Publications

2010
Yang Y, Zabludoff A, Eisenstein D, Davé R. Strong Field-to-field Variation of Lyα Nebulae Populations at z ~= 2.3. The Astrophysical Journal. 2010;719 :1654-1671. Publisher's VersionAbstract

Understanding the nature of distant Lyα nebulae, aka "blobs," andconnecting them to their present-day descendants requires constrainingtheir number density, clustering, and large-scale environment. Tomeasure these basic quantities, we conduct a deep narrowband imagingsurvey in four different fields, Chandra Deep Field South (CDFS),Chandra Deep Field North (CDFN), and two COSMOS subfields, for a totalsurvey area of 1.2 deg2. We discover 25 blobs at z = 2.3 withLyα luminosities of L Lyα= (0.7-8) ×1043 erg s-1 and isophotal areas of Aiso = 10-60 sq arcsec. The transition from compact Lyαemitters (LAEs; A iso ~ a few sq arcsec) to extendedLyα blobs (A iso > 10 sq arcsec) is continuous,suggesting a single family perhaps governed by similar emissionmechanisms. Surprisingly, most blobs (16/25) are in one survey field,the CDFS. The six brightest, largest blobs with L Lyαgsim 1.5×1043 erg s-1 and A iso> 16 sq arcsec lie only in the CDFS. These large, bright blobs have a

Seo H-J, Eckel J, Eisenstein DJ, Mehta K, Metchnik M, Padmanabhan N, Pinto P, Takahashi R, White M, Xu X. High-precision Predictions for the Acoustic Scale in the Nonlinear Regime. The Astrophysical Journal. 2010;720 :1650-1667. Publisher's VersionAbstract

We measure shifts of the acoustic scale due to nonlinear growth andredshift distortions to a high precision using a very large volume ofhigh-force-resolution simulations. We compare results from various setsof simulations that differ in their force, volume, and mass resolution.We find a consistency within 1.5σ for shift values from differentsimulations and derive shift α(z) - 1 = (0.300 ± 0.015)

2009
Yang Y, Zabludoff A, Tremonti C, Eisenstein D, Davé R. Extended Lyα Nebulae at z sime 2.3: An Extremely Rare and Strongly Clustered Population?. The Astrophysical Journal. 2009;693 :1579-1587. Publisher's VersionAbstract

To obtain an unbiased sample of bright Lyα blobs (L_{Lyα}≳ 10^{43} erg s-1), we have undertaken a blind,wide-field, narrowband imaging survey in the National Optical AstronomyObservatory Deep Wide Field Survey Boötes field with the StewardBok 2.3 m telescope. After searching over 4.82 deg2 at z =2.3, we discover four Lyα blobs with L_{Lyα} = 1.6-5.3× 1043 erg s-1, isophotal areas of 28-57⊓⊔, and broad Lyα line profiles (Δv = 900-1250km s-1). In contrast with the extended Lyα halosassociated with high-z radio galaxies, none of our four blobs areradio-loud. The X-ray luminosities and optical spectra of these blobsare diverse. Two blobs (3 and 4) are X-ray detected with LX(2-7 keV) = 2-4 × 1044 erg s-1 and havebroad optical emission lines (C IV) characteristic of active galactic

Hickox RC, Jones C, Forman WR, Murray SS, Kochanek CS, Eisenstein D, Jannuzi BT, Dey A, Brown MJI, Stern D, et al. Host Galaxies, Clustering, Eddington Ratios, and Evolution of Radio, X-Ray, and Infrared-Selected AGNs. The Astrophysical Journal. 2009;696 :891-919. Publisher's VersionAbstract

