研究者業績
基本情報
- 所属
- 国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所 教授東北大学大学院 理学研究科 (名誉教授)
- 学位
- 京都大学博士（理学）(1994年3月 京都大学)
- J-GLOBAL ID
- 202001002640673973
- researchmap会員ID
- R000014747
研究分野
1経歴
6-
2016年1月 - 現在
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2016年1月 - 現在
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2008年7月 - 2015年12月
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2000年4月 - 2008年6月
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1996年4月 - 2000年3月
学歴
2-
1989年4月 - 1994年3月
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1984年4月 - 1989年3月
論文
311-
NEW ASTRONOMY REVIEWS 53(3) 54-56 2009年6月Ly alpha Blobs (LAB), large, extended Lya emitters, are enigmatic objects that calls on much attention in the field of galaxy formation and evolution. So far, discovery of more than twenty giant (>60 kpc) LABs have been reported and new searches are on-going. Many of the groups who study LABs attended the workshop in Heidelberg, "Understanding Ly alpha Emitters", 2008 October 6-10. We had useful discussions on the various important aspects of LABs including the search or detection methods, origins of the extended Ly alpha emission, and their physical properties. (C) 2009 Elsevier B.V. All rights reserved.
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ASTROPHYSICAL JOURNAL 696(2) 1164-1175 2009年5月We report the discovery of a giant Ly alpha emitter (LAE) with a Spitzer/Infrared Array Camera (IRAC) counterpart near the reionization epoch at z = 6.595. The giant LAE is found from the extensive 1 deg(2) Subaru narrowband survey for z = 6.6 LAEs in the Subaru/XMM-Newton Deep Survey (SXDS) field, and subsequently identified by deep spectroscopy of Keck/DEIMOS and Magellan/IMACS. Among our 207 LAE candidates, this LAE is not only the brightest narrowband object with L(Ly alpha) = 3.9 +/- 0.2 x 10(43) erg s(-1) in our survey volume of 10(6) Mpc(3), but also a spatially extended Ly alpha nebula with the largest isophotal area whose major axis is at least similar or equal to 3 ''. This object is more likely to be a large Ly alpha nebula with a size of greater than or similar to 17 kpc than to be a strongly lensed galaxy by a foreground object. Our Keck spectrum with medium-high spectral and spatial resolutions suggests that the velocity width is nu(FWHM) = 251 +/- 21 km s(-1), and that the line-center velocity changes by similar or equal to 60 km s(-1) in a 10 kpc range. The stellar mass and star formation rate are estimated to be 0.9-5.0 x 10(10) M-circle dot and >34 M-circle dot yr(-1), respectively, from the combination of deep optical to infrared images of Subaru, UKIDSS-Ultra Deep Survey, and Spitzer/IRAC. Although the nature of this object is not yet clearly understood, this could be an important object for studying cooling clouds accreting onto a massive halo, or forming-massive galaxies with significant outflows contributing to cosmic reionization and metal enrichment of intergalactic medium.
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EXPERIMENTAL ASTRONOMY 23(1) 193-219 2009年3月The Space Infrared telescope for Cosmology and Astrophysics (SPICA) is planned to be the next space astronomy mission observing in the infrared. The mission is planned to be launched in 2017 and will feature a 3.5 m telescope cooled to < 5 K through the use of mechanical coolers. These coolers will also cool the focal plane instruments thus avoiding the use of consumables and giving the mission a long lifetime. SPICA's large, cold aperture will provide a two order of magnitude sensitivity advantage over current far infrared facilities (> 30 microns wavelength). We describe the scientific advances that will be made possible by this large increase in sensitivity and give details of the mission, spacecraft and focal plane conceptual design.
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ASTROPHYSICAL JOURNAL 692(2) 1287-1293 2009年2月Knowing the amount of ionizing photons from young star-forming galaxies is of particular importance to understanding the reionization process. Here we report initial results of a Subaru/Suprime-Cam deep imaging observation of the SSA22 proto-cluster region at z = 3.09, using a special narrow-band filter to optimally trace ionizing radiation from galaxies at z similar to 3. The unique wide field-of-view of Suprime-Cam enabled us to search for ionizing photons from 198 galaxies (73 Lyman break galaxies (LBGs) and 125 Ly alpha emitters (LAEs)) with spectroscopically measured redshifts z similar or equal to 3.1. We detected ionizing radiation from 7 LBGs, as well as from 10 LAE candidates. Some of the detected galaxies show significant spatial offsets of ionizing radiation from nonionizing UV emission. For some LBGs the observed nonionizing UV to Lyman continuum flux density ratios are smaller than values expected from population synthesis models with a standard Salpeter initialmass function (IMF) with moderate dust attenuation (which is suggested from the observed UV slopes), even if we assume very transparent intergalactic medium along the sightlines of these objects. This implies an intrinsically bluer spectral energy distribution, e. g., that produced by a top-heavy IMF, for these LBGs. The observed flux density ratios of nonionizing UV to ionizing radiation of 7 detected LBGs range from 2.4 to 23.8 and the median is 6.6. The observed flux density ratios of the detected LAEs are even smaller than LBGs, if they are truly at z similar or equal to 3.1. We find that the median value of the flux density ratio for the detected LBGs suggests that their escape fractions are likely to be higher than 4%, if the Lyman continuum escape is isotropic. The results imply that some of the LBGs in the proto-cluster at z similar to 3 have escape fraction significantly higher than that of galaxies (in a general field) at z similar to 1 studied previously.
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ASTROPHYSICAL JOURNAL 692(2) 1561-1570 2009年2月We present the results of a Spitzer IRAC and MIPS 24 mu m study of extended Lyman-alpha clouds (or Lyman-alpha Blobs, LABs) within the SSA22 filamentary structure at z = 3.09. We detect 6/26 LABs in all IRAC filters, four of which are also detected at 24 mu m, and find good correspondence with the 850 mu m measurements of Geach et al. An analysis of the rest-frame ultraviolet, optical, near-and mid-infrared colors reveals that these six systems exhibit signs of nuclear activity (active galactic nucleus (AGN)) and/or extreme star formation. Notably, they have properties that bridge galaxies dominated by star formation (Lyman-break galaxies (LBGs)) and those with AGNs (LBGs classified as QSOs). The LAB systems not detected in all four IRAC bands, on the other hand, are, as a group, consistent with pure star-forming systems, similar to the majority of the LBGs within the filament. These results indicate that the galaxies within LABs do not comprise a homogeneous population, though they are also consistent with scenarios in which the gas halos are ionized through a common mechanism such as galaxy-scale winds driven by the galaxies within them, or gravitational heating of the collapsing cloud itself.
