Subaru weak-lensing study of A2163: bimodal mass structure

We present a weak-lensing analysis of the merging cluster A2163 using Subaru/Suprime-Cam and CFHT/Mega-Cam data and discuss the dynamics of this cluster merger, based on complementary weak-lensing, X-ray, and optical spectroscopic datasets. From two dimensional multi-component weak-lensing analysis, we reveal that the cluster mass distribution is well described by three main components, including a two component main cluster A2163-A with mass ratio 1:8, and its cluster satellite A2163-B. The bimodal mass distribution in A2163-A is similar to the galaxy density distribution, but appears as spatially segregated from the brightest X-ray emitting gas region. We discuss the possible origins of this gas-dark matter offset and suggest the gas core of the A2163-A subcluster has been stripped away by ram pressure from its dark matter component. The survival of this gas core to the tidal forces exerted by the main cluster let us infer a subcluster accretion with a non-zero impact parameter. Dominated by the most massive component of A2163-A, the mass distribution of A2163 is well described by a universal Navarro-Frenk-White profile as shown by a one-dimensional tangential shear analysis, while the singular-isothermal sphere profile is strongly ruled out. Comparing this cluster mass profile with profiles derived assuming intracluster medium hydrostatic equilibrium (H.E.) in two opposite regions of the cluster atmosphere has allowed us to confirm the prediction of a departure from H.E. in the eastern cluster side, presumably due to shock heating. Yielding a cluster mass estimate of M_{500}=11.18_{-1.46}^{+1.64}\times10^{14}h^{-1}Msun, our mass profile confirm the exceptionally high mass of A2163, consistent with previous analyses relying on the cluster dynamical analysis and Yx mass proxy.Comment: 17 pages, 11 figures, ApJ, in press. Full resolution version is available at http://www.asiaa.sinica.edu.tw/~okabe/files/a2163_WL_astroph.pd

X-ray Spectroscopy of the Virgo Cluster out to the Virial Radius

We present results from the analysis of a mosaic of thirteen XMM-Newton pointings covering the Virgo Cluster from its center northwards out to a radius r~1.2 Mpc (~4.5 degrees), reaching the virial radius and beyond. This is the first time that the properties of a modestly sized (M_vir~1.4e14 M_sun, kT~2.3 keV), dynamically young cluster have been studied out to the virial radius. The density profile of the cluster can be described by a surprisingly shallow power-law with index 1.21+/-0.12. In the radial range of 0.3r_vir<r<r_vir, the best fit temperature drops by roughly 60 per cent. Within a radius r<450 kpc, the entropy profile has an approximate power-law form with index 1.1, as expected for gravitationally collapsed gas in hydrostatic equilibrium. Beyond r~450 kpc, however, the temperature and metallicity drop abruptly, and the entropy profile becomes flatter, staying consistently below the expected value by a factor of 2-2.5. The most likely explanation for the unusually shallow density profile and the flattening of entropy at large radius is clumping in the ICM. Our data provide direct observational evidence that the ICM is enriched by metals all the way to r_200 to at least Z=0.1 Solar.Comment: Accepted for publication in MNRA

Testing the Low-Mass End of X-Ray Scaling Relations with a Sample of Chandra Galaxy Groups

Well-determined scaling relations between X-ray observables and cluster mass are essential for using large cluster samples for cosmology. Cluster relations such as the Lx-T, M-T, Lx-M relations, have been investigated extensively, however the question remains whether these relations hold true also for groups. Some evidence supports a break at low masses, possibly caused by the influence of non-gravitational physics on low-mass systems. The main goal of this work is to test scaling relations for the low-mass range to check whether there is a systematic difference between clusters and groups, and to extend this method of reliable cluster mass determination for future samples down to the group regime. We compiled a statistically complete sample of 112 X-ray galaxy groups, 26 with Chandra data. Temperature, metallicity, and surface brightness profiles were created, and used to determine the main physical quantities and scaling relations. We then compared the group properties to the HIFLUGCS clusters and other samples. We present profiles and scaling relations of the whole sample. T and Z profiles behave universally, except for the cores. The Lx-T, M-T, Lx-M, Mg-M, M-Yx, and Lx-Yx relations are in good agreement with clusters. The Lx-T relation steepens for T<3keV, which could point to a larger impact of heating mechanisms on cooler systems. We found a strong drop in the gas mass fraction below 1keV, which indicates the ICM is less dominant in groups and the galaxies have a stronger influence on the system. In all relations the intrinsic scatter for groups is larger, which appears not correlated with merger activity but could be due to scatter caused by baryonic physics in the group cores. We also demonstrate the importance of selection effects. We have found evidence for a similarity break between groups and clusters. However this does not have a strong effect on scaling relations.Comment: 31 pages, accepted to A&