We explore the connection between different classes of active galacticnuclei (AGNs) and the evolution of their host galaxies, by deriving hostgalaxy properties, clustering, and Eddington ratios of AGNs selected inthe radio, X-ray, and infrared (IR) wavebands. We study a sample of 585AGNs at 0.25 < z < 0.8 using redshifts from the AGN and GalaxyEvolution Survey (AGES). We select AGNs with observations in the radioat 1.4 GHz from the Westerbork Synthesis Radio Telescope, X-rays fromthe Chandra XBoötes Survey, and mid-IR from the Spitzer IRACShallow Survey. The radio, X-ray, and IR AGN samples show only modestoverlap, indicating that to the flux limits of the survey, theyrepresent largely distinct classes of AGNs. We derive host galaxy colorsand luminosities, as well as Eddington ratios, for obscured or opticallyfaint AGNs. We also measure the two-point cross-correlation between AGNsand galaxies on scales of 0.3-10 h -1 Mpc, and derive typicaldark matter halo masses. We find that: (1) radio AGNs are mainly foundin luminous red sequence galaxies, are strongly clustered (with Mhalo ~ 3 × 1013 h -1 Msun), and have very low Eddington ratios λ lsim10-3 (2) X-ray-selected AGNs are preferentially found ingalaxies that lie in the "green valley" of color-magnitude space and areclustered similar to the typical AGES galaxies (M halo ~1013 h -1 M sun), with 10-3lsim λ lsim 1; (3) IR AGNs reside in slightly bluer, slightlyless luminous galaxies than X-ray AGNs, are weakly clustered (Mhalo lsim 1012 h -1 M sun),and have λ>10-2. We interpret these results interms of a simple model of AGN and galaxy evolution, whereby a "quasar"phase and the growth of the stellar bulge occurs when a galaxy's darkmatter halo reaches a critical mass between ~1012 and1013 M sun. After this event, star formationceases and AGN accretion shifts from radiatively efficient (optical- andIR-bright) to radiatively inefficient (optically faint, radio-bright)modes.

Watson CR, Kochanek CS, Forman WR, Hickox RC, Jones CJ, Brown MJI, Brand K, Dey A, Jannuzi BT, Kenter AT, et al. The Star Formation and Nuclear Accretion Histories of Normal Galaxies in the Ages Survey. The Astrophysical Journal. 2009;696 :2206-2219. Publisher's VersionAbstract

We combine IR, optical, and X-ray data from the overlapping, 9.3deg2 NOAO Deep Wide-Field Survey, AGN and Galaxy EvolutionSurvey (AGES), and XBoötes Survey to measure the X-ray evolution of6146 normal galaxies as a function of absolute optical luminosity,redshift, and spectral type over the largely unexplored redshift range0.1 lsim z lsim 0.5. Because only the closest or brightest of thegalaxies are individually detected in X-rays, we use a stacking analysisto determine the mean properties of the sample. Our results suggest thatX-ray emission from spectroscopically late-type galaxies is dominated bystar formation, while that from early-type galaxies is dominated by acombination of hot gas and active galactic nucleus (AGN) emission. Wefind that the mean star formation and supermassive black hole accretionrate densities evolve like ~(1 + z)3±1, in agreementwith the trends found for samples of bright, individually detectablestarburst galaxies and AGN. Our work also corroborates the results ofmany previous stacking analyses of faint source populations, withimproved statistics.

Dai X, Assef RJ, Kochanek CS, Brodwin M, Brown MJI, Caldwell N, Cool RJ, Dey A, Eisenhardt P, Eisenstein D, et al. Mid-Infrared Galaxy Luminosity Functions from the AGN and Galaxy Evolution Survey. The Astrophysical Journal. 2009;697 :506-521. Publisher's VersionAbstract

