Showing papers by "Warrick J. Couch published in 2011"
Swinburne University of Technology1, New York University2, University of Western Australia3, University of Queensland4, University of Copenhagen5, Australian Astronomical Observatory6, University of Sydney7, California Institute of Technology8, University of Waterloo9, University of Chicago10, Australia Telescope National Facility11, Carnegie Institution for Science12, Monash University, Clayton campus13, Australian National University14, University of British Columbia15, University of Toronto16
TL;DR: In this paper, the authors 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.
Abstract: 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-σ 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-ofstate 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 k = 0.004± 0.006.
898 citations
Swinburne University of Technology1, Australian Astronomical Observatory2, University of Sydney3, University of Queensland4, University of Copenhagen5, California Institute of Technology6, University of Waterloo7, University of Chicago8, Australia Telescope National Facility9, Carnegie Institution for Science10, Monash University, Clayton campus11, Australian National University12, University of British Columbia13, University of Toronto14
TL;DR: In this article, the power spectrum of the velocity divergence field, P_(θθ) (k), was extracted from the WiggleZ Dark Energy Survey and compared with several different models of the quasi-linear growth of structure including empirical models, fitting formulae calibrated to N-body simulations and perturbation theory techniques.
Abstract: We present precise measurements of the growth rate of cosmic structure for the redshift range 0.1 < z < 0.9, using redshift-space distortions in the galaxy power spectrum of the WiggleZ Dark Energy Survey. Our results, which have a precision of around 10 per cent in four
independent redshift bins, are well fitted by a flat Λ cold dark matter (ΛCDM) cosmological model with matter density parameter Ω_m = 0.27. Our analysis hence indicates that this model provides a self-consistent description of the growth of cosmic structure through large-scale
perturbations and the homogeneous cosmic expansion mapped by supernovae and baryon acoustic oscillations. We achieve robust results by systematically comparing our data with
several different models of the quasi-linear growth of structure including empirical models, fitting formulae calibrated to N-body simulations, and perturbation theory techniques. We extract the first measurements of the power spectrum of the velocity divergence field, P_(θθ) (k),
as a function of redshift (under the assumption that P_(gθ) (k) = − √P_(gg)(k)P_(θθ) (k), where g is the galaxy overdensity field), and demonstrate that the WiggleZ galaxy–mass cross-correlation is consistent with a deterministic (rather than stochastic) scale-independent bias model for WiggleZ galaxies for scales k < 0.3 h Mpc^(−1). Measurements of the cosmic growth rate from
the WiggleZ Survey and other current and future observations offer a powerful test of the physical nature of dark energy that is complementary to distance–redshift measures such as supernovae and baryon acoustic oscillations.
451 citations
Swinburne University of Technology1, University of Queensland2, University of Copenhagen3, Australian Astronomical Observatory4, University of Sydney5, California Institute of Technology6, University of Waterloo7, University of Chicago8, Australia Telescope National Facility9, Carnegie Institution for Science10, Monash University, Clayton campus11, Australian National University12, University of British Columbia13, University of Toronto14
TL;DR: In this article, the imprint of baryon acoustic oscillations (BAOs) in the galaxy clustering pattern at the highest redshift achieved to date, z= 0.6, using the distribution of N= 132 509 emission-line galaxies in the WiggleZ Dark Energy Survey.
