Issue |
A&A
Volume 509, January 2010
|
|
---|---|---|
Article Number | A29 | |
Number of page(s) | 6 | |
Section | Cosmology (including clusters of galaxies) | |
DOI | https://doi.org/10.1051/0004-6361/200913195 | |
Published online | 14 January 2010 |
Non-equilibrium ionization states in galaxy clusters
1
UPMC Université Paris 06, UMR 7095, Institut
d'Astrophysique de Paris, 75014 Paris, France e-mail: phdmitry@gmail.com
2
CNRS,
UMR 7095, Institut d'Astrophysique de Paris, 75014 Paris, France
3
Korea Astronomy and Space Science Institute, 61-1 Hwaam-dong,
Yuseong-gu, Daejeon 305-348, Korea
Received:
28
August
2009
Accepted:
28
October
2009
Context. X-ray imaging observatories have revealed hydrodynamic structures with linear scales of ~10 kpc in clusters of galaxies, such as shock waves in the 1E0657-56 and A520 galaxy clusters and the hot plasma bubble in the MKW 3s cluster. The future X-ray observatory IXO will for the first time resolve the metal distribution in galaxy clusters at the these scales.
Aims. Heating of plasmas by shocks and AGN activities can result in non-equilibrium ionization states of metal ions. We study the effect of the non-equilibrium ionization at linear scales of ≲50 kpc in galaxy clusters.
Methods. A condition for non-equilibrium ionization is derived by comparing the ionization time-scale with the age of hydrodynamic structures. Modeling of non-equilibrium ionization is performed at a point in time when the plasma temperature suddenly changes. An analysis of the relaxation processes of the FeXXV and FeXXVI ions by means of eigenvectors of the transition matrix is given.
Results. We conclude that the non-equilibrium ionization of iron can
occur in galaxy clusters if the baryonic overdensity δ is
smaller than , where
is the ratio of the
hydrodynamic structure age to the Hubble time. Our modeling
indicates that the emissivity in the helium-like emission lines of
iron increases as a result of the deviation from the ionization
equilibrium. A slow process of helium-like ionic fraction relaxation
was analyzed. A new way to determine a shock velocity is
proposed.
Key words: galaxies: clusters: general / atomic processes / shock waves
© ESO, 2010
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