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EXOPLANETS AND DISKS: THEIR FORMATION AND DIVERSITY 1158 251-+ 2009年SEEDS (the Subaru Strategic Exploration of Exoplanets and Disks with Hi-CIAO/AO188) is a strategic five-year campaign of direct imaging surveys of exoplanets/disks using the Subaru telescope equipped with the new adaptive optics system AO188 and our new high-contrast instrument, HiCIAO. The goals of the survey are to address the following key issues in exoplanet/disk sciences: (1) the detection and census of exoplanets; (2) the evolution of protoplanetary and debris disks; and (3) the link between exoplanets and disks. Targets prepared for the SEEDS exoplanet searches are in four categories, including nearby stars. We present our scientific motivations and current status of the SEEDS target selection in the nearby stars category.
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EXOPLANETS AND DISKS: THEIR FORMATION AND DIVERSITY 1158 135-+ 2009年We carried out a direct imaging campaign of the pre-outburst FU Ori candidate V 1331 Cyg in the H band with CIAO on the Subaru Telescope to investigate the inner structures of V 1331 Cyg and to directly detect the disk. Spatial structures revealed by direct imaging may describe the physical conditions of the disk and can restrict the theories of planetary formation. In our preliminary results, we clearly detected a bright arc interior to the known inner ring, which is likely to be the scattered light from the disk. Here, we will show the results and discuss nature of the structure including the comparison with the HST images.
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ASTROPHYSICAL JOURNAL 691(1) 687-695 2009年1月We present results from a new ultra-deep approximate to 400 ks Chandra observation of the SSA22 protocluster at z = 3.09. We have studied the X-ray properties of 234 z similar to 3 Lyman Break Galaxies (LBGs; protocluster and field) and 158 z = 3.09 Ly alpha Emitters (LAEs) in SSA22 to measure the influence of the high-density protocluster environment on the accretion activity of supermassive black holes (SMBHs) in these UV-selected star-forming populations. We detect individually X-ray emission from active galactic nuclei (AGNs) in six LBGs and five LAEs; due to small overlap between the LBG and LAE source population, ten of these sources are unique. At least six and potentially eight of these sources are members of the protocluster. These sources have rest-frame 8-32 keV luminosities in the range of L(8-32) (keV) = (3-50) x 10(43) ergs s(-1) and an average observed-frame 2-8 keV to 0.5-2 keV band ratio ( BR) of approximate to 0.8 (mean effective photon index of Gamma(eff) approximate to 1.1), suggesting significant absorption columns of N(H) greater than or similar to 10(22)-10(24) cm(-2). We find that the fraction of LBGs and LAEs in the z = 3.09 protocluster harboring an AGN with L(8-32 keV) greater than or similar to 3 x 10(43) ergs s(-1) is 9.5(-6.1)(+12.7)% and 5.1(-3.3)(+6.8)%, respectively. These AGN fractions are somewhat larger (by a mean factor of 6.1(-3.6)(+10.3); significant at the approximate to 95% confidence level) than z similar to 3 sources found in lower-density "field" environments. Theoretical models imply that these results may be due to the presence of more actively growing and/or massive SMBHs in LBGs and LAEs within the protocluster compared to the field. Such a result is expected in a scenario where enhanced merger activity in the protocluster drives accelerated galaxy and SMBH growth at z greater than or similar to 2-3. Using Spitzer IRAC imaging we found that the fraction of IRAC-detected LBGs is significantly larger in the protocluster than in the field (by a factor of 3.0(-1.3)(+2.0)). From these data, we constrained the median rest-frame H-band luminosity in the protocluster to be greater than or similar to 1.2-1.8 times larger than that for the field. When combined with our X-ray data, this suggests that both galaxies and SMBHs grew more rapidly in protocluster environments.
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STARBURST-AGN CONNECTION 408 445-451 2009年We investigate the X-ray properties of the K-band-selected galaxies at redshift 2 < z < 4 by using our deep near-infrared images obtained in the MOIRCS Deep Survey project and the published Chandra X-ray source catalog. 61 X-ray sources with the 2-10 keV luminosity L(X) = 10(42) - 10(44) erg s(-1) are identified with the K-selected galaxies and we found that they are exclusively (90%) associated with the massive objects with stellar mass larger than 10(10.5) M(circle dot). On the other hand, the AGN detection rate among the very massive galaxies with the stellar mass larger than 10(11) M(circle dot) is high, 33% (26/78). The active duration in the AGN duty cycle of the high-redshift massive galaxies seems large.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 60(6) 1347-1362 2008年12月MOIRCS is a fully cryogenic near-infrared instrument for the 8.2 m Subaru Telescope. MOIRCS has two observation modes: a wide-field imaging mode and a multiobject spectroscopy mode. This paper describes the imaging mode, its specifications, and actual performances that we confirmed through laboratory tests and commissioning observations. The imaging mode provides a 4' x 7' field of view with a pixel scale of 0 ''.117 pixel(-1) in the wave-length range of 0.85 to 2.5 mu m using cooled optics and two 2048 x 2048 HgCdTe HAWAII-2 focal plane arrays. Good-quality images are obtained over the entire field of view with practically no chromatic aberration. The limiting magnitudes for a point source estimated from observed background brightness and throughput are 23.7 in the J band, 23.0 in the H band, and 22.6 in the K-s band (Vega) with S/N = 5.0 ''.5 seeing, 1 ''.0 aperture, and 1 hr exposure.
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ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES 179(1) 124-141 2008年11月We present the X-ray source catalog in the Subaru/XMM-Newton deep survey. A continuous area of 1.14 deg(2) centered at R:A:= 02(h)18(m) and decl. = -05 degrees is mapped by seven pointings with XMM-Newton covering the 0.2-10 keV band. From the combined images of the EPIC pn and MOS cameras, we detect 866, 1114, 645, and 136 sources with sensitivity limits of 6; 10 X 16, 8; 10 X 16, 3; 10 X 15, and 5; 10 x 15 ergs cm(-2) s(-1) in the 0.5-2, 0.5-4.5, 2-10, and 4.5-10 keV bands, respectively, with detection likelihood >= 7 (corresponding to a confidence level of 99.91%). The catalog consists of 1245 sources in total including 32 extended-source candidates. The averaged log N-log S relations are in good agreement with previous results, bridging the flux range between Chandra deep surveys and brighter surveys. The log N-log S relations show significant spatial variation among pointings on a scale of 0.2 deg(2). Analyzing the autocorrelation function, we detect significant clustering signals from the 0.5-2 keV band sample, which can be fit with a power-law form (theta/theta(c))(-0.8) with a correlation length of theta c = 5.9(-0.9)(+1.0) arcsec when the integral constraint terms included. In the 2-10 keV band, however, the clustering is not significant with a 90% upper limit of theta(c) < 1.5 ''.
