Optical spectroscopy of obscured active galaxies / Espectroscopia óptica de galáxias ativas obscurecidas

AUTOR(ES)
DATA DE PUBLICAÇÃO

1998

RESUMO

We present in this work a study of obscured Active Galaxies which were identified by Sofia Kirhakos in 1990. She verified that surveys at the optical part of the spectrum are not efficient to identify Seyfert nuclei in galaxies observed edge-on. To overcome this difficulty she proposed a selection criterion in which sources identified by the IRAS satellite that were simultaneously X-rays sources in the HEAO-1 catalog were the primary targets for subsequent observations. Optical spectroscopy of these non-identified sources done by Kirhakos revelead that there is an excess of face-on objects among Seyfert 1 galaxies while the Seyfert 2 galaxies were preferentially edge-on objects. The proposed interpretation was that the Seyfert 2 nuclei are obscured Seyfert 1 nuclei. However, the spectral region covered by Kirhakos was in the blue, quite sensitive to reddening effects, Moreover, the signal-to-noise ratio was poor to classify accurately a number of fainter objects. In our work, objects previously classified as AGN and Transition Objects were observed at the Laboratorio Nacional de Astrofísica-Brazil, using the 1.6 m telescope in the region 6000- 10000 Å. Diagnostics based on line emission ratios and FWHM of the lines permited us to better classify the observed objects. We verify that the Transition Objects show characteristics of H II regions and AGN. We also studied the far infrared luminosities and hard X-rays luminosities, and found that they correlate positively, but only until a saturation value. This may indicate the presence of a barrier trapping the IR radiation. We conclude that selection effects play a role to define the classification of some objects, but not all, with the different classes of AGN presenting intrinsically different properties. We also verified that the present classification criteria are not efficient enough to positively define all classes of Active Galactic Nuclei.

ASSUNTO(S)

black holes núcleo ativo de galáxia (agn) galáxias active galactic nuclei (agn) seyfert buracos negros espectroscopia galaxies spectroscopy

ACESSO AO ARTIGO

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