The UV-upturn in brightest cluster galaxies

This paper is part of a series devoted to the investigation of a large sample of brightest cluster galaxies (BCGs), their properties and the relationships between these and the properties of the host clusters. In this paper, we compare the stellar population properties derived from high signal-to-noise, optical long-slit spectra with the GALEX ultraviolet (UV) colour measurements for 36 nearby BCGs to understand the diversity in the most rapidly evolving feature in old stellar systems, the UV-upturn. We investigate: (1) the possible differences between the UV-upturn of BCGs and those of a control sample of ordinary ellipticals in the same mass range, as well as possible correlations between the UV-upturn and other general properties of the galaxies; (2) possible correlations between the UV-upturn and the properties of the host clusters; (3) recently proposed scenarios where helium-sedimentation in the cluster centre can produce an enhanced UV-upturn. We find systematic differences between the UV-colours of BCGs and ordinary ellipticals, but we do not find correlations between these colours and the properties of the host clusters. Furthermore, the observations do not support the predictions made by the helium-sedimentation model as an enhancer of the UV-upturn.Comment: 12 pages, accepted for publication in MNRA

Detector developments for the hypernuclear programme at PANDA

The technical design of the PANDA experiment at the future FAIR facility next to GSI is progressing. At the proposed anti-proton storage ring the spectroscopy of double Lambda hypernuclei is one of the four main topics which will be addressed by the Collaboration. The hypernuclear experiments require (i) a dedicated internal target, (ii) an active secondary target of alternating silicon and absorber material layers, (iii) high purity germanium (HPGe) detectors, and (iv) a good particle identification system for low momentum kaons. All systems need to operate in the presence of a high magnetic field and a large hadronic background. The status of the detector developments for this programme is summarized.Comment: Contributed to 2008 IEEE Nuclear Science Symposium, 19-25 October 2008, Dresden, German

Chandra and optical/IR observations of CXOJ1415.2+3610, a massive, newly discovered galaxy cluster at z~1.5

(Abridged) We report the discovery of CXO J1415.2+3610, a distant (z~1.5) galaxy cluster serendipitously detected in a deep, high-resolution Chandra observation targeted to study the cluster WARP J1415.1+3612 at z=1.03. This is the highest-z cluster discovered with Chandra so far. Moreover, the total exposure time of 280 ks with ACIS-S provides the deepest X-ray observation currently achieved on a cluster at z>1.5. We perform an X-ray spectral fit of the extended emission of the intracluster medium (ICM) with XSPEC, and we detect at a 99.5% confidence level the rest frame 6.7-6.9 keV Iron K_\alpha line complex, from which we obtain z_X=1.46\pm0.025. The analysis of the z-3.6\mu m color-magnitude diagram shows a well defined sequence of red galaxies within 1' from the cluster X-ray emission peak with a color range [5 < z-3.6 \mu m < 6]. The photometric redshift obtained by spectral energy distribution (SED) fitting is z_phot=1.47\pm 0.25. After fixing the redshift to z=1.46, we perform the final spectral analysis and measure the average gas temperature with a 20% error, kT=5.8^{+1.2}_{-1.0} keV, and the Fe abundance Z_Fe = 1.3_{-0.5}^{+0.8}Z_\odot. We fit the background subtracted surface brightness with a single beta--model out to 35" and derive the deprojected electron density profile. The ICM mass is 1.09_{-0.2}^{+0.3}\times 10^{13} M_\odot within 300 kpc. The total mass is M_{2500}= 8.6_{-1.7}^{+2.1} \times 10 ^{13} M_\odot for R_{2500}=(220\pm 55) kpc. Extrapolating the profile at larger radii we find M_{500}= 2.1_{-0.5}^{+0.7} \times 10 ^{14} M_\odot for R_{500} = 510_{-50}^{+55}$ kpc. This analysis establishes CXOJ1415.2+3610 as one of the best characterized distant galaxy clusters based on X-ray data alone.Comment: 12 pages, 9 figures, A\&A in press, minor modifications in the tex