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http://hdl.handle.net/20.500.12386/32059
Titolo: | A Peculiar Type~II QSO Identified via Broad-band Detection of Extreme Nebular Line Emission | Autori: | Yu-Heng Lin Claudia Scarlata Matthew Hayes Anna Feltre Stephane Charlot BONGIORNO, ANGELA Petri Väisänen Moses Mogotsi |
Data pubblicazione: | 2022 | Rivista: | MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY | Numero: | 509 | Fascicolo: | 1 | Da pagina:: | 489 | Abstract: | We present S82-20, an unusual redshift $\approx$3 object identified in SDSS-Stripe 82 broad-band images. The rest-frame ultraviolet spectrum of S82-20 shows emission lines from highly ionized species, including HeII $\lambda$1640, and the CIV $\lambda\lambda$1548, 1550 and OVI $\lambda\lambda$1032, 1038 doublets. The high Ly$\alpha$ luminosity ($3.5\times 10^{44}$ erg s$^{-1}$), the high emission line equivalent widths ($>200$\r{A} for Ly$\alpha$), the FWHM of the emission lines ($<800$km s$^{-1}$), and the high ionization OVI line strongly support the interpretation that S82-20 is a Type~II QSO. However, photoionization models using Type~II QSO do not fully explain the measured CIV/HeII line ratio, which requires either some contribution from star-formation or high velocity shocks. Additionally, S82-20 is not detected at wavelengths longer than 2$\mu$m, in tension with the expectation of isotropically IR emission of a luminous QSO. We consider the possibility that S82-20 is a rare example of a changing-look QSO, observed in a temporarily low state, where the broad line region has faded, while the narrow line region still emits emission line. Otherwise, it may be a rare case of the short phase of the life of a massive galaxy, in which active star formation and accretion onto a supermassive black hole coexist. | URI: | http://hdl.handle.net/20.500.12386/32059 | URL: | http://arxiv.org/abs/2111.03678v1 https://academic.oup.com/mnras/article/509/1/489/6400119?login=true |
ISSN: | 0035-8711 | DOI: | 10.1093/mnras/stab2978 | Fulltext: | open |
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