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ASTROPHYSICAL JOURNAL 686(1) 649-657 2008年10月We present new spectroscopic and photometric observations of the HAT-P-1 planetary system. Spectra obtained during three transits exhibit the Rossiter-McLaughlin effect, allowing us to measure the angle between the sky projections of the stellar spin axis and orbit normal, lambda = 3.7 degrees +/- 2.1 degrees. The small value of k for this and other systems suggests that the dominant planet migration mechanism preserves spin-orbit alignment. Using two new transit light curves, we refine the transit ephemeris and reduce the uncertainty in the orbital period by an order of magnitude. We find a upper limit on the orbital eccentricity of 0.067, with 99% confidence, by combining our new radial velocity measurements with those obtained previously.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 60(4) 683-693 2008年8月We present the results of deep near-infrared imaging observations of the z = 3.1 proto-cluster region in the SSA 22a field taken by MOIRCS mounted on the Subaru Telescope. We observed a 21.7 arcmin(2) field to depths of J = 24.5, H = 24.3, and K = 23.9 (5 sigma). We examined the distribution of the K-selected galaxies at z similar to 3 by using a simple color cut for distant red galaxies (DRGs) as well as a photometric-redshift selection technique. The marginal density excess of DRGs and the photo-z selected objects were found around the two most luminous Ly alpha blobs (LABS). We investigated the correlation between the K-selected objects and the LABS, and found that several galaxies with stellar mass, M-* = 10(9)-10(11) M-circle dot, exist in the vicinity of LABS, especially around the two most luminous ones. We also found that 7 of the 8 LABS in the field have plausible K-s-band counterparts, and the sum of the stellar mass possibly associated with LABS correlates with their luminosity and surface brightness, which implies that the origin of Ly alpha emission may be closely correlated with their previous star-formation phenomena.
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ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES 176(2) 301-330 2008年6月We present luminosity functions (LFs) and various properties of Ly alpha emitters (LAEs) at z = 3.1, 3.7, and 5.7, in a 1 deg(2) sky of the Subaru/XMM-Newton Deep Survey (SXDS) Field. We obtain a photometric sample of 858 LAE candidates based on deep Subaru Suprime-Cam imaging data and a spectroscopic sample of 84 confirmed LAEs from Subaru FOCAS and VLT VIMOS spectroscopy in a survey volume of similar to 10(6) Mpc(3) with a limiting Ly alpha luminosity of similar to 3 x 10(42) ergs s(-1). We derive the LFs of the Ly alpha andUV continuum (similar or equal to 1500 angstrom) for each redshift, taking into account the statistical error and the field-to-field variation. We find that the apparent Ly alpha LF shows no significant evolution between z = 3.1 and 5.7 within factors of 1.8 and 2.7 in L* and phi*, respectively. On the other hand, the UV LF of LAEs increases from z 3: 1 to 5.7, indicating that galaxies with Ly alpha emission are more common at earlier epochs. We identify six LAEs with AGN activities from our spectra combined with VLA, Spitzer, and XMM-Newton data. Among the photometrically selected LAEs at z = 3.1 and 3.7, only similar or equal to 1% show AGN activities, while the brightest LAEs with log L(Ly alpha) greater than or similar to 43.4 43.6 ergs s(-1) appear to always host AGNs. Our LAEs are bluer in UV-continuum color than dropout galaxies, suggesting lower extinction and/or younger stellar populations. Our stacking analyses provide upper limits to the radio luminosity and the f(He) (II)/f(Ly alpha) line fraction and constrain the hidden star formation (+ low-luminosity AGN) and the primordial population in LAEs.
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ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES 176(1) 1-18 2008年5月We present multi-wave band optical imaging data obtained from observations of the Subaru/XMM-Newton Deep Survey (SXDS). The survey field, centered at R.A. = 02(h)18(m)00(s), decl. = -05 degrees 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, each of which corresponds to a single Suprime-Cam field of view (similar to 34' x 27'), in five broadband filters, B, V, R-c, i', and z', to the depths of B = 28.4, V = 27.8, R-c = 27.7, z' = 27.7, and z' = 26.6, respectively (AB, 3 sigma, phi = 2 ''). The data are reduced and compiled into five multiwave band photometric catalogs, separately for each Suprime-Cam pointing. The i'-band catalogs contain about 900,000 objects, making the SXDS catalogs one of the largest multi-wave band catalogs in corresponding depth and area coverage. The SXDS catalogs can be used for an extensive range of astronomical applications such as the number density of the Galactic halo stars to the large-scale structures at the distant 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).
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MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 384(3) 1200-1206 2008年3月We present a deep [O III] lambda lambda 4959,5007 image of the northern filamentary jet in the Crab Nebula taken with the 8.2-m Subaru telescope. Using this image and an image taken with the Kitt Peak National Observatory (KPNO) 4-m in 1988, we have computed proper motions for 35 locations in the jet. The results suggest that when compared to the main body of the remnant, the jet experienced less outward acceleration from the central pulsar's rapidly expanding synchrotron nebula. The jet's apparent expansion rate yields an undecelerated explosion date for the Crab Nebula of 1055 +/- 24 CE, a date much closer to the appearance of the historic 1054 CE guest star than the 1120-1140 CE dates estimated in previous studies using filaments located within the remnant's main nebula. Our proper motion measurements suggest the jet likely formed during the 1054 supernova explosion and represents the remnant's highest velocity knots possibly associated with a suspected N-S bipolar outflow from the supernova explosion.
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GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY II, PTS 1-4 7014 2008年The High-Contrast Coronographic Imager for Adaptive Optics (HiCIAO), is a coronographic simultaneous differential imager for the new 188-actuator AO system at the Subaru Telescope Nasmyth focus. It is designed primarily to search for faint companions, brown dwarves and young giant planets around nearby stars, but will also allow observations of disks around young stars and of emission line regions near other bright central sources. HiCIAO will work in conjunction with the new Subaru Telescope 188-actuator adaptive optics system. It is designed as a flexible, experimental instrument that will grow from the initial, simple coronographic system into more complex, innovative optics as these technologies become available. The main component of HiCIAO is an infrared camera optimized for spectral simultaneous differential imaging that uses a Teledyne 2.5 mu m HAWAII-2RG detector array operated by a Sidecar ASIC. This paper reports on the assembly, testing, and "first light" observations at the Subaru Telescope.
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PANORAMIC VIEWS OF GALAXY FORMATION AND EVOLUTION, PROCEEDINGS 399 278-+ 2008年We present the recent results and the current status of our panoramic search for Lyrnan-alpha blobs in the high redshift universe.
