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In recent years, the field of galactic-scale star formation has seen a shift
towards smaller spatial scales thanks to the improved sensitivity and spatial
resolution of new observational facilities (e.g Kennicutt et al. 2007). This
development has enabled cloud-scale observations of extragalactic systems
(Bigiel et al. 2008, Schruba et al. 2010, Leroy et al. 2013), providing a link
between Galactic and extragalactic observations of the relation between gas mass
(density) and star formation rate (density). These spatially-resolved "star
formation relations" hold a wealth of information. They may provide insight into
the physics underpinning galactic star formation relations like the
Schmidt-Kennicutt relation and thereby help us to understand how exactly
galaxies turn their gas into stars. The first observational results have
revealed that the galactic star formation relations develop substantial scatter
or even change form when considered on small spatial scales (Blanc et al. 2009,
Heiderman et al. 2010, Lada et al. 2010, Schruba et al. 2010, Gutermuth et al.
2011). At the same time, early theoretical models suggest that the way in which
star formation relations break down on small scales directly quantifies the
physics of star formation on the cloud scale (Burkert & Hartmann 2013, Kruijssen
& Longmore 2014). For instance, it allows us to measure the time-scales
characterising the star formation process with high accuracy. The exciting
prospect is that the cloud-scale physics of star formation could be derived as a
function of the galactic environment using high-sensitivity, high-resolution
maps of external galaxies (Kruijssen et al., in preparation). With the advent of
ALMA, such state-of-the-art observations will become the norm, from nearby
galaxies out to high-redshift (cf. Swinbank et al. 2011, Schinnerer et al., in
preparation). This unique opportunity to link the small and large scales of
galactic star formation would greatly benefit from a community effort including
experts in both Galactic and extragalactic star formation. In this focus group,
we aim to address the main open questions in the field of multi-scale star
formation relations (e.g. What drives the rate of star formation? What sets the
efficiency of star formation? How and why do these quantities depend on the
spatial scale?) and identify the key steps needed to fully exploit the potential
of these observational and theoretical advances.
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