Subaru Seminars

Redshift 6, one billion years after the Big Bang, marks the end of the reionization epoch. A crucial question is whether the UV flux from young starbursts at this redshift is sufficient to achieve this reionzation. We have used the Lyman break technique to identify candidate star-forming galaxies at this redshift in deep HST/ACS images, including the Hubble Ultra Deep Field. We have recently pushed our sample to galaxies at redshifts 7-10 using new WFC3 images. Some of these z~6 galaxies exhibit Balmer breaks in mid-IR Spitzer data, indicating that a subset have evolved stellar populations even within the first billion years after the Big Bang, indicating star formation commenced at even higher redshifts. Spectroscopic confirmation of this population is crucial, to guard against low-redshift interlopers and to study the Lyman-alpha emission line properties of z~6 galaxies. We have undertaken the deepest spectroscopy yet to achieve this.

The Local Cluster Substructure Survey (LoCuSS) is a study of a statistically complete sample of 80 galaxy clusters at z=0.2 with the Subaru telescope, and a wide range of space- and ground- based facilities. The main goals are (i) to measure definitively the mass-observable scaling relations upon which cluster-based attempts to measure the dark energy equation of state parameter w will rely, and (ii) to measure the cluster-cluster scatter in the star-formation rates and histories of galaxy clusters as part of a broad community-wide effort to understand the physical origin of S0 galaxies. Our results will also define a low-redshift benchmark that will aide the interpretation of the growing menagerie of high-redshift cluster samples in the coming decades. I will present an overview of the survey, and describe our recent results, including those from our ongoing Herschel Key Programme of far-infrared observations with PACS and SPIRE.

The Sunyaev-Zel'dovich effect (SZE), the inverse Compton scattering of CMB photons off hot electrons, provides a unique probe of the intracluster medium. We show how high angular resolution observations of the SZE can reveal the thermal structures of galaxy clusters including the shocks associated with violent mergers. ALMA will be particularly powerful for this purpose and play complementary roles in tracing cluster evolution to other facilities including Subaru and ASTRO-H. We also discuss how the imprint of gas inhomogeneities at even smaller scales can bias the measurements of cosmological parameters, such as H_0 from the SZE and X-ray joint analysis. Apparent agreement of the H_0 value with those derived from other methods, e.g., CMB, is shown to degrade once recent changes in the Chandra calibration database are taken into account, suggesting further the presence of residual systematics. Our results imply both galaxy clusters themselves and the details of the instruments must be better understood to enable reliable precision cosmology with clusters.

We present the results of our systematic search for optically elusive, but intrinsically luminous buried AGNs in >100 nearby (z<0.3) luminous infrared galaxies with L(IR) > 1011 Lsun, classified optically as non-Seyferts. To disentangle AGNs and stars, we have performed (1) infrared 2.5-35 micron low-resolution (R ~ 100) spectroscopy using Subaru, AKARI, and Spitzer, to estimate the strengths of PAH (polycyclic aromatic hydrocarbon) emission and dust absorption features, (2) high-spatial-resolution infrared 20 micron imaging observations using Subaru and Gemini, to constrain the emission surface brightnesses of energy sources, and (3) millimeter interferometric measurements of molecular gas flux ratios, which reflect the physical and chemical effects from AGNs and stars. Overall, all methods provided consistent pictures. We found that the energetic importance of buried AGNs is relatively higher in galaxies with higher infrared luminosities (where more stars will be formed), suggesting that AGN-starburst connections are luminosity dependent. Our results might be related to the AGN feedback scenario as the possible origin of the galaxy down-sizing phenomenon.

Only about a hundred years ago astronomers came to recognize cosmic explosive events. What was once termed as Stella Nova are now divided into two major families, novae and supernovae (with real distinct classes in each). The variables and the explosions have been interesting in their own right and contributed richly to key problems in modern astrophysics: distances to galaxies and cosmography. The area of transient and variable stars is once again undergoing a renaissance due to wide field optical surveys. The Palomar Transient Factory (PTF) was designed to explicitly to chart the transient sky with a particular focus on events which lie in the nova-supernova gap. With its innovative two-telescope architecture it achieves both high cadence and large areal rate of coverage. PTF was commissioned during the summer of 2009. PTF is now finding an extragalactic transient every 20 minutes and a Galactic (strong) variable every 10 minutes. Spectroscopy undertaken at Keck and Palomar has allowed us: identify an emerging class of ultra-luminous supernovae, discover luminous red novae, undertake UV spectroscopy of Ia supernovae, discover supernovae powered by something other than Nickel-56, clarification of sub-classes of core collapse and thermo-nuclear explosions, map the systematics of core collapse supernovae, a trove of eclipsing binaries and many others.

