Scientific article
English

A census of ultraluminous X-ray sources in the local Universe

Published inMonthly notices of the Royal Astronomical Society, vol. 498, no. 4, p. 4790-4810
Publication date2020-09-29
First online date2020-08-17
Abstract

Using the Chandra Source Catalog 2.0 and a newly compiled catalogue of galaxies in the local Universe, we deliver a census of ultraluminous X-ray source (ULX) populations in nearby galaxies. We find 629 ULX candidates in 309 galaxies with distance smaller than 40 Mpc. The foreground/background contamination is $\sim \! 20{{\ \rm per\ cent}}$. The ULX populations in bona fide star-forming galaxies scale on average with star formation rate and stellar mass (M⋆) such that the number of ULXs per galaxy is $0.45^{+0.06}_{-0.09}\times \frac{\rm SFR}{\rm M_\odot \, yr^{-1}}{+}3.3^{+3.8}_{-3.2}\times \frac{M_\star }{\rm M_\odot }$. The scaling depends strongly on the morphological type. This analysis shows that early spiral galaxies contain an additional population of ULXs that scales with M⋆. We also confirm the strong anticorrelation of the ULX rate with the host galaxy’s metallicity. In the case of early-type galaxies, we find that there is a non-linear dependence of the number of ULXs with M⋆, which is interpreted as the result of star formation history differences. Taking into account age and metallicity effects, we find that the predictions from X-ray binary population synthesis models are consistent with the observed ULX rates in early-type galaxies, as well as spiral/irregular galaxies.

Funding
  • European Commission - Accreting binary populations in Nearby Galaxies: Observations and Simulations [617001]
  • European Commission - Development of Novel Statistical Tools for the Analysis of Astronomical Data [691164]
Citation (ISO format)
KOVLAKAS, Konstantinos et al. A census of ultraluminous X-ray sources in the local Universe. In: Monthly notices of the Royal Astronomical Society, 2020, vol. 498, n° 4, p. 4790–4810. doi: 10.1093/mnras/staa2481
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Journal ISSN0035-8711
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