'Accepted 2019 June 29. Received 2019 June 29; in original form 2019 March 5'
title: 'Propagation of star formation at sub-kiloparsec scales'
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H[ii]{} regions – galaxies: photometry – galaxies: ISM – galaxies: star clusters – open clusters and associations: general

Introduction
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Physical processes such as gravitational collapse and turbulence compression are believed to play a key role in the evolution of star formation regions over a wide range of scales, from smallest clumps of young stars to star complexes [@scalo1985; @elmegreen2010]. The sequential hierarchical structures of young stellar groups in these regions are explained in terms of triggered star formation, when new stars form as the result of gravitational instabilities in shocked layers initiated by expanding H[ii]{} bubbles [@elmegreen1977; @efremov1998; @elmegreen2000; @elmegreen2002; @elmegreen2006; @elmegreen2011]. The largest coherent star formation regions are star complexes with diameters of the order of $\sim500-600$ pc [@elmegreen1996; @efremov1998].

Massive star formation complexes in turbulent discs are the result of instabilities in self-gravitating gas discs [@fisher2017]. They are observed in both nearby and distant galaxies. Large star formation regions in galaxies at $z\sim1-2$ are seen as star formation clumps in H$\alpha$ [@ali2017; @fisher2017]. Sizes of these complexes/clumps correlate with turbulence and gas fraction in 