We present the analysis of a new near-infrared ( NIR ) spectrum of a recently discovered z = 6.621 quasar PSO J006+39 in an attempt to explore the early growth of supermassive black holes ( SMBHs ) .
This NIR ( rest-frame ultraviolet , UV ) spectrum shows blue continuum slope and rich metal emission lines in addition to Ly \alpha line .
We utilize the \ion { Mg } { II } line width and the rest frame luminosity L _ { \text { 3000 \AA } } to find the mass of SMBH ( M _ { \text { BH } } ) to be \sim 10 ^ { 8 } M _ { \odot } , making this one of the lowest mass quasars at high redshift .
The power-law slope index ( \alpha _ { \lambda } ) of the continuum emission is -2.94 \pm 0.03 , significantly bluer than the slope of \alpha _ { \lambda } = -7 / 3 predicted from standard thin disc models .
We fit the spectral energy distribution ( SED ) using a model which can fit local SMBHs , which includes warm and hot Comptonisation powered by the accretion flow as well as an outer standard disc .
The result shows that the very blue slope is probably produced by a small radial ( \sim 230 gravitational radius , R _ { \text { g } } ) extent of the standard accretion disc .
All plausible SED models require that the source is super-Eddington ( L _ { \text { bol } } / L _ { \text { Edd } } \gtrsim 9 ) , so the apparently small disc may simply be the inner funnel of a puffed up flow , and clearly the SMBH in this quasar is in a rapid growth phase .
We also utilize the rest-frame UV emission lines to probe the chemical abundance in the broad line region ( BLR ) of this quasar .
We find that this quasar has super solar metallicity through photoionization model calculations .