Toru Yamada

Tohoku University, Miyagi, Japan

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Publications (148)502.03 Total impact

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    ABSTRACT: We present the largest to date sample of hydrogen Lyman continuum (LyC) emitting galaxies at any redshift, with $18$ LyA Emitters (LAEs) and $7$ Lyman Break Galaxies (LBGs), obtained from the SSA22 field with Subaru/Suprime-Cam. The sample is based on the $136$ LBGs and $159$ LAEs observed in the field, all with spectroscopically confirmed redshifts, and they are selected as galaxies with counterpart in a narrow-band filter image which traces LyC at $z\geq 3.06$. Many LyC candidates show a spatial offset between the rest-frame non-ionizing ultraviolet (UV) detection and the LyC-emitting substructure or between the LyA emission and LyC. Statistically it is highly unlikely that all candidates in our sample are contaminants, and there should be $\sim9$ and $\sim2$ viable LyC candidates among the LAEs and LBGs. There is some evidence for a positive LyC/LyA correlation, suggesting that both LyC and LyA escape via a similar mechanism. "Standard" SED models cannot explain the observed LyC LAEs colors, instead requiring more exotic models like a top-heavy IMF with an average stellar mass of $\sim100M_{sun}$ and the "Lyman limit bump" model with an escape of nebular recombination LyC. The LyC LBGs colors are consistent with a Salpeter IMF with no nebular emission. Both types of galaxies seem to require extremely metal-poor or metal-free young (zero age) stellar populations. We have obtained estimates of LyC escape fraction of $\sim20\%$ for LyC LBGs and $\sim30\%$ for LyC LAEs, assuming an SMC dust law. We cannot simultaneously explain the observed $f_{LyC}/f_{UV}$ flux density ratios and the UV slopes if we assume a Calzetti attenuation curve. The LyC emission seems to be bimodal - stacking non-detections reveals no significant LyC signal strength. The $3\sigma$ median upper limits on the flux density ratios from non-detections are [...]
    Full-text · Article · Sep 2015
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    ABSTRACT: We present the first spatially resolved polarized scattered light H-band detection of the DoAr 28 transitional disk. Our two epochs of imagery detect the scattered light disk from our effective inner working angle of 0.10" (13 AU) out to 0.50" (65 AU). This inner working angle is interior to the location of the system's gap inferred by previous studies using SED modeling (15 AU). We detected a candidate point source companion 1.08" northwest of the system; however, our second epoch of imagery strongly suggests that this object is a background star. We constructed a grid of Monte Carlo Radiative Transfer models of the system, and our best fit models utilize a modestly inclined (50 deg), 0.01 Msun disk that has a partially depleted inner gap from the dust sublimation radius out to ~8 AU. Subtracting this best fit, axi-symmetric model from our polarized intensity data reveals evidence for two small asymmetries in the disk, which could be attributable to variety of mechanisms.
    Full-text · Article · Jul 2015 · The Astronomical Journal
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    ABSTRACT: Coronagraphic imagery of the circumstellar disk around HD 169142 in H-band polarized intensity (PI) with Subaru/HiCIAO is presented. The emission scattered by dust particles at the disk surface in 0${^{\prime\prime}_{.}}$2 ≤ r ≤ 1${^{\prime\prime}_{.}}$2, or 29 ≤ r ≤ 174 au, is successfully detected. The azimuthally averaged radial profile of the PI shows a double power-law distribution, in which the PIs in r = 29–52 au and r = 81.2–145 au respectively show r−3 dependence. These two power-law regions are connected smoothly with a transition zone (TZ), exhibiting an apparent gap in r = 40–70 au. The PI in the inner power-law region shows a deep minimum whose location seems to coincide with the point source at λ = 7 mm. This can be regarded as another sign of a protoplanet in the TZ. The observed radial profile of the PI is reproduced by a minimally flaring disk with an irregular surface density distribution, an irregular temperature distribution, or with a combination of both. The depletion factor of surface density in the inner power-law region (r < 50 au) is derived to be ≥ 0.16 from a simple model calculation. The obtained PI image also shows small-scale asymmetries in the outer power-law region. Possible origins for these asymmetries include corrugation of the scattering surface in the outer region, and a shadowing effect by a puffed-up structure in the inner power-law region.
