This is the third paper in a series aimed at finding reionization-era quasars with the combination of DESI Legacy imaging Surveys (DELS), the Pan-STARRS1 (PS1) Survey, and near-infrared imaging ...surveys, such as the UKIRT Hemisphere Survey (UHS), as well as the Wide-field Infrared Survey Explorer (WISE) mid-infrared survey. In this paper, we describe the updated quasar candidate selection procedure, report the discovery of 16 quasars at 6.4 z 6.9 from an area of ∼13,020 deg2, and present the quasar luminosity function (QLF) at z ∼ 6.7. The measured QLF follows in the magnitude range −27.6 < M1450 < −25.5. We determine the quasar comoving spatial density at = 6.7 and M1450 < −26.0 to be 0.39 0.11 Gpc−3 and find the exponential density evolution parameter to be k = −0.78 0.18 from z ∼ 6 to z ∼ 6.7, corresponding to a rapid decline by a factor of ∼6 per unit redshift toward earlier epochs. This indicates that the rapid decline of quasar spatial density at z > 5 that was found by previous works continues to z > 6, at a rate significantly faster than the average decline rate between z ∼ 3 and 5. We measured quasar comoving emissivity at z ∼ 6.7, which indicates that high-redshift quasars are highly unlikely to make a significant contribution to hydrogen reionization. The broad absorption line quasar fraction at z 6.5 is measured to be 22%. In addition, we also report the discovery of six additional quasars at z ∼ 6 in the Appendix.
Lyα emission-line reconstruction for high- z QSOs Greig, Bradley; Mesinger, Andrei; McGreer, Ian D ...
Monthly notices of the Royal Astronomical Society,
04/2017, Letnik:
466, Številka:
2
Journal Article
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We introduce an intrinsic Lya emission-line profile reconstruction method for high-z quasars (QSOs). This approach utilises a covariance matrix of emission-line properties obtained from a large, ...moderate-z (2 = z = 2.5), high signal to noise (S/N > 15) sample of BOSS QSOs. For each QSO, we complete a Monte Carlo Markov Chain fitting of the continuum and emission-line properties and perform a visual quality assessment to construct a large data base of robustly fit spectra. With this data set, we construct a covariance matrix to describe the correlations between the high-ionization emission lines Lya, Civ, Siiv +Oiv and Ciii, and find it to be well approximated by an N-dimensional Gaussian distribution. This covariance matrix characterizes the correlations between the linewidth, peak height and velocity offset from systemic while also allowing for the existence of broad- and narrow-line components for Lya and Civ. We illustrate how this covariance matrix allows us to statistically characterize the intrinsic Lya line solely from the observed spectrum redward of 1275 A. This procedure can be used to reconstruct the intrinsic Lya line emission profile in cases where Lya may otherwise be obscured. Applying this reconstruction method to our sample of QSOs, we recovered the Lya line flux to within 15 per cent of the measured flux at 1205 A (1220 A) ~85 (90) per cent of the time.
We report the discovery of a quasar pair at z= 5 separated by 21''. Both objects were identified as quasar candidates using simple color selection techniques applied to photometric catalogs from the ...Canada-France-Hawaii Telescope (CFHT) Legacy Survey (CFHTLS). Spectra obtained with the MMT present no discernible offset in redshift between the two objects; on the other hand, there are clear differences in the emission line profiles and in the multiwavelength spectral energy distributions that strongly disfavor the hypothesis that they are gravitationally lensed images of a single quasar. Both quasars are surprisingly bright given their proximity (a projected separation of ~135 kpc), with i= 19.4 and i= 21.4. Previous measurements of the luminosity function demonstrate that luminous quasars are extremely rare at z= 5; the existence of this pair suggests that quasars have strong small-scale clustering at high redshift. Assuming a real-space correlation function of the form xi(r) proportional, variant (r/r sub(0)) super(-2), this discovery implies a correlation length of r sub(0)> ~ 20h super(-1) Mpc, consistent with a rapid strengthening of quasar clustering at high redshift as seen in previous observations and predicted by theoretical models where feedback effects are inefficient at shutting down black hole growth at high redshift.
