Ivan K. Baldry

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.

The Broadband Optical Properties of Galaxies with Redshifts 0.02 < z < 0.22*

Using photometry and spectroscopy of 183,487 galaxies from the Sloan Digital Sky Survey, we present bivariate distributions of pairs of seven galaxy properties: four optical colors, surface brightness, radial profile shape as measured by the Sersic index, and absolute magnitude. In addition, we present the dependence of local galaxy density (smoothed on 8 h � 1 Mpc scales) on all of these properties. Several classic, well-known relations among galaxy properties are evident at extremely high signal-to-noise ratio: the color- color relations of galaxies, the color-magnitude relations, the magnitude-surface brightness relation, and the dependence of density on color and absolute magnitude. We show that most of the i-band luminosity density in the universe is in the absolute magnitude and surface brightness ranges used: � 23:5 < M0:1i < � 17:0 mag and 17 < l0:1i < 24 mag in 1 arcsec 2 (the notation z b represents the b band shifted blueward by a factor ð1 þ zÞ). Some of the relationships between parameters, in particular the color-magnitude relations, show stronger correlations for exponential galaxies and concentrated galaxies taken separately than for all galaxies taken together. We provide a simple set of fits of the dependence of galaxy properties on luminosity for these two sets of galaxies and other quantitative details of our results. Subject headings: galaxies: fundamental parameters — galaxies: photometry — galaxies: statistics On-line material: ASCII parameter files, color figure, FITS files 1. MOTIVATION There are strong correlations among the measurable physical properties of galaxies. The classification of galaxies along the visual morphological sequence described by Hubble (1936) correlates well with the dominance of their central bulge, their surface brightnesses, and their colors. These properties also correlate with other properties, such as metallicity, emission-line strength, luminosity in visual bands, neutral gas content, and the winding angle of the spiral structure (for a review, see Roberts & Haynes 1994). The surface brightnesses of giant galaxies classified morpho- logically as elliptical are known to be strongly correlated with their sizes (Kormendy 1977; Kormendy & Djorgovski 1989). Galaxy colors (at least of morphologically elliptical galaxies) are known to be strongly correlated with galaxy luminosity (Baum 1959; Faber 1973; Visvanathan & Sandage 1977; Terlevich et al. 2001). The gravitational mass of a galaxy is closely related to the luminosity and other galaxy properties. These galaxy relations manifest them-

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.

Galaxy and Mass Assembly (GAMA): survey diagnostics and core data release

The Galaxy and Mass Assembly (GAMA) survey has been operating since 2008 February on the 3.9-m Anglo-Australian Telescope using the AAOmega fibre-fed spectrograph facility to acquire spectra with a resolution of R ≈ 1300 for 120 862 Sloan Digital Sky Survey selected galaxies. The target catalogue constitutes three contiguous equatorial regions centred at 9h (G09), 12h (G12) and 14.5h (G15) each of 12 × 4 deg2 to limiting fluxes of rpet < 19.4, rpet < 19.8 and rpet <19.4 mag, respectively (and additional limits at other wavelengths). Spectra and reliable redshifts have been acquired for over 98 per cent of the galaxies within these limits. Here we present the survey footprint, progression, data reduction, redshifting, re-redshifting, an assessment of data quality after 3 yr, additional image analysis products (including ugrizYJHK photometry, S´ersic profiles and photometric redshifts), observing mask and construction of our core survey catalogue (GamaCore). From this we create three science-ready catalogues: GamaCoreDR1 for public release, which includes data acquired during year 1 of operations within specified magnitude limits (2008 February to April); GamaCoreMainSurvey containing all data above our survey limits for use by the GAMA Team and collaborators; and GamaCore-AtlasSV containing year 1, 2 and 3 data matched to Herschel-ATLAS science demonstration data. These catalogues along with the associated spectra, stamps and profiles can be accessed via the GAMA website: http://www.gama-survey.org/

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.

