Publications

2007
Sadler EM, Cannon RD, Mauch T, Hancock PJ, Wake DA, Ross N, Croom SM, Drinkwater MJ, Edge AC, Eisenstein D, et al. Radio galaxies in the 2SLAQ Luminous Red Galaxy Survey - I. The evolution of low-power radio galaxies to z ~ 0.7. Monthly Notices of the Royal Astronomical Society. 2007;381 :211-227. Publisher's VersionAbstract

We have combined optical data from the 2dF-SDSS (Sloan Digital SkySurvey) LRG (Luminous Red Galaxy) and QSO (quasi-stellar object) (2SLAQ)redshift survey with radio measurements from the 1.4GHz VLA (Very LargeArray) FIRST (Faint Images of the Radio Sky at Twenty-cm) and NVSS (NRAOVLA Sky Survey) surveys to identify a volume-limited sample of 391 radiogalaxies at redshift 0.4 < z < 0.7. By determining an accurateradio luminosity function for luminous early-type galaxies in thisredshift range, we can investigate the cosmic evolution of theradio-galaxy population over a wide range in radio luminosity.The low-power radio galaxies in our LRG sample (those with 1.4GHz radioluminosities in the range 1024 to1025WHz-1, corresponding to Fanaroff-Riley I (FRI)radio galaxies in the local Universe) undergo significant cosmicevolution over the redshift range 0 < z < 0.7, consistent withpure luminosity evolution of the form (1 + z)k, where k = 2.0+/- 0.3. Our results appear to rule out (at the 6-7σ level) modelsin which low-power radio galaxies undergo no cosmic evolution. The mostpowerful radio galaxies in our sample (with radio luminosities above1026WHz-1) may undergo more rapid evolution overthe same redshift range.The evolution seen in the low-power radio-galaxy population implies thatthe total energy input into massive early-type galaxies from activegalactic nucleus (AGN) heating increases with redshift, and was at least50 per cent higher at z ~ 0.55 (the median redshift of the 2SLAQ LRGsample) than in the local universe.

Ross NP, da Ângela J, Shanks T, Wake DA, Cannon RD, Edge AC, Nichol RC, Outram PJ, Colless M, Couch WJ, et al. The 2dF-SDSS LRG and QSO Survey: the LRG 2-point correlation function and redshift-space distortions. Monthly Notices of the Royal Astronomical Society. 2007;381 :573-588. Publisher's VersionAbstract

We present a clustering analysis of luminous red galaxies (LRGs) usingnearly 9000 objects from the final, three-year catalogue of the 2dF-SDSSLRG and QSO (2SLAQ) Survey. We measure the redshift-space two-pointcorrelation function, ξ(s) and find that, at the mean LRG redshift ofshows the characteristic downturn at small scales(<~1h-1Mpc) expected from line-of-sight velocitydispersion. We fit a double power law to ξ(s) and measure anamplitude and slope of s0 =17.3+2.5-2.0h-1Mpc,γ = 1.03 +/-0.07 at small scales (s < 4.5h-1Mpc) and s0 =9.40 +/- 0.19h-1Mpc,γ = 2.02 +/- 0.07 at large scales(s > 4.5h-1Mpc). In the semiprojected correlationfunction, wp(σ), we find a simple power law withγ = 1.83 +/- 0.05 and r0 = 7.30 +/-0.34h-1Mpc fits the data in the range 0.4 < σ <50h-1Mpc, although there is evidence of a steeper power lawat smaller scales. A single power law also fits the deprojectedcorrelation function ξ(r), with a correlation length of r0= 7.45 +/- 0.35h-1Mpc and a power-law slope of γ = 1.72+/- 0.06 in the 0.4 < r < 50h-1Mpc range. But it is inthe LRG angular correlation function that the strongest evidence fornon-power-law features is found where a slope of γ = -2.17 +/-0.07 is seen at 1 < r < 10h-1Mpc with a flatter γ= -1.67 +/- 0.07 slope apparent at r <~ 1h-1Mpc scales.We use the simple power-law fit to the galaxy ξ(r), under theassumption of linear bias, to model the redshift-space distortions inthe 2D redshift-space correlation function, ξ(σ, π). We fitfor the LRG velocity dispersion, wz, the density parameter,Ωm and β(z), where β(z) =Ω0.6m/b and b is the linear bias parameter.We find values of wz =330kms-1m =0.10+0.35-0.10 and β = 0.40 +/- 0.05. The lowvalues for wz and β reflect the high bias of the LRGsample. These high-redshift results, which incorporate theAlcock-Paczynski effect and the effects of dynamical infall, start tobreak the degeneracy between Ωm and β found inlow-redshift galaxy surveys such as 2dFGRS. This degeneracy is furtherbroken by introducing an additional external constraint, which is thevalue β(z = 0.1) = 0.45 from 2dFGRS, and then considering theevolution of clustering from z ~ 0 to zLRG ~ 0.55. With thesecombined methods we find Ωm(z = 0) = 0.30 +/- 0.15 andβ(z = 0.55) = 0.45 +/- 0.05. Assuming these values, we find a valuefor b(z = 0.55) = 1.66 +/- 0.35. We show that this is consistent with asimple `high-peak' bias prescription which assumes that LRGs have aconstant comoving density and their clustering evolves purely undergravity.

