Slepian Z, Eisenstein DJ. Accelerating the two-point and three-point galaxy correlation functions using Fourier transforms. Monthly Notices of the Royal Astronomical Society [Internet]. 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 [Internet]. 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 [Internet]. 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 [Internet]. 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.
Kepler SO, Pelisoli I, Koester D, Ourique G, Romero AD, Reindl N, Kleinman SJ, Eisenstein DJ, Valois ADM, Amaral LA. New white dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 12. Monthly Notices of the Royal Astronomical Society [Internet]. 2016;455 :3413-3423. Publisher's VersionAbstract
We report the discovery of 6576 new spectroscopically confirmed whitedwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release12. We obtain Teff, log g and mass for hydrogen atmospherewhite dwarf stars (DAs) and helium atmosphere white dwarf stars (DBs),estimate the calcium/helium abundances for the white dwarf stars withmetallic lines (DZs) and carbon/helium for carbon-dominated spectra(DQs). We found one central star of a planetary nebula, one ultracompacthelium binary (AM CVn), one oxygen line-dominated white dwarf, 15 hotDO/PG1159s, 12 new cataclysmic variables, 36 magnetic white dwarf stars,54 DQs, 115 helium-dominated white dwarfs, 148 white dwarf +main-sequence star binaries, 236 metal-polluted white dwarfs, 300continuum spectra DCs, 230 hot subdwarfs, 2936 new hydrogen-dominatedwhite dwarf stars, and 2675 cool hydrogen-dominated subdwarf stars. Wecalculate the mass distribution of all 5883 DAs with S/N ≥ 15 inDR12, including the ones in DR7 and DR10, with an average S/N = 26,corrected to the 3D convection scale, and also the distribution aftercorrecting for the observed volume, using 1/Vmax.
Mendez AJ, Coil AL, Aird J, Skibba RA, Diamond-Stanic AM, Moustakas J, Blanton MR, Cool RJ, Eisenstein DJ, Wong KC, et al. PRIMUS + DEEP2: Clustering of X-Ray, Radio, and IR-AGNs at z~0.7. The Astrophysical Journal [Internet]. 2016;821. Publisher's VersionAbstract
We measure the clustering of X-ray, radio, and mid-IR-selected activegalactic nuclei (AGNs) at 0.2\lt z\lt 1.2 using multi-wavelength imagingand spectroscopic redshifts from the PRIMUS and DEEP2 redshift surveys,covering seven separate fields spanning ∼10 deg 2 . Using thecross-correlation of AGNs with dense galaxy samples, we measure theclustering scale length and slope, as well as the bias, of AGNs selectedat different wavelengths. Similar to previous studies, we find thatX-ray and radio AGNs are more clustered than mid-IR-selected AGNs. Wefurther compare the clustering of each AGN sample with matched galaxysamples designed to have the same stellar mass, star-formation rate(SFR), and redshift distributions as the AGN host galaxies and find nosignificant differences between their clustering properties. Theobserved differences in the clustering of AGNs selected at differentwavelengths can therefore be explained by the clustering differences oftheir host populations, which have different distributions in bothstellar mass and SFR. Selection biases inherent in AGN selectiontherefore determine the clustering of observed AGN samples. We furtherfind no significant difference between the clustering of obscured andunobscured AGNs, using IRAC or Wide-field Infrared Survey Explorercolors or X-ray hardness ratio.
