Quasar Density Research Articles

A blazar in the epoch of reionization

AbstractRelativistic jets are thought to play a crucial role in the formation and evolution of massive galaxies and supermassive black holes. Blazars, which are quasars with jets aligned along our line of sight, provide insights into the jetted population and have been observed up to redshifts of z = 6.1. Here, we report the discovery and multi-wavelength characterization of the blazar VLASS J041009.05−013919.88 at z = 7 (age of the Universe ~750 Myr), which is powered by a ~7 × 108 M⊙ black hole. The presence of this high-redshift blazar implies a large population of similar but unaligned jetted sources in the early Universe. Our findings suggest two possible scenarios. In one, the jet in J0410−0139 is intrinsically low power but appears highly luminous due to relativistic beaming, suggesting that most ultraviolet-bright quasars at this redshift host jets. Alternatively, if J0410−0139 represents an intrinsically powerful radio source, there should be hundreds to thousands of radio-quiet quasars at z ≈ 7 with properties like those of J0410−0139, a prediction in tension with observed quasar densities based on their ultraviolet luminosity function. These results support the hypothesis that the rapid growth of black holes in the early Universe may be driven by jet-enhanced or obscured super-Eddington accretion, potentially playing a key role in forming massive black holes during the epoch of reionization.

The PAU Survey: The quasar and UV luminosity functions at 2.7<z<5.3

We present the Lyman-alpha ( and ultraviolet (UV) luminosity function (LF) in bins of redshift for quasars selected in the Physics of the Accelerating Universe Survey (PAUS). A sample of 915 objects was selected at $2.7<z<5.3$ within an effective area of $ 36$ deg$^2$ observed in 40 narrow-band (NB) filters (FWHM $ We cover the intermediate--bright luminosity regime of the LF erg\,s $; $-29<M_ UV <-24$). The continuous wavelength coverage of the PAUS NB set allows very efficient target identification and precise redshift measurements. We show that our method is able to retrieve a relatively complete ($C 85<!PCT!>$) and pure ($P 90<!PCT!>$) sample of quasars for $ $. In order to obtain corrections for the LF estimation, and assess the accuracy of our selection method, we produced mock catalogs of $0<z<4.3$ quasars and galaxies that mimic our target population and their main contaminants. Our results show a clear evolution of the and UV LFs, with a declining tendency in the number density of quasars toward increasing redshifts. In addition, the faint-end power-law slope of the LF becomes steeper with redshift, suggesting that the number density of quasars declines faster than that of fainter emitters. By integrating the LF, we find that the total emitted by bright quasars per unit volume rapidly declines with increasing redshift, being subdominant to that of star-forming galaxies by several orders of magnitude by $z 4$. Finally, we stack the NB pseudo-spectra of a visually selected ``golden sample'' of 591 quasars to obtain photometric composite SEDs in bins of redshift, enabling us to measure the mean intergalactic medium absorption using the Lyman-alpha forest as a function of redshift, yielding results consistent with previous spectroscopic determinations.

Red Type-1 Quasars after Cosmic Noon and Impact on L UV-related Quasar Statistics

Over the past decades, nearly a million quasars have been explored to shed light on the evolution of supermassive black holes and galaxies. The ultraviolet-to-optical spectra of type-1 quasars particularly offer insights into their black hole activities. Recent findings, however, raise questions about the prevalence of red type-1 quasars of which colors might be due to dust obscuration and their potential influence on luminosity-related properties of quasars. We examine the fraction of red type-1 quasars within the redshift range of 0.68 ≤ z < 2.20, applying a spectral energy distribution (SED) fitting using optical-to-mid-infrared (MIR) photometric data of Sloan Digital Sky Survey Data Release 14 quasars. Approximately 10% of the type-1 quasars exhibit red colors suggestive of dust obscuration. There is an association between the brightness of the MIR luminosity and a higher fraction of red type-1 quasars, albeit with negligible redshift evolution. By employing E(B − V) values from the SED fitting, we obtained dereddened luminosity of the red type-1 quasars and reassess the quasar luminosity function (QLF) and black hole mass (M BH) estimates. Result shows a modest increase in the number density of bright quasars, linking to more flatten bright-end slope of QLFs, while M BH adjustments are minimal. Current SDSS selections with optical colors could miss a significant population of heavily dust-obscured quasars. As future MIR surveys like Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer expand, they may reveal enough obscured quasars to prompt a more profound revision of fundamental quasar properties.

