We present a measurement of the Type I quasar luminosity function at z = 5 using a large sample of spectroscopically confirmed quasars selected from optical imaging data. We measure the bright end ...(Msub 1450 < -26) with Sloan Digital Sky Survey (SDSS) data covering -6000 deg2, then extend to lower luminosities (Msub 1450 < -24) with newly discovered, faint z ~ 5 quasars selected from 235 degsup 2 of deep, coadded imaging in the SDSS Stripe 82 region (the celestial equator in the Southern Galactic Cap). Our model for the quasar luminosity function predicts that quasars generate ~30% of the ionizing photons required to keep hydrogen in the universe ionized at z = 5.
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.
We present the first discoveries from a survey of z 6 quasars using imaging data from the DECam Legacy Survey (DECaLS) in the optical, the UKIRT Deep Infrared Sky Survey (UKIDSS) and a preliminary ...version of the UKIRT Hemisphere Survey (UHS) in the near-IR, and ALLWISE in the mid-IR. DECaLS will image 9000 deg2 of sky down to zAB ∼ 23.0, and UKIDSS and UHS will map the northern sky at 0 < decl. < +60°, reaching JVEGA ∼ 19.6 (5- ). The combination of these data sets allows us to discover quasars at redshift z 7 and to conduct a complete census of the faint quasar population at z 6. In this paper, we report on the selection method of our search, and on the initial discoveries of two new, faint z 6 quasars and one new z = 6.63 quasar in our pilot spectroscopic observations. The two new z ∼ 6 quasars are at z = 6.07 and z = 6.17 with absolute magnitudes at rest-frame wavelength 1450 being M1450 = −25.83 and M1450 = −25.76, respectively. These discoveries suggest that we can find quasars close to or fainter than the break magnitude of the Quasar Luminosity Function (QLF) at z 6. The new z = 6.63 quasar has an absolute magnitude of M1450 = −25.95. This demonstrates the potential of using the combined DECaLS and UKIDSS/UHS data sets to find z 7 quasars. Extrapolating from previous QLF measurements, we predict that these combined data sets will yield ∼200 z ∼ 6 quasars to zAB < 21.5, ∼1000 z ∼ 6 quasars to zAB < 23, and ∼30 quasars at z > 6.5 to JVEGA < 19.5.
We present the North Galactic Cap sample of the Extremely Luminous Quasar Survey (ELQS-N), which targets quasars with M1450 < −27 at 2.8 ≤ z < 5 in an area of ∼7600 deg2 of the Sloan Digital Sky ...Survey (SDSS) footprint with 90° < R.A. < 270°. Based on a near-infrared/infrared JKW2 color cut, the ELQS selection efficiently uses random forest methods to classify quasars and to estimate photometric redshifts; this scheme overcomes some of the difficulties of pure optical quasar selection at z 3. As a result, we retain a completeness of >70% over z ∼ 3.0-5.0 at mi 17.5, limited toward fainter magnitudes by the depth of the Two Micron All Sky Survey. The presented quasar catalog consists of a total of 270 objects, of which 39 are newly identified in this work with spectroscopy obtained at the Vatican Advanced Technology Telescope and the MMT 6.5 m telescope. In addition to the high completeness, which allowed us to discover new quasars in the already well-surveyed SDSS North Galactic Cap, the efficiency of our selection is relatively high at ∼79%. Using 120 objects of this quasar sample we are able to extend the previously measured optical quasar luminosity function (QLF) by one magnitude toward the bright end at 2.8 ≤ z ≤ 4.5. A first analysis of the QLF suggests a relatively steep bright-end slope of β −4 for this sample. This result contrasts with previous results in the same redshift range, which find a much flatter slope around β ∼ −2.5, but agrees with recent measurements of the bright-end slope at lower and higher redshifts. Our results constrain the bright-end slope at z = 2.8-4.5 to β < −2.94 with a 99% confidence.
ABSTRACT High-redshift quasars are important tracers of structure and evolution in the early universe. However, they are very rare and difficult to find when using color selection because of ...contamination from late-type dwarfs. High-redshift quasar surveys based on only optical colors suffer from incompleteness and low identification efficiency, especially at . We have developed a new method to select quasars with both high efficiency and completeness by combining optical and mid-IR Wide-field Infrared Survey Explorer (WISE) photometric data, and are conducting a luminous quasar survey in the whole Sloan Digital Sky Survey (SDSS) footprint. We have spectroscopically observed 99 out of 110 candidates with z-band magnitudes brighter than 19.5, and 64 (64.6%) of them are quasars with redshifts of and absolute magnitudes of . In addition, we also observed 14 fainter candidates selected with the same criteria and identified 8 (57.1%) of them as quasars with . Among 72 newly identified quasars, 12 of them are at , which leads to an increase of ∼36% of the number of known quasars at this redshift range. More importantly, our identifications doubled the number of quasars with at , which will set strong constraints on the bright end of the quasar luminosity function. We also expand our method to select quasars at z 5.7. In this paper we report the discovery of four new luminous z 5.7 quasars based on SDSS-WISE selection.
