Star formation occurs across a large range of spatial scales from low-mass
cores to OB associations. An outstanding question is whether there are
universal relationships between the rate and the observable local
environment? For example, star formation may depend on the local gas
surface density either as a threshold or a power law. Based on observations
of molecular clouds in the Galactic disk, Lada et al 2010 and Heiderman et
al 2010 proposed a density threshold of about 120 Msun / pc^2 (10^4 cm^-3)
above which gas is efficiently converted into stars. This threshold also
reproduces the observed star formation rate in nearby galaxies (Lada et al
2012). In contrast, Krumholz et al 2012 and Federrath 2013 suggest that a
fixed star formation rate per free-fall time of 1% explains the observed
rates. Other observations suggest a linear relationship between the star
formation rate and surface density based on observations of nearby galaxies
(Bigiel et al 2008, 2012) or steeper power laws with the rate scaling as
the 3/2 power of the surface density (Schmidt 1959, Kennicutt et al 1998).
Distinguishing which (if any) of these relationships are correct, requires
comparing environments that predict substantially different star formation
rates. One region with conditions quite different from the Galactic disk
and also observable at high spatial resolution is the central 500 pc of the
Milky Way -- the Central Molecular Zone (CMZ). An extreme environment, the
CMZ contains 10% of the total molecular gas in the Galaxy. Compared to
clouds in the disk, the average gas density is one to two orders of
magnitude greater (Morris et al 1996), the molecular spectral line widths
are an order of magnitude larger, (c.f. Jones et al 2012), and one third of
the column density is at temperatures a factor of 10 higher (>150 K)
(Rodriguez-Fernandez et al 2002). The environment is more similar to
high-redshift galaxies and starbursts in their quiescent states (Kruijssen
and Longmore 2013) than to nearby GMCs.
This focus group will discuss whether and how we can compare observations
and simulations of clouds in the central 500 pc of the Milky Way -- the
Central Molecular Zone (CMZ)-- with observations and simulations of clouds
in the Galactic disk to test different models for the rate and efficiency
of star formation.
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