Tetsuharu Fuse

The Subaru/XMM-Newton Deep Survey (SXDS) - II. Optical Imaging and Photometric Catalogs

We present multiYwave band optical imaging data obtained from observations of the Subaru/XMM-Newton Deep Survey (SXDS). The survey field, centered at R:A: ¼ 02 h 18 m 00 s , decl: ¼� 05 � 00 0 00 00 , has been the focus of a wide range of multiwavelength observing programs spanning from X-ray to radio wavelengths. A large part of the optical imaging observations are carried out with Suprime-Cam on Subaru Telescope at Mauna Kea in the course of Subaru Telescope ‘‘Observatory Projects.’’ This paper describes our optical observations, data reduction and analysis procedures employed, and the characteristics of the data products. A total area of 1.22 deg 2 is covered in five contiguous subfields,eachof whichcorrespondstoasingleSuprime-Camfieldof view(� 34 0 ; 27 0 ),infivebroadbandfilters,B, V,Rc,i 0 ,andz 0 ,tothedepthsof B ¼ 28:4,V ¼ 27:8,Rc ¼ 27:7,i 0 ¼ 27:7,andz 0 ¼ 26:6,respectively(AB,3 � , � ¼ 2 00 ). The data are reduced and compiled into five multiYwave band photometric catalogs, separately for each SuprimeCampointing.Thei 0 -bandcatalogscontainabout900,000objects,makingtheSXDScatalogsoneof thelargestmultiY wavebandcatalogsincorrespondingdepthandareacoverage.TheSXDScatalogscanbeusedforanextensiverangeof astronomicalapplicationssuchasthenumberdensityof theGalactichalostarstothelarge-scalestructuresatthedistant universe. The number counts of galaxies are derived and compared with those of existing deep extragalactic surveys. The optical data, the source catalogs, and configuration files used to create the catalogs are publicly available via the SXDS Web page (http://www.naoj.org/Science/SubaruProject/SXDS/index.html). Subject headingg cosmology: observations — galaxies: evolution — galaxies: formation — galaxies: photometry — large-scale structure of universe

Detailed images of asteroid 25143 Itokawa from Hayabusa.

Rendezvous of the Japanese spacecraft Hayabusa with the near-Earth asteroid 25143 Itokawa took place during the interval September through November 2005. The onboard camera imaged the solid surface of this tiny asteroid (535 meters by 294 meters by 209 meters) with a spatial resolution of 70 centimeters per pixel, revealing diverse surface morphologies. Unlike previously explored asteroids, the surface of Itokawa reveals both rough and smooth terrains. Craters generally show unclear morphologies. Numerous boulders on Itokawas surface suggest a rubble-pile structure.

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’.

Current performance and on-going improvements of the 8.2 m Subaru Telescope

An overview of the current status of the 8.2m Subaru Telescope constructed and operated at Mauna Kea, Hawaii, by the National Astronomical Observatory of Japan is presented. The basic design concept and the verified performance of the telescope system are described. Also given are the status of the instrument package offered to the astronomical community, the status of operation, and some of the future plans. The status of the telescope reported in a number of SPIE papers as of the summer of 2002 are incorporated with some updates included as of 2004 February. However, readers are encouraged to check the most updated status of the telescope through the home page, http://subarutelescope.org/index.html, and/or the direct contact with the observatory staff.

Spin Temperatures of Ammonia and Water Molecules in Comets

The nuclear spin temperature, which is derived from the ortho-to-para abundance ratio of molecules measured in cometary comae, is a clue to the formation conditions of cometary materials, especially the physical temperature at which the molecules were formed. In this paper we present new results for the nuclear spin temperatures of ammonia in comets Hale-Bopp (C/1995 O1) and 153P/Ikeya-Zhang based on observations of NH2 at 26 and 32 K, respectively. These results are similar to previous measurements in two other comets, and the nuclear spin temperatures of ammonia in the four comets are concentrated at about 30 K. We emphasize that the nuclear spin temperatures of water measured thus far have also been about 30 K. In particular, the spin temperatures of ammonia and water are equal to each other within ±1 σ error bars in the case of comet Hale-Bopp. These nuclear spin temperatures of ammonia and water were measured under quite different conditions (heliocentric distances and gas production rates). There is no clear trend between the nuclear spin temperatures and the heliocentric distances, the gas production rates, or the orbital periods of the comets. The possibilities of the ortho-to-para conversion in the coma and in the nucleus are discussed. The present data set implies that the ortho-to-para ratios were not altered after the molecules were incorporated into the cometary nuclei. It appears that cometary ammonia and water molecules formed on cold grains at about 30 K.

