9208829
A New Measure for Weak-Lensing Flexion
We study the possibility of using the octopole moment of gravitationally lensed images as a direct measure of the third-order weak gravitational lensing effect, or the gravitational flexion. It turns out that there is a natural relation between flexion and certain combinations of octopole/higher multipole moments that we call the higher order lensing image's characteristics (HOLICs). This will allow one to measure directly flexion from observable octopole and higher multipole moments of background images. We show based on simulated observations how the use of HOLICs can improve the accuracy and resolution of a reconstructed mass map, in which we assume Gaussian uncertainties in the shape measurements estimated using deep i'-band data of blank fields observed with Suprime-Cam on the Subaru telescope.
7201989
The build-up of the colour–magnitude relation as a function of environment
We discuss the environmental dependence of galaxy evolution based on deep panoramic imaging of two distant clusters, RX J0152.7-1357 at z = 0.83 and CL0016+ 1609 at z = 0.55, taken with the Subaru Prime Focus Camera on the Subaru Telescope as part of the Panoramic Imaging and Spectroscopy of Cluster Evolution with Subaru project. By combining with the Sloan Digital Sky Survey data as a local counterpart for comparison, we construct a large sample of galaxies that spans wide ranges in environment, time and stellar mass (or luminosity). This allows us to conduct systematic and statistical analyses of the photometric properties of galaxies based on the colour-density diagrams, colour-magnitude relations, and luminosity functions. We find that colours of galaxies, especially those of faint galaxies (M V > M v * + 1), change from blue to red at a break density as we go to denser regions. This trend is observed at all redshifts in our sample. Based on local and global densities of galaxies, we classify three environments - field, groups and clusters - and look into the environmental dependence of galaxies in detail. In particular, we quantify how the colour-magnitude relation is built up as a function of environment. We show that the bright end of the cluster colour-magnitude relation is already built a z = 0.83, while the faint end is possibly still in the process of build-up. In contrast to this, the bright end of the field colour-magnitude relation has been vigorously built all the way down to the present-day and the build-up at the faint end has not started yet. A possible interpretation of these results is that galaxies evolve in a 'down-sizing' fashion. That is, massive galaxies complete their star formation first and the truncation of star formation is propagated to smaller objects as time progresses. This trend is likely to depend on environment since the build-up of the colour-magnitude relation is delayed in lower density environments. Therefore, we may suggest that the evolution of galaxies took place earliest in massive galaxies and in high-density regions, and it is delayed in less massive galaxies and in lower density regions. Further studies are, however, obviously needed to confirm the observed trends and establish the 'down-sizing' picture.
8691447
Star Formation and AGN Activity in Galaxies Classified Using the 1.6 μm Bump and PAH Features at z = 0.4–2
We studied the star-formation and AGN activity of massive galaxies in the redshift range z = 0.4-2, which were detected in a deep survey field using the AKARI InfraRed (IR) astronomical satellite and Subaru telescope toward the North Ecliptic Pole (NEP). The AKARI/IRC Mid-InfraRed (MIR) multiband photometry was used to trace the star-forming activities with Polycyclic Aromatic Hydrocarbon (PAH) emission, which is effective not only to distinguish between star-forming and AGN galaxies, but also to estimate the Star Formation Rate (SFR) with converting its flux to the total emitting IR (TIR) luminosity. In combination with the analyses of the stellar components, we studied the MIR SED features of star-forming and AGN-harboring galaxies, which we summarize below: (1) The rest-frame 7.7-μm and 5-μm luminosities are good tracers of star-forming and AGN activities from their PAH and dusty tori emissions, respectively. (2) For dusty star-forming galaxies without AGN, their SFR shows a correlation that is nearly proportional to their stellar mass, and their specific SFR (sSFR) per unit stellar mass increases with redshift. Extinctions estimated from their TIR luminosities are larger than those from their optical SED fittings, which may be caused by geometric variations of dust in them. (3) Even for dusty star-forming galaxies with AGN, SFRs can be derived from their TIR luminosities with subtraction of the obscured AGN contribution, which indicates that their SFRs were possibly quenched around z ≃ 0.8 compared with those without AGN. (4) The AGN activity from their rest-frame 5-μm luminosity suggests that their Super Massive Black Holes (SMBHs) could already have grown to ≃ 3 × 10 8 M ⊙ in most massive galaxies with 10 11 M ⊙ at z > 1.2, and the mass relation between SMBHs and their host galaxies has already become established by z ≃ 1-2.
