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Title: First Discoveries of z > 6 Quasars with the DECam Legacy Survey and UKIRT Hemisphere Survey

Abstract

We present the first discoveries from a survey of z ≳ 6 quasars using imaging data from the DECam Legacy Survey (DECaLS) in the optical, the UKIRT Deep Infrared Sky Survey (UKIDSS) and a preliminary version of the UKIRT Hemisphere Survey (UHS) in the near-IR, and ALLWISE in the mid-IR. DECaLS will image 9000 deg{sup 2} of sky down to z {sub AB} ∼ 23.0, and UKIDSS and UHS will map the northern sky at 0 < decl. < +60°, reaching J {sub VEGA} ∼ 19.6 (5- σ ). The combination of these data sets allows us to discover quasars at redshift z ≳ 7 and to conduct a complete census of the faint quasar population at z ≳ 6. In this paper, we report on the selection method of our search, and on the initial discoveries of two new, faint z ≳ 6 quasars and one new z = 6.63 quasar in our pilot spectroscopic observations. The two new z ∼ 6 quasars are at z = 6.07 and z = 6.17 with absolute magnitudes at rest-frame wavelength 1450 Å being M {sub 1450} = −25.83 and M {sub 1450} = −25.76, respectively. These discoveries suggest that we canmore » find quasars close to or fainter than the break magnitude of the Quasar Luminosity Function (QLF) at z ≳ 6. The new z = 6.63 quasar has an absolute magnitude of M {sub 1450} = −25.95. This demonstrates the potential of using the combined DECaLS and UKIDSS/UHS data sets to find z ≳ 7 quasars. Extrapolating from previous QLF measurements, we predict that these combined data sets will yield ∼200 z ∼ 6 quasars to z {sub AB} < 21.5, ∼1000 z ∼ 6 quasars to z {sub AB} < 23, and ∼30 quasars at z > 6.5 to J {sub VEGA} < 19.5.« less

Authors:
; ; ; ;  [1]; ; ; ;  [2];  [3];  [4];  [5];  [6]; ;  [7];  [8];  [9];  [10]; ;  [11] more »; « less
  1. Department of Astronomy, School of Physics, Peking University, Beijing 100871 (China)
  2. Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)
  3. Research School of Astronomy and Astrophysics, Australian National University, Weston Creek, ACT 2611 (Australia)
  4. Department of Astronomy, University of Michigan, 311 West Hall, 1085 S. University Avenue, Ann Arbor, MI, 48109 (United States)
  5. National Optical Astronomy Observatory, 950 N. Cherry Avenue, Tucson, AZ 85719 (United States)
  6. School of Physics and Astronomy, Nottingham University, University Park, Nottingham, NG7 2RD (United Kingdom)
  7. Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071 (United States)
  8. Cerro Tololo Inter-American Observatory, Casilla 603 La Serena (Chile)
  9. Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China)
  10. Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, Ontario, M5S 3H4 (Canada)
  11. Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ (United Kingdom)
Publication Date:
OSTI Identifier:
22661153
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 839; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; EMISSION; GALAXIES; QUASARS; RED SHIFT