    Full-text · Article · May 2015 · Publications- Astronomical Society of Japan
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    ABSTRACT: We present new high-resolution ($\sim$0\farcs09) $H$-band imaging observations of the circumstellar disk around the T Tauri star SU Aur. Our observations with Subaru-HiCIAO have revealed the presence of scattered light as close as 0\farcs15 ($\sim$20 AU) to the star. Within our image, we identify bright emission associated with a disk with a minimum radius of $\sim$90 AU, an inclination of $\sim$35$\degr$ from the plane of the sky, and an approximate P.A. of 15$\degr$ for the major axis. We find a brightness asymmetry between the northern and southern sides of the disk due to a non-axisymmetric disk structure. We also identify a pair of asymmetric tail structures extending east and west from the disk. The western tail extends at least 2\farcs5 (350 AU) from the star, and is probably associated with a reflection nebula previously observed at optical and near-IR wavelengths. The eastern tail extends at least 1\arcsec (140 AU) at the present signal-to-noise. These tails are likely due to an encounter with an unseen brown dwarf, but our results do not exclude the explanation that these tails are outflow cavities or jets.
    Full-text · Article · May 2015
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    ABSTRACT: We report the multi-wavelength identification of the X-ray sources found in the Subaru-XMM-Newton Deep Survey (SXDS) using deep imaging data covering the wavelength range between the far-UV to the mid-IR. We select a primary counterpart of each X-ray source by applying the likelihood ratio method to R-band, 3.6micron, near-UV, and 24micron source catalogs as well as matching catalogs of AGN candidates selected in 1.4GHz radio and i'-band variability surveys. Once candidates of Galactic stars, ultra-luminous X-ray sources in a nearby galaxy, and clusters of galaxies are removed there are 896 AGN candidates in the sample. We conduct spectroscopic observations of the primary counterparts with multi-object spectrographs in the optical and NIR; 65\% of the X-ray AGN candidates are spectroscopically-identified. For the remaining X-ray AGN candidates, we evaluate their photometric redshift with photometric data in 15 bands. Utilising the multi-wavelength photometric data of the large sample of X-ray selected AGNs, we evaluate the stellar masses, M*, of the host galaxies of the narrow-line AGNs. The distribution of the stellar mass is remarkably constant from z=0.1 to 4.0. The relation between M* and 2--10 keV luminosity can be explained with strong cosmological evolution of the relationship between the black hole mass and M*. We also evaluate the scatter of the UV-MIR spectral energy distribution (SED) of the X-ray AGNs as a function of X-ray luminosity and absorption to the nucleus. The scatter is compared with galaxies which have redshift and stellar mass distribution matched with the X-ray AGN. The UV-NIR SEDs of obscured X-ray AGNs are similar to those of the galaxies in the matched sample. In the NIR-MIR range, the median SEDs of X-ray AGNs are redder, but the scatter of the SEDs of the X-ray AGN broadly overlaps that of the galaxies in the matched sample.
    Preview · Article · May 2015 · Publications- Astronomical Society of Japan
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    ABSTRACT: The TMT Detailed Science Case describes the transformational science that the Thirty Meter Telescope will enable. Planned to begin science operations in 2024, TMT will open up opportunities for revolutionary discoveries in essentially every field of astronomy, astrophysics and cosmology, seeing much fainter objects much more clearly than existing telescopes. Per this capability, TMT's science agenda fills all of space and time, from nearby comets and asteroids, to exoplanets, to the most distant galaxies, and all the way back to the very first sources of light in the Universe. More than 150 astronomers from within the TMT partnership and beyond offered input in compiling the new 2015 Detailed Science Case. The contributing astronomers represent the entire TMT partnership, including the California Institute of Technology (Caltech), the Indian Institute of Astrophysics (IIA), the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), the National Astronomical Observatory of Japan (NAOJ), the University of California, the Association of Canadian Universities for Research in Astronomy (ACURA) and US associate partner, the Association of Universities for Research in Astronomy (AURA).
