Subaru Seminars

ESPRESSO (Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations) is an ultra-stable high-resolution spectrograph, located in the combined Coudé Lab of the VLT at ESO, and is able to operate either using one 8.2m-VLT UT or simultaneously with the four VLT UTs. ESPRESSO started routine operations in October 2018 at ESO, and is designed to achieve a radial velocity precision of 10 cm/s, thus opening the possibility to explore new frontiers in science such as the search for rocky planets and the measurement of the variation of physical constants. ESPRESSO is considered a precursor of the ultra-stable high-resolution spectrograph ANDES (ArmazoNes high Dispersion Echelle Spectrograph) for the 39m-ELT telescope.
ESPRESSO has been very successful so far in detecting and characterizing low-mass planets demonstrating the sub-m/s capabilities of the instrument, providing a unique ground-based facility with great synergy with exoplanet dedicated satellites such as Kepler, TESS, and CHEOPS. One of the most relevant recent achievement of ESPRESSO is the confirmation of the 11.2d Earth mass planet Proxima b in the habitable zone of Proxima Centauri, and the discovery of the sub-Earth mass planet Proxima d in a 5.1d orbit with a semiamplitude velocity of 40 cm/s together with a simultaneous, precise characterization of the activity of the star. This discovery together with the 5yr period super-Earth planet candidate Proxima c, composes the currently known planetary system in the nearest stellar neighbour to our Sun.
ESPRESSO is opening the possibility to characterize the Earth-mass and sub-Earth-mass population of exoplanets in the solar neighbourhood, thus encouraging new detailed studies of this and other nearby stars with current and future facilities such as ANDES@ELT.
In this talk I will briefly summarize the main features of ESPRESSO instrument performance, focusing on revealing the Earth-mass and sub-Earth mass planets orbiting nearby stars and future prospects.

Utilizing the unique wide-field observation capabilities of Subaru, we have been conducting panoramic studies of galaxy clusters and proto-clusters over 0.4<z<5.4. In particular, we employ narrow and medium-band filters on wide-field cameras to map star forming galaxies (line emitters) and quiescent galaxies (Balmer break), and very efficiently and robustly identify the inner/surrounding structure within narrow redshift slices. Moreover, pair narrow-band filter technique is extremely unique and can provide us with physical properties of galaxies only with imaging such as star formation rate, dust extinction, AGN contribution, and neutral gas association. With all these pieces of information put together, we will describe our current understandings of how galaxy clusters are assembled, and how the galaxies are influenced by the changing surrounding environments across cosmic times. I will also comment that PFS will be useful to investigate galaxies in filaments and large scale structures in much greater detail.

Photonic lanterns (PL) are fiber devices that enable high throughput spectroscopy at high angular resolution. The PL efficiently converts a multi-mode waveguide into several single-mode waveguides able to feed a spectrograph. When coupled with an extreme adaptive optics system, these devices significantly enhance on-sky throughput performance compared to single-mode fibers alone. They facilitate the delivery of spectral information at spatial resolutions surpassing those achievable with traditional coronagraphic instruments, and are capable of even beating the telescope spatial resolution. The Subaru Coronagraphic Extreme Adaptive Optics system recently acquired and tested several PLs at Near-IR and Visible wavelengths. From wavefront sensing to spectro-imaging at very high angular resolution, we have been exploring the various possibilities offered by the PLs. We will present the Photonic Lantern devices, explain our search to optimally use them, and present several high contrast applications.