Cosmological simulations suggest a strong correlation between high optical-depth Ly absorbers, which arise from the intergalactic medium, and 3D mass overdensities on scales of 10-30 comoving Mpc. By ...examining the absorption spectra of ∼80,000 QSO sight lines over a volume of 0.1 Gpc3 in the Sloan Digital Sky Survey III (SDSS-III), we have identified an extreme overdensity, BOSS1441, which contains a rare group of strong Ly absorbers at . This absorber group is associated with six QSOs at the same redshift on a 30 comoving Mpc scale. Using Mayall/MOSAIC narrowband and broadband imaging, we detect Ly emitters (LAEs) down to and reveal a large-scale structure of LAEs in this field. Our follow-up LBT observations have spectroscopically confirmed 20 galaxies in the density peak. We show that BOSS1441 has an LAE overdensity of 10.8 2.6 on a 15 comoving Mpc scale, which could collapse to a massive cluster with M 1015 at . This overdensity is among the most massive large-scale structures at discovered to date.
We present a new measurement of the optical quasar luminosity function (QLF), using data from the Sloan Digital Sky Survey-III: Baryon Oscillation Spectroscopic Survey (SDSS-III: BOSS). From the ...SDSS-III Data Release Nine, a uniform sample of 22,301 i lap 21.8 quasars are selected over an area of 2236 deg super(2), with confirmed spectroscopic redshifts between 2.2 < z < 3.5, filling in a key part of the luminosity-redshift plane for optical quasar studies. At z lap 2.2 our data are reasonably well fit by a pure luminosity evolution model, and only a weak signature of "AGN downsizing" is seen, in line with recent studies of the hard X-ray luminosity function. We compare our measured QLF to a number of theoretical models and find that models making a variety of assumptions about quasar triggering and halo occupation can fit our data over a wide range of redshifts and luminosities.
ABSTRACT We present the discovery of eight quasars at identified in the Sloan Digital Sky Survey (SDSS) overlap regions. Individual SDSS imaging runs have some overlap with each other, leading to ...repeat observations over an area spanning >4000 deg2 (more than one-fourth of the total footprint). These overlap regions provide a unique data set that allows us to select high-redshift quasars more than 0.5 mag fainter in the z band than those found with the SDSS single-epoch data. Our quasar candidates were first selected as i-band dropout objects in the SDSS imaging database. We then carried out a series of follow-up observations in the optical and near-IR to improve photometry, remove contaminants, and identify quasars. The eight quasars reported here were discovered in a pilot study utilizing the overlap regions at high galactic latitude ( ). These quasars span a redshift range of and a flux range of mag. Five of them are fainter than mag, the typical magnitude limit of quasars used for the SDSS single-epoch images. In addition, we recover eight previously known quasars at that are located in the overlap regions. These results validate our procedure for selecting quasar candidates from the overlap regions and confirming them with follow-up observations, and they provide guidance to a future systematic survey over all SDSS imaging regions with repeat observations.
We have designed the Extremely Luminous Quasar Survey (ELQS) to provide a highly complete census of unobscured UV-bright quasars during the cosmic noon, z = 2.8-5.0. Here we report the discovery of ...70 new quasars in the ELQS South Galactic Cap (ELQS-S) quasar sample, doubling the number of known extremely luminous quasars in 4237.3 deg2 of the Sloan Digital Sky Survey footprint. These observations conclude the ELQS and we present the properties of the full ELQS quasar catalog, containing 407 quasars over 11,838.5 deg2. Our novel ELQS quasar selection strategy resulted in unprecedented completeness at the bright end and allowed us to discover 109 new quasars in total. This marks an increase of ∼36% (109/298) in the known population at these redshifts and magnitudes, while we further are able to retain a selection efficiency of ∼80%. On the basis of 166 quasars from the full ELQS quasar catalog, which adhere to the uniform criteria of the Two Micron All Sky Survey point source catalog, we measure the bright-end quasar luminosity function (QLF) and extend it one magnitude brighter than previous studies. Assuming a single power law with exponential density evolution for the functional form of the QLF, we retrieve the best-fit parameters from a maximum likelihood analysis. We find a steep bright-end slope of β −4.1, and we can constrain the bright-end slope to β ≤ −3.4 with 99% confidence. The density is well modeled by the exponential redshift evolution, resulting in a moderate decrease with redshift (γ −0.4).
