Shutaro Ueda

Search for a non-equilibrium plasma in the merging galaxy cluster Abell 754

Abell 754 is a galaxy cluster in which an ongoing merger is evident on the plane of the sky, from the southeast to the northwest. We study the spatial variation of the X-ray spectra observed with Suzaku along the merging direction, centering on the Fe Ly-alpha / Fe He-alpha line ratio to search for possible deviation from ionization equilibrium. Fitting with a single temperature collisional non-equilibrium plasma model shows that the electron temperature increases from the southeast to the northwest. The ionization parameter is consistent with that in equilibrium (n_et>10^{13} s cm^{-3}) except for a specific region with the highest temperature (kT=13.3^{+1.4}_{-1.1} keV) where n_et=10^{11.6^{+0.6}_{-1.7}} s cm^{-3}. The elapsed time from the plasma heating estimated from the ionization parameter is 0.36-76 Myr at the 90% confidence level. This time scale is quite short but consistent with the traveling time of a shock to pass through that region. We thus interpret that the non-equilibrium ionization plasma in Abell 754 observed is a remnant of the shock heating in the merger process. We, however, note that the X-ray spectrum of the specific region where the non-equilibrium is found can also be fitted with a collisional ionization plasma model with two temperatures, low kT=4.2^{+4.2}_{-1.5} keV and very high kT > 19.3 keV. The very high temperature component is alternatively fitted with a power law model. Either of these spectral models is interpreted as a consequence of the ongoing merger process as in the case of that with the non-equilibrium ionization plasma.

Multiwavelength study of X-ray Luminous Clusters in the Hyper Suprime-Cam Subaru Strategic Program S16A field

We present a joint X-ray, optical and weak-lensing analysis for X-ray luminous galaxy clusters selected from the MCXC (Meta-Catalog of X-Ray Detected Clusters of Galaxies) cluster catalog in the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) survey field with S16A data, As a pilot study of our planned series papers, we measure hydrostatic equilibrium (H.E.) masses using XMM-Newton data for four clusters in the current coverage area out of a sample of 22 MCXC clusters. We additionally analyze a non-MCXC cluster associated with one MCXC cluster. We show that H.E. masses for the MCXC clusters are correlated with cluster richness from the CAMIRA catalog (Oguri et al. 2017), while that for the non-MCXC cluster deviates from the scaling relation. The mass normalization of the relationship between the cluster richness and H.E. mass is compatible with one inferred by matching CAMIRA cluster abundance with a theoretical halo mass function. The mean gas mass fraction based on H.E. masses for the MCXC clusters is

Embedded Spiral Patterns in the Cool Core of the Massive Cluster of Galaxies Abell 1835

\langle f_{\rm gas} \rangle = 0.125\pm0.012

A Cool Core Disturbed: Observational Evidence for the Coexistence of Subsonic Sloshing Gas and Stripped Shock-heated Gas around the Core of RX J1347.5–1145

at spherical overdensity

Gas bulk motion in galaxy clusters

\Delta=500

The Sunyaev–Zel'dovich effect at 5″: RX J1347.5−1145 imaged by ALMA

, which is

In-orbit performance of the soft X-ray imaging system aboard Hitomi (ASTRO-H)

\sim80-90

Modeling the spectral response for the soft X-ray imager onboard the ASTRO-H satellite

percent of the cosmic mean baryon fraction,

Soft X-ray Imager aboard Hitomi (ASTRO-H)

\Omega_b/\Omega_m

The Soft X-ray Imager (SXI) aboard Hitomi (ASTRO-H)

, measured by cosmic microwave background experiments. We find that the mean baryon fraction estimated from X-ray and HSC-SSP optical data is comparable to