Limits on non-canonical heating and turbulence in the intergalactic medium from the low redshift Lyman α forest

ABSTRACT We examine the column density distribution function (CDDF) and Doppler parameter from hydrodynamical simulations Cosmic Origins Spectrograph (COS) observations of Ly α forest at redshift 0 ≤ z 0.2. Allowing for a factor two uncertainty in metagalactic H $\, \rm \scriptstyle I \, $ photoionization rate, our are good agreement (1–1.5σ) with shape amplitude observed CDDF densities $10^{13.3}\rm cm^{-2}\le N_{\rm H\,{\small I}}\le 10^{14.5}\rm cm^{-2}$. However, widths simulated lines remain too narrow respect to COS data. argue that invoking AGN feedback does not resolve this discrepancy. also disfavour enhanced photoheating rates as potential solution, requires an unphysically hard UV background spectrum. If instead appealing non-canonical source heating, additional specific heat injection $u \lesssim 6.9\rm eV\, m_{\rm p}^{-1}$ is required ≲ 2.5 gas has $N_{\rm I}}\simeq 10^{13.5}\rm cm^{-2}$ by = 0.1. Alternatively, there may be unresolved line sight turbulent velocity component $v_{\rm turb}\lesssim 8.5\rm km\, s^{-1}(N_{\rm I}}/10^{13.5}\rm cm^{-2})^{0.21}$ coldest diffuse IGM.