Abstract: We measure the imprint of baryon acoustic oscillations (BAOs) in the galaxy clustering pattern at the highest redshift achieved to date, z= 0.6, using the distribution of N= 132 509 emission-line galaxies in the WiggleZ Dark Energy Survey. We quantify BAOs using three statistics: the galaxy correlation function, power spectrum and the band-filtered estimator introduced by Xu et al. The results are mutually consistent, corresponding to a 4.0 per cent measurement of the cosmic distance–redshift relation at z= 0.6 [in terms of the acoustic parameter ‘A(z)’ introduced by Eisenstein et al., we find A(z= 0.6) = 0.452 ± 0.018]. Both BAOs and power spectrum shape information contribute towards these constraints. The statistical significance of the detection of the acoustic peak in the correlation function, relative to a wiggle-free model, is 3.2σ. The ratios of our distance measurements to those obtained using BAOs in the distribution of luminous red galaxies at redshifts z= 0.2 and 0.35 are consistent with a flat Λ cold dark matter model that also provides a good fit to the pattern of observed fluctuations in the cosmic microwave background radiation. The addition of the current WiggleZ data results in a ≈30 per cent improvement in the measurement accuracy of a constant equation of state, w, using BAO data alone. Based solely on geometric BAO distance ratios, accelerating expansion (w < −1/3) is required with a probability of 99.8 per cent, providing a consistency check of conclusions based on supernovae observations. Further improvements in cosmological constraints will result when the WiggleZ survey data set is complete.
246 citations
Swinburne University of Technology1, University of Copenhagen2, University of Queensland3, Australian Astronomical Observatory4, University of Sydney5, California Institute of Technology6, University of Waterloo7, University of Chicago8, Australia Telescope National Facility9, Carnegie Institution for Science10, Monash University, Clayton campus11, Australian National University12, University of British Columbia13, University of Toronto14
TL;DR: In this article, a new determination of the cosmic expansion history by combining distant supernovae observations with a geometrical analysis of large-scale galaxy clustering within the WiggleZ Dark Energy Survey is presented.
Abstract: Astronomical observations suggest that today’s Universe is dominated by a dark energy of unknown physical origin. One of the most notable results obtained from many models is that dark energy should cause the expansion of the Universe to accelerate: but the expansion rate as a function of time has proved very difficult to measure directly. We present a new determination of the cosmic expansion history by combining distant supernovae observations with a geometrical analysis of large-scale galaxy clustering within the WiggleZ Dark Energy Survey, using the Alcock–Paczynski test to measure the distortion of standard spheres. Our result constitutes a robust and non-parametric measurement of the Hubble expansion rate as a function of time, which we measure with 10–15 per cent precision in four bins within the redshift range 0.1 < z < 0.9. We demonstrate, in a manner insensitive to the assumed cosmological model, that the cosmic expansion is accelerating. Furthermore, we find that this expansion history is consistent with a cosmological-constant dark energy.
185 citations
TL;DR: In this article, Chandra X-ray data and extensive optical spectroscopy, obtained with AAOmega on the 3.9 m Anglo-Australian Telescope, are used to study the complex merger taking place in the galaxy cluster Abell 2744.
Abstract: New Chandra X-ray data and extensive optical spectroscopy, obtained with AAOmega on the 3.9 m Anglo-Australian Telescope, are used to study the complex merger taking place in the galaxy cluster Abell 2744. Combining our spectra with data from the literature provides a catalog of 1237 redshifts for extragalactic objects lying within 15' of the cluster center. From these, we confirm 343 cluster members projected within 3 Mpc of the cluster center. Combining positions and velocities, we identify two major substructures, corresponding to the remnants of two major subclusters. The new data are consistent with a post-core-passage, major merger taking place along an axis that is tilted well out of the plane of the sky, together with an interloping minor merger. Supporting this interpretation, the new X-ray data reveal enriched, low entropy gas from the core of the approaching, major subcluster, lying ~2' north of the cluster center, and a shock front to the southeast of the previously known bright, compact core associated with the receding subcluster. The X-ray morphology of the compact core is consistent with a Bullet-like cluster viewed from within ~45° of the merger axis. An X-ray peak ~3' northwest of the cluster center, with an associated cold front to the northeast and a trail of low entropy gas to the south, is interpreted as the remnant of an interloping minor merger taking place roughly in the plane of the sky. We infer approximate paths for the three merging components.
177 citations
Princeton University1, Swinburne University of Technology2, University College London3, University of Sydney4, University of Copenhagen5, University of Queensland6, California Institute of Technology7, Carnegie Institution for Science8, Monash University, Clayton campus9, Australian National University10, University of British Columbia11
TL;DR: In this paper, an intermediate-redshift measurement for blue galaxies, using galaxy shape measurements from SDSS and spectroscopic redshifts from the WiggleZ Dark Energy Survey, was presented.
