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Hu E.M.,University of Hawaii at Manoa | Cowie L.L.,University of Hawaii at Manoa | Barger A.J.,University of Hawaii at Manoa | Barger A.J.,University of Wisconsin - Madison | And 3 more authors.
Astrophysical Journal | Year: 2010

We present an atlas of 88 z ∼ 5.7 and 30 z ∼ 6.5 Lyα emitters obtained from a wide-field narrowband survey. We combined deep narrowband imaging in 120 Å bandpass filters centered at 8150 Å and 9140 Å with deep BVRIz broadband imaging to select high-redshift galaxy candidates over an area of 4180 arcmin2. The goal was to obtain a uniform selection of comparable depth over the seven targeted fields in the two filters. For the GOODS-North region of the Hubble Deep Field-North field, we also selected candidates using a 120 Å filter centered at 9210 Å. We made spectroscopic observations with Keck DEIMOS of nearly all the candidates to obtain the final sample of Lyα emitters. At the 3.3 Å resolution of the DEIMOS observations the asymmetric profile for Lyα emission can be clearly seen in the spectra of nearly all the galaxies. We show that the spectral profiles are surprisingly similar for many of the galaxies and that the composite spectral profiles are nearly identical at z = 5.7 and z = 6.5.We analyze the distributions of line widths and Lyα equivalent widths and find that the lines are marginally narrower at the higher redshift, with median values of 0.77 Å at z = 6.5 and 0.92 Å at z = 5.7. The line widths have a dependence on the Lyα luminosity of the form ∼L 0.3α .We compare the surface densities and the luminosity functions at the two redshifts and find that there is a multiplicative factor of two decrease in the number density of bright Lyα emitters from z = 5.7 to z = 6.5, while the characteristic luminosity is unchanged. © 2010. The American Astronomical Society.

Hathi N.P.,Carnegie Institution for Science | Hathi N.P.,University of California at Riverside | Mobasher B.,University of California at Riverside | Capak P.,249 17 Caltech | And 2 more authors.
Astrophysical Journal | Year: 2012

We present near-infrared (NIR; J and Ks) survey of the Great Observatories Origins Deep Survey-North (GOODS-N) field. The publicly available imaging data were obtained using the MOIRCS instrument on the 8.2m Subaru and the WIRCam instrument on the 3.6m Canada-France-Hawaii Telescope (CFHT). These observations fulfill a serious wavelength gap in the GOODS-N data, i.e., lack of deep NIR observations. We combine the Subaru/MOIRCS and CFHT/WIRCam archival data to generate deep J- and Ks-band images, covering the full GOODS-N field (∼169 arcmin2) to an AB magnitude limit of ∼25mag (3σ). We applied z850-band dropout color selection criteria, using the NIR data generated here. We have identified two possible Lyman break galaxy (LBG) candidates at z ≳ 6.5 with J ≲ 24.5. The first candidate is a likely LBG at z ≃ 6.5 based on a weak spectral feature tentatively identified as Lyα line in the deep Keck/DEIMOS spectrum, while the second candidate is a possible LBG at z ≃ 7 based on its photometric redshift. These z 850-dropout objects, if confirmed, are among the brightest such candidates found so far. At z ≳ 6.5, their star formation rate is estimated as 100-200 M⊙yr-1. If they continue to form stars at this rate, they assemble a stellar mass of ∼ 5 × 1010 M⊙ after about 400 million years, becoming the progenitors of massive galaxies observed at z ≃ 5. We study the implication of the z850-band dropout candidates discovered here, in constraining the bright end of the luminosity function and understanding the nature of high-redshift galaxies. © 2012. The American Astronomical Society. All rights reserved.

Ikeda H.,Ehime University | Ikeda H.,Kyoto University | Nagao T.,Kyoto University | Matsuoka K.,Ehime University | And 14 more authors.
Astrophysical Journal | Year: 2012

We present the result of our low-luminosity quasar survey in the redshift range of 4.5 ≲ z ≲ 5.5 in the COSMOS field. Using the COSMOS photometric catalog, we selected 15 quasar candidates with 22 < i′ < 24 at z ∼ 5 that are ∼ 3mag fainter than the Sloan Digital Sky Survey quasars in the same redshift range. We obtained optical spectra for 14 of the 15 candidates using FOCAS on the Subaru Telescope and did not identify any low-luminosity type-1 quasars at z ∼ 5, while a low-luminosity type-2 quasar at z ∼ 5.07 was discovered. In order to constrain the faint end of the quasar luminosity function at z ∼ 5, we calculated the 1σ confidence upper limits of the space density of type-1 quasars. As a result, the 1σ confidence upper limits on the quasar space density are Φ < 1.33 × 10-7Mpc-3mag-1 for -24.52 < M 1450 < -23.52 and Φ < 2.88 × 10-7Mpc -3mag-1 for -23.52 < M 1450 < -22.52. The inferred 1σ confidence upper limits of the space density are then used to provide constraints on the faint-end slope and the break absolute magnitude of the quasar luminosity function at z ∼ 5. We find that the quasar space density decreases gradually as a function of redshift at low luminosity (M 1450 ∼ -23), being similar to the trend found for quasars with high luminosity (M 1450 < -26). This result is consistent with the so-called downsizing evolution of quasars seen at lower redshifts. © 2012. The American Astronomical Society. All rights reserved.

Capak P.,Spitzer Science Center | Mobasher B.,University of California at Riverside | Scoville N.Z.,249 17 Caltech | McCracken H.,University Pierre and Marie Curie | And 21 more authors.
Astrophysical Journal | Year: 2011

We present three bright z +-dropout candidates selected from deep near-infrared (NIR) imaging of the COSMOS 2 deg2 field. All three objects match the 0.8-8 μm colors of other published z > 7 candidates but are 3 mag brighter, facilitating further study. Deep spectroscopy of two of the candidates covering 0.64-1.02 μm with Keck-DEIMOS and all three covering 0.94-1.10 μm and 1.52-1.80 μm with Keck-NIRSPEC detects weak spectral features tentatively identified as Lyα at z = 6.95 and z = 7.69 in two of the objects. The third object is placed at z 1.6 based on a 24 μm and weak optical detection. A comparison with the spectral energy distributions of known z < 7 galaxies, including objects with strong spectral lines, large extinction, and large systematic uncertainties in the photometry, yields no objects with similar colors. However, the λ > 1 μm properties of all three objects can be matched to optically detected sources with photometric redshifts at z 1.8, so the non-detection in the i + and z + bands is the primary factor which favors a z > 7 solution. If any of these objects are at z 7, the bright end of the luminosity function is significantly higher at z > 7 than suggested by previous studies, but consistent within the statistical uncertainty and the dark matter halo distribution. If these objects are at low redshift, the Lyman break selection must be contaminated by a previously unknown population of low-redshift objects with very strong breaks in their broadband spectral energy distributions and blue NIR colors. The implications of this result on luminosity function evolution at high redshift are discussed. We show that the primary limitation of z > 7 galaxy searches with broad filters is the depth of the available optical data. © 2011. The American Astronomical Society. All rights reserved.

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