55 research outputs found
Hydrodynamic Simulations of Merging Galaxy Clusters: Non-Equilibrium Ionization State and Two-Temperature Structure
We investigate a non-equilibrium ionization state and an electron-ion
two-temperature structure of the intracluster medium (ICM) in merging galaxy
clusters using a series of N-body and hydrodynamic simulations. Mergers with
various sets of mass ratios and impact parameters are systematically
investigated, and it is found that, in most cases, ICM significantly departs
from the ionization equilibrium state at the shock layers with a Mach number of
~1.5-2.0 in the outskirts of the clusters, and the shock layers with a Mach
number of ~2-4 in front of the ICM cores. Accordingly, the intensity ratio
between Fe xxv and Fe xxvi K alpha line emissions is significantly altered from
that in the ionization equilibrium state. If the effect of the two-temperature
structure of ICM is incorporated, the electron temperature is ~10-20 % and
~30-50 % lower than the mean temperature of ICM at the shock layers in the
outskirts and in front of the ICM cores, respectively, and the deviation from
the ionization equilibrium state becomes larger. We also address the dependence
of the intensity ratio on the viewing angle with respect to the merging plane.Comment: 11 pages, 10 figures. Submitted to PASJ; Accepted for publication in
PAS
Non-Equilibrium Ionization State and Two-Temperature Structure in the Bullet Cluster 1E0657-56
We investigate a non-equilibrium ionization state and an electron-ion
two-temperature structure of the intracluster medium in the merging galaxy
cluster, 1E0657-56 (the Bullet cluster), using a series of N-body and
hydrodynamic simulations. We find that the electron temperature at the shock
layer associated with the X-ray sub peak (bullet) is quite different depending
on the thermal relaxation model between electrons and ions; ~25 keV for the
Coulomb thermal relaxation model and ~45 keV for the instantaneous thermal
relaxation model in the simulations which reproduce the observed X-ray
morphology. Furthermore, both of Fe xxv and Fe xxvi are overabundant compared
with the ionization equilibrium state around the shock layer, and thus, the
intensity ratio between Fe xxv and Fe xxvi K alpha lines are significantly
altered from that in the ionization equilibrium state. We also carry out the
simulations with various sets of merger parameters, and discuss a possible
range of the non-equilibrium effects in this system. Our results could be
tested with future X-ray observations such as Astro-H with better sensitivity
in high energy band.Comment: 11 pages, 9 figures. To appear in PAS
Non-Equilibrium Ionization State and Two-Temperature Structure in the Linked Region of Abell 399/401
We investigate a non-equilibrium ionization state and two-temperature
structure of the intracluster medium in the linked region of Abell 399/401,
using a series of N-body + SPH simulations, and find that there exist
significant shock layers at the edge of the linked region, and that the
ionization state of iron departs from the ionization equilibrium state at the
shock layers and around the center of the linked region. As for the
two-temperature structure, an obvious difference of temperature between
electrons and ions is found in the edge of the linked regions. K alpha line
emissions of Fe xxiv and Fe xxv are not severely affected by the deviation from
the ionization equilibrium state around the center of the linked region,
suggesting that the detection of relatively high metallicity in this area
cannot be ascribed to the non-equilibrium ionization state of the intracluster
medium. On the other hand, the K alpha emissions are significantly deviated
from the equilibrium values at the shock layers, and the intensity ratio of K
alpha lines between Fe xxiv-xxv and Fe xxvi is found to be significantly
altered from that in the ionization equilibrium state.Comment: 4 pages, 2 figures, submitted to PASJ Letter; accepted June
Core Structure of Intracluster Gas: Isothermal Hydrostatic Equilibrium
We investigate core structures of X-ray emitting intracluster gas based on
the so-called beta-model, which is an isothermal hydrostatic model often used
in observational studies. We reconsider the beta-model and find that the virial
temperature T_vir of a cluster may be represented better by beta T_X than T_X,
where beta is the parameter obtained from the X-ray surface brightness and T_X
is the emission-weighted mean temperature of the gas. We investigate 121
clusters observed by ROSAT and ASCA and find that the luminosity-temperature
relation L_X - beta T_X is less steep than L_X - T_X. We classify the clusters
into two core-size groups in order to investigate their properties in detail.
While in the larger core group the core radius is marginally proportional to
the virial radius, no significant relation is found for the smaller core group.
This may suggest that the smaller cores reflect the presence of cD galaxies,
effect of radiative cooling or asymmetry in the surface brightness. We examine
such possibilities, and find that the clusters of smaller cores have shorter
cooling time than the Hubble time, while no significant correlation is found
with cD or asymmetry. We carry out hydrodynamical calculations to simulate the
beta-model, intending to see the behavior of the isothermal gas under the
gravitational potential including the dark matter and galaxies with or without
a central cD galaxy. Calculations show r_c \propto r_vir and T_vir \simeq beta
T consistently with our consideration to the beta-model. Also is found from
calculations that the presence of a large cD galaxy may form a gas core \sim 40
kpc, which seems too small to account for the range of the core sizes, 40--80
kpc, of the smaller core group.Comment: 9 pages, 10 figures; To be published in PASJ vol 57, No. 3 (June
2005
Effects of Depolarizing Intervening Galaxies on Background Radio Emission I. Global Disk Magnetic Field
External galaxies often intervene in front of background radio sources such
as quasars and radio galaxies. Linear polarization of the background emission
is depolarized by Faraday rotation of inhomogeneous magnetized plasma of the
intervening galaxies. Exploring the depolarizing intervening galaxies (DINGs)
can be a powerful tool to investigate the cosmological evolution of the
galactic magnetic field. In this paper, we investigate the effects of DINGs on
background radio emission using theoretical DING models. We find that complex
structures of galaxy result in complicated depolarization features and the
Faraday dispersion functions (FDFs), but, for the features of depolarizations
and FDFs, the global component of magnetic fields is important. We show the
simplest results with ring magnetic field in the galactic disk. We find that
the degree of depolarization significantly depends on the inclination angle and
the impact parameter of the DING. We found that the larger the standard
deviation, the more likely it is that depolarization will occur. The FDF
represents the RM structure within the beam. The FDF exhibits multi-components
due mainly to the RM structure within the beam and the fraction of the DING
that covers the background emission (the filling factor). The peak Faraday
depth of the FDF is different from the beam-averaged RM of the DING. The
Monte-Carlo simulations indicate that DING's contribution to the standard
deviation of observed RMs follows with and exhibits a steeper redshift dependence than the wavelength
squared. DINGs will have a significant impact on RM catalogs created by future
survey projects such as the SKA and SKA Precursor/Pathfinder.Comment: 30 pages, 11 figures, accepted for publication in PAS
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