A possible origin of the mass-metallicity relation of galaxies

Abstract

Observations show that galaxies follow a mass–metallicity relation over a wide range of masses. One currently favoured explanation is that less massive galaxies are less able to retain the gas and stellar ejecta and thus may lose the freshly produced metals in the form of galactic outflows. Galaxies with a low current star formation rate have been found to contain star clusters up to a lower mass limit. Since stars are predominately born in clusters, and less massive clusters have been found to be less likely to contain very massive stars, this implies that in environments or at times of low star formation, the stellar initial mass function does not extend to as high masses as during high star formation epochs. It is found that the oxygen yield is reduced by a factor of 30 when the star formation rate is decreased by 3 to 4 orders of magnitude. With this concept, chemical evolution models for galaxies of a range of masses are computed and shown to provide an excellent fit to the mass–metallicity relation derived recently by Tremonti et al. Furthermore, the models match the relation between galaxy mass and effective yield. Thus, the scenario of a variable integrated stellar initial mass function, which is based on the concept of formation of stars in clusters, may offer an attractive alternative or partial explanation of the mass–metallicity relation in galaxies.

Galaxy metallicity scaling relations in the EAGLE simulations

“…However, the lack of SN-feedback model prevented de Rossi et al (2007) from reproducing the observed slope of the MZR due to overcooling. According to Köppen, Weidner & Kroupa (2007), the MZR might simply reflect variations in the stellar initial mass function (IMF).…”

Mass-metallicity relation explored with CALIFA

“…The scenarios proposed to explain its origin can be broadly categorized as 1) the loss of enriched gas by outflows (T04; Kobayashi et al 2007); 2) the accretion of pristine gas by inflows (Finlator & Davé 2008); 3) variations of the initial mass function with galaxy mass (Köppen et al 2007); 4) selective star-formation efficiency or downsizing (Brooks et al 2007;Ellison et al 2008;Calura et al 2009;Vale Asari et al 2009); or a combination of them. A&A 554, A58 (2013) Despite the local nature of the star-formation processes, it has only recently become possible to analyze the M-Z relation for spatially resolved, external galaxies.…”

The evolution of galaxy metallicity scaling relations in cosmological hydrodynamical simulations

“…However, without SN feedback, they were not able to reproduce the observed slope of the relation (and neglect of SN feedback also leads to significant overcooling). Finally, the MZR need not result from the efficiency of winds as a function of stellar mass, but might simply reflect variations in the stellar initial mass function (IMF) (Köppen, Weidner & Kroupa 2007).…”