Radiation-pressure-driven dust transport to galaxy haloes at z α 10

The origin of dust in galaxy haloes or in the circum-galactic medium (CGM) is still a mystery. We investigate if the radiation pressure in high-redshift (z α 10) galaxies can efficiently transport dust to haloes. To clarify the first dust enrichment of galaxy haloes in the early Universe, we solve the motion of a dust grain considering radiation pressure, gas drag, and gravity in the vertical direction of the galactic disc. Radiation pressure is estimated in a consistent manner with the stellar spectra and dust extinction. As a consequence, we find that dust grains with radii a α 0.1 μm successfully escape from the galactic disc if the ongoing star formation episode converts more than 15 per cent of the baryon content into stars and lasts ≳ 30 Myr, while larger and smaller grains are trapped in the disc because of gravity and gas drag, respectively. We also show that grain charge significantly enhances gas drag at a few to 10 scale heights of the galactic disc, where the grain velocities are suppressed to α1 km s-1. There is an optimum dust-to-gas ratio (α10-3) in the galactic disc and an optimum virial mass α1010-1011 M for the transport of a α 0.1 μm grains to the halo. We conclude that early dust enrichment of galaxy haloes at z ≳ 10 is important for the origin of dust in the CGM.