Peak metallicities of metal–rich ( MR ) populations of globular clusters ( GCs ) belonging to spheroids of different mass fall within the somewhat conservative -0.7 \leq [ Fe/H ] \leq - 0.3 range .
Indeed , if possible age effects are taken into account , this metallicity range might become smaller .
Irregulars , like the Large Magellanic Cloud ( LMC ) , with longer timescales of their formation and lower star formation ( SF ) efficiency do not contain the old MRGCs with [ Fe/H ] > -1.0 , but they are observed to form populations of young/intermediate–age massive star clusters ( MSCs ) with masses exceeding 10 ^ { 4 } M _ { \odot } .
Their formation is widely believed to be accidental process fully depending on external factors .
From analysis of data available on the populations and their hosts , including intermediate–age populous star clusters in the LMC , we find that their most probable mean metallicities fall within -0.7 \leq [ Fe/H ] \leq - 0.3 , as the peak metallicities of MRGCs do , irrespective of sings of interaction .
Moreover , both the disk giant metallicity distribution function ( MDF ) in the LMC and the MDFs for old giants in the halos of massive spheroids exhibit significant increasing toward [ Fe/H ] \approx - 0.5 .
That is in agreement with a correlation found between SF activity in galaxies and their metallicity .
The formation of both the old MRGCs in spheroids and MSC populations in irregulars probably occurs approximately at the same stage of the host galaxies ’ chemical evolution and is related to the essentially increased SF activity in the hosts around the same metallicity that is achieved very soon in massive spheroids , later in lower–mass spheroids , and much more later in irregulars .
Changes in the interstellar dust , particularly in elemental abundances in dust grains and in the mass distribution function of the grains , may be among the factors regulating star and MSC formation activity in galaxies .
Strong interaction and merger affecting the MSC formation play presumably additional role , although they can substantially intensify the internally regulated MSC formation process .
Several implications of our suggestions are briefly discussed .