We present galaxy luminosity functions at 3.6, 4.5, 5.8, and 8.0 μmmeasured by combining photometry from the IRAC Shallow Survey withredshifts from the AGN and Galaxy Evolution Survey (AGES) of the NOAODeep Wide-Field Survey Boötes field. The well defined IRAC samplescontain 3800-5800 galaxies for the 3.6-8.0 μm bands withspectroscopic redshifts and z < 0.6. We obtained relatively completeluminosity functions in the local redshift bin of z < 0.2 for allfour IRAC channels that are well fitted by Schechter functions. Afteranalyzing the samples for the whole redshift range, we found significantevolution in the luminosity functions for all four IRAC channels thatcan be fitted as an evolution in M * with redshift, ΔM* = Qz. While we measured Q = 1.2 ± 0.4 and 1.1± 0.4 in the 3.6 and 4.5 μm bands consistent with thepredictions from a passively evolving population, we obtained Q = 1.8± 1.1 in the 8.0 μm band consistent with other evolving starformation rate estimates. We compared our luminosity functions with thepredictions of semianalytical galaxy formation and found the bestagreement at 3.6 and 4.5 μm, rough agreement at 8.0 μm, and alarge mismatch at 5.8 μm. These models also predicted a comparableQ-value to our luminosity functions at 8.0 μm, but predicted smallervalues at 3.6 and 4.5 μm. We also measured the luminosity functionsseparately for early- and late-type galaxies. While the luminosityfunctions of late-type galaxies resemble those for the total population,the luminosity functions of early-type galaxies in the 3.6 and 4.5 μmbands indicate deviations from the passive evolution model, especiallyfrom the measured flat luminosity density evolution. Combining ourestimates with other measurements in the literature, we found 53

Abazajian KN, Adelman-McCarthy JK, Agüeros MA, Allam SS, Allende Prieto C, An D, Anderson KSJ, Anderson SF, Annis J, Bahcall NA, et al. The Seventh Data Release of the Sloan Digital Sky Survey. The Astrophysical Journal Supplement Series. 2009;182 :543-558. Publisher's VersionAbstract

This paper describes the Seventh Data Release of the Sloan Digital SkySurvey (SDSS), marking the completion of the original goals of the SDSSand the end of the phase known as SDSS-II. It includes 11,663deg2 of imaging data, with most of the ~2000 deg2increment over the previous data release lying in regions of lowGalactic latitude. The catalog contains five-band photometry for 357million distinct objects. The survey also includes repeat photometry ona 120° long, 2fdg5 wide stripe along the celestial equator in theSouthern Galactic Cap, with some regions covered by as many as 90individual imaging runs. We include a co-addition of the best of thesedata, going roughly 2 mag fainter than the main survey over 250deg2. The survey has completed spectroscopy over 9380deg2 the spectroscopy is now complete over a large contiguousarea of the Northern Galactic Cap, closing the gap that was present inprevious data releases. There are over 1.6 million spectra in total,including 930,000 galaxies, 120,000 quasars, and 460,000 stars. The datarelease includes improved stellar photometry at low Galactic latitude.The astrometry has all been recalibrated with the second version of theUSNO CCD Astrograph Catalog, reducing the rms statistical errors at thebright end to 45 milliarcseconds per coordinate. We further quantify asystematic error in bright galaxy photometry due to poor skydetermination; this problem is less severe than previously reported forthe majority of galaxies. Finally, we describe a series of improvementsto the spectroscopic reductions, including better flat fielding andimproved wavelength calibration at the blue end, better processing ofobjects with extremely strong narrow emission lines, and an improveddetermination of stellar metallicities.

Thompson RI, Bechtold J, Black JH, Eisenstein D, Fan X, Kennicutt RC, Martins C, Prochaska XJ, Shirley YL. An Observational Determination of the Proton to Electron Mass Ratio in the Early Universe. The Astrophysical Journal. 2009;703 :1648-1662. Publisher's VersionAbstract

In an effort to resolve the discrepancy between two measurements of thefundamental constant μ, the proton to electron mass ratio, at earlytimes in the universe we reanalyze the same data used in the earlierstudies. Our analysis of the molecular hydrogen absorption lines inarchival Very Large Telescope/Ultraviolet and Visible EchelleSpectrometer (UVES) spectra of the damped Lyman alpha systems in thequasi-stellar objects Q0347-383 and Q0405-443 yields a combinedmeasurement of a Δμ/μ value of (-7 ± 8) ×10-6, consistent with no change in the value of μ over atime span of 11.5 Gyr. Here, we define Δμ as (μ z - μ0) where μ z is the value of μat a redshift of z and μ0 is the present-day value. Ournull result is consistent with the recent measurements of King et al.,Δμ/μ = (2.6 ± 3.0) × 10-6, andinconsistent with the positive detection of a change in μ by Reinholdet al. Both of the previous studies and this study are based on the samedata but with differing analysis methods. Improvements in the wavelengthcalibration over the UVES pipeline calibration is a key element in bothof the null results. This leads to the conclusion that the fundamentalconstant μ is unchanged to an accuracy of 10-5 over the