Reid B, Ho S, Padmanabhan N, Percival WJ, Tinker J, Tojeiro R, White M, Eisenstein DJ, Maraston C, Ross AJ, et al. SDSS-III Baryon Oscillation Spectroscopic Survey Data Release 12: galaxy target selection and large-scale structure catalogues. Monthly Notices of the Royal Astronomical Society [Internet]. 2016;455 :1553-1573. Publisher's VersionAbstract
The Baryon Oscillation Spectroscopic Survey (BOSS), part of the SloanDigital Sky Survey (SDSS) III project, has provided the largest surveyof galaxy redshifts available to date, in terms of both the number ofgalaxy redshifts measured by a single survey, and the effectivecosmological volume covered. Key to analysing the clustering of thesedata to provide cosmological measurements is understanding the detailedproperties of this sample. Potential issues include variations in thetarget catalogue caused by changes either in the targeting algorithm orproperties of the data used, the pattern of spectroscopic observations,the spatial distribution of targets for which redshifts were notobtained, and variations in the target sky density due to observationalsystematics. We document here the target selection algorithms used tocreate the galaxy samples that comprise BOSS. We also present thealgorithms used to create large-scale structure catalogues for the finalData Release (DR12) samples and the associated random catalogues thatquantify the survey mask. The algorithms are an evolution of those usedby the BOSS team to construct catalogues from earlier data, and havebeen designed to accurately quantify the galaxy sample. The code used,designated MKSAMPLE, is released with this paper.
Dawson KS, Kneib J-P, Percival WJ, Alam S, Albareti FD, Anderson SF, Armengaud E, Aubourg É, Bailey S, Bautista JE, et al. The SDSS-IV Extended Baryon Oscillation Spectroscopic Survey: Overview and Early Data. The Astronomical Journal [Internet]. 2016;151. Publisher's VersionAbstract
In a six-year program started in 2014 July, the Extended BaryonOscillation Spectroscopic Survey (eBOSS) will conduct novel cosmologicalobservations using the BOSS spectrograph at Apache Point Observatory.These observations will be conducted simultaneously with the Time DomainSpectroscopic Survey (TDSS) designed for variability studies and theSpectroscopic Identification of eROSITA Sources (SPIDERS) programdesigned for studies of X-ray sources. In particular, eBOSS will measurewith percent-level precision the distance-redshift relation with baryonacoustic oscillations (BAO) in the clustering of matter. eBOSS will usefour different tracers of the underlying matter density field to vastlyexpand the volume covered by BOSS and map the large-scale-structuresover the relatively unconstrained redshift range 0.6 < z < 2.2.Using more than 250,000 new, spectroscopically confirmed luminous redgalaxies at a median redshift z = 0.72, we project that eBOSS will yieldmeasurements of the angular diameter distance dA(z) to an
Slepian Z, Eisenstein DJ. A simple analytic treatment of linear growth of structure with baryon acoustic oscillations. Monthly Notices of the Royal Astronomical Society [Internet]. 2016;457 :24-37. Publisher's VersionAbstract
In linear perturbation theory, all information about the growth ofstructure is contained in the Green's function, or equivalently,transfer function. These functions are generally computed usingnumerical codes or by phenomenological fitting formula anchored inaccurate analytic results in the limits of large and small scale. Here,we present a framework for analytically solving all scales, inparticular the intermediate scales relevant for the baryon acousticoscillations (BAO). We solve for the Green's function and transferfunction using spherically averaged overdensities and the approximationthat the density of the coupled baryon-photon fluid is constant interiorto the sound horizon.
