arXiv subjects

K. Yoshikawa

Publications and source records attributed to K. Yoshikawa.

22 records · Page 2Linked to original sources

arXiv2004

Exploring Cluster Physics with High-Resolution Sunyaev-Zel'dovich Effect Images and X-Ray Data: The Case of the Most X-Ray-Luminous Galaxy Cluster RX J1347-1145

Foreseeing the era of high spatial resolution measurements of the Sunyaev-Zel'dovich effect (SZE) in clusters of galaxies, we present a prototype analysis of this sort combined with Chandra X-ray data. It is applied specifically to RX J1347-1145 at z=0.451, the most X-ray-luminous galaxy cluster known, for which the highest resolution SZE and X-ray images are currently available. We demonstrate that the combined analysis yields a unique probe of complex structures in the intracluster medium, offering determinations of their temperature, density, and line-of-sight extent. For a subclump in RX J1347-1145, previously discovered in our SZE map, the temperature inferred after removing the foreground and background components is well in excess of 20 keV, indicating that the cluster has recently undergone a violent merger. Excluding the region around this subclump, the SZE signals in submillimeter to centimeter bands (350, 150, and 21 GHz) are all consistent with those expected from Chandra X-ray observations. We further present a temperature deprojection technique based on the SZE and X-ray images, without any knowledge of spatially resolved X-ray spectroscopy. The methodology presented here will be applicable to a statistical sample of clusters available in the future SZE surveys.

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arXiv2002

The UV (GALEX) and FIR (ASTRO-F) All Sky Surveys: the measure of the dust extinction in the local universe

Before the end of 2002 will be launched the GALEX satellite (a NASA/SMEX project) which will observe all the sky in Ultraviolet (UV) through filters at 1500 and 2300 A down to m(AB) 21. In 2004 will be launched the ASTRO-F satellite which will perform an all sky survey at Far-Infrared (FIR) wavelengths. The cross-correlation of both surveys will lead to very large samples of galaxies for which FIR and UV fluxes will be available. Using the FIR to UV flux ratio as a quantitative tracer of the dust extinction we will be able to measure the extinction in the nearby universe (z<0.2) and to perform a statistically significant analysis of the extinction as a function of galactic properties. Of particular interest is the construction of pure FIR and UV selected samples for which the extinction will be measured as templates for the observation of high redshift galaxies.

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arXiv2001

Theoretical Models of Multi-waveband QSO Luminosity Functions

Cosmological evolution of the QSO luminosity functions (LFs) at NIR/optical/X-ray bands for 1.3 < z < 3.5 is investigated based on the realistic QSO spectra. The accretion-disk theory predicts that although QSO luminosities only depend on mass-accretion rate, \Mdot, QSO spectra have a dependence on black-hole mass, M_{BH}, as well. The smaller M_{BH} is and/or the larger \Mdot is, the harder becomes the QSO NIR/optical/UV spectrum. We model disk spectra which can reproduce these features and calculated LFs for redshift z ~ 3 with the assumption of new-born QSOs being shining at the Eddington luminosity. The main results are: (i) the observed LFs at optical and X-rays can be simultaneously reproduced. (ii) LFs at optical and X-ray bands are not sensitive to M_{BH}, while LFs at NIR bands are; about one order of magnitude difference is expected in volume number densities at L_{I, J} ~ 10^{46} erg s^{-1} between the case that all QSOs would have the same spectral shape as that of M_{BH} = 10^{9} M_sun and the case with M_{BH} = 10^{11} M_sun. (iii) The resultant LFs at NIR are dominated by 10^{7} M_sun black-holes at L_{I, J} ~ 10^{44} erg s^{-1}, and by 10^{11} M_sun black-holes at L_{I, J} \~ 10^{46} erg s^{-1}. Future infrared observations from space(e.g.NGST) will probe cosmological evolution of black hole masses. For redshift z < 3, on the other hand, the observed optical/X-ray LFs can be fitted, if the initial QSO luminosity L_0 is below the Eddington luminosity. Interestingly, the best fitting values of l = L_0/L_{Edd} are different in B- and X-ray bands; l_B ~ 2.5 l_X. The reason for this discrepancy is briefly discussed.

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arXiv2000

Cosmic Star Formation History Required from Infrared Galaxy Number Count : Future Prospect for Infrared Imaging Surveyor (IRIS)

We constructed a model of infrared and sub-mm (hereafter IR) galaxy number count and estimated history of the IR luminosity density. We treat the evolutionary change of galaxy luminosities as a stepwise nonparametric form, in order to explore the most suitable evolutionary history which reproduces the present observational results. We found the evolutionary patterns which satisfy both constraints required from Cosmic Infrared Background (CIRB) and IR galaxy number counts. One order of magnitude increase of luminosity at redshift $z=0.75 - 1.0$ was found in IR $60 μ$m luminosity density evolution. We also found that a large number of galaxies ($\sim 10^7$ in the whole sky) will be detected in all-sky survey at far-infrared by Infrared Imaging Surveyor (IRIS); Japanese infrared satellite project Astro-F.

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