Ashby MLN, Stern D, Brodwin M, Griffith R, Eisenhardt P, Kozłowski S, Kochanek CS, Bock JJ, Borys C, Brand K, et al. The Spitzer Deep, Wide-field Survey. The Astrophysical Journal. 2009;701 :428-453. Publisher's VersionAbstract

The Spitzer Deep, Wide-Field Survey (SDWFS) is a four-epoch infraredsurvey of 10 deg2 in the Boötes field of the NOAO DeepWide-Field Survey using the IRAC instrument on the Spitzer SpaceTelescope. SDWFS, a Spitzer Cycle 4 Legacy project, occupies a uniqueposition in the area-depth survey space defined by other Spitzersurveys. The four epochs that make up SDWFS permit—for the firsttime—the selection of infrared-variable and high proper motionobjects over a wide field on timescales of years. Because of its largesurvey volume, SDWFS is sensitive to galaxies out to z ~ 3 withrelatively little impact from cosmic variance for all but the richestsystems. The SDWFS data sets will thus be especially useful forcharacterizing galaxy evolution beyond z ~ 1.5. This paper explains theSDWFS observing strategy and data processing, presents the SDWFS mosaicsand source catalogs, and discusses some early scientific findings. Thepublicly released, full-depth catalogs contain 6.78, 5.23, 1.20, and0.96 × 105 distinct sources detected to the average5σ, 4''-diameter, aperture-corrected limits of 19.77, 18.83,16.50, and 15.82 Vega mag at 3.6, 4.5, 5.8, and 8.0 μm, respectively.The SDWFS number counts and color-color distribution are consistent withother, earlier Spitzer surveys. At the 6 minute integration time of the

Zheng Z, Zehavi I, Eisenstein DJ, Weinberg DH, Jing YP. Halo Occupation Distribution Modeling of Clustering of Luminous Red Galaxies. The Astrophysical Journal. 2009;707 :554-572. Publisher's VersionAbstract

We perform halo occupation distribution (HOD) modeling to interpretsmall-scale and intermediate-scale clustering of 35,000 luminousearly-type galaxies and their cross-correlation with a reference imagingsample of normal L * galaxies in the Sloan Digital SkySurvey. The modeling results show that most of these luminous redgalaxies (LRGs) are central galaxies residing in massive halos oftypical mass M~ a few times 1013-1014 h-1 M sun, while a few percent of them have to besatellites within halos in order to produce the strong auto-correlationsexhibited on smaller scales. The mean luminosity Lc ofcentral LRGs increases with the host halo mass, with a rough scalingrelation of Lc vprop M 0.5. The halo mass requiredto host on average one satellite LRG above a luminosity threshold isfound to be about 10 times higher than that required to host a centralLRG above the same threshold. We find that in massive halos thedistribution of L * galaxies roughly follows that of the darkmatter and their mean occupation number scales with halo mass as M1.5. The HOD modeling results also allow for an intuitiveunderstanding of the scale-dependent luminosity dependence of thecross-correlation between LRGs and L * galaxies. Constraintson the LRG HOD provide tests for models of formation and evolution ofmassive galaxies, and they are also useful for cosmological parameterinvestigations. In one of the appendices, we provide LRG HOD parameterswith dependence on cosmology inferred from modeling the two-pointauto-correlation functions of LRGs.

2008
Inada N, Oguri M, Becker RH, Shin M-S, Richards GT, Hennawi JF, White RL, Pindor B, Strauss MA, Kochanek CS, et al. The Sloan Digital Sky Survey Quasar Lens Search. II. Statistical Lens Sample from the Third Data Release. The Astronomical Journal. 2008;135 :496-511. Publisher's VersionAbstract