Ensemble power spectral density of SDSS quasars in UV/optical bands

Context. Quasar variability has proven to be a powerful tool to constrain the properties of their inner engine and the accretion process onto supermassive black holes. Correlations between UV/optical variability and physical properties have been long studied with a plethora of different approaches and time-domain surveys, although the detailed picture is not yet clear. Aims. We analysed archival data from the SDSS Stripe-82 region to study how the quasar power spectral density (PSD) depends on the black hole mass, bolometric luminosity, accretion rate, redshift, and rest-frame wavelength. We developed a model-independent analysis framework that could be easily applied to upcoming large surveys such as the Legacy Survey of Space and Time (LSST). Methods. We used light curves of 8042 spectroscopically confirmed quasars, observed in at least six yearly seasons in five filters ugriz. We split the sample into bins of similar physical properties containing at least 50 sources, and we measured the ensemble PSD in each of them. Results. We find that a simple power law is a good fit to the power spectra in the frequency range explored. Variability does not depend on the redshift at a fixed wavelength. Instead, both PSD amplitude and slope depend on the black hole mass, accretion rate, and rest-frame wavelength. We provide scaling relations to model the observed variability as a function of the physical properties, and discuss the possibility of a universal PSD shape for all quasars, where frequencies scale with the black hole mass, while normalization and slope(s) are fixed (at any given wavelength and accretion rate).

Quasars and the Intergalactic Medium at Cosmic Dawn

Quasars at cosmic dawn provide powerful probes of the formation and growth of the earliest supermassive black holes (SMBHs) in the Universe, their connections to galaxy and structure formation, and the evolution of the intergalactic medium (IGM) at the epoch of reionization (EoR). Hundreds of quasars have been discovered in the first billion years of cosmic history, with the quasar redshift frontier extended to z ∼ 7.6. Observations of quasars at cosmic dawn show the following: ▪The number density of luminous quasars declines exponentially at z &gt; 5, suggesting that the earliest quasars emerge at z ∼ 10; the lack of strong evolution in their average spectral energy distribution indicates a rapid buildup of the active galactic nucleus environment.▪Billion-solar-mass black holes (BHs) already exist at z &gt; 7.5; they must form and grow in less than 700 Myr, by a combination of massive early BH seeds with highly efficient and sustained accretion.▪The rapid quasar growth is accompanied by strong star formation and feedback activity in their host galaxies, which show diverse morphological and kinetic properties, with typical dynamical mass lower than that implied by the local BH/galaxy scaling relations.▪Hi absorption in quasar spectra probes the tail end of cosmic reionization at z ∼ 5.3–6 and indicates the EoR midpoint at 6.9 &lt; z &lt; 7.6, with large spatial fluctuations in IGM ionization. Observations of heavy element absorption lines suggest that the circumgalactic medium also experiences evolution in its ionization structure and metal enrichment during the EoR.

The Pan-STARRS1 z > 5.6 Quasar Survey. III. The z ≈ 6 Quasar Luminosity Function

We present the z ≈ 6 type-1 quasar luminosity function (QLF), based on the Pan-STARRS1 (PS1) quasar survey. The PS1 sample includes 125 quasars at z ≈ 5.7–6.2, with −28 ≲ M 1450 ≲ −25. With the addition of 48 fainter quasars from the SHELLQs survey, we evaluate the z ≈ 6 QLF over −28 ≲ M 1450 ≲ −22. Adopting a double power law with an exponential evolution of the quasar density (Φ(z) ∝ 10 k(z−6); k = −0.7), we use a maximum likelihood method to model our data. We find a break magnitude of , a faint-end slope of , and a steep bright-end slope of . Based on our new QLF model, we determine the quasar comoving spatial density at z ≈ 6 to be . In comparison with the literature, we find the quasar density to evolve with a constant value of k ≈ −0.7, from z ≈ 7 to z ≈ 4. Additionally, we derive an ionizing emissivity of , based on the QLF measurement. Given standard assumptions, and the recent measurement of the mean free path by Becker et al. at z ≈ 6, we calculate an H i photoionizing rate of ΓH I(z = 6) ≈ 6 × 10−16 s−1, strongly disfavoring a dominant role of quasars in hydrogen reionization.