Topic 1: Many high-z (z > 6) quasar surveys have been executed in the past two decades, and more than 300 quasars have been discovered to date. In recent years, JWST is further making groundbreaking results. Roughly a half of the known high-z quasars have been identified based on the Subaru/HSC-SSP survey, at about two orders of magnitude lower luminosities compared to other wide-field surveys. Some of these quasars were observed with near-IR spectrographs to examine the black hole masses in order to, e.g., compare with their host galaxies observed with ALMA. While the mass is a key parameter to describe the SMBH evolution, it was not measured in most of the HSC-based high-z quasars due to their faintness. We devised a novel method to exploit a large sample of low-z quasars from SDSS, and tried to estimate CIV line profile (a tracer of SMBH masses) of the high-z quasars by finding their low-z “counterparts” with similar spectra in the overlapping wavelength around Ly alpha. We found that the resulting black hole masses show a good correlation with those actually measured from near-IR spectroscopy. We will show the estimated distribution of SMBH mass and Eddington ratio of the high-z low-luminosity quasars, and discuss its implication.
Topic 2: How SMBHs formed and grew quickly from the Big Bang is still an open question. Quasar-driven massive outflow extending on galactic scales was detected in significant fractions of quasars. A large C IV BAL fraction of ~50 % was recently reported for 30 high-z luminous quasars, which is ~2.4 times higher than measured in the low-z universe. We are carrying out near-IR spectroscopy of our HSC-based low-luminosity high-z quasars, in order to measure the BAL fraction. Our observations will provide significant insight into whether black hole outflows contribute to putative AGN feedback in the early universe and the evolutionary sequence of the galaxies hosting high- and low-luminosity quasars.

Water ice plays many important roles in the planet formation, however, observations of the water ice in the protoplanetary disk are lmited so far. Here we introduce our efforts to map the water ice in the disk and ultimately trace the "snow line" in the disk. I also would like to comment some thoughts/ideas on the ground-based mid-IR astronomy.

In ground-based astronomy in optical and near-infrared wavelength, turbulence in the Earth's atmosphere causes wavefront distortion, which results in much poorer angular resolution or worse sensitivity compared to the original performance of large telescopes. One of the solutions is using an adaptive optics (AO) system, which controls the wavefront distortion with a loop speed faster than the atmosphere changes. Recently, AO using multiple laser guide stars (LGS) and atmospheric tomography techniques have been developed and demonstrated for AO working with a wider field of view, at shorter wavelength ranges, and over larger sky coverage, compared to the classical AO. The AO with multiple LGS is also important in terms of the technique being a standard observation mode in the era of extremely large telescopes. In this work, we measure atmospheric turbulence profiles at the Subaru telescope, which is crucial for designing AO parameters, optimizing the tomographic wavefront reconstruction matrix, and evaluating AO performance, in the context of the ULTIMATE projects. To investigate free atmospheric turbulence with a high altitude range and strong ground layer turbulence with a fine altitude resolution at the same time, we develop a novel atmospheric turbulence profiler comprising two Shack-Hartmann sensors with a fine pupil sampling of 2 cm. Through two engineering observations at the Subaru telescope, we obtain free atmospheric profiles with a range of 1-20 km and a resolution of a few km and ground layer profiles with a range of up to 400 m and a resolution of 10-20 m, which is applicable to tomography and performance simulation for the ULTIMATE AO systems. Besides, we measure total seeing and wind profile based on the slope and scintillation measurements by a single Shack-Hartmann sensor.

This research aims to identify dust-obscured proto-clusters of galaxies in the early universe using the HSC-SSP and Planck data. The Planck has identified more than 2,000 Planck High-z (PHz) sources (Planck Collaboration 2016), among which we identified 72 sources are covered by Subaru HSC-SSP survey footprints (PDR3). By examining the spatial distribution of the Lyman Break Galaxies (LBGs) toward these PHz sources, we discovered candidates of >20 proto-clusters at z~4 and z~5. The large sample of these newly discovered candidate proto-clusters will be an excellent laboratory to study the early stages of galaxy evolution along the structure formation of the universe.

