Wet disc contraction to galactic blue nuggets and quenching to red nuggets
Abstract
We study the origin of high-redshift, compact, quenched spheroids (red nuggets) through the dissipative shrinkage of gaseous discs into compact star-forming systems (blue nuggets). The discs, fed by cold streams, undergo violent disc instability that drives gas into the centre (along with mergers). The inflow is dissipative when its time-scale is shorter than the star formation time-scale. This implies a threshold of ∼0.28 in the cold-to-total mass ratio within the disc radius. For the typical gas fraction ∼0.5 at z ∼ 2, this threshold is traced back to a maximum spin parameter of ∼0.05, implying that ∼half the star-forming galaxies contract to blue nuggets, while the rest form extended stellar discs. Thus, the surface density of blue galaxies is expected to be bimodal about ∼109 M⊙ kpc-2, slightly increasing with mass. The blue nuggets are expected to be rare at low z when the gas fraction is low. The blue nuggets quench to red nuggets by complementary internal and external mechanisms. Internal quenching by a compact bulge, in a fast mode and especially at high z, may involve starbursts, stellar and active galactic nucleus feedback, or Q-quenching. Quenching due to hot-medium haloes above 1012 M⊙ provides maintenance and a slower mode at low redshift. These predictions are confirmed in simulations and are consistent with observations at z = 0-3.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- February 2014
- DOI:
- 10.1093/mnras/stt2331
- arXiv:
- arXiv:1310.1074
- Bibcode:
- 2014MNRAS.438.1870D
- Keywords:
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- galaxies: elliptical and lenticular;
- cD;
- galaxies: evolution;
- galaxies: formation;
- galaxies: kinematics and dynamics;
- galaxies: spiral;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 12 pages, 2 figures, minor revisions, a new schematic figure