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.
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The authors are thankful to the anonymous referee for her/his useful comments which improved our original manuscript. We acknowledge stimulating discussions with Guillermo Barro, Sandy Faber, Reinhard Genzel, Mark Krumholz, Simon Lilly, Benny Trakhtenbrot, Joanna Woo, and Adi Zolotov. We thank the referee for constructive and useful comments, which helped to improve the manuscript. ST thanks AD and his group for the hospitality during his visit at HUJI. Development and most of the analysis have been performed in the astro cluster at HU. The simulations were performed at the National Energy Research Scientific Computing Center (NERSC), Lawrence Berkeley National Laboratory, and at NASA Advanced Supercomputing (NAS) at NASA Ames Research Center. This work was supported by ISF grant 24/12, by GIF grant G-1052-104.7/2009, by the I-CORE Program of the PBC, ISF grant 1829/12, by MINECO grant AYA2012-32295, by CANDELS grant HST-GO-12060.12-A, and by NSF grants AST-1010033 and AST- 1405962. We acknowledge support by the Swiss National Science Foundation.
© 2016 The Authors.
- Galaxies: evolution
- Galaxies: formation
- Galaxies: fundamental parameters