福島 光太郎

Observations of the hot X-ray emitting interstellar medium in the Milky Way are important for studying the stellar feedback and for understanding the formation and evolution of galaxies. We present measurements of the soft X-ray background emission for 130 Suzaku observations at 75° < l < 285° and |b| > 15°. With the standard soft X-ray background model consisting of the local hot bubble and of the Milky Way halo, residual structures remain at 0.7-1 keV in the spectra of some regions. Adding a collisional-ionization-equilibrium component with a temperature of ∼0.8 keV, much higher than the virial temperature of the Milky Way, significantly reduces the derived C-statistic for 56 out of 130 observations. The emission measure of the 0.8 keV component varies by more than an order of magnitude: assuming the solar abundance, the median value is and the 16th-84th percentile range is. Regions toward the Orion-Eridanus superbubble, having a large cavity extending from the Ori OB1 association, have the highest emission measures of the 0.8 keV component. While the scatter is large, the emission measures tend to be higher toward lower galactic latitudes. We discuss possible biases caused by the solar wind charge exchange, stars, and background groups. The 0.8 keV component is probably heated by supernovae in the Milky Way disk, possibly related to Galactic fountains.

Chemical elements in the hot medium permeating early-type galaxies, groups, and clusters make such objects an excellent laboratory for studying metal enrichment and cycling processes on the largest scales of the universe. Here, we report the analysis by the XMM-Newton Reflection Grating Spectrometer of 14 early-type galaxies, including the well-known brightest cluster galaxies of Perseus, for instance. The spatial distribution of the O/Fe, Ne/Fe, and Mg/Fe ratios is generally flat in the central 60″ regions of each object, irrespective of whether or not a central Fe abundance drop has been reported. Common profiles between noble gas and normal metal suggest that the dust depletion process does not work predominantly in these systems. Therefore, observed abundance drops are possibly attributed to other origins, such as systematics in the atomic codes. Giant systems with a high ratio of gas mass to luminosity tend to hold a hot gas (∼2 keV) yielding the solar N/Fe, O/Fe, Ne/Fe, Mg/Fe, and Ni/Fe ratios. Contrarily, light systems in a sub-keV temperature regime, including isolated or group-centered galaxies, generally exhibit supersolar N/Fe, Ni/Fe, Ne/O, and Mg/O ratios. We find that the latest supernova nucleosynthesis models fail to reproduce such a supersolar abundance pattern. Possible systematic uncertainties contributing to these high abundance ratios of cool objects are also discussed in tandem with the crucial role of future X-ray missions.

We present measurements of the soft X-ray background emission for 130 Suzaku observations at 75◦ < l < 285◦ and |b| > 15◦ obtained from 2005 to 2015, covering nearly one solar cycle. In addition to the standard soft X-ray background model consisting of the local hot bubble and the Milky Way Halo (MWH), we include a hot collisional-ionization-equilibrium component with a temperature of ∼0.8 keV to reproduce spectra of a significant fraction of the lines of sight. Then, the scatter in the relation between the emission measure vs. temperature of the MWH component is reduced. Here, we exclude time ranges with high count rates to minimize the effect of the solar wind charge exchange (SWCX). However, the spectra of almost the same lines of sight are inconsistent. The heliospheric SWCX emissions likely contaminate and give a bias in measurements of temperature and the emission measure of the MWH. Excluding the data around the solar maximum and using the data taken before the end of 2009, at |b| > 35◦ and 105◦ < l < 255◦, the temperature (0.22 keV) and emission measure (2 × 10−3 cm−6 pc) of the MWH are fairly uniform. The increase of the emission measure toward the lower Galactic latitude at |b| < 35◦ indicates the presence of a disk-like morphology component. A composite model which consists of disk-like and spherical-morphology components also reproduces the observed emission measure distribution of MWH. In this case, the hydrostatic mass at a few tens of kiloparsec from the Galactic center agrees with the gravitational mass of the Milky Way. The plasma with the virial temperature likely fills the Milky Way halo in nearly hydrostatic equilibrium. Assuming a gas metallicity of 0.3 solar, the upper limit of the gas mass of the spherical component out to 250 kpc, or the virial radius, is ∼ a few × 1010 M☉

Here, we present results from over 500 ksChandra and XMM-Newton observations of the cool core of the Centaurus cluster. We investigate the spatial distributions of the O, Mg, Si, S, Ar, Ca, Cr, Mn, Fe, and Ni abundances in the intracluster medium with CCD detectors, and those of N, O, Ne, Mg, Fe, and Ni with the Reflection Grating Spectrometer (RGS). The abundances of most of the elements show a sharp drop within the central 18 arcsec, although different detectors and atomic codes give significantly different values. The abundance ratios of the above elements, including Ne/Fe with RGS, show relatively flat radial distributions. In the innermost regions with the dominant Fe-L lines, the measurements of the absolute abundances are challenging. For example, AtomDB and SPEXACT give Fe = 0.5 and 1.4 solar, respectively, for the spectra from the innermost region. These results suggest some systematic uncertainties in the atomic data and response matrices at least partly cause the abundance drop rather than the metal depletion into the cold dust. Except for super-solar N/Fe and Ni/Fe, sub-solar Ne/Fe, and Mg/Fe, the abundance pattern agrees with the solar composition. The entire pattern is challenging to reproduce with the latest supernova nucleosynthesis models. Observed super-solar N/O and comparable Mg abundance to stellar metallicity profiles imply that the mass-loss winds dominate the intracluster medium in the brightest cluster galaxy. The solar Cr/Fe and Mn/Fe ratios indicate a significant contribution of near-and sub-Chandrasekhar mass explosions of Type Ia supernovae.