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Register a new userThe Infrared Medium-deep Survey. VIII. Quasar Luminosity Function at $zsim5$
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Faint $zsim5$ quasars with $M_{1450}sim-23$ mag are known to be the potentially important contributors to the ultraviolet ionizing background in the post-reionization era. However, their number density has not been well determined, making it difficult to assess their role in the early ionization of the intergalactic medium (IGM). In this work, we present the updated results of our $zsim5$ quasar survey using the Infrared Medium-deep Survey (IMS), a near-infrared imaging survey covering an area of 85 deg$^{2}$. From our spectroscopic observations with the Gemini Multi-Object Spectrograph (GMOS) on the Gemini-South 8 m Telescope, we discovered eight new quasars at $zsim5$ with $-26.1leq M_{1450} leq -23.3$. Combining our IMS faint quasars ($M_{1450}>-27$ mag) with the brighter Sloan Digital Sky Survey (SDSS) quasars ($M_{1450}<-27$ mag), we derive the $zsim5$ quasar luminosity function (QLF) without any fixed parameters down to the magnitude limit of $M_{1450}=-23$ mag. We find that the faint-end slope of the QLF is very flat ($alpha=-1.2^{+1.4}_{-0.6}$), with a characteristic luminosity of $M^{*}_{1450}=-25.8^{+1.4}_{-1.1}$ mag. The number density of $zsim5$ quasars from the QLF gives an ionizing emissivity at 912 $unicode{x212B}$ of $epsilon_{912}=(3.7$--$7.1)times10^{23}$ erg s$^{-1}$ Hz$^{-1}$ Mpc$^{-3}$ and an ionizing photon density of $dot{n}_{rm ion}=(3.0$--$5.7)times10^{49}$ Mpc$^{-3}$ s$^{-1}$. These results imply that quasars are responsible for only 10-20% (up to 50% even in the extreme case) of the photons required to completely ionize the IGM at $zsim5$, disfavoring the idea that quasars alone could have ionized the IGM at $zsim5$.
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In this paper, we provide updated constraints on the bolometric quasar luminosity function (QLF) from $z=0$ to $z=7$. The constraints are based on an observational compilation that includes observations in the rest-frame IR, B band, UV, soft and hard X-ray in past decades. Our method follows Hopkins et al. 2007 with an updated quasar SED model and bolometric and extinction corrections. The new best-fit bolometric quasar luminosity function behaves qualitatively different from the Hopkins et al. 2007 model at high redshift. Compared with the old model, the number density normalization decreases towards higher redshift and the bright-end slope is steeper at $zgtrsim 2$. Due to the paucity of measurements at the faint end, the faint end slope at $zgtrsim 5$ is quite uncertain. We present two models, one featuring a progressively steeper faint-end slope at higher redshift and the other featuring a shallow faint-end slope at $zgtrsim 5$. Further multi-band observations of the faint-end QLF are needed to distinguish between these models. The evolutionary pattern of the bolometric QLF can be interpreted as an early phase likely dominated by the hierarchical assembly of structures and a late phase likely dominated by the quenching of galaxies. We explore the implications of this model on the ionizing photon production by quasars, the CXB spectrum, the SMBH mass density and mass functions. The predicted hydrogen photoionization rate contributed by quasars is subdominant during the epoch of reionization and only becomes important at $zlesssim 3$. The predicted CXB spectrum, cosmic SMBH mass density and SMBH mass function are generally consistent with existing observations.
We present the quasar luminosity function at $z sim 5$ derived from the optical wide-field survey data obtained as a part of the Subaru strategic program (SSP) with Hyper Suprime-Cam (HSC). From $sim$81.8 deg$^2$ area in the Wide layer of the HSC-SSP survey, we selected 224 candidates of low-luminosity quasars at $z sim 5$ by adopting the Lyman-break method down to $i = 24.1$ mag. Based on our candidates and spectroscopically-confirmed quasars from the Sloan Digital Sky Survey (SDSS), we derived the quasar luminosity function at $z sim 5$ covering a wide luminosity range of $-28.76 < M_{rm 1450} < -22.32$ mag. We found that the quasar luminosity function is fitted by a double power-law model with a break magnitude of $M^{*}_{1450} = -25.05^{+0.10}_{-0.24}$ mag. The inferred number density of low-luminosity quasars is lower, and the derived faint-end slope, $-1.22^{+0.03}_{-0.10}$, is flatter than those of previous studies at $z sim 5$. A compilation of the quasar luminosity function at $4 leq z leq 6$ from the HSC-SSP suggests that there is little redshift evolution in the break magnitude and in the faint-end slope within this redshift range, although previous studies suggest that the faint-end slope becomes steeper at higher redshifts. The number density of low-luminosity quasars decreases more rapidly from $z sim 5$ to $z sim 6$ than from $z sim 4$ to $z sim 5$.
