tokens: The standard approach has been to compare measurements of different statistics to cosmological hydrodynamical simulations (Zaldarriaga et al. 2001 ; Theuns et al. 2002b ; Viel et al. 2009 ; Lidz et al. 2010 ; Becker et al. 2011 ; Garzilli et al. 2012 ; Rorai et al. 2013 , 2017a , 2017b ; Iršič Viel 2014 ) to deduce the thermal parameters (e.g., T 0 , γ or ) that best describe the IGM thermal state. As a larger number of high-resolution spectra of quasars have become available at higher redshifts , the same approach has been applied to study the thermal state of the IGM at these redshifts, where the Ly α forest is more sensitive to the timing and nature of hydrogen reionization (Theuns et al. 2002b ; Hui Haiman 2003 ; Cen et al. 2009 ; Furlanetto Oh 2009 ; Becker et al. 2011 ; Viel et al. 2013a ; Lidz Malloy 2014 ; Garzilli et al. 2015 ; Nasir et al. 2016 ). In the light of the new Planck constraints on reionization, as well as the increasing number of quasars discovered at high- z (e.g., Bañados et al. 2014 , 2016 ; Matsuoka et al. 2016 ), it is pertinent to revisit what Ly α observations with current and upcoming facilities can tell us about reionization. This work aims to explore in detail the possibilities of using the Ly α forest 1D flux power spectrum at high- z to constrain H i reionization. For this we have used a new method that has recently been introduced by Oñorbe et al. ( 2017 ). It builds on the Haardt Madau ( 2012 ) model, but enables one to vary the redshifts of and reionization, as well as their associated heat injection, allowing one to consistently simulate a more diverse range of reionization histories. This allows for a much comprehensive and consistent exploration of the space of thermal parameters than previously done. We present here the results of the 1D flux power spectrum at high- z of a new set of hydrodynamical simulations that also improve the resolution used in previous studies at these redshifts. Additionally, we compare these power spectra with some recent measurements at these redshifts (Viel et al. 2013a ). The structure of this paper is as follows. In Section 2 we describe the characteristics of our hydrodynamical simulations and the different reionization models studied in this work. Section 3 presents the thermal evolution of the different reionization models obtained from the cosmological hydrodynamical simulations. In Section 4 we compare the 1D flux power spectrum of each model at as well as with the best available observations. We discuss in Section 5 the relevance of our findings in the context of current observational and theoretical limitations. We conclude by presenting a summary of our results and an outlook in Section 6 . In the Appendix we perform a set of convergence test for the optical depth and the 1D flux power spectrum at . Throughout this paper we assumed a flat ΛCDM cosmology with the following fundamental parameters: , , , h = 0.67038, , and . These values agree within 1 σ with the
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