ORTHO-TO-PARA RATIOS OF WATER AND AMMONIA IN COMET C/2001 Q4 (NEAT): COMPARISON OF NUCLEAR SPIN TEMPERATURES OF WATER, AMMONIA, AND METHANE

Cold nuclear spin temperatures found in cometary molecules have been simply interpreted as the physical temperature when the population distribution among different nuclear spin isomers was determined through thermal equilibrium processes. However, the real meaning of cold nuclear spin temperatures is unclear due to a lack of experimental studies about the ortho-to-para ratios (OPRs) of molecules in cometary ice analogs. Here we report the nuclear spin temperatures (Tspin) of water and ammonia in comet C/2001 Q4 (NEAT). Measurements of the nuclear spin temperatures of these species and methane from previous work are all consistent with ~30 K. Consistency of the nuclear spin temperatures among different molecular species may suggest that OPRs (or abundance ratios of different nuclear spin isomers) of these molecules were last determined in thermal equilibrium. The obtained nuclear spin temperature of cometary ices is not consistent with molecular formation by hydrogen-atom addition reactions on cold grains, where the H atoms accreted from the gas phase onto grains. The condensation process on the grains might control the ortho-to-para ratios of the precometary ices, or conversion of OPRs within the ices might occur. The small diversity of the nuclear spin temperatures and lack of clear correlation between Tspin and chemical composition in several comets are consistent with the hypothesis that Tspin reflects the temperatures in the presolar nebula.

Organic volatiles in comet 73P-B/Schwassmann-Wachmann 3 observed during its outburst : A clue to the formation region of the jupiter-family comets

We report the chemical composition of organic molecules in fragment B of comet 73P/Schwassmann-Wachmann 3 (SW3). Comet SW3 is a Jupiter-family comet that split into three fragments during its 1995 apparition and later into additional components. It was expected that fresh ices from deep within the presplit nucleus were exposed on the surface of each fragment. We observed SW3 with the Subaru telescope in 2006 early May when component B was disintegrating rapidly. If this exposed fresh ices from deeper layers of the original nucleus, mixing ratios obtained from our observations may reflect the pristine nature of the comet. Based on our results, comet SW3-B was depleted in C2H6 and C2H 2 with respect to most comets from the Oort Cloud reservoir, suggesting its formation region might have differed from that of the dominant Oort Cloud comets. Furthermore, the chemical composition of SW3-B was similar to that of SW3-C, suggesting that the presplit nucleus was almost homogeneous in volatile composition. The combined results demonstrate that depleted-organics comets from a common formation zone entered both reservoirs, of Jupiter-family comets and and Oort Cloud comets, but likely in different fractions.

Evidence of Icy Grains in Comet C/2002 T7 (LINEAR) at 3.52 AU

We present evidence of icy grains in the coma of comet C/2002 T7 (LINEAR) at 3.52 AU from the Sun. This comet will approach the Sun in the spring of 2004, and it is expected to be very bright near its perihelion passage. The comet was observed using the Subaru Telescope with the Cooled Infrared Spectrograph and Camera for OHS (CISCO) on 2003 September 14.6 (UT). The near-infrared (J, H, K) spectrum was extracted from the near-nucleus region (1250 km × 1250 km at the comet), and it showed clear absorption features at 1.5 and 2.05 μm that originated from water ice grains. The calculated reflectance spectrum, based on the intimate mixture model for water ice grains and astronomical silicate grains (the diameters are 5 and 0.5 μm, respectively), can reproduce the observed reflectance spectrum of the comet up to 2.1 μm. The poor fit for the wavelength region longer than 2.1 μm is probably indicative of other grain species to be included in the model. Furthermore, the absence of the 1.65 μm feature of crystalline water ice may indicate that the water ice was in an amorphous state during the observation.

Nuclear Spin Temperature and Deuterium-to-Hydrogen Ratio of Methane in Comet C/2001 Q4 (NEAT)*

We carried out high-dispersion, spectroscopic observations of comet C/2001 Q4 (NEAT) in the near-infrared with the 8 m Subaru telescope and detected the R-branch emission series of the ν3 vibrational band of methane. The signal-to-noise ratio of the observed spectrum was sufficient to make the first determination of the nuclear spin temperature of methane, derived to be 33 K, which reflects the temperature of formation or condensation of molecules on cold grains. The upper limit of the CH3D/CH4 ratio was determined to be 0.04 (95% confidence limit), indicating the formation of methane in a dense molecular cloud at temperatures higher than about 30 K. On the basis of these observational results, we conclude that the Sun was born in a warm molecular cloud near 30 K, not in a cold dark cloud near 10 K, as is usually assumed.

Mature and Fresh Surfaces on the Newborn Asteroid Karin

Here we report a near-infrared (J, H, and K bands) spectroscopy of 832 Karin, the brightest asteroid among the Karin cluster group, which is thought to be the remnants of a collisional breakup only 5.8 million years ago. The spectroscopic observation was performed by the Subaru telescope with the Cooled Infrared Spectrograph and Camera for OHS on 2003 September 14. For different rotational phases of Karin, we derived different spectra such as a reddened spectrum like that of an S-type asteroid and an unreddened spectrum like that of ordinary chondrite. Karin could be an impact fragment preserving an old surface and is probably one of the cone-shaped fragments at the low-velocity impact that formed the Karin cluster group. Our result supports the idea that S-type asteroids are parent bodies of ordinary chondrites.