The sources of intergalactic metals

Abstract

We study the clustering properties of metals in the intergalactic medium (IGM) as traced by 619 C iv and 81 Si iv absorption components with N≥ 1012 cm−2 and 316 Mg ii and 82 Fe ii absorption components with N≥ 1011.5 cm−2 in 19 high signal-to-noise ratio (60–100 pixel−1), high-resolution (R = 45 000) quasar spectra. C iv and Si iv trace each other closely and their line-of-sight correlation functions ξ(v) exhibit a steep decline at large separations and a flatter profile below ≈150 km s−1, with a large overall bias. These features do not depend on absorber column densities, although there are hints that the overall amplitude of ξC iv (v) increases with time over the redshift range detected (1.5–3). Carrying out a detailed smoothed particle hydrodynamic simulation (2 × 3203, 57 Mpc3 comoving), we show that the C iv correlation function cannot be reproduced by models in which the IGM metallicity is constant or a local function of overdensity (Z∝Δ2/3). However, the properties of ξC iv(v) are generally consistent with a model in which metals are confined within bubbles with a typical radius Rs about sources of mass ≥Ms. We derive best-fitting values of Rs≈ 2 comoving Mpc and Ms≈ 1012 M⊙ at z = 3. Our lower-redshift (0.5–2) measurements of the Mg ii and Fe ii correlation functions also uncover a steep decline at large separations and a flatter profile at small separations, but the clustering is even higher than in the z = 1.5−3 measurements, and the turnover is shifted to somewhat smaller distances, ≈75 km s−1. Again, these features do not change with column density, but there are hints that the amplitudes of ξMg ii(v) and ξFe ii(v) increase with time. We describe an analytic ‘bubble’ model for these species, which come from regions that are too compact to be accurately simulated numerically, deriving best-fitting values of Rs≈ 2.4 Mpc and Ms≈ 1012 M⊙. Equally good analytic fits to all four species are found in a similarly biased high-redshift enrichment model in which metals are placed within 2.4 comoving Mpc of Ms≈ 3 × 109 sources at z = 7.5.