2025/02/11 by Q. Daniel Wang, Juergen Ott, J. Ott +2 · 1 voice · 1 citation
Mathematics · Physics and Astronomy · #Astrophysical Phenomena and Observations #History and Theory of Mathematics #astro-ph.HE
paper · pdf · doi:10.48550/arxiv.2502.07304
openalex publication_date 2025/02/11 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We explore what unusual products a starburst of about 6% solar metallicity and a mean estimated age of ~0.5 Myr can produce in KUG 1138 + 327 at a distance of 24.5 Mpc. Chandra X-ray observations show a dominant point-like source with an average 0.3-10 keV luminosity of 1040.3 erg/s and variability by a factor of ~2 over months. This extreme ultraluminous X-ray source (ULX) is apparently associated with the young central cluster. A multicolor disk modeling of the X-ray spectrum of the source suggests a standard accretion around a black hole. It also has a morphologically elongated nonthermal radio continuum counterpart on the scale of ~200 pc, probably the longest detected from such a source. The radio, optical, and X-ray findings suggest that it could well be an intermediate-mass black hole undergoing sub-Eddington accretion from a massive star companion. Accounting for the presence of the ULX and the prominent emission lines HeIIλ4658 and [ArIV]λ4711 while lacking Wolf-Rayet spectral features, we estimate the true age of the starburst to be about 2-4 Myr. Only with such a moderate age can the starburst host this extraordinary ULX, probably triggered by a recent influx of extremely low-metallicity gas. This study demonstrates the potential of multiwavelength studies of low-metallicity starbursts to provide insights into what may commonly occur in high-redshift galaxies.