The Subaru Coronographique Extreme Adaptive Optics (SCExAO) project is an upgrade developed in the context of SEEDS, Subaru Strategic Exploration of Exoplanets and Disks with HiCIAO/AO-188. This system is designed for high contrast coronagraphic imaging at small angular separations from a star, and is scheduled to see first light on the Subaru Telescope in early 2011. The SCExAO bench takes light from AO188, which performs further wavefront correction/calibration and coronagraphic suppression of starlight, and uses the HiCIAO near-IR camera, specifically designed for high contrast imaging as a science detector. A separate visible light channel is used for both visible wavefront sensing and visible light imaging. We will give an overview of the project and describe its current status.

In our series of talks, we present the recent progress of our newly launched "MAHALO-Subaru" project (MApping HAlpha and Lines of Oxygen with Subaru). We aim to study the star forming activity of galaxies via H-alpha and/or [OII] lines in various environments (i.e. from cluster to field) at z ~ 0.4-2.5, exploiting the narrow-band filters installed on the Subaru Telescope. In my talk, I will focus on the results from our H-alpha imaging survey for two galaxy clusters at z=0.4 and z=0.8. Taking advantage of the wide-field capability of Subaru, we map out the star forming activity in and around the clusters. In particular, we found a large number of red star forming galaxies (probably the transition galaxies) especially in galaxy groups and/or in the filamentary structures relatively far away from the cluster. Our results suggest that properties of galaxies are indeed changing 'before' entering cluster environment and that group environment at z<1 may have played an important role in the evolution of the present-day cluster galaxies.

We are executing "MAHALO-Subaru" project (MApping HAlpha and Lines of Oxygen with Subaru) to reveal star formation activities in different environments at z~0.4-2.5 comprehensively. In my talk, I will present a [OII] emission survey for XMMXCS J2215.9-1738 cluster at z=1.46, which is one of highest-redshift clusters, with a narrow-band filter on Subaru/Suprime-Cam. We found a large scale structure of [OII] emitters from east to south of the cluster. Interestingly, we also found that there are many [OII] emitters even in the central high-density region of the cluster, suggesting active star formation in the cluster core. On the other hand, it is revealed that such star formation is not seen in high density regions at lower redshifts. I will discuss the star forming activities in and around this high-z cluster, and present the implication that galaxy formation is biased in a core of high-z clusters.

We have started a new project, "MAHALO-Subaru" (MApping HAlpha and Lines of Oxygen with Subaru). In my talk, I will make a presentation of the H-alpha emitter survey in a blank field with a custom-made narrow-band filter on MOIRCS. From this survey, we have identified 12 H-alpha emitters at z=2.2 on the basis of a narrow-band excess and photometric redshift. Most of them have been confirmed by spectroscopic follow-up. Our samples are not homogeneously distributed across field. In our project, there are large samples of star-forming galaxies in various environments and redshifts. For these galaxies, we have estimated the stellar mass and star formation rate in the same but different method and compared the results in the low density regions to those in the high density regions. This result suggests that the evolution of star formation activity is different among environments.

During the verification period of Sprime-Cam we obtained high-resolution images of the southwest part of the M31 disk (500 squarearcminutes). Using these images, a full-field search for compact non-stellar objects with apparent size less than 3arcsec (corresponding to about 10pc) was carried out, to identify about 300 candidates for compact star clusters. They looked similar to globular star clusters but some with little irregularities, and included many blue objects of B-V<0.5. After closer inspections we selected 238 highly probable candidates for compact star clusters (V<20.5mag) and performed an accurate surface-photometric study. The calibrated UBVRI data were applied to derive cluster parameters related to structure, age, mass, metallicity, and interstellar extinction. The outcome of this study indicates that there are abundant star clusters, which have the intermediate properties between the open clusters and the globular clusters well known in our Galaxy, bridging between the two populations. Their spatial distribution on the M31 disk shows loose connection to 24micron warm cloud structures. Whether this new population of clusters identified in M31 disk does also exist or not in our Galaxy disk, is still an open question. These clusters might be powerful tool to elucidate the evolution history of galaxy disks.

