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Using the Spektr-RG (SRG) space observatory, astronomers from the Russian Academy of Sciences have investigated dozens of X-ray sources in all-sky surveys, which resulted in the detection of 11 new active galactic nuclei. The finding was reported in a research paper in Astronomy Letters.

Active galactic nuclei (AGNs) are small regions at the center of a galaxy dominated by the light emitted by dust and gas. They are more luminous than the surrounding galaxy's light and also very energetic due either to the presence of a black hole or star formation activity at the core of the galaxy. In general, AGNs are the most luminous persistent sources of electromagnetic radiation in the universe.

A group of astronomers led by Grigory Uskov is conducting an inspection of X-ray sources discovered with SRG's ART-XC telescope and also previously known X-ray sources whose nature remains unknown. So far, their studies have resulted in the identification of more than 50 AGNs and several cataclysmic variables. Now, they report their newest findings.

"In this paper we present the results of our optical identification and classification of another 11 AGNs from the ARTSS1-5 catalog," the researchers wrote.

All the 11 newly found AGNs turned out to be located relatively nearby, at redshifts of 0.028-0.258. The X-ray luminosities of these sources are within the range of 2 to 300 tredecillion erg/s, therefore typical for AGNs at the present epoch.

Based on the collected data, the astronomers classified the galaxies of the 11 AGNs as Seyfert galaxies—seven type 1 (Sy 1), three type 1.9 (Sy 1.9) and one type 2 (Sy 2). In general, Seyfert galaxies are the most common active galaxies. Although they look like normal galaxies in visible light, they emit considerable infrared radiation, having broad optical emission lines, the latter with narrower emission lines. Observations show that Sy 1 galaxies have broad optical emission lines, while those of Sy 2 type showcase narrower emission lines.

The researchers also calculated the masses of black holes of the seven Seyfert galaxies reported in the paper. It was found that their masses are between 4.68 and 150 million solar masses.

According to the study, the spectrum of one of the new AGNs, designated SRGA J000132.9+240237, is described by a power law with a slope smaller than 0.5, which suggests a strong absorption and a significant contribution of the radiation reflected from the galaxy's dusty torus. The authors of the paper noted that longer X-ray observations are required to determine the physical properties of this AGN.

"We are planning to take a higher-quality X-ray spectrum of this source in the pointing mode with the SRG/ART-XC telescope to study in detail its physical properties," the scientists wrote.

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