Citation Formats

Wang, Feige, Yang, Jinyi, Wu, Xue-Bing, Yang, Qian, Li, Zefeng, Fan, Xiaohui, McGreer, Ian D., Ding, Jiani, Green, Richard, Bian, Fuyan, Li, Jiang-Tao, Dey, Arjun, Dye, Simon, Findlay, Joseph R., Myers, Adam D., James, David, Jiang, Linhua, Lang, Dustin, Lawrence, Andy, Ross, Nicholas P., and and others. First Discoveries of z > 6 Quasars with the DECam Legacy Survey and UKIRT Hemisphere Survey. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA689F.
Wang, Feige, Yang, Jinyi, Wu, Xue-Bing, Yang, Qian, Li, Zefeng, Fan, Xiaohui, McGreer, Ian D., Ding, Jiani, Green, Richard, Bian, Fuyan, Li, Jiang-Tao, Dey, Arjun, Dye, Simon, Findlay, Joseph R., Myers, Adam D., James, David, Jiang, Linhua, Lang, Dustin, Lawrence, Andy, Ross, Nicholas P., & and others. First Discoveries of z > 6 Quasars with the DECam Legacy Survey and UKIRT Hemisphere Survey. United States. doi:10.3847/1538-4357/AA689F.
Wang, Feige, Yang, Jinyi, Wu, Xue-Bing, Yang, Qian, Li, Zefeng, Fan, Xiaohui, McGreer, Ian D., Ding, Jiani, Green, Richard, Bian, Fuyan, Li, Jiang-Tao, Dey, Arjun, Dye, Simon, Findlay, Joseph R., Myers, Adam D., James, David, Jiang, Linhua, Lang, Dustin, Lawrence, Andy, Ross, Nicholas P., and and others. Mon . "First Discoveries of z > 6 Quasars with the DECam Legacy Survey and UKIRT Hemisphere Survey". United States. doi:10.3847/1538-4357/AA689F.
@article{osti_22661153,
title = {First Discoveries of z > 6 Quasars with the DECam Legacy Survey and UKIRT Hemisphere Survey},
author = {Wang, Feige and Yang, Jinyi and Wu, Xue-Bing and Yang, Qian and Li, Zefeng and Fan, Xiaohui and McGreer, Ian D. and Ding, Jiani and Green, Richard and Bian, Fuyan and Li, Jiang-Tao and Dey, Arjun and Dye, Simon and Findlay, Joseph R. and Myers, Adam D. and James, David and Jiang, Linhua and Lang, Dustin and Lawrence, Andy and Ross, Nicholas P. and and others},
abstractNote = {We present the first discoveries from a survey of z ≳ 6 quasars using imaging data from the DECam Legacy Survey (DECaLS) in the optical, the UKIRT Deep Infrared Sky Survey (UKIDSS) and a preliminary version of the UKIRT Hemisphere Survey (UHS) in the near-IR, and ALLWISE in the mid-IR. DECaLS will image 9000 deg{sup 2} of sky down to z {sub AB} ∼ 23.0, and UKIDSS and UHS will map the northern sky at 0 < decl. < +60°, reaching J {sub VEGA} ∼ 19.6 (5- σ ). The combination of these data sets allows us to discover quasars at redshift z ≳ 7 and to conduct a complete census of the faint quasar population at z ≳ 6. In this paper, we report on the selection method of our search, and on the initial discoveries of two new, faint z ≳ 6 quasars and one new z = 6.63 quasar in our pilot spectroscopic observations. The two new z ∼ 6 quasars are at z = 6.07 and z = 6.17 with absolute magnitudes at rest-frame wavelength 1450 Å being M {sub 1450} = −25.83 and M {sub 1450} = −25.76, respectively. These discoveries suggest that we can find quasars close to or fainter than the break magnitude of the Quasar Luminosity Function (QLF) at z ≳ 6. The new z = 6.63 quasar has an absolute magnitude of M {sub 1450} = −25.95. This demonstrates the potential of using the combined DECaLS and UKIDSS/UHS data sets to find z ≳ 7 quasars. Extrapolating from previous QLF measurements, we predict that these combined data sets will yield ∼200 z ∼ 6 quasars to z {sub AB} < 21.5, ∼1000 z ∼ 6 quasars to z {sub AB} < 23, and ∼30 quasars at z > 6.5 to J {sub VEGA} < 19.5.},
doi = {10.3847/1538-4357/AA689F},
journal = {Astrophysical Journal},
number = 1,
volume = 839,
place = {United States},
year = {Mon Apr 10 00:00:00 EDT 2017},
month = {Mon Apr 10 00:00:00 EDT 2017}
}
  • In this paper, we present the first discoveries from a survey of z ≳ 6 quasars using imaging data from the DECam Legacy Survey (DECaLS) in the optical, the UKIRT Deep Infrared Sky Survey (UKIDSS) and a preliminary version of the UKIRT Hemisphere Survey (UHS) in the near-IR, and ALLWISE in the mid-IR. DECaLS will image 9000 deg 2 of sky down to z AB ~ 23.0, and UKIDSS and UHS will map the northern sky at 0 < decl. < +60°, reaching J VEGA ~ 19.6 (5-σ). The combination of these data sets allows us to discover quasars atmore » redshift z ≳ 7 and to conduct a complete census of the faint quasar population at z ≳ 6. In this paper, we report on the selection method of our search, and on the initial discoveries of two new, faint z ≳ 6 quasars and one new z = 6.63 quasar in our pilot spectroscopic observations. The two new z ~ 6 quasars are at z = 6.07 and z = 6.17 with absolute magnitudes at rest-frame wavelength 1450 Å being M 1450 = -25.83 and M 1450 = -25.76, respectively. These discoveries suggest that we can find quasars close to or fainter than the break magnitude of the Quasar Luminosity Function (QLF) at z ≳ 6. The new z = 6.63 quasar has an absolute magnitude of M 1450 = -25.95. This demonstrates the potential of using the combined DECaLS and UKIDSS/UHS data sets to find z ≳ 7 quasars. Finally, extrapolating from previous QLF measurements, we predict that these combined data sets will yield ~200 z ~ 6 quasars to z AB < 21.5, ~1000 z ~ 6 quasars to z AB < 23, and ~30 quasars at z > 6.5 to J VEGA < 19.5.« less
