THE RELATION BETWEEN GAS DENSITY AND VELOCITY POWER SPECTRA IN GALAXY CLUSTERS: QUALITATIVE TREATMENT AND COSMOLOGICAL SIMULATIONS
- Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, 452 Lomita Mall, Stanford, CA 94305 (United States)
- Max Planck Institute for Astrophysics, Karl-Schwarzschild-Strasse 1, D-85741 Garching (Germany)
- The Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Oxford OX1 3NP (United Kingdom)
- Department of Physics, Yale University, New Haven, CT 06520 (United States)
- Department of Astronomy, Yale University, New Haven, CT 06520 (United States)
We address the problem of evaluating the power spectrum of the velocity field of the intracluster medium using only information on the plasma density fluctuations, which can be measured today by Chandra and XMM-Newton observatories. We argue that for relaxed clusters there is a linear relation between the rms density and velocity fluctuations across a range of scales, from the largest ones, where motions are dominated by buoyancy, down to small, turbulent scales: (δρ{sub k}/ρ){sup 2}=η{sub 1}{sup 2}(V{sub 1,k}/c{sub s}){sup 2}, where δρ {sub k}/ρ is the spectral amplitude of the density perturbations at wavenumber k, V{sub 1,k}{sup 2}=V{sub k}{sup 2}/3 is the mean square component of the velocity field, c{sub s} is the sound speed, and η{sub 1} is a dimensionless constant of the order of unity. Using cosmological simulations of relaxed galaxy clusters, we calibrate this relation and find η{sub 1} ≈ 1 ± 0.3. We argue that this value is set at large scales by buoyancy physics, while at small scales the density and velocity power spectra are proportional because the former are a passive scalar advected by the latter. This opens an interesting possibility to use gas density power spectra as a proxy for the velocity power spectra in relaxed clusters across a wide range of scales.
- OSTI ID:
- 22365793
- Journal Information:
- Astrophysical Journal Letters, Vol. 788, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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