Karl Glazebrook

DETECTION OF THE BARYON ACOUSTIC PEAK IN THE LARGE-SCALE CORRELATION FUNCTION OF SDSS LUMINOUS RED GALAXIES

We present the large-scale correlation function measured from a spectroscopic sample of 46,748 luminous red galaxies from the Sloan Digital Sky Survey. The survey region covers 0.72h −3 Gpc 3 over 3816 square degrees and 0.16 < z < 0.47, making it the best sample yet for the study of large-scale structure. We find a well-detected peak in the correlation function at 100h −1 Mpc separation that is an excellent match to the predicted shape and location of the imprint of the recombination-epoch acoustic oscillations on the low-redshift clustering of matter. This detection demonstrates the linear growth of structure by gravitational instability between z ≈ 1000 and the present and confirms a firm prediction of the standard cosmological theory. The acoustic peak provides a standard ruler by which we can measure the ratio of the distances to z = 0.35 and z = 1089 to 4% fractional accuracy and the absolute distance to z = 0.35 to 5% accuracy. From the overall shape of the correlation function, we measure the matter density mh 2 to 8% and find agreement with the value from cosmic microwave background (CMB) anisotropies. Independent of the constraints provided by the CMB acoustic scale, we find m = 0.273 ±0.025+0.123(1+ w0)+0.137K. Including the CMB acoustic scale, we find that the spatial curvature is K = −0.010 ± 0.009 if the dark energy is a cosmological constant. More generally, our results provide a measurement of cosmological distance, and hence an argument for dark energy, based on a geometric method with the same simple physics as the microwave background anisotropies. The standard cosmological model convincingly passes these new and robust tests of its fundamental properties. Subject headings: cosmology: observations — large-scale structure of the universe — distance scale — cosmological parameters — cosmic microwave background — galaxies: elliptical and lenticular, cD

The 2dF Galaxy Redshift Survey: Spectra and redshifts

The 2dF Galaxy Redshift Survey (2dFGRS) is designed to measure redshifts for approximately 250 000 galaxies. This paper describes the survey design, the spectroscopic observations, the redshift measurements and the survey data base. The 2dFGRS uses the 2dF multifibre spectrograph on the Anglo-Australian Telescope, which is capable of observing 400 objects simultaneously over a 2° diameter field. The source catalogue for the survey is a revised and extended version of the APM galaxy catalogue, and the targets are galaxies with extinction-corrected magnitudes brighter than b J = 19.45. The main survey regions are two declination strips, one in the southern Galactic hemisphere spanning 80° × 15° around the SGP, and the other in the northern Galactic hemisphere spanning 75° × 10° along the celestial equator; in addition, there are 99 fields spread over the southern Galactic cap. The survey covers 2000 deg 2 and has a median depth of z = 0.11. Adaptive tiling is used to give a highly uniform sampling rate of 93 per cent over the whole survey region. Redshifts are measured from spectra covering 3600-8000 A at a two-pixel resolution of 9.0 A and a median S/N of 13 pixel - 1 . All redshift identifications are visually checked and assigned a quality parameter Q in the range 1-5; Q ≥ 3 redshifts are 98.4 per cent reliable and have an rms uncertainty of 85 km s - 1 . The overall redshift completeness for Q ≥ 3 redshifts is 91.8 per cent, but this varies with magnitude from 99 per cent for the brightest galaxies to 90 per cent for objects at the survey limit. The 2dFGRS data base is available on the World Wide Web at http://www. mso.anu.edu.au/2dFGRS.

The 2dF Galaxy Redshift Survey: power-spectrum analysis of the final data set and cosmological implications

We present a power-spectrum analysis of the final 2dF Galaxy Redshift Survey (2dFGRS), employing a direct Fourier method. The sample used comprises 221 414 galaxies with measured redshifts. We investigate in detail the modelling of the sample selection, improving on previous treatments in a number of respects. A new angular mask is derived, based on revisions to the photometric calibration. The redshift selection function is determined by dividing the survey according to rest-frame colour, and deducing a self-consistent treatment of k-corrections and evolution for each population. The covariance matrix for the power-spectrum estimates is determined using two different approaches to the construction of mock surveys, which are used to demonstrate that the input cosmological model can be correctly recovered. We discuss in detail the possible differences between the galaxy and mass power spectra, and treat these using simulations, analytic models and a hybrid empirical approach. Based on these investigations, we are confident that the 2dFGRS power spectrum can be used to infer the matter content of the universe. On large scales, our estimated power spectrum shows evidence for the ‘baryon oscillations’ that are predicted in cold dark matter (CDM) models. Fitting to a CDM model, assuming a primordial n s = 1 spectrum, h = 0.72 and negligible neutrino mass, the preferred

