Evaluating hydrodynamical simulations with green valley galaxies
  We test cosmological hydrodynamical simulations of galaxy formation regarding
the properties of the Blue Cloud (BC), Green Valley (GV) and Red Sequence (RS),
as measured on the 4000$\small{ \mathring {\mathrm A}}$ break strength vs
stellar mass plane at $z=0.1$. We analyse the RefL0100N1504 run of EAGLE and
the TNG100 run of IllustrisTNG project, by comparing them with the Sloan
Digital Sky Survey, while taking into account selection bias. Our analysis
focuses on the GV, within stellar mass $\log\,\mathrm{M_\star/M_{\odot}} \simeq
10-11$, selected from the bimodal distribution of galaxies on the D$_n$(4000)
vs stellar mass plane, following Angthopo et al. methodology. Both simulations
match the fraction of AGN in the green-valley. However, they over-produce
quiescent GV galaxies with respect to observations, with IllustrisTNG yielding
a higher fraction of quiescent GV galaxies than EAGLE. In both, GV galaxies
have older luminosity-weighted ages with respect to the SDSS, while a better
match is found for mass-weighted ages. We find EAGLE GV galaxies quench their
star formation early, but undergo later episodes of star formation, matching
observations. In contrast, IllustrisTNG GV galaxies have a more extended SFH,
and quench more effectively at later cosmic times, producing the excess of
quenched galaxies in GV compared with SDSS, based on the 4000$\small{ \mathring
{\mathrm A}}$ break strength. These results suggest the AGN feedback subgrid
physics, more specifically, the threshold halo mass for black hole input and
the black hole seed mass, could be the primary cause of the over-production of
quiescent galaxies found with respect to the observational constraints.
