Michitoshi Yoshida

The Subaru/XMM-Newton Deep Survey (SXDS). IV. Evolution of Lyα Emitters from z = 3.1 to 5.7 in the 1 deg2 Field: Luminosity Functions and AGN*

We present luminosity functions (LFs) and various properties of Lyα emitters (LAEs) at z = 3.1, 3.7, and 5.7, in a 1 deg2 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 ~106 Mpc3 with a limiting Lyα luminosity of ~3 × 1042 ergs s−1. We derive the LFs of the Lyα and UV continuum (1500 A) for each redshift, taking into account the statistical error and the field-to-field variation. We find that the apparent Lyα LF shows no significant evolution between z = 3.1 and 5.7 within factors of 1.8 and 2.7 in L* and *, respectively. On the other hand, the UV LF of LAEs increases from z = 3.1 to 5.7, indicating that galaxies with Lyα 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 1% show AGN activities, while the brightest LAEs with log L(Ly α) 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 fHe II/fLyα line fraction and constrain the hidden star formation (+low-luminosity AGN) and the primordial population in LAEs.

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

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’.

The Discovery of Primeval Large-Scale Structures with Forming Clusters at Redshift 6

We report the discovery of primeval large-scale structures (LSSs) including two protoclusters in a forming phase at z = 5.7. We carried out extensive deep narrowband imaging in the 1 deg2 sky of the Subaru/XMM-Newton Deep Field and obtained a cosmic map of 515 Lyα emitters (LAEs) in a volume with a transverse dimension of 180 Mpc × 180 Mpc and a depth of ~40 Mpc in comoving units. This cosmic map shows filamentary LSSs, including clusters and surrounding 10-40 Mpc scale voids, similar to the present-day LSSs. Our spectroscopic follow-up observations identify overdense regions in which two dense clumps of LAEs with a sphere of 1 Mpc diameter in physical units are included. These clumps show about 130 times higher star formation rate density, mainly due to a large overdensity, ~80, of LAEs. These clumps would be clusters in a formation phase involving a burst of galaxy formation.

Errata : The SUBARU Deep Field Project: Lyman α Emitters at a Redshift of 6.6

We present new results of a deep optical imaging survey using a narrow band filter (NB921) centered at λ = 9196 u A together with B, V, R, i � ,a ndzbroadband filters in the sky area of the Subaru Deep Field, which has been promoted as one of legacy programs of the 8.2m Subaru Telescope. We obtained a photometric sample of 58 Ly α emitter candidates at z ≈ 6.5-6.6 among ∼ 180 strong NB921-excess (z � −NB921 > 1.0) objects together with a color criterion of i � −z � > 1.3. We then obtained optical spectra of 20 objects in our NB921-excess sample, and identified at least nine Ly α emitters at z ∼ 6.5-6.6, including the two emitters reported by Kodaira et al. (2003, PASJ, 55, L17). Since our Ly α-emitter candidates are free from strong amplification of gravitational lensing, we are able to discuss their observational properties from a statistical point of view. Based on these new results, we obtained a lower limit of the star-formation rate density of ρSFR � 5.7 ×10 −4 h0.7 Myr −1 Mpc −3 at z ≈ 6.6, being

A planetary companion to the hyades giant ε tauri

Wereportthedetection of anextrasolarplanet orbitingTau,oneof thegiantstarsintheHyadesopencluster.This is the first planet ever discovered in an open cluster. Precise Doppler measurements of this star from Okayama Astrophysical Observatory have revealed Keplerian velocity variations with an orbital period of 594:9 � 5:3 days, a semiamplitude of 95:9 � 1: 8ms � 1 , and an eccentricity of 0:151 � 0:023. The minimum mass of the companion is 7:6 � 0:2MJ,andthesemimajoraxisis1:93 � 0:03AUadoptingastellarmassof 2:7 � 0:1M� .Theageof 625Myr for the cluster sets the most secure upper limit ever on the timescale of giant planet formation. The mass of 2.7 Mfor thehoststarisrobustlydeterminedbyisochronefitting,whichmakesthestartheheaviestamongplanet-harboringstars. Puttingtogetherthefactthatnoplanetshavebeenfoundaroundabout100low-massdwarfsinthecluster,thefrequency of massive planets is suggested to be higher around high-mass stars than around low-mass ones. Subject headingg open clusters and associations: individual (Hyades) — planetary systems — stars: individual (� Tauri) — techniques: radial velocities

