A Global Census of Metals in the Universe

TL;DR

This paper provides a comprehensive census of metals in the universe, tracking their distribution and evolution across different cosmic structures and gas phases from high redshift to the present.

Contribution

It offers the first global, multi-phase metal census combining data from stars, gas, and galaxy clusters over a wide redshift range, revealing the evolution of metal reservoirs.

Findings

Stellar metal mass density increased by an order of magnitude from z~2.5 to 0.7.

At low redshift, stars contain about 30% of the total metals.

The metal density in cool ionized gas doubled from z~3 to z<1.

Abstract

We present a census of the mass density of metals and their evolution with cosmic time on a global scale throughout the Universe, synthesizing robust estimates of metals in stars, hot intra-cluster gas, and gaseous absorbers tracing neutral gas as well as ionized gas in the circumgalactic and intergalactic media. We observe an order of magnitude increase in the stellar metal mass density from z~2.5 to 0.7, over which time stars emerge as the most important metal reservoir at low redshifts, housing ~30% of the total expected metal density at z~0.1. Hot virialized intracluster/intragroup gas accounts for ~15% and 10% of metals at z~0.1 and 0.7, respectively. Using metallicity measurements from CCC, KODIAQ-Z, and HD-LLS surveys covering redshifts z<1 to z~2-3.5, we investigate the global distribution of metals in extragalactic cool ionized gas as a function of HI column density. During the period from z~3 to z<1, the global metal density of cool (T~10^{4-5} K) gas has doubled. However, the fractional contribution of the ionized gas to the total expected metal density decreased from ~20% at z~3 to ~4% at z<1. The cosmic metal density of all gas phases has increased with cosmic time, reflecting an ``inside-out'' metal dispersion by feedback mechanisms and galactic outflows.