García Pérez AE, Allende Prieto C, Holtzman JA, Shetrone M, Mészáros S, Bizyaev D, Carrera R, Cunha K, García-Hernández DA, Johnson JA, et al. ASPCAP: The APOGEE Stellar Parameter and Chemical Abundances Pipeline. The Astronomical Journal [Internet]. 2016;151. Publisher's VersionAbstract
The Apache Point Observatory Galactic Evolution Experiment (APOGEE) hasbuilt the largest moderately high-resolution (R ≈ 22,500)spectroscopic map of the stars across the Milky Way, and includingdust-obscured areas. The APOGEE Stellar Parameter and ChemicalAbundances Pipeline (ASPCAP) is the software developed for the automatedanalysis of these spectra. ASPCAP determines atmospheric parameters andchemical abundances from observed spectra by comparing observed spectrato libraries of theoretical spectra, using χ2minimization in a multidimensional parameter space. The package consistsof a fortran90 code that does the actual minimization and a wrapper IDLcode for book-keeping and data handling. This paper explains in detailthe ASPCAP components and functionality, and presents results from anumber of tests designed to check its performance. ASPCAP providesstellar effective temperatures, surface gravities, and metallicities
Favole G, McBride CK, Eisenstein DJ, Prada F, Swanson ME, Chuang C-H, Schneider DP. Building a better understanding of the massive high-redshift BOSS CMASS galaxies as tools for cosmology. Monthly Notices of the Royal Astronomical Society [Internet]. 2016;462 :2218-2236. Publisher's VersionAbstract
We explore the massive bluer star-forming population of the SloanDigital Sky Survey (SDSS) III/BOSS CMASS DR11 galaxies at z > 0.55 toquantify their differences, in terms of redshift-space distortions andlarge-scale bias, with respect to the luminous red galaxy sample. Weperform a qualitative analysis to understand the significance of thesedifferences and whether we can model and reproduce them in mockcatalogues. Specifically, we measure galaxy clustering in CMASS on smalland intermediate scales (0.1 ≲ r ≲ 50 h-1 Mpc) bycomputing the two-point correlation function - both projected andredshift-space - of these galaxies, and a new statistic, Σ(π),able to separate the coherent and dispersed redshift-space distortioncontributions and the large-scale bias. We interpret our clusteringmeasurements by adopting a Halo Occupation Distribution (HOD) schemethat maps them on to high-resolution N-body cosmological simulations toproduce suitable mock galaxy catalogues. The traditional HODprescription can be applied to the red and the blue samples,independently, but this approach is unphysical since it allows the samemock galaxies to be either red or blue. To overcome this ambiguity, wemodify the standard formulation and infer the red and the blue models bysplitting the full mock catalogue into two complementary andnon-overlapping submocks. This separation is performed by constrainingthe HOD with the observed CMASS red and blue galaxy fractions andproduces reliable and accurate models.
Chuang C-H, Prada F, Pellejero-Ibanez M, Beutler F, Cuesta AJ, Eisenstein DJ, Escoffier S, Ho S, Kitaura F-S, Kneib J-P, et al. The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: single-probe measurements from CMASS anisotropic galaxy clustering. Monthly Notices of the Royal Astronomical Society [Internet]. 2016;461 :3781-3793. Publisher's VersionAbstract
With the largest spectroscopic galaxy survey volume drawn from theSDSS-III Baryon Oscillation Spectroscopic Survey (BOSS), we can extractcosmological constraints from the measurements of redshift and geometricdistortions at quasi-linear scales (e.g. above 50 h-1 Mpc).We analyse the broad-range shape of the monopole and quadrupolecorrelation functions of the BOSS Data Release 12 (DR12) CMASS galaxysample, at the effective redshift z = 0.59, to obtain constraints on theHubble expansion rate H(z), the angular- diameter distanceDA(z), the normalized growth rate f(z)σ8(z),and the physical matter density Ωm h2. Weobtain robust measurements by including a polynomial as the model forthe systematic errors, and find it works very well against thesystematic effects, e.g. ones induced by stars and seeing. We provideaccurate measurements{DA(0.59)rs,fid/rs,H(0.59)rs/rs,fid,f(0.59)σ8(0.59), Ωm h2} ={1427 ± 26 Mpc, 97.3 ± 3.3 km s-1Mpc-1, 0.488 ± 0.060, 0.135 ± 0.016}, wherers is the comoving sound horizon at the drag epoch andrs,fid = 147.66 Mpc is the sound scale of the fiducialcosmology used in this study. The parameters which are not wellconstrained by our galaxy clustering analysis are marginalized over withwide flat priors. Since no priors from other data sets, e.g. cosmicmicrowave background (CMB), are adopted and no dark energy models areassumed, our results from BOSS CMASS galaxy clustering alone may becombined with other data sets, i.e. CMB, SNe, lensing or other galaxyclustering data to constrain the parameters of a given cosmologicalmodel. The uncertainty on the dark energy equation of state parameter,w, from CMB+CMASS is about 8 per cent. The uncertainty on the curvaturefraction, Ωk, is 0.3 per cent. We do not find deviationfrom flat ΛCDM.