We report the first results of our systematic search for strongly lensedquasars using the spectroscopically confirmed quasars in the SloanDigital Sky Survey (SDSS). Among 46,420 quasars from the SDSS DataRelease 3 (~4188 deg2), we select a subsample of 22,683quasars that are located at redshifts between 0.6 and 2.2 and arebrighter than the Galactic extinction-corrected i-band magnitude of19.1. We identify 220 lens candidates from the quasar subsample, forwhich we conduct extensive and systematic follow-up observations inoptical and near-infrared wavebands, in order to construct a completelensed quasar sample at image separations between 1'' and 20'' and fluxratios of faint to bright lensed images larger than 10-0.5.We construct a statistical sample of 11 lensed quasars. Ten of these aregalaxy-scale lenses with small image separations (~ 1''-2'') and one isa large separation (15'') system which is produced by a massive clusterof galaxies, representing the first statistical sample of lensed quasarsincluding both galaxy- and cluster-scale lenses. The Data Release 3spectroscopic quasars contain an additional 11 lensed quasars outsidethe statistical sample.

Oguri M, Inada N, Strauss MA, Kochanek CS, Richards GT, Schneider DP, Becker RH, Fukugita M, Gregg MD, Hall PB, et al. The Sloan Digital Sky Survey Quasar Lens Search. III. Constraints on Dark Energy from the Third Data Release Quasar Lens Catalog. The Astronomical Journal. 2008;135 :512-519. Publisher's VersionAbstract

We present cosmological results from the statistics of lensed quasars inthe Sloan Digital Sky Survey (SDSS) Quasar Lens Search. By taking properaccount of the selection function, we compute the expected number ofquasars lensed by early-type galaxies and their image separationdistribution assuming a flat universe, which is then compared with sevenlenses found in the SDSS Data Release 3 to derive constraints on darkenergy under strictly controlled criteria. For a cosmological constantmodel (w = -1) we obtain ΩΛ =0.74+0.11-0.15(stat.)+0.13-0.06(syst.). Allowing w to be a free parameter we findΩM = 0.26+0.07-0.06(stat.)+0.03-0.05(syst.) and w =-1.1 ± 0.6(stat.)+0.3-0.5(syst.) whencombined with the constraint from the measurement of baryon acousticoscillations in the SDSS luminous red galaxy sample. Our results are ingood agreement with earlier lensing constraints obtained using radiolenses, and provide additional confirmation of the presence of darkenergy consistent with a cosmological constant, derived independently oftype Ia supernovae.

Assef RJ, Kochanek CS, Brodwin M, Brown MJI, Caldwell N, Cool RJ, Eisenhardt P, Eisenstein D, Gonzalez AH, Jannuzi BT, et al. Low-Resolution Spectral Templates for Galaxies from 0.2 to 10 μm. The Astrophysical Journal. 2008;676 :286-303. Publisher's VersionAbstract

We built an optimal basis of low-resolution templates for galaxies overthe wavelength range from 0.2 to 10 μm using a variant of thealgorithm presented by Budavari and coworkers. We derived them using 11bands of photometry from the NDWFS, FLAMEX, zBoötes, and IRACShallow surveys for 16,033 galaxies in the NDWFS Boötes field withspectroscopic redshifts measured by the AGN and Galaxy Evolution Survey.We also developed algorithms to accurately determine photometricredshifts, K-corrections, and bolometric luminosities using thesetemplates. Our photometric redshifts have an accuracy of

Okumura T, Matsubara T, Eisenstein DJ, Kayo I, Hikage C, Szalay AS, Schneider DP. Large-Scale Anisotropic Correlation Function of SDSS Luminous Red Galaxies. The Astrophysical Journal. 2008;676 :889-898. Publisher's VersionAbstract

We study the large-scale anisotropic two-point correlation functionusing 46,760 luminous red galaxies at redshifts 0.16-0.47 from the SloanDigital Sky Survey. We measure the correlation function as a function ofseparations parallel and perpendicular to the line of sight in order totake account of anisotropy of the large-scale structure in redshiftspace. We find a slight signal of baryonic features in the anisotropiccorrelation function, i.e., a ``baryon ridge'' corresponding to a baryonacoustic peak in the spherically averaged correlation function, whichhas already been reported using the same sample. The baryon ridge hasprimarily a spherical structure with a known radius in comovingcoordinates. It enables us to divide the redshift distortion effectsinto dynamical and geometrical components and provides furtherconstraints on cosmological parameters, including the dark energyequation-of-state. With an assumption of a flat Λ cosmology, wefind the best-fit values ofΩm=0.218+0.047-0.037 and

