SUBARU HIGH-z EXPLORATION OF LOW-LUMINOSITY QUASARS (SHELLQs). I. DISCOVERY OF 15 QUASARS AND BRIGHT GALAXIES AT 5.7 < z < 6.9

By Y. Matsuoka, M. Onoue, N. Kashikawa, K. Iwasawa, M. Strauss, Tohru Nagao, M. Imanishi, M. Niida, Y. Toba, M. Akiyama and 29 more. 2016

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We report the discovery of 15 quasars and bright galaxies at 5.7 < z < 6.9. This is the initial result from the Subaru High-z Exploration of Low-Luminosity Quasars project, which exploits the exquisite multiband imaging data produced by the Subaru Hyper Suprime-Cam (HSC) Strategic Program survey. The candidate selection is performed by combining several photometric approaches including a Bayesian probabilistic algorithm to reject stars and dwarfs. The spectroscopic identification was carried out with the Gran Telescopio Canarias and the Subaru Telescope for the first 80 deg2 of the survey footprint. The success rate of our photometric selection is quite high, approaching 100% at the brighter magnitudes (zAB < 23.5 mag). Our selection also recovered all the known high-z quasars on the HSC images. Among the 15 discovered objects, six are likely quasars, while the other six with interstellar absorption lines and in some cases narrow emission lines are likely bright Lyman-break galaxies. The remaining three objects have weak continua and very strong and narrow Lyα lines, which may be excited by ultraviolet light from both young stars and quasars. These results indicate that we are starting to see the steep rise of the luminosity function of z ≥ 6 galaxies, compared with that of quasars, at magnitudes fainter than M1450 ∼ −22 mag or zAB ∼ 24 mag. Follow-up studies of the discovered objects as well as further survey observations are ongoing.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/b12a1926a2e09fa74fe26afe61c9c6ec1ba15ab0

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Citations in the corpus

An ALMA [C ii] Survey of 27 Quasars at z > 5.94 (2018, unknown): “…in the literature at >z 5.5, 119 at >z 6.0, 15 at >z 6.5, and only two at >z 7.0 (see, e.g., Fan et al. 2006; Mortlock et al. 2011; Venemans et al. 2013; Bañados et al. 2016, 2018; Jiang et al. 2016; Matsuoka et al. 2016, 2017; Mazzucchelli et al. 2017; Wang et al. 2017, and references therein).”
Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). V. Quasar Luminosity Function and Contribution to Cosmic Reionization at z = 6 (2018, methodology): “…of high-z quasar candidates imaged by the HSC, and have so far identified 150 candidates over 650 deg2, which include 74 high-z quasars, 25 high-z luminous galaxies, 6 [O III] emitters at z ∼ 0.8, and 45 Galactic cool dwarfs (Matsuoka et al. 2016, 2018a,b, Matsuoka et al. 2018c, in preparation).”
Physical Properties of 15 Quasars at z ≳ 6.5 (2017, methodology): “The frequency of the observations of HSC1205 was tuned for a redshift of z =6.85, in the range of redshifts originally reported in the discovery paper (Matsuoka et al. 2016).”
THE PAN-STARRS1 DISTANT z > 5.6 QUASAR SURVEY: MORE THAN 100 QUASARS WITHIN THE FIRST GYR OF THE UNIVERSE (2016, background): “…e ELAIS1091000446 (J1603+5510) could be a Lyα emitter (see Kashikawa et al. 2015). f HSC J2236+0032 and HSC J2236+0032 have very uncertain redshifts (see Matsuoka et al. 2016). g HSC J1207–0005, HSC J2228+0128, and HSC J2232+0012 are classified as “possible quasars” and they could be…”
The Hyper Suprime-Cam SSP Survey: Overview and Survey Design (2017, methodology): “The UKIDSS and VIKING surveys have also carried out deep near-infrared imaging in the equatorial fields, which is particularly useful for quasar studies (Toba et al. 2015; Matsuoka et al. 2016).”
THE FINAL SDSS HIGH-REDSHIFT QUASAR SAMPLE OF 52 QUASARS AT z > 5.7 (2016, methodology): “Our results suggest that the faint-end slope at ~z 6 may be marginally steeper than –1.5 based on the faintest data points shown in Figure 8, as already pointed out by Kashikawa et al. (2015) and Matsuoka et al. (2016).”
New constraints on lyman-α opacity with a sample of 62 quasars at z > 5.7 (2018, methodology): “Out of these objects, 4 are discovery spectra from the SHELLQs survey, 10 were discovered by Dark Energy Survey– VISTA Hemisphere Survey (DES–VHS, out of which four are currently unpublished), 13 are SDSS discovery spectra, 13 are new reductions of archival data, 19 are adopted from previous studies”
Evolution of the AGN UV luminosity function from redshift 7.5 (2018, background): “These include, but are not limited to, comprehensive surveys for faint high-z quasars selected by broadband photometry (Matsuoka et al. 2016; Wang et al. 2017) or variability (Hönig et al. 2017), infrared-selected highly complete surveys at z ∼ 3 (Schindler et al. 2017; Yang et al. 2018),…”
Great Optically Luminous Dropout Research Using Subaru HSC (GOLDRUSH). I. UV Luminosity Functions at $z \sim 4-7$ Derived with the Half-Million Dropouts on the 100 deg$^2$ Sky (2017, background): “…Willott et al. 2013; Le Fèvre et al. 2013; Kashikawa et al. 2015; Kriek et al. 20154; Wang et al. 2016; Toshikawa et al. 2016; Momcheva et al. 2016; Matsuoka et al. 2016; Pâris et al. 2017; Tasca et al. 2017; Yang et al. 2017; Masters et al. 2017; Matsuoka et al. 2017; Shibuya et al. 2017b; R.…”