arXiv subjects

Matthew Colless

Publications and source records attributed to Matthew Colless.

At least 109 records · Page 6Linked to original sources

arXiv2013

The WiggleZ Dark Energy Survey: constraining galaxy bias and cosmic growth with 3-point correlation functions

Higher-order statistics are a useful and complementary tool for measuring the clustering of galaxies, containing information on the non-gaussian evolution and morphology of large-scale structure in the Universe. In this work we present measurements of the three-point correlation function (3PCF) for 187,000 galaxies in the WiggleZ spectroscopic galaxy survey. We explore the WiggleZ 3PCF scale and shape dependence at three different epochs z=0.35, 0.55 and 0.68, the highest redshifts where these measurements have been made to date. Using N-body simulations to predict the clustering of dark matter, we constrain the linear and non-linear bias parameters of WiggleZ galaxies with respect to dark matter, and marginalise over them to obtain constraints on sigma_8(z), the variance of perturbations on a scale of 8 Mpc/h and its evolution with redshift. These measurements of sigma_8(z), which have 10-20% accuracies, are consistent with the predictions of the LCDM concordance cosmology and test this model in a new way.

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arXiv2013

The WiggleZ Dark Energy Survey: measuring the cosmic growth rate with the two-point galaxy correlation function

The growth history of large-scale structure in the Universe is a powerful probe of the cosmological model, including the nature of dark energy. We study the growth rate of cosmic structure to redshift $z = 0.9$ using more than $162{,}000$ galaxy redshifts from the WiggleZ Dark Energy Survey. We divide the data into four redshift slices with effective redshifts $z = [0.2,0.4,0.6,0.76]$ and in each of the samples measure and model the 2-point galaxy correlation function in parallel and transverse directions to the line-of-sight. After simultaneously fitting for the galaxy bias factor we recover values for the cosmic growth rate which are consistent with our assumed $Λ$CDM input cosmological model, with an accuracy of around 20% in each redshift slice. We investigate the sensitivity of our results to the details of the assumed model and the range of physical scales fitted, making close comparison with a set of N-body simulations for calibration. Our measurements are consistent with an independent power-spectrum analysis of a similar dataset, demonstrating that the results are not driven by systematic errors. We determine the pairwise velocity dispersion of the sample in a non-parametric manner, showing that it systematically increases with decreasing redshift, and investigate the Alcock-Paczynski effects of changing the assumed fiducial model on the results. Our techniques should prove useful for current and future galaxy surveys mapping the growth rate of structure using the 2-dimensional correlation function.

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arXiv2013

The Stellar Masses of ~40,000 UV Selected Galaxies from the WiggleZ Survey at 0.3<z<1.0: Analogues of Lyman Break Galaxies?

We characterise the stellar masses and star formation rates in a sample of almost 40000 spectroscopically confirmed UV luminous galaxies at 0.3 5sigma in the UKIDSS-LAS at all redshifts. An even more luminous subset of 15% are also detected in the WISE 3.4 and 4.6um bands. We compute stellar masses for this very large sample of extremely blue galaxies and quantify the sensitivity of the stellar mass estimates to various assumptions made during the SED fitting. The median stellar masses are log10(M*/M0)=9.6\pm0.7, 10.2\pm0.5 and 10.4\pm0.4 for the IR-undetected, UKIDSS detected and UKIDSS+WISE detected galaxies respectively. We demonstrate that the inclusion of NIR photometry can lead to tighter constraints on the stellar masses. The mass estimates are found to be most sensitive to the inclusion of secondary bursts of star formation as well as changes in the stellar population synthesis models, both of which can lead to median discrepancies of the order of 0.3dex in the stellar masses. We find that the best-fit M/LK is significantly lower (by ~0.4 dex) than that predicted by simple optical colour based estimators, in particular for the bluer galaxies with younger best-fit ages. The WiggleZ galaxies have star formation rates of 3-10 M0/yr and mostly lie at the upper end of the main sequence of star-forming galaxies at these redshifts. Their rest-frame UV luminosities and stellar masses are comparable to both local compact UV-luminous galaxies as well as Lyman break galaxies at z~2-3.(abridged)