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OBSERVATORY OPERATIONS: STRATEGIES, PROCESSES, AND SYSTEMS II 7016 2008年Subaru Telescope has recently replaced most equipment of Subaru Telescope Network II with the new equipment which includes 124TB of RAID system for data archive. Switching the data storage from tape to RAID enables users to access the data faster. The STN-III dropped some important components of STN-II, such as supercomputers, development & testing subsystem for Subaru Observation Control System, or data processing subsystem. Oil the other hand, we invested more computers to the remote operation system. Thanks to IT innovations, our LAN as well as the network between Hilo and summit were upgraded to gigabit network at the similar or even reduced cost from the previous system. As the result of the redesigning of the computer system by more focusing on the observatory operation, we greatly reduced the total cost for computer rental, purchase and maintenance.
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PANORAMIC VIEWS OF GALAXY FORMATION AND EVOLUTION, PROCEEDINGS 399 214-215 2008年
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PANORAMIC VIEWS OF GALAXY FORMATION AND EVOLUTION, PROCEEDINGS 399 296-+ 2008年We used very deep near-infrared imaging data taken with Subaru/MOIRCS in the MOIRCS Deep Survey (MODS) to investigate the number counts of distant red galaxies (DRCs) down to K-Vega = 23. We also performed the broad-band SED fitting analysis of galaxies at 2 < z < 4 with the combination. of MOIRCS and publicly available data from HST/ACS and Spitzer/IRAC to estimate the stellar mass, stellar age, and dust extinction of these galaxies.
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PANORAMIC VIEWS OF GALAXY FORMATION AND EVOLUTION, PROCEEDINGS 399 135-+ 2008年We conducted an extensive narrow-band survey (NB497; CW4977 angstrom /BW77 angstrom, which corresponds to Lyman-alpha wavelength at z = 3.06 similar to 3.12) using the Suprime-Cam (Miyazaki, et al. 2002) 7FoVs (200MpcX80Mpc) over the SSA22 proto-cluster regions, as well as in the general fields (SXDS 3FoVs, SDF, GOODS-N) at z = 3.1. We detected 260 Lyman-alpha absorbers (LAA), namely objects whose flux show significant deficit in the narrow band. We will discuss the spatial distribution and a very large overdensity of the LAAs by comparing them with those for the Lyman-alpha emitters (LAEs). In addition, we will compare the results of the Millennium Simulation with our observational results.
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PANORAMIC VIEWS OF GALAXY FORMATION AND EVOLUTION, PROCEEDINGS 399 65-+ 2008年We introduce our on-going search for Ly alpha emitters and z-dropouts at z = 7 - 9 in the GOODS-N field with Subaru/MOIRCS. In the course of MOIRCS Deep Survey started in 2006, we perform deep imaging with a set of broad- and narrow-band filters for z = 8.8 LAEs and z-dropouts. We plan to complete our observations by early 2009.
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PANORAMIC VIEWS OF GALAXY FORMATION AND EVOLUTION, PROCEEDINGS 399 373-+ 2008年Using deep near-infrared imaging data taken by MOIRCS, we study K-selected objects in the z = 3.1 proto-cluster region in the SSA22a field. The distribution of galaxies at z similar to 3 is investigated by using the color cut for distant red galaxies (DRGs) and the photometric-redshift selection technique. The marginal density excess of DRGs and the photo-z selected objects is found around the two distinctive luminous Ly alpha blobs (LABs). We also find that the stellar mass derived for several galaxies in vicinity of each LAB is M* = 10(9) - 10(11)M(circle dot) and the sum of the stellar mass possibly associated with LABs increases with the. Lya luminosity and surface brightness. This result suggests that the origin of Lya emission appear to be correlated with the previous star formation.
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PANORAMIC VIEWS OF GALAXY FORMATION AND EVOLUTION, PROCEEDINGS 399 219-226 2008年We present the early results from the two on-going wide-field imaging survey using Subaru Telescope. Combination with the large-aperture telescope, such as Subaru, and wide-field camera, Suprime Cam, makes the deep and wide-field survey of distant galaxies realized and enable us to study galaxy formation and evolution in terms of the structure formation in enough large. volume. First, We introduce the results of DXS Ten-square degree (SCDXT) survey, where similar to 10-deg(2) area was deeply imaged in optical, i' < 25.5 - 26, to match with the data taken in UKIDSS DXS and Spitzer SWIRE survey. The method to identify the aged galaxies and to measure their photometric redshift using optical-NIR colors is demonstrated, and the properties of the extremely red and bright galaxies are studied. The cluster candidates at z = 1..2 selected by the method is also presented. Second, we also introduce the results of the deep and wide-area narrow-band survey which covers the 1.75 deg(2) at the z = 3.1 high-density region in and around SSA22 area as well as the 1.25 deg(2) of the blank fields. Large overdensity of Ly alpha Emitters (LAE) at z = 3.1 at large scale (> 50 Mpc) is probed by the data. Properties of the LAEs in this unique region are investigated.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59(6) 1081-1094 2007年12月We present the first measurement of clustering properties of low-mass galaxies with a stellar mass down to M-* similar to 10(9)M(circle dot) at 1 < z < 4 in 24.4 arcmin(2) of the GOODS-North region with a depth of K-AB similar to 25. Luminous galaxies in the K-band have a larger correlation length than faint galaxies. For color-selected samples at 2 < z < 4, distant red galaxies with J-K > 1.3 show a large bias of b similar to 7.2 +/- 1.3 on scales of up to theta similar to 100 '' or 3.1 comoving Mpc, while blue galaxies with 0.5 < J-K < 1.3 have a weak clustering signal on large scales, but a possible strong small-scale excess at theta < 10 ''. For massive galaxies with M-* greater than or similar to 10(10)M(circle dot), we estimate the correlation length and bias to be r(0) similar to 4.5 h(-1) Mpc and b = 1.9-3.5, which are much larger than those of low-mass (M-* similar to 10(9)-10(10)M(circle dot)) galaxies. The comparison of our measurements with analytic CDM models constrains the properties of hosting dark halos, and indicates that the low-mass galaxies would be progenitors of galaxies with a typical luminosity of L less than or similar to L-* in the local Universe. The blue galaxies in low-mass samples are more strongly clustered in more massive halos with higher occupation numbers than low-mass red galaxies. This fact suggests an environment effect due to the halo mass on the star-formation activity at high-z.
