Yasushi Ikebe - Academia.edu (original) (raw)

Papers by Yasushi Ikebe

arXiv (Cornell University), Feb 23, 2004

We present XMM-Newton results on the spatially resolved temperature profiles of eight massive gal... more We present XMM-Newton results on the spatially resolved temperature profiles of eight massive galaxy clusters of a volume-limited sample at redshifts z ∼ 0.3 (REFLEX-DXL sample) and an additional luminous cluster at z = 0.2578, selected from the REFLEX survey. Useful temperature measurements could be performed out to radii with overdensity 500 (r500). The scaled temperature distributions show good similarities. We discovered diversities in the temperature gradients at the outer cluster radii with examples of both flat and strongly decreasing profiles which call for different physical interpretations. We found an indication of the 'warm-hot' gas existing in or around the hot clusters. Using RXCJ0307.0−2840 we demonstrate that the errors on the mass estimates are within 25% up to r500.

We present XMM-Newton results on the spatially resolved X-ray properties of the galaxy clusters a... more We present XMM-Newton results on the spatially resolved X-ray properties of the galaxy clusters at medium redshifts. Useful temperature measurements could be performed out to radii with overdensity 500. The scaled temperature distributions show good similarities. The high resolution temperature and pressure distributions contribute to a more accurate gravitational mass and gas mass fraction measurements, which can be used not

Origin of Matter and Evolution of Galaxies 2003, 2004

ABSTRACT

Implications of the abundance measurement in the hot plasma in clusters of galaxies and in ellipt... more Implications of the abundance measurement in the hot plasma in clusters of galaxies and in elliptical galaxies with ASCA are summarized. Clusters show narrow concentration of the iron abundance at 0.35 solar for different temperatures of the intracluster medium for 2 - 7 keV. Four clusters with kT = 3-5 keV show very good agreement with the isothermal hot gas. Elliptical galaxies indicate low (<1 solar) metal abundance in the interstellar medium, which is now established with the detection of silicon K lines. The abundances are close to or even lower than the stellar metallicity. The authors discuss possible causes of the low metal abundance in elliptical galaxies.

Advances in Space Research, 2000

ABSTRACT Recent ASCA results on the distributions of METALLICITY and temperature are presented. F... more ABSTRACT Recent ASCA results on the distributions of METALLICITY and temperature are presented. Following the discovery of a large-scale gradient in the iron abundance in AWM7, Perseus cluster and A4059 also show very similar features. The close distribution of iron mass density with that of galaxies suggests that the metals are not significantly mixed or settled in the intracluster medium. The north-east and south regions of the Virgo cluster have been mapped with ASCA by more than 30 pointings. The energy spectrum shows a remarkable hardening in the region between M87 and M49. This feature is possibly related with the falling of M49 subcluster into the main M87 cluster.

The Astrophysical Journal, 1992

Observations of the cD galaxy NGC 1399 in the Fornax cluster of galaxies with Ginga have detected... more Observations of the cD galaxy NGC 1399 in the Fornax cluster of galaxies with Ginga have detected extended X-ray emission out to a radius of more than about 360 kpc. The energy spectrum of this emission is well fitted with an optically thin thermal spectrum with kT = 1.46 +0.05/-0.21 keV with a strong iron emission line corresponding to an iron abundance of 1.1 +1.3/-0.5 times solar. The mass of the hot gas responsible for X-ray emission is nearly the same as the total stellar mass of the cluster. Therefore the presence of iron at near-solar abundance suggests that the mass of the hot gas ejected from galaxies is comparable to the total stellar mass. This result indicates that most of the hot gas in a very poor cluster is created through ejections from galaxies, rather than being primordial.

Publications of the Astronomical Society of Japan, 1996

We report on the first result concerning the Ophiuchus cluster of galaxies observed with ASCA dur... more We report on the first result concerning the Ophiuchus cluster of galaxies observed with ASCA during the performance-verification phase. The obtained image in the energy range of 0.7-10 keV is nearly circular, and the peak of the X-ray surface brightness is coincident with the position of the cD galaxy. We analyzed the ASCA GIS data within a 13.'8 radius of the cluster center while considering the energy-dependent fluxcontaminated effect due to ASCA X-ray telescope. This data can be well explained with the isothermal /3 model, in which the density profile is expressed with a j3 profile of r core = 3.'8 and f3 = 0.62, and the temperature and metal abundances are constant at kT = 9.8 keV and Z = 0.24 Z®. The central excess density profile obtained with Einstein HRI is also consistent with the ASCA GIS data.