Abstract: Correlations between the intrinsic shapes of galaxy pairs, and between the intrinsic shapes of galaxies and the large-scale density field, may be induced by tidal fields. These correlations, which have been detected at low redshifts (z < 0.35) for bright red galaxies in the Sloan Digital Sky Survey (SDSS), and for which upper limits exist for blue galaxies at z similar to 0.1, provide a window into galaxy formation and evolution, and are also an important contaminant for current and future weak lensing surveys. Measurements of these alignments at intermediate redshifts (z similar to 0.6) that are more relevant for cosmic shear observations are very important for understanding the origin and redshift evolution of these alignments, and for minimizing their impact on weak lensing measurements. We present the first such intermediate-redshift measurement for blue galaxies, using galaxy shape measurements from SDSS and spectroscopic redshifts from the WiggleZ Dark Energy Survey. Our null detection allows us to place upper limits on the contamination of weak lensing measurements by blue galaxy intrinsic alignments that, for the first time, do not require significant model-dependent extrapolation from the z similar to 0.1 SDSS observations. Also, combining the SDSS and WiggleZ constraints gives us a long redshift baseline with which to constrain intrinsic alignment models and contamination of the cosmic shear power spectrum. Assuming that the alignments can be explained by linear alignment with the smoothed local density field, we find that a measurement of Sigma(8) in a blue-galaxy dominated, CFHTLS-like survey would be contaminated by at most +0.02(-0.03) (95 per cent confidence level, SDSS and WiggleZ) or +/- 0.03 (WiggleZ alone) due to intrinsic alignments. We also allow additional power-law redshift evolution of the intrinsic alignments, due to (for example) effects like interactions and mergers that are not included in the linear alignment model, and find that our constraints on cosmic shear contamination are not significantly weakened if the power-law index is less than similar to 2. The WiggleZ sample (unlike SDSS) has a long enough redshift baseline that the data can rule out the possibility of very strong additional evolution.
155 citations
TL;DR: In this article, the authors investigate numerically the morphological transformation of spirals into S0s through group-related physical processes and show that spiral-to-S0s transformed from spirals in this way have young and metal-rich stellar populations in the inner regions of their bulges.
Abstract: Recent observations have revealed that the time evolution of the S0 number fraction at intermediate and high redshifts (0.2 < z < 0.8) is more dramatic in groups of galaxies than in clusters. In order to understand the origin of S0s in groups, we investigate numerically the morphological transformation of spirals into S0s through group-related physical processes. Our chemodynamical simulations show that spirals in group environments can be strongly influenced by repetitive slow encounters with group member galaxies so that those with thin disks and prominent spiral arm structures can be transformed into S0s with thick disks and without prominent spiral arm structure. Such tidal interactions can also trigger repetitive starbursts within the bulges of spirals and consequently increase significantly the masses of their bulges. Owing to rapid consumption of gas initially in spirals during the bulge growth, the S0s can become gas-poor. The S0s transformed from spirals in this way have young and metal-rich stellar populations in the inner regions of their bulges. The simulated S0s have lower maximum rotational velocities and flatter radial line-of-sight velocity dispersion profiles in comparison to their progenitor spirals. The formation processes of S0s due to tidal interactions depend not only on the masses and orbits of the progenitor spirals, but also on group mass. A significant fraction (10 30%) of stars and gas can be stripped during this spiral to S0 morphological transformation so that intragroup stars and gas can be formed. Based on these results, we discuss structures, kinematics, chemical properties, and the Tully-Fisher relation of S0s in groups.
