Subaru Seminars

Message in a bottle is a project carried out in a framework of a JAXA-ISS artistic mission to bring back a bottle of the "space" collected through extravehicular activities by astronauts. (http://iss.jaxa.jp/en/kiboexp/news/130225_epo.html) It is now made into a small glass tube, and people can have it in hands to feel the "vacuum of the space" We are now travelling around the globe and providing people to have this experience to hold in their hands the delicate glass bottle containing the powerful vacuum of space. In this talk, I will overview of the mission, and show outreach activities we have been doing so far. For more detailes, please see the flyer.

So far, many galaxy properties correlated with the quenching of star formation are found, however the physical mechanisms responsible for these correlations are still unclear. To reveal that, it is important to investigate molecular gas, because it is a direct fuel for star formation, and therefore SF activity is strongly dominated by its properties. In my talk, I will focus on galaxy environment and morphology, which are the candidates for SF quenching trigger, and introduce my study for the environmental and morphological dependence of molecular gas properties with the nobeyama 45m radio telescope.

The Paranal Observatory in Chile hosts a high density of Adaptive Optics (AO) systems. The latest addition, not a small one, is the Adaptive Optics Facility (AOF) which transformed the Yepun telescope into an adaptive one thanks to the combined works of 4 Laser Guide Stars (LGS), a Deformable Secondary Mirror (DSM), and two Wavefront Sensor (WFS) modules GRAAL and GALACSI feeding the instruments already in place with an improved image quality: the HAWK-I wide field IR imager and the MUSE visible Integral Field Spectrograph. After years of design and assembly, it took two years of lab testing and two more years of commissioning to deliver this complex yet robust and easily operable system to the Science community. During this seminar I will provide an overview of the system, highlight challenges and successes of the commissioning and go through some showcase results obtained.

Over the last years we gathered large samples of distant (up to z=1.5) disk galaxies in clusters and the field with both HST imaging and spectroscopy both from SUBARU and ESO/VLT allowing the determination of accurate structural parameters and internal kinematics as well as stellar population parameters and gas metallicities. Only the combination of all these important aspects enables us to constrain galaxy evolution on physical bases. In my talk I will focus on the chemical evolution compared to bathtub models and on kinematic evolution presenting scaling relations like the Tully-Fischer relation both in field and clusters.

Multiple systems of stars and substellar objects prove to be excellent benchmarks for testing evolutionary models. By monitoring the motions of the components in the systems we can derive orbital solutions that yield robust dynamical masses to test against the theoretical models, as they are not alway in agreement and especially apparent for low-mass systems. Because not many multiple systems in the low-mass regime with short enough periods to obtain orbital solutions in reasonable time-frames have been observed, systems with constrained orbits become important calibrators for the models. In this talk I will present results from some of our ongoing astrometric surveys using different direct imaging techniques to detect and monitor multiple systems, stretching from low-mass stars down to planetary-mass brown dwarfs, and how we can better improve their orbital solutions to obtain better constrained dynamical masses.

Observations at (sub)millimeter wavelengths are a powerful tool to detect star-forming activity obscured by dust, and to uncover molecular gas, which is the fuel for star formation (and the growth super massive black holes, SMBHs). I will talk about an extragalactic survey at submm/mm in a z=3 proto-cluster field, mainly taken by ALMA, which aims to uncover these aspects in the remarkable overdense environment in the early Universe.

Precise radial velocity (PRV) observations of nearby main sequence stars enable the discovery, mass determination, and orbit characterization of exoplanets. An Earth-mass planet orbiting in the Habitable Zone of a Sun-like star produces a reflex velocity of ~10 cm/s. However, activity from the stellar surface can introduce false apparent velocity changes of ~1 m/s. Multi-wavelength observations, high cadence, extreme spectral resolution, line-by-line analysis, simultaneous photometry, polarization and other approaches are all being pursued to distinguish this "jitter" activity from the signals of orbiting exoplanets. The next generation of visible and near-IR PRV spectrographs will continue to investigate the mitigation of stellar activity, but the ultimate solution may require a space-based platform. I will highlight several PRV projects underway at George Mason University, including EarthFinder, a probe-class mission currently under study for the Astro 2020 Decadal. I will also highlight our work with iSHELL at the NASA IRTF, and simulation work to quantify the benefit of PRV surves for a future flagship direct imagine mission.

The discovery of C_60 in the laboratory three decades ago has triggered an intensive search of fullerenes in the interstellar medium. Followed by the first firm detection of C_60 and C_70 in the planetary nebulae Tc1 (Cami et al. 2010), fullerenes have been stipulated in a wide range of environments, including planetary nebulae in the Galaxy and the Magellanic Clouds, circumstellar envelopes of post-AGB stars, in molecular outflows from YSOs, and in reflection nebulae. The long-standing claim that gas-phase C_60^+ is the carrier of two diffuse interstellar bands has recently been substantiated by accurate laboratory data (Campbell et al. 2015). Here we present a review of the molecular phase of the interstellar medium, and address some open questions related to the presence of fullerenes in the interstellar medium.

Lithium abundances of very metal-poor stars are almost constant irrespective of metallicity (so-called Spite plateau), suggesting a direct connection to the Big Ban nucleosynthesis. However, the standard Big Bang nucleosynthesis models with cosmological parameters obtained from cosmic microwave background observations predict significantly higher primordial lithium abundance than the observed stellar lithium abundances. A new hint to this unsolved problem could be obtained from extremely metal-poor stars ([Fe/H]<-3.0). It has been known that some of extremely metal-poor stars show slightly lower lithium abundance than the Spite plateau value, which indicates that lithium depletion mechanism is at work in some stars, although it is not yet clear if there is a scatter or what governs the depletion mechanism. To better understand the possible lithium depletion mechanism, we observe 7 extremely metal-poor stars with [Fe/H]<-3.5. As a result of chemical abundance analysis, lithium abundances of the 7 stars do not show significant scatter, but are lower than the Spite plateau. We argue that the lithium depletion mechanism is exclusively controlled by metallicity.