    Full-text · Article · May 2015
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    Yi-Ping Wang · Wei He · Toru Yamada · Ichi Tanaka · Masanori Iye · Tuo Ji
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    ABSTRACT: We have obtained deep J and Ks-band images centered on a bright radio quiet QSO UM 402 (zem = 2.856) using the IRCS camera and adaptive optics systems that are part of the Subaru Telescope, as well as retrieved WFC3/F140W archive images of this object. A faint galaxy (mk = 23.32±0.05 in the Vega magnitude system) that lies ~ 2.4'' north of the QSO sightline has been clearly resolved in all three deep high resolution datasets, and appears as an irregular galaxy with two close components in the Ks-band images (separation ~ 0.3''). Given the small impact parameter (b = 19.6 kpc, at zlls = 2.531), as well as the red color of (J - Ks)Vega ~ 1.6, it might be a candidate galaxy giving rise to the Lyman Limit system absorption at zabs = 2.531 seen in the QSO spectrum. After carefully subtracting the point spread function from the QSO images, the host galaxy of this bright radio quiet QSO at z ~ 3 was marginally revealed. We placed a lower limit on the host component of mk ~ 23.3 according to our analyses.
    Full-text · Article · May 2015 · Research in Astronomy and Astrophysics
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    ABSTRACT: We exploit wide-field Ly α imaging with Subaru to probe the environment around TN J1338−1942, a powerful radio galaxy with a > 100 kpc Ly α halo at z = 4.11. We used a sample of Ly α emitters (LAEs) down to log (LLyα[ erg s−1]) ∼ 42.8 to measure the galaxy density around TN J1338−1942, compared to a control sample from a blank field taken with the same instrument. We found that TN J1338−1942 resides in a region with a peak overdensity of δLAE = 2.8 ± 0.5 on scales of 8 h− 1 Mpc (on the sky) and 112 h− 1 Mpc (line of sight) in comoving coordinates. Adjacent to this overdensity, we found a strong underdensity where virtually no LAEs are detected. We used a semi-analytical model of LAEs derived from the Millennium Simulation to compare our results with theoretical predictions. While the theoretical density distribution is consistent with the blank field, overdense regions such as that around TN J1338−1942 are very rare, with a number density of 6.4 × 10− 8 Mpc− 3 (comoving), corresponding to the densest <0.4 percentile at z ≃ 4.1. We also found that the Ly α luminosity function in the TN J1338−1942 field differs from that in the blank field: the number of bright LAEs (log (LLyα[ erg s− 1]) ≳ 43.3) is enhanced, while the number of fainter LAEs is relatively suppressed. These results suggest that some powerful radio galaxies associated with Ly α nebulae reside in extreme overdensities on ∼3–6 Mpc scales, where star formation and AGN activity may be enhanced via frequent galaxy mergers or high rates of gas accretion from the surroundings.
    No preview · Article · Feb 2015 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: We present the results of near-infrared spectroscopic observations of the $K$-band selected candidate galaxies in the protocluster at $z=3.09$ in the SSA22 field. We observed 67 candidates with $K_{\rm AB}<24$ and confirmed redshifts of the 39 galaxies at $2.0< z_{\rm spec}< 3.4$. Of the 67 candidates, 24 are certainly protocluster members with $3.04\leq z_{\rm spec}\leq 3.12$, which are massive red galaxies those have been unidentified in previous optical observations of the SSA22 protocluster. Many distant red galaxies (DRGs; $J-K_{\rm AB}>1.4$), hyper extremely red objects (HEROs; $J-K_{\rm AB}>2.1$), {\it Spitzer} MIPS 24 $\mu$m sources, active galactic nuclei (AGNs) as well as the counterparts of Ly$\alpha$ blobs and the AzTEC/ASTE 1.1-mm sources in the SSA22 field are also found to be the protocluster members. The mass of the SSA22 protocluster is estimated to be $\sim2-5\times10^{14}~M_{\odot}$ and this system is plausibly a progenitor of the most massive clusters of galaxies in the current Universe. The reddest ($J-K_{\rm AB}\geq 2.4$) protocluster galaxies are massive galaxies with $M_{\rm star}\sim10^{11}~M_{\odot}$ showing quiescent star formation activities and plausibly dominated by old stellar populations. Most of these massive quiescent galaxies host moderately luminous AGNs detected by X-ray. There are no significant differences in the [O{\footnotesize III}] $\lambda$5007/H$\beta$ emission line ratios, and [O{\footnotesize III}] $\lambda$5007 line widths and spatial extents of the protocluster galaxies from those of massive galaxies at $z\sim2-3$ in the general field.
