Ji-Jia Tang(ASIAA, NTU), Tomotsugu Goto(NTHU), Youichi Ohyama(ASIAA), Chichuan Jin(MPIE), Chris Done(U of Durham)
We explore the early growth of supermassive black holes (SMBHs) by using a near-infrared (NIR) spectrum of a recently discovered z = 6.621 QSO PSO J006+39 in three physical properties: (1) According to the standard thin disk model, the NIR (rest-frame FUV) spectrum of this QSO is dominated by the emission from the accretion disk. We found that the power-law slope of the continuum αλ of this QSO in NIR, −2.94 ± 0.03, is much bluer than the expected slope −1.5 from the standard thin disk model. We will discuss two possibilities to explain this unique slope: the black hole spin and the Comptonisation corona of the accretion disk. (2) The growth rate can be estimated by the Eddington ratio (Lbol/LEdd). We first estimated the SMBH mass by using the Mg ii line width and the rest frame luminosity L3000Å to be ∼ 108 M⊙ . Then we derived Eddington ratio Lbol/LEdd ∼ 1. (3) There are surprisingly many metal-rich QSOs found in the early universe, given the required time for metal formation. We present two probes to estimate the metallicity of this QSO. The Fe ii/Mg ii ratio is often used as an indicator for high-z QSOs because Fe metallicity requires a certain time to be enhanced by the Type-Ia supernovae. The detection of the faint He ii line in this QSO provides another path to measure the metallicity. We used N v/He ii ratio to estimate the metallicity by considering the blue FUV continuum in the photoionization calculation. We will discuss implications of these physical properties of this QSO about the growth of SMBHs in the early universe.