We will present overviews of the two cluster projects that we have been conducting on Subaru, namely PISCES for 0.4 < z < 1.6 and HzRG for 1.5 < z < 5. From these projects, a consistent picture has been emerging that the star forming activity is once enhanced and then truncated in galaxy groups in the outskirts of clusters during the course of cluster assembly at z<1. However, such activity is shifted into cluster cores as we go further back in time to z~1.5. At z=2-2.5, we begin to enter the epoch where massive galaxies are actually forming in the cluster core. And by z~3, we eventually go beyond the major epoch of massive galaxy formation. It is likely that the environmental dependence of star forming activity is at least partly due to the external environmental effect such as galaxy-galaxy interaction in medium density regions at z<1, while the intrinsic effect of galaxy formation bias overtakes the external effect at higher redshifts, resulting in a large star formation activity in the cluster centre. Together with the mass dependence of galaxy properties, which is also clearly reproduced in our data, we will sketch the propagation of galaxy formation and truncation from massive galaxies in high density regions to less massive galaxies in low density regions.

After the IRAS observations, main-sequence stars that have circumstellar debris disks and thus show infrared excess have been discovered. Since debris disks are thought to be the final stage of planet formation, it is very important to investigate property and evolution of debris disks statistically. However, little is known about the properties of the warm (Tdust > 150 K) debris disk material located close to stars, which is likely to have a more direct link to the formation of terrestrial planets than the low temperature debris dust which has been detected to date. Mid-infrared (MIR) observations become a key method for planet formation study since MIR excess traces the thermal emission from debris dust in inner planet forming region. We are carrying on an survey of warm debris disks that show MIR excess by using the AKARI/IRC MIR All-Sky Survey data. So far, we have identified several new debris disk candidates that show large 18 micron excess. In this presentation, we will show the recent results of the debris disk survey with the AKARI/IRC MIR All-Sky Survey data. We will also show the results of follow-up spectroscopic observations of AKARI-discovered debris disks, which provide mineralogical information on debris dust.

We are searching for Active Galactic Nuclei (AGNs) using the AKARI Mid-infrared (MIR) All-Sky Survey Catalogue. AKARI is the Japanese infrared sattelite dedicated for the infrared astronomy. Main purpose of AKARI is all-sky survey with new sensitivity and new spatial resolution in the mid- and far-infrared. The infrared search of AGNs is not affected by the dust extinction and the disadvantage of heavy extinction in optical surveys can turn into a valuable detection tool, when observing dust-surrounded AGN in the infrared wavelengths.
Our new survey will have the advantage of following scientific topics;
* The MIR selection can minimize wavelength-dependent selection effects, while the UV and optical emission is easily affected by dust extinction and the radio emission shows big variety. Thus, we can make the unbiased statistical studies.
* According to synthesis models of the X-ray background (XRB; e.g. Ueda et al. 2003), much of the peak intensity of the XRB at 30 keV should be produced by AGNs subject to absorption with a line-of-site hydrogen column density logNH > 23.5 cm^-2. The number density of such AGNs is a key parameter in understanding the accretion history of the universe.
* Using all-sky survey with new sensitivity, we can collect missing population from current catalogs. We can extend the faint end of nearby AGN luminosity functions using new sensitivity as well as the bright end of the distant AGNs using the survey area.
In this talk, we will explain what AKARI is, our AGN search and early results. We will also report that we have started to detect new hidden AGNs in nearby Universe.

It is well known that one of the most important direct consequences of inflationary universe is that it leads to the flat three dimensional space. This means, theoretically, that the de Sitter Space solution of the Einstein equation gives the flat three dimensional space. I use this fact and extend this to the five dimensional space-time. I find that the the five dimensional anti de Sittter space gives the flat four dimensional space-time, namely, the vanishing cosmological constant. Interesting aspect of this is that it has nothing to do with supersymmetry. I, then consider the contribution of the "instanton" which violates the five dimensional Lorentz symmetry. I get rather satisfactory value for the vacuum energy.

Saturn's F ring has brightened markedly in the last 25 years. It is twice as bright in the Cassini data as it was in the Voyager ata from 1980 and 1981. This conclusion is based on photometric comparisons of Cassini and Voyager images, and is supported by occultation data. We attribute this change to increasing perturbations by nearby Prometheus, which passes closer to the ring now that it did in the Voyager era, yielding more dust.

I will talk about the detection of radio QPOs that may reflect structure in the disk around the supermassive black hole Sgr A*. Our data obtained with the Very Long Baseline Array (VLBA) at 43 GHz showed conspicuous periodic time variation that can be attributed to the disk structure with the periods of P = 16.8±1.4, 22.2±1.4, 31.2±1.5, 56.4±6 min, roughly in a 3 : 4 : 6 : 10 ratio. The first two periods correspond to a rotating one-arm structure, while the P = 31.4 min mode is consistent with a rotating 3-arm structure, when the disk is viewed edge-on. At the central region smaller than 50 micro-arcsec in radius, the P = 56.4 min period shows a double amplitude variation.