    Preview · Article · Nov 2014 · The Astrophysical Journal
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    ABSTRACT: We present the first resolved near infrared imagery of the transition disk Oph IRS 48 (WLY 2-48), which was recently observed with ALMA to have a strongly asymmetric sub-millimeter flux distribution. H-band polarized intensity images show a $\sim$60AU radius scattered light cavity with two pronounced arcs of emission, one from Northeast to Southeast and one smaller, fainter and more distant arc in the Northwest. K-band scattered light imagery reveals a similar morphology, but with a clear third arc along the Southwestern rim of the disk cavity. This arc meets the Northwestern arc at nearly a right angle, revealing the presence of a spiral arm or local surface brightness deficit in the disk, and explaining the East-West brightness asymmetry in the H-band data. We also present 0.8-5.4$\mu$m IRTF SpeX spectra of this object, which allow us to constrain the spectral class to A0$\pm$1 and measure a low mass accretion rate of 10$^{-8.5}$M$_{\odot}$/yr, both consistent with previous estimates. We investigate a variety of reddening laws in order to fit the mutliwavelength SED of Oph IRS 48 and find a best fit consistent with a younger, higher luminosity star than previous estimates.
    Full-text · Article · Nov 2014 · The Astrophysical Journal
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    ABSTRACT: A high angular resolution near-infrared image that shows the intensity of polarization for the GG Tau A binary system was obtained with the Subaru Telescope. The image shows a circumbinary disk scattering the light from the central binary. The azimuthal profile of the intensity of polarization for the circumbinary disk is roughly reproduced by a simple disk model with the Henyey-Greenstein phase function and the Rayleigh function, indicating there are small dust grains at the surface of the disk. Combined with a previous observation of the circumbinary disk, our image indicates that the gap structure in the circumbinary disk orbits counterclockwise, but material in the disk orbits clockwise. We propose that there is a shadow caused by material located between the central binary and the circumbinary disk. The separations and position angles of the stellar components of the binary in the past 20 yr are consistent with the binary orbit with a = 33.4 AU and e = 0.34.
    No preview · Article · Nov 2014 · Research in Astronomy and Astrophysics
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    ABSTRACT: We compared the number of faint stars detected in deep survey fields with the current stellar distribution model of the Galaxy and found that the detected number in the H band is significantly smaller than the predicted number. This indicates that M-dwarfs, the major component, are fewer in the halo and the thick disk. We used archived data of several surveys in both the north and south field of GOODS (Great Observatories Origins Deep Survey), MODS (MOIRCS Deep Survey) in GOODS-N, and ERS (Early Release Science) and CANDELS (Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey) in GOODS-S. The number density of M-dwarfs in the halo has to be 20% ± 13% relative to that in the solar vicinity, in order for the detected number of stars fainter than 20.5 mag in the H band to match with the predicted value from the model. In the thick disk, the number density of M-dwarfs must be reduced (52% ± 13%) or the scale height must be decreased (∼ 600 pc). Alternatively, overall fractions of the halo and thick disks can be significantly reduced to achieve the same effect, because our sample mainly consists of faint M-dwarfs. Our results imply that the M-dwarf population in regions distant from the Galactic plane is significantly smaller than previously thought. We then discussed the implications this has on the suitability of the model predictions for the prediction of non-companion faint stars in direct imaging extrasolar planet surveys by using the best-fitting number densities.
    Full-text · Article · Sep 2014 · Publications- Astronomical Society of Japan
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    ABSTRACT: We present a new method of analysis for determining the surface geometry of five protoplanetary disks observed with near-infrared imaging polarimetry using Subaru-HiCIAO. Using as inputs the observed distribution of polarized intensity (PI), disk inclination, assumed properties for dust scattering, and other reasonable approximations, we calculate a differential equation to derive the surface geometry. This equation is numerically integrated along the distance from the star at a given position angle. We show that, using these approximations, the local maxima in the PI distribution of spiral arms (SAO 206462, MWC 758) and rings (2MASS J16042165-2130284, PDS 70) is associated with local concave-up structures on the disk surface. We also show that the observed presence of an inner gap in scattered light still allows the possibility of a disk surface that is parallel to the light path from the star, or a disk that is shadowed by structures in the inner radii. Our analysis for rings does not show the presence of a vertical inner wall as often assumed in studies of disks with an inner gap. Finally, we summarize the implications of spiral and ring structures as potential signatures of ongoing planet formation.