Percival WJ, Cole S, Eisenstein DJ, Nichol RC, Peacock JA, Pope AC, Szalay AS. Measuring the Baryon Acoustic Oscillation scale using the Sloan Digital Sky Survey and 2dF Galaxy Redshift Survey. Monthly Notices of the Royal Astronomical Society. 2007;381 :1053-1066. Publisher's VersionAbstract

We introduce a method to constrain general cosmological models usingBaryon Acoustic Oscillation (BAO) distance measurements from galaxysamples covering different redshift ranges, and apply this method toanalyse samples drawn from the Sloan Digital Sky Survey (SDSS) and 2dFGalaxy Redshift Survey (2dFGRS). BAOs are detected in the clustering ofthe combined 2dFGRS and SDSS main galaxy samples, and measure thedistance-redshift relation at z = 0.2. BAOs in the clustering of theSDSS luminous red galaxies measure the distance-redshift relation at z =0.35. The observed scales of the BAOs calculated from these samples andfrom the combined sample are jointly analysed using estimates of thecorrelated errors, to constrain the form of the distance measureDV(z) ≡ [(1 +z)2D2Acz/H(z)]1/3. HereDA is the angular diameter distance, and H(z) is the Hubbleparameter. This gives rs/DV(0.2) = 0.1980 +/-0.0058 and rs/DV(0.35) = 0.1094 +/- 0.0033(1σ errors), with a correlation coefficient of 0.39, wherers is the comoving sound horizon scale at recombination.Matching the BAOs to have the same measured scale at all redshifts thengives DV(0.35)/DV(0.2) = 1.812 +/- 0.060. Therecovered ratio is roughly consistent with that predicted by the higherredshift Supernova Legacy Survey (SNLS) supernova data for Λ colddark matter cosmologies, but does require slightly stronger cosmologicalacceleration at a low redshift. If we force the cosmological model to beflat with constant w, then we find Ωm = 0.249 +/- 0.018and w = -1.004 +/- 0.089 after combining with the SNLS data, andincluding the WMAP measurement of the apparent acoustic horizon angle inthe cosmic microwave background.

Hickox RC, Jones C, Forman WR, Murray SS, Brodwin M, Brown MJI, Eisenhardt PR, Stern D, Kochanek CS, Eisenstein D, et al. A Large Population of Mid-Infrared-selected, Obscured Active Galaxies in the Boötes Field. The Astrophysical Journal. 2007;671 :1365-1387. Publisher's VersionAbstract

We identify a population of 640 obscured and 839 unobscured AGNs atredshifts 0.72 NOAO Deep Wide-Field Survey (NDWFS) region inBoötes. We select AGNs on the basis of Spitzer IRAC colors obtainedby the IRAC Shallow Survey. Redshifts are obtained from opticalspectroscopy or photometric redshift estimators. We classify theIR-selected AGNs as IRAGN 1 (unobscured) and IRAGN 2 (obscured) using asimple criterion based on the observed optical to mid-IR color, with aselection boundary of R-[4.5]=6.1, where R and [4.5] are the Vegamagnitudes in the R and IRAC 4.5 μm bands, respectively. We verifythis selection using X-ray stacking analyses with data from the ChandraXBoötes survey, as well as optical photometry from NDWFS andspectroscopy from MMT/AGES. We show that (1) these sources are indeedAGNs, and (2) the optical/IR color selection separates obscured sources(with average NH~3×1022 cm-2obtained from X-ray hardness ratios, and optical colors and morphologiestypical of galaxies) and unobscured sources (with no X-ray absorption,