The Quasar Luminosity Function at z ∼ 5 via Deep Learning and Bayesian Information Criterion

Understanding the faint end of quasar luminosity function (LF) at a high redshift is important since the number density of faint quasars is a critical element in constraining ultraviolet (UV) photon budgets for ionizing the intergalactic medium (IGM) in the early universe. Here, we present quasar LF reaching M 1450 ∼ −22.0 AB mag at z ∼ 5, about 1 mag deeper than previous UV LFs. We select quasars at z ∼ 5 with a deep learning technique from deep data taken by the Hyper Suprime-Cam Subaru Strategic Program, covering a 15.5 deg2 area. Beyond the traditional color selection method, we improved the quasar selection by training an artificial neural network to distinguish z ∼ 5 quasars from nonquasar sources based on their colors and adopting the Bayesian information criterion that can further remove high-redshift galaxies from the quasar sample. When applied to a small sample of spectroscopically identified quasars and galaxies, our method is successful in selecting quasars at ∼83% efficiency (5/6) while minimizing the contamination rate of high-redshift galaxies (1/8) by up to three times compared to the selection using color selection alone (3/8). The number of our final quasar candidates with M 1450 < −22.0 mag is 35. Our quasar UV LF down to M 1450 = −22 mag or even fainter (M 1450 = −21 mag) suggests a rather low number density of faint quasars and the faint-end slope of , favoring a scenario where quasars play a minor role in ionizing the IGM at high redshift.

Paving the way forEuclid and JWST via probabilistic selection of high-redshift quasars

ABSTRACT We introduce a probabilistic approach to select 6 ≤ $z$ ≤ 8 quasar candidates for spectroscopic follow-up, which is based on density estimation in the high-dimensional space inhabited by the optical and near-infrared photometry. Densities are modelled as Gaussian mixtures with principled accounting of errors using the extreme deconvolution (XD) technique, generalizing an approach successfully used to select lower redshift ($z$ ≤ 3) quasars. We train the probability density of contaminants on 1902 071 7-d flux measurements from the 1076 deg2 overlapping area from the Dark Energy Camera Legacy Survey (DECaLS) ($z$), VIKING (YJHKs), and unWISE (W1W2) imaging surveys, after requiring they dropout of DECaLS g and r, whereas the distribution of high-$z$ quasars are trained on synthetic model photometry. Extensive simulations based on these density distributions and current estimates of the quasar luminosity function indicate that this method achieves a completeness of $\ge 56{{\ \rm per\ cent}}$ and an efficiency of $\ge 5{{\ \rm per\ cent}}$ for selecting quasars at 6 &amp;lt; $z$ &amp;lt; 8 with JAB &amp;lt; 21.5. Among the classified sources are 8 known 6 &amp;lt; $z$ &amp;lt; 7 quasars, of which 2/8 are selected suggesting a completeness $\simeq 25{{\ \rm per\ cent}}$, whereas classifying the 6 known (JAB &amp;lt; 21.5) quasars at $z$ &amp;gt; 7 from the entire sky, we select 5/6 or a completeness of $\simeq 80{{\ \rm per\ cent}}$. The failure to select the majority of 6 &amp;lt; $z$ &amp;lt; 7 quasars arises because our quasar density model is based on an empirical quasar spectral energy distribution model that underestimates the scatter in the distribution of fluxes. This new approach to quasar selection paves the way for efficient spectroscopic follow-up of Euclid quasar candidates with ground-based telescopes and James Webb Space Telescope.

