Fine Classification of QSOs and Seyferts for Activity Types Based on SDSS Spectroscopy

Abstract

Using the SDSS spectroscopy, we have carried out fine optical spectral classification for activity types for 710 AGN candidates. These objects come from a larger sample of some 2,500 candidate AGN using pre-selection by various samples; bright objects of the Catalog of Quasars and Active Galactic Nuclei, AGN candidates among X-ray sources, optically variable radio sources, IRAS extragalactic objects, etc. A number of papers have been published with the results of this spectral classification. More than 800 QSOs have been identified and classified, including 710 QSOs, Seyferts and Composites. The fine classification shows that many QSOs show the same features as Seyferts, i.e., subtypes between S1 and S2 (S1.2, S1.5, S1.8 and S1.9). We have introduced subtypes for the QSOs: QSO1.2, QSO1.5, QSO1.8, QSO1.9, though the last subtype does not appear in SDSS wavelength range due to mostly highly redshifted Hα (the main line for identification of the 1.9 subtype). Thus, independent of the luminosity (which serves as a separator between QSOs and Seyferts), AGN show the same features. We also have classified many objects as Composites, spectra having composite characteristics between Sy and LINERs, Sy and HII or LINERs and HII; in some cases all three characteristics appear together resulting as Sy/LINER/HII subtype. The QSOs subtypes together with Seyfert ones allow to follow AGN properties along larger redshift range expanding our knowledge on the evolution of AGN to more distant Universe represented by QSOs.

Fine classification of the emission-line spectra of active galaxies

“…In addition in Table 2, we also describe the types and subtypes used in many known catalogs, such as VCV-13. Some of the spectra are taken from our similar SDSS based classification papers, as here our goal is to explain the most typical features for each type and subtype (Mickaelian et al (2021) and references therein).…”

“…In this paper we give this classification scheme and describe all possible classes and subclasses based on their emission-line features, both main emission lines (H, NII, OIII, OI, SII) and other minor details. Our scheme is based on our research carried out during the last 10-15 years (HyperLEDA (2007), Mickaelian (2015), Mickaelian et al (2007Mickaelian et al ( , 2011Mickaelian et al ( , 2018Mickaelian et al ( , 2021, Gavrilović et al (2007), Abrahamyan (2020), Abrahamyan et al (2018aAbrahamyan et al ( ,b, 2019aAbrahamyan et al ( ,b, 2020, Paronyan et al (2019Paronyan et al ( , 2020, Mikayelyan et al (2019), and many others.) and has a strong observational basis.…”

Analysis of emission line spectra of active galaxies and fine classification for activity types

“…Here we give in Figures 1 and 2 some examples of fine classification spectra. Some of the spectra are taken from our similar SDSS based classification papers, as here our goal is to explain the most typical features for each type and subtype (Mickaelian et al (2021) and references therein).…”

“…In this paper we give this classification scheme and describe all possible classes and subclasses based on their emission-line features, both main emission lines (H, NII, OIII, OI, SII) and other minor details. Our scheme is based on our research carried out during the last 10-15 years (HyperLEDA (2007), Mickaelian (2015), Mickaelian et al (2007Mickaelian et al ( , 2011Mickaelian et al ( , 2018Mickaelian et al ( , 2021, Gavrilovic et al (2007), Abrahamyan (2020) 2019a,b, 2020)), Paronyan et al (2019Paronyan et al ( , 2020, Mikayelyan et al (2019), and many others.) and has a strong observational basis.…”

Changing-look Active Galactic Nuclei. I. Tracking the Transition on the Main Sequence of Quasars

“…A primary feature of the type 1 AGNs is the presence of both broad and narrow emission lines in their spectra, whereas type 2 AGNs show only narrow lines (see, e.g., Weedman 1977;Antonucci 1993;Padovani et al 2017). From the literature, we are aware that the intermediate AGN types (e.g., 1.5 or 1.8; Osterbrock 1981) are primarily based on the gradual weakening of the broad component of the Hα and Hβ emission lines in the spectra (see also Runco et al 2016;Mickaelian et al 2021). Such static classifications based on the study of different AGNs and, more recently, continuous follow-up of single sources, have become blended.…”