Quantifying the Bimodal Color-Magnitude Distribution of Galaxies

We analyze the bivariate distribution, in color versus absolute magnitude (u-r vs. Mr), of a low-redshift sample of galaxies from the Sloan Digital Sky Survey (2400 deg2, 0.004 < z < 0.08, -23.5 < Mr < -15.5). We trace the bimodality of the distribution from luminous to faint galaxies by fitting double Gaussians to the color functions separated in absolute magnitude bins. Color-magnitude (CM) relations are obtained for red and blue distributions (early- and late-type, predominantly field, galaxies) without using any cut in morphology. Instead, the analysis is based on the assumption of normal Gaussian distributions in color. We find that the CM relations are well fitted by a straight line plus a tanh function. Both relations can be described by a shallow CM trend (slopes of about -0.04, -0.05) plus a steeper transition in the average galaxy properties over about 2 mag. The midpoints of the transitions (Mr = -19.8 and -20.8 for the red and blue distributions, respectively) occur around 2 × 1010 ☉ after converting luminosities to stellar mass. Separate luminosity functions are obtained for the two distributions. The red distribution has a more luminous characteristic magnitude and a shallower faint-end slope (M* = -21.5, α = -0.8) compared to the blue distribution (α ≈ -1.3, depending on the parameterization). These are approximately converted to galaxy stellar mass functions. The red distribution galaxies have a higher number density per magnitude for masses greater than about 3 × 1010 ☉. Using a simple merger model, we show that the differences between the two functions are consistent with the red distribution being formed from major galaxy mergers.

Cosmological constraints from the SDSS luminous red galaxies

We measure the large-scale real-space power spectrum P(k) using luminous red galaxies (LRGs) in the Sloan Digital Sky Survey (SDSS) and use this measurement to sharpen constraints on cosmological parameters from the Wilkinson Microwave Anisotropy Probe (WMAP). We employ a matrix-based power spectrum estimation method using Pseudo-Karhunen-Loeve eigenmodes, producing uncorrelated minimum-variance measurements in 20 k-bands of both the clustering power and its anisotropy due to redshift-space distortions, with narrow and well-behaved window functions in the range 0.01h/Mpc 0.1h/Mpc and associated nonlinear complications, yet agree well with more aggressive published analyses where nonlinear modeling is crucial.

The 2dF galaxy redshift survey: near-infrared galaxy luminosity functions

We combine the Two Micron All Sky Survey (2MASS) Extended Source Catalogue and the 2dF Galaxy Redshift Survey to produce an infrared selected galaxy catalogue with 17 173 measured redshifts. We use this extensive data set to estimate the galaxy luminosity functions in the J- and K-S-bands. The luminosity functions are fairly well fitted by Schechter functions with parameters M-J(*) - 5 log h = -22.36 +/-0.02, alpha (J) = -0.93 +/-0.04, Phi (*)(J)= 0.0104 +/-0.0016 h(3) Mpc(-3) in the J-band and M-K s(*) - 5 log h = -23.44 +/-0.03, alphaK(S) = -0.96 +/-0.05, PhiK(S)(*) = 0.0108 +/-0.0016 h(3) Mpc(-3) in the K-S-band (2MASS Kron magnitudes). These parameters are derived assuming a cosmological model with Omega (0) = 0.3 and Lambda (0) = 0.7. With data sets of this size, systematic rather than random errors are the dominant source of uncertainty in the determination of the luminosity function. We carry out a careful investigation of possible systematic effects in our data. The surface brightness distribution of the sample shows no evidence that significant numbers of low surface brightness or compact galaxies are missed by the survey. We estimate the present-day distributions of b(J) - Ks and J- Ks colours as a function of the absolute magnitude and use models of the galaxy stellar populations, constrained by the observed optical and infrared colours, to infer the galaxy stellar mass function. Integrated over all galaxy masses, this yields a total mass fraction in stars (in units of the critical mass density) of Omega (stars)h = (1.6 +/-0.24) x 10(-3) for a Kennicutt initial mass function (IMF) and Omega (stars)h = (2.9 +/-0.43) x 10(-3) for a Salpeter IMF. These values are consistent with those inferred from observational estimates of the total star formation history of the Universe provided that dust extinction corrections are modest.

The 2dF Galaxy Redshift Survey: correlation functions, peculiar velocities and the matter density of the Universe

