This is the second paper in a series on a new luminous z ∼ 5 quasar survey using optical and near-infrared colors. Here we present a new determination of the bright end of the quasar luminosity function (QLF) at z ∼ 5. Combined our 45 new quasars with previously known quasars that satisfy our selections, we construct the largest uniform luminous z ∼ 5 quasar sample to date, with 99 quasars in the range 4.7 ≤ z < 5.4 and −29 < M 1450 ≤ −26.8, within the Sloan Digital Sky Survey (SDSS) footprint. We use a modified 1/V a method including flux limit correction to derive a binned QLF, and we model the parametric QLF using maximum likelihood estimation. With the faint-end slope of the QLF fixed as α = −2.03 from previous deeper samples, the best fit of our QLF gives a flatter bright end slope β = −3.58 ± 0.24 and a fainter break magnitude M * 1450 = −26.98 ± 0.23 than previous studies at similar redshift. Combined with previous work at lower and higher redshifts, our result is consistent with a luminosity evolution and density evolution (LEDE) model. Using the best fit QLF, the contribution of quasars to the ionizing background at z ∼ 5 is found to be 18% − 45% with a clumping factor C of 2 − 5. Our sample suggests an evolution of radio loud fraction with optical luminosity but no obvious evolution with redshift.

The temperature and pressure of the hydrothermal process occurring in a batch reactor are typically coupled. Herein, we develop a decoupled temperature and pressure hydrothermal system that can heat the cellulose at a constant pressure, thus lowering the degradation temperature of cellulose significantly and enabling the fast production of carbon sub-micron spheres. Carbon sub-micron spheres can be produced without any isothermal time, much faster compared to the conventional hydrothermal process. High-pressure water can help to cleave the hydrogen bonds in cellulose and facilitate dehydration reactions, thus promoting cellulose carbonization at low temperatures. A life cycle assessment based on a conceptual biorefinery design reveals that this technology leads to a substantial reduction in carbon emissions when hydrochar replacing fuel or used for soil amendment. Overall, the decoupled temperature and pressure hydrothermal treatment in this study provides a promising method to produce sustainable carbon materials from cellulose with a carbon-negative effect.

High-redshift quasars are important tracers of structure and evolution in the early universe. However, they are very rare and difficult to find when using color selection because of contamination from late-type dwarfs. High-redshift quasar surveys based on only optical colors suffer from incompleteness and low identification efficiency, especially at z 4.5. We have developed a new method to select 4.7 z 5.4 quasars with both high efficiency and completeness by combining optical and mid-IR Wide-field Infrared Survey Explorer (WISE) photometric data, and are conducting a luminous z ∼ 5 quasar survey in the whole Sloan Digital Sky Survey (SDSS) footprint. We have spectroscopically observed 99 out of 110 candidates with z-band magnitudes brighter than 19.5 and 64 (64.6%) of them are quasars with redshifts of 4.4 z 5.5 and absolute magnitudes of −29 M 1450 −26.4. In addition, we also observed 14 fainter candidates selected with the same criteria and identified 8 (57.1%) of them as quasars with 4.7 < z < 5.4 . Among 72 newly identified quasars, 12 of them are at 5.2 < z < 5.7, which leads to an increase of ∼36% of the number of known quasars at this redshift range. More importantly, our identifications doubled the number of quasars with M 1450 < −27.5 at z > 4.5, which will set strong constraints on the bright end of the quasar luminosity function. We also expand our method to select quasars at z 5.7. In this paper we report the discovery of four new luminous z 5.7 quasars based on SDSS-WISE selection.

No abstract