Hot Baryons and the Distribution of Metals in the Intergalactic Medium

Abstract

We use the observed number and column-density distributions of intergalactic O VI absorbers to constrain the distribution of metals in the low-redshift intergalactic medium (IGM). In this simple model the metals in the O VI absorbers are assumed to be produced in and propagated from low-redshift galaxies drawn from a real sample, in this case the Sloan Digital Sky Survey (SDSS). This model can explain the observed dN/dz of metals seen in O VI absorbers if these metals are dispersed out to ~ 200 kpc by galaxies down to L \~ 0.01 - 0.1 L_r^*. Massive galaxies (L ~ L_r^*) by themselves cannot provide the necessary enrichment unless they can enrich volumes out to $\gtrsim 0.5 - 1 Mpc. Alternatively, our model allows an estimate of the fraction of O VI absorbers directly caused by galaxies rather than hot IGM. With this assumption we explore the possible connections between the intergalactic O VI absorbers and the known populations of highly-ionized high-velocity clouds (HVCs) surrounding the Milky Way. Our model predicts that more sensitive, complete surveys optimized to uncover weaker O VI absorbers will find the tentative turnover below log N(O VI) ~ 13.5 to be a real effect resulting from the apparently limited volumes over which galaxies can enrich the IGM. If so, it would indicate that metals are not as widespread throughout the low-density IGM as they are assumed to be in cosmological simulations of the WHIM.