Speagle JS, Eisenstein DJ. Deriving photometric redshifts using fuzzy archetypes and self-organizing maps - I. Methodology. Monthly Notices of the Royal Astronomical Society. 2017;469 :1186-1204. Publisher's VersionAbstract
We propose a method to substantially increase the flexibility and powerof template fitting-based photometric redshifts by transforming a largenumber of galaxy spectral templates into a corresponding collection of'fuzzy archetypes' using a suitable set of perturbative priors designedto account for empirical variation in dust attenuation and emission-linestrengths. To bypass widely separated degeneracies in parameter space(e.g. the redshift-reddening degeneracy), we train self-organizing maps(SOMs) on large 'model catalogues' generated from Monte Carlo samplingof our fuzzy archetypes to cluster the predicted observables in atopologically smooth fashion. Subsequent sampling over the SOM thenallows full reconstruction of the relevant probability distributionfunctions (PDFs). This combined approach enables the multimodalexploration of known variation among galaxy spectral energydistributions with minimal modelling assumptions. We demonstrate thepower of this approach to recover full redshift PDFs using discreteMarkov chain Monte Carlo sampling methods combined with SOMs constructedfrom Large Synoptic Survey Telescope ugrizY and Euclid YJH mockphotometry.
Speagle JS, Eisenstein DJ. Deriving photometric redshifts using fuzzy archetypes and self-organizing maps - II. Implementation. Monthly Notices of the Royal Astronomical Society. 2017;469 :1205-1224. Publisher's VersionAbstract
With an eye towards the computational requirements of future large-scalesurveys such as Euclid and Large Synoptic Survey Telescope (LSST) thatwill require photometric redshifts (photo-z's) for ≳ 109objects, we investigate a variety of ways that 'fuzzy archetypes' can beused to improve photometric redshifts and explore their respectivestatistical interpretations. We characterize their relative performanceusing an idealized LSST ugrizY and Euclid YJH mock catalogue of 10 000objects spanning z = 0-6 at Y = 24 mag. We find most schemes are able torobustly identify redshift probability distribution functions that aremultimodal and/or poorly constrained. Once these objects are flagged andremoved, the results are generally in good agreement with the strictaccuracy requirements necessary to meet Euclid weak lensing goals formost redshifts between 0.8 ≲ z ≲ 2. These results demonstratethe statistical robustness and flexibility that can be gained bycombining template-fitting and machine-learning methods and provideuseful insights into how astronomers can further exploit thecolour-redshift relation.
Slepian Z, Eisenstein DJ, Brownstein JR, Chuang C-H, Gil-Marín H, Ho S, Kitaura F-S, Percival WJ, Ross AJ, Rossi G, et al. Detection of baryon acoustic oscillation features in the large-scale three-point correlation function of SDSS BOSS DR12 CMASS galaxies. Monthly Notices of the Royal Astronomical Society. 2017;469 :1738-1751. Publisher's VersionAbstract
We present the large-scale three-point correlation function (3PCF) ofthe Sloan Digital Sky Survey DR12 Constant stellar Mass (CMASS) sampleof 777 202 Luminous Red Galaxies, the largest-ever sample used for a3PCF or bispectrum measurement. We make the first high-significance(4.5σ) detection of baryon acoustic oscillations (BAO) in the3PCF. Using these acoustic features in the 3PCF as a standard ruler, wemeasure the distance to z = 0.57 to 1.7 per cent precision (statisticalplus systematic). We find DV = 2024 ± 29 Mpc (stat)± 20 Mpc (sys) for our fiducial cosmology (consistent with Planck2015) and bias model. This measurement extends the use of the BAOtechnique from the two-point correlation function (2PCF) and powerspectrum to the 3PCF and opens an avenue for deriving additionalcosmological distance information from future large-scale structureredshift surveys such as DESI. Our measured distance scale from the 3PCFis fairly independent from that derived from the pre-reconstruction 2PCFand is equivalent to increasing the length of BOSS by roughly 10 percent; reconstruction appears to lower the independence of the distancemeasurements. Fitting a model including tidal tensor bias yields amoderate-significance (2.6σ) detection of this bias with a valuein agreement with the prediction from local Lagrangian biasing.
