Open AccessCosmological simulations of intergalactic medium enrichment from galactic outflows
Author(s) -
Oppenheimer Benjamin D.,
Davé Romeel
Publication year - 2006
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2006.10989.x
Subject(s) - physics , astrophysics , metallicity , outflow , galaxy , redshift , star formation , intergalactic medium , ionization , galaxy formation and evolution , meteorology , ion , quantum mechanics
We investigate models of self‐consistent chemical enrichment of the intergalactic medium (IGM) from z = 6.0 → 1.5 , based on hydrodynamic simulations of structure formation that explicitly incorporate outflows from star‐forming galaxies. Our main result is that outflow parametrizations derived from observations of local starburst galaxies, in particular momentum‐driven wind scenarios, provide the best agreement with observations of C iv absorption at z ∼ 2–5 . Such models sufficiently enrich the high‐ z IGM to produce a global mass density of C iv absorbers that is relatively invariant from z = 5.5 → 1.5 , in agreement with observations. This occurs despite continual IGM enrichment causing an increase in volume‐averaged metallicity by ∼× 5–10 over this redshift range, because energy input accompanying the enriching outflows causes a drop in the global ionization fraction of C iv . Comparisons to observed C iv column density and linewidth distributions and C iv ‐based pixel optical depth ratios provide significant constraints on wind models. Our best‐fitting outflow models show mean IGM temperatures only slightly above our no‐outflow case, metal filling factors of just a few per cent with volume‐weighted metallicities around 10 −3 at z ∼ 3 , significant amounts of collisionally ionized C iv absorption and a metallicity–density relationship that rises rapidly at low overdensities and flattens at higher ones. In general, we find that outflow speeds must be high enough to enrich the low‐density IGM at early times but low enough not to overheat it, and concurrently must significantly suppress early star formation while still producing enough early metals. It is therefore non‐trivial that locally calibrated momentum‐driven wind scenarios naturally yield the desired strength and evolution of outflows, and suggest that such models represent a significant step towards understanding the impact of galactic outflows on galaxies and the IGM across cosmic time.