Context. Substellar objects have extremely long life spans. Thecosmological consequence for older objects are low abundances for heavyelements, which in turn results in a wide distribution of objects overmetallicity, hence over age. Within their cool atmosphere, dust cloudsbecome a dominant feature, affecting the opacity and the remaining gasphase abundance of heavy elements. Aims. We investigate the influence of the stellar metallicity onthe dust formation in substellar atmospheres and on the dust cloudstructure and its feedback on the atmosphere. This work hasimplications for the general questions of star formation and of dustformation in the early universe. Methods. We utilise numerical simulations to solve a set of moment equations to determine the quasi-static dust cloud structure (D RIFT).These equations model the nucleation, the kinetic growth of compositeparticles, their evaporation, and the gravitational settling as astationary dust formation process. Element conservation equationsaugment this system of equations by including the element replenishmentby convective overshooting. The integration with an atmosphere code (P HOENIX) allows determination of a consistent -structure (T - local temperature, p - local pressure, - convective velocity), hence, to calculate synthetic spectra. Results. A grid of D RIFT-P HOENIX model atmospheres was calculated for a wide range of metallicity, [M/H][+0.5,-0.0, -0.5, ..., -6.0], to allow for systematic study of atmosphericcloud structures throughout the evolution of the universe. We find dustclouds in even the most metal-poor ([M/H] = -6.0) atmosphere of browndwarfs. Only the most massive among the youngest brown dwarfs and giantgas planets can resist dust formation. For very low heavy elementabundances, a temperature inversion develops that has a drastic impacton the dust cloud structure. Conclusions. The combination of metal depletion by dustformation and the uncertainty of interior element abundances makes themodelling of substellar atmospheres an intricate problem in particularfor old substellar objects. We furthermore show that the dust-to-gasratio does not scale linearly with the object's [M/H] for agiven effective temperature. The mean grain sizes and the compositionof the grains change depending on [M/H], which influences the dustopacity that determines radiative heating and cooling, as well as thespectral appearance. Key words: astrochemistry - methods: numerical - stars: atmospheres - stars: low-mass, brown dwarfs
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