We determine the number counts and z=0-5 luminosity function for a well-defined, homogeneous sample of quasars from the Sloan Digital Sky Survey (SDSS). We conservatively define the most uniform statistical sample possible, consisting of 15,343 quasars within an effective area of 1622 deg^2 that was derived from a parent sample of 46,420 spectroscopically confirmed broad-line quasars in the 5282 deg^2 of imaging data from SDSS Data Release Three. The sample extends from i=15 to i=19.1 at z<3 and to i=20.2 for z>3. The number counts and luminosity function agree well with the results of the 2dF QSO Survey, but the SDSS data probe to much higher redshifts than does the 2dF sample. The number density of luminous quasars peaks between redshifts 2 and 3, although uncertainties in the selection function in this range do not allow us to determine the peak redshift more precisely. Our best fit model has a flatter bright end slope at high redshift than at low redshift. For z<2.4 the data are best fit by a redshift-independent slope of beta = -3.1 (Phi(L) propto L^beta). Above z=2.4 the slope flattens with redshift to beta=-2.37 at z=5. This slope change, which is significant at a >5-sigma level, must be accounted for in models of the evolution of accretion onto supermassive black holes.
The Galactic HII region luminosity function (LF) is an important metric for understanding global star formation properties of the Milky Way, but only a few studies have been done and all use relatively small numbers of HII regions. We use a sample of 797 first Galactic quadrant HII regions compiled from the WISE Catalog of Galactic HII Regions to examine the form of the LF at multiple infrared and radio wavelengths. Our sample is statistically complete for all regions powered by single stars of type O9.5V and earlier. We fit the LF at each wavelength with single and double power laws. Averaging the results from all wavelengths, the mean of the best-fit single power law index is $langlealpharangle=-1.75,pm,0.01$. The mean best-fit double power law indices are $langlealpha_1rangle=-1.40,pm,0.03$ and $langlealpha_2rangle=-2.33,pm,0.04$. We conclude that neither a single nor a double power law is strongly favored over the other. The LFs show some variation when we separate the HII region sample into subsets by heliocentric distance, physical size, Galactocentric radius, and location relative to the spiral arms, but blending individual HII regions into larger complexes does not change the value of the power law indices of the best-fit LF models. The consistency of the power law indices across multiple wavelengths suggests that the LF is independent of wavelength. This implies that infrared and radio tracers can be employed in place of H$alpha$.
The intergalactic medium (IGM) at $zsim$ 5 to 6 is largely ionized, and yet the main source for the IGM ionization in the early universe is uncertain. Of the possible contributors are faint quasars with $-26 lesssim M_{rm 1450} lesssim -23$, but their number density is poorly constrained at $zsim5$. In this paper, we present our survey of faint quasars at $zsim5$ in the European Large-Area {it ISO} Survey-North 1 (ELAIS-N1) field over a survey area of 6.51 deg$^2$ and examine if such quasars can be the dominant source of the IGM ionization. We use the deep optical/near-infrared data of the ELAIS-N1 field as well as the additional medium-band observations to find $z sim 5$ quasars through a two-step approach using the broadband color selection, and SED fitting with the medium-band information included. Adopting Bayesian information criterion, we identify ten promising quasar candidates. Spectra of three of the candidates are obtained, confirming all of them to be quasars at $zsim5$ and supporting the reliability of the quasar selection. Using the promising candidates, we derive the $zsim5$ quasar luminosity function at $-26 lesssim M_{rm 1450} lesssim -23$. The number density of faint $zsim5$ quasars in the ELAIS-N1 field is consistent with several previous results that quasars are not the main contributors to the IGM-ionizing photons at $zsim5$
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