Koyama Astronomical Observatory in Kyoto Sangyo University, Japan is currently developing two adaptive optics-related instruments: Compact Refractive Adaptive Optics (CRAO) and the atmospheric disturbance monitor system MAMO. CRAO aims to improve typical seeing from 3.0" to a good site seeing of 0.8" mounted on the 1.3-m Araki telescope as a test model for small AO with a 1-m class telescope. MAMO is an instrument that measures the atmospheric structure constant Cn2 and Seeing at different altitudes in real-time using a Shack-Hartmann wavefront sensor. Combining these two, we are considering an integrated system that corrects real-time measured altitude profiles of atmospheric turbulence with optimal AO parameters previously calculated by AO simulations. In this presentation, we will report on the status of development and future plans for CRAO and MAMO, respectively.

Between 1999 and 2012, a collaboration of Observatories strived to connect telescopes at the summit of Maunakea with single mode optical fibres into a kilometric baseline interferometer to operate at near infrared wavelengths; it was the OHANA project, (Optical Hawaiian Array for Nanoradian Astronomy, with all the telescopes operating as a family). We achieved some success, first injecting starlight into single mode fibres (at CFHT, Keck and Gemini in 2001, 2002 and 2003 respectively) and then succeeding in coherently transporting light from the two Kecks through fibres and measuring stellar fringes in 2005. Unfortunately, luck was not with us and adverse weather conditions prevented us from performing astronomical observations of YSOs and AGNs at Keck until 2009. The ‘OHANA iki experiment was concurrently developed using 8” telescopes to demonstrate the interferometric chain, from acquisition and fringe capture to reduced data for outdoor fiber links. At that time, the lengths of the fibers were not servoed and this was clearly identified as an issue that would need to be addressed to link telescopes with fibers for coherent detection in the future. The project came to an end in 2012, leaving some of us feeling that we had been young and foolish to embark on such an ambitious project.

Now that we are older and presumably wiser, we propose to revive the idea of interferometric connection of the Maunakea telescopes, but this time in the visible and using quantum optics. The technique of intensity interferometry, developed by Hanbury-Brown and Twiss in the 1950s and used with great success in the 1960s at the Narrabri Interferometer, fell into neglect with the advent of amplitude interferometry, pioneered by Antoine Labeyrie in the 1970s. But technological progress driven by quantum optics and telecommunications has led to the development of new components (SPADs, SNSPDS) which have allowed to extend the sensitivity of the technique by orders of magnitude. We have developed a collaboration between quantum optics physicist and astronomers at Universite Cote d'Azur since 2016 and have demonstrated the promise of the technique using our 1m telescopes to achieve original and meaningful astrophysical measurements. One of the main advantages of the technique, besides being insensitive to atmospheric turbulence, is that it requires no physical link between the telescopes, making it ideally suited for implementation on a site such as Maunakea, with no impact on the mountain whatsoever.

The longest baselines on the mountain would allow to obtain a visibility measurement in one night of integration on Sirius B, the closest known white dwarf. These exotic objects are supported by Fermi electron degeneracy, and their diameter is estimated from their luminosity; such a measurement would uniquely constrain the diameter and demonstrate quantum mechanics at work on an astrophysical size object!

The art of cosmography, i.e. map-making of the Universe, is essential for progress in astronomy. In this talk, I present a new technique to map the large-scale structure of the intergalactic medium (IGM) using ultra-deep Subaru/HSC narrow-band imaging. This so-called “photometric IGM tomography” detects faint Lyman-alpha forest transmission along all background galaxies photometrically, allowing us to reconstruct the tomographic map of the IGM at high redshifts from z~4 to 6. Using the publicly available HSC data, I demonstrate the proof-of-concept and present the first co-spatial, large-scale map of the cosmic web of both galaxies and the IGM at z~5 in the COSMOS field. By analysing the IGM tomographic map with theory/numerical simulations, I discuss the physical implications of the result on the source of reionization, escape fractions and ionizing capabilities of galaxies, and the radiative growth history of supermassive black holes. I conclude by discussing how this technique could be improved further by using the data from Subaru/PFS and JWST.