Slepian Z, Eisenstein DJ, Beutler F, Chuang C-H, Cuesta AJ, Ge J, Gil-Marín H, Ho S, Kitaura F-S, McBride CK, et al. The large-scale three-point correlation function of the SDSS BOSS DR12 CMASS galaxies. Monthly Notices of the Royal Astronomical Society. 2017;468 :1070-1083. Publisher's VersionAbstract
We report a measurement of the large-scale three-point correlationfunction of galaxies using the largest data set for this purpose todate, 777 202 luminous red galaxies in the Sloan Digital Sky SurveyBaryon Acoustic Oscillation Spectroscopic Survey (SDSS BOSS) DR12 CMASSsample. This work exploits the novel algorithm of Slepian &Eisenstein to compute the multipole moments of the 3PCF in O(N^2) time,with N the number of galaxies. Leading-order perturbation theory modelsthe data well in a compressed basis where one triangle side isintegrated out. We also present an accurate and computationallyefficient means of estimating the covariance matrix. With thesetechniques, the redshift-space linear and non-linear bias are measured,with 2.6 per cent precision on the former if σ8 isfixed. The data also indicate a 2.8σ preference for the BAO,confirming the presence of BAO in the three-point function.
Bautista JE, Busca NG, Guy J, Rich J, Blomqvist M, du Mas des Bourboux H, Pieri MM, Font-Ribera A, Bailey S, Delubac T, et al. Measurement of baryon acoustic oscillation correlations at z = 2.3 with SDSS DR12 Lyα-Forests. Astronomy and Astrophysics. 2017;603. Publisher's VersionAbstract
We have used flux-transmission correlations in Lyα forests tomeasure the imprint of baryon acoustic oscillations (BAO). The studyuses spectra of 157 783 quasars in the redshift range 2.1 ≤ z ≤3.5 from the Sloan Digital Sky Survey (SDSS) data release 12 (DR12).Besides the statistical improvements on our previous studies using SDSSDR9 and DR11, we have implemented numerous improvements in the analysisprocedure, allowing us to construct a physical model of the correlationfunction and to investigate potential systematic errors in thedetermination of the BAO peak position. The Hubble distance,DH = c/H(z), relative to the sound horizon is DH(z= 2.33) /rd = 9.07 ± 0.31. The best-determinedcombination of comoving angular-diameter distance, DM, andthe Hubble distance is found to beDH0.7DM0.3 /rd =13.94 ± 0.35. This value is 1.028 ± 0.026 times theprediction of the flat-ΛCDM model consistent with the cosmicmicrowave background (CMB) anisotropy spectrum. The errors includemarginalization over the effects of unidentified high-density absorptionsystems and fluctuations in ultraviolet ionizing radiation.Independently of the CMB measurements, the combination of our resultsand other BAO observations determine the open-ΛCDM densityparameters to be ΩM = 0.296 ± 0.029,ΩΛ = 0.699 ± 0.100 andΩk = -0.002 ± 0.119.
Slepian Z, Eisenstein DJ. Modelling the large-scale redshift-space 3-point correlation function of galaxies. Monthly Notices of the Royal Astronomical Society. 2017;469 :2059-2076. Publisher's VersionAbstract
We present a configuration-space model of the large-scale galaxy 3-pointcorrelation function (3PCF) based on leading-order perturbation theoryand including redshift-space distortions (RSD). This model should beuseful in extracting distance-scale information from the 3PCF via thebaryon acoustic oscillation method. We include the first redshift-spacetreatment of biasing by the baryon-dark matter relative velocity.Overall, on large scales the effect of RSD is primarily arenormalization of the 3PCF that is roughly independent of both physicalscale and triangle opening angle; for our adopted Ωmand bias values, the rescaling is a factor of ˜1.8. We also presentan efficient scheme for computing 3PCF predictions from our model,important for allowing fast exploration of the space of cosmologicalparameters in future analyses.
