Title:Stellar sources of dust in the high redshift Universe

Abstract: With the aim of investigating whether stellar sources can account for the >10^8 Msun dust masses inferred from mm/sub-mm observations of samples of 5<z<6.4 quasars,we develop a chemical evolution model which follows the evolution of metals and dust on the stellar characteristic lifetimes, taking into account dust destruction this http URL a grid of stellar dust yields as a function of the initial mass and metallicity over the range 1-40 Msun and 0-1 Zsun,we show that the role of AGB stars in cosmic dust evolution at high redshift might have been this http URL apply the chemical evolution model with dust to the host galaxy of the most distant quasar at z=6.4, SDSS J1148+this http URL the current uncertainties on the star formation history of the host galaxy, we have considered two models: (i) a star formation history obtained in a numerical simulation by Li et al.(2007) which predicts that a large stellar bulge is already formed at z=6.4,and (ii) a constant star formation rate of 1000 Msun/yr, as suggested by the observations if most of the FIR luminosity is due to young this http URL total mass of dust predicted at z=6.4 by the first model is 2x10^8Msun,within the range of values inferred by observations,with a substantial contribution (80%) of this http URL a constant star formation rate is adopted,the contribution of AGB-dust decreases to 50% but the total mass of dust formed is a factor 2 this http URL models predict a rapid enrichment of the ISM with metals and a relatively mild evolution of the carbon abundance,in agreement with observational constraints. This supports the idea that stellar sources can account for the dust observed but show that the contribution of AGB stars to dust production cannot be neglected, even at the most extreme redshifts currently accessible to observations.