153 citations
Swinburne University of Technology1, California Institute of Technology2, Australian National University3, Australian Astronomical Observatory4, University of Sydney5, University of Queensland6, University of Waterloo7, University of Chicago8, Australia Telescope National Facility9, Carnegie Institution for Science10, Monash University, Clayton campus11, University of British Columbia12, University of Toronto13
TL;DR: In this article, integral field spectroscopy (IFS) observations were performed with the OH Suppressing InfraRed Imaging Spectrograph (OSIRIS) system assisted by laser guide star adaptive optics on the Keck telescope, of 13 star-forming galaxies selected from the WiggleZ Dark Energy Survey.
Abstract: We report evidence of ordered orbital motion in luminous star-forming galaxies at z~ 1.3. We present integral field spectroscopy (IFS) observations, performed with the OH Suppressing InfraRed Imaging Spectrograph (OSIRIS) system, assisted by laser guide star adaptive optics on the Keck telescope, of 13 star-forming galaxies selected from the WiggleZ Dark Energy Survey. Selected via ultraviolet and [O ii] emission, the large volume of the WiggleZ survey allows the selection of sources which have comparable intrinsic luminosity and stellar mass to IFS samples at z > 2. Multiple 1–2 kpc size subcomponents of emission, or ‘clumps’, are detected within the Hα spatial emission which extends over 6–10 kpc in four galaxies, resolved compact emission (r 100 km s^(−1)) in the most compact sources. This unique data set reveals that the most luminous star-forming galaxies at z > 1 are gaseous unstable discs indicating that a different mode of star formation could be feeding gas to galaxies at z > 1, and lending support to theories of cold dense gas flows from the intergalactic medium.
108 citations
TL;DR: In this article, the authors present evidence for the existence of substructures in the "relaxed appearing" cold front clusters Abell 2142 and RXJ1720.1+2638.
Abstract: We present evidence for the existence of substructure in the "relaxed appearing" cold front clusters Abell 2142 and RXJ1720.1+2638. The detection of these substructures was made possible by comprehensive multi-object optical spectroscopy obtained with the Hectospec and DEep Imaging Multi-Object Spectrograph instruments on the 6.5 m MMT and 10 m Keck II telescope, respectively. These observations produced 956 and 400 spectroscopically confirmed cluster members within a projected radius of 3 Mpc from the centers of A2142 and RXJ1720.1+2638, respectively. The substructure manifests itself as local peaks in the spatial distribution of member galaxies and also as regions of localized velocity substructure. For both Abell 2142 and RXJ1720.1+2638, we identify group-scale substructures which, when considering the morphology of the cold fronts and the time since pericentric passage of a perturber estimated from the cold front radii, could plausibly have perturbed the cluster cores and generated the cold fronts observed in Chandra images. The results presented here are consistent with cold fronts being the result of merger activity and with cold fronts in relaxed appearing clusters being due to minor merger activity.
93 citations
TL;DR: In this paper, a catalog containing the properties of galaxies observed by the wings SPEctroscopic (WINGS-SPE) survey is presented, which were derived using stellar populations synthesis modelling approach.
Abstract: Context The WIde-field Nearby Galaxy clusters Survey (wings) is a project whose primary goal is to study the galaxy populations in clusters in the local universe (z < 007) and of the influence of environment on their stellar populations This survey has provided the astronomical community with a high quality set of photometric and spectroscopic data for 77 and 48 nearby galaxy clusters, respectively
Aims In this paper we present the catalog containing the properties of galaxies observed by the wings SPEctroscopic (WINGS-SPE) survey, which were derived using stellar populations synthesis modelling approach We also check the consistency of our results with other data in the literature
Methods Using a spectrophotometric model that reproduces the main features of observed spectra by summing the theoretical spectra of simple stellar populations of different ages, we derive the stellar masses, star formation histories, average age and dust attenuation of galaxies in our sample
Results similar to 5300 spectra were analyzed with spectrophotometric techniques, and this allowed us to derive the star formation history, stellar masses and ages, and extinction for the wings spectroscopic sample that we present in this paper
Conclusions The comparison with the total mass values of the same galaxies derived by other authors based on sdss data, confirms the reliability of the adopted methods and data
90 citations
TL;DR: In this paper, the authors studied the properties of the red sequence and blue fraction of 72 X-ray selected galaxy clusters at z ǫ = 0.04−0.07 from the WINGS survey.
