Get access

On the puzzling plateau in the specific star formation rate at z= 2–7


  • Simone M. Weinmann,

    Corresponding author
    1. Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, the Netherlands
    Search for more papers by this author
  • Eyal Neistein,

    1. Max-Planck-Institute for Extraterrestrial Physics, Giessenbachstrasse 1, 85748 Garching, Germany
    2. Max-Planck Institut für Astrophysik, Karl-Schwarzschild-Str. 1, Postfach 1317, 85741 Garching, Germany
    Search for more papers by this author
  • Avishai Dekel

    1. Racah Institute of Physics, Hebrew University, Jerusalem 91904, Israel
    Search for more papers by this author



The observational indications for a constant specific star formation rate (sSFR) in the redshift range z= 2–7 are puzzling in the context of current galaxy-formation models. Despite the tentative nature of the data, their marked conflict with theory motivates a study of the possible implications. The plateau at sSFR ∼ 2 Gyr−1 is hard to reproduce because (a) its level is low compared to the cosmological specific accretion rate at z≥ 6, (b) it is higher than the latter at z∼ 2, (c) the natural correlation between SFR and stellar mass makes it difficult to manipulate their ratio, and (d) a low SFR at a high z makes it hard to produce enough massive galaxies by z∼ 2. Using a flexible semi-analytic model, we explore ad hoc modifications to the standard physical recipes trying to obey the puzzling observational constraints. Successful models involve non-trivial modifications, such as (a) a suppressed SFR at z≥ 4 in galaxies of all masses, by enhanced feedback or reduced SFR efficiency, following an initial active phase at z > 7; (b) a delayed gas consumption into stars, allowing the gas that was prohibited from forming stars or ejected at high z to form stars later in more massive galaxies; and (c) enhanced growth of massive galaxies, in terms of either faster assembly or more efficient starbursts in mergers, or by efficient star formation in massive haloes.

Get access to the full text of this article