S19B0093abst
S19B0093
The formation of supermassive black holes (SMBHs) has been a long-standing, fundamental subject of astronomy. Hundreds of QSOs have been discovered back to z∼7. The most recent observation has revealed a QSO with black hole mass of ∼8 × 108 M⊙ at zspec. = 7.54. The formation mechanism of such SMBHs, however, is still under much debate and further observational constrains at higher redshift are required. In this proposal, we aim at spectroscopically confirming a robust QSO candidate at z∼8.1 with Keck/MOSFIRE. The target was recently identified in our HST observing program, the Brightest of Re-ionizing Galaxies (BoRG), which aims at searching bright galaxy and QSO candidates in the early universe. Among candidates that are selected with the color cut selection/photometric redshift analysis/point-source morphology, this target is sufficiently bright (J125 = 25 mag), and the Lyα emission line will be obtained at 7.6 σ with 5 hr on-source exposure with MOSFIRE/Y-band. Upon the detection of Lyα, we not only confirm the highest redshift QSO (and therefore the number density, too), but also earn opportunity to infer the neutral hydrogen fraction at this redshift.
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