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.
We present the data release 14 Quasar catalog (DR14Q) from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) of the Sloan Digital Sky Survey IV (SDSS-IV). This catalog includes all ...SDSS-IV/eBOSS objects that were spectroscopically targeted as quasar candidates and that are confirmed as quasars via a new automated procedure combined with a partial visual inspection of spectra, have luminosities Mi z = 2 < −20.5 $M_{\textrm{i}} \left z=2 \right < -20.5$ Mi z=2 <−20.5 (in a Λ CDM cosmology with H0 = 70 km s−1 Mpc−1, Ω M =0.3, and Ω Λ = 0.7), and either display at least one emission line with a full width at half maximum larger than 500 km s−1 or, if not, have interesting/complex absorption features. The catalog also includes previously spectroscopically-confirmed quasars from SDSS-I, II, and III. The catalog contains 526 356 quasars (144 046 are new discoveries since the beginning of SDSS-IV) detected over 9376 deg2 (2044 deg2 having new spectroscopic data available) with robust identification and redshift measured by a combination of principal component eigenspectra. The catalog is estimated to have about 0.5% contamination. Redshifts are provided for the Mg II emission line. The catalog identifies 21 877 broad absorption line quasars and lists their characteristics. For each object, the catalog presents five-band (u, g, r, i, z) CCD-based photometry with typical accuracy of 0.03 mag. The catalog also contains X-ray, ultraviolet, near-infrared, and radio emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra, covering the wavelength region 3610–10 140 Å at a spectral resolution in the range 1300 < R < 2500, can be retrieved from the SDSS Science Archiver Server.
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).
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
Recenzirano
Odprti dostop
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 present the final results from our survey of luminous z ∼ 5.5 quasars. This is the first systematic quasar survey focusing on quasars at z ∼ 5.5, during the post-reionization epoch. It has been ...challenging to select quasars at 5.3 < z < 5.7 using conventional color selections, due to their similar optical colors to those of late-type stars, especially M dwarfs. We developed a new selection technique for z ∼ 5.5 quasars based on optical, near-infrared (IR), and mid-IR photometry, using data from the Sloan Digital Sky Survey (SDSS), PanSTARR1 (PS1), the UKIRT Infrared Deep Sky Surveys-Large Area Survey, the UKIRT Hemisphere Survey, the VISTA Hemisphere Survey, and the Wide Field Infrared Survey Explorer, covering ∼11,000 deg2 of high galactic latitude sky. In this paper, we present the discovery of 15 new quasars at 5.22 ≤ z ≤ 5.78. Together with results from Yang et al., our survey provides a complete, flux-limited sample of 31 quasars at 5.3 ≤ z ≤ 5.7. We measure the quasar spatial density at z ∼ 5.5 and M1450 < −26.2. Our result is consistent with the rapid decline of the quasar spatial density from z = 5 to 6, with k = −0.66 0.05 ( (z) ∝ 10kz). In addition, we present a new survey using optical colors only from the full PS1 area for luminous quasars at z = 5.0-5.5, which is beyond the SDSS footprint, and report the preliminary results from this survey, including 51 new quasars discovered at 4.61 ≤ z ≤ 5.71.
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.
We present initial results from the first systematic survey of luminous z ∼ 5.5 quasars. Quasars at z ∼ 5.5, the post-reionization epoch, are crucial tools to explore the evolution of intergalactic ...medium, quasar evolution, and the early super-massive black hole growth. However, it has been very challenging to select quasars at redshifts 5.3 ≤ z ≤ 5.7 using conventional color selections, due to their similar optical colors to late-type stars, especially M dwarfs, resulting in a glaring redshift gap in quasar redshift distributions. We develop a new selection technique for z ∼ 5.5 quasars based on optical, near-IR, and mid-IR photometric data from Sloan Digital Sky Survey (SDSS), UKIRT InfraRed Deep Sky Surveys-Large Area Survey (ULAS), VISTA Hemisphere Survey (VHS), and Wide Field Infrared Survey Explorer. From our pilot observations in the SDSS-ULAS/VHS area, we have discovered 15 new quasars at 5.3 ≤ z ≤ 5.7 and 6 new lower redshift quasars, with SDSS z band magnitude brighter than 20.5. Including other two z ∼ 5.5 quasars already published in our previous work, we now construct a uniform quasar sample at 5.3 ≤ z ≤ 5.7, with 17 quasars in a ∼4800 square degree survey area. For further application in a larger survey area, we apply our selection pipeline to do a test selection by using the new wide field J-band photometric data from a preliminary version of the UKIRT Hemisphere Survey (UHS). We successfully discover the first UHS selected z ∼ 5.5 quasar.
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.
Abstract
We present reverberation mapping results from the first year of combined spectroscopic and photometric observations of the Sloan Digital Sky Survey Reverberation Mapping Project. We ...successfully recover reverberation time delays between the
g
+
i
band emission and the broad H
β
emission line for a total of 44 quasars, and for the broad H
α
emission line in 18 quasars. Time delays are computed using the
JAVELIN
and
CREAM
software and the traditional interpolated cross-correlation function (ICCF): using well-defined criteria, we report measurements of 32 H
β
and 13 H
α
lags with
JAVELIN
, 42 H
β
and 17 H
α
lags with
CREAM
, and 16 H
β
and eight H
α
lags with the ICCF. Lag values are generally consistent among the three methods, though we typically measure smaller uncertainties with
JAVELIN
and
CREAM
than with the ICCF, given the more physically motivated light curve interpolation and more robust statistical modeling of the former two methods. The median redshift of our H
β
-detected sample of quasars is 0.53, significantly higher than that of the previous reverberation mapping sample. We find that in most objects, the time delay of the H
α
emission is consistent with or slightly longer than that of H
β
. We measure black hole masses using our measured time delays and line widths for these quasars. These black hole mass measurements are mostly consistent with expectations based on the local
–
relationship, and are also consistent with single-epoch black hole mass measurements. This work increases the current sample size of reverberation-mapped active galaxies by about two-thirds and represents the first large sample of reverberation mapping observations beyond the local universe (
z
< 0.3).
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