Theoretical simulation studies suggest that dust-obscured AGNs appear for a certain period when merger-driven star-forming galaxies evolve to unobscured type 1 AGNs. The dust-obscured AGNs would have red colors due to the dust extinction in their host galaxies, and they are expected to have higher BH accretion rates than unobscured type 1 AGNs. Red AGNs are found by selecting type 1 AGNs with very red colors, and they have been suspected as the intermediate-stage, dusty AGNs. However, it is not yet clear if red AGNs really correspond to the dusty AGNs due to a lack of intrinsic properties of red AGNs. For unveiling intrinsic properties of red AGNs, we study the NIR and MIR spectra of unobscured type 1 AGNs and red AGNs. There are three main themes: (i) derivation of NIR and MIR BH mass estimators can be used for red AGN study; (ii) investigation of red AGN selection methods to test its usefulness to identify dusty red AGNs; and (iii) investigation of the accretion rates of red AGNs to see if they have the properties as predicted in the simulation studies.

Galaxy clusters are the largest gravitationally bound structures in the universe and located in the densest peak of the dark matter. They can constraint on the cosmological model from their dark matter halo distribution and they are good laboratories to study how galaxy evolution varies with their environment. Especially, studies of galaxy clusters at z >~ 1 are important because (i) galaxy evolution at z >1 is still controversial (Elbaz et al. 2007; Faloon et al. 2013) and (ii) some studies show that mass of galaxy clusters at z>1 seems to be higher than expected value from the cosmological model (Kang & Im 2009; Gonzales et al. 2012). In spite of their significance, there have not been many studies of galaxy clusters at z >~ 1 because of the lack of wide and deep multi-wavelength data. In this talk, we present newly discovered galaxy clusters at z >~ 1 and a LSS spanning over 100Mpc at z~0.9 in ELAIS-N1 field which is one of the IMS (Infrared Medium-deep Survey; Im et al. 2017, in preparation) fields. With multi-wavelength data from the Pan-STARRS (g, r, i, z, y bands), HSC (g, r, i, z, Y bands), CFHT (z band), IMS (J band), UKIDSS DXS (J and K bands) and SWIRE (4 IRAC bands), we found new galaxy cluster candidates at 0.2 < z < 1.4 based on photometric redshift. Among them, we discovered unusual and interesting galaxy cluster candidates showing high star formation activity even they have high mass (M> 10^14M_Sun) at z >~ 1 which are expected to be already quenched. Furthermore, we found a LSS spanning over 100Mpc in co-moving scale around confirmed supercluster of Swinbank et al. 2007 at z~0.9. Interestingly, the newly discovered structure is more massive and larger than Swinbank supercluster.

An AGN (active galactic nucleus) is an object which emits very strong radiation from the nuclear compact region of a galaxy. It is now widely believed that a mass-accreting supermassive black hole (SMBH) is the main energy generation mechanism of an AGN. According to the AGN unification paradigm, a dusty gaseous torus is thought to be present around a mass-accreting supermassive black hole (SMBH), because this model can naturally explain various observational results of AGNs. However, since the putative torus is spatially compact, say <10 pc or <0.15" at the distance of 15 Mpc, its observational understanding is still highly incomplete. ALMA high-spatial-resolution observations are expected to play a vital role to unravel the properties of the AGN torus. We present our results of ALMA 0.04" x 0.07" resolution observations of the nearby (~14 Mpc) well-studied type-2 AGN NGC 1068 in the HCN J=3-2 and HCO+ J=3-2 molecular lines. Previous observations of NGC 1068 have shown that the morphologies of the optical ionized gas emission and radio jet are extended along the N-S direction. Thus, it is expected that the putative torus is aligned roughly along the E-W direction. We have clearly demonstrated, for the first time, that both HCN J=3-2 and HCO+ J=3-2 emission lines (dense molecular tracers) are elongated along the E-W direction (PA = 105 deg east of north) both morphologically and dynamically, as expected for NGC 1068. The estimated molecular mass and size are comparable to those expected from the classical AGN torus model. However, we found that (1) torus molecular emission is highly asymmetric in that the western part is brighter and shows higher turbulence the eastern part, and (2) the torus dynamics is far from the Keplerian motion governed by the gravity of the central SMBH. We will discuss detailed physical/morphological/dynamical properties of the torus in NGC 1068 revealed from our ALMA high-spatial-resolution data.

We are interested in how the AGN affects its surrounding material, and consequently whether it has strong impacts on the galaxy evolution. In this seminar, I would like to talk on our recent study of inter stellar medium irradiated by AGN X-ray emission in Circinus galaxy using Chandra and ALMA 10 pc resolution data. We create maps of 6.4 keV iron-Kalpha line emitting regions based on ~300 ksec Chandra/ACIS data. The maps enable us to know gas distribution irrespective of its atomic/molecular phases. They are compared with those of molecular emission observed with ALMA. A noticeable finding is that the iron emission line is bright around the nucleus (< 60 pc) and therein the molecular line emission is suppressed. This suggests that the molecular gas close to the AGN tends to be dissociated into the atomic gas. We quantitatively discuss this in accordance with the X-ray Dominated Region (so called XDR) model. We estimate a key parameter of an effective ionization parameter (xi_eff = L_X/(R^2 n_H2 N_H^1.1)) at R = 60 pc, corresponding to an outer limb of the iron line bright region, given the X-ray luminosity (L_X) and the attenuating column density (N_H) for incident X-rays. The hydrogen density (n_H2) is constrained by fitting the observed molecular line ratios to those predicted from a non-LTE model. Then, we find that the estimated ionization parameter is consistent with an atomic-to-molecular hydrogen transition boundary predicted from an XDR model (Maloney 1996). Thus, we suggest that the X-ray radiation likely dissociates molecules within the Circinus galaxy nucleus. Given a correlation between the molecular gas surface density and the starformation rate, the result implies the suppression of the star formation therein.