We present a detailed analysis of the two-point correlation function, xi(sigma, pi), from the 2dF Galaxy Redshift Survey (2dFGRS). The large size of the catalogue, which contains similar to220 000 redshifts, allows us to make high-precision measurements of various properties of the galaxy clustering pattern. The effective redshift at which our estimates are made is z(s) approximate to 0.15, and similarly the effective luminosity, L-s approximate to 1.4L*. We estimate the redshift-space correlation function, xi(s), from which we measure the redshift-space clustering length, s(o) = 6.82 +/- 0.28 h(-1) Mpc. We also estimate the projected correlation function, Xi(sigma), and the real-space correlation function, xi(r), which can be fit by a power law (r/r(o))(-gamma), with r(o) = 5.05 +/- 0.26 h(-1) Mpc, gamma(r) = 1.67 +/- 0.03. For r greater than or similar to 20 h(-1) Mpc, xi drops below a power law as, for instance, is expected in the popular Lambda cold dark matter model. The ratio of amplitudes of the real- and redshift-space correlation functions on scales of 8-30 h(-1) Mpc gives an estimate of the redshift-space distortion parameter beta. The quadrupole moment of xi(sigma, pi) on scales 30-40 h(-1) Mpc provides another estimate of beta. We also estimate the distribution function of pairwise peculiar velocities, f (nu), including rigorously the significant effect due to the infall velocities, and we find that the distribution is well fit by an exponential form. The accuracy of our xi(sigma, pi) measurement is sufficient to constrain a model, which simultaneously fits the shape and amplitude of xi(r) and the two redshift-space distortion effects parametrized by beta and velocity dispersion, a. We find beta = 0.49 +/- 0.09 and a = 506 +/- 52 km s(-1), although the best-fitting values are strongly correlated. We measure the variation of the peculiar velocity dispersion with projected separation, a(or), and find that the shape is consistent with models and simulations. This is the first time that beta and f (v) have been estimated from a self-consistent model of galaxy velocities. Using the constraints on bias from recent estimates, and taking account of redshift evolution, we conclude that beta(L = L*, z = 0) = 0.47 +/- 0.08, and that the present-day matter density of the Universe, Omega(m) approximate to 0.3, consistent with other 2dFGRS estimates and independent analyses.

The 2dF Galaxy Redshift Survey: the environmental dependence of galaxy star formation rates near clusters

We have measured the equivalent width of the Hα emission line for 11 006 galaxies brighter than M_b-=-−19 (Ω_Λ = 0.7, Ω_m = 0.3, H_0 = 70 km s^(−1) Mpc^(−1)) at 0.05 < z < 0.1 in the 2dF Galaxy Redshift Survey (2dFGRS), in the fields of 17 known galaxy clusters. The limited redshift range ensures that our results are insensitive to aperture bias, and to residuals from night sky emission lines. We use these measurements to trace μ*, the star formation rate normalized to L*, as a function of distance from the cluster centre, and local projected galaxy density. We find that the distribution of μ* steadily skews toward larger values with increasing distance from the cluster centre, converging to the field distribution at distances greater than ∼3 times the virial radius. A correlation between star formation rate and local projected density is also found, which is independent of cluster velocity dispersion and disappears at projected densities below ∼1 galaxy Mpc^(−2) (brighter than M_b = −19). This characteristic scale corresponds approximately to the mean density at the cluster virial radius. The same correlation holds for galaxies more than two virial radii from the cluster centre. We conclude that environmental influences on galaxy properties are not restricted to cluster cores, but are effective in all groups where the density exceeds this critical value. The present-day abundance of such systems, and the strong evolution of this abundance, makes it likely that hierarchical growth of structure plays a significant role in decreasing the global average star formation rate. Finally, the low star formation rates well beyond the virialized cluster rule out severe physical processes, such as ram pressure stripping of disc gas, as being completely responsible for the variations in galaxy properties with environment.

The 2dF Galaxy Redshift Survey: the power spectrum and the matter content of the Universe

The 2dF Galaxy Redshift Survey has now measured in excess of 160 000 galaxy redshifts. This paper presents the power spectrum of the galaxy distribution, calculated using a direct Fourier transform based technique. We argue that, within the k-space region 0.02 less than or similar to k less than or similar to 0.15 h Mpc(-1), the shape of this spectrum should be close to that of the linear density perturbations convolved with the window function of the survey. This window function and its convolving effect on the power spectrum estimate are analysed in detail. By convolving model spectra, we are able to fit the power-spectrum data and provide a measure of the matter content of the Universe. Our results show that models containing baryon oscillations are mildly preferred over featureless power spectra. Analysis of the data yields 68 per cent confidence limits on the total matter density times the Hubble parameter Omega (m) h = 0.20 +/- 0.03, and the baryon fraction Omega (b)/Omega (m) = 0.15 +/- 0.07, assuming scale-invariant primordial fluctuations.

Galaxy bimodality versus stellar mass and environment

We analyse a z < 0.1 galaxy sample from the Sloan Digital Sky Survey focusing on the variation in the galaxy colour bimodality with stellar mass M and projected neighbour density Σ, and on measurements of the galaxy stellar mass functions. The characteristic mass increases with environmental density from about 10 10. 6 to 10 10.9 M ⊙ (Kroupa initial mass function, H 0 = 70) for Σ in the range 0.1-10 Mpc -2 . The galaxy population naturally divides into a red and blue sequence with the locus of the sequences in colour-mass and colour-concentration indices not varying strongly with environment. The fraction of galaxies on the red sequence is determined in bins of 0.2 in log Σ and log M (12 x 13 bins). The red fraction f r generally increases continuously in both Σ and M such that there is a unified relation: f, = F(Σ, M). Two simple functions are proposed which provide good fits to the data. These data are compared with analogous quantities in semi-analytical models based on the Millennium N-body simulation: the Bower et al. and Croton et al. models that incorporate active galactic nucleus feedback. Both models predict a strong dependence of the red fraction on stellar mass and environment that is qualitatively similar to the observations. However, a quantitative comparison shows that the Bower et al. model is a significantly better match; this appears to be due to the different treatment of feedback in central galaxies.