Dust production scenarios in galaxies at z ~ 6-8.3
  The mechanism of dust formation in galaxies at high redshift is still
unknown. Asymptotic giant branch (AGB) stars and explosions of supernovae (SNe)
are possible dust producers, and non-stellar processes may substantially
contribute to dust production, for example grain growth in the interstellar
medium (ISM). Our aim is to determine the contribution to dust production of
AGB stars and SNe in nine galaxies at z ~ 6-8.3, for which observations of dust
have been recently attempted. In order to determine the origin of the observed
dust we have determined dust yields per AGB star and SN required to explain the
total amounts of dust in these galaxies. We find that AGB stars were not able
to produce the amounts of dust observed in the galaxies in our sample. In order
to explain these dust masses, SNe would have to have maximum efficiency and not
destroy the dust which they formed. Therefore, the observed amounts of dust in
the galaxies in the early universe were formed either by efficient supernovae
or by a non-stellar mechanism, for instance the grain growth in the
interstellar medium.