The spatial distribution of the oscillation periods suggest that the disk of Sgr A* is near edge-on and is rotating around a projected axis of PA = -10 degree. The observed VLBI images at 43 GHz may retain some features of the Sgr A* black hole accretion disk although the disk is obscured and blurred by the scattering of surrounding plasma.

Eta Carinae is the best studied supermassive star on the way to end its life as a supernova or hypernova explosion and/or a gamma-ray burst. Intensive multi-wavelength observations since the late 1990's uncovered evidence of a binary system at the core of the bipolar envelope ejected in the Great Eruption of the 1840's. However, the characteristics of the two stellar components are not well constrained as they are deeply cloaked in their massive interacting winds. I introduce the latest picture of Eta Carinae obtained from an observing campaign heavily focused on 2003 and 2008-9 observing seasons, coincident with the two most recent periastron passages.

The primary aim of the E-ELT design is to provide facility adaptive optics as the basic mode of operation of the telescope. However, simulations suggest that this mode may only be utilised for ~50% of the available observting time. EVE is an instrument concept to work with medium resolution spectroscopy (R~5000-30000) in the visible and NIR over the widest field of view accessible to the E-ELT to provide a workhorse facility instrument that can begin science from first light in natural- or GLAO-assisted seeing conditions. This talk will discuss the instrument concept design, the major scientific objectives, and a possible precursor instrument for an existing 4m-class telescope. I will conclude with a brief summary of the current status of the VISTA telescope.

I will present two topics related to the cosmic reionization which are thought to have happened about 1 billion years after the beginning of the universe.

(1) Search for ionizing radiation from high-z galaxies: How much the ionizing photons emitted from star-forming galaxies is an important parameter to understand the ionizing background radiation and process of the cosmic reionization. We recently succeeded in detecting ionizing radiation from 17 galaxies at z~3 and significantly increased the number of direct detections of ionizing radiation from high-z galaxies (previously only two) via Subaru / Suprime-Cam deep narrow-band imaging. Some of these galaxies show unexpectedly strong ionizing radiation which are difficult to explain without considering primordial (metal-free) stellar populations. I will present the results by Suprime-Cam and on-going follow-up observations, and also discuss the possibility of further exploration with Hyper Suprime-Cam.

(2) WISH - Wide-filed Imaging Surveyor for High-redshift: We are currently developing a space telescope project named WISH which is a L2 mission with cooled 1.5m telescope and wide-field near-infrared (1-5 microns) camera. WISH will survey more than 100 square degrees and achieve depth unreachable with any ground-based telescopes. The primary goal of the mission is to detect first generation of galaxies and unveil the cosmic reionization process. I will present the current status of WISH and discuss its role as a unique sample provider for TMT.

The history, current situation, future directions and education of modern Mongolian space science and astronomy is reviewed. The lecture discusses recent efforts to develop astronomy education and research capacity in Mongolia with cooperation of the International Astronomical Union and Japanese Astronomical Community. The National Astronomical Observatory of Japan was among the first international organizations to offer assistance. The talk will tempt to establish possible academic collaboration with Subaru Telescope, NAOJ.

The lecture will also present how Astronomy is used as the the astrological practices for nomadic life in Mongolia. Mongolian Nomad's home (GER) also may be called as the first and portable astrological research focus for human life. Mongolia has continental climate, so its sky is usually clear and transparent blue without much of fog and mist. The Mongolians observed since very ancient time as the sky is contacted with its sun, moon and stars, so they included about it in ancient folklores, paints and other historical items.

In near UV region (λλ3400 ～4000Å) Be-shell stars show two remarkable features (1) the appearance of sharp absorption lines in the Balmer higher members (H10 to even H37) and (2) strong Balmer discontinuity as compared to that of normal B stars. Both features reveal the existence of an optically thick region in front of the stellar disk. Based on the absorption line analysis we can estimate the optical depth τ(Hα) and the fractional area β of this region relative to the stellar disk (Kogure and Leung 2007). Balmer discontinuity increases in the shell phase serving as an indicator of the shell activity (Moujtahid et al. 1998). Long-term variation of shell activity in both features is compared in two cases of Be-shell stars, Pleione and EW Lacertae. In both stars it is found that when the optical depth τ(Hα) is high, the discontinuity is also high. In addition, remarkable results are (1) shell activity occurs even in slowly rotating stars with small V sin i, and (2) the covering fractional area β often reaches as high as unity From these behaviors, we suggest that Be-shell stars are not necessarily the equator-on stars surrounded by vertically thin disk-like envelopes. Instead, the optically thick region often expands sufficiently high from the equatorial plane, and shell activity occasionally appears in Be stars with smaller inclination angles. (Kogure, T. and Leung, K. C. 2007, Astrophysics of Emission Line Stars Springer, Chapters 4 and 5 / Moujtahid, A. et al. 1998, A&A, S.129, 289)