Forecasts for WEAVE-QSO: 3D clustering and connectivity of critical points with Lyman-α tomography

ABSTRACT The upcoming WEAVE-QSO survey will target a high density of quasars over a large area, enabling the reconstruction of the 3D density field through Lyman-α (Ly-α) tomography over unprecedented volumes smoothed on intermediate cosmological scales (≈ 16 Mpc h−1). We produce mocks of the Ly-α forest using Ly-α Mass Association Scheme, and reconstruct the 3D density field between sightlines through Wiener filtering in a configuration compatible with the future WEAVE-QSO observations. The fidelity of the reconstruction is assessed by measuring one- and two-point statistics from the distribution of critical points in the cosmic web. In addition, initial Lagrangian statistics are predicted from the first principles, and measurements of the connectivity of the cosmic web are performed. The reconstruction captures well the expected features in the auto- and cross-correlations of the critical points. This remains true after a realistic noise is added to the synthetic spectra, even though sparsity of sightlines introduces systematics, especially in the cross-correlations of points with mixed signature. Specifically, the most striking clustering features involving filaments and walls could be measured with up to 4σ of significance with a WEAVE-QSO-like survey. Moreover, the connectivity of each peak identified in the reconstructed field is globally consistent with its counterpart in the original field, indicating that the reconstruction preserves the geometry of the density field not only statistically, but also locally. Hence, the critical points’ relative positions within the tomographic reconstruction could be used as standard rulers for dark energy by WEAVE-QSO and similar surveys.

Quasar UV Luminosity Function at 3.5 &lt; z &lt; 5.0 from SDSS Deep Imaging Data

Abstract We present a well-designed sample of more than 1000 type 1 quasars at 3.5 &lt; z &lt; 5 and derive UV quasar luminosity functions (QLFs) in this redshift range. These quasars were selected using the Sloan Digital Sky Survey (SDSS) imaging data in the Stripe 82 and overlap regions with repeat imaging observations that are about 1 mag fainter than the SDSS single-epoch data. The follow-up spectroscopic observations were conducted by the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS) as one of the BOSS ancillary programs. Reaching i ∼ 21.5 mag, our sample bridges previous samples from brighter and deeper surveys. We use a 1/V a method to derive binned QLFs at 3.6 &lt; z &lt; 4.0, 4.0 &lt; z &lt; 4.5, and 4.5 &lt; z &lt; 4.9 and then use a double power-law model to parameterize the QLFs. We also combine our data with literature QLFs to better constrain the QLFs across a much wider luminosity baseline. The faint- and bright-end slopes of the QLFs in this redshift range are around −1.7 and −3.7, respectively, with uncertainties from 0.2 to 0.3 to &gt;0.5. The evolution of the QLFs from z ∼ 5 to 3.5 can be described by a pure density evolution model (∝10 kz ) with a parameter k similar to that at 5 &lt; z &lt; 7, suggesting a nearly uniform evolution of the quasar density at z = 3.5–7.

Quasars' physical properties study based on the medium‐band photometric survey

AbstractThe study is about the quasars' cosmological evolution. We used the medium‐band photometric survey at the 1‐m Schmidt telescope of the Byurakan Astrophysical Observatory. The HS47‐22 field with an area of 2.38 square degrees has been selected. We have classified objects and composed a sample of quasars using broadband photometric data and morphological classification from the DECaLS survey (Dey et al. 2019), infrared photometry from the WISE survey (Meisner et al. 2018), spectroscopy from the Sloan Digital Sky Survey (Pâris et al. 2018), ROSAT X‐ray data (Molthagen et al. 1997), FIRST radio data (Becker et al. 1995), and stellar parallax data from the GAIA survey (Gaia Collaboration et al. 2018). We have compiled a sample of 682 quasars, determined their photometric redshifts from the medium‐band photometric data, and calculated the absolute stellar magnitudes. The space density of quasars was calculated for different luminosity ranges at different redshifts using the λ‐CDM model with and (Hogg 1999). In this paper, we present the comparison of our results with other works.