Quasar broad emission lines are largely powered by photoionization from the accretion continuum. Increased central luminosity will enhance line emissivity in more distant clouds, leading to increased ...average distance of the broad-line-emitting clouds and decreased averaged line width, which is known as the "breathing" broad-line region. However, different lines breathe differently, and some high-ionization lines, such as C iv, can even show "anti-breathing" where the line broadens when luminosity increases. Using multi-year photometric and spectroscopic monitoring data from the Sloan Digital Sky Survey Reverberation Mapping project, we quantify the breathing effect ( ) of broad H , Hβ, Mg ii, C iv, and C iii for statistical quasar samples over z 0.1-2.5. We find that Hβ displays the most consistent normal breathing expected from the virial relation ( ∼ −0.25), Mg ii and H on average show no breathing ( ∼ 0), and C iv (and similarly C iii and Si iv) mostly shows anti-breathing ( > 0). The anti-breathing of C iv can be well understood by the presence of a non-varying core component in addition to a reverberating broad-base component, which is consistent with earlier findings. The deviation from canonical breathing introduces extra scatter (a luminosity-dependent bias) in single-epoch virial BH mass estimates due to intrinsic quasar variability, which underlies the long-argued caveats of C iv single-epoch masses. Using the line dispersion instead of FWHM leads to fewer, albeit still substantial, deviations from canonical breathing in most cases. Our results strengthen the need for reverberation mapping to provide reliable quasar BH masses and to quantify the level of variability-induced bias in single-epoch BH masses based on various lines.
Abstract
We utilize the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope to search for extended Ly
α
emission around the
z
∼ 6.6 QSO J0305−3150. After carefully subtracting the ...point spread function, we reach a nominal 5
σ
surface-brightness limit of SB
5
σ
= 1.9 × 10
−18
erg s
−1
cm
−2
arcsec
−2
over a 1 arcsec
2
aperture, collapsing five wavelength slices centered at the expected location of the redshifted Ly
α
emission (i.e., at 9256 Å). Current data suggest the presence (5
σ
accounting for systematics) of a Ly
α
nebula that extends for 9 kpc around the QSO. This emission is displaced and redshifted by 155 km s
−1
with respect to the location of the QSO host galaxy traced by the
158
μ
m emission line. The total luminosity is
= (3.0 ± 0.4) × 10
42
erg s
−1
. Our analysis suggests that this emission is unlikely to rise from optically thick clouds illuminated by the ionizing radiation of the QSO. It is more plausible that the Ly
α
emission is due to the fluorescence of the highly ionized optically thin gas. This scenario implies a high hydrogen volume density of
cm
−3
. In addition, we detect a Ly
α
emitter (LAE) in the immediate vicinity of the QSO, i.e., with a projected separation of ∼12.5 kpc and a line-of-sight velocity difference of 560 km s
−1
. The luminosity of the LAE is
= (2.1 ± 0.2) × 10
42
erg s
−1
and its inferred star-formation rate is SFR ∼ 1.3
M
⊙
yr
−1
. The probability of finding such a close LAE is one order of magnitude above the expectations based on the QSO–galaxy cross-correlation function. This discovery is in agreement with a scenario where dissipative interactions favor the rapid build-up of supermassive black holes at early cosmic times.
Studies of the most luminous quasars at high redshift directly probe the evolution of the most massive black holes in the early universe and their connection to massive galaxy formation. However, ...extremely luminous quasars at high redshift are very rare objects. Only wide-area surveys have a chance to constrain their population. The Sloan Digital Sky Survey (SDSS) has so far provided the most widely adopted measurements of the quasar luminosity function at . However, a careful re-examination of the SDSS quasar sample revealed that the SDSS quasar selection is in fact missing a significant fraction of quasars at the brightest end. We identified the purely optical-color selection of SDSS, where quasars at these redshifts are strongly contaminated by late-type dwarfs, and the spectroscopic incompleteness of the SDSS footprint as the main reasons. Therefore, we designed the Extremely Luminous Quasar Survey (ELQS), based on a novel near-infrared JKW2 color cut using Wide-field Infrared Survey Explorer mission (WISE) AllWISE and 2MASS all-sky photometry, to yield high completeness for very bright ( ) quasars in the redshift range of . It effectively uses random forest machine-learning algorithms on SDSS and WISE photometry for quasar-star classification and photometric redshift estimation. The ELQS will spectroscopically follow-up ∼230 new quasar candidates in an area of ∼12,000 deg2 in the SDSS footprint to obtain a well-defined and complete quasar sample for an accurate measurement of the bright-end quasar luminosity function (QLF) at . In this paper, we present the quasar selection algorithm and the quasar candidate catalog.
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