2006
Pindor B, Eisenstein DJ, Gregg MD, Becker RH, Inada N, Oguri M, Hall PB, Johnston DE, Richards GT, Schneider DP, et al. SDSS J102111.02+491330.4: A Newly Discovered Gravitationally Lensed Quasar. The Astronomical Journal. 2006;131 :41-48. Publisher's VersionAbstract

We report follow-up observations of two gravitational lens candidatesidentified in the Sloan Digital Sky Survey (SDSS) data set. We haveconfirmed that SDSS J102111.02+491330.4 is a previously unknowngravitationally lensed quasar. This lens system exhibits two images of az=1.72 quasar, with an image separation of 1.14"+/-0.04". Optical andnear-IR imaging of the system reveals the presence of the lensing galaxybetween the two quasar images. Observations of SDSS J112012.12+671116.0indicate that it is more likely a binary quasar than a gravitationallens. This system has two quasars at a redshift of z=1.49, with anangular separation of 1.49"+/-0.02". However, the two quasars havemarkedly different spectral energy distributions, and no lens galaxy isapparent in optical and near-IR images of this system. We also present alist of 31 SDSS lens candidates that follow-up observations haveconfirmed are not gravitational lenses.Observations reported here were obtained at the MMT Observatory, a jointfacility of the University of Arizona and the Smithsonian Institution.

Richards GT, Haiman Z, Pindor B, Strauss MA, Fan X, Eisenstein D, Schneider DP, Bahcall NA, Brinkmann J, Fukugita M. A Snapshot Survey for Gravitational Lenses among z>=4.0 Quasars. II. Constraints on the 4.0. The Astronomical Journal. 2006;131 :49-54. Publisher's VersionAbstract

We report on i-band snapshot observations of 157 Sloan Digital SkySurvey quasars at 4.0-3.8 (3 σ), assuming a break in the quasar luminosityfunction at M*1450~-24.5. This constraint isconsiderably stronger than the limit of β>-4.63 obtained fromthe absence of lensing in four z>5.7 quasars. Such constraints areimportant to our understanding of the true space density ofhigh-redshift quasars and the ionization state of the early universe.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS5-26555. These observations are associated with program9472.

Harris HC, Munn JA, Kilic M, Liebert J, Williams KA, von Hippel T, Levine SE, Monet DG, Eisenstein DJ, Kleinman SJ, et al. The White Dwarf Luminosity Function from Sloan Digital Sky Survey Imaging Data. The Astronomical Journal. 2006;131 :571-581. Publisher's VersionAbstract

A sample of white dwarfs is selected from the Sloan Digital Sky Survey(SDSS) Data Release 3 using their reduced proper motions, based onimproved proper motions from combined SDSS and USNO-B data. NumerousSDSS and follow-up spectra (Kilic and coworkers) are used to quantifycompleteness and contamination of the sample; kinematics models are usedto understand and correct for velocity-dependent selection biases. Aluminosity function is constructed covering the range7bol<16, and its sensitivity to various assumptionsand selection limits is discussed. The white dwarf luminosity functionbased on 6000 stars is remarkably smooth and rises nearly monotonicallyto Mbol=15.3. It then drops abruptly, although the smallnumber of low-luminosity stars in the sample and their unknownatmospheric composition prevent quantitative conclusions about thisdecline. Stars are identified that may have high tangential velocities,and a preliminary luminosity function is constructed for them.

Adelman-McCarthy JK, Agüeros MA, Allam SS, Anderson KSJ, Anderson SF, Annis J, Bahcall NA, Baldry IK, Barentine JC, Berlind A, et al. The Fourth Data Release of the Sloan Digital Sky Survey. The Astrophysical Journal Supplement Series. 2006;162 :38-48. Publisher's VersionAbstract

This paper describes the Fourth Data Release of the Sloan Digital SkySurvey (SDSS), including all survey-quality data taken through 2004June. The data release includes five-band photometric data for 180million objects selected over 6670 deg2 and 673,280 spectraof galaxies, quasars, and stars selected from 4783 deg2 ofthose imaging data using the standard SDSS target selection algorithms.