A Physical Model for the Quasar Luminosity Function Evolution between Cosmic Dawn and High Noon

Abstract Modeling the evolution of the number density distribution of quasars through the quasar luminosity function (QLF) is critical to improving our understanding of the connection between black holes, galaxies, and their halos. Here we present a novel semiempirical model for the evolution of the QLF that is fully defined after the specification of a free parameter, the internal duty cycle, ε DC, along with minimal other assumptions. All remaining model parameters are fixed upon calibration against the QLF at two redshifts, z = 4 and z = 5. Our modeling shows that the evolution at the bright end results from the stochasticity in the median quasar luminosity versus halo mass relation, while the faint end shape is determined by the evolution of the halo mass function (HMF) with redshift. Additionally, our model suggests the overall quasar density is determined by the evolution of the HMF, irrespective of the value of ε DC. The z ≥ 4 QLFs from our model are in excellent agreement with current observations for all ε DC, with model predictions suggesting that observations at z ≳ 7.5 are needed to discriminate between different ε DC. We further extend the model at z ≤ 4, successfully describing the QLF between 1 ≤ z ≤ 4, albeit with additional assumptions on Σ and ε DC. We use the existing measurements of quasar duty cycle from clustering to constrain ε DC, finding ε DC ∼ 0.01 or ε DC ≳ 0.1 dependent on observational data sets used for reference. Finally, we present forecasts for future wide-area surveys with promising expectations for the Nancy Grace Roman Telescope to discover N ≳ 10, bright, m UV &lt; 26.5 quasars at z ∼ 8.

Constraining dark energy using the cross correlations of weak lensing with post-reionization probes of neutral hydrogen

We investigate the prospects of detecting the cross correlation of CMBR weak-lensing convergence field with the large scale tracers of the underlying dark matter distribution in the post-reionization epoch. The cross-correlation is then used to make error projections for dark energy equation of state (EoS)for models with a time evolving dark energy. We study the cross-correlation angular power spectrum of the weak-lensing field with the Lyman-α forest and the redshifted HI 21 cm signal from the post reionization epoch. The angular power spectra is expressed as a line of sight average over the tomographic slices. We find that on using multiple 400 hrs observation with an extended uGMRT like instrument or with a BOSS like survey with quasar (QSO) density of 16 deg−2 the cross-correlation with weak-lensing convergence field covering half the sky can be detected at a very high SNR (> 20). The cross-correlation of weak-lensing with Lyman-α forest allows the 1−σ errors on the dark energy EoS parameters for different parametrizations to be constrained at a level of precision comparable to combined Planck+SNIa+BAO+HST projections. The 21-cm weak-lensing cross-correlation is found to provide strong constraints on the present value of the dark energy EoS parameter at 4% for the 7CPL model. The constraints on wa is comparable (~12%) for models other than the 7CPL model. We also find that the CPL parametrization may not be the best constrained parametrization for dark energy evolution. The cross-correlation of CMBR weak-lensing with the post-reionization probes of neutral hydrogen thus holds the potential to give us valuable understanding about the nature of evolving dark energy.

High-redshift SMBHs can grow from stellar-mass seeds via chaotic accretion

ABSTRACT Extremely massive black holes, with masses $M_{\rm BH} \gt 10^9 {\, \rm M_{\odot }}$, have been observed at ever higher redshifts. These results create ever tighter constraints on the formation and growth mechanisms of early black holes. Here we show that even the most extreme black hole known, Pōniuā’ena, can grow from a $10 {\, \rm M_{\odot }}$ seed black hole via Eddington-limited luminous accretion, provided that accretion proceeds almost continuously, but is composed of a large number of episodes with individually uncorrelated initial directions. This chaotic accretion scenario ensures that the growing black hole spins slowly, with the dimensionless spin parameter $a \lower.5ex\hbox{$\,\, \buildrel\lt \over \sim \,\,$}0.2$, so its radiative efficiency is also low, ϵ ≃ 0.06. If accretion is even partially aligned, with $20\!-\!40{{\ \rm per\ cent}}$ of accretion events happening in the same direction, the black hole spin and radiative efficiency are much higher, leading to significantly slower growth. We suggest that the chaotic accretion scenario can be completely falsified only if a $10^9 {\, \rm M_{\odot }}$ black hole is discovered at z ≥ 9.1, approximately 150 Myr before Pōniuā’ena. The space density of extreme quasars suggests that only a very small fraction, roughly one in 4 × 107, of seed black holes need to encounter favourable growth conditions to produce the observed extreme quasars. Other seed black holes grow much less efficiently, mainly due to lower duty cycles, so are much more difficult to detect.