Recent observations have suggested that the C iii emission lines could be alternative diagnostic lines for galaxies in the reionization epoch. We use the F128N narrowband filter on the Hubble Space ...Telescope's (HST) Wide Field Camera 3 (WFC3) to search for C iii emission in a sample of five galaxies at z = 5.7 in the Subaru Deep Field and the Subaru/XMM-Newton Deep Field. Using the F128N narrowband imaging, together with the broadband imaging, we do not detect C iii emission for the five galaxies with ranging from 24.10 to 27.00 in our sample. For the brightest galaxy J132416.13+274411.6 in our sample (z = 5.70, ), which has a significantly higher signal to noise, we report a C iii flux of , which places a stringent 3 upper limit of on C iii flux and 6.57 on the C iii equivalent width. Using the stacked image, we put a 3 upper limit on the mean C iii flux of and a 3 upper limit on the mean C iii equivalent width of 4.20 for this sample of galaxies at z = 5.70. Combined with strong C iii detection reported among high-z galaxies in the literature, our observations suggest that the equivalent widths of C iii from galaxies at z > 5.70 exhibit a wide range of distribution. Our strong limits on C iii emission could be used as a guide for future observations in the reionization epoch.
ABSTRACT This is the second paper in a series on a new luminous z ∼ 5 quasar survey using optical and near-infrared colors. Here we present a new determination of the bright end of the quasar ...luminosity function (QLF) at z ∼ 5. Combining our 45 new quasars with previously known quasars that satisfy our selections, we construct the largest uniform luminous z ∼ 5 quasar sample to date, with 99 quasars in the range of 4.7 ≤ z < 5.4 and −29 < M1450 ≤ −26.8, within the Sloan Digital Sky Survey (SDSS) footprint. We use a modified 1/Va method including flux limit correction to derive a binned QLF, and we model the parametric QLF using maximum likelihood estimation. With the faint-end slope of the QLF fixed as = −2.03 from previous deeper samples, the best fit of our QLF gives a flatter bright end slope β = −3.58 0.24 and a fainter break magnitude = −26.98 0.23 than previous studies at similar redshift. Combined with previous work at lower and higher redshifts, our result is consistent with a luminosity evolution and density evolution model. Using the best-fit QLF, the contribution of quasars to the ionizing background at z ∼ 5 is found to be 18%-45% with a clumping factor C of 2-5. Our sample suggests an evolution of radio loud fraction with optical luminosity but no obvious evolution with redshift.
The Sloan Digital Sky Survey Reverberation Mapping (SDSS-RM) project is a dedicated multi-object RM experiment that has spectroscopically monitored a sample of 849 broad-line quasars in a single 7 ...deg super(2) field with the SDSS-III Baryon Oscillation Spectroscopic Survey spectrograph. The RM quasar sample is flux-limited to i sub(psf) = 21.7 mag, and covers a redshift range of 0.1 < z < 4.5 without any other cuts on quasar properties. Optical spectroscopy was performed during 2014 January-July dark/gray time, with an average cadence of ~4 days, totaling more than 30 epochs. Supporting photometric monitoring in the g and i bands was conducted at multiple facilities including the Canada-France-Hawaii Telescope (CFHT) and the Steward Observatory Bok telescope in 2014, with a cadence of ~2 days and covering all lunar phases. The RM field (R.A., decl. = 14:14:49.00, +53:05:00.0) lies within the CFHT-LS W3 field, and coincides with the Pan-STARRS 1 (PS1) Medium Deep Field MD07, with three prior years of multi-band PS1 light curves. The SDSS-RM six month baseline program aims to detect time lags between the quasar continuum and broad line region (BLR) variability on timescales of up to several months (in the observed frame) for ~10% of the sample, and to anchor the time baseline for continued monitoring in the future to detect lags on longer timescales and at higher redshift. SDSS-RM is the first major program to systematically explore the potential of RM for broad-line quasars at z > 0.3, and will investigate the prospects of RM with all major broad lines covered in optical spectroscopy. SDSS-RM will provide guidance on future multi-object RM campaigns on larger scales, and is aiming to deliver more than tens of BLR lag detections for a homogeneous sample of quasars. We describe the motivation, design, and implementation of this program, and outline the science impact expected from the resulting data for RM and general quasar science.
We analyze extensive spectroscopic and photometric data of the hypervariable quasar SDSS J141324+530527 (RMID 017) at z = 0.456, an optical "changing-look" quasar from the Sloan Digital Sky Survey ...Reverberation Mapping project that increased in optical luminosity by a factor 10 between 2014 and 2017. The observed broad emission lines all respond in luminosity and width to the changing optical continuum, as expected for photoionization in a stratified, virialized broad emission line region. The luminosity changes therefore result from intrinsic changes in accretion power rather than variable obscuration. The variability is continuous and apparently stochastic, disfavoring an origin as a discrete event such as a tidal disruption flare or microlensing event. It is coordinated on day timescales with blue leading red, consistent with reprocessing powering the entire optical spectral energy distribution. We show that this process cannot work in a standard thin disk geometry on energetic grounds, and would instead require a large covering factor reprocessor. Disk instability models could potentially also explain the data, provided that the instability sets in near the inner radius of a geometrically thick accretion disk.
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![Constraining C iii] Emissio...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/2041-8205/small "Constraining C iii] Emission in a Sample of Five Luminous z = 5.7 Galaxies")
