The Sloan Digital Sky Survey (SDSS) provides a large number of medium-resolution spectra (spectral resolution is from 1850 to 2200) over the spectral range from 3600A to 10400A, and is a relevant homogeneous database for classification of galaxies. It contains spectra for 4,151,126 objects, most of which, 2,541,424 are galaxies and 680,843 are QSOs (in total, 78%). Most of the important spectral lines (Balmer lines, OIII, OII, OI, NII, SII, etc.) for most of active galaxies are in this range (excluding very high-z galaxies displaying redshifted Lyman, MgII, CIII, CIV and other lines at these wavelengths). We have used SDSS spectra for the classification for activity types of a number of samples, from X-ray to radio, including the Markarian (Mrk) galaxies, X-ray selected AGN, ULIRGs/HLIRGs, Blazars from BZCAT, a sample of radio variable objects from NVSS/FIRST cross-correlations, etc. We aimed at obtaining homogeneous classifications of all these objects by means of the SDSS spectra. In addition, SDSS spectra provide many spectral features and details that were not available before, when using the old spectra. Three diagnostic diagrams and eye examination have been used and the combined activity types have been derived. A fine classification scheme was developed, where QSOs have subtypes like Seyferts (S1.0/Q1.0, S1.2/Q1.2, etc.), Narrow Line QSOs are introduced (NLQ), subclasses for Narrow Line Seyfert 1s and NLQs are used (NLS1.0/NLQ1.0, NLS1.2/NLQ1.2, etc.) and Composite spectrum objects have their subtypes (S2/LINER, S2/HII, LINER/HII, also S2/LINER/HII). This classification scheme much better describes all fine details in the optical spectra and allows further study of active galaxies by the subtypes for better understanding the Unified model and the physical properties of AGN and Starbursts. The new scheme has 6 sequences: Broad Line QSOs, Broad Line Seyferts, Narrow Line QSOs, Narrow Line Seyferts, Narrow Line Active Galaxies (S2, LINER, HII/Starburst) and Composite Spectrum Objects. A webpage with this new classification scheme has been built (https://www.bao.am/activities/projects/21AG-1C053/mickaelian/).
Dr. Areg Mickaelian is the Head of the Research Department at the Byurakan Astrophysical Observatory (BAO) in Armenia. As the BAO Director since 2017, he has held pivotal roles in international astronomical bodies, including the International Astronomical Union (IAU) South West and Central Asian region. Dr. Mickaelian's research spans diverse astronomical phenomena, from blue stellar objects to extragalactic radio sources. Actively engaged in projects like the Revelation of Early Stages of Galaxies Evolution, his commitment to advancing cosmic understanding is evident. Dr. Mickaelian has made significant academic contributions throughout his career through visits to esteemed institutions globally. He has garnered numerous honors, including the Republic of Armenia President's Annual Prize in Physics, the World Summit Award for the best e-Science Project, Top-100 Most Productive Scientists of Armenia, Tigran Metz medal from Aspetats Academy of International Security (2017), Russian International Academy of Tourism medal (2019). He has 425 publications, according to NASA/ADS, including 168 papers in refereed journals, 131 proceedings of meetings, 24 books and booklets, 17 papers in books, 22 electronic catalogs, etc.