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Yoshiaki Taniguchi

Bio: Yoshiaki Taniguchi is an academic researcher from Tohoku University. The author has contributed to research in topics: Galaxy & Redshift. The author has an hindex of 48, co-authored 221 publications receiving 6932 citations. Previous affiliations of Yoshiaki Taniguchi include Astronomical Institute & Association of Universities for Research in Astronomy.


Papers
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Journal ArticleDOI
TL;DR: In this paper, the angular correlation of LAEs up to ~15' separations was calculated for a very deep and wide-field narrowband imaging on a 543 arcmin2 area of the Subaru Deep Field.
Abstract: We report on early results from very deep and wide-field narrowband imaging on a 543 arcmin2 area of the Subaru Deep Field. We find 87 Lyα emitters (LAEs) at z = 4.86 ± 0.03 that are photometrically selected by a combination of two broad bands (R and i') and one narrow band (NB711; λc = 7126 A, Δλ = 73 A). We derive the luminosity functions (LFs) of the LAEs at Lyα luminosity and at UV-continuum (rest frame 1700 A) luminosity. The LFs show little evolution between z = 3.4 and 4.86 either in Lyα or UV-continuum emission. The amplitude of the LAE LF tends to decline at the bright magnitudes more rapidly than that of the LBG LF at similar redshifts. We calculate the angular correlation function of our LAEs up to ~15' separations. The angular correlation ω(θ) is found to increase with decreasing angular separations, showing a clear signal of clustering. It is also found that the distribution of LAEs shows a large-density gradient with a scale of 15', which would indicate the existence of a large-scale structure of LAEs on 20 h-1 Mpc scales. We fit the observed correlation function by Aωθ-0.8 to find Aω = 29 arcsec0.8. The estimated correlation length is r0 = 3.5h-1 Mpc in comoving units (Ωm = 0.3 and ΩΛ = 0.7), which is slightly larger than the value for z ~ 4 LBGs with i' < 26. We calculate the angular correlation function for two subsamples of the 87 LAEs divided by Lyα luminosity, UV-continuum luminosity, and Lyα equivalent width (EW). The Lyα-bright subsample shows a larger correlation amplitude than the Lyα-faint subsample, while no significant difference is found for the subsamples divided by UV-continuum luminosity or EW. This may indicate that galaxies with bright Lyα emission are possibly biased against the underlying dark matter halos more strongly than those with bright UV continuum.

296 citations

Journal ArticleDOI
TL;DR: In this article, the authors carried out extended spectroscopic confirmations of Ly-alpha emitters (LAEs) at z=6.5 and 5.7 in the Subaru Deep Field.
Abstract: We carried out extended spectroscopic confirmations of Ly-alpha emitters (LAEs) at z=6.5 and 5.7 in the Subaru Deep Field. Now, the total number of spectroscopically confirmed LAEs is 45 and 54 at z=6.5 and 5.7, respectively, and at least 81% (70%) of our photometric candidates at z=6.5 (5.7) have been spectroscopically identified as real LAEs. We made careful measurements of the Ly-alpha luminosity, both photometrically and spectroscopically, to accurately determine the Ly-alpha and rest-UV luminosity functions (LFs). The substantially improved evaluation of the Ly-alpha LF at z=6.5 shows an apparent deficit from z=5.7 at least at the bright end, and a possible decline even at the faint end, though small uncertainties remain. The rest-UV LFs at z=6.5 and 5.7 are in good agreement, at least at the bright end, in clear contrast to the differences seen in the Ly-alpha LF. These results imply an increase in the neutral fraction of the intergalactic medium from z=5.7 to 6.5. The rest-frame equivalent width (EW_0) distribution at z=6.5 seems to be systematically smaller than z=5.7, and it shows an extended tail toward larger EW_0. The bright end of the rest-UV LF can be reproduced from the observed Ly-alpha LF and a reasonable EW_0-UV luminosity relation. Integrating this rest-UV LF provides the first measurement of the contribution of LAEs to the photon budget required for reionization. The derived UV LF suggests that the fractional contribution of LAEs to the photon budget among Lyman break galaxies significantly increases towards faint magnitudes. Low-luminosity LAEs could dominate the ionizing photon budget, though this inference depends strongly on the uncertain faint-end slope of the Ly-alpha LF.