The transmission of UV photons through the intergalactic medium between the trees of the Lyman-alpha forest proves that most of the hydrogen in the universe has been highly ionized for (at least) the last ~12.5 billion years of cosmic time. At the earliest epochs observable in the spectra of distant quasars, z > 6, the Lyman-alpha forest rapidly becomes extremely patchy and opaque, suggesting that we are probing the final stages of the reionization process. However, giant opaque troughs larger than 50 Mpc have been discovered as late as z ~ 5.5, long after reionization is thought to be over, and the late-time existence of these "Gunn-Peterson troughs" cannot be explained by cosmic variance of the cosmological density field alone. I will discuss my theoretical modeling to understand the nature of these regions -- do they represent voids or dense environments? -- and present results from the observational campaign we are undertaking with Hyper Suprime-Cam to shed light on the physics of the post-reionization universe.

Intracluster stars are believed to be unbound from their progenitor galaxies and diffused throughout the galaxy cluster, creating intracluster light (ICL). However, when and how exactly these stars form are unclear to date. To directly constrain the origin, one powerful method is to study clusters at the epoch when mature galaxy clusters began to appear. In this talk, I will present measurements of the spatial distribution, color, and quantity of diffuse intracluster stars for a massive galaxy cluster at a redshift of 1.24, using exceptionally deep near-IR imaging data from HST. This is the most distant galaxy cluster to date for which those three properties of the ICL have been quantified simultaneously. Finally, I will discuss what our measurements suggest about the origin of the ICL.

Nearly half of all core-collapse supernovae expected on the basis of the cosmic star formation rate are missed by optical, seeing-limited surveys. The problem is even worse in Luminous Infrared Galaxies, despite their having the highest star formation rates, and hence supernova rates. Over the past decade we have used laser guide star adaptive optics facilities on the VLT, Gemini North and South, Keck, and now Subaru to reveal this "missing" population of supernovae. Correcting for this missed fraction of supernovae will be vitally important to interpreting findings from the LSST and even JWST.

In AIST, we are developing astro-comb from 2014 in collaboration with the NAOJ, Yokohama National University, and the University of Electro-Communications. So far, the first system was developed at AIST, transported to, and installed at Okayama Astrophysical Observatory, and compared with the conventional wavelength standards. In this presentation I will talk about the outline and problems of the first system, the outline of the second system being developed now, and the future schedule.

Paul Dirac proposed the baryon symmetric universe in 1933. This proposal has become very attractive now since it seems that all pre-existing asymmetry would have been diluted if we had an inflationary stage in the early universe. However, if our universe began baryon symmetric, the tiny imbalance in numbers of baryons and anti-baryons which leads to our existence, must have been generated by some physical processes in the early universe. In my talk I will show why the small neutrino mass is a key for solving this long standing problem in understanding the universe we observe.

Thanks to modern technology - wide-field detectors, high computing power, massive data storage, and robotic observation - it is possible to obtain many asteroid light curves within a short period of time. Therefore, several important applications can be conducted on asteroids in a more comprehensive way. For instance, the interior structure can be studied through the spin-barrier and the odd objects called super-fast rotator, the mechanisms changing asteroid spin-status can be learned through the spin-rate distribution, and binary asteroid discovery....etc. I will talk about our asteroid time-series survey using wide-field facility, like the PTF/ZTF and the PS1, and what we have learned so far.

Superluminous supernovae are a newly recognized class of core-collapse supernovae. Their existence is realized only about a decade ago. They are more than 10 times brighter than other core-collapse supernovae. The reasons why they can become very bright are still not understood well. I will discuss the diversity of superluminous supernovae and possible mechanisms to make them superluminous. I will introduce a high-redshift supernova survey recently conducted by Subaru telescope which led to a discovery of a superluminous supernova at z = 2.4. Future infrared transient surveys to detect superluminous supernovae at even higher redshifts will also be discussed.

The first generation of (Population III or Pop III) stars are responsible for the first metal-enrichment and producing the first ionizing photons in the early universe. Their physical properties, most importantly, masses are therefore critically important in better understanding the early galaxy formation and the cosmic reionization. Extremely metal-poor (EMP) stars in the Milky Way Galaxy are likely second-generation stars formed out of gas primarily enriched by nucleosynthetic products ejected by supernova explosions of the first stars and thus provide us with an opportunity to observationally access the yet-unknown properties the first stars. We calculate supernova yields of the first stars that best reproduce observed elemental abundance patterns of ~ 200 EMP stars to obtain possible insights into the typical masses of the first stars. We find that the abundance patterns of the EMP stars are predominantly reproduced with the supernova/hypernova yields of the first stars with M<40M_sun leaving behind compact remnants (neutron stars or black holes) with masses up to a few tens of M_sun. I'd like to summarize the possible signatures of the first stars on the EMP stars as well as underlying assumptions and future prospects in this field of study.

The advent of ultra-wide cameras and all-sky surveys have greatly facilitated time-domain and gravitational lensing studies. In this talk, I will showcase how we can make use of these public surveys, especially using eclipsing binaries to constrain the stellar parameters and structures in the Milky Way, as well as utilizing microlensing to probe exoplanets in the solar neighborhood. I will then move on to our closest neighbor spiral galaxy, i.e. M31, to demonstrate how we can use different variables to determine its properties, e.g. distance, metallicity gradient, star formation process, as well as using microlensing to investigate the compact object in the halo of M31. In the end, I will discuss how joining the forces of time-domain and gravitational lensing can improve our knowledge of cosmology, especially in the lights of time-delays from multiply lensed SNe Ia.