Berti AM, Coil AL, Behroozi PS, Eisenstein DJ, Bray AD, Cool RJ, Moustakas J. PRIMUS: One- and Two-halo Galactic Conformity at 0.2 < z < 1. The Astrophysical Journal. 2017;834. Publisher's VersionAbstract
We test for galactic conformity at 0.2< z< 1.0 to a projecteddistance of 5 Mpc using spectroscopic redshifts from the PRismMUlti-object Survey (PRIMUS). Our sample consists of ˜60,000galaxies in five separate fields covering a total of ˜5.5 squaredegrees, which allows us to account for cosmic variance. We identifystar-forming and quiescent “isolated primary” (I.e.,central) galaxies using isolation criteria and cuts in specific starformation rate. We match the redshift and stellar mass distributions ofthese samples to control for correlations between quiescent fraction andredshift and stellar mass. We detect a significant (>3σ)one-halo conformity signal, or an excess of star-forming neighbors
Coil AL, Mendez AJ, Eisenstein DJ, Moustakas J. PRIMUS+DEEP2: The Dependence of Galaxy Clustering on Stellar Mass and Specific Star Formation Rate at 0.2 < z < 1.2. The Astrophysical Journal. 2017;838. Publisher's VersionAbstract
We present results on the clustering properties of galaxies as afunction of both stellar mass and specific star formation rate (sSFR)using data from the PRIMUS and DEEP2 galaxy redshift surveys spanning0.2< z< 1.2. We use spectroscopic redshifts of over 100,000galaxies covering an area of 7.2 deg2 over five separatefields on the sky, from which we calculate cosmic variance errors. Wefind that the galaxy clustering amplitude is as strong of a function ofsSFR as of stellar mass, and that at a given sSFR, it does notsignificantly depend on stellar mass within the range probed here. Wefurther find that within the star-forming population and at a givenstellar mass, galaxies above the main sequence of star formation withhigher sSFR are less clustered than galaxies below the main sequencewith lower sSFR. We also find that within the quiescent population,galaxies with higher sSFR are less clustered than galaxies with lowersSFR, at a given stellar mass. We show that the galaxy clusteringamplitude smoothly increases with both increasing stellar mass anddecreasing sSFR, implying that galaxies likely evolve across the mainsequence, not only along it, before galaxies eventually becomequiescent. These results imply that the relation of stellar mass to halomass, which connects galaxies to dark matter halos, likely depends onsSFR.
Blanton MR, Bershady MA, Abolfathi B, Albareti FD, Allende Prieto C, Almeida A, Alonso-García J, Anders F, Anderson SF, Andrews B, et al. Sloan Digital Sky Survey IV: Mapping the Milky Way, Nearby Galaxies, and the Distant Universe. The Astronomical Journal. 2017;154. Publisher's VersionAbstract
We describe the Sloan Digital Sky Survey IV (SDSS-IV), a projectencompassing three major spectroscopic programs. The Apache PointObservatory Galactic Evolution Experiment 2 (APOGEE-2) is observinghundreds of thousands of Milky Way stars at high resolution and highsignal-to-noise ratios in the near-infrared. The Mapping Nearby Galaxiesat Apache Point Observatory (MaNGA) survey is obtaining spatiallyresolved spectroscopy for thousands of nearby galaxies (median z˜0.03). The extended Baryon Oscillation Spectroscopic Survey (eBOSS) ismapping the galaxy, quasar, and neutral gas distributions between z˜0.6 and 3.5 to constrain cosmology using baryon acoustic oscillations,redshift space distortions, and the shape of the power spectrum. WithineBOSS, we are conducting two major subprograms: the SPectroscopicIDentification of eROSITA Sources (SPIDERS), investigating X-ray AGNsand galaxies in X-ray clusters, and the Time Domain Spectroscopic Survey(TDSS), obtaining spectra of variable sources. All programs use the 2.5m Sloan Foundation Telescope at the Apache Point Observatory;observations there began in Summer 2014. APOGEE-2 also operates a secondnear-infrared spectrograph at the 2.5 m du Pont Telescope at LasCampanas Observatory, with observations beginning in early 2017.Observations at both facilities are scheduled to continue through 2020.In keeping with previous SDSS policy, SDSS-IV provides regularlyscheduled public data releases; the first one, Data Release 13, was madeavailable in 2016 July.
