arXiv subjects

Matthew Colless

Publications and source records attributed to Matthew Colless.

At least 181 records · Page 10Linked to original sources

arXiv2003

Cosmological results from the 2dF Galaxy Redshift Survey

The 2dF Galaxy Redshift Survey (2dFGRS) has produced a three-dimensional map of the distribution of 221,000 galaxies covering 5% of the sky and reaching out to a redshift z=0.3. This is first map of the large-scale structure in the local Universe to probe a statistically representative volume, and provides direct evidence that the large-scale structure of the Universe grew through gravitational instability. Measurements of the correlation function and power spectrum of the galaxy distribution have provided precise measurements of the mean mass density of the Universe and the relative contributions of cold dark matter, baryons, and neutrinos. The survey has produced the first measurements of the galaxy bias parameter and its variation with galaxy luminosity and type. Joint analysis of the 2dFGRS and cosmic microwave background power spectra gives independent new estimates for the Hubble constant and the vacuum energy density, and constrains the equation of state of the vacuum.

astro-ph↗

arXiv2003

A Photometric and Spectroscopic Study of Dwarf and Giant Galaxies in the Coma Cluster - IV. The Luminosity Function

A large spectroscopic survey is constructed of galaxies in the Coma cluster. The survey covers a wide area (1 deg$^2$) to deep magnitudes (R ~ 19.5), covering both the core (high density) and outskirts (intermediate to low density) of the cluster. The spectroscopic sample consists of a total of 1191 galaxies, of which, 760 galaxies are confirmed members of the Coma cluster. A statistical technique is developed to correct the spectroscopic sample for incompletness. The corrected sample is then used to construct R-band luminosity function (LF) spanning a range of 7 magnitudes (-23 < M_R < -16) both at the core and outskirts of the cluster. Dependence of the LF on local environment in Coma is explored. The LFs are found to be the same, within the errors, between the inner and outer regions and close to those from recent measurements for field galaxies. The total B-band LF for the Coma cluster, fitted to a Schecter form is also measured and shows a dip at M(B) = -18 mag., in agreement with previous studies. The implications of this feature are discussed. The LF is studied in B-R color intervals and shows a steep faint-end slope for red (B-R > 1.35) galaxies, both at the core and outskirts of the cluster. This population of low luminosity red galaxies has a higher surface density than the blue (B-R < 1.35) star-forming population, dominating the faint-end of the Coma cluster LF. It is found that relative number of high surface brightness galaxies is larger at the cluster core, implying destruction of low surface brightness galaxies in dense core environment.

astro-ph↗

arXiv2002

The puzzlingly small CaII triplet absorption in elliptical galaxies

We measure the central values (within Re/8) of the CaII triplet line indices CaT* and CaT and the Paschen index PaT at 8600 AA for a 93%-complete sample of 75 nearby early-type galaxies with BT<12 and Vgal<2490 km/s. We find that the values of CaT* are constant to within 5% over the range of central velocity dispersions 100<sigma<340 km/s, while the PaT (and CaT) values are mildly anti-correlated with sigma. Using simple and composite stellar population models, we show that: a) The measured CaT* and CaT are lower than expected from simple stellar population models (SSPs) with Salpeter initial mass functions (IMFs) and with metallicities and ages derived from optical Lick (Fe, Mg and Hbeta) indices. Uncertainties in the calibration, the fitting functions and the SSP modeling taken separately cannot explain the discrepancy. On the average, the observed PaT values are within the range allowed by the models and the large uncertainties in the fitting functions. b) The steepening of the IMF at low masses required to lower the CaT* and CaT indices to the observed values is incompatible with the measured FeH index at 9916 AA and the dynamical mass-to-light ratios of ellipticals. c) Composite stellar populations with a low-metallicity component reduce the disagreement, but rather artificial metallicity distributions are needed. Another explanation may be that calcium is indeed underabundant in ellipticals.

