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- Seminars and Workshops
- Institute of Astronomy and Astrophysics
- Location
R1203 of the Astronomy-Mathematics Building, National Taiwan University
- Speaker Name
Yu-Heng Lin (USA)
- State
Definitive
- Url
Identify the ionization source of the Lyα emitter at z~3
2021-02-24 14:00 - 15:30
We present S82-20, an unusual object identified at redshift z~ 3 from excess g-band imaging in SDSS-Stripe 82. The rest frame ultraviolet spectrum of this object shows emission lines from highly ionized species, including HeII λ1640 and CIV λλ 1548, 1550 doublets and OVI λλ 1032, 1038 doublets. The high Lyα luminosity (3.5x10^44 erg/s), the high emission line EWs ( >200\AA for Lyα), the FWHM of the emission lines ( <800 km/s), and the detection of the high ionization OVI line strongly support the interpretation that S82-20 is a Type II QSO. However, some evidence suggests that the Type II QSO interpretation may not be sufficient to explain all the available observables, as the CIV/HeII ratio is not fully reproduced by photonionization models of AGN only, and requires either some contribution from metal rich star-formation or high velocity shocks. Fully understanding the ionization power of S82-20 is crucial. If indeed it is a Type~II QSO, it would be likely missed in searches based on the detection at WISE wavelengths. This in turn would imply that our current estimates of the overall accretion rate of the QSO population may be underestimated.
