The role of metallicity in high mass X-ray binaries in galaxy formation models

Departamento de Ciencias Fisicas, Universidad Andres Bello, Av. Republica 220, Santiago, ChileReceived / AcceptedABSTRACTContext.Recent theoretical works claim that high-mass X-ray binaries could have been important sources of energy feedback intothe interstellar and intergalactic media, playing a major role in both the early stages of galaxy formation and the physical state of theintergalactic medium during the reionization epoch. A metallicity dependence of the production rate or luminosity of the sources is akey ingredient generally assumed but not yet probed.Aims.Our goal is to explore the relation between the X-ray luminosity and star formation rate of galaxies as a possible tracer of ametallicity dependence of the production rates and/or X-ray luminosities of high-mass X-ray binaries.Methods. We developed a model to estimate the X-ray luminosities of star forming galaxies based on stellar evolution modelswhich include metallicity dependences. We applied our X-ray binary models to galaxies selected from hydrodynamical cosmologicalsimulations which include chemical evolution of the stellar populations in a self-consistent way. This allows us to predict the X-rayluminosity – star formation rate relation under different hypotheses for the effects of metallicity.Results. Our models successfully reproduce the dispersion in the observed relations as an outcome of the combined effects of themixture of stellar populations with heterogeneous chemical abundances and the metallicity dependence of the X-ray sources. We findthat the evolution of the X-ray luminosity as a function of the star formation rate of galaxies could store information on possiblemetallicity dependences of the high-mass X-ray sources. A non-metallicity dependent model predicts a non-evolving relation whileany metallicitydependence should affect the slope and the dispersion as a function of redshift. Our results suggest the characteristics ofthe X-ray luminosity evolution can be linked to the nature ofthe metallicity dependence of the production rate or the X-ray luminosityof the stellar sources. By confronting our models with current available observations of strong star-forming galaxies, we find that onlychemistry-dependent models reproduce the observed trend for z < 4. However, with the current available observations is not possibleto prove the nature of this dependence yet.Key words. X-ray: binaries – galaxies: abundances, evolution