Over the last decade, deep studies of nearby galaxies have led to the discovery of vast stellar envelopes that are often rich in substructure. These components are naturally predicted in models of hierarchical galaxy assembly, and their observed properties place important constraints on the amount, nature, and history of satellite accretion. One of the most effective ways of mapping the peripheral regions of galaxies is through resolved star studies. Using wide-field cameras equipped to 8 m class telescopes, it has recently become possible to extend these studies to systems beyond the Local Group. Located at a distance of 3.6 Mpc, M81 is a prime target for wide-field mapping of its resolved stellar content.In this talk, we present the detailed results from our deep wide-field imaging survey of the M81 group with the Hyper Suprime-Cam (HSC), on the Subaru Telescope. We report on the analysis of the structures, stellar populations, and metallicities of old dwarf galaxies such as NGC3077, IKN, KDG061, as well as young stellar systems such as Arp's Loop and Holmberg IX. Several candidates for yet-undiscovered faint dwarf galaxies and young stellar clumps in the M81 group will also be introduced. The peculiar galaxy NGC3077 has been classified as the irregular galaxy. Okamoto et al. (2015, ApJ 809, L1) discovered an extended halo structure with S-shape elongated tails, obvious feature of tidal interaction. With a help of numerical simulation by Penarrubia et al. (2009, ApJ 698, 222), we will demonstrate that this tidal feature was formed during the latest close encounters between M81, M82, and NGC 3077, which induced star formation in tidally stripped gas far from the main bodies of galaxies. It is not clear whether the latest tidal interaction was the first close encounters of three galaxies. If NGC3077 is still surrounded by the dark matter halo, it implies that NGC3077 has undergone the first tidal stripping by larger companions. Kinematic studies of inter galactic globular clusters and planetary nebulae would tell us the past history of tidal interaction in this group of galaxies.

Gravitational microlensing provides a powerful tool to study a wide range of astrophysical phenomena -- from detecting dark matter and exoplanets to measuring the masses of white dwarfs, neutron stars and black holes. After an introduction to microlensing, I will discuss the results on planet detections through microlensing, with a special emphasis on the results from the PLANET collaboration. I will also discuss the detection of transiting planets around stars in the Galactic bulge through our SWEEPS program with HST, and subsequent implications on the frequency of exoplanets across the Milky Way. I will then discuss our astrometric microlensing measurements by the nearby white dwarf Stein 2051 B -- the first such measurement by a star outside the solar system -- to determine its mass. Finally, I will discuss our HST programs aimed at the first detections of isolated stellar-mass black holes and their mass measurements.

Detection and detailed characterization of sub-Jupiter mass exoplanets through extreme adaptive optics (ExAO) is a key science goal of future extremely large telescopes. This achievement, however, will be limited in sensitivity by quasi-static wavefront errors. Additional limitations arise from residual AO-corrected atmospheric wavefront error, generating ~millisecond-lifetime atmospheric speckles that will average to a smooth halo (but not to zero) over a long exposure. A solution to both of these problems is to use the science camera with a dedicated fast wavefront sensing and correction method. We develop the framework for one such method, the self-coherent camera, to be applied to ground-based telescopes. We show that with the use of a specially designed coronagraph and post-processing algorithm, recording millisecond NIR images on a photon counting camera allows a full dark hole phase and amplitude correction of both atmospheric and static speckles, without removing the incoherent planet light. Detailed simulations reach a contrast of a few times the photon noise limit after 30 seconds for a 1% bandpass on both 0th and 5th magnitude stars, illustrating that sensitivity improvement from this method could play a major role in future high contrast imaging instruments.

Today, the fastest Petascale Supercomputers from the Top500 list expose million of cores and the scientific community anticipates concurrency of a billion threads moving forward with the Exascale era. The current linear algebra software stack relies on the bulk synchronous programming model, which has been around for decades. This programming model impedes parallel performance and underutilizes current and future hardware resources. New disruptive algorithmic adaptations to extreme scale are required to efficiently exploit the underlying hardware architectures. Although this may look like a daunting challenge, e.g., in terms of scientific code rewriting, this is also a unique opportunity to create and design new synchronization-reducing and communication-reducing numerical linear algebra algorithms, for which most of scientific applications rely on for high performance computing. This talk will focus on linear algebra matrix operations critical for computational astronomy applications, i.e., basic linear algebra subroutines (BLAS), linear solvers and singular value decomposition (SVD).

Planets that are still forming inside circumstellar disks can directly constraint planet formation theory. While there are no direct methods to detect them, we can infer their existence, even their properties, though their gravitational influence on the disks. Two prominent features of disk-planet interaction are spirals and gaps, and similar features have been observed in state-of-the-art near-infrared and mm observations. Using hydrodynamical and radiative transfer simulations, we link together numerical models and observed disk features. I will discuss the physical mechanisms behind the formation of these structures, and answer some long-standing questions such as how many spiral arms do one planet excite, and why sometimes we see spirals and other times we see gaps. I will also present a number of methods to weigh planets and measure disk parameters, focusing mainly on scattered light observations. Finally, I will discuss what current observations have already revealed to us, and how that matches or challenges our current understanding of planet and disk evolution.

Dust-enshrouded, starbursting, submillimeter galaxies (SMGs) at z >= 3 have been proposed as progenitors of z >= 2 compact quiescent galaxies (cQGs). To test this connection, we present a detailed spatially resolved study of the stars, dust and stellar mass in a sample of six submillimeter-bright starburst galaxies at z ~ 4.5. The stellar UV emission probed by HST is extended, irregular and shows evidence of multiple components, undergoing minor mergers with a typical stellar mass ratio of 1:7. The FIR dust continuum emission traced by ALMA locates the bulk of star formation in extremely compact regions. We compare spatially resolved UV slope maps with the FIR dust continuum to study the infrared excess (IRX)-beta relation. The SGMs display systematically higher IRX values than expected from the nominal trend, demonstrating that the FIR and UV emissions are disconnected. Finally, we show that the SMGs fall on the mass-size plane at smaller stellar masses and sizes than cQGs at z = 2. Taking into account the expected evolution in stellar mass and size between z = 4.5 and z = 2 due to the ongoing starburst and mergers with minor companions, this is in agreement with a direct evolutionary connection between the two populations.