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ASTROPHYSICAL JOURNAL 667(2) 667-672 2007年10月We present similar to 2 '' resolution submillimeter observations of the submillimeter luminous giant Ly alpha blob ( LAB1) in the SSA 22 protocluster at redshift z = 3.1 with the Submillimeter Array ( SMA). Although the expected submillimeter flux density is 16 mJy at 880 mu m, no emission is detected with the 2. 4 '' x 1.9 '' ( 18 x 14 kpc) beam at the 3 sigma level of 4.2 mJy beam(-1) in the SMA field of view of 35 ''. This is in contrast to the previous lower angular resolution ( 1500) observations where a bright ( 17 mJy) unresolved submillimeter source was detected at 850 mu m toward the LAB1 using the Submillimeter Common-User Bolometer Array on the James Clerk Maxwell Telescope. The SMA nondetection suggests that the spatial extent of the submillimeter emission of LAB1 should be larger than 400 (> 30 kpc). The most likely interpretation of the spatially extended submillimeter emission is that starbursts occur throughout the large area in LAB1. Some part of the submillimeter emission may come from spatially extended dust expelled from starburst regions by galactic superwind. The spatial extent of the submillimeter emission of LAB1 is similar to those of high-redshift radio galaxies rather than submillimeter galaxies.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59(4) 763-770 2007年8月We report a measurement of the Rossiter-McLaughlin effect in the transiting extrasolar planetary system TrES-1, via simultaneous spectroscopic and photometric observations with the Subaru and MAGNUM telescopes. By modeling the radial velocity anomaly that was observed during a transit, we determine the sky-projected angle between the stellar spin axis and the planetary orbital axis to be lambda = 30 degrees +/- 21 degrees. This is the third case for which, has been measured in a transiting exoplanetary system, and the first demonstration that such measurements are possible for relatively faint host stars (V similar to 12, as compared to V similar to 8 for the other systems). We also derive a time of mid-transit, constraints on the eccentricity of the TrES-1b orbit (e = 0.048 +/- 0.025), and upper limits on the mass of the Trojan companions (less than or similar to 14 M-circle plus) at the 3 sigma level.
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MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 379(4) 1343-1351 2007年8月We analyse the first publicly released deep field of the UK Infrared Deep Sky Survey (UKIDSS) Deep eXtragalactic Survey to identify candidate galaxy overdensities at z similar to 1 across similar to 1 deg(2) in the ELAIS-N1 field. Using I - K, J - K and K - 3.6 mu m colours, we identify and spectroscopically follow up five candidate structures with Gemini/Gemini Multi-Object Spectrograph and confirm that they are all true overdensities with between five and 19 members each. Surprisingly, all five structures lie in a narrow redshift range at z = 0.89 +/- 0.01, although they are spread across 30 Mpc on the sky. We also find a more distant overdensity at z = 1.09 in one of the spectroscopic survey regions. These five overdense regions lying in a narrow redshift range indicate the presence of a supercluster in this field and by comparing with mock cluster catalogues from N-body simulations we discuss the likely properties of this structure. Overall, we show that the properties of this supercluster are similar to the well-studied Shapley and Hercules superclusters at lower redshift.
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ASTROPHYSICAL JOURNAL 659(1) 862-862 2007年4月
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59(1) 277-277 2007年2月
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NUOVO CIMENTO DELLA SOCIETA ITALIANA DI FISICA B-GENERAL PHYSICS RELATIVITY ASTRONOMY AND MATHEMATICAL PHYSICS AND METHODS 121(12) 1427-1429 2006年12月 査読有りWe present the results of deep imaging of the field of GRB 050904 with Suprime-Cam on the Subaru 8.2 m telescope. We have obtained a narrow-band (130 angstrom) image centered at 9200 angstrom (NB921) and an iota '-band image with total integration times of 56700 and 24060 s, respectively. The host galaxy was not detected within 1 '' of the afterglow position. An object was found at 1.5 '' NE from the position of the afterglow, but clear detection of this object in the iota '-band image rules out its association with the burst. We obtained a limit of > 26.4 AB magnitude (2 '' diameter, 3 sigma) in the NB921 image for the host galaxy, corresponding to a flux of 6.0 x 10(28) erg/s/Hz at rest 1500 angstrom assuming a flat spectrum of the host galaxy. The star formation rate should be less than 7.5 (M circle dot/y) based on the conversion rate by Madau, Pozzetti and Dickinson (Astrophys. J., 498 (1998) 106). This upper limit for the host of GRB 050904 is consistent with the star formation rate of other gamma-ray burst host galaxies. around redshift of 2 or less.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 58(6) 951-956 2006年12月We used very deep near-infrared imaging data taken with the Multi-Object InfraRed Camera and Spectrograph (MOIRCS) on the Subaru Telescope to investigate the number Counts of Distant Red Galaxies (DRGs). We observed a 4' x 7' field in the Great Observatories Origins Deep Survey-North (GOODS-N), and our data reached J = 24.6 and K = 23.2 (5 sigma, Vega magnitude). The surface density of DRGs selected by J - K > 2.3 is 2.35 +/- 0.31 arcmin(-2) at K < 22 and 3.54 +/- 0.38 arcinin(-2) at K < 23, respectively. These values are consistent with those in the GOODS-South and FIRES. Our deep and wide data Suggest that the number counts of DRGs turn over at K - 22, and the surface density of the faint DRGs with K > 22 is smaller than that expected from the number counts at the brighter magnitude. The result indicates that while there are many bright galaxies at 2 < z < 4 with the relatively old stellar Population and/or heavy dust extinction, the number of faint galaxies with a similar red color is relatively small. Different behavior patterns of the number counts of the DRGs and bluer galaxies with 2 < z(phot) < 4 at K > 22 suggest that the mass-dependent color distribution, where most of the low-inass galaxies are blue, while more massive galaxies tend to have redder colors, had already been established at that epoch.
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ASTROPHYSICAL JOURNAL 653(2) 988-1003 2006年12月We investigate the luminosity functions of Lyman break galaxies (LBGs) at z similar to 4 and z similar to 5 based on optical imaging data obtained in the Subaru Deep Field project. Three samples of LBGs in a contiguous area of 875 arcmin(2) are constructed. One consists of 3808 LBGs at z similar to 4 down to i' = 26.85 selected with the B-R versus R-i' diagram. The other two consist of 539 and 240 LBGs at z similar to 5 down to z' = 26.05 selected with two kinds of two-color diagram: V-i' versus i'-z' and R-i' versus i'-z'. The adopted selection criteria are proved to be fairly reliable by spectroscopic observations. We derive the luminosity functions of the LBGs at rest- frame ultraviolet wavelengths down to M-UV = -19.2 at z similar to 4 and M-UV = -20.3 at z similar to 5. We find clear evolution of the luminosity function over the redshift range 0 <= z <= 6, which is accounted for solely by a change in the characteristic magnitude M*. We examine the evolution of the cosmic star formation rate (SFR) density and its luminosity dependence over 0 <= z less than or similar to 6. The SFR density contributed from brighter galaxies is found to change more drastically with cosmic time. The contribution from brighter galaxies has a sharp peak around z = 3-4, while that from fainter galaxies evolves relatively mildly with a broad peak at earlier epochs. Combining the observed SFR density with the standard cold dark matter model, we compute the cosmic SFR per unit baryon mass in dark halos, that is, the specific SFR. The specific SFR is found to scale with redshift as (1 + z)(3) up to z similar to 4, implying that the efficiency of star formation is on average higher at higher redshift in proportion to the cooling rate within dark halos, while this is not simply the case at z greater than or similar to 4.