astro-ph↗

arXiv2002

Parameter constraints for flat cosmologies from CMB and 2dFGRS power spectra

We constrain flat cosmological models with a joint likelihood analysis of a new compilation of data from the cosmic microwave background (CMB) and from the 2dF Galaxy Redshift Survey (2dFGRS). Fitting the CMB alone yields a known degeneracy between the Hubble constant h and the matter density Omega_m, which arises mainly from preserving the location of the peaks in the angular power spectrum. This `horizon-angle degeneracy' is considered in some detail and shown to follow a simple relation Omega_m h^{3.4} = constant. Adding the 2dFGRS power spectrum constrains Omega_m h and breaks the degeneracy. If tensor anisotropies are assumed to be negligible, we obtain values for the Hubble constant h=0.665 +/- 0.047, the matter density Omega_m=0.313 +/- 0.055, and the physical CDM and baryon densities Omega_c h^2 = 0.115 +/- 0.009, Omega_b h^2 = 0.022 +/- 0.002 (standard rms errors). Including a possible tensor component causes very little change to these figures; we set a upper limit to the tensor-to-scalar ratio of r<0.7 at 95% confidence. We then show how these data can be used to constrain the equation of state of the vacuum, and find w<-0.52 at 95% confidence. The preferred cosmological model is thus very well specified, and we discuss the precision with which future CMB data can be predicted, given the model assumptions. The 2dFGRS power-spectrum data and covariance matrix, and the CMB data compilation used here, are available from http://www.roe.ac.uk/~wjp/

astro-ph↗

arXiv2002

Early-type galaxies in low-density environments

We describe the construction and study of an objectively-defined sample of early-type galaxies in low-density environments. The sample galaxies are selected from a recently-completed redshift survey using uniform and readily-quantified isolation criteria, and are drawn from a sky area of ~700 deg^2, to a depth of 7000 k/ms and an apparent magnitude limit of b_J < 16.1. Their early-type (E/S0) morphologies are confirmed by subsequent CCD imaging. Five out of the nine sample galaxies show signs of morphological peculiarity such as tidal debris or blue circumnuclear rings. We confirm that E/S0 galaxies are rare in low-density regions, accounting for only ~8% of the total galaxy population in such environments. We present spectroscopic observations of nine galaxies in the sample, which are used, in conjunction with updated stellar population models, to investigate star-formation histories. Environmental effects on early-type galaxy evolution are investigated by comparison with a sample of Fornax cluster E/S0s. Results from both samples are compared with predictions from semi-analytic galaxy formation models. The Mg-sig relation of E/S0s in low-density regions is shown to be indistinguishable from that of the Fornax sample. Luminosity-weighted stellar ages and metallicities are determined by considering various combinations of line-indices. At a given luminosity, the E/S0 galaxies in low-density regions are younger than the E/S0s in clusters (by ~2-3 Gyr), and also more metal-rich (by ~0.2 dex). We infer that an anti-correlation of age and metallicity effects is responsible for maintaining the zero-point of the Mg-sig relation. The youngest galaxies in our sample show clear morphological signs of interaction. (Abridged)

astro-ph↗

arXiv2002

The 2dF Galaxy Redshift Survey: The amplitudes of fluctuations in the 2dFGRS and the CMB, and implications for galaxy biasing

We compare the amplitudes of fluctuations probed by the 2dF Galaxy Redshift Survey and by the latest measurements of the Cosmic Microwave Background anisotropies. By combining the 2dFGRS and CMB data we find the linear-theory rms mass fluctuations in 8 Mpc/h spheres to be sigma_8 = 0.73 +-0.05 (after marginalization over the matter density parameter Omega_m and three other free parameters). This normalization is lower than the COBE normalization and previous estimates from cluster abundance, but it is in agreement with some revised cluster abundance determinations. We also estimate the scale-independent bias parameter of present-epoch L_s = 1.9L_* APM-selected galaxies to be b(L_s,z=0) = 1.10 +- 0.08 on comoving scales of 0.02 < k < 0.15 h/Mpc. If luminosity segregation operates on these scales, L_* galaxies would be almost un-biased, b(L_*,z=0) = 0.96. These results are derived by assuming a flat Lambda-CDM Universe, and by marginalizing over other free parameters and fixing the spectral index n=1 and the optical depth due to reionization tau=0. We also study the best fit pair (Omega_m,b), and the robustness of the results to varying n and tau. Various modelling corrections can each change the resulting b by 5-15 per cent. The results are compared with other independent measurements from the 2dFGRS itself, and from the SDSS, cluster abundance and cosmic shear.