The recent direct detection of gravitational waves has provided exciting opportunities to probe previously unseen astronomical systems, opening up a new window on the universe and helping develop our knowledge of relativistic physics. This exciting discovery has been many decades in the making and represents a prolonged effort by the gravitational wave community to provide instruments with increasing sensitivity to gravitational waves. Current gravitational wave detectors (Advanced LIGO and Advanced Virgo) utilize laser interferometry to measure the change in length induced by a gravitational wave, less than 1000th the width of a proton. Here I will present an overview of the detector technology, explaining the motivation for the current detector layout and the technological advances which have enabled the suppression of different noise sources and the eventual detection of gravitational waves. In addition I will discuss the future of gravitational wave detectors, including possible upgrades to the existing systems and ideas for future instruments.

Discovering the accelerating expansion of the universe in 1999 was a revolution in physics. Although it brought a concordance universe consisting of dark matter, dark energy, and ordinary matter, the derived current expansion rate (H0) based on the standard cosmological model has tension with the direct measurements at the local universe. It is important to emphasize that the value of H0 critically depends on the curvature of the universe, dark energy equation of state, and neutrino physics, which are all fixed in the standard cosmological model. If we start relaxing all the assumptions, the degeneracies in the parameters of space appear. Thus, these assumptions must be tested empirically. If this tension between the H0 derived from CMB and the local measurements is not caused by any systematic effect, it might be a hint of new physics. Time-delay gravitational lens system serves a powerful tool to measure H0. Recently, H0LiCOW group has shown that the new H0 measurement by using three HST lensing imaging agrees with the H0 measured by using supernova data, but is mildly in tension with the derived H0 by using CMB from the Planck team. Since adaptive optics imaging can provide higher angular resolution than HST imaging but suffers from the unknown point spread function problem, in this talk, I will present a new method, which overcomes this obstacle, to constrain H0 by using three AO imaging from the SHARP team.

The study of the evolution of quasars and their influence on their host galaxies provides unique insight into how supermassive black holes became a ubiquitous feature of galaxies today. Dust-reddened quasars appear to represent a transitional phase in merger-driven models of quasar/galaxy co-evolution. I will present results from recent and ongoing surveys to identify these transitional systems using infrared and radio selection. The results of these surveys reveal that red quasars are among the most intrinsically-luminous quasars in the universe, and make up ~20% of the overall quasar population. They reside in actively merging galaxies, and their rest-frame UV spectra exhibit outflows in absorption and emission. I will discuss how reddened quasars fit into the larger picture of AGN evolution which includes both mergers and secular growth. Finally, I will present new work on surveys to explore red-quasars' parameter space to fully understand the connection between galaxy mergers and black hole growth.

Compact elliptical galaxies (cEs) are rare in the local Universe, with only about two hundred reported to date. With very compact sizes (100-1000kpc) and intermediate stellar masses (10^8-10^10Msun), they have very high densities that resemble those seen in the cores of massive ellipticals or disks. This suggest that cEs could be, in fact, the remnant of a larger, more massive galaxy that lost its stars via a stripping process. Other evidences support this claim, like the fact that they are typically found near a massive galaxy in dense environments or the fact that some have been caught in the act of stripping. However, some other recently found isolated cEs and cosmological models challenge this view, showing properties that demand another mechanisms of formation. Therefore, as it usually happens in nature, things are not simply white or black, and many factors come into play. Determining the origin and evolutionary stage of these rare cEs is not an easy task, but in this talk I will present a set of tools that can help discriminate between the possible formation mechanisms for cEs.

I will give a brief description of the Subaru Telescope adaptive optics campaign (Rusu et al. 2016) which resulted in high-resolution imaging of 25 gravitationally lensed quasars. I will present some of the interesting objects, as well as show results concerning the SMBH-host galaxy coevolution and the relation between the mass and light profiles of lensing galaxies. In the second half of the talk, I will talk about the recent H0licow analysis which measured the Hubble constant with 3.8% precision from a sample of just 3 lenses.

I will present some recent results using HSC wide data to study the star formation activity of galaxies down to i ~ 26 in different environments. We make use of the HSC CAMIRA cluster catalog and Mizuki photo-z galaxy catalog constructed in the HSC wide field (S16A) to explore the environmental impact on the star-formation quenching via the stacking technique over 0.2 ~ z ~ 1.1. From our results, we find that the environmental quenching persists to halt the star formation in the low-mass regime due to the existence of the red sequence for low stellar mass galaxies in groups and clusters. In addition, we also find that star-forming galaxies in dense regions are systematically biased toward lower values of specific star formation rate by 0.1 - 0.3 dex with respect to those in the field, and the offsets show no strong redshift evolution, implying a universal slow quenching mechanism acting in the dense environments since z ~ 1.1.

In the first part of my talk, I am going to introduce a two-years-long multi-band photometric monitoring project on Classical T Tauri stars (GI Tau). We find evidence of star-disk interactions including disk warp extinction (dV > 2 mag) and variable accretion process. An empirical relationship between B-band excess luminosity and accretion luminosity is proposed in this work. In the second part of this talk, I will present our observation project on Subaru telescope. Star formation is an inefficient mechanism. Only a few percent of the available gas in molecular clouds forms stars, leading to the observed low star formation rate. Stellar feedback is considered to be one of the major physical mechanisms to counteract the quick global collapse of molecular clouds. In this talk, I will present our recent observational analysis on selected Galactic giant molecular clouds to understand the feedback mechanisms and its possible outcome on the subsequent star formation properties, such as, IMF, star formation efficiency, and rate.

