Galactic conformity measured in semi-analytic models

We study the correlation between the specific star formation rate of central galaxies and neighbour galaxies, also known as 'galactic conformity', out to several Mpc scales using three different semi-analytic models (SAMs). It has been suggested that SAMs may not show the strong signal of conformity measured in observations. In all the models, when the selection of primary galaxies is based on an isolation criterion in real space, we measure a strong galactic conformity where the mean quenched fraction around quenched primary galaxies is higher than that around star-forming primary galaxies of the same stellar mass. The cumulative signal-to-noise ratio, which is used to evaluate the significance and extension in distance of conformity, depends strongly on the SAM. The two-halo conformity is significant as far as ~5 Mpc/h. The overall signal of galactic conformity decreases when we remove satellites in the selection of primary galaxies. In this case, there is no significant two-halo conformity in two SAMs. For the other SAM, the two-halo conformity is only detected between isolated, central galaxies in relatively low-mass haloes ($M_{\rm halo}$ $< 10^{12.4}$ $h^{-1}~\rm{ M_{\bigodot}}$) and their neighbours. Finally, we explore the case when the secondary galaxies correspond to central galaxies in the SAMs as an attempt to measure the conformity between distinct haloes. Our results show that there is no conformity beyond ~3 Mpc/h. The conformity measured out to scales of 3$-$4 Mpc/h can be related to the environmental influence of large galaxy clusters around near central galaxies.