Oral Presentation
One step toward understanding cosmic re-ionization: absorption tests with a new QSO we discovered at z=6.6
Presenter: Tomo Goto (NTHU)
Investigating the Gunn-Peterson trough of high redshift quasars (QSOs) is a powerful way to reveal the cosmic reionization. As one of such attempts, we perform a series of absorption tests with one of the highest redshift QSOs, PSO J006.1240+39.2219 at z = 6.62 we previously discovered. Using the Subaru telescope, we obtained medium-resolution spectra with a total exposure time of 7.5 hours. We calculate the Lya transmission in different redshift bins to determine the near zone radius and the optical depth (tau). We find a sudden change in the Lya transmission at 5.716, we have detected flux. Thus, tau is lower than previously measured. Due to the improved depths and resolution of the spectra, we possibly detect faint flux previous work missed. The near zone radius of the QSO is 5.79±0.09 pMpc, which is consistent with the decreasing near zone size at higher redshift. We also analyze the dark gap distributions to probe the neutral hydrogen fractions beyond the saturation limit of the Gunn-Peterson trough. We find the median of the dark gap width becomes larger with increasing redshift. In contrast to these three analyses, we perform a model free analysis by counting dark pixels, to find the upper limit of x_i<0.6 (0.8) at z<6 (z>6). All four analyses based on this QSO show increasingly neutral hydrogen towards higher redshifts, adding precious measurements at z>6.5.
Using the deep near-infrared (NIR) spectrum we obtained with Gemini/GNIRS, we explore the early growth of supermassive black holes (SMBHs). This NIR (rest-frame UV) spectrum shows blue continuum slope and rich metal emission lines in addition to Lya line. We utilize the [MgII] line width and the rest frame luminosity L3000Å to find the MBH to be 10^8Msun, making this one of the lowest mass QSOs at z>6. The power-law slope of the continuum emission is 2.94±0.03, significantly bluer than the slope of -7/3 predicted from standard thin disc models. We fit the spectral energy distribution (SED) using a model which can fit local SMBH, 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 (230Rg) extent of the standard accretion disc. All the SED fits require that the source is super-Eddington (Lbol/LEdd>9), so the apparently small disc may simply be the inner funnel of a puffed up flow, but clearly the SMBH in this QSO is in a rapid growth phase.
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