Favole G, Comparat J, Prada F, Yepes G, Jullo E, Niemiec A, Kneib J-P, Rodríguez-Torres SA, Klypin A, Skibba RA, et al. Clustering properties of g-selected galaxies at z ˜ 0.8. Monthly Notices of the Royal Astronomical Society [Internet]. 2016;461 :3421-3431. Publisher's VersionAbstract
Current and future large redshift surveys, as the Sloan Digital SkySurvey IV extended Baryon Oscillation Spectroscopic Survey(SDSS-IV/eBOSS) or the Dark Energy Spectroscopic Instrument (DESI), willuse emission-line galaxies (ELGs) to probe cosmological models bymapping the large-scale structure of the Universe in the redshift range0.6 < z < 1.7. With current data, we explore the halo-galaxyconnection by measuring three clustering properties of g-selected ELGsas matter tracers in the redshift range 0.6 < z < 1: (i) theredshift-space two-point correlation function using spectroscopicredshifts from the BOSS ELG sample and VIPERS; (ii) the angulartwo-point correlation function on the footprint of the CFHT-LS; (iii)the galaxy-galaxy lensing signal around the ELGs using the CFHTLenS. Weinterpret these observations by mapping them on to the latesthigh-resolution MultiDark Planck N-body simulation, using a novel(Sub)Halo-Abundance Matching technique that accounts for the ELGincompleteness. ELGs at z ˜ 0.8 live in haloes of (1 ± 0.5)× 1012 h-1M and 22.5± 2.5 per cent of them are satellites belonging to a larger halo.The halo occupation distribution of ELGs indicates that we are samplingthe galaxies in which stars form in the most efficient way, according totheir stellar-to-halo mass ratio.
Speagle JS, Capak PL, Eisenstein DJ, Masters DC, Steinhardt CL. Exploring photometric redshifts as an optimization problem: an ensemble MCMC and simulated annealing-driven template-fitting approach. Monthly Notices of the Royal Astronomical Society [Internet]. 2016;461 :3432-3442. Publisher's VersionAbstract
Using a 4D grid of ˜2 million model parameters (Δz = 0.005)adapted from Cosmological Origins Survey photometric redshift (photo-z)searches, we investigate the general properties of template-basedphoto-z likelihood surfaces. We find these surfaces are filled withnumerous local minima and large degeneracies that generally confoundsimplistic gradient-descent optimization schemes. We combine ensembleMarkov Chain Monte Carlo sampling with simulated annealing to robustlyand efficiently explore these surfaces in approximately constant time.Using a mock catalogue of 384 662 objects, we show our approach samples˜40 times more efficiently compared to a `brute-force' counterpartwhile maintaining similar levels of accuracy. Our results representfirst steps towards designing template-fitting photo-z approacheslimited mainly by memory constraints rather than computation time.