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ASTROPHYSICAL JOURNAL 650(1) 12-17 2006年10月We use deep multiband optical and near-infrared data for four general fields, GOODS-South, HDF-North/South, and IRAC UDF in GOODS-North to investigate the evolution of the observed rest-frame U - V color of field galaxies as a function of the stellar mass evaluated by fitting the galaxy spectral models to the observed broadband SEDs. In these four fields, the U - V color distributions of the galaxies at each mass and redshift interval are very similar. We found that at 0.3 < z < 2.7, more massive galaxies always tend to have a redder U - V color. High- and low-mass galaxies exhibit quite different color evolutions. As seen in our previous study in HDF-N, the color distribution of low-mass ( M star less than or similar to 3 x 10(9) M-circle dot) galaxies becomes significantly bluer with an increase in the redshift. This evolution of the average color can be explained by a constant star formation rate model with z(form) similar to 4. On the other hand, the average color of high-mass galaxies ( M star greater than or similar to 3 x 10(10) M-circle dot) evolves more strongly at high redshifts. Such mass-dependent color distribution and its evolution indicate that galaxies with a larger stellar mass appear to have shorter star formation timescales, and on average they form the larger fraction of their stars in the earlier epoch.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 58(5) 869-881 2006年10月We report the results of a prototype photometric search for transiting extrasolar planets using Subaru Suprime-Cam. Out of about 100000 stars monitored around the Galactic plane (l = 90 degrees, b = 0 degrees), we find that 7700 show photometric precision better than 1% for 60 s exposures, which is required to detect extrasolar planets by the transit method. Thus, Suprime-Cam has the photometric stability and accuracy necessary for a transiting planet survey. During this observing run, we detected three objects (around 18.5 mag for i'-band) that exhibit a single full transit-like light curve with a fractional depth of < 5%. While a spectroscopic follow-up remains to be done using future telescopes in the 20-30 m class, the estimated parameters for the three systems are consistent with the planetary size companions around main-sequence stars. We also found two eclipsing binary candidates and eleven variable stars exhibiting W UMa-like light curves.
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MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 371(2) 577-582 2006年9月We report the discovery of protocluster candidates around high-redshift radio galaxies at z similar to 2.5 on the basis of clear statistical excess of colour-selected galaxies around them seen in the deep near-infrared imaging data obtained with CISCO on the Subaru Telescope. We have observed six targets, all at similar redshifts at z similar to 2.5, and our data reach J = 23.5, H = 22.6 and K = 21.8 (5s) and cover a 1.6 x 1.6 arcmin(2) field centred on each radio galaxy. We apply colour cuts in JHK bands in order to exclusively search for galaxies located at high redshifts, z > 2. Over the magnitude range of 19.5 < K < 21.5, we see a significant excess of red galaxies with J - K > 2.3 by a factor of 2 around the combined radio galaxies fields compared to those found in the general field of the Great Observatories Origins Deep Survey- South (GOODS-S). The excess of galaxies around the radio galaxies fields becomes more than a factor of 3 around 19.5 < K < 20.5 when the two-colour cuts are applied with JHK bands. Such overdensity of the colour-selected galaxies suggests that those fields tend to host high-density regions at high redshifts, although there seems to be the variety of the density of the colour-selected galaxies in each field. In particular, two radio galaxies fields out of the six observed fields show very strong density excess and these are likely to be protoclusters associated with the radio galaxies which would evolve into rich clusters of galaxies dominated by old passively evolving galaxies.
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MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 369(4) 1929-1938 2006年7月We examine masses of hosting haloes of two photometrically selected high-z galaxy samples: the old passively evolving galaxies (OPEGs) at z similar to 1 and Lyman break galaxies (LBGs) at z similar to 4 both taken from the Subaru/XMM- Newton Deep Survey (SXDS). The large survey area of the SXDS (1 deg(2)) allows us to measure the angular two-point correlation functions to a wide separation of > 10 arcmin with a good statistical quality. We utilize the halo model prescription for estimating characteristic masses of hosting haloes from the measured large-scale clustering amplitudes. It is found that the hosting halo mass positively correlates with the luminosity of galaxies. Then, adopting the extended Press-Schechter (EPS) model, we compute the predictions for the mass evolution of the hosting haloes in the framework of the cold dark matter (CDM) cosmology in order to make an evolutionary link between the two galaxy samples at different redshifts and to identify their present-day descendants by letting their haloes evolve forward in time. It is found that, in the view of the mass evolution of hosting haloes in the CDM model, bright (i' less than or similar to i'* + 1) LBGs are consistent with being the progenitor of the OPEGs, whereas it is less likely that the LBG population, as a whole, has evolved into the OPEG population. It is also found that the present-day descendants of both the bright LBGs and OPEGs are likely to be located in massive systems such as groups of galaxies or clusters of galaxies. Finally, we estimate the hosting halo mass of local early-type galaxy samples from the 2dF and Sloan Digital Sky Survey (SDSS) based on the halo model, and it turns out that their expected characteristic mass of hosting haloes is in good agreement with the EPS predictions for the descendant's mass of both the bright LBGs and OPEGs.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 58(3) 485-498 2006年6月The gamma-ray burst (GRB) 050904 at z = 6.3 provides the first opportunity to probe the intergalactic medium (IGM) by GRBs at the epoch of reionization. Here, we present a spectral modeling analysis of the optical afterglow spectrum taken by the Subaru Telescope, aiming to constrain the reionization history. The spectrum shows a clear damping wing at wavelengths redward of the Lyman break, and the wing shape can be fitted either by a damped Ly alpha system with a column density of log[N-H1 (cm(-2))] similar to 21.6 at a redshift close to the detected metal absorption lines (z(metal) = 6.295), or by almost neutral IGM extending to a slightly higher redshift of Z(IGM,u) similar to 6.36. In the latter case, the difference between the two redshifts may be explained by the acceleration of metal absorbing shells in the activities of the GRB or its progenitor. However, we exclude this possibility by using the light transmission feature around the Ly beta resonance, leading to a firm upper limit Of Z(IGM,u) <= 6.314. We then show evidence that the IGM was already largely ionized at z = 6.3 with the best-fit neutral fraction of IGM, X-H1 ( n(H1)/n(H)) = 0.00, and upper limits of x(H1) < 0.17 and 0.60 at 68% and 95% confidence levels, respectively. This is the first direct and quantitative upper limit on X-H1 at z greater than or similar to 6. Various systematic uncertainties are examined, but none of them appears large enough to change our conclusion. To get further information on the reionization, it is important to increase the sample size of z 6 GRBs, in order to find GRBs with low column densities (log N-H1 less than or similar to 20) within their host galaxies and to make statistical studies of Lya line emission from host galaxies.
