CAN A 'STANDARD' INITIAL MASS FUNCTION EXPLAIN THE METAL ENRICHMENT IN CLUSTERS OF GALAXIES?

摘要

It is frequently debated in literature whether a "standard" initial mass function (IMF)―meaning an IMF of the kind usually adopted to explain the chemical evolution in the local solar neighborhood―can account for the observed metal enrichment and iron mass-to-light ratio in clusters of galaxies. We address this problem by means of straightforward estimates that should hold independently of the details of chemical evolution models. It is crucial to compute self-consistently the amount of mass and metals locked-up in stars by accounting for the stellar mass-to-light ratio predicted by a given IMF. It then becomes clear that a "standard" solar neighborhood IMF cannot provide enough metals to account for the observed chemical properties in clusters: clusters of galaxies and the local environment must be characterized by different IMFs. Alternatively, if we require the IMF to be universal, in order to explain clusters such an IMF must be much more efficient in metal production than usually estimated for the solar vicinity. In this case, substantial loss of metals is required from the solar neighborhood and from disk galaxies in general. This "nonstandard" scenario of the local chemical evolution would challenge our present understanding of the Milky Way and of disk galaxy formation.