251 citations

Journal ArticleDOI
TL;DR: In this article, the X-ray Baldwin effect was found for type 1 Seyfert galaxies and quasars in the 2-10 keV band, which is basically similar to the well-known relation known as the Baldwin effect, which means that the equivalent width of the C IV λ 1550 emission line is inversely correlated with the UV continuum luminosity.
Abstract: Using the X-ray data of active galactic nuclei (type 1 Seyfert galaxies and quasars) obtained by the X-ray satellite Ginga, we have found that the equivalent width of the Fe K emission line at 6.4 keV, EW(Fe K), is inversely correlated with the X-ray luminosity in the 2-10 keV band. This inverse correlation is basically similar to the well-known relation known as the Baldwin effect, which means that the equivalent width of the C IV λ1550 emission line is inversely correlated with the UV continuum luminosity (Baldwin 1977). Hence, we may call our finding the X-ray Baldwin effect. The X-ray Baldwin effect is pronounced for type 1 Seyfert galaxies

234 citations

Journal ArticleDOI
TL;DR: This paper performed a deep optical imaging survey using a narrow-band filter (NB921) centered at λ=9196 u A together with a single camera and a narrowband filter.
Abstract: We performed a deep optical imaging survey using a narrow-band filter (NB921) centered at λ=9196 u A together

212 citations

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a new model for the extended Lyα blobs found recently at high redshift (z ~ 3) to explain the observed properties of these blobs.
Abstract: We propose a new model for the extended Lyα blobs found recently at high redshift (z ~ 3). The observational properties of these blobs are as follows: (1) the observed Lyα luminosities are ~1043 h-2 ergs s-1, (2) they appear elongated morphologically, (3) their sizes amount to ~100 kpc, (4) the observed line widths amount to ~1000 km s-1, and (5) they are not associated with strong radio continuum sources. All these observational properties seem to be explained in terms of galactic winds driven by successive supernova explosions shortly after the initial burst of massive star formation in the galactic centers. The observed number density of Lyα blobs (~3.4 × 10-5 h3 Mpc-3) may be explained if their present-day counterparts are elliptical galaxies with a luminosity above ~1L*.

185 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, the authors review the range of complementary techniques and theoretical tools that allow astronomers to map the cosmic history of star formation, heavy element production, and reionization of the Universe from the cosmic "dark ages" to the present epoch.
Abstract: Over the past two decades, an avalanche of data from multiwavelength imaging and spectroscopic surveys has revolutionized our view of galaxy formation and evolution. Here we review the range of complementary techniques and theoretical tools that allow astronomers to map the cosmic history of star formation, heavy element production, and reionization of the Universe from the cosmic "dark ages" to the present epoch. A consistent picture is emerging, whereby the star-formation rate density peaked approximately 3.5 Gyr after the Big Bang, at z~1.9, and declined exponentially at later times, with an e-folding timescale of 3.9 Gyr. Half of the stellar mass observed today was formed before a redshift z = 1.3. About 25% formed before the peak of the cosmic star-formation rate density, and another 25% formed after z = 0.7. Less than ~1% of today's stars formed during the epoch of reionization. Under the assumption of a universal initial mass function, the global stellar mass density inferred at any epoch matches reasonably well the time integral of all the preceding star-formation activity. The comoving rates of star formation and central black hole accretion follow a similar rise and fall, offering evidence for co-evolution of black holes and their host galaxies. The rise of the mean metallicity of the Universe to about 0.001 solar by z = 6, one Gyr after the Big Bang, appears to have been accompanied by the production of fewer than ten hydrogen Lyman-continuum photons per baryon, a rather tight budget for cosmological reionization.

3,104 citations

Journal ArticleDOI
TL;DR: At the highest luminosities (Lir > 1012 ), nearly all objects appear to be advanced mergers powered by a mixture of circumnuclear starburst and active galactic nucleus energy sources, both of which are fueled by an enormous concentration of molecular gas that has been funneled into the merger nucleus as discussed by the authors.
Abstract: ▪ Abstract At luminosities above 1011 , infrared galaxies become the dominant population of extragalactic objects in the local Universe (z ≲ 0.3), being more numerous than optically selected starburst and Seyfert galaxies and quasi-stellar objects at comparable bolometric luminosity. The trigger for the intense infrared emission appears to be the strong interaction/merger of molecular gas-rich spirals, and the bulk of the infrared luminosity for all but the most luminous objects is due to dust heating from an intense starburst within giant molecular clouds. At the highest luminosities (Lir > 1012 ), nearly all objects appear to be advanced mergers powered by a mixture of circumnuclear starburst and active galactic nucleus energy sources, both of which are fueled by an enormous concentration of molecular gas that has been funneled into the merger nucleus. These ultraluminous infrared galaxies may represent an important stage in the formation of quasi-stellar objects and powerful radio galaxies. They may al...

