The impact of cold gas accretion above a mass floor on galaxy scaling relations

N. Bouché*, A. Dekel, R. Genzel, S. Genel, G. Cresci, N. M. Förster Schreiber, K. L. Shapiro, R. I. Davies, L. Tacconi

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

503 Scopus citations

Abstract

Using the cosmological baryonic accretion rate and normal star formation (SF) efficiencies, we present a very simple model for star-forming galaxies that accounts for the mass and redshift dependences of the star formation rate (SFR)-mass and Tully-Fisher (TF) relations from z ∼ 2 to the present. The time evolution follows from the fact that each modeled galaxy approaches a steady state where the SFR follows the (net) cold gas accretion rate. The key feature of the model is a halo mass floor Mmin ≃ 10 11M below which accretion is quenched in order to simultaneously account for the observed slopes of the SFR-mass and TF relations. The same successes cannot be achieved via an SF threshold (or delay) nor by varying the SF efficiency or the feedback efficiency. Combined with the mass ceiling for cold accretion due to virial shock heating, the mass floor M min explains galaxy "downsizing," where more massive galaxies formed earlier and over a shorter period of time. It turns out that the model also accounts for the observed galactic baryon and gas fractions as a function of mass and time, and the cosmic SFR density, which are all resulting from the mass floor Mmin. The model helps us to understand that it is the cosmological decline of accretion rate that drives the decrease of cosmic SFR density between z ∼ 2 and z = 0 and the rise of the cosmic SFR density from z ∼ 6 to z ∼ 2 that allows us to put a constraint on our main parameter Mmin ≃ 1011M. Among the physical mechanisms that could be responsible for the mass floor, our view is that photoionization feedback (from first in situ hot stars) lowering the cooling efficiency is likely to play a large role.

Original languageEnglish
Pages (from-to)1001-1018
Number of pages18
JournalAstrophysical Journal
Volume718
Issue number2
DOIs
StatePublished - 1 Aug 2010

Keywords

  • Cosmology: observations
  • Galaxies: evolution
  • Galaxies: high-redshift

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