    Full-text · Article · Sep 2014 · The Astrophysical Journal
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    ABSTRACT: We conduct a deep narrow-band imaging survey of 13 Ly$\alpha$ blobs (LABs) located in the SSA22 proto-cluster at z~3.1 in the CIV and HeII emission lines in an effort to constrain the physical process powering the Ly$\alpha$ emission in LABs. Our observations probe down to unprecedented surface brightness limits of 2.1 $-$ 3.4 $\times$ 10$^{-18}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$ per 1 arcsec$^2$ aperture (5$\sigma$) for the HeII$\lambda$1640 and CIV$\lambda$1549 lines, respectively. We do not detect extended HeII and CIV emission in any of the LABs, placing strong upper limits on the HeII/Ly$\alpha$ and CIV/Ly$\alpha$ line ratios, of 0.11 and 0.16, for the brightest two LABs in the field. We conduct detailed photoionization modeling of the expected line ratios and find that, although our data constitute the deepest ever observations of these lines, they are still not deep enough to rule out a scenario where the Ly$\alpha$ emission is powered by the ionizing luminosity of an obscured AGN. Our models can accommodate HeII/Ly$\alpha$ and CIV/Ly$\alpha$ ratios as low as $\simeq$0.05 and $\simeq$0.07 respectively, implying that one needs to reach surface brightness as low as 1 $-$ 1.5 $\times$ 10$^{-18}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$ (at 5$\sigma$) in order to rule out a photoionization scenario. These depths will be achievable with the new generation of image-slicing integral field units such as VLT/MUSE or Keck/KCWI. We also model the expected HeII/Ly$\alpha$ and CIV/Ly$\alpha$ in a different scenario, where Ly$\alpha$ emission is powered by shocks generated in a large-scale superwind, but find that our observational constraints can only be met for shock velocities $v_{\rm s} \gtrsim$ 250 km s$^{-1}$, which appear to be in conflict with recent observations of quiescent kinematics in LABs.
    Full-text · Article · Jul 2014 · The Astrophysical Journal
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    ABSTRACT: We present wide-field Lya imaging observations of the field around TN J1338-1942, a powerful radio galaxy associated with an extended Lya nebula (>100 kpc) at z=4.11, with Subaru Prime-focus Camera to probe the environment of the radio galaxy. We used a sample of Lya emitters (LAEs) down to the Lya luminosity of $\log(L_{\rm Lya}\rm [erg\, s^{-1}])\sim 42.8$ to measure the galaxy density of this field, calibrating by direct comparison with a control sample in a blank field taken with the same instrument. We found that the radio galaxy resides in a region with a peak overdensity of $\delta_{\rm LAE}=3.1\pm 0.5$, after being smoothed on $8\, h^{-1}$ Mpc scales on the sky and $160\, h^{-1}$ Mpc along the line of sight (both in comoving coordinates). Adjacent to this overdense region, we found a highly underdense region where virtually no LAEs are detected. We used a semi-analytical model of LAEs derived from the Millennium Simulation to compare our results with theoretical predictions. This comparison suggests that, while the density distribution of the simulation is consistent with that of the blank field, overdense regions such as the one found in the radio galaxy field are very rare, with the number density of $2\times 10^{-7}h^{3}$ Mpc$^{-3}$ (comoving), corresponding to the densest <0.1 percentile at these redshifts. We also found a difference in the Lya luminosity function in the radio galaxy field compared with the blank field: the number of bright LAEs ($\log(L_{\rm Lya}\rm [erg\, s^{-1}])<43.3$) is enhanced, while the number of fainter LAEs is relatively suppressed. These results suggest that some powerful radio galaxies associated with Lya nebulae reside in extreme overdensities on $\sim 10-20\, h^{-1}$ Mpc scales, where star-formation and AGN activities may be enhanced via more frequent galaxy mergers or higher rates of gas accretion from the surroundings.