Majewski SR, Schiavon RP, Frinchaboy PM, Allende Prieto C, Barkhouser R, Bizyaev D, Blank B, Brunner S, Burton A, Carrera R, et al. The Apache Point Observatory Galactic Evolution Experiment (APOGEE). The Astronomical Journal. 2017;154. Publisher's VersionAbstract
The Apache Point Observatory Galactic Evolution Experiment (APOGEE), oneof the programs in the Sloan Digital Sky Survey III (SDSS-III), has nowcompleted its systematic, homogeneous spectroscopic survey sampling allmajor populations of the Milky Way. After a three-year observingcampaign on the Sloan 2.5 m Telescope, APOGEE has collected a halfmillion high-resolution (R ˜ 22,500), high signal-to-noise ratio(>100), infrared (1.51-1.70 μm) spectra for 146,000 stars,with time series information via repeat visits to most of these stars.This paper describes the motivations for the survey and its overalldesign—hardware, field placement, target selection,operations—and gives an overview of these aspects as well as thedata reduction, analysis, and products. An index is also given to thecomplement of technical papers that describe various critical surveycomponents in detail. Finally, we discuss the achieved surveyperformance and illustrate the variety of potential uses of the dataproducts by way of a number of science demonstrations, which span fromtime series analysis of stellar spectral variations and radial velocityvariations from stellar companions, to spatial maps of kinematics,metallicity, and abundance patterns across the Galaxy and as a functionof age, to new views of the interstellar medium, the chemistry of starclusters, and the discovery of rare stellar species. As part of SDSS-IIIData Release 12 and later releases, all of the APOGEE data products arepublicly available.
Albareti FD, Allende Prieto C, Almeida A, Anders F, Anderson S, Andrews BH, Aragón-Salamanca A, Argudo-Fernández M, Armengaud E, Aubourg E, et al. The 13th Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-IV Survey Mapping Nearby Galaxies at Apache Point Observatory. The Astrophysical Journal Supplement Series. 2017;233. Publisher's VersionAbstract
The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) beganobservations in 2014 July. It pursues three core programs: the ApachePoint Observatory Galactic Evolution Experiment 2 (APOGEE-2), MappingNearby Galaxies at APO (MaNGA), and the Extended Baryon OscillationSpectroscopic Survey (eBOSS). As well as its core program, eBOSScontains two major subprograms: the Time Domain Spectroscopic Survey(TDSS) and the SPectroscopic IDentification of ERosita Sources(SPIDERS). This paper describes the first data release from SDSS-IV,Data Release 13 (DR13). DR13 makes publicly available the first 1390spatially resolved integral field unit observations of nearby galaxiesfrom MaNGA. It includes new observations from eBOSS, completing theSloan Extended QUasar, Emission-line galaxy, Luminous red galaxy Survey(SEQUELS), which also targeted variability-selected objects andX-ray-selected objects. DR13 includes new reductions of the SDSS-IIIBOSS data, improving the spectrophotometric calibration and redshiftclassification, and new reductions of the SDSS-III APOGEE-1 data,improving stellar parameters for dwarf stars and cooler stars. DR13provides more robust and precise photometric calibrations. Value-addedtarget catalogs relevant for eBOSS, TDSS, and SPIDERS and an updatedred-clump catalog for APOGEE are also available. This paper describesthe location and format of the data and provides references to importanttechnical papers. The SDSS web site,, provides links tothe data, tutorials, examples of data access, and extensivedocumentation of the reduction and analysis procedures. DR13 is thefirst of a scheduled set that will contain new data and analyses fromthe planned ∼6 yr operations of SDSS-IV.
