosmic Origin Spectrograph (COS) on board the Hubble Space Telescope. The analysis required careful masking of all contaminating, coincident absorption from HI and metal-line transitions of the Galactic interstellar medium and intervening absorbers as well as proper treatment of the complex COS line-spread function. From the P(k) measurements, we estimate the HI photoionization rate ($Γ_{\rm HI}$) in the z<0.5 intergalactic medium. Our results confirm most of the previous $Γ_{\rm HI}$ estimates. We conclude that previous concerns of a photon underproduction crisis are now resolved by demonstrating that the measured $Γ_{\rm HI}$ can be accounted for by ultraviolet emission from quasars alone. In a companion paper, we will present constraints on the thermal state of the $z<0.5$ intergalactic medium from the P(k) measurements presented here.

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Vikram Khaire, Michael Walther, Joseph F. Hennawi, Jose Oñorbe, Zarija Lukić, J. Xavier Prochaska, Todd M. Tripp, Joseph N. Burchett, Christian Rodriguez. 2019-04-09. The Power Spectrum of the Lyman-$α$ Forest at z < 0.5. https://doi.org/10.1093/mnras%2Fstz344

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