astro-ph↗

arXiv2002

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

We have measured the equivalent width of the H-alpha emission line for 11006 galaxies brighter than M_b=-19 (LCDM) at 0.05<z<0.1 in the 2dF Galaxy Redshift Survey (2dF), in the fields of seventeen 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 mustar, the star formation rate normalized to Lstar, as a function of distance from the cluster centre, and local projected galaxy density. We find that the distribution of mustar 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 (brighter than M_b=-19) per Mpc^2. 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 virialised cluster rule out severe physical processes, such as ram pressure stripping of disk gas, as being completely responsible for the variations in galaxy properties with environment.

astro-ph↗

arXiv2002

Stellar populations in early-type Coma cluster galaxies - I. The data

We present a homogeneous and high signal-to-noise data set (mean S/N of ~60 per Å) of Lick/IDS stellar population line indices and central velocity dispersions for a sample of 132 bright (b_j < 18.0) galaxies within the central 1 deg (= 1.26 h^-1 Mpc) of the nearby rich Coma cluster (A1656). Our observations include 73 per cent (100 out of 137) of the total early-type galaxy population (b_j < 18.0). Observations were made with the WHT 4.2 metre and the AUTOFIB2/WYFFOS multi-object spectroscopy instrument (resolution of 2.2 ÅFWHM) using 2.7'' diameter fibres (= 0.94 h^-1 kpc). The data in this paper have well characterised errors, calculated in a rigorous and statistical way. Data are compared to previous studies and are demonstrated to be of high quality and well calibrated on to the Lick/IDS system. Our data have median errors of ~0.1 Åfor atomic line indices, ~0.008 mag for molecular line indices, and 0.015 dex for velocity dispersions. This work provides a well-defined, high-quality baseline at z~0 for studies of medium to high redshift clusters. Subsequent papers will use this data set to probe the stellar populations (which act as fossil records of galaxy formation and evolution) and the spectro-photometric relations of the bright early-type galaxies within the core of the Coma cluster.

astro-ph↗

arXiv2002

The 2dF Galaxy Redshift Survey: The Number and Luminosity Density of Galaxies

We present the bivariate brightness distribution (BBD) for the 2dF Galaxy Redshift Survey (2dFGRS) based on a preliminary subsample of 45,000 galaxies. The BBD is an extension of the galaxy luminosity function incorporating surface brightness information. It allows the measurement of the local luminosity density, j_B, and the galaxy luminosity and surface brightness distributions while accounting for surface brightness selection biases. The recovered 2dFGRS BBD shows a strong surface brightness-luminosity relation (M_B~2.4μ_e). The luminosity-density is dominated by normal galaxies and the luminosity-density peak lies away from the selection boundaries implying that the 2dFGRS is complete and that luminous low surface brightness galaxies are rare. The final value we derive for the local luminosity-density, inclusive of surface brightness corrections, is: j_B=2.49+/-0.20x10^8 h L_solar Mpc^-3. Representative Schechter function parameters are: M*=-19.75+/-0.05, phi*=2.02+/-0.02x10^-2 and alpha=-1.09+/-0.03. Extending the conventional methodology to incorporate surface brightness selection effects has resulted in an increase in the luminosity-density of 37%.

astro-ph↗

arXiv2002

The 2dF Galaxy Redshift Survey: A targeted study of catalogued clusters of galaxies

We have carried out a study of known clusters within the 2dF Galaxy Redshift Survey (2dFGRS) observed areas and have identified 431 Abell, 173 APM and 343 EDCC clusters. Precise redshifts, velocity dispersions and new centroids have been measured for the majority of these objects, and this information has been used to study the completeness of these catalogues, the level of contamination from foreground and background structures along the cluster's line of sight, the space density of the clusters as a function of redshift, and their velocity dispersion distributions. We find that the Abell and EDCC catalogues are contaminated at the level of about 10%, whereas the APM catalogue suffers only 5% contamination. If we use the original catalog centroids, the level of contamination rises to approximately 15% for the Abell and EDCC catalogues, showing that the presence of foreground and background groups may alter the richness of clusters in these catalogues. There is a deficiency of clusters at $z \sim 0.05$ that may correspond to a large underdensity in the Southern hemisphere. From the cumulative distribution of velocity dispersions for these clusters, we derive an upper limit to the space density of $σ> 1000 \kms$ clusters of $3.6 \times 10^{-6} \hdens$. This result is used to constrain models for structure formation; our data favour low-density cosmologies, subject to the usual assumptions concerning the shape and normalization of the power spectrum.