The Faint End of the Quasar Luminosity Function at z ∼ 5 from the Subaru Hyper Suprime-Cam Survey

Abstract We present the quasar luminosity function at z ∼ 5 derived from the optical wide-field survey data obtained as a part of the Subaru strategic program (SSP) with the Hyper Suprime-Cam (HSC). From a ∼81.8 deg2 area in the Wide layer of the HSC-SSP survey, we selected 224 candidates of low-luminosity quasars at z ∼ 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 ∼ 5, covering a wide luminosity range of −28.76 &lt; M 1450 &lt; −22.32 mag. We found that the quasar luminosity function is fitted by a double power-law model with a break magnitude of mag. The inferred number density of low-luminosity quasars is lower, and the derived faint-end slope, , is flatter than those of previous studies at z ∼ 5. A compilation of the quasar luminosity function at 4 ≤ z ≤ 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 ∼ 5 to z ∼ 6 than from z ∼ 4 to z ∼ 5.

Spectroscopic classification of a complete sample of astrometrically-selected quasar candidates using Gaia DR2

Here we explore the efficiency and fidelity of a purely astrometric selection of quasars as point sources with zero proper motions in the Gaia data release 2 (DR2). We have built a complete candidate sample including 104 Gaia-DR2 point sources, which are brighter than 20th magnitude in the Gaia G-band within one degree of the north Galactic pole (NGP); all of them have proper motions that are consistent with zero within 2σ uncertainty. In addition to pre-existing spectra, we have secured long-slit spectroscopy of all the remaining candidates and find that all 104 stationary point sources in the field can be classified as either quasars (63) or stars (41). One of the new quasars that we discover is particularly interesting as the line-of-sight to it passes through the disc of a foreground (z = 0.022) galaxy, which imprints both NaD absorption and dust extinction on the quasar spectrum. The selection efficiency of the zero-proper-motion criterion at high Galactic latitudes is thus ≈60%. Based on this complete quasar sample, we examine the basic properties of the underlying quasar population within the imposed limiting magnitude. We find that the surface density of quasars is 20 deg−2 (at G &lt; 20 mag), the redshift distribution peaks at z ∼ 1.5, and only eight systems (13-3+5%) show significant dust reddening. We then explore the selection efficiency of commonly used optical, near-, and mid-infrared quasar identification techniques and find that they are all complete at the 85−90% level compared to the astrometric selection. Finally, we discuss how the astrometric selection can be improved to an efficiency of ≈70% by including an additional cut requiring parallaxes of the candidates to be consistent with zero within 2σ. The selection efficiency will further increase with the release of future, more sensitive astrometric measurements from the Gaia mission. This type of selection, which is purely based on the astrometry of the quasar candidates, is unbiased in terms of colours and intrinsic emission mechanisms of the quasars and thus provides the most complete census of the quasar population within the limiting magnitude of Gaia.

ALMA High-frequency Long-baseline Campaign in 2017: A Comparison of the Band-to-band and In-band Phase Calibration Techniques and Phase-calibrator Separation Angles