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arXiv2012

The 6dF Galaxy Survey: Dependence of halo occupation on stellar mass

In this paper we study the stellar-mass dependence of galaxy clustering in the 6dF Galaxy Survey. The near-infrared selection of 6dFGS allows more reliable stellar mass estimates compared to optical bands used in other galaxy surveys. Using the Halo Occupation Distribution (HOD) model, we investigate the trend of dark matter halo mass and satellite fraction with stellar mass by measuring the projected correlation function, $w_p(r_p)$. We find that the typical halo mass ($M_1$) as well as the satellite power law index ($α$) increase with stellar mass. This indicates, (1) that galaxies with higher stellar mass sit in more massive dark matter halos and (2) that these more massive dark matter halos accumulate satellites faster with growing mass compared to halos occupied by low stellar mass galaxies. Furthermore we find a relation between $M_1$ and the minimum dark matter halo mass ($M_{\rm min}$) of $M_1 \approx 22\,M_{\rm min}$, in agreement with similar findings for SDSS galaxies. The satellite fraction of 6dFGS galaxies declines with increasing stellar mass from 21% at $M_{\rm stellar} = 2.6\times10^{10}h^{-2}\,M_{\odot}$ to 12% at $M_{\rm stellar} = 5.4\times10^{10}h^{-2}\,M_{\odot}$ indicating that high stellar mass galaxies are more likely to be central galaxies. We compare our results to two different semi-analytic models derived from the Millennium Simulation, finding some disagreement. Our results can be used for placing new constraints on semi-analytic models in the future, particularly the behaviour of luminous red satellites. Finally we compare our results to studies of halo occupation using galaxy-galaxy weak lensing. We find good overall agreement, representing a valuable crosscheck for these two different tools of studying the matter distribution in the Universe.

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arXiv2012

Measuring H0 from the 6dF Galaxy Survey and future low-redshift surveys

Baryon acoustic oscillations (BAO) at low redshift provide a precise and largely model-independent way to measure the Hubble constant, H0. The 6dF Galaxy Survey measurement of the BAO scale gives a value of H0 = 67 +/- 3.2 km/s/Mpc, achieving a 1-sigma precision of 5%. With improved analysis techniques, the planned WALLABY (HI) and TAIPAN (optical) redshift surveys are predicted to measure H0 to 1-3% precision.

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arXiv2012

First Science with SAMI: A Serendipitously Discovered Galactic Wind in ESO 185-G031

We present the first scientific results from the Sydney-AAO Multi-Object IFS (SAMI) at the Anglo-Australian Telescope. This unique instrument deploys 13 fused fibre bundles (hexabundles) across a one-degree field of view allowing simultaneous spatially-resolved spectroscopy of 13 galaxies. During the first SAMI commissioning run, targeting a single galaxy field, one object (ESO 185-G031) was found to have extended minor axis emission with ionisation and kinematic properties consistent with a large-scale galactic wind. The importance of this result is two-fold: (i) fibre bundle spectrographs are able to identify low-surface brightness emission arising from extranuclear activity; (ii) such activity may be more common than presently assumed because conventional multi-object spectrographs use single-aperture fibres and spectra from these are nearly always dominated by nuclear emission. These early results demonstrate the extraordinary potential of multi-object hexabundle spectroscopy in future galaxy surveys.

