Revealing the physical properties of gas accreting to haloes in the EAGLE simulations

Ruby J. Wright, Claudia Del P. Lagos, Chris Power, Camila A. Correa

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)


The inflow of cosmological gas on to haloes, while challenging to directly observe and quantify, plays a fundamental role in the baryon cycle of galaxies. Using the eagle suite of hydrodynamical simulations, we present a thorough exploration of the physical properties of gas accreting on to haloes - namely, its spatial characteristics, density, temperature, and metallicity. Classifying accretion as 'hot' or "cold' based on a temperature cut-off 105.5 K, we find that the covering fraction (fcov) of cold-mode accreting gas is significantly lower than the hot-mode, with z = 0 fcov values of ${\approx}50{{\ \rm per\ cent}}$ and ${\approx}80{{\ \rm per\ cent}}$, respectively. Active galactic nucleus (AGN) feedback in eagle reduces inflow fcov values by ${\approx}10{{\ \rm per\ cent}}$, with outflows decreasing the solid angle available for accretion flows. Classifying inflow by particle history, we find that gas on first-infall on to a halo is metal depleted by ≈2 dex compared to pre-processed gas, which we find to mimic the circum-galactic medium (CGM) in terms of metal content. We also show that high (low) halo-scale gas accretion rates are associated with metal-poor (rich) CGM in haloes below $10^{12}\, \mathrm{M}_{\odot }$, and that variation in halo-scale gas accretion rates may offer a physical explanation for the enhanced scatter in the star-forming main sequence at low (${\lesssim}10^{9}\, \mathrm{M}_{\odot }$) and high (${\gtrsim}10^{10}\, \mathrm{M}_{\odot }$) stellar masses. Our results highlight how gas inflow influences several halo- and galaxy-scale properties, and the need to combine kinematic and chemical data in order to confidently break the degeneracy between accreting and outgoing gas in CGM observations.

Original languageEnglish
Pages (from-to)5702-5725
Number of pages24
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - 1 Jul 2021


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