Hiroyuki Hirashita (ASIAA); Akio K. Inoue (Waseda University, Japan)
The origin of dust in galaxy halos or in the circum-galactic medium (CGM) is still a mystery. We investigate if the radiation pressure in high-redshift (around 10) galaxies can efficiently transport dust to halos. To clarify the first dust enrichment of galaxy halos 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 around 0.1 micron 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 longer than 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--10 scale heights of the galactic disc, where the grain velocities are suppressed to 1 km/s. There is an optimum dust-to-gas ratio (around 0.001) in the galactic disc and an optimum virial mass (around 1e10--1e11 solar masses) for the transport of grains to the halo. We conclude that early dust enrichment of galaxy halos at high redshift is important for the origin of dust in the CGM.