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arXiv2012

The WiggleZ Dark Energy Survey: Final data release and cosmological results

This paper presents cosmological results from the final data release of the WiggleZ Dark Energy Survey. We perform full analyses of different cosmological models using the WiggleZ power spectra measured at z=0.22, 0.41, 0.60, and 0.78, combined with other cosmological datasets. The limiting factor in this analysis is the theoretical modelling of the galaxy power spectrum, including non-linearities, galaxy bias, and redshift-space distortions. In this paper we assess several different methods for modelling the theoretical power spectrum, testing them against the Gigaparsec WiggleZ simulations (GiggleZ). We fit for a base set of 6 cosmological parameters, {Omega_b h^2, Omega_CDM h^2, H_0, tau, A_s, n_s}, and 5 supplementary parameters {n_run, r, w, Omega_k, sum m_nu}. In combination with the Cosmic Microwave Background (CMB), our results are consistent with the LambdaCDM concordance cosmology, with a measurement of the matter density of Omega_m =0.29 +/- 0.016 and amplitude of fluctuations sigma_8 = 0.825 +/- 0.017. Using WiggleZ data with CMB and other distance and matter power spectra data, we find no evidence for any of the extension parameters being inconsistent with their LambdaCDM model values. The power spectra data and theoretical modelling tools are available for use as a module for CosmoMC, which we here make publicly available at http://smp.uq.edu.au/wigglez-data . We also release the data and random catalogues used to construct the baryon acoustic oscillation correlation function.

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arXiv2012

The WiggleZ Dark Energy Survey: the transition to large-scale cosmic homogeneity

We have made the largest-volume measurement to date of the transition to large-scale homogeneity in the distribution of galaxies. We use the WiggleZ survey, a spectroscopic survey of over 200,000 blue galaxies in a cosmic volume of ~1 (Gpc/h)^3. A new method of defining the 'homogeneity scale' is presented, which is more robust than methods previously used in the literature, and which can be easily compared between different surveys. Due to the large cosmic depth of WiggleZ (up to z=1) we are able to make the first measurement of the transition to homogeneity over a range of cosmic epochs. The mean number of galaxies N(<r) in spheres of comoving radius r is proportional to r^3 within 1%, or equivalently the fractal dimension of the sample is within 1% of D_2=3, at radii larger than 71 \pm 8 Mpc/h at z~0.2, 70 \pm 5 Mpc/h at z~0.4, 81 \pm 5 Mpc/h at z~0.6, and 75 \pm 4 Mpc/h at z~0.8. We demonstrate the robustness of our results against selection function effects, using a LCDM N-body simulation and a suite of inhomogeneous fractal distributions. The results are in excellent agreement with both the LCDM N-body simulation and an analytical LCDM prediction. We can exclude a fractal distribution with fractal dimension below D_2=2.97 on scales from ~80 Mpc/h up to the largest scales probed by our measurement, ~300 Mpc/h, at 99.99% confidence.

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arXiv2012

'MOHAWK' : a 4000-fiber positioner for DESpec

We present a concept for a 4000-fibre positioner for DESpec, based on the Echidna 'tilting spine' technology. The DESpec focal plane is 450mm across and curved, and the required pitch is ~6.75mm. The size, number of fibers and curvature are all comparable with various concept studies for similar instruments already undertaken at the AAO, but present new challenges in combination. A simple, low-cost, and highly modular design is presented, consisting of identical modules populated by identical spines. No show-stopping issues in accommodating either the curvature or the smaller pitch have been identified, and the actuators consist largely of off-the-shelf components. The actuators have been prototyped at AAO, and allow reconfiguration times of ~15s to reach position errors 7 microns or less. Straightforward designs for metrology, acquisition, and guiding are also proposed. The throughput losses of the entire positioner system are estimated to be ~15%, of which 6.3% is attributable to the tilting-spine technology.