Symposium - International Astronomical Union, 2004

Based on XMM-Newton observations of M 87 and the Centaurus cluster, abundance profiles of various... more Based on XMM-Newton observations of M 87 and the Centaurus cluster, abundance profiles of various elements of the intracluster medium (ICM) are derived. The abundances of Si and Fe show strong decreasing gradients. In contrast, the O and Mg abundances are about half of the Si abundance at the center.From the gas mass to stellar mass ratio and the comparison of Mg abundance with the stellar metallicity, the stellar mass loss from the central galaxies is indicated to be the main source of gas in the very central region of the clusters.The observed O, Si and Fe abundance pattern determines the contribution of supernova (SN) Ia and SN II, with the abundance pattern of ejecta of SN Ia. Most of the Si and Fe of the ICM in the central region of the clusters comes from SN Ia which occured in the central galaxies. In order to explain the observed O/Si ratio of a half solar, SN Ia products should have similar abundances of Si and Fe, which may reflect dimmer SN Ia observed in old stellar syst...

New Century of X Ray Astronomy, 2001

Astronomy and Astrophysics

We report the analysis of a very deep ROSAT HRI observation on one of the most interesting, dista... more We report the analysis of a very deep ROSAT HRI observation on one of the most interesting, distant lensing clusters, Cl0024+17. Using the X-ray surface brightness we analyse the cluster morphology and constrain the gas and gravitational mass of the cluster. We confirm the small core radius of the mass halo of 66 −25 +38 h −1 50 kpc for this cluster inferred previously from a detailed strong lensing analysis by Tyson et al. (1998) and Smail et al. (1997). Using estimated gas temperatures we find a cluster mass of about 3-14 • 10 14 h −1 50 M for a fiducial radius of 3h −1 50 Mpc. This mass is lower than the mass implied by the weak lensing result of Bonnet et al. (1994) and inconsistent with a virial analysis based on the high observed galaxy velocity dispersion. The lower gravitational mass found in the present study implies, however, a gas mass fraction of the cluster e.g. at 1h −1 50 Mpc radius of 17(11-28) h −1.5 50 % well consistent with the general observations in rich clusters. This favours a lower mass value for the relaxed part of Cl0024+17 which could still be embedded in a larger structure achieving a consistency with the weak lensing observations.

Publications of the Astronomical Society of Japan, 2001

We present two-dimensional temperature maps of three bright clusters of galaxies (Abell 1060, AWM... more We present two-dimensional temperature maps of three bright clusters of galaxies (Abell 1060, AWM 7, and the Centaurus cluster), based on multi-pointing observations with the ASCA GIS. The temperatures were derived from hardness ratios by taking into account the XRT response. For the Centaurus cluster, we subtracted the central cool component using the previous ASCA and ROSAT results, and the metallicity gradients observed in AWM 7 and the Centaurus cluster were included in deriving the temperatures. The intracluster medium in Abell 1060 and AWM 7 is almost isothermal from the center to the outer regions with temperatures of 3.3 and 3.9 keV, respectively. The Centaurus cluster exhibits remarkable hot regions within about 30 from the cluster center, showing a temperature increase of + 0.8 keV from the surrounding level of 3.5 keV, and the outer cool regions with lower temperatures by −1.3 keV. These results imply that a strong merger has occurred in the Centaurus in the recent 2-3 Gyr, and that the central cool component has survived it. In contrast, the gas in Abell 1060 was well-mixed in an early period, which probably has prevented the development of a central cool component. In AWM 7, mixing of the gas should have occurred in a period earlier than the epoch of metal enrichment.

Using XMM-Newton, we observed 14 distant X-ray luminous (¢ ¡ ¤ £ ¦ ¥ §) galaxy clusters selected ... more Using XMM-Newton, we observed 14 distant X-ray luminous (¢ ¡ ¤ £ ¦ ¥ §) galaxy clusters selected from the REFLEX survey (REFLEX-DXL sample). We derived the X-ray properties of the REFLEX-DXL galaxy clusters using a double background subtraction method in Zhang et al. (2004). Cluster mass measurements based on the X-ray data have been used to study the X-ray galaxy cluster scaling relations and their intrinsic scatter. This is important for the use of clusters of galaxies as cosmological probes. We found that the X-ray properties of the REFLEX-DXL sample show an approximate self-similar behavior above 0.15-0.2 virial radii. This helps us to establish tight cluster mass-observables scaling relations, in particular the¨-© relation with a scatter of 0.3 for .

Based on a detailed study of the temperature structure of the intracluster medium in the halo of ... more Based on a detailed study of the temperature structure of the intracluster medium in the halo of M 87 and the Centaurus cluster, abundance profiles of O, Mg, Si and Fe are derived. In addition, abundance ratios are derived from the ratios of line strengths, whose temperature dependences are small within the temperature range of the ICM. The abundances of Si and Fe show strong decreasing gradients. The Fe/Si ratio is determined to be 0.9 solar with no radial gradient. In contrast, the O abundance is less than a half of the Si abundance at the center and has a flatter gradient. The Mg abundance is close to stellar abundance within the same radius. The observed O/Si/Fe pattern is located at the simple extension of that of Galactic stars. The O/Si/Fe ratio indicates that the SN Ia contribution to Si and Fe becomes important towards the center and SN Ia products have similar abundances of Si and Fe at the center, which may reflect dimmer SN Ia observed in old stellar systems.