An X-Ray Detection Possibility of Star-Formation-Bursting Proto-Elliptical Galaxies

A possibility to detect X-rays from star-formation burst activities in proto-elliptical galaxies is considered. The X-ray flux of an emission due to inverse Compton scattering of the cosmic microwave background (CMB) by high energy electrons accelerated in SNRs is shown to increase as z increases far beyond unity, since the local CMB flux largely increases in association with a z-increase. The flux is estimated for the case of a very high rate of type II supernovae at an initial star formation burst of a proto-elliptical galaxy and is found to be detectable with a future large X-ray telescope such as intended in the XEUS mission.Comment: 4 pages, 1 figure, will appear in PAS

Detection of highly ionized O and Ne absorption lines in the X-ray spectrum of 4U1820-303 in the globular cluster, NGC 6624

We searched for absorption lines of highly ionized O and Ne in the energy spectra of two Low-mass X-ray binaries, 4U1820-303 in the globular cluster NGC6624 and Cyg X-2, observed with the Chandra LETG, and detected O VII, O VIII and Ne IX absorption lines for 4U1820-303. The equivalent width of the O VII K alpha line was 1.19 +0.47/-0.30 eV (90 % errors) and the significance was 6.5 sigma. Absorption lines were not detected for Cyg X-2 with a 90 % upper limit on the equivalent width of 1.06 eV for O VII K alpha. The absorption lines observed in 4U1820-303 are likely due to hot interstellar medium, because O will be fully photo-ionized if the absorbing column is located close to the binary system. The velocity dispersion is restricted to b = 200 - 420 km/s from consistency between O VII K alpha and K beta lines, Ne/O abundance ratio, and H column density. The average temperature and the O VII density are respectively estimated to be log(T[K]) = 6.2 - 6.3 and n(OVII) = (0.7 - 2.3) x 10^{-6} cm^{-3}. The difference of O VII column densities for the two sources may be connected to the enhancement of the soft X-ray background (SXB) towards the Galactic bulge region. Using the polytrope model of hot gas to account for the SXB we corrected for the density gradient and estimated the midplane O VII density at the solar neighborhood. The scale height of hot gas is then estimated using the AGN absorption lines. It is suggested that a significant portion of both the AGN absorption lines and the high-latitude SXB emission lines can be explained by the hot gas in our Galaxy.Comment: Accepted for publication in ApJ. 7 pages, 9 eps figure

Metallicity of the Fossil Group NGC 1550 Observed with Suzaku

We studied the temperature and metal abundance distributions of the intra-cluster medium (ICM) in a group of galaxies NGC 1550 observed with Suzaku. The NGC 1550 is classified as a fossil group, which have few bright member galaxies except for the central galaxy. Thus, such a type of galaxy is important to investigate how the metals are enriched to the ICM. With the Suzaku XIS instruments, we directly measured not only Si, S, and Fe lines but also O and Mg lines and obtained those abundances to an outer region of ~0.5 r_180 for the first time, and confirmed that the metals in the ICM of such a fossil group are indeed extending to a large radius. We found steeper gradients for Mg, Si, S, and Fe abundances, while O showed almost flat abundance distribution. Abundance ratios of alpha-elements to Fe were similar to those of the other groups and poor clusters. We calculated the number ratio of type II to type Ia supernovae for the ICM enrichment to be 2.9 +- 0.5 within 0.1 r_180, and the value was consistent with those for the other groups and poor clusters observed with Suzaku. We also calculated metal mass-to-light ratios (MLRs) for Fe, O and Mg with B-band and K-band luminosities of the member galaxies of NGC 1550. The derived MLRs were comparable to those of NGC 5044 group in the r<0.1 r_180 region, while those of NGC 1550 are slightly higher than those of NGC 5044 in the outer region.Comment: 11 pages, 7 figures, accepted for publication in PAS