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arXiv2012

The WiggleZ Dark Energy Survey: Joint measurements of the expansion and growth history at z < 1

We perform a joint determination of the distance-redshift relation and cosmic expansion rate at redshifts z = 0.44, 0.6 and 0.73 by combining measurements of the baryon acoustic peak and Alcock-Paczynski distortion from galaxy clustering in the WiggleZ Dark Energy Survey, using a large ensemble of mock catalogues to calculate the covariance between the measurements. We find that D_A(z) = (1205 +/- 114, 1380 +/- 95, 1534 +/- 107) Mpc and H(z) = (82.6 +/- 7.8, 87.9 +/- 6.1, 97.3 +/- 7.0) km/s/Mpc at these three redshifts. Further combining our results with other baryon acoustic oscillation and distant supernovae datasets, we use a Monte Carlo Markov Chain technique to determine the evolution of the Hubble parameter H(z) as a stepwise function in 9 redshift bins of width dz = 0.1, also marginalizing over the spatial curvature. Our measurements of H(z), which have precision better than 7% in most redshift bins, are consistent with the expansion history predicted by a cosmological-constant dark-energy model, in which the expansion rate accelerates at redshift z < 0.7.

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arXiv2012

The 6dF Galaxy Survey: The Near-Infrared Fundamental Plane of Early-Type Galaxies

We determine the near-infrared Fundamental Plane (FP) for $\sim10^4$ early-type galaxies in the 6dF Galaxy Survey (6dFGS). We fit the distribution of central velocity dispersion, near-infrared surface brightness and half-light radius with a three-dimensional Gaussian model using a maximum likelihood method. For the 6dFGS $J$ band sample we find a FP with $R_{e}$\,$\propto$\,$σ_0^{1.52\pm0.03}I_{e}^{-0.89\pm0.01}$, similar to previous near-IR determinations and consistent with the $H$ and $K$ band Fundamental Planes once allowance is made for differences in mean colour. The overall scatter in $R_e$ about the FP is $σ_r$,=,29%, and is the quadrature sum of an 18% scatter due to observational errors and a 23% intrinsic scatter. Because of the distribution of galaxies in FP space, $σ_r$ is not the distance error, which we find to be $σ_d$,=,23%. Using group richness and local density as measures of environment, and morphologies based on visual classifications, we find that the FP slopes do not vary with environment or morphology. However, for fixed velocity dispersion and surface brightness, field galaxies are on average 5% larger than galaxies in higher-density environments, and the bulges of early-type spirals are on average 10% larger than ellipticals and lenticulars. The residuals about the FP show significant trends with environment, morphology and stellar population. The strongest trend is with age, and we speculate that age is the most important systematic source of offsets from the FP, and may drive the other trends through its correlations with environment, morphology and metallicity.

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arXiv2012

The 6dF Galaxy Survey: z \approx 0 measurement of the growth rate and sigma_8

We present a detailed analysis of redshift-space distortions in the two-point correlation function of the 6dF Galaxy Survey (6dFGS). The K-band selected sub-sample which we employ in this study contains 81971 galaxies distributed over 17000deg^2 with an effective redshift z = 0.067. By modelling the 2D galaxy correlation function, xi(r_p,pi), we measure the parameter combination f(z)sigma_8(z) = 0.423 +/- 0.055. Alternatively, by assuming standard gravity we can break the degeneracy between sigma_8 and the galaxy bias parameter, b. Combining our data with the Hubble constant prior from Riess et al (2011), we measure sigma_8 = 0.76 +/- 0.11 and Omega_m = 0.250 +/- 0.022, consistent with constraints from other galaxy surveys and the Cosmic Microwave Background data from WMAP7. Combining our measurement of fsigma_8 with WMAP7 allows us to test the relationship between matter and gravity on cosmic scales by constraining the growth index of density fluctuations, gamma. Using only 6dFGS and WMAP7 data we find gamma = 0.547 +/- 0.088, consistent with the prediction of General Relativity. We note that because of the low effective redshift of 6dFGS our measurement of the growth rate is independent of the fiducial cosmological model (Alcock-Paczynski effect). We also show that our conclusions are not sensitive to the model adopted for non-linear redshift-space distortions. Using a Fisher matrix analysis we report predictions for constraints on fsigma_8 for the WALLABY survey and the proposed TAIPAN survey. The WALLABY survey will be able to measure fsigma_8 with a precision of 4-10%, depending on the modelling of non-linear structure formation. This is comparable to the predicted precision for the best redshift bins of the Baryon Oscillation Spectroscopic Survey (BOSS), demonstrating that low-redshift surveys have a significant role to play in future tests of dark energy and modified gravity.

