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Search Results: 1 - 10 of 73 matches for " Nobunari Kashikawa "
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Search for z~7 Ly-alpha emitters with Suprime-Cam at the Subaru Telescope
Pascale Hibon,Nobunari Kashikawa,Christopher Willott,Masanori Iye,Takatoshi Shibuya
Physics , 2011, DOI: 10.1088/0004-637X/744/2/89
Abstract: We report a search for z=7 Ly-alpha emitters (LAEs) using a custom-made Narrow-Band filter, centered at 9755 Angstroms, with the instrument Suprime-Cam installed at the Subaru telescope. We observed two different fields and obtained two sample of 7 Ly-alpha emitters of which 4 are robust in each field. We are covering the luminosity range of 9.10^{42} - 2.10^{43} erg/s in comoving volumes of ~ 4.10^{5} and 4.3.10^{5} Mpc^{3}. From this result, we derived possible z~7 Ly-alpha luminosity functions for the full samples and for a subsample of 4 objects in each field. We do not observe, in each case, any strong evolution between the z=6.5 and z~7 Ly-alpha luminosity functions. Spectroscopic confirmation for these candidate samples is required to establish a definitive measure of the luminosity function at z~7.
A Large Number of z > 6 Galaxies around a QSO at z = 6.43: Evidence for a Protocluster?
Yousuke Utsumi,Tomotsugu Goto,Nobunari Kashikawa,Satoshi Miyazaki,Yutaka Komiyama,Hisanori Furusawa,Roderik Overzier
Physics , 2010, DOI: 10.1088/0004-637X/721/2/1680
Abstract: QSOs have been thought to be important for tracing highly biased regions in the early universe, from which the present-day massive galaxies and galaxy clusters formed. While overdensities of star-forming galaxies have been found around QSOs at 26 is less clear. Previous studies with HST have reported the detection of small excesses of faint dropout galaxies in some QSO fields, but these surveys probed a relatively small region surrounding the QSOs. To overcome this problem, we have observed the most distant QSO at z=6.4 using the large field of view of the Suprime-Cam (34' x 27'). Newly-installed CCDs allowed us to select Lyman break galaxies (LBG) at z~6.4 more efficiently. We found seven LBGs in the QSO field, whereas only one exists in a comparison field. The significance of this apparent excess is difficult to quantify without spectroscopic confirmation and additional control fields. The Poisson probability to find seven objects when one expects four is ~10%, while the probability to find seven objects in one field and only one in the other is less than 0.4%, suggesting that the QSO field is significantly overdense relative to the control field. We find some evidence that the LBGs are distributed in a ring-like shape centered on the QSO with a radius of ~3 Mpc. There are no candidate LBGs within 2 Mpc from the QSO, i.e., galaxies are clustered around the QSO but appear to avoid the very center. These results suggest that the QSO is embedded in an overdense region when defined on a sufficiently large scale. This suggests that the QSO was indeed born in a massive halo. The central deficit of galaxies may indicate that (1) the strong UV radiation from the QSO suppressed galaxy formation in its vicinity, or (2) that star-formation closest to the QSO occurs mostly in an obscured mode that is missed by our UV selection.
A Search for z=7.3 Lyα Emitters behind Gravitationally Lensing Clusters
Kazuaki Ota,Johan Richard,Masanori Iye,Takatoshi Shibuya,Eiichi Egami,Nobunari Kashikawa
Physics , 2012, DOI: 10.1111/j.1365-2966.2012.21091.x
Abstract: We searched for z=7.3 Lya emitters (LAEs) behind two lensing clusters, Abell 2390 and CL 0024, with the Subaru Telescope Suprime-Cam and a narrowband NB1006 (FWHM ~ 21 nm centered at 1005 nm). We investigated if there exist objects consistent with the color of z=7.3 LAEs behind the clusters but could not detect any LAEs to the unlensed line limit F(Lya) ~ 6.9 x 10^{-18} erg/s/cm^2. Using several z=7 Lya luminosity functions (LFs) from the literature, we estimated and compared the expected detection numbers of z ~ 7 LAEs in lensing and blank field surveys in the case of using an 8m class ground based telescope. Given the steep bright-end slope of the LFs, when the detector field-of view (FOV) is comparable to the angular extent of a massive lensing cluster, imaging cluster(s) is more efficient in detecting z ~ 7 LAEs than imaging a blank field. However, the gain is expected to be modest, a factor of two at most and likely much less depending on the adopted LFs. The main advantage of lensing-cluster survey, therefore, remains to be the gain in depth and not necessarily in detection efficiency. For much larger detectors, the lensing effect becomes negligible and the efficiency of LAE detection is proportional to the instrumental FOV. We also inspected NB1006 images of three z ~ 7 z-dropouts previously detected in Abell 2390 and found that none of them are detected in NB1006. Two of them are consistent with predictions from the previous studies that they would be at lower redshifts. The other one has a photometric redshift of z ~ 7.3, and if it is at z=7.3, its unlensed Lya line flux would be very faint: F(Lya) < 4.4 x 10^{-18} erg/s/cm^2 (1 sigma upper limit) or rest frame equivalent width of W(Lya) < 26A. Its Lya emission might be attenuated by neutral hydrogen, as recent studies show that the fraction of Lyman break galaxies displaying strong Lya emission is lower at z ~ 7 than at z <~ 6.