du Mas des Bourboux H, Le Goff J-M, Blomqvist M, Busca NG, Guy J, Rich J, Yèche C, Bautista JE, Burtin É, Dawson KS, et al. Baryon acoustic oscillations from the complete SDSS-III Lyα-quasar cross-correlation function at z = 2.4. Astronomy and Astrophysics. 2017;608. Publisher's VersionAbstract
We present a measurement of baryon acoustic oscillations (BAO) in thecross-correlation of quasars with the Lyα-forest flux transmissionat a mean redshift of z = 2.40. The measurement uses the complete SloanDigital Sky Survey (SDSS-III) data sample: 168 889 forests and 234 367quasars from the SDSS data release DR12. In addition to the statisticalimprovement on our previous study using DR11, we have implementednumerous improvements at the analysis level enabling a more accuratemeasurement of this cross-correlation. We have also developed the firstsimulations of the cross-correlation that allow us to test differentaspects of our data analysis and to search for potential systematicerrors in the determination of the BAO peak position. We measure the tworatios DH(z = 2.40) /rd = 9.01 ± 0.36 andDM(z = 2.40) /rd = 35.7 ± 1.7, where theerrors include marginalization over the non-linear velocity of quasarsand the cross-correlation of metals and quasars, among other effects.These results are within 1.8σ of the prediction of theflat-ΛCDM model describing the observed cosmic microwavebackground anisotropies. We combine this study with the Lyα-forestauto-correlation function, yielding DH(z = 2.40)/rd = 8.94 ± 0.22 and DM(z = 2.40)/rd = 36.6 ± 1.2, within 2.3σ of the sameflat-ΛCDM model.
Chuang C-H, Pellejero-Ibanez M, Rodríguez-Torres S, Ross AJ, Zhao G-bo, Wang Y, Cuesta AJ, Rubiño-Martín JA, Prada F, Alam S, et al. The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: single-probe measurements from DR12 galaxy clustering - towards an accurate model. Monthly Notices of the Royal Astronomical Society. 2017;471 :2370-2390. Publisher's VersionAbstract
We analyse the broad-range shape of the monopole and quadrupolecorrelation functions of the Baryon Oscillation Spectroscopic SurveyData Release 12 (DR12) CMASS and LOWZ galaxy sample to obtainconstraints on the Hubble expansion rate H(z), the angular-diameterdistance DA(z), the normalized growth ratef(z)σ8(z) and the physical matter densityΩm h2. We adopt wide and flat priors on allmodel parameters in order to ensure the results are those of a'single-probe' galaxy clustering analysis. We also marginalize overthree nuisance terms that account for potential observationalsystematics affecting the measured monopole. However, such Monte CarloMarkov Chain analysis is computationally expensive for advancedtheoretical models. We develop a new methodology to speed up theanalysis. Using the range 40 h-1 Mpc < s < 180h-1 Mpc, we obtain{DA(z)rs,fid/rs (Mpc),H(z)rs/rs,fid km s-1 Mpc-1,f(z)σ8(z), Ωm h2} = {956± 28, 75.0 ± 4.0, 0.397 ± 0.073, 0.143 ±0.017} at z = 0.32 and {1421 ± 23, 96.7 ± 2.7, 0.497± 0.058, 0.137 ± 0.015} at z = 0.59 where rs isthe comoving sound horizon at the drag epoch and rs,fid =147.66 Mpc for the fiducial cosmology used in this study. Combining ourmeasurements with Planck data, we obtain Ωm = 0.306± 0.009, H0 = 67.9 ± 0.7 km s-1Mpc-1 and σ8 = 0.815 ± 0.009 assumingΛcold dark matter (CDM); Ωk = 0.000 ±0.003 and w = -1.02 ± 0.08 assuming owCDM. Our results show notension with the flat ΛCDM cosmological paradigm. This paper ispart of a set that analyses the final galaxy clustering data set fromBaryon Oscillation Spectroscopic Survey.
