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An Unobscured Type II Quasar Candidate: SDSS J012032.19-005501.9

【标题】An Unobscured Type II Quasar Candidate: SDSS J012032.19-005501.9

【Title】An Unobscured Type II Quasar Candidate: SDSS J012032.19-005501.9

【DOI】10.1088/0004-6256/149/2/75

【作者】 W. Yuan; Y. Li; 周宏岩; S. Komossa; Y. L. Ai; W. J. Liu; J. H. Boisvert

【Author】 W. Yuan ; Y. Li ; Zhou Hongyan ; S. Komossa ; Y. L. Ai ; W. J. Liu ; J. H. Boisvert

【期刊】The Astronomical Journal

【Journal】The Astronomical Journal

【期刊年份】2015

【卷】149

【期】2

【关键词】 black hole physics, galaxies: active, galaxies: nuclei, galaxies: Seyfert

【Keywords】 black hole physics, galaxies: active, galaxies: nuclei, galaxies: Seyfert

【摘要】We report the finding of an unobscured type II active galactic nucleus (AGN) candidate, SDSS J012032.19-005501.9, at a relatively high redshift of 0.601, which shows a number of unusual properties. It varies significantly on timescales of years, typical of type I AGNs, and marginally on timescales of weeks. The color-magnitude relation and the structure function are also consistent with that of type I AGNs, which implies that its variability likely originates from the black hole accretion system. However, no broad emission line (BEL) is detected in the Sloan Digital Sky Survey spectrum, and the upper limit of the equivalent width of the Hβ BEL is much less than that of type I AGNs. These properties suggest that SDSS J012032.19-005501.9 may be an unobscured quasar without intrinsically broad emission lines, namely, an unobscured type II AGN or “true” type II AGN. Furthermore, its continuum luminosity is at least one order of magnitude fainter than the average value over the past century from the [O iii] emission line. This indicates that SDSS J012032.19-005501.9 may be switching off. Additional possible scenarios to explain this intriguing source are also discussed. Future deep observations at multiwavelengths are needed to reveal the nature of this peculiar and intriguing AGN.

【Abstract】We report the finding of an unobscured type II active galactic nucleus (AGN) candidate, SDSS J012032.19-005501.9, at a relatively high redshift of 0.601, which shows a number of unusual properties. It varies significantly on timescales of years, typical of type I AGNs, and marginally on timescales of weeks. The color-magnitude relation and the structure function are also consistent with that of type I AGNs, which implies that its variability likely originates from the black hole accretion system. However, no broad emission line (BEL) is detected in the Sloan Digital Sky Survey spectrum, and the upper limit of the equivalent width of the Hβ BEL is much less than that of type I AGNs. These properties suggest that SDSS J012032.19-005501.9 may be an unobscured quasar without intrinsically broad emission lines, namely, an unobscured type II AGN or “true” type II AGN. Furthermore, its continuum luminosity is at least one order of magnitude fainter than the average value over the past century from the [O iii] emission line. This indicates that SDSS J012032.19-005501.9 may be switching off. Additional possible scenarios to explain this intriguing source are also discussed. Future deep observations at multiwavelengths are needed to reveal the nature of this peculiar and intriguing AGN.

【基金/项目】 the Natural Sciences Foundation of China (grant No. 11033007, 11103071 and 11273027) ; the Strategic Priority Research Program of the Chinese Academy of Sciences (grant No. XDB09000000) ; Chinese Natural Science Foundation (NSFC-11473025) ; the 973 project (2013CB834905) ; Chinese Polar Environment Comprehensive Investigation & Assessment Programmes (CHINARE-2014-02-03)

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