The formation of ultra compact dwarf galaxies and massive globular clusters

Quasar-like objects to test for a variable stellar initial mass function

¹ Astronomical Institute, Charles University in Prague, V Holešovičkách 2, 180 00 Praha 8, Czech Republic
e-mail: tjerabko@eso.org
² Helmholtz Institut für Strahlen und Kernphysik, Universität Bonn, Nussallee 14–16, 53115 Bonn, Germany
e-mail: pavel@astro.uni-bonn.de
³ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748, Garching bei München, Germany
⁴ ICRAR, The University of Western Australia, 35 Stirling Hwy, 6009 Crawley Western Australia, Australia

Received: 24 May 2017
Accepted: 21 August 2017

Abstract

The stellar initial mass function (IMF) has been described as being invariant, bottom-heavy, or top-heavy in extremely dense star-burst conditions. To provide usable observable diagnostics, we calculate redshift dependent spectral energy distributions of stellar populations in extreme star-burst clusters, which are likely to have been the precursors of present day massive globular clusters (GCs) and of ultra compact dwarf galaxies (UCDs). The retention fraction of stellar remnants is taken into account to assess the mass to light ratios of the ageing star-burst. Their redshift dependent photometric properties are calculated as predictions for James Webb Space Telescope (JWST) observations. While the present day GCs and UCDs are largely degenerate concerning bottom-heavy or top-heavy IMFs, a metallicity- and density-dependent top-heavy IMF implies the most massive UCDs, at ages < 100 Myr, to appear as objects with quasar-like luminosities with a 0.1−10% variability on a monthly timescale due to core collapse supernovae.