Alam S, Ata M, Bailey S, Beutler F, Bizyaev D, Blazek JA, Bolton AS, Brownstein JR, Burden A, Chuang C-H, et al. The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: cosmological analysis of the DR12 galaxy sample. Monthly Notices of the Royal Astronomical Society. 2017;470 :2617-2652. Publisher's VersionAbstract
We present cosmological results from the final galaxy clustering dataset of the Baryon Oscillation Spectroscopic Survey, part of the SloanDigital Sky Survey III. Our combined galaxy sample comprises 1.2 millionmassive galaxies over an effective area of 9329 deg2 andvolume of 18.7 Gpc3, divided into three partially overlappingredshift slices centred at effective redshifts 0.38, 0.51 and 0.61. Wemeasure the angular diameter distance DM and Hubble parameterH from the baryon acoustic oscillation (BAO) method, in combination witha cosmic microwave background prior on the sound horizon scale, afterapplying reconstruction to reduce non-linear effects on the BAO feature.Using the anisotropic clustering of the pre-reconstruction densityfield, we measure the product DMH from the Alcock-Paczynski(AP) effect and the growth of structure, quantified byfσ8(z), from redshift-space distortions (RSD). Wecombine individual measurements presented in seven companion papers intoa set of consensus values and likelihoods, obtaining constraints thatare tighter and more robust than those from any one method; inparticular, the AP measurement from sub-BAO scales sharpens constraintsfrom post-reconstruction BAOs by breaking degeneracy betweenDM and H. Combined with Planck 2016 cosmic microwavebackground measurements, our distance scale measurements simultaneouslyimply curvature ΩK = 0.0003 ± 0.0026 and a darkenergy equation-of-state parameter w = -1.01 ± 0.06, in strongaffirmation of the spatially flat cold dark matter (CDM) model with acosmological constant (ΛCDM). Our RSD measurements offσ8, at 6 per cent precision, are similarly consistentwith this model. When combined with supernova Ia data, we findH0 = 67.3 ± 1.0 km s-1 Mpc-1even for our most general dark energy model, in tension with some directmeasurements. Adding extra relativistic species as a degree of freedomloosens the constraint only slightly, to H0 = 67.8 ±1.2 km s-1 Mpc-1. Assuming flat ΛCDM, wefind Ωm = 0.310 ± 0.005 and H0 = 67.6± 0.5 km s-1 Mpc-1, and we find a 95 percent upper limit of 0.16 eV c-2 on the neutrino mass sum.
Zhao G-bo, Raveri M, Pogosian L, Wang Y, Crittenden RG, Handley WJ, Percival WJ, Beutler F, Brinkmann J, Chuang C-H, et al. Dynamical dark energy in light of the latest observations. Nature Astronomy. 2017;1 :627-632. Publisher's VersionAbstract
A flat Friedmann-Robertson-Walker universe dominated by a cosmologicalconstant (Λ) and cold dark matter (CDM) has been the workingmodel preferred by cosmologists since the discovery of cosmicacceleration1,2. However, tensions of various degrees ofsignificance are known to be present among existing datasets within theΛCDM framework3-11. In particular, the Lyman-αforest measurement of the baryon acoustic oscillations (BAO) by theBaryon Oscillation Spectroscopic Survey3 prefers a smallervalue of the matter density fraction ΩM than thatpreferred by cosmic microwave background (CMB). Also, the recentlymeasured value of the Hubble constant, H0 = 73.24 ±1.74 km s-1 Mpc-1 (ref. 12), is3.4σ higher than the 66.93 ± 0.62 km s-1Mpc-1 inferred from the Planck CMB data7. In thiswork, we investigate whether these tensions can be interpreted asevidence for a non-constant dynamical dark energy. Using theKullback-Leibler divergence13 to quantify the tension betweendatasets, we find that the tensions are relieved by an evolving darkenergy, with the dynamical dark energy model preferred at a 3.5σsignificance level based on the improvement in the fit alone. While, atpresent, the Bayesian evidence for the dynamical dark energy isinsufficient to favour it over ΛCDM, we show that, if the currentbest-fit dark energy happened to be the true model, it would bedecisively detected by the upcoming Dark Energy Spectroscopic Instrumentsurvey14.