Abstract: We study the color − magnitude red sequence and blue fraction of 72 X-ray selected galaxy clusters at z = 0.04−0.07 from the WINGS survey, searching for correlations between the characteristics of the red sequence (RS) and the environment. We consider the slope and scatter of the red sequence, the number ratio of red luminous-to-faint galaxies, the blue fraction, and the fractions of ellipticals, S0s, and spirals that compose the RS. None of these quantities correlate with the cluster velocity dispersion, X-ray luminosity, number of cluster substructures, BCG prevalence over next brightest galaxies, and the spatial concentration of ellipticals. The properties of the RS, instead, depend strongly on local galaxy density. Higher density regions have a smaller RS scatter, a higher luminous-to-faint ratio, a lower blue fraction, and a lower spiral fraction on the RS. Our results clearly illustrate the prominent effect of the local density in setting the epoch when galaxies become passive and join the red sequence, as opposed to the mass of the galaxy host structure.
Swinburne University of Technology1, Australian Astronomical Observatory2, University of Sydney3, University of Queensland4, University of Copenhagen5, California Institute of Technology6, University of Waterloo7, University of Chicago8, Australia Telescope National Facility9, Carnegie Institution for Science10, Monash University, Clayton campus11, Australian National University12, University of British Columbia13, University of Toronto14
TL;DR: In this article, the growth rate of cosmic structure for the redshift range 0.1 < z < 0.9 was measured using redshift-space distortions in the galaxy power spectrum of the WiggleZ Dark Energy Survey.
Abstract: We present precise measurements of the growth rate of cosmic structure for the redshift range 0.1 < z < 0.9, using redshift-space distortions in the galaxy power spectrum of the WiggleZ Dark Energy Survey. Our results, which have a precision of around 10% in four independent redshift bins, are well-fit by a flat LCDM cosmological model with matter density parameter Omega_m = 0.27. Our analysis hence indicates that this model provides a self-consistent description of the growth of cosmic structure through large-scale perturbations and the homogeneous cosmic expansion mapped by supernovae and baryon acoustic oscillations. We achieve robust results by systematically comparing our data with several different models of the quasi-linear growth of structure including empirical models, fitting formulae calibrated to N-body simulations, and perturbation theory techniques. We extract the first measurements of the power spectrum of the velocity divergence field, P_vv(k), as a function of redshift (under the assumption that P_gv(k) = -sqrt[P_gg(k) P_vv(k)] where g is the galaxy overdensity field), and demonstrate that the WiggleZ galaxy-mass cross-correlation is consistent with a deterministic (rather than stochastic) scale-independent bias model for WiggleZ galaxies for scales k < 0.3 h/Mpc. Measurements of the cosmic growth rate from the WiggleZ Survey and other current and future observations offer a powerful test of the physical nature of dark energy that is complementary to distance-redshift measures such as supernovae and baryon acoustic oscillations.
TL;DR: The Integral Field Unit (IFU) spectroscopy of four brightest cluster galaxies (BCGs) atz 0:1.35 Gyr in major, dry mergers is presented in this paper.
Abstract: We present Integral Field Unit (IFU) spectroscopy of four brightest cluster galaxies (BCGs) atz 0:1. Three of the BCGs have close companions within a projected radius of 20 kpc and one has no companion within that radius. We calculate the dynamical masses of the BCGs and their companions to be 1:4 10 11 < Mdyn(M ) < 1:5 10 12 . We estimate the probability that the companions of the BCGs are bound using the observed masses and velocity osets. We show that the lowest mass companion (1:4) is not bound while the two nearly equal mass (1:1.45 and 1:1.25) companions are likely to merge with their host BCGs in 0.35 Gyr in major, dry mergers. We conclude that some BCGs continue to grow from major merging even at z 0. We analyse the stellar kinematics of these systems using the R parameter developed by the SAURON team. This oers a new and unique means to measure the stellar angular momentum of BCGs and make a direct comparison to other early-type galaxies. The BCGs and their companions have similar ellipticities to those of other early-type galaxies but are more massive. We nd that not all these massive galaxies have low Re as one might expect. One of the four BCGs and the two massive companions are found to be fast-rotating galaxies with high angular momentum, thereby providing a new test for models of galaxy evolution and the formation of Intra-Cluster Light.