We have continuously monitored Nova V1280 Sco (Nova Sco 2007 #1) at Osaka Kyoiku University since its explosion (2007, February). The observed light curve shows some unusual features. Its V (visual) and y (yellow) magnitudes remain bright (around 10 mag.) 800 days after the optical maximum. The bright y magnitude indicates that the Nova is still dominated by the continuous radiation. In 2009, we observed the Nova with the High Dispersion Spectrograph (HDS) of the Subaru telescope in order to examine the nature of the continuous radiation. Unexpectedly, we have discovered highly blue-shifted (from -900 to -650 km/s) multiple sharp absorption components of the Na I D2 and D1 lines. Some of the sharp components had deepened during the two months period from 2009 May to July. We discuss the origin of the mysterious absorptions observed in V1280 Sco.

It is widely recognized that magnetars have ultra-strong magnetic fields of 10^14-10^15 Gauss, which is about 100-1000 times stronger than ordinary neutron stars (Thompson & Duncan, 1995; 1996). Magnetars have faint optical/infrared counterparts (Hulleman et al. 2000), but the emission mechanism is poorly understood. The optical/infrared SED shows a peculiar shape, and hence it is difficult to explain by a simple model.
As for the optical emission, the emission region would be magnetosphere, because the emission is pulsed (Kern & Martin, 2002). But the mechanism is still unclear. On the other hand, the infrared emission might come from the fall-back debris disk (Wang et al., 2006).
Pulsation search is essential because, if pulsation is detected, the emission region is restricted within the magnetosphere. Therefore, we can also constrain the emission mechanism. To search for pulsation, we observed AXP 4U 0142+61 with Subaru/IRCS fast readout mode. We obtained a best upper limit of 17% (90% confidence level) for the root-mean-square pulse fraction in K' band. I'll present recent Subaru/IRCS results as well as future plans by FOCAS and other instruments to reveal the emission mechanism.
Reference:
Thompson & Duncan, 1995, MNRAS
Thompson & Duncan, 1996, ApJ
Hulleman et al., 2000, Nature
Kern & Martin, 2002, Nature
Wang et al., 2006, Nature
Morii et al., 2009, PASJ

I will talk about the laboratory demonstration of a very high-dynamic range, diffraction limited imaging instrument FIRST (Fibered Imager foR Single Telescope). FIRST will allow us to achieve very high dynamic range imaging very near the central object (a fraction of lambda/D) at visible to near-infrared wavelengths, which makes this instrument very complementary to adaptive-optics assisted coronagraph systems. The fundamental idea is to apply techniques developed for long baseline interferometry to the case of a single-aperture telescope. With FIRST, a dynamic range is no longer limited by atmospheric turbulence which can be totally filtered out and a raw dynamic range up to 10^6 will be possible thanks to spatial filtering and pupil remapping with single-mode fibers. We successfully demonstrated that the original image can be reconstructed through a pupil remapping system in our laboratory. A prototype system will be tested on a 1-meter telescope at the Paris observatory in this Autumn, followed by a test on a 3-4 meter telescope.
Lastly, I will briefly present the present status of the OHANA project, which aims at linking large telescopes on Maun Kea, including Subaru, with single-mode fibers in order to realize a huge infrared interferometer.

Observations of the internal kinematics of local galaxies have played a key role in the development of our current picture of galaxy formation. Recently, it has become possible to measure the internal kinematics of large samples of galaxies (~500+) at high redshift (z~1) due to the advent of multi- object spectrographs on 8-meter class telescopes. The focus of this talk will be on the relation between galaxy stellar mass and rotation velocity (the stellar mass Tully-Fisher relation) using data from the DEEP2 Survey. Studying this relation over the last half of the age of the Universe (0.1

Diverse Field spectroscopy combines the best features of multiple- object and integral-field spectroscopy (MOS, IFS) by allowing completely arbitrary regions of interest to be routed from the field to various spectrographs, which may be separately optimised. This approach is specially relevant to ELTs which are likely to target spatially-complex fields containing galaxy progenitors for which traditional MOS and IFS may be inefficient.

I will introduce rapid and exciting expansion of gamma-ray bursts research by Swift satellite and ESO/VLT with newest unpublished results.