    Full-text · Article · Mar 2014
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    ABSTRACT: To reveal the structures of a transition disk around a young stellar object in Lupus, Sz 91 , we have performed aperture synthesis 345 GHz continuum and CO(3-2) observations with the Submillimeter Array (~1''-3'' resolution) and high-resolution imaging of polarized intensity at the Ks-band using the HiCIAO instrument on the Subaru Telescope (025 resolution). Our observations successfully resolved the inner and outer radii of the dust disk to be 65 and 170 AU, respectively, which indicates that Sz 91 is a transition disk source with one of the largest known inner holes. The model fitting analysis of the spectral energy distribution reveals an H2 mass of 2.4 × 10–3M ☉ in the cold (T < 30 K) outer part at 65 AU <r < 170 AU by assuming a canonical gas-to-dust mass ratio of 100, although a small amount (>3 × 10–9M ☉) of hot (T ~ 180 K) dust possibly remains inside the inner hole of the disk. The structure of the hot component could be interpreted as either an unresolved self-luminous companion body (not directly detected in our observations) or a narrow ring inside the inner hole. Significant CO(3-2) emission with a velocity gradient along the major axis of the dust disk is concentrated on the Sz 91 position, suggesting a rotating gas disk with a radius of 420 AU. The Sz 91 disk is possibly a rare disk in an evolutionary stage immediately after the formation of protoplanets because of the large inner hole and the lower disk mass than other transition disks studied thus far.
    Full-text · Article · Feb 2014 · The Astrophysical Journal
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    ABSTRACT: We measure the angular clustering of 33 415 extremely red objects (EROs) in the Elais-N1 field covering 5.33 deg2, which cover the redshift range z = 0.8 to 2. This sample was made by merging the UKIDSS Deep eXtragalactic Survey (DXS) with the optical Subaru and Pan-STARRS PS1 data sets. We confirm the existence of a clear break in the angular correlation function at ∼0.02° corresponding to 1 h−1 Mpc at z ∼ 1. We find that redder or brighter EROs are more clustered than bluer or fainter ones. Halo occupation distribution (HOD) model fits imply that the average mass of dark matter haloes which host EROs is over 1013 h−1 M⊙ and that EROs have a bias ranging from 2.7 to 3.5. Compared to EROs at z ∼ 1.1, at z ∼ 1.5 EROs have a higher bias and fewer are expected to be satellite galaxies. Furthermore, EROs reside in similar dark matter haloes to those that host 1011.0 M⊙ < M* < 1011.5 M⊙ galaxies. We compare our new measurement and HOD fits with the predictions of the galform semi-analytical galaxy formation model. Overall, the clustering predicted by galform gives an encouraging match to our results. However, compared to our deductions from the measurements, galform puts EROs into lower mass haloes and predicts that a larger fraction of EROs are satellite galaxies. This suggests that the treatment of gas cooling may need to be revised in the model. Our analysis illustrates the potential of clustering analyses to provide observational constraints on theoretical models of galaxy formation.
    No preview · Article · Jan 2014 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: The unprecedentedly bright optical afterglow of GRB 130606A located by Swift at a redshift close to the reionization era (z = 5.913) provides a new opportunity to probe the ionization status of the intergalactic medium (IGM). Here we present an analysis of the red Lyα damping wing of the afterglow spectrum taken by Subaru/FOCAS during 10.4–13.2 hr after the burst. We find that the minimal model including only the baseline power-law and H i absorption in the host galaxy does not give a good fit, leaving residuals showing concave curvature in 8400–8900 Å with an amplitude of about 0.6% of the flux. Such a curvature in the short wavelength range cannot be explained either by extinction at the host with standard extinction curves, intrinsic curvature of afterglow spectra, or by the known systematic uncertainties in the observed spectrum. The red damping wing by intervening H i gas outside the host can reduce the residual by about 3 σ statistical significance. We find that a damped Lyα system is not favored as the origin of this intervening H i absorption, from the observed Lyβ and metal absorption features. Therefore absorption by diffuse IGM remains as a plausible explanation. A fit by a simple uniform IGM model requires an H i neutral fraction of fH i ∼ 0.1–0.5 depending on the distance to the GRB host, implying high fH i IGM associated with the observed dark Gunn–Peterson (GP) troughs. This gives new evidence that the reionization is not yet complete at z = 6.