A Lotus japonicus cytoplasmic kinase connects Nod factor perception by the NFR5 LysM receptor to nodulation

The establishment of nitrogen-fixing root nodules in legume-rhizobia symbiosis requires an intricate communication between the host plant and its symbiont. We are, however, limited in our understanding of the symbiosis signaling process. In particular, how membrane-localized receptors of legumes activate signal transduction following perception of rhizobial signaling molecules has mostly remained elusive. To address this, we performed a coimmunoprecipitation-based proteomics screen to identify proteins associated with Nod factor receptor 5 (NFR5) in Lotus japonicus. Out of 51 NFR5-associated proteins, we focused on a receptor-like cytoplasmic kinase (RLCK), which we named NFR5-interacting cytoplasmic kinase 4 (NiCK4). NiCK4 associates with heterologously expressed NFR5 in Nicotiana benthamiana, and directly binds and phosphorylates the cytoplasmic domains of NFR5 and NFR1 in vitro. At the cellular level, Nick4 is coexpressed with Nfr5 in root hairs and nodule cells, and the NiCK4 protein relocates to the nucleus in an NFR5/NFR1-dependent manner upon Nod factor treatment. Phenotyping of retrotransposon insertion mutants revealed that NiCK4 promotes nodule organogenesis. Together, these results suggest that the identified RLCK, NiCK4, acts as a component of the Nod factor signaling pathway downstream of NFR5

Long-duration gamma-ray emissions from 2007 and 2008 winter thunderstorms

The Gamma-Ray Observation of Winter THunderclouds (GROWTH) experiment, consisting of two radiation-detection subsystems, has been operating since 2006 on the premises of Kashiwazaki-Kariwa nuclear power plant located at the coastal area of Japan Sea. By 2010 February, GROWTH detected 7 long-duration $\gamma$-rays emissions associated with winter thunderstorms. Of them, two events, obtained on 2007 December 13 and 2008 December 25, are reported.On both occasions, all inorganic scintillators (NaI, CsI, and BGO) of the two subsystems detected significant gamma-ray signals lasting for >1 minute. Neither of these two events were associated with any lightning. In both cases, the gamma-ray energy spectra extend to 10 MeV, suggesting that the detected gamma-rays are produced by relativistic electrons via bremsstrahlung. Assuming that the initial photon spectrum at the source is expressed by a power-law function,the observed photons can be interpreted as being radiated from a source located at a distance of 290-560 m for the 2007 event and 110-690 m for the 2008 one, both at 90% confidence level.Employing these photon spectra, the number of relativistic electrons is estimated as 10^9 - 10^{11}. The estimation generally agrees with those calculated based on the relativistic runaway electron avalanche model. A GROWTH photon spectrum, summed over 3 individual events including the present two events and another reported previously, has similar features including a cut-off energy, to an averaged spectrum of terrestrial gamma-ray flashes.Comment: 46 pages, 13 figures, accepted for publication in JGR-Atmospher

Hard X-ray Detector (HXD) on Board Suzaku

The Hard X-ray Detector (HXD) on board Suzaku covers a wide energy range from 10 keV to 600 keV by combination of silicon PIN diodes and GSO scintillators. The HXD is designed to achieve an extremely low in-orbit back ground based on a combination of new techniques, including the concept of well-type active shield counter. With an effective area of 142 cm^2 at 20 keV and 273 cm2 at 150 keV, the background level at the sea level reached ~1x10^{-5} cts s^{-1} cm^{-2} keV^{-1} at 30 keV for the PI N diodes, and ~2x10^{-5} cts s^{-1} cm^{-2} keV^{-1} at 100 keV, and ~7x10^{-6} cts s^{-1} cm^{-2} keV^{-1} at 200 keV for the phoswich counter. Tight active shielding of the HXD results in a large array of guard counters surrounding the main detector parts. These anti-coincidence counters, made of ~4 cm thick BGO crystals, have a large effective area for sub-MeV to MeV gamma-rays. They work as an excellent gamma-ray burst monitor with limited angular resolution (~5 degree). The on-board signal-processing system and the data transmitted to the ground are also described.Comment: 35 pages, 25 figures and 4 tables; acceted for Publication of the Astronomical Society of Japa