Dust grain growth in the interstellar medium of 5 < z < 6.5 quasars

¹ Scottish Universities Physics Alliance, Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh, EH9 3HJ UK
e-mail: mm@roe.ac.uk
² Spitzer Science Center, MC 314-6, California Institute of Technology, Pasadena, CA 91125, USA
³ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
⁴ Department of Physics &amp; Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada

Received: 30 April 2010
Accepted: 28 June 2010

Abstract

Aims. We investigate whether stellar dust sources i.e. asymptotic giant branch (AGB) stars and supernovae (SNe) can account for dust detected in 5 < z < 6.5 quasars (QSOs).

Methods. We calculate the required dust yields per AGB star and per SN using the dust masses of QSOs inferred from their millimeter emission and stellar masses approximated as the difference between the dynamical and the H₂ gas masses of these objects.

Results. We find that AGB stars are not efficient enough to form dust in the majority of the z > 5 QSOs, whereas SNe may be able to account for dust in some QSOs. However, they require very high dust yields even for a top-heavy initial mass function.

Conclusions. This suggests additional non-stellar dust formation mechanism e.g. significant dust grain growth in the interstellar medium of at least three out of nine z > 5 QSOs. SNe (but not AGB stars) may deliver enough heavy elements to fuel this growth.