ULX contribution to stellar feedback: an intermediate-mass black hole candidate and the population of ULXs in the low-metallicity starburst galaxy ESO338-4

Oskinova, L. M., Bik, A., Mas Hesse, J. M., Hayes, M., Adamo, A., Ostlin, G., Furst, F., Oti Floranes, H. 2019. ULX contribution to stellar feedback: an intermediate-mass black hole candidate and the population of ULXs in the low-metallicity starburst galaxy ESO338-4. Astronomy and Astrophysics 627, DOI: 10.1051/0004-6361/201935414

X-ray radiation from accreting compact objects is an important part of stellar feedback. The metal-poor galaxy ESO 338-4 has experienced vigorous starburst during the last <40 Myr and contains some of the most massive super star clusters in the nearby Universe. Given its starburst age and its star-formation rate, ESO 338-4 is one of the most efficient nearby manufactures of neutron stars and black holes, hence providing an excellent laboratory for feedback studies.

Aims. We aim to use X-ray observations with the largest modern X-ray telescopes XMM-Newton and Chandra to unveil the most luminous accreting neutron stars and black holes in ESO 338-4.

Methods. We compared X-ray images and spectra with integral field spectroscopic observations in the optical to constrain the nature of strong X-ray emitters.

Results. X-ray observations uncover three ultraluminous X-ray sources (ULXs) in ESO 338-4. The brightest among them, ESO 338 X-1, has X-ray luminosity in excess of 10(40) erg s(-1). We speculate that ESO 338-4 X-1 is powered by accretion on an intermediate-mass (greater than or similar to 300 M-circle dot)black hole. We show that X-ray radiation from ULXs and hot superbubbles strongly contributes to He II ionization and general stellar feedback in this template starburst galaxy.

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