Magnetic fields and Sunyaev-Zel'dovich effect in galaxy clusters

Abstract

In this work we study the contribution of magnetic fields to the Sunyaev Zeldovich (SZ) effect in the intracluster medium. In particular we calculate the SZ angular power spectrum and the central temperature decrement. The effect of magnetic fields is included in the hydrostatic equilibrium equation by splitting the Lorentz force into two terms -one being the force due to magnetic pressure which acts outwards and the other being magnetic tension which acts inwards. A perturbative approach is adopted to solve for the gas density profile for weak magnetic fields (≤ 4µG). This leads to an enhancement of the gas density in the central regions for nearly radial magnetic field configurations. Previous works had considered the force due to magnetic pressure alone which is the case only for a special set of field configurations. However, we see that there exists possible sets of configurations of ICM magnetic fields where the force due to magnetic tension will dominate. Subsequently, this effect is extrapolated for typical field strengths (∼ 10µG) and scaling arguments are used to estimate the angular power due to secondary anisotropies at cluster scales. In particular we find that it is possible to explain the excess power reported by CMB experiments like CBI, BIMA, ACBAR at ℓ > 2000 with σ 8 ∼ 0.8 (WMAP 5 year data) for typical cluster magnetic fields. In addition we also see that the magnetic field effect on the SZ temperature decrement is more pronounced for low mass clusters ( T ∼ 2 keV). Future SZ detections of low mass clusters at few arc second resolution will be able to probe this effect more precisely. Thus, it will be instructive to explore the implications of this model in greater detail in future works.

Magnetic fields in galaxy clusters

“…Other magnetic field configurations will have different effects on cluster gas profiles, and therefore on the SZ signal. Also, they find that radial fields of tens of μG may bring the SZ σ 8 into agreement with the WMAP 5 result (Gopal & Roychowdhury 2010;Komatsu et al 2009).…”

“…Indeed, there is a some disagreement between the SZ and WMAP 7 measurements of σ 8 (Komatsu et al 2011;Lueker et al 2010), which can be remedied if the predicted SZ power is roughly halved (Shaw et al 2010, and references therein). Gopal & Roychowdhury (2010) show that the strength and topology of cluster magnetic fields change the ICM density profiles and thus impact the SZ power. In particular, they find that a radial cluster magnetic field with a strength of ∼ 3 μG will increase the central SZ decrement by 25 % in a 10 14 M cluster.…”

A fast and accurate method for computing the Sunyaev-Zel'dovich signal of hot galaxy clusters

“…Dolag et al ; Lau, Kravtsov & Nagai ; Vazza et al ; Nelson et al ) or magnetic fields (e.g. Koch, Jetzer & Puy ; Gopal & Roychowdhury ), on the SZ signal. For accurate predictions and interpretation of the SZ signals, all these processes must be included.…”

Primordial magnetic fields with X-ray and Sunyaev-Zel’divich cluster surveys

“…However, in order to obtain a highly accurate constraint on primordial magnetic fields, it is necessary to study the modification on the electron density profile and the relation between the X‐ray temperature and the cluster mass by primordial magnetic fields. For example, Zhang (2004) and Gopal & Roychowdhury (2010) pointed out that magnetic fields of several micro‐gauss in a halo modify the electron density profile, and this modification changes the S‐Z‐effect signal. The adiabatic contraction in the halo formation easily amplifies primordial magnetic field strengths of the order of nano‐gauss to the order of micro‐gauss.…”