Stellar sources of dust in the high-redshift Universe (original) (raw)

2009, Monthly Notices of the Royal Astronomical Society

With the aim of investigating whether stellar sources can account for the 10 8 M ⊙ 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 mechanisms. Using a grid of stellar dust yields as a function of the initial mass and metallicity over the range 1 − 40M ⊙ and 0 − 1Z ⊙ , we show that the role of AGB stars in cosmic dust evolution at high redshift might have been over-looked. In particular, we find that (i) for a stellar population forming according to a present-day Larson initial mass function (IMF) with m ch = 0.35M ⊙ , the characteristic timescale at which AGB stars dominate dust production ranges between 150 and 500 Myr, depending both on the assumed star formation history and on the initial stellar metallicity; (ii) this result is only moderately dependent on the adopted stellar lifetimes, but it is significantly affected by variations of the IMF: for a m ch = 5M ⊙ , dust from AGB starts to dominate only on timescales larger than 1 Gyr and SNe are found to dominate dust evolution when m ch 10M ⊙ . We apply the chemical evolution model with dust to the host galaxy of the most distant quasar at z = 6.4, SDSS J1148+5251. Given the current uncertainties on the star formation history of the host galaxy, we have considered two models: (i) the star formation history obtained in a numerical simulation by which predicts that a large stellar bulge is already formed at z = 6.4, and (ii) a constant star formation rate of 1000M ⊙ /yr, as suggested by the observations if most of the FIR luminosity is due to young stars. The total mass of dust predicted at z = 6.4 by the first model is 2 × 10 8 M ⊙ , within the range of values inferred by observations, with a substantial contribution (∼ 80%) of AGB-dust. When 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 smaller. Both 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.