Metallicity dependence of high-mass X-ray binary populations

DOUNA, V.M.; PELLIZZA, L.J.; MIRABEL, I.F.; PEDROSA, S.E.

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2015 vol. 579 p. 1 - 9

0004-6361

Context. High-mass X-ray binaries (HMXBs) might have contributed anon-negligible fraction of the energy feedback to the interstellar andintergalactic media at high redshift, becoming important sources for theheating and ionization history of the Universe. However, the importanceof this contribution depends on the hypothesized increase in the numberof HMXBs formed in low-metallicity galaxies and in their luminosities. Aims: In this work we test the aforementioned hypothesis, andquantify the metallicity dependence of HMXB population properties. Methods: We compile from the literature a large set of data on thesizes and X-ray luminosities of HMXB populations in nearby galaxies withknown metallicities and star formation rates. We use Bayesian inferenceto fit simple Monte Carlo models that describe the metallicitydependence of the size and luminosity of the HMXB populations. Results: We find that HMXBs are typically ten times more numerous perunit star formation rate in low-metallicity galaxies (12 + log (O / H)< 8, namely <20% solar) than in solar-metallicity galaxies. Themetallicity dependence of the luminosity of HMXBs is small compared tothat of the population size. Conclusions: Our results support thehypothesis that HMXBs are more numerous in low-metallicity galaxies,implying the need to investigate the feedback in the form of X-rays andenergetic mass outflows of these high-energy sources during cosmic dawn.