Cool RJ, Eisenstein DJ, Johnston D, Scranton R, Brinkmann J, Schneider DP, Zehavi I. Broadband Optical Properties of Massive Galaxies: The Dispersion around the Field Galaxy Color-Magnitude Relation Out to z~0.4. The Astronomical Journal. 2006;131 :736-746. Publisher's VersionAbstract

Using a sample of nearly 20,000 massive early-type galaxies selectedfrom the Sloan Digital Sky Survey, we study the color-magnitude relationfor the most luminous (L>~2.2L*) field galaxies in theredshift range 0.1

Knapp GR, Tremonti CA, Rockosi CM, Schlegel DJ, Yanny B, Beers TC, Allende Prieto C, Wilhelm R, Lupton RH, Gunn JE, et al. SDSS J103913.70+533029.7: A Super Star Cluster in the Outskirts of a Galaxy Merger. The Astronomical Journal. 2006;131 :859-865. Publisher's VersionAbstract

We describe the serendipitous discovery in the spectroscopic data of theSloan Digital Sky Survey of a starlike object, SDSS J103913.70+533029.7,at a heliocentric radial velocity of +1012 km s-1. Itsproximity in position and velocity to the spiral galaxy NGC 3310suggests an association with the galaxy. At this distance, SDSSJ103913.70+533029.7 has the luminosity of a super star cluster and aprojected distance of 17 kpc from NGC 3310. Its spectroscopic andphotometric properties imply a mass of >106Msolar and an age close to that of the tidal shells seenaround NGC 3310, suggesting that it formed in the event that formed theshells.

Silvestri NM, Hawley SL, West AA, Szkody P, Bochanski JJ, Eisenstein DJ, McGehee P, Schmidt GD, Smith AJ, Wolfe MA, et al. A Catalog of Spectroscopically Selected Close Binary Systems from the Sloan Digital Sky Survey Data Release Four. The Astronomical Journal. 2006;131 :1674-1686. Publisher's VersionAbstract

We present a spectroscopic sample of 747 detached close binary systemsfrom the Sloan Digital Sky Survey (SDSS) Fourth Data Release. Themajority of these binaries consist of a white dwarf primary and alow-mass secondary (typically M dwarf) companion. We have determined thetemperature and gravity for 496 of the white dwarf primaries and thespectral type and magnetic activity properties for 661 of the low-masssecondaries. We have estimated the distances for each of the whitedwarf-main-sequence star binaries and use white dwarf evolutionary gridsto establish the age of each binary system from the white dwarf coolingtimes. With respect to a spectroscopically identified sample of ~8000isolated M dwarf stars in the SDSS, the M dwarf secondaries showenhanced activity with a higher active fraction at a given spectraltype. The white dwarf temperatures and gravities are similar to thedistribution of ~1900 DA white dwarfs from the SDSS. The ages of thebinaries in this study range from ~0.5 Myr to nearly 3 Gyr (average age~0.20 Gyr).

Castanheira BG, Kepler SO, Mullally F, Winget DE, Koester D, Voss B, Kleinman SJ, Nitta A, Eisenstein DJ, Napiwotzki R, et al. Discovery of eleven new ZZ Ceti stars. Astronomy and Astrophysics. 2006;450 :227-231. Publisher's VersionAbstract

We report the discovery of eleven new ZZ Cetis using telescopes at OPD(Observatório do Pico dos Dias/LNA) in Brazil, the 4.1 m SOAR(Southern Astrophysical Research) telescope at Cerro Pachon, Chile, andthe 2.1 m Otto Struve telescope at McDonald observatory. The candidateswere selected from the SDSS (Sloan Digital Sky Survey) and SPY (ESO SNIa progenitor survey), based on their Teff obtained fromoptical spectra fitting. This selection criterion yields the highest

Yang Y, Zabludoff AI, Davé R, Eisenstein DJ, Pinto PA, Katz N, Weinberg DH, Barton EJ. Probing Galaxy Formation with He II Cooling Lines. The Astrophysical Journal. 2006;640 :539-552. Publisher's VersionAbstract