2,911 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present an analysis of the host properties of 85224 emission-line galaxies selected from the Sloan Digital Sky Survey and derive a new empirical classification scheme which cleanly separates star-forming galaxies, composite AGN-H ii galaxies, Seyferts and LINERs and study the host galaxy properties of these different classes of objects.
Abstract: We present an analysis of the host properties of 85224 emission-line galaxies selected from the Sloan Digital Sky Survey. We show that Seyferts and LINERs form clearly separated branches on the standard optical diagnostic diagrams. We derive a new empirical classification scheme which cleanly separates star-forming galaxies, composite AGN-H ii galaxies, Seyferts and LINERs and we study the host galaxy properties of these different classes of objects. LINERs are older, more massive, less dusty and more concentrated, and they and have higher velocity dispersions and lower [OIII] luminosities than Seyfert galaxies. Seyferts and LINERs are most strongly distinguished by their [OIII] luminosities. We then consider the quantity L[OIII]/σ 4 , which is an indicator of the black hole accretion rate relative to the Eddington rate. Remarkably, we find that at fixed L[OIII]/σ 4 , all differences between Seyfert and LINER host properties disappear. LINERs and Seyferts form a continuous sequence, with LINERs dominant at low L/LEDD and Seyferts dominant at high L/LEDD . These results suggest that the majority of LINERs are AGN and that the Seyfert/LINER dichotomy is analogous to the high/low-state transition for X-ray binary systems. We apply theoretical photo-ionization models and show that pure LINERs require a harder ionizing radiation field with lower ionization parameter than Seyfert galaxies, consistent with the low and high X-ray binary states.

2,116 citations

Journal ArticleDOI
TL;DR: In this article, a robust method to constrain average galaxy star formation rates, star formation histories (SFHs), and the intracluster light (ICL) as a function of halo mass is presented.
Abstract: We present a robust method to constrain average galaxy star formation rates (SFRs), star formation histories (SFHs), and the intracluster light (ICL) as a function of halo mass. Our results are consistent with observed galaxy stellar mass functions, specific star formation rates (SSFRs), and cosmic star formation rates (CSFRs) from z = 0 to z = 8. We consider the effects of a wide range of uncertainties on our results, including those affecting stellar masses, SFRs, and the halo mass function at the heart of our analysis. As they are relevant to our method, we also present new calibrations of the dark matter halo mass function, halo mass accretion histories, and halo-subhalo merger rates out to z = 8. We also provide new compilations of CSFRs and SSFRs; more recent measurements are now consistent with the buildup of the cosmic stellar mass density at all redshifts. Implications of our work include: halos near 1012 M ☉ are the most efficient at forming stars at all redshifts, the baryon conversion efficiency of massive halos drops markedly after z ~ 2.5 (consistent with theories of cold-mode accretion), the ICL for massive galaxies is expected to be significant out to at least z ~ 1-1.5, and dwarf galaxies at low redshifts have higher stellar mass to halo mass ratios than previous expectations and form later than in most theoretical models. Finally, we provide new fitting formulae for SFHs that are more accurate than the standard declining tau model. Our approach places a wide variety of observations relating to the SFH of galaxies into a self-consistent framework based on the modern understanding of structure formation in ΛCDM. Constraints on the stellar mass-halo mass relationship and SFRs are available for download online.

2,085 citations

Journal ArticleDOI
TL;DR: In this paper, the authors review the range of complementary techniques and theoretical tools that allow astronomers to map the cosmic history of star formation, heavy element production, and reionization of the Universe from the cosmic "dark ages" to the present epoch.
Abstract: Over the past two decades, an avalanche of data from multiwavelength imaging and spectroscopic surveys has revolutionized our view of galaxy formation and evolution. Here we review the range of complementary techniques and theoretical tools that allow astronomers to map the cosmic history of star formation, heavy element production, and reionization of the Universe from the cosmic "dark ages" to the present epoch. A consistent picture is emerging, whereby the star-formation rate density peaked approximately 3.5 Gyr after the Big Bang, at z~1.9, and declined exponentially at later times, with an e-folding timescale of 3.9 Gyr. Half of the stellar mass observed today was formed before a redshift z = 1.3. About 25% formed before the peak of the cosmic star-formation rate density, and another 25% formed after z = 0.7. Less than ~1% of today's stars formed during the epoch of reionization. Under the assumption of a universal initial mass function, the global stellar mass density inferred at any epoch matches reasonably well the time integral of all the preceding star-formation activity. The comoving rates of star formation and central black hole accretion follow a similar rise and fall, offering evidence for co-evolution of black holes and their host galaxies. The rise of the mean metallicity of the Universe to about 0.001 solar by z = 6, one Gyr after the Big Bang, appears to have been accompanied by the production of fewer than ten hydrogen Lyman-continuum photons per baryon, a rather tight budget for cosmological reionization.

1,626 citations