at $z$$\sim$ 1. They find a reversal of the SFR-density relation: specifically that the median $<$SFR$>$ decreases with increasing galaxy density in the local sample, while at $z$$\sim$1, the median $<$SFR$>$ first increases with increasing galaxy density before peaking and then decreasing again at the highest densities. They claim that the increase of $<$SFR$>$ with local galaxy density is caused by increases of both M$_*$ and sSFR with galaxy density. Because in general sSFR decreases with increasing M$_*$ (e.g. Blanton et al. 2003; Baldry et al. 2004), they conclude that at $z$$\sim$1 the environment must enhance the SFR of galaxies in order for sSFR to increase while M$_*$ increases.

Cooper et al. (2008; C08) also observed the reversal of the SFR-density relation by comparing a local SDSS sample to the $z$$\sim$1 DEEP2 sample (not limited to star-forming galaxies), but came to a somewhat different conclusion. Because they find that the sSFR decreases with local density at both $z$$\sim$0 and $z$$\sim$1, they conclude that the reversal of the SFR-density relation is mainly due to the different luminosity-density (and mass-density) relations of the blue galaxies in their samples at the two redshifts: at $z$$\sim$1 M$_{\mathrm{B}}$ increases with local density, while at $z$$\sim$0, 