Primordial star clusters at extreme magnification

TL;DR

This paper investigates the potential to detect extremely magnified, small Population III star clusters at high redshifts using upcoming large-area surveys and telescopes, highlighting their detectability and scientific importance.

Contribution

It demonstrates that planned surveys like WISH could detect Population III star clusters with high magnification, and discusses follow-up methods to confirm their nature and properties.

Findings

WISH survey may detect a few Population III star clusters.

Follow-up spectroscopy can confirm their Population III nature.

Photometry can reveal a top-heavy initial mass function.

Abstract

Gravitationally lensed galaxies with magnification ~10-100 are routinely detected at high redshifts, but magnifications significantly higher than this are hampered by a combination of low probability and large source sizes. Magnifications of ~1000 may nonetheless be relevant in the case of intrinsically small, high-redshift objects with very high number densities. Here, we explore the prospects of detecting compact (< 10 pc), high-redshift (z > 7) Population III star clusters at such extreme magnifications in large-area surveys with planned telescopes like Euclid, WFIRST and WISH. We find that the planned WISH 100 sq. deg ultradeep survey may be able to detect a small number of such objects, provided that the total stellar mass of these star clusters is > 10000 solar masses. If candidates for such lensed Population III star clusters are found, follow-up spectroscopy of the surrounding nebula with the James Webb Space Telescope or groundbased Extremely Large Telescopes should be able to confirm the Population III nature of these objects. Multiband photometry of these objects with the James Webb Space Telescope also has the potential to confirm that the stellar initial mass function in these Population III star clusters is top-heavy, as supported by current simulations.