118543928
Detailed cluster mass and light profiles of A1703, A370 and RXJ1347−11 from deep Subaru imaging*
Weak lensing work can be badly compromised by unlensed foreground and cluster members which dilute the true lensing signal. We show how the lensing amplitude in multicolour space can be harnessed to securely separate cluster members from the foreground and background populations for three massive clusters, A1703 (z= 0.258), A370 (z= 0.375) and RXJ1347−11 (z= 0.451) imaged with Subaru. The luminosity functions of these clusters when corrected for dilution show similar faint-end slopes, α≃− 1.0, with no marked faint-end upturn to our limit of MR≃− 15.0, and only a mild radial gradient. In each case, the radial profile of the mass-to-light ratio (M/L) peaks at intermediate radius, ≃ 0.2rvir, at a level of 300–500(M/LR)⊙, and then falls steadily towards ∼ 100(M/LR)⊙ at the virial radius, similar to the mean field level. This behaviour is likely due to the relative paucity of central late-type galaxies, whereas for the E/S0 sequence only a mild radial decline in M/L is found for each cluster. We discuss this behaviour in the context of detailed simulations where predictions for tidal stripping may now be tested accurately with observations.
16007678
AMiBA WIDEBAND ANALOG CORRELATOR
A wideband analog correlator has been constructed for the Yuan-Tseh Lee Array for Microwave Background Anisotropy. Lag correlators using analog multipliers provide large bandwidth and moderate frequency resolution. Broadband intermediate frequency distribution, back-end signal processing, and control are described. Operating conditions for optimum sensitivity and linearity are discussed. From observations, a large effective bandwidth of around 10 GHz has been shown to provide sufficient sensitivity for detecting cosmic microwave background variations.
122282339
The Yuan Tseh Lee AMiBA project
The Array for Microwave Background Anisotropy is a 7-element interferometer sited on Mauna Loa, Hawaii. The seven 60cm telescopes are mounted on a 6-meter platform, and operates at 3mm wavelength. In October 2006, the telescope was officially dedicated and renamed as the Y. T. Lee AMiBA. During 2007, scientific operations have begun, after a long process of calibration and testing. At the time of this meeting, six clusters of galaxies have been detected and mapped via the inverse Compton scattering of the Cosmic Microwave Background radiation, also known as the Sunyaev-Zel'dovich Effect.
6921270
Ward Identities in the derivation of Hawking radiation from Anomalies
Robinson and Wilczek suggested a new method of deriving Hawking radiation by the consideration of anomalies. The basic idea of their approach is that the flux of Hawking radiation is determined by anomaly cancellation conditions in the Schwarzschild black hole (BH) background. Iso et al. extended the method to a charged Reissner-Nordstroem BH and a rotating Kerr BH, and they showed that the flux of Hawking radiation can also be determined by anomaly cancellation conditions and regularity conditions of currents at the horizon. Their formulation gives the correct Hawking flux for all the cases at infinity and thus provides a new attractive method of understanding Hawking radiation. We present some arguments clarifying for this derivation. We show that the Ward identities and boundary conditions for covariant currents without referring to the Wess-Zumino terms and the effective action are sufficient to derive Hawking radiation. Our method, which does not use step functions, thus simplifies some of the technical aspects of the original formulation.
118634145
Hawking radiation as tunneling from squashed Kaluza-Klein black hole
We discuss Hawking radiation from a five-dimensional squashed Kaluza-Klein black hole on the basis of the tunneling mechanism. A simple method, which was recently suggested by Umetsu, may be used to extend the original derivation by Parikh and Wilczek to various black holes. That is, we use the two-dimensional effective metric, which is obtained by the dimensional reduction near the horizon, as the background metric. Using the same method, we derive both the desired result of the Hawking temperature and the effect of the backreaction associated with the radiation in the squashed Kaluza-Klein black hole background.