The confinement of star-forming galaxies into a main sequence through episodes of gas compaction, depletion and replenishment

Sandro Tacchella*, Avishai Dekel, C. Marcella Carollo, Daniel Ceverino, Colin DeGraf, Sharon Lapiner, Nir Mandelker, Joel R. Primack

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

244 Scopus citations


Using cosmological simulations,we address the properties of high-redshift star-forming galaxies (SFGs) across their main sequence (MS) in the plane of star formation rate (SFR) versus stellar mass. We relate them to the evolution of galaxies through phases of gas compaction, depletion, possible replenishment, and eventual quenching. We find that the high-SFR galaxies in the upper envelope of the MS are compact, with high gas fractions and short depletion times ('blue nuggets'), while the lower SFR galaxies in the lower envelope have lower central gas densities, lower gas fractions, and longer depletion times, consistent with observed gradients across the MS. Stellar-structure gradients are negligible. The SFGs oscillate about the MS ridge on time-scales ~0.4tHubble (~1 Gyr at z ~ 3). The propagation upwards is due to gas compaction, triggered, e.g. by mergers, counter-rotating streams, and/or violent disc instabilities. The downturn at the upper envelope is due to central gas depletion by peak star formation and outflows while inflow from the shrunken gas disc is suppressed. An upturn at the lower envelope can occur once the extended disc has been replenished by fresh gas and a new compaction can be triggered, namely as long as the replenishment time is shorter than the depletion time. The mechanisms of gas compaction, depletion, and replenishment confine the SFGs to the narrow (±0.3 dex) MS. Full quenching occurs in massive haloes (Mvir > 1011.5M) and/or at low redshifts (z < 3), where the replenishment time is long compared to the depletion time, explaining the observed bending down of the MS at the massive end.

Original languageAmerican English
Article numberstw122
Pages (from-to)2790-2813
Number of pages24
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - 11 Apr 2016

Bibliographical note

Publisher Copyright:
© 2016 The Authors.


  • Galaxies: evolution
  • Galaxies: formation
  • Galaxies: fundamental parameters


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