astro-ph↗

arXiv2001

The 2dF Galaxy Redshift Survey: Near Infrared Galaxy Luminosity Functions

We combine the 2MASS extended source catalogue and the 2dFGRS to produce an IR selected galaxy catalogue with 17,173 measured redshifts. We use this extensive dataset to estimate the J and K-band galaxy luminosity functions. The LFs are fairly well fit by Schechter functions with J: M*-5log h= -22.36+/-0.02, alpha= -0.93+/-0.04, Phi=0.0104+/-0.0016 h^3/Mpc^3 and K: M*-5log h= -23.44+/-0.03, alpha=-0.96+/-0.05, Phi=0.0108+/-0.0016 h^3/Mpc^3 (2MASS Kron magnitudes). These parameters assume a cosmological model with Omega=0.3 and Lambda=0.7. With datasets of this size, systematic rather than random errors are the dominant source of uncertainty in the determination of the LF. 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-K and J-K colours as a function of 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_*.h= (1.6+/-0.24)/10^3 for a Kennicutt IMF and Omega_*.h= (2.9+/-0.43)/10^3 for a Salpeter IMF. These values agree with those inferred from observational estimates of the star formation history of the universe provided that dust extinction corrections are modest.

astro-ph↗

arXiv2001

The 2dF Galaxy Redshift Survey: Spectra and redshifts

The 2dF Galaxy Redshift Survey (2dFGRS) is designed to measure redshifts for approximately 250000 galaxies. This paper describes the survey design, the spectroscopic observations, the redshift measurements and the survey database. The 2dFGRS uses the 2dF multi-fibre spectrograph on the Anglo-Australian Telescope, which is capable of observing 400 objects simultaneously over a 2-degree 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 80deg x 15deg around the SGP, and the other in the northern Galactic hemisphere spanning 75deg x 10deg along the celestial equator; in addition, there are 99 fields spread over the southern Galactic cap. The survey covers 2000 sq.deg and has a median depth of z=0.11. Adaptive tiling is used to give a highly uniform sampling rate of 93% over the whole survey region. Redshifts are measured from spectra covering 3600A-8000A at a two-pixel resolution of 9.0A and a median S/N of 13 per pixel. All redshift identifications are visually checked and assigned a quality parameter Q in the range 1-5; Q>=3 redshifts are 98.4% reliable and have an rms uncertainty of 85 km/s. The overall redshift completeness for Q>=3 redshifts is 91.8%, but this varies with magnitude from 99% for the brightest galaxies to 90% for objects at the survey limit. The 2dFGRS database is available on the WWW at http://www.mso.anu.edu.au/2dFGRS

astro-ph↗

arXiv2001

Substructure in the Coma Cluster: Giants vs Dwarfs

The processes that form and shape galaxy clusters, such as infall, mergers and dynamical relaxation, tend to generate distinguishable differences between the distributions of a cluster's giant and dwarf galaxies. Thus the dynamics of dwarf galaxies in a cluster can provide valuable insights into its dynamical history. With this in mind, we look for differences between the spatial and velocity distributions of giant (b<18) and dwarf (b>18) galaxies in the Coma cluster. Our redshift sample contains new measurements from the 2dF and WYFFOS spectrographs, making it more complete at faint magnitudes than any previously studied sample of Coma galaxies. It includes 745 cluster members - 452 giants and 293 dwarfs. We find that the line-of-sight velocity distribution of the giants is significantly non-Gaussian, but not that for the dwarfs. A battery of statistical tests of both the spatial and localised velocity distributions of the galaxies in our sample finds no strong evidence for differences between the giant and dwarf populations. These results rule out the cluster as a whole having moved significantly towards equipartition, and they are consistent with the cluster having formed via mergers between dynamically-relaxed subclusters.

