A team of researchers led by Andrea Maselli of the Institute of Space Astrophysics and Space Physics of Palermo, Italy, campaigned to observe a group of radio sources unrelated to known sources in other bands of the electromagnetic spectrum using NASA's Swift Space Observatory. These observations were aimed at revealing the true nature of these hitherto unidentified sources.
Maselli and his team recently observed 21 bright radio sources from the Swift satellite, which are included in the updated Third Cambridge Catalog of Radio Sources (3CR). This catalog contains radio sources discovered at 178 MHz, the study of which can deepen our knowledge of the nature and evolution of intensely emitting radio galaxies and quasars.
However, some of the sources described in the 3CR catalog, including those found with the NRAO VLA Sky Survey (NVSS), have not only never been observed in the X-ray range before, but, in fact, have remained completely unidentified until now. that is, unrelated to their corresponding sources in the optical or infrared ranges.
In this new study, conducted by Mazelli's team, each of the 21 studied sources was observed with two telescopes aboard the Swift satellite, an X-ray telescope and an optical / UV telescope.
According to this study, out of 21 sources studied, nine sources exhibit very intense radiation in "soft" X-rays. Scientists were able to match infrared sources to these nine sources in a catalog compiled using the AllWISE (All Wide-field Infrared Survey Explorer) sky survey, in addition, a similar correspondence with infrared sources from this catalog was established for four sources from the studied pool. not emitting in soft X-ray.
The results of this study, to some extent, surprised its authors, since no correspondence was found for any of the studied radio sources in the optical / UV ranges. According to a working hypothesis put forward by Mazelli's team, this may be due to the fact that these unidentified radio sources are active galaxies enveloped in dense clouds of dust, but additional spectroscopic observations are required to test this assumption.
The study was published in the Monthly Notices of the Royal Astronomical Society.