Galaxy ecology: groups and low-density environments in the SDSS and 2dFGRS

We analyse the observed correlation between galaxy environment and Halpha emission-line strength, using volume-limited samples and group catalogues of 24 968 galaxies at 0.05 < z < 0.095, drawn from the 2dF Galaxy Redshift Survey (M-bJ < -19.5) and the Sloan Digital Sky Survey (M-r < -20.6). We characterize the environment by: (1) Sigma(5), the surface number density of galaxies determined by the projected distance to the fifth nearest neighbour; and (2) rho(1.1) and rho(5.5), three-dimensional density estimates obtained by convolving the galaxy distribution with Gaussian kernels of dispersion 1.1 and 5.5 Mpc, respectively. We find that star-forming and quiescent galaxies form two distinct populations, as characterized by their H equivalent width, W-0(Halpha). The relative numbers of star-forming and quiescent galaxies vary strongly and continuously with local density. However, the distribution of W-0(Halpha) amongst the star-forming population is independent of environment. The fraction of star-forming galaxies shows strong sensitivity to the density on large scales, rho(5.5), which is likely independent of the trend with local density, rho(1.1). We use two differently selected group catalogues to demonstrate that the correlation with galaxy density is approximately independent of group velocity dispersion, for sigma = 200-1000 km s(-1). Even in the lowest-density environments, no more than similar to70 per cent of galaxies show significant Halpha emission. Based on these results, we conclude that the present-day correlation between star formation rate and environment is a result of short-time-scale mechanisms that take place preferentially at high redshift, such as starbursts induced by galaxy-galaxy interactions.

The Bimodal Galaxy Color Distribution: Dependence on Luminosity and Environment

We analyze the u - r color distribution of 24,346 galaxies with Mr ≤ -18 and z < 0.08, drawn from the Sloan Digital Sky Survey first data release, as a function of luminosity and environment. The color distribution is well fitted with two Gaussian distributions, which we use to divide the sample into a blue and red population. At fixed luminosity, the mean color of the blue (red) distribution is nearly independent of environment, with a weakly significant (~3 σ) detection of a trend for colors to become redder by 0.1-0.14 (0.03-0.06) mag with a factor of ~100 increase in local density, as characterized by the surface density of galaxies within a ±1000 km s-1 redshift slice. In contrast, at fixed luminosity the fraction of galaxies in the red distribution is a strong function of local density, increasing from ~10%-30% of the population in the lowest density environments to ~70% at the highest densities. The strength of this trend is similar for both the brightest (-23 < Mr < -22) and faintest (-19 < Mr < -18) galaxies in our sample. The fraction of red galaxies within the virialized regions of clusters shows no significant dependence on velocity dispersion. Even at the lowest densities explored, a substantial population of red galaxies exists, which might be fossil groups. We propose that most star-forming galaxies today evolve at a rate that is determined primarily by their intrinsic properties and independent of their environment. Any environmentally triggered transformations from blue to red colors must occur either on a short timescale or preferentially at high redshift to preserve the simple Gaussian nature of the color distribution. The mechanism must be effective for both bright and faint galaxies.

The 2dF Galaxy Redshift Survey: The bJ-band galaxy luminosity function and survey selection function

We use more than 110 500 galaxies from the 2dF Galaxy Redshift Survey (2dFGRS) to estimate the bJ-band galaxy luminosity function at redshift z = 0, taking account of evolution, the distri- bution of magnitude measurement errors and small corrections for incompleteness in the galaxy catalogue. Throughout the interval −16.5 > MbJ − 5 log10 h > −22, the luminosity function is accurately described by a Schechter function with MJ − 5 log10 h =− 19.66 ± 0.07, α = −1.21 ± 0.03 and � � = (1.61 ± 0.08) × 10 −2 h 3 Mpc −3 , giving an integrated luminosity den- sity of ρL = (1.82 ± 0.17) × 10 8 h LMpc −3 (assuming an � 0 = 0.3, 0 = 0.7 cosmology). The quoted errors have contributions from the accuracy of the photometric zero-point, from large-scale structure in the galaxy distribution and, importantly, from the uncertainty in the ap- propriate evolutionary corrections. Our luminosity function is in excellent agreement with, but has much smaller statistical errors than, an estimate from the Sloan Digital Sky Survey (SDSS) data when the SDSS data are accurately translated to the bJ band and the luminosity functions are normalized in the same way. We use the luminosity function, along with maps describing the redshift completeness of the current 2dFGRS catalogue, and its weak dependence on ap- parent magnitude, to define a complete description of the 2dFGRS selection function. Details and tests of the calibration of the 2dFGRS photometric parent catalogue are also presented.