Thus, spectroscopic follow-up was often biased against the brightest and potentially most exciting candidates as they were by far the least likely to be QSOs. And at bright levels, where the luminosity function of high- z QSOs plummets towards zero space density, stars vastly outnumber real QSOs. Even though QSO colours differ from star colours to some degree, the scatter in star colours leads to overlapping loci in colour space. Prior to GAIA DR2, ultra-luminous QSOs were discovered only serendipitously, because QSO candidate lists were inflated by staggering contamination from cool stars. 2018) and its unprecedented precision on proper motion measurements. The discovery of SMSS J215728.21−360215.1 (hereafter, J2157−3602) was helped by the Data Release 2 from GAIA (Gaia Collaboration et al. We adopt a standard flat ΛCDM cosmology with parameters H 0 = 70 km s −1 Mpc −1, Ω M = 0.3, and $\Omega _\Lambda = 0.7$. Throughout the paper, 2MASS and WISE magnitudes are used in the Vega system, while optical magnitudes are in the AB system (Oke & Gunn Reference Oke and Gunn1983). Here, we report a newly identified high-redshift QSO with the highest unlensed UV-optical luminosity known at present. ( Reference Wu2015) on the bolometric correction. ( Reference Tsai2015) claim the bolometrically most luminous object in the Universe is the ELIRG WISE J224607.57-052635.0 at z = 4.593 with log L bol/ L ⊙ = 14.54 but disagree with Wu et al. Reference Wu2015) both of them radiate at their Eddington limit. Reference Wang2015), and J0100+2802 at z = 6.3 with a black hole of 12 billion M ⊙ (Wu et al. Reference Liske2008).Īmong optically luminous QSOs at high redshift, the most impressive objects are J0306+1853 at z = 5.36, which is powered by a black hole of 10 billion solar masses (Wang et al. Reference Simcoe2011) and (iv) they will eventually enable the most sensitive direct observations of the expansion of the Universe (Liske et al. Reference Wu2015) (iii) they reveal the metal enrichment in the early universe by shining like beacons through the gas content of high-redshift galaxies along the line-of-sight that are otherwise hard to observe (Ryan-Weber et al. ![]() Reference Lacy2013) at present, we can only measure the masses of their black holes when we have a clear view.įinding the most luminous, optically bright, QSOs is important for several reasons: (i) they point us to the most massive black holes that pose the greatest challenge to any physical growth scenario (ii) they ionise large volumes of neutral gas around them and contribute to cosmic reionisation (Fan, Carilli, & Keating Reference Fan, Carilli and Keating2006a Wu et al. This makes them appear as very luminous quasi-stellar objects (QSOs, Schmidt Reference Schmidt1963) when we have a clear view of the accretion disk around the black hole, and as type-2 QSOs and infrared-luminous galaxies when that view is blocked by dust (e.g. They must have grown at super-Eddington rates for a long period of time, or they originate from massive seed black holes that formed during the dark early ages by direct collapse (Bromm & Loeb Reference Bromm and Loeb2003 Pacucci, Volonteri, & Ferrara Reference Pacucci, Volonteri and Ferrara2015).Ĭurrently, we can only discover such super-massive black holes in the distant early universe while they grow rapidly and accrete vast amounts of matter. How they grew to such mass so early after the Big Bang is a profound puzzle for physics. Surprisingly, we have found such massive black holes already in the early Universe, just 800 million years after the Big Bang (Wu et al. Black holes at the centres of galaxies reach masses of over 10 billion times that of our Sun.
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