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ASTROPHYSICAL JOURNAL 640(2) L123-L126 2006年4月We present the results of intermediate-resolution (similar to 2 angstrom) spectroscopy of a sample of 37 candidate Ly alpha blobs and emitters at redshift z = 3.1 using the DEIMOS spectrograph on the 10 m Keck telescope. The emission lines are detected for all 37 objects and show variety in their line profiles. The Ly alpha velocity widths (FWHM) of the 28 objects with higher quality spectra, measured by fitting a single Gaussian profile, are in the range of 150-1700 km s(-1) and correlate with the Ly alpha spatial extents. All 12 Ly alpha blobs (>= 16 arcsec(2)) have large velocity widths of greater than or similar to 500 km s(-1). While there are several possible physical interpretations of the Ly alpha velocity widths ( the motion of gravitationally bound gas clouds, inflows, the merging of clumps, or outflows from superwinds), the large velocity widths of the Ly alpha blobs suggest that they are the sites of massive galaxy formation. If we assume gravitationally bound gas clouds, the dynamical masses of the Ly alpha blobs are estimated to be similar to 10(12)-10(13) M-circle dot. Even for the case of outflows, the outflow velocities are likely to be comparable to the rotation velocities as inferred from the observational evidence for local starburst galaxies.
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MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 366(4) 1551-1552 2006年3月
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ASTROPHYSICAL JOURNAL 637(2) 631-647 2006年2月We explored the clustering properties of Lyman break galaxies at z = 4 and 5 with an angular two-point correlation function on the basis of the very deep and wide Subaru Deep Field data. We confirmed the previous result that the clustering strength of LBGs depends on the UV luminosity in the sense that brighter LBGs are more strongly clustered. In addition, we found an apparent dependence of the correlation function slope on UV luminosity for LBGs at both z = 4 and 5. More luminous LBGs have a steeper correlation function. The bias parameter was found to be a scale-dependent function for bright LBGs, whereas it appears to be almost scale-independent for faint LBGs. Luminous LBGs have a higher bias at smaller angular scales, which decreases as the scale increases. To compare these observational results, we constructed numerical mock LBG catalogs based on a semianalytic model of hierarchical clustering combined with high-resolution N-body simulation, carefully mimicking the observational selection effects. The luminosity functions and the overall correlation functions for LBGs at z = 4 and 5 predicted by this mock catalog were found to be almost consistent with the observation. The observed dependence of the clustering on UV luminosity was not reproduced by the model, unless subsamples of distinct halo mass were considered. That is, LBGs belonging to more massive dark halos had steeper and larger amplitude correlation functions. With this model, we found that LBG multiplicity in massive dark halos amplifies the clustering strength at small scales, which steepens the correlation function. The hierarchical clustering model could therefore be reconciled with the observed luminosity dependence of the correlation function if there is a tight correlation between UV luminosity and halo mass. Our finding that the slope of the correlation function depends on luminosity could be an indication that massive dark halos hosted multiple bright LBGs.
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Nature 440(7081) 184-186 2006年 査読有り
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GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY, PTS 1- 3 6269 2006年MOIRCS is a new Cassegrain instrument of Subaru telescope, dedicated for wide field imaging and multi-object spectroscopy in near-infrared. MOIRCS has been constructed jointly by Tohoku University and the Subaru Telescope and saw the first light in Sep, 2004. The commissioning observations to study both imaging and spectroscopic performance were conducted for about one year. MOIRCS mounts two 2048 x 2048 HAWAII2 arrays and provides a field of view of 4' x 7' with a pixel scale of 0."117. All-lens optical design is optimized for 0.8 to 2.5 mu m with no practical chromatic aberration. Observations confirm the high image quality over the field of view without any perceptible degradation even at the field edge. The best seeing we have obtained so far is FWHM=0."18. A novel design of MOIRCS enables us to perform multi-object spectroscopy with aluminum slit masks, which are housed in a carrousel dewar and cooled to similar to 110 K. When choosing MOS mode, a manipulator pulls out a slit mask from the carrousel into the MOIRCS main dewar and sets it properly at the Cassegrain focus. The carrousel is shuttered by a gate valve, so that it can be warmed and cooled independently to exchange slit-mask sets during daytime. We have tested various configurations of 30 or more multi-slit positions in various sky fields and found that targets are dropped at the centers of slits or guide holes within a dispersion of about 0.3 pixels (0."03). MOIRCS has been open to common use specifically for imaging observations since Feb. 2006. The MOS function will be available in next August.
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ASTROPHYSICAL JOURNAL 634(2) L125-L128 2005年12月We report the discovery of a large-scale coherent filamentary structure of Ly alpha emitters in the redshift space at. We carried out spectroscopic observations to map the three-dimensional structure of the beltlike z = 3.1 feature of the Ly alpha emitters discovered by our previous narrowband imaging observations centered on the protocluster at. The feature was found to consist of at least three physical filaments connecting with each z = 3.1 other. The result is in qualitative agreement with the prediction of the " biased" galaxy formation theories that galaxies preferentially formed in large-scale filamentary or sheetlike mass overdensities in the early universe. We also found that the two known giant Ly alpha emission-line nebulae showing high star formation activities are located near the intersection of these filaments, which presumably evolves into a massive cluster of galaxies in the local universe. This may suggest that massive galaxy formation occurs at a characteristic place in the surrounding large-scale structure at high redshift.
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ASTROPHYSICAL JOURNAL 635(2) L117-L120 2005年12月We present an angular correlation function (ACF) of LBGs with unprecedented statistical quality, based on measurements of 16,920 LBGs obtained in the 1 deg(2) sky of the Subaru/XMM-Newton Deep Field. The ACF significantly departs from a power law, and shows an excess on small scales. In particular, the ACFs of LBGs with show a clear break between the small- and large-scale regimes at an angular separation of similar or equal to 7" with i' < 27.5 whose projected length corresponds to the virial radius of dark halos with a mass of 10(11)-10(12) M(circle dot), indicating multiple LBGs residing in a single dark halo. At both small (2" < theta < 3") and large (40" < theta < 400") scales, clustering amplitudes increase monotonically with luminosity for the magnitude range i = 24.5-27.5 small- scale clustering shows a stronger luminosity dependence than the large-scale clustering. The small- scale bias reaches, and the outskirts of small- scale excess extend to a larger angular separation for brighter b similar or equal to 10-50 LBGs. The ACF and number density of LBGs can be explained by the cold dark matter model.
