Wet compaction to a blue nugget: a critical phase in galaxy evolution

ABSTRACT We utilize high-resolution cosmological simulations to reveal that high-redshift galaxies tend undergo a robust ‘wet compaction’ event when near ‘golden’ stellar mass of $\sim \!\!10^{10}\, \rm M_\odot$ . This is gaseous shrinkage compact star-forming phase, ‘blue nugget’ (BN), followed by central quenching star formation passive bulge, ‘red (RN), and buildup an extended disc ring. Such nuggets are observed at cosmic noon seed today’s early-type galaxies. The compaction triggered drastic loss angular momentum due to, e.g. wet mergers, counter-rotating cold streams, or violent instability. BN phase marks transitions in the galaxy structural, compositional, kinematic properties. from forming quenched inside-out, diffuse with ring envelope, dark matter baryon dominance, prolate oblate shape, pressure rotation support, low high metallicity, supernova AGN feedback. black hole growth, first suppressed feedback below golden mass, boosted compaction, keeps growing once halo massive enough lock ejecta.