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

Abstract

Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. ABSTRACTWe study the distribution and evolution of highly ionised intergalactic metals in the Evolution and Assembly of Galaxies and their Environment (EAGLE) cosmological, hydrodynamical simulations. EAGLE has been shown to reproduce a wide range of galaxy properties while its subgrid feedback was calibrated without considering gas properties. We compare the predictions for the column density distribution functions (CDDFs) and cosmic densities of Siiv, Civ, Nv, Ovi and Neviii absorbers with observations at redshift z = 0 to ∼ 6 and find reasonable agreement, although there are some differences. We show that the typical physical densities of the absorbing gas increase with column density and redshift, but decrease with the ionization energy of the absorbing ion. The typical metallicity increases with both column density and time. The fraction of collisionally ionized metal absorbers increases with time and ionization energy. While our results show little sensitivity to the presence or absence of AGN feedback, increasing/decreasing the efficiency of stellar feedback by a factor of two substantially decreases/increases the CDDFs and the cosmic densities of the metal ions. We show that the impact of the efficiency of stellar feedback on the CDDFs and cosmic densities is largely due to its effect on the metal production rate. However, the temperatures of the metal absorbers, particularly those of strong Ovi, are directly sensitive to the strength of the feedback.

Bimodality of low-redshift circumgalactic O vi in non-equilibrium eagle zoom simulations

“…Despite the high O VI column densities around L * galaxies, the summed O VI ionization fractions are only 0.9-1.3 per cent in CGM gas within R 200 and increase to 2.2-3.4 per cent when including CGM oxygen within 2R 200 . This is still higher than the global IGM O VI correction of ∼1 per cent reported by Rahmati et al (2016) for the EAGLE 100 Mpc box at low-z. Assuming x O VI = 20 per cent thus severely underestimates the CGM oxygen content.…”

“…This enables us to consider the total metal budget inside and beyond galaxies as done by Bouché et al (2007), Zahid et al (2012), and Peeples et al (2014). We also compare our results to the related work of Rahmati et al (2016), who explored IGM metal-line statistics, including O VI, in the EAGLE cosmological boxes. Throughout we use the EAGLE-RECAL prescription for all zooms as discussed in S2; however, it should be noted that the main EAGLE cosmological boxes use two different prescriptions (REF and RECAL) at two different resolutions, which we discuss in Appendix B and show that there is not a significant difference for our main results.…”

“…Recalibrating the EAGLE model is necessary at higher resolution, and it may be that through the generation of more stars, more oxygen is produced and ejected into the CGM, which creates even higher O VI column densities than in the M4.4 zooms. Indeed, Rahmati et al (2016) found that across different EAGLE models, the integrated metal ion column density distributions scaled nearly linearly with the integrated stellar mass. It may also be possible that there exists enough freedom in superwind feedback implementations to change O VI columns by a factor of 2, while still successfully reproducing the large array of galaxy observables at many redshifts as the EAGLE prescription does.…”

“…M6.2 Zooms. We simulate a selection of haloes at the resolution of the L100N1504 box, m SPH = 1.8 × 10 6 M and m DM = 9.7 × 10 6 M , and also compare directly to the same galaxies in the 100 Mpc box, which allows us to link our results to the global IGM results of Rahmati et al (2016), who use this box as their fiducial simulation.…”

“…These observations could be confronted with cosmological hydrodynamical simulations that included metal enrichment from galactic superwinds to learn how the nucleosynthetic products of star formation enrich the diffuse CGM and IGM (e.g. Aguirre et al 2001;Schaye et al 2003;Springel & Hernquist 2003b;Oppenheimer & Davé 2006Tornatore et al 2010;Wiersma et al 2010;Cen & Chisari 2011;Smith et al 2011;Tepper-Garcia et al 2011;Tescari et al 2011;Oppenheimer et al 2012;Crain et al 2013;Rahmati et al 2016).…”