An environment-dependent halo mass function as a driver for the early quenching of z ≥ 1.5 cluster galaxies

Many z ≈1.5 galaxies with a stellar mass (M⋆) ≥ 10¹⁰\, M_ are already quenched in both galaxy clusters (>50 per cent) and the field (>20 per cent), with clusters having a higher quenched fraction at all stellar masses compared to the field. A puzzling issue is that these massive quenched galaxies have stellar populations of similar age in both clusters and the field. This suggests that, despite the higher quenched fraction in clusters, the dominant quenching mechanism for massive galaxies is similar in both environments. In this work, we use data from the cosmological hydrodynamic simulations Hydrangea and EAGLE to test whether the excess quenched fraction of massive galaxies in z=1.5 clusters results from fundamental differences in their halo properties compared to the field. We find that (i) at 10¹⁰≤ \, M/M_ \, ≤ 10¹¹, quenched fractions at 1.5