Angular correlation studies of the cosmic X-ray background: A new frontier of ICM structure studies

Fluctuations of the surface brightness of the cosmic X-ray background (CXB)  carry  unique information about  faint and low luminosity source populations, which is inaccessible for conventional large-scale structure (LSS) studies based on resolved sources.We  used Chandra data of the XBOOTES field (~9 deg^2) to conduct the most accurate measurement to date of the power spectrum of fluctuations of the unresolved CXB on the angular scales from ~3 arcsec to ~3 degWe find that at sub-arcmin angular scales, the power spectrum is  consistent with the shot noise of unresolved point sources (AGN and normal galaxies), without much need for any significant contribution from the one-halo term of AGN. This is consistent with the theoretical expectation that low-luminosity AGN reside alone in their dark matter halos.However, at larger angular scales above > ~1 arcmin we detect a non-trivial LSS signal, which dominates over the shot-noise of unresolved point sources. After subtracting the latter, the LSS signal follows a power law with an amplitude much larger than what can be plausibly explained by the two-halo term of AGN. We could demonstrate that the detected LSS signal is produced by unresolved clusters and groups of galaxies. The energy spectrum of fluctuations is well described by the redshifted emission spectrum of optically thin plasma with the best fit temperature of T~1.3 keV and the redshift of z~0.40. These numbers are in good agreement with theoretical expectations based on the X-ray luminosity function. From the best fit values we estimate the typical mass and luminosity of the objects responsible for CXB fluctuations, M_500 ~10^{13.6} M_Sun/h and L_{0.5-2.0keV} ~ 10^{42.5} erg/s. On the other hand, the flux weighted mean temperature and redshift of resolved clusters of galaxies are T~2.4 keV and z~0.23, confirming that fluctuations of unresolved CXB are caused by cooler (i.e. less massive) and more distant clusters and groups of galaxies, as expected. We show that the shape of the power spectrum is sensitive to the intra-cluster medium (ICM) structure out to ~few x R_500 (i.e. outskirts). These results underline significant diagnostics potential of the CXB fluctuation analysis in studying the ICM structure in clusters and groups of galaxies.

Alexander Kolodzig (KIAA)
KIAA first floor meeting room
Tue, 2017-08-01 12:00 to 13:00