Early Phase Obserbations of Extermely Luminous Type Ia Supernova 2009dc

We present early phase observations in optical and near-infrared wavelengths for the extremely luminous Type Ia supernova (SN Ia) 2009dc. The decline rate of the light curve is ?m 15(B) = 0.65 ? 0.03, which is one of the slowest among SNe Ia. The peak V-band absolute magnitude is estimated to be MV = ?19.90 ? 0.15?mag if no host extinction is assumed. It reaches MV = ?20.19 ? 0.19?mag if we assume the host extinction of AV = 0.29?mag. SN 2009dc belongs to the most luminous class of SNe Ia, like SNe 2003fg and 2006gz. Our JHKs -band photometry shows that this SN is also one of the most luminous SNe Ia in near-infrared wavelengths. We estimate the ejected 56Ni mass of 1.2 ? 0.3 M ? for the no host extinction case (and of 1.6 ? 0.4 M ? for the host extinction of AV = 0.29?mag). The C II ?6580 absorption line remains visible until a week after the maximum brightness, in contrast to its early disappearance in SN 2006gz. The line velocity of Si II ?6355 is about 8000?km?s?1 around the maximum, being considerably slower than that of SN 2006gz. The velocity of the C II line is similar to or slightly less than that of the Si II line around the maximum. The presence of the carbon line suggests that the thick unburned C+O layer remains after the explosion. Spectropolarimetric observations by Tanaka et?al. indicate that the explosion is nearly spherical. These observational facts suggest that SN 2009dc is a super-Chandrasekhar mass SN Ia.

A PLANETARY COMPANION TO THE G-TYPE GIANT STAR HD 104985

We report the detection of a planetary-mass companion to the G9 III giant star HD 104985 from precise Doppler velocity measurements made using the High Dispersion Echelle Spectrograph (HIDES) at Okayama Astrophysical Observatory. The radial velocity variability of this star is best explained by an orbital motion with a period of 198.2 ± 0.3 days, a velocity semiamplitude of 161 ± 2 m s-1, and an eccentricity of 0.03 ± 0.02. Assuming a stellar mass of 1.6 M☉, we obtained a minimum mass and a semimajor axis of 6.3MJ and 0.78 AU, respectively, for the companion. A probable upper limit to the stellar mass of 3 M☉ yielded m2 sin i = 9.6MJ, which falls in the planetary-mass regime. This is the first discovery of a planetary companion orbiting a G-type giant star.

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.

TYPE Ib SUPERNOVA 2008D ASSOCIATED WITH THE LUMINOUS X-RAY TRANSIENT 080109: AN ENERGETIC EXPLOSION OF A MASSIVE HELIUM STAR

We present a theoretical model for supernova SN 2008D associated with the luminous X-ray transient 080109. The bolometric light curve and optical spectra of the SN are modeled based on the progenitor models and the explosion models obtained from hydrodynamic/nucleosynthetic calculations. We find that SN 2008D is a more energetic explosion than normal core-collapse supernovae, with an ejecta mass of M ej = 5.3 ± 1.0 M ☉ and a kinetic energy of E K = 6.0 ± 2.5 × 1051 erg. The progenitor star of the SN has a 6-8 M ☉ He core with essentially no H envelope (<5 × 10–4 M ☉) prior to the explosion. The main-sequence mass of the progenitor is estimated to be M MS = 20-25 M ☉, with additional systematic uncertainties due to convection, mass loss, rotation, and binary effects. These properties are intermediate between those of normal SNe and hypernovae associated with gamma-ray bursts. The mass of the central remnant is estimated as 1.6-1.8 M ☉, which is near the boundary between neutron star and black hole formation.