Subaru high resolution spectroscopy of complex metal absorption lines of QSO HS1603+3820
Toru Misawa,Toru Yamada,Masahide Takada-Hidai,Yiping Wang,Nobunari Kashikawa,Masanori Iye,Ichi Tanaka
Physics , 2002, DOI: 10.1086/346276
Abstract: We present a high resolution spectrum of the quasar, HS1603+3820 (z_em=2.542), observed with the High Dispersion Spectrograph (HDS) on Subaru Telescope. This quasar, first discovered in the Hamburg/CfA Quasar Survey, has 11 C IV lines at 1.96 < z_abs < 2.55. Our spectrum covers 8 of the 11 C IV lines at z_abs > 2.29 and resolves some of them into multiple narrow components with b < 25 km/s because of the high spectral resolution R=45000, while other lines show broad profiles (b > 65 km/s). We use three properties of C IV lines, specifically, time variability, covering factor, and absorption line profile, to classify them into quasar intrinsic absorption lines (QIALs) and spatially intervening absorption lines (SIALs). The C IV lines at 2.42 < z_abs < 2.45 are classified as QIALs in spite of their large velocity shifts from the quasar. Perhaps they are produced by gas clouds ejected from the quasar with the velocity of v_ej = 8000 km/s -- 10000 km/s. On the other hand, three C IV lines at 2.48 < z_abs < 2.55 are classified as SIALs, which suggests there exist intervening absorbers near the quasar. We, however, cannot rule out QIALs for the two lines at z_abs ~ 2.54 and 2.55, because their velocity shifts, 430 km/s blueward and 950 km/s redward of the quasar, are very small. The C IV line at z_abs ~ 2.48 consists of many narrow components, and has also corresponding low-ionization metal lines (Al II, Si II, and Fe II). The velocity distribution of these low-ionization ions is concentrated at the center of the system compared to that of high-ionization C IV ion. Therefore we ascribe this system of absorption lines to an intervening galaxy.
Subaru Mid-infrared Imaging of the Quadruple Lenses. II. Unveiling Lens Structure of MG0414+0534 and Q2237+030
Takeo Minezaki,Masashi Chiba,Nobunari Kashikawa,Kaiki Taro Inoue,Hirokazu Kataza
Physics , 2009, DOI: 10.1088/0004-637X/697/1/610
Abstract: We present mid-infrared imaging at 11.7 $\mu$m for the quadruple lens systems, MG0414+0534 and Q2237+030, using the cooled mid-infrared camera and spectrometer (COMICS) attached on the Subaru telescope. MG0414+0534 is characterized by a bright pair of lensed images (A1, A2) and their optical flux ratio A2/A1 deviates significantly from the prediction of a smooth lens model. Q2237+030 is comprised of four lensed images, which are significantly affected by microlensing in a foreground lensing galaxy. Our mid-infrared observations of these lensed images have revealed that the mid-infrared flux ratio for A2/A1 of MG0414+0534 is nearly unity (0.90 +- 0.04). We find that this flux ratio is systematically small, at 4 to 5 sigma level, compared with the prediction of a best smooth lens model (1.09) represented by a singular isothermal ellipsoid and external shear, thereby suggesting the presence of substructures to explain our observational result. In contrast, for Q2237+030, our high signal-to-noise observation indicates that the mid-infrared flux ratios between all the four images of Q2237+030 are virtually consistent with the prediction of a smooth lens model. Based on the size estimate of the dust torus surrounding the nuclei of these QSOs, we set limits on the mass of a substructure in these lens systems, which can cause anomalies in the flux ratios. For MG0414+0534, since the required mass of a substructure inside its Einstein radius is > 360 M_sun, millilensing by a CDM substructure is most likely. If it is modeled as a singular isothermal sphere, the mass inside radius of 100 pc is given as > 1.0x10^5 M_sun. For Q2237+030, there is no significant evidence of millilensing, so the reported anomalous flux ratios in shorter wavelengths are entirely caused by microlensing by stars (abridged).