Stutz AM, Papovich C, Eisenstein DJ. On the Stellar Populations in Faint Red Galaxies in the Hubble Ultra Deep Field. The Astrophysical Journal. 2008;677 :828-845. Publisher's VersionAbstract

We study the nature of faint red-selected galaxies at z~2-3 using theHubble Ultra Deep Field (HUDF) and Spitzer Infrared Array Camera (IRAC)photometry. Given the magnitude limit of the HST data, we detectcandidate galaxies to HAB<26 mag, probing lower luminosity(lower mass) galaxies at these redshifts. We identify 32 galaxiessatisfying the (J110-H160)AB>1.0 magcolor selection, 16 of which have unblended [3.6 μm] and [4.5 μm]photometry from Spitzer. Using this multiwavelength data set, we derivephotometric redshifts, masses, and stellar population parameters forthese objects. We find that the selected objects span a diverse range ofproperties over a large range of redshifts, 1<~z<~3.5. Asubstantial fraction (11/32) of the(J110-H160)AB>1.0 mag populationappear to be lower redshift (z<~2.5), heavily obscured dusty galaxiesor edge-on spiral galaxies, while others (12/32) appear to be galaxiesat 2<~z<~3.5 whose light at rest-frame optical wavelengths isdominated by evolved stellar populations. We argue that longerwavelength data (>~1 μm, rest frame) are essential forinterpreting the properties of the stellar populations in red-selectedgalaxies at these redshifts. Interestingly, by including Spitzer data,many candidates for galaxies dominated by evolved stellar populationsare rejected, and for only a subset of the sample (6/16) do the datafavor this interpretation. These objects have a surface density of ~1arcmin-2. We place an upper limit on the space density ofcandidate massive evolved galaxies with 2.5AB160<=26 mag ofn=6.6+2.0-3.0×10-4Mpc-3, with a corresponding upper limit on the stellar massdensity ofρ*=5.6+4.4-2.8×107Msolar Mpc-3. The z>2.5 objects that aredominated by evolved stellar populations have a space density at mostone-third that of z~0 red early-type galaxies. Therefore, at leasttwo-thirds of present-day early-type galaxies assemble or evolve intotheir current configuration at redshifts below 2.5. We find a dearth ofcandidates for low-mass (<~2×1010 Msolar)galaxies at 1.5

Adelman-McCarthy JK, Agüeros MA, Allam SS, Allende Prieto C, Anderson KSJ, Anderson SF, Annis J, Bahcall NA, Bailer-Jones CAL, Baldry IK, et al. The Sixth Data Release of the Sloan Digital Sky Survey. The Astrophysical Journal Supplement Series. 2008;175 :297-313. Publisher's VersionAbstract

This paper describes the Sixth Data Release of the Sloan Digital SkySurvey. With this data release, the imaging of the northern Galactic capis now complete. The survey contains images and parameters of roughly287 million objects over 9583 deg2, including scans over alarge range of Galactic latitudes and longitudes. The survey alsoincludes 1.27 million spectra of stars, galaxies, quasars, and blank sky(for sky subtraction) selected over 7425 deg2 . This releaseincludes much more stellar spectroscopy than was available in previousdata releases and also includes detailed estimates of stellartemperatures, gravities, and metallicities. The results of improvedphotometric calibration are now available, with uncertainties of roughly

Angel R, Worden SP, Borra EF, Eisenstein DJ, Foing B, Hickson P, Josset J-L, Ma KB, Seddiki O, Sivanandam S, et al. A Cryogenic Liquid-Mirror Telescope on the Moon to Study the Early Universe. The Astrophysical Journal. 2008;680 :1582-1594. Publisher's VersionAbstract