Yuan S, Eisenstein DJ, Garrison LH. Using galaxy pairs to investigate the three-point correlation function in the squeezed limit. Monthly Notices of the Royal Astronomical Society. 2017;472 :577-590. Publisher's VersionAbstract
We investigate the three-point correlation function (3PCF) in thesqueezed limit by considering galaxy pairs as discrete objects andcross-correlating them with the galaxy field. We develop an efficientalgorithm using fast Fourier transforms to compute suchcross-correlations and their associated pair-galaxy bias bp,g and the squeezed 3PCF coefficient Qeff. We implementour method using N-body cosmological simulations and a fiducial halooccupation distribution (HOD) and present the results in both the realspace and redshift space. In real space, we observe a peak in bp,g and Qeff at pair separation of ∼2 Mpc, attributedto the fact that galaxy pairs at 2 Mpc separation trace the most massivedark matter haloes. We also see strong anisotropy in the bp,g and Qeff signals that track the large-scalefilamentary structure. In redshift space, both the 2 Mpc peak and theanisotropy are significantly smeared out along the line of sight due tofinger-of-God effect. In both the real space and redshift space, thesqueezed 3PCF shows a factor of 2 variation, contradicting thehierarchical ansatz, but offering rich information on the galaxy-haloconnection. Thus, we explore the possibility of using the squeezed 3PCFto constrain the HOD. When we compare two simple HOD models that areclosely matched in their projected two-point correlation function(2PCF), we do not yet see a strong variation in the 3PCF that is clearlydisentangled from variations in the projected 2PCF. Nevertheless, wepropose that more complicated HOD models, e.g. those incorporatingassembly bias, can break degeneracies in the 2PCF and show adistinguishable squeezed 3PCF signal.
Slepian Z, Eisenstein DJ. Accelerating the two-point and three-point galaxy correlation functions using Fourier transforms. Monthly Notices of the Royal Astronomical Society. 2016;455 :L31-L35. Publisher's VersionAbstract
Though Fourier transforms (FTs) are a common technique for findingcorrelation functions, they are not typically used in computations ofthe anisotropy of the two-point correlation function (2PCF) about theline of sight in wide-angle surveys because the line-of-sight directionis not constant on the Cartesian grid. Here we show how FTs can be usedto compute the multipole moments of the anisotropic 2PCF. We also showhow FTs can be used to accelerate the 3PCF algorithm of Slepian &Eisenstein. In both cases, these FT methods allow one to avoid thecomputational cost of pair counting, which scales as the square of thenumber density of objects in the survey. With the upcoming large datasets of Dark Energy Spectroscopic Instrument, Euclid, and Large SynopticSurvey Telescope, FT techniques will therefore offer an importantcomplement to simple pair or triplet counts.
Cuesta AJ, Vargas-Magaña M, Beutler F, Bolton AS, Brownstein JR, Eisenstein DJ, Gil-Marín H, Ho S, McBride CK, Maraston C, et al. The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: baryon acoustic oscillations in the correlation function of LOWZ and CMASS galaxies in Data Release 12. Monthly Notices of the Royal Astronomical Society. 2016;457 :1770-1785. Publisher's VersionAbstract
We present distance scale measurements from the baryon acousticoscillation signal in the constant stellar mass and low-redshift samplesamples from the Data Release 12 of the Baryon Oscillation SpectroscopicSurvey. The total volume probed is 14.5 Gpc3, a 10 per centincrement from Data Release 11. From an analysis of the sphericallyaveraged correlation function, we infer a distance to z = 0.57 ofD_V(z)r^fid_d/r_d = 2028± 21 Mpc and a distance to z = 0.32 ofD_V(z)r^fid_d/r_d = 1264± 22 Mpc assuming a cosmology in whichr^fid_d = 147.10 Mpc. From the anisotropic analysis, we find an angulardiameter distance to z = 0.57 of D_A(z)r^fid_d/r_d = 1401± 21 Mpcand a distance to z = 0.32 of 981 ± 20 Mpc, a 1.5 and 2.0 percent measurement, respectively. The Hubble parameter at z = 0.57 isH(z)r_d/r^fid_d = 100.3± 3.7 km s-1 Mpc-1and its value at z = 0.32 is 79.2 ± 5.6 km s-1Mpc-1, a 3.7 and 7.1 per cent measurement, respectively.These cosmic distance scale constraints are in excellent agreement witha Λ cold dark matter model with cosmological parameters releasedby the recent Planck 2015 results.