In this seminar, a new method of distance measurement of Active Galactic Nuclei (AGNs) using the reverberation mapping method on dust tori is presented. AGNs are known for their photometric variability over wide range of wavelength, not only by their high luminosity. Photometric monitoring of AGN revealed that variation patterns of type 1 AGNs in optical/UV wavelength were reproduced as near infra-red (NIR) variation patterns with certain time lags (e.g. Clavel et al. 1989). The time lag can be interpreted according to the unified model of AGNs as the difference of light path between optical/UV emission from accretion disk around super massive black hole traveling directly to an observer, and NIR emission from dust torus surrounding the accretion disk as a thermally reprocessed emission of the dust heating UV emission from the accretion disk. In other words, the lag is a good indicator of an inner radius of a dust torus. Inner radii of dust tori could be calculated with a certain thermal reprocessing model so that it is possible to estimate the intrinsic optical/UV luminosity of AGNs from the time lag. MAGNUM project (e.g. Yoshii 2002) have executed an accurate and frequent photometric monitor of AGN up to redshift 0.6 in optical and NIR wavelength though 8 years from 2000 to 2008. They showed that there is a strong correlation between the time lag and the optical absolute magnitude (Minezaki et al. 2004, Suganuma et al, 2006, Koshida et al, 2014), that dust thermal reprocessing model parameters that is generally accepted explains the correlation (Yoshii et al 2014), and that the distances measured by the reverberation mapping method consists the distance estimated by type Ia supernovae (Koshida et al. 2017). This distance measurement method is new and physical based method, independent of any other distance ladder methods. The preliminary results from AGN variability study using the HSC SSP catalog data will be also introduced in the seminar.

Star-forming galaxies are found to form a tight relation in the star formation rate (SFR) and stellar mass plane, the so-called 'star forming main sequence'. The origin of this relation and how star forming galaxies migrate into the quiescent population remain unanswered. In this talk, I will show that the main sequence may be a result of local correlation between the SFR surface density and the stellar mass surface density on kpc scale based on the resolved stellar populations obtained by the Mapping Nearby Galaxies at Apache Point Observatory IFU survey (MaNGA). In addition, I'll discuss the role of molecular gas in the galaxies that are in transit from the main sequence to the quiescent population from our recent ALMA observations.

I will present some recent results using HSC wide data to study the star formation activity of galaxies down to i ~ 26 in different environments. We make use of the HSC CAMIRA cluster catalog and Mizuki photo-z galaxy catalog constructed in the HSC wide field (S16A) to explore the environmental impact on the star-formation quenching via the stacking technique over 0.2 ~ z ~ 1.1. From our results, we find that the environmental quenching persists to halt the star formation in the low-mass regime due to the existence of the red sequence for low stellar mass galaxies in groups and clusters. In addition, we also find that star-forming galaxies in dense regions are systematically biased toward lower values of specific star formation rate by 0.1 - 0.3 dex with respect to those in the field, and the offsets show no strong redshift evolution, implying a universal slow quenching mechanism acting in the dense environments since z ~ 1.1.

Modern day galaxies populate a bimodal distribution, in both morphology and color space. Their morphological and color properties are also inter-related, with lenticular and elliptical galaxies usually exhibiting red colors and spiral galaxies usually exhibiting blue colors. In color space, there is a genuine dearth of intermediate colored galaxies, suggesting that the transition a galaxy undergoes to transform must be rapid, and quenching galaxies, rare. Gas - its presence, absence, and mechanics - serves as the anchor of a galaxy's transformation from blue to red. I will discuss the nature of gas in transitioning and transitioned galaxies through two lenses: (1) How a galaxy transition is able to impact the behavior of molecular gas, and (2) how new observations of molecular gas in quenching and quenched galaxies has recast our understanding of how they ultimately metamorphose from blue, star-forming spirals into red, quiescent ellipticals and lenticulars.

In this seminar, I will present about my latest paper (Ogura et al. 2017) related to the relationship between damped Ly-alpha absorption systems (DLAs) and Ly-alpha emitters (LAE). The DLA is a class of quasar absorption-line systems with N_HI>10^20.3 cm^-2 and is a key population to understand the early phase of galaxy evolution. This is because DLAs dominate the neutral-gas content in a wide redshift range and they are thought to be gas reservoirs for the star-formation in the high-z Universe. The LAE are also important as a population of young galaxies with typical mass and age of 10^8a?“10^9 M_sun and order of 100 Myr, respectively. Although most of the galaxy counterparts that have been identified to date show the Ly-alpha emission, the relation between those two population is still unclear. Here we focus on concentrated regions of DLAs to investigate the physical relationship between DLAs and LAEs and conducted narrow-band imaging observation of LAEs. We have found no difference between properties of LAEs, such as Ly-alpha luminosity function and the distribution of rest-frame equivalent wifth, in the target field and those in blank fields at similar redshift in the 50 Mpc scale. On the other hand, in the 10 Mpc scale, we have found a possible overdensity of LAEs around a DLA. This DLA has higher HI column density (logN_HI=21.08 cm^-2) than any other absorbers in the target field. These results imply a possible interrelation between DLAs with high N_IH and LAEs.