  • We present the discovery of six new quasars at z {approx} 6 selected from the Sloan Digital Sky Survey (SDSS) southern survey, a deep imaging survey obtained by repeatedly scanning a stripe along the celestial equator. The six quasars are about 2 mag fainter than the luminous z {approx} 6 quasars found in the SDSS main survey and 1 mag fainter than the quasars reported in Paper I. Four of them comprise a complete flux-limited sample at 21 < z {sub AB} < 21.8 over an effective area of 195 deg{sup 2}. The other two quasars are fainter than zmore » {sub AB} = 22 and are not part of the complete sample. The quasar luminosity function at z {approx} 6 is well described as a single power law {phi}(L {sub 1450}) {proportional_to} L {sup {beta}} {sub 1450} over the luminosity range -28 < M {sub 1450} < -25. The best-fitting slope {beta} varies from -2.6 to -3.1, depending on the quasar samples used, with a statistical error of 0.3-0.4. About 40% of the quasars discovered in the SDSS southern survey have very narrow Ly{alpha} emission lines, which may indicate small black hole masses and high Eddington luminosity ratios, and therefore short black hole growth timescales for these faint quasars at early epochs.« less
  • We present the discovery of one or two extremely faint z ∼ 6 quasars in 6.5 deg{sup 2} utilizing a unique capability of the wide-field imaging of the Subaru/Suprime-Cam. The quasar selection was made in (i'-z{sub B} ) and (z{sub B} -z{sub R} ) colors, where z{sub B} and z{sub R} are bandpasses with central wavelengths of 8842 Å and 9841 Å, respectively. The color selection can effectively isolate quasars at z ∼ 6 from M/L/T dwarfs without the J-band photometry down to z{sub R} < 24.0, which is 3.5 mag deeper than the Sloan Digital Sky Survey (SDSS). Wemore » have selected 17 promising quasar candidates. The follow-up spectroscopy for seven targets identified one apparent quasar at z = 6.156 with M {sub 1450} = –23.10. We also identified one possible quasar at z = 6.041 with a faint continuum of M {sub 1450} = –22.58 and a narrow Lyα emission with HWHM =427 km s{sup –1}, which cannot be distinguished from Lyman α emitters. We derive the quasar luminosity function at z ∼ 6 by combining our faint quasar sample with the bright quasar samples by SDSS and CFHQS. Including our data points invokes a higher number density in the faintest bin of the quasar luminosity function than the previous estimate employed. This suggests a steeper faint-end slope than lower z, though it is yet uncertain based on a small number of spectroscopically identified faint quasars, and several quasar candidates still remain to be diagnosed. The steepening of the quasar luminosity function at the faint end does increase the expected emission rate of the ionizing photon; however, it only changes by a factor of approximately two to six. This was found to still be insufficient for the required photon budget of reionization at z ∼ 6.« less
  • We present the discovery and spectroscopic confirmation with the ESO NTT and Gemini South telescopes of eight new 6.0 < z < 6.5 quasars with zmore » $$_{AB}$$ < 21.0. These quasars were photometrically selected without any star-galaxy morphological criteria from 1533 deg$$^{2}$$ using SED model fitting to photometric data from the Dark Energy Survey (g, r, i, z, Y), the VISTA Hemisphere Survey (J, H, K) and the Wide-Field Infrared Survey Explorer (W1, W2). The photometric data was fitted with a grid of quasar model SEDs with redshift dependent Lyman-{\alpha} forest absorption and a range of intrinsic reddening as well as a series of low mass cool star models. Candidates were ranked using on a SED-model based $$\chi^{2}$$-statistic, which is extendable to other future imaging surveys (e.g. LSST, Euclid). Our spectral confirmation success rate is 100% without the need for follow-up photometric observations as used in other studies of this type. Combined with automatic removal of the main types of non-astrophysical contaminants the method allows large data sets to be processed without human intervention and without being over run by spurious false candidates. We also present a robust parametric redshift estimating technique that gives comparable accuracy to MgII and CO based redshift estimators. We find two z $$\sim$$ 6.2 quasars with HII near zone sizes < 3 proper Mpc which could indicate that these quasars may be young with ages < 10$^6$ - 10$^7$ years or lie in over dense regions of the IGM. The z = 6.5 quasar VDESJ0224-4711 has J$$_{AB}$$ = 19.75 is the second most luminous quasar known with z > 6.5.« less
  • We present imaging and spectroscopic observations for six quasars at z {>=} 5.9 discovered by the Canada-France High-z Quasar Survey (CFHQS). The CFHQS contains subsurveys with a range of flux and area combinations to sample a wide range of quasar luminosities at z {approx} 6. The new quasars have luminosities 10-75 times lower than the most luminous Sloan Digital Sky Survey quasars at this redshift. The least luminous quasar, CFHQS J0216-0455 at z = 6.01, has absolute magnitude M {sub 1450} = -22.21, well below the likely break in the luminosity function. This quasar is not detected in a deepmore » XMM-Newton survey showing that optical selection is still a very efficient tool for finding high-redshift quasars.« less