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arXiv2012

The WiggleZ Dark Energy Survey: Cosmological neutrino mass constraint from blue high-redshift galaxies

The absolute neutrino mass scale is currently unknown, but can be constrained from cosmology. The WiggleZ high redshift star-forming blue galaxy sample is less sensitive to systematics from non-linear structure formation, redshift-space distortions and galaxy bias than previous surveys. We obtain a upper limit on the sum of neutrino masses of 0.60eV (95% confidence) for WiggleZ+Wilkinson Microwave Anisotropy Probe. Combining with priors on the Hubble Parameter and the baryon acoustic oscillation scale gives an upper limit of 0.29eV, which is the strongest neutrino mass constraint derived from spectroscopic galaxy redshift surveys.

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arXiv2012

The WiggleZ Dark Energy Survey: Galaxy Evolution at 0.25 < z < 0.75 Using The Second Red-Sequence Cluster Survey (RCS-2)

We study the evolution of galaxy populations around the spectroscopic WiggleZ sample of starforming galaxies at 0.25 < z < 0.75 using the photometric catalog from the Second Red-Sequence Cluster Survey (RCS2). We probe the optical photometric properties of the net excess neighbor galaxies. The key concept is that the marker galaxies and their neighbors are located at the same redshift, providing a sample of galaxies representing a complete census of galaxies in the neighborhood of star-forming galaxies. The results are compared with those using the RCS WiggleZ Spare-Fibre (RCS-WSF) sample as markers, representing galaxies in cluster environments at 0.25 < z < 0.45. By analyzing the stacked color-color properties of the WiggleZ neighbor galaxies, we find that their optical colors are not a strong function of indicators of star-forming activities such as EW([OII]) or GALEX NUV luminoisty of the markers. The galaxies around the WiggleZ markers exhibit a bimodal distribution on the color-magnitude diagram, with most of them located in the blue cloud. The optical galaxy luminosity functions (GLF) of the blue neighbor galaxies have a faint-end slope αof \sim -1.3, similar to that for galaxies in cluster environments drawn from the RCS-WSF sample. The faint-end slope of the GLF for the red neighbors, however, is \sim -0.4, significantly shallower than the \sim -0.7 found for those in cluster environments. This suggests that the build-up of the faint-end of the red sequence in cluster environments is in a significantly more advanced stage than that in the star-forming and lower galaxy density WiggleZ neighborhoods. We find that the red galaxy fraction (fred) around the star-forming WiggleZ galaxies has similar values from z \sim 0.3 to z \sim 0.6 with fred \sim 0.28, but drops to fred \sim 0.20 at z > \sim0.7. This change of fred with redshift suggests that (and more...)

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arXiv2011

The Sydney-AAO Multi-object Integral field spectrograph (SAMI)

We demonstrate a novel technology that combines the power of the multi-object spectrograph with the spatial multiplex advantage of an integral field spectrograph (IFS). The Sydney-AAO Multi-object IFS (SAMI) is a prototype wide-field system at the Anglo-Australian Telescope (AAT) that allows 13 imaging fibre bundles ("hexabundles") to be deployed over a 1-degree diameter field of view. Each hexabundle comprises 61 lightly-fused multimode fibres with reduced cladding and yields a 75 percent filling factor. Each fibre core diameter subtends 1.6 arcseconds on the sky and each hexabundle has a field of view of 15 arcseconds diameter. The fibres are fed to the flexible AAOmega double-beam spectrograph, which can be used at a range of spectral resolutions (R=lambda/delta(lambda) ~ 1700-13000) over the optical spectrum (3700-9500A). We present the first spectroscopic results obtained with SAMI for a sample of galaxies at z~0.05. We discuss the prospects of implementing hexabundles at a much higher multiplex over wider fields of view in order to carry out spatially--resolved spectroscopic surveys of 10^4 to 10^5 galaxies.