The cosmic noon is not only a key transitional epoch for star-formation and AGN activity within galaxies but also the period when protoclusters experience major albeit rapid changes in their internal structure, setting the (pre-)conditions for environmental effects over their galaxy populations. We use Keck/MOSFIRE and VLT/KMOS to investigate the role of cluster assembly over star formation and metal enrichment in >60 galaxies in two dynamically distinct protoclusters at 2<z<3: USS1553 and PKS1138. Objects within the ‘younger’ protocluster, USS1558, exhibit enhanced SFRs and gas-phase metallicity deficit with respect to the field, suggesting that young galaxies are experiencing a rapid phase of mass assembly mediated by prominent gas accretion. On the other hand, the massive and en route to virialization PKS1138 protocluster is indistinguishable from the field in terms of the star formation activities of its members and shows early signs of metal enrichment, hinting that the protocluster's assembly stage significantly impacts the evolution of its galaxy populations. We put in context these results by exploring the gas fractions of a subsample of objects with molecular gas masses from ALMA and ATCA in both protoclusters and discuss the relative importance of in-/outflow processes on regulating star-formation and metal enrichment during the early phases of cluster assembly.

Galaxies are distributed inhomogeneously on small scales in the Universe and thus define large-scale structures (LSS). Understanding the evolution of cluster galaxies is to determine how galaxies change their properties as a result of the hierarchical growth of LSS. This work studies the environmental dependence of narrow-band (NB) selected star-forming galaxies at z~0.4 in the DEEP2-3 field. We demonstrate a method to estimate accurate redshifts of star-forming galaxies by measuring the flux ratio of the same emission line observed through two adjacent narrow-band filters taken with Hyper Suprime-Cam on the Subaru Telescope. We find a significant positive correlation between SF rate and overdensity at z~ 0.4, particularly in high-density regions, which is weak or absent locally in star-forming galaxies. We also measure the Hα and stellar continuum sizes and find that the re(Hα)/re(cont) around the cluster core is smaller than outskirt and field galaxies. This may suggest the effect of ram-pressure stripping in cluster core galaxies. We also explore the 3-D exploration of the huge cosmic web at z=0.4 with HSC triple NB imaging.

In the local universe, physical properties of galaxies (e.g. color, age, star formation activity, morphology, etc.) strongly depend on their surrounding environment. For example, it is known that the fraction of old, red, quiescent galaxies in galaxy clusters is high, while that of young, blue, star-forming galaxies in the field is high. It is very important to understand when, where, and how this environmental dependence occurred in the past in order to unveil the history of galaxy formation and evolution. However, studies of the environmental dependence in the distant universe have been limited due to a small sample of galaxy clusters, and have been biased toward clusters with evolved evolutionary stages. Therefore, we have conducted a large distant galaxy cluster survey using the Subaru HSC, which provide us with a wider and deeper imaging data than the previous survey. We used emission-line galaxies selected from the narrow-band filters on the HSC to search for overdense regions of young star-forming galaxies at z~1.5. We plan to show two extremely high dense regions of emission line galaxies in the COSMOS field and member galaxy properties, and future prospect of this project.

We measure the size and morphology of Hα-emitters (HAEs) in four protoclusters at z ~ 2 (PKS 1138-262, USS 1558-003, PHz G237.0+42.5, and CC 2.2) observed by Hα emission line surveys using the Hubble Space Telescope Advanced Camera Surveys (HST/ACS) F814W data. We compare the measurement of 138 HAEs in protoclusters detected by HST/ACS to a coeval comparison field sample of 462 HAEs. We find the size distributions of protocluster and field HAEs at are similar with typical half-light radius of ~ 2.5 kpc. At fixed stellar mass, there is no significant difference between HAE in protocluster and in field, which is also supported by stacking analyses. This result suggests that the environment does not significantly affect the size of galaxies during the star-forming phase at this epoch. Based on Sersic index and non-parametric morphologies, HAE morphologies at z~2 in rest-frame UV are consistent with disk-like star-forming galaxies, although we also find ~20% HAEs have peculiar morphologies, which is more prevalent in protocluster environment.