Dust Attenuation and H-alpha Star Formation Rates of z~0.5 Galaxies
Chun Ly,Matthew A. Malkan,Nobunari Kashikawa,Kazuaki Ota,Kazuhiro Shimasaku,Masanori Iye,Thayne Currie
Physics , 2012, DOI: 10.1088/2041-8205/747/1/L16
Abstract: Using deep narrow-band and broad-band imaging, we identify 401 z~0.40 and 249 z~0.49 H-alpha line-emitting galaxies in the Subaru Deep Field. Compared to other H-alpha surveys at similar redshifts, our samples are unique since they probe lower H-alpha luminosities, are augmented with multi-wavelength (rest-frame 1000AA--1.5 microns) coverage, and a large fraction (20%) of our samples has already been spectroscopically confirmed. Our spectra allow us to measure the Balmer decrement for nearly 60 galaxies with H-beta detected above 5-sigma. The Balmer decrements indicate an average extinction of A(H-alpha)=0.7^{+1.4}_{-0.7} mag. We find that the Balmer decrement systematically increases with higher H-alpha luminosities and with larger stellar masses, in agreement with previous studies with sparser samples. We find that the SFRs estimated from modeling the spectral energy distribution (SED) is reliable---we derived an "intrinsic" H-alpha luminosity which is then reddened assuming the color excess from SED modeling. The SED-predicted H-alpha luminosity agrees with H-alpha narrow-band measurements over 3 dex (rms of 0.25 dex). We then use the SED SFRs to test different statistically-based dust corrections for H-alpha and find that adopting one magnitude of extinction is inappropriate: galaxies with lower luminosities are less reddened. We find that the luminosity-dependent dust correction of Hopkins et al. yields consistent results over 3 dex (rms of 0.3 dex). Our comparisons are only possible by assuming that stellar reddening is roughly half of nebular reddening. The strong correspondence argue that with SED modeling, we can derive reliable intrinsic SFRs even in the absence of H-alpha measurements at z~0.5.
Kinematics and excitation of the ram pressure stripped ionized gas filaments in the Coma cluster of galaxies
Michitoshi Yoshida,Masafumi Yagi,Yutaka Komiyama,Hisanori Furusawa,Nobunari Kashikawa,Takashi Hattori,Sadanori Okamura
Physics , 2012, DOI: 10.1088/0004-637X/749/1/43
Abstract: We present the results of deep imaging and spectroscopic observations of very extended ionized gas (EIG) around four member galaxies of the Coma cluster of galaxies: RB199, IC4040, GMP2923 and GMP3071. The EIGs were serendipitously found in an H-alpha narrow band imaging survey of the central region of the Coma cluster. The relative radial velocities of the EIGs with respect to the systemic velocities of the parent galaxies from which they emanate increase almost monotonically with the distance from the nucleus of the respective galaxies, reaching -400 - -800 km/s at around 40 - 80 kpc from the galaxies. The one-sided morphologies and the velocity fields of the EIGs are consistent with the predictions of numerical simulations of ram pressure stripping. We found a very low-velocity filament (v_rel = -1300 km/s) at the southeastern edge of the disk of IC4040. Some bright compact knots in the EIGs of RB199 and IC4040 exhibit blue continuum and strong H-alpha emission. The equivalent widths of the H-alpha emission exceed 200 A, and are greater than 1000 A for some knots. The emission line intensity ratios of the knots are basically consistent with those of sub-solar abundance HII regions. These facts indicate that intensive star formation occurs in the knots. Some filaments, including the low velocity filament of the IC4040 EIG, exhibit shock-like emission line spectra, suggesting that shock heating plays an important role in ionization and excitation of the EIGs.
