Trial of “Radio Fingerprint Authentication” on galaxies
~ Molecular catalog on the three nearby galaxies was completed! ~

In the universe, there are luminous galaxies which emit intensive radiation. One class of galaxy has “active galactic nuclei (AGNs)” that release enormous energy from super massive black holes as power sources. Another class is known as a “starburst galaxy” where many massive stars are born in relatively short intervals. The energy sources of these two types of galaxies derive from different physical phenomena. Although they may be related to galactic evolution, the relationship is uncertain. One reason for this uncertainty is that the active central regions of the galaxies have large amounts of gas and dust, which make observations at optical wavelengths difficult. However, radio telescopes can receive spectral frequencies from molecular gas in these active regions. Therefore, the central activities of AGNs and starburst galaxies can be studied with radio observations.
With the Nobeyama 45-m radio telescope, the research team led by Prof. Shuro Takano (Nihon University) and Dr. Taku Nakajima (Nagoya University) observed three famous nearby galaxies: NGC 1068 (M 77), which harbors an AGN, and two typical starburst galaxies, NGC 253 and IC 342. These observations were performed as one of the Nobeyama Legacy Projects using a type of observations called molecular line surveys. This project ran from 2007 to 2012. With a long allocated time of about 500 hours, the researchers observed a large number of molecular lines systematically in a ~30 GHz width, in the 3 mm wavelength region that is appropriate for the 45-m radio telescope.
As results of the observations, 25 atomic hydrogen and assorted molecular emission lines were detected in NGC 1068, 34 such lines were detected in NGC 253, and 31 such lines detected in IC 342. The data of highest spatial resolution in the wavelength region were obtained with the 45-m telescope, one of the largest radio telescopes operating at millimeter wavelengths. High spatial-resolution molecular line catalogs for the central regions of the three galaxies were completed, with the one for IC 342 reported for the first time. The observations revealed that the CN (cyanide) radical, HCN, and their isotopic species in the AGN host galaxy, NGC 1068, are more abundant than those in the starburst galaxies, NGC 253 and IC 342.
By applying such methods to other galaxies, “Radio fingerprint authentication” to distinguish the activity of the supermassive black hole in central regions of AGNs will be expected.
One observational report was published in “Publications of the Astronomical Society of Japan” (PASJ) on February 19, 2018 and another was done as an online paper on March 30, 2019 and will be printed in the Nobeyama special issue of PASJ*.
*It has been published on December 2019.