Astronomical School’s Report, 2020, Volume 16, Issue 1, Pages 1–7
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UDC 524.7; 520.6; 519.6

Extragalactic X-ray discrete sources

Zadorozhna L.V., Tugay A.V., Shevchenko S.Yu.

Taras Shevchenko National University of Kyiv, Hlushkova Avenue 4a, 03127 Kyiv, Ukraine


Extra-galactic X-ray research with the launch of XMM-Newton has become the forefront of X-ray astronomy. X-ray sources outside our galaxy are the other galaxies – normal galaxies, radio galaxies, quasars, blazars, Seyfert galaxies, as well as extended sources in galaxy clusters – the glow of cluster's halo. X-ray space observatory's equipment reach a high level of angular separation that allow to discern the individual sources within the galaxies nearest to us. The observations have shown that X-rays from galaxies are mainly the radiation of the central region – the active nucleus of the galaxy, which, according to generally accepted theory, is the radiation from the central supermassive black hole, and the set of X-ray sources in the galaxy's disk. Such sources could be the areas of star formation, the populations of X-ray binaries, etc. We cross-correlate the 4XMM-DR9 catalog and the HyperLeda galaxy database. The 4XMM-DR9 catalog contains 550124 unique sources covering 2.85% of the sky. As a result, we received 1207 galaxies with an X-ray flux exceeding 10-13 erg/(сm2·s). This range was chosen, since a spectrum could be constructed for such sources; therefore, they are of particular interest. About 600 galaxies from our sample were identified and classified. The leading place is occupied by galaxies whose optical angular sizes are in the range exceed 60″, total number of such galaxies is 364. Among them, 19 galaxies are in clusters with a bright X-ray halo; 20 galaxies without an X-ray nucleus; 13 galaxies don't have X-ray radiation within a specified range. Most galaxies have an extended core with a visible surface distribution of brightness, which decreases from the center to the periphery. With more than one X-ray source, we have 184 galaxies. In future, it will be interesting to obtain spectra and light curves of the discrete X-ray sources in galaxies for a more detailed study of their radiation's nature.

Keywords: X-ray galaxy; 4XMM-DR9 catalog; HyperLeda; active galaxy nuclei; extragalactic discrete X-ray sources; Seyfert galaxies; quasars; cluster's halo


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