We present the Ly$\alpha$ luminosity functions (LFs) at $z=$5.7 and 6.6 derived from a new large sample of 1,266 Ly$\alpha$ emitters (LAEs) identified in total areas of 14 and 21 deg$^2$, respectively, based on the early narrowband data of the Subaru/Hyper Suprime-Cam (HSC) survey. Together with careful Monte-Carlo simulations that account for the incompleteness of the LAE selection and the flux estimate systematics in the narrowband imaging, we have determined the Ly$\alpha$ LFs with the unprecedentedly small statistical and systematic uncertainties in a wide Ly$\alpha$ luminosity range of $10^{42.8-43.8}$ erg s$^{-1}$. We obtain the best-fit Schechter parameters of $L^{*}_{\rm Lya}=1.6^{+2.2}_{-0.6} (1.7^{+0.3}_{-0.7}) \times10^{43}$ erg s$^{-1}$, $\phi^{*}_{\rm Lya}=0.85^{+1.87}_{-0.77}\ (0.47^{+1.44}_{-0.44})\times10^{-4}$ Mpc$^{-3}$, and $\alpha=-2.6^{+0.6}_{-0.4}\ (-2.5^{+0.5}_{-0.5})$ at $z=5.7$ ($6.6$). We confirm that our best-estimate Ly$\alpha$ LFs are consistent with the majority of the previous studies, but find that our Ly$\alpha$ LFs do not agree with the high number densities of LAEs recently claimed by Matthee/Santos et al.'s studies that may overcorrect the incompleteness and the flux systematics. Our Ly$\alpha$ LFs at $z=5.7$ and $6.6$ show an indication that the faint-end slope is very steep ($\alpha \simeq -2.5$), although it is also possible that the bright-end LF results are enhanced by systematic effects such as the contribution from AGNs, blended merging galaxies, and/or large ionized bubbles around bright LAEs. Comparing our Ly$\alpha$ LF measurements with four independent reionization models, we estimate the neutral hydrogen fraction of the IGM to be $x_{\rm HI}=0.3\pm0.2$ at $z=$6.6 that is consistent with the small Thomson scattering optical depth obtained by Planck 2016.

SILVERRUSH. IV. Ly$\alpha$ Luminosity Functions at $z = 5.7$ and $6.6$ Studied with $\sim$ 1,300 LAEs on the $14-21$ deg$^2$ Sky

SILVERRUSH. IV. Lyα luminosity functions at z = 5.7 and 6.6 studied with ∼1300 Lyα emitters on the 14-21 deg2 sky

We report discovery of 41 new high-z quasars and luminous galaxies, which were spectroscopically identified at 5.7 < z < 6.9. This is the fourth in a series of papers from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, based on the deep multi-band imaging data collected by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. We selected the photometric candidates by a Bayesian probabilistic algorithm, and then carried out follow-up spectroscopy with the Gran Telescopio Canarias and the Subaru Telescope. Combined with the sample presented in the previous papers, we have now spectroscopically identified 137 extremely-red HSC sources over about 650 deg2, which include 64 high-z quasars, 24 high-z luminous galaxies, 6 [O III] emitters at z ~ 0.8, and 43 Galactic cool dwarfs (low-mass stars and brown dwarfs). The new quasars span the luminosity range from M1450 ~ -26 to -22 mag, and continue to populate a few magnitude lower luminosities than have been probed by previous wide-field surveys. In a companion paper, we derive the quasar luminosity function at z ~ 6 over an unprecedentedly wide range of M1450 ~ -28 to -21 mag, exploiting the SHELLQs and other survey outcomes.

Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). II. Discovery of 32 Quasars and Luminous Galaxies at 5.7 < z < 6.8

The optical–UV continuum of quasars is broadly consistent with the emission from a geometrically thin optically thick accretion disc (AD). The AD produces the ionizing continuum which powers the broad and narrow emission lines. The maximum AD effective temperature is given by , where M is the black hole mass, the accretion rate and fmax is set by the black hole spin a*. For a low enough value of , the AD may become too cold to produce ionizing photons. Such an object will form a lineless quasar. This occurs for a local blackbody (BB) AD with a luminosity Lopt= 1046 erg s−1 for M > 3.6 × 109 M⊙, when a*= 0, and for M > 1.4 × 1010 M⊙, when a*= 0.998. Using the AD-based , derived from M and Lopt, and the reverberation-based M, derived from Lopt and the Hβ full width at half-maximum, v, gives Teff, max∝L−0.13optv−1.45. Thus, Teff, max is mostly set by v. Quasars with a local BB AD become lineless for v > 8000 km s−1, when a*= 0, and for v > 16 000 km s−1, when a*= 0.998. Higher values of v are required if the AD is hotter than a local BB. The AD becoming non-ionizing may explain why line-emitting quasars with v > 10 000 km s−1 are rare. Weak low-ionization lines may still be present if the X-ray continuum is luminous enough, and such objects may form a population of weak line quasars (WLQ). If correct, such WLQ should show a steeply falling spectral energy distribution (SED) at λ < 1000 A. Such an SED was observed by Hryniewicz et al. in SDSS J094533.99+100950.1, a WLQ observed down to 570 A, which is well modelled by a rather cold AD SED. UV spectroscopy of z∼ 1–2 quasars is required to eliminate potential intervening Lyman limit absorption by the intergalactic medium and to explore if the SEDs of lineless quasars and some additional WLQ are also well fitted by a cold AD SED.

/pdf/cold-accretion-discs-and-lineless-quasars-2c93tn3azg.pdf

Cold accretion discs and lineless quasars

/pdf/subaru-high-z-exploration-of-low-luminosity-quasars-shellqs-3l30w7c27h.pdf

Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). II. Discovery of 32 quasars and luminous galaxies at 5.7 < z ≤ 6.8

The Sloan Digital Sky Survey has discovered a z = 2.4917 radio-loud active galactic nucleus (AGN) with a luminous, variable, low-polarization UV continuum, H I two-photon emission, and a moderately broad Lyα line (FWHM≃1430 km s −1 ) but without obvious metal-line emission. SDSS J113658.36+024220.1 does have associated metal-line absorption in three distinct, narro w systems spanning a velocity range of 2710 km s −1 . Despite certain spectral similarities, SDSS J1136+0242 is not a Lyman-break galaxy. Instead, the Lyα and twophoton emission can be attributed to an extended, low-metallicity narrow-line region. The unpolarized continuum argues that we see SDSS J1136+0242 very close to the axis of any ionization cone present. We can conceive of two plausible explanations for why we see a strong UV continuum but no broad-line emission in this ‘face-on radio galaxy’ model for SDSS J1136+0242: the continuum could be relativistically beamed synchrotron emission which swamps the broad-line emission; or, more likely, SDSS J1136+0242 could be similar to PG 1407+265, a quasar in which for some unknown reason the high-ionization emission lines are very broad, very weak, and highly blueshifted.

https://arxiv.org/pdf/astro-ph/0402648.pdf

A LYMAN-α-ONLY AGN FROM THE SLOAN DIGITAL SKY SURVEY

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A LYMAN-α-ONLY AGN FROM THE SLOAN DIGITAL SKY SURVEY