TL;DR: In this article, the authors present the ellipticity distribution and its evolution for early-type galaxies in clusters from z~ 0.8 to the current epoch, based on the WIde-field Nearby Galaxy-cluster Survey (0.4 ≤ z ≤ 0.07) and the ESO Distant Cluster Survey ( 0.208z > −21.8).
Abstract: We present the ellipticity distribution and its evolution for early-type galaxies in clusters from z~ 0.8 to the current epoch, based on the WIde-field Nearby Galaxy-cluster Survey (0.04 ≤ z ≤ 0.07) and the ESO Distant Cluster Survey (0.4 ≤ z ≤ 0.8). We first investigate a mass-limited sample and we find that above a fixed mass limit (M_(*) ≥ 10^(10.2) M_⊙), the ellipticity (e) distribution of early-type galaxies notably evolves with redshift. In the local Universe, there are proportionally more galaxies with higher ellipticity, hence flatter, than in distant clusters. This evolution is due partly to the change in
the mass distribution and mainly to the change in the morphological mix with z among the early types, the fraction of ellipticals goes from ~70 per cent at high z to ~40 per cent at low z). Analysing separately the ellipticity distribution of the different morphological types, we find no evolution both for ellipticals and for S0s. However, for ellipticals a change with redshift in the median value of the distributions is detected. This is due to a larger population of very round (e M_(B)+ 1.208z > −21. Analysing this sample, we do not recover exactly the same results as the mass-limited sample. This indicates that the selection criteria are crucial to characterize the galactic properties: the choice of the magnitude-‘delimited’ sample implies the loss of many less-massive galaxies and so it biases the final conclusions. Moreover, although we are adopting the same selection criteria, our results in the magnitude-‘delimited’ sample are also not in agreement with those of Holden et al. This is due to the fact that our and their low-zsamples have a different magnitude distribution because the Holden et al. sample suffers from incompleteness at faint magnitudes.
TL;DR: In this paper, the authors present the results of a spectroscopic analysis of the stellar populations of early-type galaxies aimed at addressing the question of the degree of influence that the environment and mass have on the stellar population.
Abstract: The degree of influence that the environment and mass have on the stellar populations of early-type galaxies is uncertain. In this paper, we present the results of a spectroscopic analysis of the stellar populations of early-type galaxies aimed at addressing this question. The sample of galaxies is drawn from four clusters, with 〈z〉 = 0.04, and their surrounding structure extending to ∼ 10R vir . We find that the distributions of the absorption-line strengths and the stellar population parameters, age, metallicity and α-element abundance ratio, do not differ significantly between the clusters and their outskirts, but the tight correlations found between these quantities and the velocity dispersion within the clusters are weaker in their outskirts. All three stellar population parameters of cluster galaxies are positively correlated with the velocity dispersion. Galaxies in clusters form a homogeneous class of objects that have similar distributions of line-strengths and stellar population parameters, and follow similar scaling relations, regardless of the cluster richness or morphology. We estimate the intrinsic scatter of the Gaussian distribution of metallicities to be 0.3 dex, while that of the α-element abundance ratio is 0.07 dex. The e-folding time of the exponential distribution of galaxy ages is estimated to be 900 Myr. The intrinsic scatters of the metallicity and α-element abundance ratio distributions can almost entirely be accounted for by the correlations with the velocity dispersion and the intrinsic scatter about these relations. This implies that the galaxy mass plays a major role in determining its stellar population.
TL;DR: In this article, the stellar mass of early-type galaxies (hereafter ETGs), as parameterized by the Sersic index n, and their stellar mass-to-light ratio M*/L were discovered.
