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2012-07

Measurement of Mass Distribution of Dark Matter Using Weak Gravitational Lensing /Nature and Nurture Effects on the Formation and Evolution of Cluster Galaxies /the determination of the masses of dark matter halos by clustering properties of sBzK galaxies

[Speaker 1]
Junya Sakurai
[Title]
Measurement of Mass Distribution of Dark Matter Using Weak Gravitational Lensing
[Abstract]
According to the observational results from high-z supernovae and CMB, the universe almost consists of the dark matter and the dark energy.
Unfortunately, these components haven’t entirely understood yet. To understand these unknown objects, some techniques are proposed. One of these techniques is the gravitational lensing. The gravitational lensing is the effect that the shape of the background galaxy is distorted by the foreground object. We can estimate the mass
distribution of the foreground object from the distortion of the background galaxy. Even if the foreground object is the dark matter, we can estimate the mass distribution of the dark matter. In my talk,
I present the gravitational lensing of the basis of this technique.
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[Speaker 2]
Rhythm Shimakawa
[Title]
Nature and Nurture Effects on the Formation and Evolution of Cluster Galaxies
[Abstract]
In low-redshift clusters, most galaxies appear to be quiescent.
These galaxies tend to be elliptical or S0 galaxies, which constitute conspicuous red-sequence on the color-magnitude diagrams.
In contrast, in high-redshift proto-clusers, galaxies tend to have complicated morphologies and high star-formation rates (SFRs) of 100s $M_\odot/yr$.
Such truncation in star formation activities can be caused by “nature” effects, i.e.\ accelerated galaxy formation in dense environments, and/or by “nurture” effects, i.e.\ galaxy-galaxy interactions/mergers and gas-stripping (e.g.\ Kodama et al. 2001).
Recent works (Daddi et al 2007; Mannucci et al. 2010) have presented double (main and sub) sequences of star forming galaxies on the SFR versus gas-mass plane, and a fundamental metallicity relation (FMR) where gaseous metallicity of star forming galaxies in the SDSS are determined as a function of stellar mass and SFR, both of which describe the modes of star formation and the evolutionary stages of galaxies.
Motivated by these observational phenomena, we now aim to explore these relationships (main/sub sequenes and FMR) in clusters/proto-clusters based on near-infrared specroscopy (FMOS/MOIRCS on Subaru) and ALMA observations (Mahalo-Subaru and Gracias-ALMA projects).
By comparing these relationships in clusters with the field counterparts, we will quantify the roles of environments to shape galaxies, and thus understand the origin of environmentally dependent galaxy formation and evolution.
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[Speaker 3]
Shogo Ishikawa
[Title]
the determination of the masses of dark matter halos by clustering properties of sBzK galaxies
[Abstract]
The existence of vast “dark matter halos” around luminous galaxies is strongly implied by some evidence. It is extremely difficult, however, to measure the masses of high-redshift galaxies’ dark matter halos.
One method to quantify them is to measure the amplitude of galaxy clustering, since CDM models predict a monotonic correlation that more massive halos are clustered more strongly. Measuring galaxy clustering requires a large sample from wide area.However, it is still hard to do this at z~2, where BzK color selection can allow us to accumulate larger samples, due to a lack of combination of wide optical and NIR data. I will show our challenge to overcome this difficulty.
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Spectroscopy of blue straggler stars in Galactic open cluster NGC 2682 (M67) / VERA observations of SiO masers in Symbiotic star R Aquarii

[Speaker 1]
Zhao Zhengshi
[Title]
Spectroscopy of blue straggler stars in Galactic open cluster NGC 2682 (M67)
[Abstract]
In this presentation, we report spectroscopic analysis of eight blue straggler stars (BSSs) and three turn-off stars (TOs) in the old open cluster (OC) NGC 2682. From the high resolution (R~60,000) spectra obtained by the Subaru / HDS, we derived radial velocity, rotation velocity, and calculated chemical abundances of lithium, carbon and oxygen. Radial velocity of the target stars is consistent with the mean radial velocity of member stars of the cluster. Thus, we confirm the targets are indeed the real members of the cluster. Rotation velocity of BSSs distributes in a wide range of few km/s to hundred km/s, while those of TOs is restricted to a small value (vsini ≦7 km/s) . Both mass transfer scenario and collision scenario are expected to spin up BSSs. Target stars with measured Li abundances show a good agreement to the trend between A(Li) and Teff found in previous works . Moreover, BSSs have C and O abundances not significantly different from those of the TOs. Exceptions are BSS S997 and S1273. S997 shows a slight enhancement in O abundance, while S1273 shows a significant depletion in C abundance and a slight depletion in O abundance compared to other BSSs and TOs in the same cluster. These anomalies in C and O abundances may be interpreted by mass transfer scenario.
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[Speaker 2]
Cheul Hong Min
[Title]
VERA observations of SiO masers in Symbiotic star R Aquarii
[Abstract]
R Aquarii (R Aqr) is one of the closest symbiotic systems and one of the SiO maser sources associated with the Mira variable in Symbiotic star. These systems are very interesting target, and R Aqr is very exciting laboratory because of the existence of jet-like feature.
Though observations of the system have not yielded consistent values of the orbital parameters, the binary parameters of the orbit give an evidence whether or not Roche lobe outflow in the long period variable and interacting stellar winds of the formation of accretion disk and jet in secondary star. VERA has performed the observations toward R
Aqr since 2004. VERA its unique observation system is a powerful tool for astrometry, and we can hopefully obtain information about its orbital motions. In this presentation, I will present the result of VERA observations for R Aqr.

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