Masanori Iye

Down‐sizing in galaxy formation at z∼ 1 in the Subaru/XMM–Newton Deep Survey (SXDS)

We use the deep wide-field optical imaging data of the Subaru/XMM‐Newton Deep Survey to discuss the luminosity- (mass-)dependent galaxy colours down to z � = 25.0 (5 × 10 9 h −2 70 M� ) for z ∼ 1 galaxies in colour-selected high-density regions. We find an apparent absence of galaxies on the red colour‐magnitude sequence below z � ∼ 24.2, corresponding to ∼M ∗ + 2( ∼ 10 10 M� ) with respect to passively evolving galaxies at z ∼ 1. Galaxies brighter than M ∗ − 0.5 (8 × 10 10 M� ), however, are predominantly red passively evolving systems, with few blue star-forming galaxies at these magnitudes. This apparent age gradient, where massive galaxies are dominated by old stellar populations while less massive galaxies have more extended star formation histories, supports the ‘downsizing’ idea where the mass of galaxies hosting star formation decreases as the Universe ages. Combined with the lack of evolution in the shape of the stellar mass function for massive galaxies since at least z ∼ 1, it appears that galaxy formation processes (both star formation and mass assembly) should have occurred in an accelerated way in massive systems in highdensity regions, while these processes should have been slower in smaller systems. This result provides an interesting challenge for modern cold dark matter based galaxy formation theories which predict later formation epochs of massive systems, commonly referred to as ‘bottom-up’.

First results from the Subaru AO system

An adaptive optics system was developed for the 8.2-m Subaru Telescope operated by the National Astronomical Observatory of Japan on the summit of Mauna Kea in Hawaii. The system saw first light on 2 December 2000 and achieved diffraction limited imaging in the K- and L- band. The system is located at the Cassegrain focus of Subaru and can feed either IRCS, an infrared camera and spectrograph (used for first light) or CIAO, an infrared coronagraphic imager. The system features a 36-elements curvature sensor using avalanche photo diodes and a 36-electrodes bimorph deformable mirror. The curvature sensor and deformable mirror were custom designed for an optimum match. Wavefront sensing is performed in the visible range while AO-corrected observations are made in the infrared. In this paper the first AO observations are described and the system performances are compared with the design values. A comparison is also made with other existing AO systems. First scientific demonstrations are shown.

Membrane deformable mirror for SUBARU adaptive optics

The prototype membrane deformable mirror for the Cassegrain adaptive optics of SUBARU (Japanese 8 m telescope under construction at Mauna Kea). It was made of 2 micrometers thick nitrocellulose, 50.8 mm in diameter, and had an effective area of 25 mm in diameter. The surface was coated with aluminum that acts both as a reflective surface and as an electrode. The deformation of mirror surface was produced by applying electrostatic force between the membrane and adjacent multi-element electrodes. The mirror surface quality was 0.03 (lambda) rms at 0.632 micrometers in wave front with and without applying bias voltages. The strong resonance was observed under vacuum condition at 1.6 kHz, but disappeared when the inner pressure was controlled at about 10 Torr, for which the mirror bandwidth became 3.3 kHz at 45 deg phase delay.

Performance of Subaru adaptive optics system and the scientific results

We present an overview of Subaru Cassegrain adaptive optics system and its performance verified at the engineering run. The system is based on a curvature wavefront sensor with 36-element sub-apertures and a bimorph deformable mirror with identical number of elements. We had the first light in Dec. 2000. The AO system has been in service for two instruments, IRCS; infrared camera and spectrograph, and CIAO; coronagraph imager with adaptive optics. The Strehl ratio at the K band is around 0.30 under 0.4- 0.5 arcsec K-band seeing condition for bright guide stars. The sensitivity of the wavefront sensor is so high that we have significant improvement of image quality even for a faint guide star down to R=18th magnitude. The measurement of stars in a globular cluster suggests an isoplanatic angle, about 40 arcsec, wider than that expected from the equivalent turbulence layer assumed at the height of 6.5 km. The system has been offered for common use since Apr. 2002. Some scientific results using this AO system are shown in this paper.

Faint Object Camera and Spectrograph for the 8-m SUBARU Telescope

The concept design of the faint object camera and spectrograph (FOCAS) for the 8.2 m SUBARU telescope (JNLT) is presented. The FOCAS is designed for enabling observations of extremely faint galaxies distributed over a 6 arcmin FOV with spectral resolution of R equals 1000. Fully transmitting optics will produce high quality images better than about 20 micrometers rms diameter over the entire FOV in white light of a wavelength range of 0.365 - 0.9 micrometers . A pair of abuttable CCDs with 4000 x 2000 pixels of 15 micrometers square pixel size are considered to be used. Several observing modes are available with the automated multislit assembly and changable optical elements. Control software coupled with telescope control software enables an automatic observation of several tens of galaxies simultaneously.

