Open AccessOn breaking the age–metallicity degeneracy in early‐type galaxies: infall versus star formation efficiency
Author(s) -
Ferreras Ignacio,
Silk Joseph
Publication year - 2003
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2003.06839.x
Subject(s) - physics , astrophysics , galaxy , star formation , metallicity , redshift , stellar mass , galaxy formation and evolution , range (aeronautics) , outflow , astronomy , materials science , meteorology , composite material
ABSTRACT The correlation between [Mg/Fe] and galaxy mass found in elliptical galaxies imposes a strong constraint on the duration of star formation. Furthermore, the colour–magnitude relation restricts the range of ages and metallicities of the stellar populations. We combine these two constraints with a model of star formation and chemical enrichment including infall and outflow of gas to find that the trend towards supersolar [Mg/Fe] in massive ellipticals excludes a pure metallicity sequence as an explanation of the colour–magnitude relation. An age spread from galaxy to galaxy is thereby required, attributable either to a range of star formation efficiencies ( C eff ) or to a range of infall time‐scales (τ f ) . We find that the inferred range of stellar ages is compatible with the small scatter and the redshift evolution of the colour–magnitude relation. Two alternative scenarios can explain the data: a fixed τ f with a mass‐dependent efficiency, C eff ∝ M ; or a fixed C eff with mass‐dependent infall, . We conclude that the actual scenario may well involve a combination of these two parameters, with mass dependences that should span the range of those given above.