The distribution of neutral hydrogen around high-redshift galaxies and quasars in the EAGLE simulation

Abstract

The observed high covering fractions of neutral hydrogen (Hi) with column densities above ∼ 10 17 cm −2 around Lyman-Break Galaxies (LBGs) and bright quasars at redshifts z ∼ 2 − 3 has been identified as a challenge for simulations of galaxy formation. We use the EAGLE cosmological, hydrodynamical simulation, which has been shown to reproduce a wide range of galaxy properties and for which the subgrid feedback was calibrated without considering gas properties, to study the distribution of Hi around high-redshift galaxies. We predict the covering fractions of strong Hi absorbers (N HI 10 17 cm −2 ) inside haloes to increase rapidly with redshift but to depend only weakly on halo mass. For massive (M 200 10 12 M ⊙ ) halos the covering fraction profiles are nearly scale-invariant and we provide fitting functions that reproduce the simulation results. While efficient feedback is required to increase the Hi covering fractions to the high observed values, the distribution of strong absorbers in and around halos of a fixed mass is insensitive to factor of two variations in the strength of the stellar feedback. In contrast, at fixed stellar mass the predicted Hi distribution is highly sensitive to the feedback efficiency. The fiducial EAGLE simulation reproduces both the observed global column density distribution function of Hi and the observed radial covering fraction profiles of strong Hi absorbers around LBGs and bright quasars.

Cosmic distribution of highly ionized metals and their physical conditions in the EAGLE simulations

“…This is consistent with what we found to be the case for Hi absorbers at z ∼ 2 in (Rahmati et al 2015). The physical properties of the absorbers, on the other hand, are insensitive to whether HM01 or HM12 is used, as shown in Thin red and thick blue curves show the CDDFs at z = 0.1 and z = 3 respectively.…”

“…The same simulation also shows very good agreement with a large number of other observed galaxy properties which were not considered in the calibration (S15; Crain et al 2015;Furlong et al 2015;Schaller et al 2014;Trayford et al 2015;Rahmati et al 2015). , has a periodic box of L = 100 comoving Mpc (cMpc) and contains 1504 3 dark matter particles with mass 9.7 × 10 6 M⊙ and initially an equal number of baryonic particles with mass 1.81×10 6 M⊙.…”

“…As we showed in Rahmati et al (2015), EAGLE successfully reproduces both the observed global column density distribution function of Hi and the observed radial covering fraction profiles of strong Hi absorbers around Lyman Break galaxies and bright quasars. This shows that the EA-GLE reference model which is calibrated based on present day stellar content of galaxies is also capable of reproducing the observed cosmic distribution of gas and its connection with galaxies.…”

“…We note that our fiducial UVB model is consistent with constraints on the photoionization rate of the background radiation at different redshifts (e.g., ? ), and has been used to successfully reproduce Hi CDDF and its evolution (e.g., Rahmati et al 2013aRahmati et al , 2015, the connection between strong Hi absorbers and galaxies , as well as relative strengths of different high ionization metal ions (e.g., Aguirre et al 2008). However, the constraints on properties of the UVB are also consistent with other UVB models such as the models proposed by HM12 and Faucher-Giguère et al (2008) which predict different UVB radiation fields compared to HM01.…”

Gas around galaxy haloes - III: hydrogen absorption signatures around galaxies and QSOs in the Sherwood simulation suite

“…The wind model shows excess absorption over the non-wind model within the virial radii for the most massive haloes, but the amount still falls short of the measured values. The central two data points are more dominated by haloes with z ≃ 2.0 (Rahmati et al 2015). The values for δF in the simulation at z = 2.0 agree within the errors with those at z = 2.4 or are somewhat smaller.…”