Grism and immersion grating for space telescope

The grism is a versatile dispersion element for an astronomical instrument ranging from ultraviolet to infrared. Major benefit of using a grism in a space application, instead of a reflection grating, is the size reduction of optical system because collimator and following optical elements could locate near by the grism. The surface relief (SR) grism is consisted a transmission grating and a prism, vertex angle of which is adjusted to redirect the diffracted beam straight along the direct vision direction at a specific order and wavelength. The volume phase holographic (VPH) grism consists a thick VPH grating sandwiched between two prisms, as specific order and wavelength is aligned the direct vision direction. The VPH grating inheres ideal diffraction efficiency on a higher dispersion application. On the other hand, the SR grating could achieve high diffraction efficiency on a lower dispersion application. Five grisms among eleven for the Faint Object Camera And Spectrograph (FOCAS) of the 8.2m Subaru Telescope with the resolving power from 250 to 3,000 are SR grisms fabricated by a replication method. Six additional grisms of FOCAS with the resolving power from 3,000 to 7,000 are VPH grisms. We propose “Quasi-Bragg grism” for a high dispersion spectroscopy with wide wavelength range. The germanium immersion grating for instance could reduce 1/64 as the total volume of a spectrograph with a conventional reflection grating since refractive index of germanium is over 4.0 from 1.6 to 20 μm. The prototype immersion gratings for the mid-InfraRed High dispersion Spectrograph (IRHS) are successfully fabricated by a nano-precision machine and grinding cup of cast iron with electrolytic dressing method.

Subaru laser guide adaptive optics system: performance and science operation

The Subaru adaptive optics system (AO188) is a 188-element curvature sensor adaptive optics system that is operated in both natural and laser guide star modes. AO188 is installed at Nasmyth platform of the 8m Subaru telescope as a facility AO system. The laser guide star mode for AO188 has been commissioned and offered for use in science operation since 2011. The performance of AO188 in the laser guide star mode has been well verified from on-sky data obtained with the infrared camera and spectrograph (IRCS). In this paper, we describe the operation procedure and observing efficiency for the laser guide star mode. We also show the result of the on-sky performance evaluation of AO188 in the laser guide star mode and the characterization of the laser guide star, together with the obtained science results.

1 W 589 nm Coherent Light-Source Achieved by Quasi-Intracavity Sum-Frequency Generation

We proposed a novel configuration for efficient generation of coherent 589-nm light by sum-frequency generation mixing 1064 and 1319 nm emitted from two continuous-wave Nd:YAG lasers. A 5-mm-long periodically-poled KTiOPO4 was used as a nonlinear optical crystal and it was set in the 1064-nm-Nd:YAG laser. Output beam oscillated from the 1319-nm-Nd:YAG laser was superimposed on a propergation axis of 1064-nm beam stored in the 1064-nm laser using a beam combiner from outside of the laser.?Output power of sum frequency reached to 1 W and it was ten times higher than that by extracavity sum-frequency generation using the same appatatus.

Recent development in real time control system of Subaru LGSAO-188

We report recent development in real-time control system of 188-element Laser Guide Star Adaptive Optics for Subaru Telescope (Subaru LGSAO-188). The current status is reported, and plans for improvements to enhance the performance are reported as well. A major item is to invoke the optimum gain control, which is being implemented on the data handling system and to be attached to the real time control system. We also explain about other new features on the control system including general response acquisition system as an expansion of response matrix acquisition system.

Subaru Adaptive Optics Program

The system overview and the current status of an adaptive optics system for the Cassegrain focus of Subaru 8.2 m telescope under construction atop Mauna Kea is presented. The system is composed of a wavefront curvature sensor with 36 elements photon-counting APD modules and a 36-element bimorph deformable mirror. We aim to get the Strehl ratio of greater than 0.6 at the K band (2.2 micron) using natural guide stars as wavefront reference under the average seeing condition (approximately 0.45 arcsec) at Mauna Kea. It is scheduled to be in operation in 1998. Expected performance, especially the sky coverage when employing natural guide stars are also presented. currently we are testing prototype system with basically identical specifications as those of the final system. We present here the optical system, deformable mirror, wavefront sensor, control system of the final system, and simple introduction and experimental results of the prototype system.