Extended Lyman-alpha emission from a high-z DLA at z=3.115
Nobunari Kashikawa,Toru Misawa,Yosuke Minowa,Katsuya Okoshi,Takashi Hattori,Jun Toshikawa,Shogo Ishikawa,Masafusa Onoue
Physics , 2013, DOI: 10.1088/0004-637X/780/2/116
Abstract: We searched for star formation activity associated with high-z Damped Lyman-alpha systems (DLAs) with Subaru telescope. We used a set of narrow-band (NB) filters whose central wavelengths correspond to the redshifted Lyman-alpha emission lines of targeted DLA absorbers at 3
The First Systematic Survey for Lyman Alpha Emitters at z=7.3 with Red-sensitive Subaru/Suprime-Cam
Takatoshi Shibuya,Nobunari Kashikawa,Kazuaki Ota,Masanori Iye,Masami Ouchi,Hisanori Furusawa,Kazuhiro Shimasaku,Takashi Hattori
Physics , 2011, DOI: 10.1088/0004-637X/752/2/114
Abstract: We have performed deep imaging surveys for LyA emitters (LAEs) at redshift ~7.3 in two blank fields, the Subaru Deep Field (SDF) and the Subaru/XMM-Newton Deep survey Field (SXDF), using the Subaru/Suprime-Cam equipped with new red-sensitive CCDs and a new narrow-band filter, NB1006 (lambda_c=10052 Ang, FWHM=214 Ang). We identified four objects as LAE candidates that exhibit luminosity excess in NB1006. By carrying out deep follow-up spectroscopy for three of them using Subaru/FOCAS and Keck/DEIMOS, a definitively asymmetric emission line is detected for one of them, SXDF-NB1006-2. Assuming this line is LyA, this object is a LAE at z=7.215 which has luminosity of 1.2^{+1.5}_{-0.6} x 10^43 [erg s-1] and a weighted skewness S_w=4.90+-0.86. Another object, SDF-NB1006-2, shows variable photometry and is thus probably a quasar (QSO) or an active galactic nucleus (AGN). It shows an asymmetric emission line at 10076 Ang, which may be due to either LyA at z=7.288 or [OII] at z=1.703. The third object, SDF-NB1006-1, is likely a galaxy with temporal luminosity enhancement associated with a supernova explosion, as the brightness of this object varies between the observed epochs. Its spectrum does not show any emission lines. The inferred decrease in the number density of LAEs toward higher redshift is n_LyA(z=7.3)/n_LyA(z=5.7) = 0.05^+0.11_-0.05 from z=5.7 to 7.3 down to L(LyA)=1.0 x 10^43 [erg s-1]. The present result is consistent with the interpretation in previous studies that the neutral hydrogen fraction is rapidly increasing from z=5.7 to 7.3.
"Direct" Gas-phase Metallicities, Stellar Properties, and Local Environments of Emission-line Galaxies at Redshift below 0.90
Chun Ly,Matthew A. Malkan,Tohru Nagao,Nobunari Kashikawa,Kazuhiro Shimasaku,Masao Hayashi
Physics , 2013, DOI: 10.1088/0004-637X/780/2/122
Abstract: Using deep narrow-band (NB) imaging and optical spectroscopy from the Keck telescope and MMT, we identify a sample of 20 emission-line galaxies (ELGs) at z=0.065-0.90 where the weak auroral emission line, [OIII]4363, is detected at >3\sigma. These detections allow us to determine the gas-phase metallicity using the "direct'' method. With electron temperature measurements and dust attenuation corrections from Balmer decrements, we find that 4 of these low-mass galaxies are extremely metal-poor with 12+log(O/H) <= 7.65 or one-tenth solar. Our most metal-deficient galaxy has 12+log(O/H) = 7.24^{+0.45}_{-0.30} (95% confidence), similar to some of the lowest metallicity galaxies identified in the local universe. We find that our galaxies are all undergoing significant star formation with average specific star formation rate (SFR) of (100 Myr)^{-1}, and that they have high central SFR surface densities (average of 0.5 Msun/yr/kpc^2. In addition, more than two-thirds of our galaxies have between one and four nearby companions within a projected radius of 100 kpc, which we find is an excess among star-forming galaxies at z=0.4-0.85. We also find that the gas-phase metallicities for a given stellar mass and SFR lie systematically below the local M-Z-(SFR) relation by \approx0.2 dex (2\sigma\ significance). These results are partly due to selection effects, since galaxies with strong star formation and low metallicity are more likely to yield [OIII]4363 detections. Finally, the observed higher ionization parameter and electron density suggest that they are lower redshift analogs to typical z>1 galaxies.
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