We have studied the feasibility and scientific potential of zenithobserving liquid-mirror telescopes having 20-100 m diameters located onthe Moon. They would carry out deep infrared surveys to study thedistant universe and follow up discoveries made with the 6 m James WebbSpace Telescope (JWST), with more detailed images and spectroscopicstudies. They could detect objects 100 times fainter than JWST,observing the first high-redshift stars in the early universe and theirassembly into galaxies. We explored the scientific opportunities, keytechnologies, and optimum location of such telescopes. We havedemonstrated critical technologies. For example, the primary mirrorwould necessitate a high-reflectivity liquid that does not evaporate inthe lunar vacuum and remains liquid at less than 100 K. We have made acrucial demonstration by successfully coating an ionic liquid that hasnegligible vapor pressure. We also successfully experimented with aliquid mirror spinning on a superconducting bearing, as will be neededfor the cryogenic, vacuum environment of the telescope. We haveinvestigated issues related to lunar locations, concluding thatlocations within a few kilometers of a pole are ideal for deep sky coverand long integration times. We have located ridges and crater rimswithin 0.5° of the north pole that are illuminated for at least somesun angles during lunar winter, providing power and temperature control.We also have identified potential problems, like lunar dust. Issuesraised by our preliminary study demand additional in-depth analyses.These issues must be fully examined as part of a scientific debate thatwe hope to start with the present article.

Eisenstein DJ. Observing dark energy. Classical and Quantum Gravity. 2008;25 :4001. Publisher's VersionAbstract

I review the observational evidence for dark energy, arguing that thelarge-scale structure observed at low redshift and in the cosmicmicrowave background offers a strong corroboration of the supernova Iaresults. The angular scale of the acoustic oscillations in the cosmicmicrowave background strongly support a nearly flat universe, while manyarguments from low-redshift cosmology support a matter density around

Seo H-J, Eisenstein DJ, Zehavi I. Passive Evolution of Galaxy Clustering. The Astrophysical Journal. 2008;681 :998-1016. Publisher's VersionAbstract

We present a numerical study of the evolution of galaxy clustering whengalaxies flow passively from high redshift, respecting the continuityequation throughout. While passive flow is a special case of galaxyevolution, it allows a well-defined study of galaxy ancestry and servesas an interesting limit to be compared to nonpassive cases. We usedissipationless N-body simulations, assign galaxies to massive halos atz=1 and 2 using various halo occupation distribution (HOD) models, andtrace these galaxy particles to lower redshift while conserving theirnumber. We find that passive flow results in an asymptotic convergenceat low redshift in the HOD and in galaxy clustering on scales above ~3h-1 Mpc for a wide range of initial HODs. As galaxies becomeless biased with respect to mass asymptotically with time, the HODparameters evolve such that M1/Mmin decreaseswhile α converges toward unity, whereg(M)>=exp(-Mmin/M)[1+(M/M1)α].The satellite populations converge toward the Poisson distribution atlow redshift. The convergence is robust for different number densitiesand is enhanced when galaxies evolve from higher redshift. We compareour results with the observed luminous red galaxy (LRG) sample from SDSSthat has the same number density. We claim that if LRGs have experienceda strict passive flow, their g(M)> should be close toa power law with an index of unity in halo mass. Discrepancies could bedue to dry galaxy merging or new members arising between the initial andthe final redshifts. The spatial distribution of passively flowinggalaxies within halos appears on average more concentrated than the halomass profile at low redshift. The evolution of bias for passivelyflowing galaxies is consistent with linear bias evolution onquasi-linear as well as large scales.

Thompson RI, Bechtold J, Eisenstein D, Fan X, Arnett D, Martins C, Kennicutt R, Black J. A molecular probe of dark energy. Advances in Space Research. 2008;42 :596-598. Publisher's VersionAbstract

Many theoretical models of dark energy invoke rolling scaler fieldswhich in turn predict time varying values of the fundamental constants.Establishing the value of the fundamental constants at various times inthe universe can probe and test the various dark energy theories. One ofthe constants that is predicted to vary is the ratio of the electron toproton mass μ. It was established early on that molecular spectra aresensitive to the value of μ and can be used as probes of that value.This article describes the use of the spectrum of molecular hydrogen inhigh redshift Damped Lyman Alpha systems (DLAs) as a sensitive probe ofthe time evolution of μ.

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