Green Peas in X-rays

Reionization of the Universe after the Dark Ages played an important role in the galaxy formation and observability. The source of the ionizing radiation is, however, not yet clearly determined. The main contribution is commonly attributed to strong AGN activity or tremendous star formation. Whether ionizing radiation from high star-forming galaxies can escape to the intergalactic medium is being discussed. Green Peas represent a class of compact high star-forming galaxies that have recently been found to show signatures of the escape of the ionizing flux. In this paper, we present the first measurements of Green Peas in the X-ray domain to constrain their flux at high energies. We reduced the X-ray data of XMM-Newton observations of three Green Peas sources and derived X-ray fluxes of two of them. An upper limit only could be constrained for the last observation, because its exposure was shortened due to contamination by high background flares. We found that the X-ray flux of both measured sources is larger than expected from empirical relations for star-forming galaxies between the X-ray flux and the star formation rate, even considering their metallicity measurements. Our results thus indicate that Green Peas galaxies produce more high-energetic flux than other star-forming galaxies, and can therefore be considered as sources with potentially large significant ionizing radiation escape.