Croft RAC, Miralda-Escudé J, Zheng Z, Bolton A, Dawson KS, Peterson JB, York DG, Eisenstein D, Brinkmann J, Brownstein J, et al. Large-scale clustering of Lyman α emission intensity from SDSS/BOSS. Monthly Notices of the Royal Astronomical Society. 2016;457 :3541-3572. Publisher's VersionAbstract
We present a tentative detection of the large-scale structure of Lyα emission in the Universe at redshifts z = 2-3.5 by measuring thecross-correlation of Ly α surface brightness with quasars in SloanDigital Sky Survey/Baryon Oscillation Spectroscopic Survey. We use amillion spectra targeting luminous red galaxies at z < 0.8, aftersubtracting a best-fitting model galaxy spectrum from each one, as anestimate of the high-redshift Ly α surface brightness. Thequasar-Ly α emission cross-correlation is detected on scales 1˜ 15 h-1 Mpc, with shape consistent with a ΛCDMmodel with Ω _m =0.30^{+0.10}_{-0.07}. The predicted amplitude ofthis cross-correlation is proportional to the product of the mean Lyα surface brightness, <μα>, theamplitude of mass fluctuations and the quasar and Ly α emissionbias factors. We infer <μα>(bα/3) = (3.9 ± 0.9) × 10-21erg s-1 cm-2 Å-1arcsec-2, where bα is the Ly αemission bias. If star-forming galaxies dominate this emission, we findρSFR = (0.28 ± 0.07)(3/bα)yr-1 Mpc-3. For bα = 3, thisvalue is ˜30 times larger than previous estimates fromindividually detected Ly α emitters, but consistent with the totalρSFR derived from dust-corrected, continuum UV galaxysurveys, if most of the Ly α photons from these galaxies avoiddust absorption and are reemitted after diffusing in large gas haloes.Heating of intergalactic gas by He II photoionization from quasarradiation or jets may alternatively explain the detected correlation,and cooling radiation from gas in galactic haloes may also contribute.We also detect redshift space anisotropy of the quasar-Ly αemission cross-correlation, finding evidence at the 3.0σ levelthat it is radially elongated, which may be explained byradiative-transfer effects. Our measurements represent the firstapplication of the intensity mapping technique to optical observations.
Bray AD, Pillepich A, Sales LV, Zhu E, Genel S, Rodriguez-Gomez V, Torrey P, Nelson D, Vogelsberger M, Springel V, et al. Modelling galactic conformity with the colour-halo age relation in the Illustris simulation. Monthly Notices of the Royal Astronomical Society. 2016;455 :185-198. Publisher's VersionAbstract
Comparisons between observational surveys and galaxy formation modelsfind that dark matter haloes' mass can largely explain their galaxies'stellar mass. However, it remains uncertain whether additionalenvironmental variables, known as assembly bias, are necessary toexplain other galaxy properties. We use the Illustris simulation toinvestigate the role of assembly bias in producing galactic conformityby considering 18 000 galaxies with Mstellar > 2 ×109 M. We find a significant signal ofgalactic conformity: out to distances of about 10 Mpc, the mean redfraction of galaxies around redder galaxies is higher than around bluergalaxies at fixed stellar mass. Dark matter haloes exhibit an analogousconformity signal, in which the fraction of haloes formed at earliertimes (old haloes) is higher around old haloes than around younger onesat fixed halo mass. A plausible interpretation of galactic conformity isthe combination of the halo conformity signal with the galaxycolour-halo age relation: at fixed stellar mass, particularly towardsthe low-mass end, Illustris' galaxy colours correlate with halo age,with the reddest galaxies (often satellites) preferentially found in theoldest haloes. We explain the galactic conformity effect with a simplesemi-empirical model, assigning stellar mass via halo mass (abundancematching) and galaxy colour via halo age (age matching). Regardingcomparison to observations, we conclude that the adoptedselection/isolation criteria, projection effects, and stackingtechniques can have a significant impact on the measured amplitude ofthe conformity signal.