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\section{Science 2: Mass-metallicity}  The formation and evolution of galaxies is controlled by the accretion and outflow of  baryons (Bouch\'e et al.\ 2010; Dav\'e et al. 2011). The gas-phase metallicities of galaxies are sensitive to this cycle. On one hand, pristine gas inflows dilute metallicity and drive star-formation which creates metals. On the other hand, feedback from star-formation driven outflows removes gas (which may be preferentially enriched) and halts further star and metal production. Consequently, the correlation between galaxies' stellar mass and metallicity, observed in the SDSS by Tremonti et al. (2004), \citet{Tremonti_2004},  is one of the key scaling relations that can constrain cosmological models for galaxy formation (Peeples \& Shankar 2011; Zahid et al. 2011; Henry et al. 2013a,b; Lilly et al. 2013; Wuyts et al. 2014; Sanders et al. 2015; Guo et al. 2016; Ma et al. 2016). \cite{Peeples_2011,Zahid_2011,Henry_2013a,Henry_2013b,Lilly_2013,Wuyts_2014,Sanders_2015,Guo_2016,Ma_2016}.  Recent studies have shown that the scatter in the mass-metallicity relation contains even more information about the ways that galaxies grow. For example, it is now established (for low-redshifts) that-- for fixed stellar mass-- galaxies with higher SFRs have lower metallicities, and vise versa (XXX I think this is too informal XXX?;;; Mannucci et al. 2010; 2011, Andrews \& Martini 2013; Yates \& Kauffman 2014; Salim et al 2014). The simple interpretation of this result is that stochastic variations in gas accretion alter both metallicity and SFRs. However, another source of scatter has been detected, which is not so easily explained in this context: galaxy size. Using the same SDSS data, Ellison et al. (2008) show strong anti-correlation between half-light radius and metallicity (at fixed mass) for SDSS galaxies. Nevertheless, this result relied on SDSS imaging (XXX insert some awesome GZ stuff here?).