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ASTROPHYSICAL JOURNAL 634(2) 861-878 2005年12月We obtained the number counts and the rest-frame B-band luminosity function of color-selected old passively evolving galaxies (OPEGs) at z = 1 with very high statistical accuracy using a large and homogeneous sample of about 4000 such objects with z' < 25 detected in an area of 1.03 deg(2) in the Subaru/XMM-Newton Deep Survey (SXDS) field. Our selection criteria are defined on the i' - z' and R - z' color-magnitude plane so that OPEGs at z = 0.9-1.1 with formation redshift z(f) = 2-10 are properly sampled with minimum contamination by other populations. The limiting magnitude corresponds to the luminosity of galaxies with M-* + 3 at z = 0. We made pilot redshift observations for 99 OPEG candidates with 19 < z' < 22 and found that at least 78% (73 of 93) of the entire sample, or 95% (73 of 77) of those whose redshifts were obtained, indeed lie between z = 0.87 and 1.12, and most of their spectra show a continuum break and strong Ca H and K lines, indicating that these objects are indeed dominated by the old stellar populations. The relationship between the observed redshift and the color closely follows the models used in defining the selection criteria in a consistent manner. We found that the surface number density of OPEGs varies by 10%-30% of the average of the entire sample from field to field even at a 300 scale and that the poorest field, SXDS-South, has only 65% of that of the richest one, SXDS-East. We then compared our results with the luminosity functions of the color- or morphologically selected early-type galaxies at z 0, taking the evolutionary factor into account, and found that the number density of old passive galaxies with similar to M-* magnitude at z similar to 1 averaged over the SXDS area is 40%-60% that of equivalently red galaxies and 60%-85% that of morphologically selected E/S0 galaxies at z = 0 depending on their luminosity evolution. It is revealed that more than half, but not all, of the present-day early-type galaxies had already evolved into quiescent passive galaxies at z = 1.
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MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 363(4) 1398-1408 2005年11月We present the results from a submillimetre (submm) survey of a sample of 23 giant Lyman a (Ly alpha) emitting nebulae in the overdensity at z = 3.09 in the SA 22 field. These objects, which have become known as Lya Blobs (LABs), have a diverse range of morphology and surface brightness, but the nature of their power source remains unclear, with both cooling flows or starburst/active galactic nucleus (AGN) ionized winds being possibilities. Using the Submillimetre Common-User Bolometer Array ( SCUBA) submm camera on the James Clerk Maxwell Telescope (JCMT), we measure the 850-mu m flux of a sample of LABs. We present detections of submm emission from four LABs at > 3.5 sigma individually, and obtain a modest statistical detection of the full sample at an average flux of 3.0 +/- 0.9 mJy. These detections indicate significant activity within the LAB haloes, with bolometric luminosities in the ultra-luminous regime (> 10(12) L-circle dot), equivalent to a star formation rate (SFR) of similar to 10(3) M-circle dot yr(-1). By comparisons to LAB-like objects in other regions, we show that there is an apparent trend (although weak) between observed Lya emission and bolometric luminosity. Combined with our detection of ultraluminous activity in this population and the lack of any strong morphological correlations in our sample, this provides evidence that the interaction of an ambient halo of gas with a Galactic-scale 'superwind' is most likely to be responsible for the extended Lya emission in the majority of LABs. Assuming the extent of the LABs reflects outflows from a superwind, we estimate the age of starbursts in the submm LABs to be in the range 10-100 Myr. Using the average submm flux of the LABs, we determine an SFR density in the SA 22 structure of > 3M(circle dot) yr(-1) Mpc(-3), greater than the field at this epoch. The submm detection of these four LABs means there are now seven luminous submm galaxies in the z = 3.09 structure in SA 22, making this the largest known association of these intensely active galaxies. This clustering further strengthens the proposed evolutionary link between these galaxies and local cluster ellipticals. Finally, we suggest that the highly extended Lya haloes (which define the LAB class) may be a common feature of the submm galaxy population in general, underlining their role as potentially important sources of metal enrichment and heating of the intergalactic medium (IGM).
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MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 362(1) 268-288 2005年9月We discuss the environmental dependence of galaxy evolution based on deep panoramic imaging of two distant clusters, RX J0152.7-1357 at z = 0.83 and CL0016+1609 at z = 0.55, taken with the Subaru Prime Focus Camera on the Subaru Telescope as part of the Panoramic Imaging and Spectroscopy of Cluster Evolution with Subaru project. By combining with the Sloan Digital Sky Survey data as a local counterpart for comparison, we construct a large sample of galaxies that spans wide ranges in environment, time and stellar mass (or luminosity). This allows us to conduct systematic and statistical analyses of the photometric properties of galaxies based on the colour-density diagrams, colour-magnitude relations, and luminosity functions. We find that colours of galaxies, especially those of faint galaxies (M-V > M*(V) + 1), change from blue to red at a break density as we go to denser regions. This trend is observed at all redshifts in our sample. Based on local and global densities of galaxies, we classify three environments - field, groups and clusters - and look into the environmental dependence of galaxies in detail. In particular, we quantify how the colour-magnitude relation is built up as a function of environment. We show that the bright end of the cluster colour-magnitude relation is already built at z = 0.83, while the faint end is possibly still in the process of build-up. In contrast to this, the bright end of the field colour-magnitude relation has been vigorously built all the way down to the present-day and the build-up at the faint end has not started yet. A possible interpretation of these results is that galaxies evolve in a 'down-sizing' fashion. That is, massive galaxies complete their star formation first and the truncation of star formation is propagated to smaller objects as time progresses. This trend is likely to depend on environment since the build-up of the colour-magnitude relation is delayed in lower density environments. Therefore, we may suggest that the evolution of galaxies took place earliest in massive galaxies and in high-density regions, and it is delayed in less massive galaxies and in lower density regions. Further studies are, however, obviously needed to confirm the observed trends and establish the 'down-sizing' picture.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 57(4) 705-705 2005年8月
MISC
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Astrophysical Journal Letters 849 L31, 6pp 2017年11月10日 査読有り重力マイクロレンズイベントを利用した、銀河バルジにある77木星質量の低質量星または褐色矮星の発見の論文である。通常の単星のマイクロレンズ現象の場合、レンズの質量と、レンズまでの距離、ソースまでの距離が縮退した結果しか得られない。このイベントでは、Kepler, Spitzer という二つの衛星と地上での異なる3地点での観測のおかげでその縮退を解くことができた。
所属学協会
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1993年4月 - 現在
共同研究・競争的資金等の研究課題
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日本学術振興会 科学研究費助成事業 2022年4月 - 2025年3月
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日本学術振興会 科学研究費助成事業 2014年4月 - 2017年3月
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日本学術振興会 科学研究費助成事業 2013年4月 - 2016年3月
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日本学術振興会 科学研究費助成事業 2009年4月 - 2013年3月
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日本学術振興会 科学研究費助成事業 2008年 - 2010年
