Browsing by Author "Damsted, S."

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    Clustering of CODEX clusters
    (2021) Lindholm, V.; Finoguenov, A.; Comparat, J.; Kirkpatrick, C. C.; Rykoff, E.; Clerc, N.; Collins, C.; Damsted, S.; Chitham, J. Ider; Padilla, Nelson David
    Context. The clustering of galaxy clusters links the spatial nonuniformity of dark matter halos to the growth of the primordial spectrum of perturbations. The amplitude of the clustering signal is widely used to estimate the halo mass of astrophysical objects. The advent of cluster mass calibrations enables using clustering in cosmological studies. Aims. We analyze the autocorrelation function of a large contiguous sample of galaxy clusters, the Constrain Dark Energy with X-ray (CODEX) sample, in which we take particular care of cluster definition. These clusters were X-ray selected using the ROentgen SATellite All-Sky Survey and then identified as galaxy clusters using the code redMaPPer run on the photometry of the Sloan Digital Sky Survey. We develop methods for precisely accounting for the sample selection effects on the clustering and demonstrate their robustness using numerical simulations. Methods. Using the clean CODEX sample, which was obtained by applying a redshift-dependent richness selection, we computed the two-point autocorrelation function of galaxy clusters in the 0.1 < z < 0.3 and 0.3 < z < 0.5 redshift bins. We compared the bias in the measured correlation function with values obtained in numerical simulations using a similar cluster mass range. Results. By fitting a power law, we measured a correlation length r0 = 18.7 ± 1.1 and slope γ = 1.98 ± 0.14 for the correlation function in the full redshift range. By fixing the other cosmological parameters to their nine-year Wilkinson Microwave Anisotropy Probe values, we reproduced the observed shape of the correlation function under the following cosmological conditions: Ωm0 = 0.22−0.03+0.04 and S8 = σ8(Ωm0/0.3)0.5 = 0.85−0.08+0.10 with estimated additional systematic errors of σΩm0 = 0.02 and σS8 = 0.20. We illustrate the complementarity of clustering constraints by combining them with CODEX cosmological constraints based on the X-ray luminosity function, deriving Ωm0 = 0.25 ± 0.01 and σ8 = 0.81−0.02+0.01 with an estimated additional systematic error of σΩm0 = 0.07 and σσ8 = 0.04. The mass calibration and statistical quality of the mass tracers are the dominant source of uncertainty.
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    Gravitational redshifting of galaxies in the SPIDERS cluster catalogue
    (2021) Mpetha, C. T.; Collins, C. A.; Clerc, N.; Finoguenov, A.; Peacock, J. A.; Comparat, J.; Schneider, D.; Capasso, R.; Damsted, S.; Furnell, K.; Merloni, A.; Padilla, N. D.; Saro, A.
    Data from the SPectroscopic IDentification of ERosita Sources (SPIDERS) are searched for a detection of the gravitational redshifting of light from similar to 20 000 galaxies in similar to 2500 galaxy clusters using three definitions of the cluster centre: its Brightest Cluster Galaxy (BCG), the redMaPPer identified Central Galaxy (CG), or the peak of X-ray emission. Distributions of velocity offsets between galaxies and their host cluster's centre, found using observed redshifts, are created. The quantity (Delta) over cap, the average of the radial velocity difference between the cluster members and the cluster systemic velocity, reveals information on the size of a combination of effects on the observed redshift, dominated by gravitational redshifting. The change of (Delta) over cap with radial distance is predicted for SPIDERS galaxies in General Relativity (GR), and f(R) gravity, and compared to the observations. The values of (Delta) over cap = -13.5 +/- 4.7 kms(-1), (Delta) over cap = -12.5 +/- 5.1 kms(-1), and (Delta) over cap = -18.6 +/- 4.8 kms(-1) for the BCG, X-ray, and CG cases, respectively, broadly agree with the literature. There is no significant preference of one gravity theory over another, but all cases give a clear detection (>2.5 sigma) of (Delta) over cap. The BCG centroid is deemed to be the most robust method in this analysis, due to no well-defined central redshift when using an X-ray centroid, and CGs identified by redMaPPer with no associated spectroscopic redshift. For future gravitational redshift studies, an order-of-magnitude more galaxies, similar to 500 000, will be required - a possible feat with the forthcoming Vera C. Rubin Observatory, Euclid and eROSITA.
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    SPIDERS : overview of the X-ray galaxy cluster follow-up and the final spectroscopic data release
    (2020) Clerc, N.; Kirkpatrick, C. C.; Finoguenov, A.; Capasso, R.; Comparat, J.; Damsted, S.; Furnell, K.; Kukkola, A. E.; Chitham, J. I.; Padilla, Nelson; Merloni, A.; Salvato, M.; Gueguen, A.; Dwelly, T.; Collins, C.; Saro, A.; Erfanianfar, G.; Schneider, D. P.; Brownstein, J.; Mamon, G. A.; Jullo, E.; Bizyaev, D.
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    SPIDERS: an overview of the largest catalogue of spectroscopically confirmed x-ray galaxy clusters
    (2021) Kirkpatrick, C. C.; Clerc, N.; Finoguenov, A.; Damsted, S.; Chitham, J. Ider; Kukkola, A. E.; Gueguen, A.; Furnell, K.; Rykoff, E.; Comparat, J.; Saro, A.; Capasso, R.; Padilla, N.; Erfanianfar, G.; Mamon, G. A.; Collins, C.; Merloni, A.; Brownstein, J. R.; Schneider, D. P.
    SPIDERS is the spectroscopic follow-up effort of the Sloan Digital Sky Survey IV (SDSS-IV) project for the identification of X-ray selected galaxy clusters. We present our catalogue of 2740 visually inspected galaxy clusters as part of the SDSS Data Release 16 (DR16). Here we detail the target selection, our methods for validation of the candidate clusters, performance of the survey, the construction of the final sample, and a full description of what is found in the catalogue. Of the sample, the median number of members per cluster is approximately 10, with 818 having 15 or greater. We find that we are capable of validating over 99 per cent of clusters when five redshifts are obtained below z < 0.3 and when nine redshifts are obtained above z > 0.3. We discuss the improvements in this catalogue's identification of cluster using 33 340 redshifts, with Delta Z(phot)/Delta Z(spec) similar to 100, over other photometric and spectroscopic surveys, as well as presenting an update to previous (sigma-L-X) and (sigma-lambda) relations. Finally, we present our cosmological constraints derived using the velocity dispersion function.