Montero-Dorta AD, Bolton AS, Brownstein JR, Swanson M, Dawson K, Prada F, Eisenstein D, Maraston C, Thomas D, Comparat J, et al. The high-mass end of the red sequence at z ˜ 0.55 from SDSS-III/BOSS: completeness, bimodality and luminosity function. Monthly Notices of the Royal Astronomical Society [Internet]. 2016;461 :1131-1153. Publisher's VersionAbstract
We have developed an analytical method based on forward-modellingtechniques to characterize the high-mass end of the red sequence (RS)galaxy population at redshift z ˜ 0.55, from the DR10 BOSS (BaryonOscillation Spectroscopic Survey) CMASS spectroscopic sample, whichcomprises ˜600 000 galaxies. The method, which follows an unbinnedmaximum likelihood approach, allows the deconvolution of the intrinsicCMASS colour-colour-magnitude distributions from photometric errors andselection effects. This procedure requires modelling the covariancematrix for the i-band magnitude, g - r colour and r - i colour usingStripe 82 multi-epoch data. Our results indicate that theerror-deconvolved intrinsic RS distribution is consistent, within thephotometric uncertainties, with a single point (<0.05 mag) in thecolour-colour plane at fixed magnitude, for a narrow redshift slice. Wehave computed the high-mass end (0.55Mi ≲-22) of the 0.55i-band RS luminosity function (RS LF) inseveral redshift slices within the redshift range 0.52 < z < 0.63.In this narrow redshift range, the evolution of the RS LF is consistent,within the uncertainties in the modelling, with a passively evolvingmodel with Φ* = (7.248 ± 0.204) × 10-4 Mpc-3 mag-1, fading at a rate of 1.5± 0.4 mag per unit redshift. We report RS completeness as afunction of magnitude and redshift in the CMASS sample, which willfacilitate a variety of galaxy-evolution and clustering studies usingBOSS. Our forward-modelling method lays the foundations for futurestudies using other dark-energy surveys like the Extended BaryonOscillation Spectroscopic Survey or the Dark Energy SpectroscopicInstrument, which are affected by the same type of photometricblurring/selection effects.
Garrison LH, Eisenstein DJ, Ferrer D, Metchnik MV, Pinto PA. Improving initial conditions for cosmological N-body simulations. Monthly Notices of the Royal Astronomical Society [Internet]. 2016;461 :4125-4145. Publisher's VersionAbstract
In cosmological N-body simulations, the representation of dark matter asdiscrete `macroparticles' suppresses the growth of structure, such thatsimulations no longer reproduce linear theory on small scales nearkNyquist. Marcos et al. demonstrate that this is due tosparse sampling of modes near kNyquist and that theoften-assumed continuum growing modes are not proper growing modes ofthe particle system. We develop initial conditions (ICs) that respectthe particle linear theory growing modes and then rescale the modeamplitudes to account for growth suppression. These ICs also allow us totake advantage of our very accurate N-body code ABACUS to implementsecond-order Lagrangian perturbation theory (2LPT) in configurationspace. The combination of 2LPT and rescaling improves the accuracy ofthe late-time power spectra, halo mass functions, and halo clustering.In particular, we achieve 1 per cent accuracy in the power spectrum downto kNyquist, versus kNyquist/4 without rescalingor kNyquist/13 without 2LPT, relative to an oversampledreference simulation. We anticipate that our 2LPT will be useful forlarge simulations where fast Fourier transforms are expensive and thatrescaling will be useful for suites of medium-resolution simulationsused in cosmic emulators and galaxy survey mock catalogues. Code togenerate ICs is available at
O'Connell R, Eisenstein D, Vargas M, Ho S, Padmanabhan N. Large covariance matrices: smooth models from the two-point correlation function. Monthly Notices of the Royal Astronomical Society [Internet]. 2016;462 :2681-2694. Publisher's VersionAbstract
We introduce a new method for estimating the covariance matrix for thegalaxy correlation function in surveys of large-scale structure. Ourmethod combines simple theoretical results with a realisticcharacterization of the survey to dramatically reduce noise in thecovariance matrix. For example, with an investment of only ≈1000 CPUhours we can produce a model covariance matrix with noise levels thatwould otherwise require ˜35 000 mocks. Non-Gaussian contributionsto the model are calibrated against mock catalogues, after which themodel covariance is found to be in impressive agreement with the mockcovariance matrix. Since calibration of this method requires fewer mocksthan brute force approaches, we believe that it could dramaticallyreduce the number of mocks required to analyse future surveys.