Abstract: We report on the discovery of a relation between the stellar mass M* of early-type galaxies (hereafter ETGs), their shape, as parameterized by the Sersic index n, and their stellar mass-to-light ratio M*/L. In a three-dimensional log space defined by these variables, the ETGs populate a plane surface with small scatter. This relation tells us that galaxy shape and stellar population are not independent physical variables, a result that must be accounted for by theories of galaxy formation and evolution.
Swinburne University of Technology1, University of Copenhagen2, University of Queensland3, Australian Astronomical Observatory4, University of Sydney5, California Institute of Technology6, University of Waterloo7, University of Chicago8, Australia Telescope National Facility9, Carnegie Institution for Science10, Monash University, Clayton campus11, Australian National University12, University of British Columbia13, University of Toronto14
TL;DR: In this paper, the imprint of baryon acoustic oscillations (BAOs) in the galaxy clustering pattern at the highest redshift achieved to date, z=0.6, using the distribution of N=132,509 emission-line galaxies in the WiggleZ Dark Energy Survey.
Abstract: We measure the imprint of baryon acoustic oscillations (BAOs) in the galaxy clustering pattern at the highest redshift achieved to date, z=0.6, using the distribution of N=132,509 emission-line galaxies in the WiggleZ Dark Energy Survey. We quantify BAOs using three statistics: the galaxy correlation function, power spectrum and the band-filtered estimator introduced by Xu et al. (2010). The results are mutually consistent, corresponding to a 4.0% measurement of the cosmic distance-redshift relation at z=0.6 (in terms of the acoustic parameter "A(z)" introduced by Eisenstein et al. (2005) we find A(z=0.6) = 0.452 +/- 0.018). Both BAOs and power spectrum shape information contribute toward these constraints. The statistical significance of the detection of the acoustic peak in the correlation function, relative to a wiggle-free model, is 3.2-sigma. The ratios of our distance measurements to those obtained using BAOs in the distribution of Luminous Red Galaxies at redshifts z=0.2 and z=0.35 are consistent with a flat Lambda Cold Dark Matter model that also provides a good fit to the pattern of observed fluctuations in the Cosmic Microwave Background (CMB) radiation. The addition of the current WiggleZ data results in a ~ 30% improvement in the measurement accuracy of a constant equation-of-state, w, using BAO data alone. Based solely on geometric BAO distance ratios, accelerating expansion (w < -1/3) is required with a probability of 99.8%, providing a consistency check of conclusions based on supernovae observations. Further improvements in cosmological constraints will result when the WiggleZ Survey dataset is complete.
Swinburne University of Technology1, University of Queensland2, University of Copenhagen3, Australian Astronomical Observatory4, University of Sydney5, California Institute of Technology6, University of Waterloo7, University of Chicago8, Australia Telescope National Facility9, Carnegie Institution for Science10, Monash University, Clayton campus11, Australian National University12, University of British Columbia13, University of Toronto14
TL;DR: In this article, a new determination of the cosmic expansion history is presented by combining distant supernovae observations with a geometrical analysis of large-scale galaxy clustering within the WiggleZ Dark Energy Survey, using the Alcock-Paczynski test to measure the distortion of standard spheres.
Abstract: Astronomical observations suggest that today's Universe is dominated by a dark energy of unknown physical origin. One of the most notable consequences in many models is that dark energy should cause the expansion of the Universe to accelerate: but the expansion rate as a function of time has proven very difficult to measure directly. We present a new determination of the cosmic expansion history by combining distant supernovae observations with a geometrical analysis of large-scale galaxy clustering within the WiggleZ Dark Energy Survey, using the Alcock-Paczynski test to measure the distortion of standard spheres. Our result constitutes a robust and non-parametric measurement of the Hubble expansion rate as a function of time, which we measure with 10-15% precision in four bins within the redshift range 0.1 < z < 0.9. We demonstrate that the cosmic expansion is accelerating, in a manner independent of the parameterization of the cosmological model (although assuming cosmic homogeneity in our data analysis). Furthermore, we find that this expansion history is consistent with a cosmological-constant dark energy.
