Pozzetti et al. (2010). We note that the 95% completeness limit for star-forming galaxies appears to be surprisingly high in this diagram (formally slightly higher than the PSB population). This is caused by the wide range in mass-to-light ratios within the star-forming population.

As outlined in Wild et al. (2016), the PSB mass function evolves strongly with redshift, so that the comoving space density of massive PSBs (M$_{\ast}> 10^{10} ~$M$_{\sun}$) is several times higher at $z\sim 2$ than at $z\sim 0.5$. This trend is apparent in Figure \[fig:zmass\], which shows a sharp decline in the number of massive PSBs at $z<1$. The majority of PSBs at $z<1$ are close to the 95% completeness limit (see Figure \[fig:zmass\]) and typically very faint; the median $K$-band magnitude for PSBs at $z<1$ is $K=23.0$, compared to $K=21.8$ at $z>1$. In this work we therefore concentrate on the structural properties of PSBs at $z>1$, and defer an examination of the low-redshift ground-based sample to future work using deeper $K$-band imaging. In the redshift range $1<z<2$, our initial sample consists of 24,880 star-forming galaxies, 2043 passive galaxies and 502 PSBs, of which 9183, 2001 and 385, respectively, have stellar masses M$_{\ast}> 10^{10} ~$M$_{\sun}$.

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