Using high-resolution cosmological simulations, we study hydrogen andhelium gravitational cooling radiation from gas accretion by younggalaxies. We focus on the He II cooling lines, which arise from gas witha different temperature history (Tmax~105 K) thanH I line-emitting gas. We examine whether three major atomic coolinglines, H I λ1216, He II λ1640, and He II λ304, areobservable, finding that Lyα and He II λ1640 coolingemission at z=2-3 are potentially detectable with deep narrowband(R>100) imaging and/or spectroscopy from the ground. While theexpected strength of H I λ1216 cooling emission depends stronglyon the treatment of the self-shielded phase of the IGM in thesimulations, our predictions for the He II λ1640 line are morerobust, because the He II emissivity is negligible belowT~104.5 K and less sensitive to the UV background. AlthoughHe II λ1640 cooling emission is fainter than Lyα by atleast a factor of 10 and, unlike Lyα, might not be resolvedspatially with current observational facilities, it is more suitable tostudy gas accretion in the galaxy formation process because it isoptically thin and less contaminated by the recombination lines fromstar-forming galaxies. The He II λ1640 line can be used todistinguish among mechanisms for powering the so-called Lyαblobs-including gravitational cooling radiation, photoionization bystellar populations, and starburst-driven superwinds-because (1) He IIλ1640 emission is limited to very low metallicity[log(Z/Zsolar)<~-5.3] and Population III stars and (2) theblob's kinematics are probed unambiguously through the He II line width,which for cooling radiation is narrower (σ<400 kms-1) than typical wind speeds.

Cool RJ, Eisenstein DJ, Hogg DW, Blanton MR, Schlegel DJ, Brinkmann J, Schneider DP, Vanden Berk DE. SDSS Preburst Observations of Recent Gamma-Ray Burst Fields. Publications of the Astronomical Society of the Pacific. 2006;118 :733-739. Publisher's VersionAbstract

We present Sloan Digital Sky Survey (SDSS) photometry and spectroscopyin the fields of 27 gamma-ray bursts observed by Swift, including burstslocalized by Swift, HETE-2, and INTEGRAL, after 2004 December. Afterthis bulk release, we plan to provide individual releases of similardata shortly after the localization of future bursts falling in the SDSSsurvey area. These data provide a solid basis for the astrometric andphotometric calibration of follow-up afterglow searches and monitoring.Furthermore, the images provided with this release will allow observersto find transient objects up to a magnitude fainter than is possiblewith Digitized Sky Survey images.

Jiang L, Fan X, Cool RJ, Eisenstein DJ, Zehavi I, Richards GT, Scranton R, Johnston D, Strauss MA, Schneider DP, et al. A Spectroscopic Survey of Faint Quasars in the SDSS Deep Stripe. I. Preliminary Results from the Co-added Catalog. The Astronomical Journal. 2006;131 :2788-2800. Publisher's VersionAbstract

In this paper we present the first results of a deep spectroscopicsurvey of faint quasars in the Sloan Digital Sky Survey (SDSS) SouthernSurvey, a deep survey carried out by repeatedly imaging a 270deg2 area. Quasar candidates were selected from the deep datawith good completeness over 02, contains 414 quasars, and

Masjedi M, Hogg DW, Cool RJ, Eisenstein DJ, Blanton MR, Zehavi I, Berlind AA, Bell EF, Schneider DP, Warren MS, et al. Very Small Scale Clustering and Merger Rate of Luminous Red Galaxies. The Astrophysical Journal. 2006;644 :54-60. Publisher's VersionAbstract

We present the small-scale (0.01 Mpc-1 Mpc)projected correlation function wp(rp) andreal-space correlation function ξ(r) of 24,520 luminous early-typegalaxies from the Sloan Digital Sky Survey (SDSS) Luminous Red Galaxy(LRG) sample (0.16-2 power law over more than 4 orders of magnitudein separation r. This result is too steep at small scales to beexplained in current versions of the halo model for galaxy clustering.We infer an LRG-LRG merger rate of <~0.6×104Gyr-1 Gpc-3 for this sample. This result suggeststhat the LRG-LRG mergers are not the main mode of mass growth for LRGsat z<0.36.