TL;DR: In this article, the authors investigate numerically the morphological transformation of spirals into S0s through group-related physical processes and show that the S 0s transformed from spirals in this way have young and metal-rich stellar populations in the inner regions of their bulges.
Abstract: Recent observations have revealed that the time evolution of the S0 number fraction at intermediate and high redshifts (0.2
TL;DR: In this article, the authors apply a statistical field correction technique originally designed to determine membership of high redshift galaxy clusters to Hubble Space Telescope imaging of the Antlia Dwarf Galaxy; a galaxy at the very edge of the Local Group.
Abstract: We apply a statistical field correction technique originally designed to determine membership of high redshift galaxy clusters to Hubble Space Telescope imaging of the Antlia Dwarf Galaxy; a galaxy at the very edge of the Local Group. Using the tip of the red giant branch standard candle method coupled with a simple Sobel edge detection filter we find a new distance to Antlia of 1.31 +/- 0.03 Mpc. For the first time for a Local Group Member, we compute the concentration, asymmetry and clumpiness (CAS) quantitative morphology parameters for Antlia from the distribution of resolved stars in the HST/ACS field, corrected with a new method for contaminants and complement these parameters with the Gini coefficient (G) and the second order moment of the brightest 20 per cent of the flux (M_20). We show that it is a classic dwarf elliptical (C = 2.0, A = 0.063, S = 0.077, G = 0.39 and M_20 = -1.17 in the F814W band), but has an appreciable blue stellar population at its core, confirming on-going star-formation. The values of asymmetry and clumpiness, as well as Gini and M_20 are consistent with an undisturbed galaxy. Although our analysis suggests that Antlia may not be tidally influenced by NGC 3109 it does not necessarily preclude such interaction.
TL;DR: In this paper, the authors presented a morphological catalog of galaxies in nearby clusters of the WINGS survey, which contains a total number of 39923 galaxies, for which they provided the automatic estimates of the morphological type applying the devised tool MORPHOT to the V-band WINGS imaging.
Abstract: We present the morphological catalog of galaxies in nearby clusters of the WINGS survey (Fasano et al. 2006). The catalog contains a total number of 39923 galaxies, for which we provide the automatic estimates of the morphological type applying the purposely devised tool MORPHOT to the V-band WINGS imaging. For ~3000 galaxies we also provide visual estimates of the morphological types. A substantial part of the paper is devoted to the description of the MORPHOT tool, whose application is limited, at least for the moment, to the WINGS imaging only. The approach of the tool to the automation of morphological classification is a non parametric and fully empiri- cal one. In particular, MORPHOT exploits 21 morphological diagnostics, directly and easily computable from the galaxy image, to provide two independent classifications: one based on a Maximum Likelihood (ML), semi-analytical technique, the other one on a Neural Network (NN) machine. A suitably selected sample of ~1000 visually clas- sified WINGS galaxies is used to calibrate the diagnostics for the ML estimator and as a training set in the NN machine. The final morphological estimator combines the two techniques and proves to be effective both when applied to an additional test sample of ~1000 visually classified WINGS galaxies and when compared with small samples of SDSS galaxies visually classified by Fukugita et al. (2007) and Nair et al. (2010). Finally, besides the galaxy morphology distribution (corrected for field contamination) in the WINGS clusters, we present the ellipticity ({\epsilon}), color (B-V) and Sersic index (n) distributions for different morphological types, as well as the morphological fractions as a function of the clustercentric distance (in units of R200).
TL;DR: In this article, the authors present Integral Field Unit (IFU) spectroscopy of four brightest cluster galaxies (BCGs) at z~0.35 Gyr in major, dry mergers.
Abstract: We present Integral Field Unit (IFU) spectroscopy of four brightest cluster galaxies (BCGs) at z~0.1. Three of the BCGs have close companions within a projected radius of 20 kpc and one has no companion within that radius. We calculate the dynamical masses of the BCGs and their companions to be 1.4x10^11