ULX contribution to stellar feedback: an intermediate-mass black hole candidate and the population of ULXs in the low-metallicity starburst galaxy ESO 338-4

Context. 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 10⁴⁰ erg s^-1. We speculate that ESO 338-4 X-1 is powered by accretion on an intermediate-mass (≳300 M_⊙) 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.

Based on observations obtained with the science missions XMM-Newton (ObsID 0780790201) and Chandra (ObsID 21866).