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arXiv2011

Accretion of the Magellanic system onto the Galaxy

Our Galaxy is surrounded by a large family of dwarf galaxies of which the most massive are the Large and Small Magellanic Clouds (LMC and SMC). Recent evidence suggests that systems with the mass of the Local Group accrete galaxies in smaller groups rather than individually. If so, at least some of the Galaxy's dwarfs may have fallen in with the LMC and SMC, and were formed as part of the Magellanic system in the nearby universe. We use the latest measurements of the proper motions of the LMC and SMC and a multicomponent model of the Galactic potential to explore the evolution of these galaxy configurations under the assumption that the Magellanic system may once have contained a number of bound dwarf galaxies. We compare our results to the available kinematic data for the local dwarf galaxies, and examine whether this model can account for recently discovered stellar streams and the planar distribution of Milky Way satellites. We find that in situations where the LMC and SMC are bound to the Milky Way, the kinematics of Draco, Sculptor, Sextans, Ursa Minor and the Sagittarius Stream are consistent with having fallen in along with the Magellanic system. These dwarfs, if so associated, will likely have been close to the tidal radius of the LMC originally and are unlikely to have affected each other throughout the orbit. However there are clear cases, such as Carina and Leo I, that cannot be explained this way

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arXiv2011

The 6dF Galaxy Survey: Stellar Population Trends Across and Through the Fundamental Plane

We present results from an analysis of stellar population parameters for 7132 galaxies in the 6dFGS Fundamental Plane (FP) sample. We bin the galaxies along the axes, $v_1$, $v_2$, and $v_3$, of the tri-variate Gaussian to which we have fit the galaxy distribution in effective radius, surface brightness, and central velocity dispersion (FP space), and compute median values of stellar age, [Fe/H], [Z/H], and [$α$/Fe]. We determine the directions of the vectors in FP space along which each of the binned stellar population parameters vary most strongly. In contrast to previous work, we find stellar population trends not just with velocity dispersion and FP residual, but with radius and surface brightness as well. The most remarkable finding is that the stellar population parameters vary through the plane ($v_1$ direction) and across the plane ($v_3$ direction), but show no variation at all along the plane ($v_2$ direction). The $v_2$ direction in FP space roughly corresponds to `luminosity density'. We interpret a galaxy's position along this vector as being closely tied to its merger history, such that early-type galaxies with lower luminosity density are more likely to have undergone major mergers. This conclusion is reinforced by an examination of the simulations of Kobayashi (2005), which show clear trends of merger history with $v_2$.

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arXiv2011

The WiggleZ Dark Energy Survey: mapping the distance-redshift relation with baryon acoustic oscillations

We present measurements of the baryon acoustic peak at redshifts z = 0.44, 0.6 and 0.73 in the galaxy correlation function of the final dataset of the WiggleZ Dark Energy Survey. We combine our correlation function with lower-redshift measurements from the 6-degree Field Galaxy Survey and Sloan Digital Sky Survey, producing a stacked survey correlation function in which the statistical significance of the detection of the baryon acoustic peak is 4.9-sigma relative to a zero-baryon model with no peak. We fit cosmological models to this combined baryon acoustic oscillation (BAO) dataset comprising six distance-redshift data points, and compare the results to similar fits to the latest compilation of supernovae (SNe) and Cosmic Microwave Background (CMB) data. The BAO and SNe datasets produce consistent measurements of the equation-of-state w of dark energy, when separately combined with the CMB, providing a powerful check for systematic errors in either of these distance probes. Combining all datasets we determine w = -1.03 +/- 0.08 for a flat Universe, consistent with a cosmological constant model. Assuming dark energy is a cosmological constant and varying the spatial curvature, we find Omega_k = -0.004 +/- 0.006.

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