arXiv subjects

Peter A Thomas

Publications and source records attributed to Peter A Thomas.

5 recordsLinked to original sources

arXiv2003

The power spectrum amplitude from clusters revisited: σ_8 using simulations with preheating and cooling

The amplitude of density perturbations, for the currently-favoured LambdaCDM cosmology, is constrained using the observed properties of galaxy clusters. The catalogue used is that of Ikebe et al. (2002). The cluster temperature to mass relation is obtained via N-body/hydrodynamical simulations including radiative cooling and preheating of cluster gas, which we have previously shown to reproduce well the observed temperature--mass relation in the innermost parts of clusters (Thomas et al. 2002). We generate and compare mock catalogues via a Monte Carlo method, which allows us to constrain the relation between X-ray temperature and luminosity, including its scatter, simultaneously with cosmological parameters. We find a luminosity-temperature relation in good agreement with the results of Ikebe et al. (2002), while for the matter power spectrum normalization, we find $σ_8 = 0.78_{-0.06}^{+0.30}$ at 95 per cent confidence for $Ω_0 = 0.35$. Scaling to WMAP's central value of $Ω_0 = 0.27$ would give a best-fit value of $σ_8 \simeq 0.9$.

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arXiv2001

The impact of cooling and pre-heating on the Sunyaev-Zel'dovich effect

We use hydrodynamical simulations to assess the impact of radiative cooling and `pre-heating' on predictions for the Sunyaev--Zel'dovich (SZ) effect. Cooling significantly reduces both the mean SZ signal and its angular power spectrum, while pre-heating can give a higher mean distortion while leaving the angular power spectrum below that found in a simulation without heating or cooling. We study the relative contribution from high and low density gas, and find that in the cooling model about 60 per cent of the mean thermal distortion arises from low overdensity gas. We find that haloes dominate the thermal SZ power spectrum in all models, while in the cooling simulation the kinetic SZ power spectrum originates predominantly in lower overdensity gas.

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arXiv2001

Sunyaev-Zel'dovich Predictions for the Planck Surveyor Satellite using the Hubble Volume Simulations

We use the billion-particle Hubble Volume simulations to make statistical predictions for the distribution of galaxy clusters that will be observed by the Planck Surveyor satellite through their effect on the cosmic microwave background -- the Sunyaev-Zel'dovich effect. We utilize the lightcone datasets for both critical density (tauCDM) and flat low-density (LambdaCDM) cosmologies: a `full-sky' survey out to $z \sim 0.5$, two `octant' datasets out to beyond $z=1$ and a 100 square degree dataset extending to $z \sim 4$. Making simple, but robust, assumptions regarding both the thermodynamic state of the gas and the detection of objects against an unresolved background, we present the expected number of SZ sources as a function of redshift and angular size, and also by flux (for both the thermal and kinetic effects) for 3 of the relevant HFI frequency channels. We confirm the expectation that Planck will detect around $5\times 10^4$ clusters, though the exact number is sensitive to the choice of several parameters including the baryon fraction, and also to the cluster density profile, so that either cosmology may predict more clusters. We also find that the majority of detected sources should be at $z<1.5$, and we estimate that around one per cent of clusters will be spatially resolved by Planck, though this has a large uncertainty.

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arXiv2000

Hydrodynamical simulations of the Sunyaev-Zel'dovich effect: the kinetic effect

We use hydrodynamical N-body simulations to study the kinetic Sunyaev-Zel'dovich effect. We construct sets of maps, one square degree in size, in three different cosmological models. We confirm earlier calculations that on the scales studied the kinetic effect is much smaller than the thermal (except close to the thermal null point), with an rms dispersion smaller by about a factor five in the Rayleigh-Jeans region. We study the redshift dependence of the rms distortion and the pixel distribution at the present epoch. We compute the angular power spectra of the maps, including their redshift dependence, and compare them with the thermal Sunyaev-Zel'dovich effect and with the expected cosmic microwave background anisotropy spectrum as well as with determinations by other authors. We correlate the kinetic effect with the thermal effect both pixel-by-pixel and for identified thermal sources in the maps to assess the extent to which the kinetic effect is enhanced in locations of strong thermal signal.

astro-ph↗

arXiv2000

Hydrodynamical simulations of the Sunyaev--Zel'dovich effect

We use a hydrodynamical N-body code to generate simulated maps, of size one square degree, of the thermal SZ effect. We study three different cosmologies; the currently-favoured low-density model with a cosmological constant, a critical-density model and a low-density open model. We stack simulation boxes corresponding to different redshifts in order to include contributions to the Compton y-parameter out to the highest necessary redshifts. Our main results are: 1. The mean y-distortion is around $4 \times 10^{-6}$ for low-density cosmologies, and $1 \times 10^{-6}$ for critical density. These are below current limits, but not by a wide margin in the former case. 2. In low-density cosmologies, the mean y-distortion comes from a broad range of redshifts, the bulk coming from $z < 2$ and a tail out to $z \sim 5$. For critical-density models, most of the contribution comes from $z < 1$. 3. The number of SZ sources above a given $y$ depends strongly on instrument resolution. For a one arcminute beam, there is around 0.1 sources per square degree with $y > 10^{-5}$ in a critical-density Universe, and around 8 such sources per square degree in low-density models. Low-density models with and without a cosmological constant give very similar results. 4. We estimate that the {\sc Planck} satellite will be able to see of order 25000 SZ sources if the Universe has a low density, or around 10000 if it has critical density.

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