TY - JOUR
T1 - On the puzzling plateau in the specific star formation rate at z= 2-7
AU - Weinmann, Simone M.
AU - Neistein, Eyal
AU - Dekel, Avishai
PY - 2011/11
Y1 - 2011/11
N2 - 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 ~ 2Gyr-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.
AB - 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 ~ 2Gyr-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.
KW - Galaxies: evolution
KW - Galaxies: formation
KW - Galaxies: high-redshift
KW - Galaxies: statistics
UR - http://www.scopus.com/inward/record.url?scp=80255138305&partnerID=8YFLogxK
U2 - 10.1111/j.1365-2966.2011.19440.x
DO - 10.1111/j.1365-2966.2011.19440.x
M3 - ???researchoutput.researchoutputtypes.contributiontojournal.article???
AN - SCOPUS:80255138305
SN - 0035-8711
VL - 417
SP - 2737
EP - 2751
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 4
ER -