We use deep wide-field V-band imaging obtained with the Wide Field Camera at the prime focus of the Issac Newton Telescope to study the spatial and luminosity distribution of galaxies in three low ...redshift (0.04 < z < 0.2) clusters: Abell 119, Abell 2443 and Abell 2218. The absolute magnitude limits probed in these clusters are MV− 5 log h0.7=-13.3, -15.4 and -16.7 mag, respectively. The galaxy population, at all luminosities, along the line-of-sight to the clusters can be described by the linear combination of a King profile and a constant surface density of field galaxies. We find that, for these three clusters, the core radius is invariant with intrinsic luminosity of the cluster population to the above limits and thus there is no evidence for luminosity segregation in these clusters. The exception is the brightest galaxies in A2218 which exhibit a more compact spatial distribution. We find that the total projected luminosity distribution (within 1 h−10.7 Mpc of the cluster centre) can be well represented by a single Schechter function with moderately flat faint-end slopes: α=-1.22+0.07−0.06 (A119), α=-1.11+0.10−0.09 (A2443) and α=-1.14+0.08−0.07 (A2218). We perform a geometric deprojection of the cluster galaxy population and confirm that no ‘statistically significant’ evidence of a change in the shape of the luminosity distribution with cluster-centric radius exists. Again, the exception being A2218 which exhibits a core region with a flatter faint-end slope.
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 data set 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 4.9σ relative to a zero-baryon model with no peak. We fit cosmological models to this combined baryon acoustic oscillation (BAO) data set comprising six distance-redshift data points, and compare the results with similar cosmological fits to the latest compilation of supernovae (SNe) and cosmic microwave background (CMB) data. The BAO and SNe data sets 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 data sets 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 Ωk=−0.004 ± 0.006.
The dwarf galaxy population in Abell 2218 Pracy, Michael B.; De Propris, Roberto; Driver, Simon P. ...
Monthly notices of the Royal Astronomical Society,
08/2004, Letnik:
352, Številka:
4
Journal Article
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We present results from a deep photometric study of the rich galaxy cluster Abell 2218 (z= 0.18) based on archival Hubble Space Telescope WFPC2 F606W images. These have been used to derive the ...luminosity function to extremely faint limits (MF606W≈−13.2 mag, μ0≈ 24.7 mag arcsec−2) over a wide field of view (1.3 h−2 Mpc2). We find the faint-end slope of the luminosity function to vary with environment within the cluster, going from α=−1.23 ± 0.13 within the projected central core of the cluster (100 < r < 300 h−1 kpc) to α=−1.49 ± 0.06 outside this radius (300 < r < 750 h−1 kpc). We infer that the core is ‘dwarf depleted’, and further quantify this by studying the ratio of ‘dwarf’ to ‘giant’ galaxies and its dependency as a function of clustercentric radius and local galaxy density. We find that this ratio varies strongly with both quantities, and that the dwarf galaxy population in A2218 has a more extended distribution than the giant galaxy population.
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.
We determine colour gradients of −0.15 ± 0.08 mag per decade in radius in F450W−F606W and −0.07 ± 0.06 mag per decade in radius in F606W−F814W for a sample of 22 E/S0 galaxies in Abell 2218. These ...gradients are consistent with the existence of a mild (∼−0.3 dex per decade in radius) gradient in metal abundance (cf. previous work at lower and higher redshifts for field and cluster galaxies). The size of the observed gradients is found to be independent of luminosity over a range spanning M*−1 to M*+1.5 and also to be independent of morphological type. These results suggest a fundamental similarity in the distributions of stellar populations in ellipticals and the bulges of lenticular galaxies. These results are not consistent with simple models of either monolithic collapse or hierarchical mergers.
Abstract
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 h
−3 Gpc3. 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 per cent, or equivalently the fractal dimension of the sample is within 1 per cent of D
2 = 3, at radii larger than 71 ± 8 h
−1Mpc at z ∼ 0.2, 70 ± 5 h
−1 Mpc at z ∼ 0.4, 81 ± 5 h
−1 Mpc at z ∼ 0.6 and 75 ± 4 h
−1 Mpc at z ∼ 0.8. We demonstrate the robustness of our results against selection function effects, using a Λ cold dark matter (ΛCDM) N-body simulation and a suite of inhomogeneous fractal distributions. The results are in excellent agreement with both the ΛCDM N-body simulation and an analytical ΛCDM prediction. We can exclude a fractal distribution with fractal dimension below D
2 = 2.97 on scales from ∼80 h
−1 Mpc up to the largest scales probed by our measurement, ∼300 h
−1 Mpc, at 99.99 per cent confidence.
We present results from the 2D anisotropic baryon acoustic oscillation (BAO) signal present in the final data set from the WiggleZ Dark Energy Survey. We analyse the WiggleZ data in two ways: first ...using the full shape of the 2D correlation function and secondly focusing only on the position of the BAO peak in the reconstructed data set. When fitting for the full shape of the 2D correlation function we use a multipole expansion to compare with theory. When we use the reconstructed data we marginalize over the shape and just measure the position of the BAO peak, analysing the data in wedges separating the signal along the line of sight from that parallel to the line of sight. We verify our method with mock data and find the results to be free of bias or systematic offsets. We also redo the pre-reconstruction angle-averaged (1D) WiggleZ BAO analysis with an improved covariance and present an updated result. The final results are presented in the form of Ω
,
(
), and
(
) for three redshift bins with effective redshifts
= 0.44, 0.60, and 0.73. Within these bins and methodologies, we recover constraints between 5 and 22 per cent error. Our cosmological constraints are consistent with flat ΛCDM cosmology and agree with results from the Baryon Oscillation Spectroscopic Survey.
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