astro-ph↗

arXiv2001

FLASH redshift survey - I. Observations and Catalogue

The FLAIR Shapley-Hydra (FLASH) redshift survey catalogue consists of 4613 galaxies brighter than $\bJ = 16.7$ (corrected for Galactic extinction) over a 605 sq. degree region of sky in the general direction of the Local Group motion. The survey region is an approximately $60\degr \times 10\degr$ strip spanning the sky from the Shapley Supercluster to the Hydra cluster, and contains 3141 galaxies with measured redshifts. Designed to explore the effect of the galaxy concentrations in this direction (in particular the Supergalactic plane and the Shapley Supercluster) upon the Local Group motion, the 68% completeness allows us to sample the large-scale structure better than similar sparsely-sampled surveys. The survey region does not overlap with the areas covered by ongoing wide-angle (Sloan or 2dF) complete redshift surveys. In this paper, the first in a series, we describe the observation and data reduction procedures, the analysis for the redshift errors and survey completeness, and present the survey data.

astro-ph↗

arXiv2001

Evidence for a non-zero Lambda and a low matter density from a combined analysis of the 2dF Galaxy Redshift Survey and Cosmic Microwave Background Anisotropies

We perform a joint likelihood analysis of the power spectra of the 2dF Galaxy Redshift Survey (2dFGRS) and the cosmic microwave background (CMB) anisotropies under the assumptions that the initial fluctuations were adiabatic, Gaussian and well described by power laws with scalar and tensor indices of n_s and n_t. On its own, the 2dFGRS sets tight limits on the parameter combination Omega_m h, but relatively weak limits on the fraction of the cosmic matter density in baryons Omega_b/Omega_m. The CMB anisotropy data alone set poor constraints on the cosmological constant and Hubble constant because of a `geometrical degeneracy' among parameters. Furthermore, if tensor modes are allowed, the CMB data allow a wide range of values for the physical densities in baryons and cold dark matter. Combining the CMB and 2dFGRS data sets helps to break both the geometrical and tensor mode degeneracies. The values of the parameters derived here are consistent with the predictions of the simplest models of inflation, with the baryon density derived from primordial nucleosynthesis and with direct measurements of the Hubble parameter. In particular, we find strong evidence for a positive cosmological constant with a pm 2sigma range of 0.65 < Omega_Lambda < 0.85, completely independently of constraints on Omega_Λderived from Type Ia supernovae.

astro-ph↗

arXiv2001

MAXIMUS: Exploiting the Full Power of OzPoz

We propose a new multi-object spectrograph for the VLT. MAXIMUS (MAXimum MUltiplex Spectrograph) will fully exploit the multiplexing capabilities of the OzPoz fibre positioner in order to extend and complement FLAMES and VIMOS in covering observational parameter space, and to meet the increasing demand for multi-object spectroscopy by ESO users in the next decade.

astro-ph↗

arXiv2001

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 160000 galaxy redshifts. This paper presents the power spectrum of the galaxy distribution, calculated using a direct FFT-based technique. We argue that, within the k-space region 0.02<k<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 analyzed 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% confidence limits on the total matter density times the Hubble parameter Ω_m h = 0.20 +/- 0.03, and the baryon fraction Ω_b/Ω_m = 0.15 +/- 0.07, assuming scale-invariant primordial fluctuations.

astro-ph↗

arXiv2000

The Peculiar Motions of Early-Type Galaxies in Two Distant Regions VI: The Maximum Likelihood Gaussian Algorithm

The EFAR project is designed to measure the properties and peculiar motions of early-type galaxies in two distant regions. Here we describe the maximum likelihood algorithm we developed to investigate the correlations between the parameters of the EFAR database. One-, two-, and three-dimensional gaussian models are constructed to determine the mean value and intrinsic spread of the parameters, and the slopes and intrinsic parallel and orthogonal spread of the Mgb'-Mg2, Mg2-sigma, Mgb'-sigma relations, and the Fundamental Plane. In the latter case, the cluster peculiar velocities are also determined. We show that this method is superior to ``canonical'' approaches of least-squares type, which give biased slopes and biased peculiar velocities. We test the algorithm with Monte Carlo simulations of mock EFAR catalogues and derive the systematic and random errors on the estimated parameters. We find that random errors are always dominant. We estimate the influence of systematic errors due to the way clusters were selected and the hard limits and uncertainties in the selection function parameters for the galaxies. We explore the influence of uniform distributions in the Fundamental Plane parameters and the errors. We conclude that the mean peculiar motions of the EFAR clusters can be determined reliably. In particular, the placement of the two EFAR sample regions relative to the Lauer and Postman dipole allows us to strongly constrain the amplitude of the bulk motion in this direction.

astro-ph↗