    Preview · Article · Dec 2013 · Publications- Astronomical Society of Japan
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    ABSTRACT: We measure the angular clustering of 33 415 extremely red objects (EROs) in the Elais-N1 field covering 5.33 deg$^{2}$, which cover the redshift range $z=0.8$ to $2$. This sample was made by merging the UKIDSS Deep eXtragalactic Survey (DXS) with the optical Subaru and Pan-STARRS PS1 datasets. We confirm the existence of a clear break in the angular correlation function at $\sim 0.02^{\circ}$ corresponding to $1 h^{-1}$ Mpc at $z\sim1$. We find that redder or brighter EROs are more clustered than bluer or fainter ones. Halo Occupation Distribution (HOD) model fits imply that the average mass of dark matter haloes which host EROs is over $10^{13} h^{-1} M_{\odot}$ and that EROs have a bias ranging from 2.7 to 3.5. Compared to EROs at $z\sim1.1$, at $z\sim1.5$ EROs have a higher bias and fewer are expected to be satellite galaxies. Furthermore, EROs reside in similar dark matter haloes to those that host $10^{11.0} M_{\odot}<M_{*}<10^{11.5} M_{\odot}$ galaxies. We compare our new measurement and HOD fits with the predictions of the GALFORM semi-analytical galaxy formation model. Overall, the clustering predicted by GALFORM gives an encouraging match to our results. However, compared to our deductions from the measurements, GALFORM puts EROs into lower mass haloes and predicts that a larger fraction of EROs are satellite galaxies. This suggests that the treatment of gas cooling may need to be revised in the model. Our analysis illustrates the potential of clustering analyses to provide observational constraints on theoretical models of galaxy formation.
    Full-text · Article · Nov 2013
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    ABSTRACT: Most exoplanets detected by direct imaging thus far have been characterized by relatively hot (1000 K) and cloudy atmospheres. A surprising feature in some of their atmospheres has been a distinct lack of methane, possibly implying non-equilibrium chemistry. Recently, we reported the discovery of a planetary companion to the Sun-like star GJ 504 using Subaru/HiCIAO within the Strategic Exploration of Exoplanets and Disks with Subaru survey. The planet is substantially colder (<600 K) than previously imaged planets, and has indications of fewer clouds, which implies that it represents a new class of planetary atmospheres with expected similarities to late T-type brown dwarfs in the same temperature range. If so, one might also expect the presence of significant methane absorption, which is characteristic of such objects. Here, we report the detection of deep methane absorption in the atmosphere of GJ 504 b, using the Spectral Differential Imaging mode of HiCIAO to distinguish the absorption features around 1.6 μm. We also report updated JHK photometry based on new K s-band data and a re-analysis of the existing data. The results support the notion that GJ 504 b has atmospheric properties distinct from other imaged exoplanets, and will become a useful reference object for future planets in the same temperature range.
    Full-text · Article · Oct 2013 · The Astrophysical Journal Letters

Publication Stats

4k Citations
502.03 Total Impact Points

Institutions

  • 5-2015
    • Tohoku University
      • • Astronomical Institute
      • • Graduate School of Science
      Miyagi, Japan
  • 2014
    • University of Washington Seattle
      Seattle, Washington, United States
    • University of Amsterdam
      Amsterdamo, North Holland, Netherlands
  • 2013
    • Princeton University
      • Department of Astrophysical Sciences
      Princeton, New Jersey, United States
  • 2010-2012
    • The University of Tokyo
      • Department of Astronomy
      Edo, Tōkyō, Japan
  • 2000-2008
    • National Astronomical Observatory of Japan
      • Division of Optical and Infrared Astronomy
      Edo, Tōkyō, Japan
  • 2002
    • Observatoire de Paris
      Lutetia Parisorum, Île-de-France, France
  • 1996
    • Meteorological Research Institute, Japan Meteorological Agency
      Tsukuba, Ibaraki, Japan
  • 1992-1994
    • Kyoto University
      • Department of Astronomy
      Kioto, Kyōto, Japan