Papovich C, Cool R, Eisenstein D, Le Floc'h E, Fan X, Kennicutt, Robert C. J, Smith JDT, Rieke GH, Vestergaard M. An MMT Hectospec Redshift Survey of 24 μm Sources in the Spitzer First Look Survey. The Astronomical Journal. 2006;132 :231-241. Publisher's VersionAbstract

We present a spectroscopic survey using the MMT Hectospec fiberspectrograph of 24 μm sources selected with the Spitzer SpaceTelescope in the Spitzer First Look Survey. We report 1296 new redshiftsfor 24 μm sources, including 599 with fν(24μm)>=1 mJy. Combined with 291 additional redshifts for sourcesfrom the Sloan Digital Sky Survey (SDSS), our observing program was

Blanton MR, Eisenstein D, Hogg DW, Zehavi I. The Scale Dependence of Relative Galaxy Bias: Encouragement for the ``Halo Model'' Description. The Astrophysical Journal. 2006;645 :977-985. Publisher's VersionAbstract

We investigate the relationship between the colors, luminosities, andenvironments of galaxies in the Sloan Digital Sky Survey spectroscopicsample, using environmental measurements on scales ranging from 0.2 to 6h-1 Mpc. We find that (1) the relationship between color andenvironment persists even to the lowest luminosities we probe(Mr-5log10h~-14) (2) at luminosities and colors for which thegalaxy correlation function has a large amplitude, it also has a steepslope; and (3) in regions of a given overdensity on small scales (1h-1 Mpc), the overdensity on large scales (6 h-1Mpc) does not appear to relate to the recent star formation history ofthe galaxies. Of these results, the last has the most immediateapplication to galaxy formation theory. In particular, it lends supportto the notion that a galaxy's properties are related only to the mass ofits host dark matter halo, and not to the larger scale environment.Based on observations obtained with the Sloan Digital Sky Survey.

Eisenstein DJ, Liebert J, Koester D, Kleinmann SJ, Nitta A, Smith PS, Barentine JC, Brewington HJ, Brinkmann J, Harvanek M, et al. Hot DB White Dwarfs from the Sloan Digital Sky Survey. The Astronomical Journal. 2006;132 :676-691. Publisher's VersionAbstract

We present ugriz photometry and optical spectroscopy for 28 DB and DOwhite dwarfs with temperatures between 28,000 and 45,000 K. About 10 ofthese are particularly well observed; the remainder are candidates.These are the hottest DB stars yet found, and they populate the ``DBgap'' between the hotter DO stars and the familiar DB stars cooler than30,000 K. Nevertheless, after carefully matching the survey volumes wefind that the ratio of DA stars to DB stars is a factor of 2.5 larger at30,000 than at 20,000 K, suggesting that the ``DB gap'' is indeeddeficient and that some kind of atmospheric transformation takes place

Cool RJ, Kochanek CS, Eisenstein DJ, Stern D, Brand K, Brown MJI, Dey A, Eisenhardt PR, Fan X, Gonzalez AH, et al. The Discovery of Three New z>5 Quasars in the AGN and Galaxy Evolution Survey. The Astronomical Journal. 2006;132 :823-830. Publisher's VersionAbstract

We present the discovery of three z>5 quasars in the AGN and GalaxyEvolution Survey spectroscopic observations of the NOAO Deep Wide-FieldSurvey (NDWFS) Bootes Field. These quasars were selected as part of alarger Spitzer mid-infrared quasar sample, with no selection based onoptical colors. The highest redshift object, NDWFS J142516.3+325409, atz=5.85, is the lowest luminosity z>5.8 quasar currently known. Wecompare mid-infrared techniques for identifying z>5 quasars to moretraditional optical techniques and show that mid-infrared colors allowfor the selection of high-redshift quasars even at redshifts at whichquasars lie near the optical stellar locus and at z>7, where opticalselection is impossible. Using the superb multiwavelength coverageavailable in the NDWFS Bootes field, we construct the spectral energydistributions (SEDs) of high-redshift quasars from observedBW band to 24 μm (rest-frame 600 Å-3.7 μm). Weshow that the three high-redshift quasars have quite similar SEDs, andthe rest-frame composite SED of low-redshift quasars from the literatureshows little evolution compared to our high-redshift objects. We comparethe number of z>5 quasars we have discovered to the expected numberfrom published quasar luminosity functions. While analyses of the quasarluminosity function are tenuous based on only three objects, we findthat a relatively steep luminosity function with Ψ~L-3.2provides the best agreement with the number of high-redshift quasarsdiscovered in our survey.

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