The interstellar medium content is crucial to understand the physics of AGNs and the co-evolution between supermassive black holes and their host galaxies. However, direct gas measurements are time consuming, and not without their own limitations and uncertainties. We advocate the alternative strategy of using dust as an efficient and effective indirect probe of the total (atomic and molecular) gas content of AGNs. I will introduce a detailed study of the infrared spectral energy distributions of bright, low-redshift (z lt 0.5) quasars selected from the Palomar-Green sample, using complete (1 to 500 micron) data obtained from 2MASS, WISE, Spitzer (IRS spectra) and Herschel. With a newly developed Bayesian Markov Chain Monte Carlo fitting method, we quantitatively decompose various overlapping contributions to the integrated spectral energy distribution, including starlight from the host, hot dust from the central engine and torus, and cooler dust emanating from larger scales in the host galaxy. This procedure yields a robust total dust mass, which we use to infer the total gas mass, using a dust-to-gas ratio estimated from the host galaxy stellar mass. Most quasar host galaxies have gas fractions similar to those of massive, star-forming galaxies, although a minority seem genuinely deficient in gas, resembling early-type galaxies. I will discuss the reliability of our gas estimates and the implication of our results for AGN feedback.

In this talk, I will discuss recent results from collaborators and I using the Subaru Telescope to directly image and characterize young extrasolar planets and planet-forming disks, primarily with the Subaru Coronagraphic Extreme Adaptive Optics project. I will summarize the architecture of SCExAO (wavefront control, coronagraphy) and science instruments currently in use and planned for use in the near future. SCExAO's first science results reveal high contrast imaging capabilities roughly comparable to that from the Gemini Planet Imager at first light, newly resolved debris disks, simultaneous JHK spectra of benchmark planetary companions, and new candidate companions. Additionally, I will discuss detailed atmospheric characterization of moderate-contrast, wide-separation exoplanets with AO188, a forerunner of the science we plan to do with SCExAO in the near future. I will close by discussing the instrumentation and scientific trajectory of SCExAO, how it will mature technologies necessary to imaging planets in reflected light, including with the Thirty Meter Telescope, and plans to conduct an Intensive Proposal focused on exoplanet discovery and characterization that exceeds current rival programs using GPI and SPHERE.

Low-mass (dwarf) galaxies are the most abundant systems of the Universe at all cosmic epochs, and they are considered the building blocks from which more massive galaxies assemble. This assembly process is not constant, but it peaks at z ~ 2 and then declines exponentially at later times. Almost 25% of the stellar mass observed today has been assembled after this peak, and a significant part of it formed in young low-mass galaxies in strong, short-lived starbursts. Tracing the galaxy-averaged properties of large, representative samples of star-forming dwarf galaxies out to z ~ 1 is a necessary step for understanding the evolution of low mass galaxies and and the build-up of stellar mass during the last 9-10 billion years. In this talk I will show the discovery and spectrophotometric characterization of a large sample of 164 faint star-forming dwarf galaxies at redshift 0.13 ≤ z ≤ 0.88 selected by the presence of bright optical emission lines in the VIMOS Ultra Deep Survey (VUDS). I will present their integrated physical properties, including oxygen abundances and ionization conditions, which are used to discuss the low-mass end of the mass-metallicity relation (MZR) and other key scaling relations. The MZR for this sample shows a flatter slope compared to previous studies of galaxies in the same mass range and redshift, while the increasing scatter toward the low-mass end (already found in other works) is partly explained by varying specific SFRs and gas fractions. Comparing the results with simple chemical evolution models, I will show that most star-forming dwarf galaxies do not follow the predictions of a "closed-box" model, but those from a gas-regulating model in which gas flows are considered. While strong stellar feedback may produce large-scale outflows favoring the cessation of vigorous star formation and promoting the removal of metals, younger and more metal-poor dwarfs may have recently accreted large amounts of fresh, very metal-poor gas, that is used to fuel current star formation.

Metallicity is one of the most fundamental properties of galaxies. It reflects star formation history and gas flows of galaxies. In this seminar, we will talk about our study on chemical evolution of galaxies near and far. We attempt to extract information about star formation and gas flows of dwarf galaxies in the Local Group and distant star-forming galaxies by comparing the observational data with simple chemical evolution models. The results on dwarf galaxies suggest that more massive galaxies may have (i) higher star formation rate and/or (ii) lower outflow rate. On the other hand, our results on more massive distant star-forming galaxies show that more massive galaxies may have (i) lower star formation rate and/or (ii) higher outflow rate. We will discuss the results and our interpretations.

We focus on the epoch of z=3-3.6, which corresponds to 1-2 Gyr before the highest peak of the galaxy formation and evolution, i.e. z~2. Our final goal is to reveal what physical processes are involved in the increasing star formation rates in the universe towards z~2. We have constructed samples of star-forming galaxies at z > 3 by the NB imaging surveys, namely Mahalo-Subaru (Kodama et al. 2013) and HiZELS (Best et al. 2013). At z>3, the Halpha emission line is no longer accessible from the ground, and we try to use the [OIII]I≫5007 emission line as a tracer of star-forming galaxies at this epoch. We investigate the star-forming activity and the interstellar medium (ISM) conditions of the [OIII]-selected galaxies using the photometric and spectroscopic data and compare these quantities with those of the star-forming galaxies at the peak epoch. Our results suggest that the star-forming activity and the ISM conditions do not strongly evolve since z~3.2 to z~2.2 and that the stellar masses are likely to determine the evolutionary stage of star-forming galaxies between the two epochs. In this talk, I would like to introduce a series of our studies about the [OIII] emitters at z>3.