The Atacama Large millimeter/submillimeter Array (ALMA) obtains spatial resolutions of 15 to 5 milli-arcsecond (mas) at 275-950GHz (0.87-0.32mm) with 16km baselines. Calibration at higher-frequencies is challenging as ALMA sensitivity and quasar density decrease. The Band-to-Band (B2B) technique observes a detectable quasar at lower frequency that is closer to the target, compared to one at the target high-frequency. Calibration involves a nearly constant instrumental phase offset between the frequencies and the conversion of the temporal phases to the target frequency. The instrumental offsets are solved with a differential-gain-calibration (DGC) sequence, consisting of alternating low and high frequency scans of strong quasar. Here we compare B2B and in-band phase referencing for high-frequencies ($>$289GHz) using 2-15km baselines and calibrator separation angles between $\sim$0.68 and $\sim$11.65$^{\circ}$. The analysis shows that: (1) DGC for B2B produces a coherence loss $<$7% for DGC phase RMS residuals $<$30$^{\circ}$. (2) B2B images using close calibrators ( $<$1.67$^{\circ}$ ) are superior to in-band images using distant ones ( $>$2.42$^{\circ}$ ). (3) For more distant calibrators, B2B is preferred if it provides a calibrator $\sim$2$^{\circ}$ closer than the best in-band calibrator. (4) Decreasing image coherence and poorer image quality occur with increasing phase calibrator separation angle because of uncertainties in the antenna positions and sub-optimal phase referencing. (5) To achieve $>$70% coherence for long-baseline (16 km) band 7 (289GHz) observations, calibrators should be within $\sim$4$^{\circ}$ of the target.

ISW in ΛCDM or something else?

ABSTRACT We investigate a correlation between the Planck’s CMB temperature map and statistics based on the space density of quasars in the SDSS catalogue. It is shown that the amplitude of the positive correlation imposes a lower limit on the amplitude of the Integrated Sachs–Wolfe effect independent of the quasar bias factor. Implications of this constraint for the ISW effect in the Λ cold dark matter (ΛCDM) model are examined. Strength of the correlation indicates that the rms of temperature fluctuations associated with the quasars distributed between 1500 and 3000 Mpc likely exceeds $11{\!-\!}12\, \mu$K. The signal seems to be related to an overall space distribution of quasars rather than to a few exceptionally dominant structures like supervoids. Although, the present estimates are subject to sizable uncertainties, the signal apparently exceeds the model predictions of the ISW effect for the standard ΛCDM cosmology. This conclusion is consistent with several other investigations that also claim some disparity between the observed ISW signal and the theoretical predictions.

A rapidly evolving quasar population at the epoch of reionzation

AbstractI will present results from our on-going large area survey of high-redshift quasars, which has discovered more than 20 new quasars at z &gt; 6.5, at the epoch of reionization, forming the first large statistical sample of EoR quasars. I will discuss the rapid evolution of quasar density at that epoch, which suggests that we are witnessing the emergence of the first supermassive black hole population. I will also present multiwavelength followup observation results, especially from ALMA and Chandra, which reveals a diverse environment of quasar activities and yields new insights into the supermassive black hole/massive galaxy co-evolution.

The quasar luminosity function at redshift 4 with the Hyper Suprime-Cam Wide Survey

Abstract We present the luminosity function of z ∼ 4 quasars based on the Hyper Suprime-Cam Subaru Strategic Program Wide layer imaging data in the g, r, i, z, and y bands covering 339.8 deg2. From stellar objects, 1666 z ∼ 4 quasar candidates are selected via the g-dropout selection down to i = 24.0 mag. Their photometric redshifts cover the redshift range between 3.6 and 4.3, with an average of 3.9. In combination with the quasar sample from the Sloan Digital Sky Survey in the same redshift range, a quasar luminosity function covering the wide luminosity range of M1450 = −22 to −29 mag is constructed. The quasar luminosity function is well described by a double power-law model with a knee at M1450 = −25.36 ± 0.13 mag and a flat faint-end slope with a power-law index of −1.30 ± 0.05. The knee and faint-end slope show no clear evidence of redshift evolution from those seen at z ∼ 2. The flat slope implies that the UV luminosity density of the quasar population is dominated by the quasars around the knee, and does not support the steeper faint-end slope at higher redshifts reported at z &amp;gt; 5. If we convert the M1450 luminosity function to the hard X-ray 2–10 keV luminosity function using the relation between the UV and X-ray luminosity of quasars and its scatter, the number density of UV-selected quasars matches well with that of the X-ray-selected active galactic nuclei (AGNs) above the knee of the luminosity function. Below the knee, the UV-selected quasars show a deficiency compared to the hard X-ray luminosity function. The deficiency can be explained by the lack of obscured AGNs among the UV-selected quasars.