Patej A, Eisenstein D. Quantifying the colour-dependent stochasticity of large-scale structure. Monthly Notices of the Royal Astronomical Society [Internet]. 2016;460 :1310-1317. Publisher's VersionAbstract
We address the question of whether massive red and blue galaxies tracethe same large-scale structure at z ˜ 0.6 using the CMASS sampleof galaxies from Data Release 12 of the Sloan Digital Sky Survey III.After splitting the catalogue into subsamples of red and blue galaxiesusing a simple colour cut, we measure the clustering of both subsamplesand construct the correlation coefficient, r, using two statistics. Thecorrelation coefficient quantifies the stochasticity between the twosubsamples, which we examine over intermediate scales (20 ≲ R≲ 100 h-1 Mpc). We find that on these intermediatescales, the correlation coefficient is consistent with 1; in particular,we find r > 0.95 taking into account both statistics and r > 0.974using the favoured statistic.
Kitaura F-S, Chuang C-H, Liang Y, Zhao C, Tao C, Rodríguez-Torres S, Eisenstein DJ, Gil-Marín H, Kneib J-P, McBride C, et al. Signatures of the Primordial Universe from Its Emptiness: Measurement of Baryon Acoustic Oscillations from Minima of the Density Field. Physical Review Letters [Internet]. 2016;116. Publisher's VersionAbstract
Sound waves from the primordial fluctuations of the Universe imprintedin the large-scale structure, called baryon acoustic oscillations(BAOs), can be used as standard rulers to measure the scale of theUniverse. These oscillations have already been detected in thedistribution of galaxies. Here we propose to measure BAOs from thetroughs (minima) of the density field. Based on two sets of accuratemock halo catalogues with and without BAOs in the seed initialconditions, we demonstrate that the BAO signal cannot be obtained fromthe clustering of classical disjoint voids, but it is clearly detectedfrom overlapping voids. The latter represent an estimate of all troughsof the density field. We compute them from the empty circumspherecenters constrained by tetrahedra of galaxies using Delaunaytriangulation. Our theoretical models based on an unprecedented largeset of detailed simulated void catalogues are remarkably well confirmedby observational data. We use the largest recently publicly availablesample of luminous red galaxies from SDSS-III BOSS DR11 to unveil forthe first time a >3 σ BAO detection from voids in observations.Since voids are nearly isotropically expanding regions, their centersrepresent the most quiet places in the Universe, keeping in mind thecosmos origin and providing a new promising window in the analysis ofthe cosmological large-scale structure from galaxy surveys.
Holtzman JA, Shetrone M, Johnson JA, Allende Prieto C, Anders F, Andrews B, Beers TC, Bizyaev D, Blanton MR, Bovy J, et al. Abundances, Stellar Parameters, and Spectra from the SDSS-III/APOGEE Survey. The Astronomical Journal [Internet]. 2015;150. Publisher's VersionAbstract
The SDSS-III/Apache Point Observatory Galactic Evolution Experiment(APOGEE) survey operated from 2011-2014 using the APOGEEspectrograph, which collects high-resolution (R ˜ 22,500), near-IR(1.51-1.70 μm) spectra with a multiplexing (300 fiber-fedobjects) capability. We describe the survey data products that arepublicly available, which include catalogs with radial velocity, stellarparameters, and 15 elemental abundances for over 150,000 stars, as wellas the more than 500,000 spectra from which these quantities arederived. Calibration relations for the stellar parameters({T}{eff}, {log} g, [M/H], [α/M]) and abundances (C, N,O, Na, Mg, Al, Si, S, K, Ca, Ti, V, Mn, Fe, Ni) are presented anddiscussed. The internal scatter of the abundances within clustersindicates that abundance precision is generally between 0.05 and 0.09dex across a broad temperature range; it is smaller for some elementalabundances within more limited ranges and at high signal-to-noise ratio.We assess the accuracy of the abundances using comparison of meancluster metallicities with literature values, APOGEE observations of thesolar spectrum and of Arcturus, comparison of individual star abundanceswith other measurements, and consideration of the locus of derivedparameters and abundances of the entire sample, and find that it ischallenging to determine the absolute abundance scale; external accuracymay be good to 0.1-0.2 dex. Uncertainties may be larger at coolertemperatures ({T}{eff} \lt 4000 {{K}}). Access to thepublic data release and data products is described, and some guidancefor using the data products is provided.