The Earth is thought to have formed in a part of the Solar Nebula deficient in organic material, and to have acquired its water and organics through bombardment by minor bodies. When we directly observe this process we obtain insight into the origin and composition of the bombarding parent bodies. If the system is firmly dated, and a series of such systems identified, we can map when such activity begins, how long it lasts, and the implications for the history of our solar system. The mid-A star I2 Pictoris provided the first such look into a young planetary system, with imaging of its debris belts (Golimowski et al. 2006), detection of circumstellar gas (Dent et al. 2014; Roberge et al. 2006), and detailed modeling of star- grazing planetesimals (Beust & Morbidelli 2000) which have recently been shown to include water ice dissociation products (Wilson et al. 2016). Temporal variability in these objects was used to predict the existence of a giant planet a decade before its direct imaging discovery (Lagrange et al. 2010). A second star in the same moving group, HD 172555, also has star-grazing bodies. The available spectroscopic data, including HST FUV spectra, demonstrate the presence of super-refractory elements, lithophiles such as silicon ions, as well as more volatile gas including carbon ions and O I. most searches for exoplanetary systems have focussed on two-debris belt systems where warm debris is joined by a Kuiper belt analog. The example of HD 172555 suggests that planet searches should be extended to systems lacking cold debris.

yα emitters (LAEs) play an important role in the cosmic re-ionization. However, the ionization properties of LAEs are poorly understood. The ionization parameter and gas-phase metallicity are key quantities to understand the ionization properties of LAEs. With deep optical and near-infrared spectroscopy, we estimate the ionization parameter and metallicity of LAEs by the direct electron temperature (Te) method (Kojima et al. 2017). Our sample consists of five typical LAEs at z=1.7-2.3 with log(M*/M_sun)~9.5 and rest-frame Lyα± equivalent width of EW_0(Lyα±)=30-160A. The direct Te method enables the robust estimates of Te=13,000-14,000 K, metallicity 12+log(O/H)=8.05-8.14, and ionization parameter q_ion=8.1-8.2 cm/s of these LAEs with a typical error of ~10%, excluding the systematic bias that the previous studies cannot remove. Comparing these LAEs to 30 Lyman break galaxies (LBGs) with EW_0(Lyα)~0 on the similar M*, SFR and O/H basis, we have revealed that LAEs have ionization parameters three times higher than those of LBGs based on the direct Te method. With these robust estimates obtained by the direct Te method, we have confirmed that the nature of LAEs is characterized by the high ionization parameter as well as the large Lyα± equivalent width.

We focus on mid-infrared selected obscured AGNs and fit their optical to far-infrared photometry by the state-of-art SED technique. We derive their stellar masses, star formation rates, dust properties, AGN contribution, obscuration, and the morphologies of their hosts through HST images. Comparing to normal star-forming galaxies at similar redshift and stellar mass, AGN hosts are more compact and their merger fraction is not higher at z~1. We postulate that obscured AGNs are hosted by galaxies experiencing a mode of compaction, as recently discussed in the literature from hydrodynamic simulations of gas-rich disk galaxy formation. I will also talk about my recent plan related to the HSC survey.

Galaxy clusters trace the most massive dark matter halos and the densest galaxy environment, hence are invaluable cosmological probes, and also ideal laboratories to study environmental effects on galaxy evolution. Galaxy clusters in the local universe (and up to z~1.5) are exclusively dominated by massive ellipticals in the core. Both galaxy cluster archaeology and cosmological simulations suggest that these galaxies formed in a short time scale at z>~2, however, structures with clear evidence suggestive of such a rapid formation phase have been lacking so far, and the (trans)formation mechanisms of cluster ellipticals remain a mystery. In this talk I will present our recent discovery of the most distant galaxy cluster known to date at z=2.51(named "CLJ1001", 17 confirmed members). In addition to its record-breaking distance, CLJ1001 is the first X-ray cluster discovered so far that is dominated by massive star-forming galaxies in the core (instead of massive ellipticals found in low-redshift clusters). With an exceptional star formation rate of ~3400 Msun/yr and a gas depletion time of ~200 Myrs in the cluster core, CLJ1001 was caught in a rapid formation phase of cluster ellipticals, and likely represents a critical transition phase between young, proto-clusters and mature clusters. I will discuss what we have learned so far on CLJ1001 from extensive follow-up observations with ALMA, IRAM-NOEMA, VLA, and VLT, focusing on its implications on the formation of massive cluster ellipticals.

We present the recent results of our W-band survey with CFHT/WIRCam. Substellar candidates were selected with the reddening-insensitive index 'Q', which is derived from J-, H-, and W-band photometry. We tested the Q index with a sample of substellar objects and stars in IC348 and Taurus and found the accuracy to be better than 75%. Using the Q index alone, two new L-type objects in Serpens have been confirmed in spectroscopic followup this July. More candidates in Taurus are going to be observed with IRTF follow up in the end of December. The spectra of observed candidates will also be presented in this talk.

Jupiter Trojans (JTs), two asteroid swarms librating around the L4 and L5 Lagrangian points of Jupiter's orbit, are an important small-body population for investigating the migration of outer planets and extensive dynamical evolution of small bodies in the early solar system. However, the origin and capture mechanism of JTs remain unclear. We performed a wide-field survey targeting L4 JTs using Hyper Suprime-Cam and measured the size distribution of the km-size JT population which has been characterized by collisional evolution depending on the body physical properties. We detected 631 JTs and 130 Hilda asteroids mostly between ~1-10 km in diameter from the survey area of 26 deg^2. The data allowed us to find that (1) the size distribution of JTs is well approximated by a single-slope power law and (2) the shape of Hilda's size distribution is very similar to that of JTs in the km size range.

The coevolution of supermassive black holes (SMBHs) and their host galaxies is one of the most important astrophysical processes due to the ubiquity of SMBHs. Although they are believed to coevolve through various physical processes, such as gas accretion and mergers, the details of these processes are still under hard scrutiny: what governs BH formation and growth, what regulates host galaxy growth, and if their growths have different phases with respect to each other. I will present results and progresses of various projects which I have been working to study the link between the growth of BHs via active galactic nucleus (AGN) activity and the growth of host galaxies through star formation (SF) activity. Most studies utilize a suite of NIR surveys and AKARI space telescope projects. A few highlights include; a discovery of z~6 low luminosity quasar, a census of SF activity of galaxies within North Ecliptic Pole surveys, and a strong correlation between AGN and SF activities of type-1 AGN host galaxies