arXiv subjects

Nao Suzuki

Publications and source records attributed to Nao Suzuki.

71 records · Page 4Linked to original sources

arXiv2011

The SDSS-III Baryon Oscillation Spectroscopic Survey: Quasar Target Selection for Data Release Nine

The SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS), a five-year spectroscopic survey of 10,000 deg^2, achieved first light in late 2009. One of the key goals of BOSS is to measure the signature of baryon acoustic oscillations in the distribution of Ly-alpha absorption from the spectra of a sample of ~150,000 z>2.2 quasars. Along with measuring the angular diameter distance at z\approx2.5, BOSS will provide the first direct measurement of the expansion rate of the Universe at z > 2. One of the biggest challenges in achieving this goal is an efficient target selection algorithm for quasars over 2.2 < z < 3.5, where their colors overlap those of stars. During the first year of the BOSS survey, quasar target selection methods were developed and tested to meet the requirement of delivering at least 15 quasars deg^-2 in this redshift range, out of 40 targets deg^-2. To achieve these surface densities, the magnitude limit of the quasar targets was set at g <= 22.0 or r<=21.85. While detection of the BAO signature in the Ly-alpha absorption in quasar spectra does not require a uniform target selection, many other astrophysical studies do. We therefore defined a uniformly-selected subsample of 20 targets deg^-2, for which the selection efficiency is just over 50%. This "CORE" subsample will be fixed for Years Two through Five of the survey. In this paper we describe the evolution and implementation of the BOSS quasar target selection algorithms during the first two years of BOSS operations. We analyze the spectra obtained during the first year. 11,263 new z>2.2 quasars were spectroscopically confirmed by BOSS. Our current algorithms select an average of 15 z > 2.2 quasars deg^-2 from 40 targets deg^-2 using single-epoch SDSS imaging. Multi-epoch optical data and data at other wavelengths can further improve the efficiency and completeness of BOSS quasar target selection. [Abridged]

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arXiv2009

Subaru FOCAS Spectroscopic Observations of High-Redshift Supernovae

We present spectra of high-redshift supernovae (SNe) that were taken with the Subaru low resolution optical spectrograph, FOCAS. These SNe were found in SN surveys with Suprime-Cam on Subaru, the CFH12k camera on the Canada-France-Hawaii Telescope (CFHT), and the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST). These SN surveys specifically targeted z>1 Type Ia supernovae (SNe Ia). From the spectra of 39 candidates, we obtain redshifts for 32 candidates and spectroscopically identify 7 active candidates as probable SNe Ia, including one at z=1.35, which is the most distant SN Ia to be spectroscopically confirmed with a ground-based telescope. An additional 4 candidates are identified as likely SNe Ia from the spectrophotometric properties of their host galaxies. Seven candidates are not SNe Ia, either being SNe of another type or active galactic nuclei. When SNe Ia are observed within a week of maximum light, we find that we can spectroscopically identify most of them up to z=1.1. Beyond this redshift, very few candidates were spectroscopically identified as SNe Ia. The current generation of super red-sensitive, fringe-free CCDs will push this redshift limit higher.

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arXiv2009

Galaxy Clusters in Formation: Determining the Age of the Red-Sequence in Optical and X-ray Clusters at z~1 with HST

Using deep two-band imaging from the Hubble Space Telescope, we measure the color-magnitude relations (CMR) of E/S0 galaxies in a set of 9 optically-selected clusters principally from the Red-Sequence Cluster Survey (RCS) at 0.9 < z < 1.23. We find that the mean scatter in the CMR in the observed frame of this set of clusters is 0.049 +/- 0.008, as compared to 0.031 +/- 0.007 in a similarly imaged and identically analyzed X-ray sample at similar redshifts. Single-burst stellar population models of the CMR scatter suggest that the E/S0 population in these RCS clusters truncated their star-formation at z~1.6, some 0.9 Gyrs later than their X-ray E/S0 counterparts which were truncated at z~2.1. The notion that this is a manifestation of the differing evolutionary states of the two populations of cluster galaxies is supported by comparison of the fraction of bulge-dominated galaxies found in the two samples which shows that optically-selected clusters contain a smaller fraction of E/S0 galaxies at the their cores

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arXiv2009

The XMM Cluster Survey: Galaxy Morphologies and the Color-Magnitude Relation in XMMXCS J2215.9-1738 at z=1.46

We present a study of the morphological fractions and color-magnitude relation in the most distant X-ray selected galaxy cluster currently known, XMMXCS J2215.9-1738 at z=1.46, using a combination of optical imaging data obtained with the Hubble Space Telescope Advanced Camera for Surveys, and infrared data from the Multi-Object Infrared Camera and Spectrograph, mounted on the 8.2m Subaru telescope. We find that the morphological mix of the cluster galaxy population is similar to clusters at z~1: approximately ~62% of the galaxies identified as likely cluster members are ellipticals or S0s; and ~38% are spirals or irregulars. We measure the color-magnitude relations for the early type galaxies, finding that the slope in the z_850-J relation is consistent with that measured in the Coma cluster, some ~9 Gyr earlier, although the uncertainty is large. In contrast, the measured intrinsic scatter about the color-magnitude relation is more than three times the value measured in Coma, after conversion to rest frame U-V. From comparison with stellar population synthesis models, the intrinsic scatter measurements imply mean luminosity weighted ages for the early type galaxies in J2215.9-1738 of ~3 Gyr, corresponding to the major epoch of star formation coming to an end at z_f = 3-5. We find that the cluster exhibits evidence of the `downsizing' phenomenon: the fraction of faint cluster members on the red sequence expressed using the Dwarf-to-Giant Ratio (DGR) is 0.32+/-0.18. This is consistent with extrapolation of the redshift evolution of the DGR seen in cluster samples at z < 1. In contrast to observations of some other z > 1 clusters, we find a lack of very bright galaxies within the cluster.

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arXiv2005

Signature of Galactic Outflows as Absorption-Free Gaps in the Ly-alpha Forest

Powerful outflows from star-forming galaxies are expected to push away the neutral intergalactic medium (IGM) around those galaxies, and produce absorption-free gaps in the Ly-alpha forest. We analyze the abundance of gaps of various sizes in three high resolution spectra of quasars at z ~ 3 - 3.5. The gap statistics agrees well with a model in which galactic halos above a minimum mass scale of M_min ~ 10^10 M_sun produce bubbles with a characteristic radius of R_b ~ 0.48 Mpc/h. Both numbers are consistent with naive theoretical expectations, where the minimum galaxy mass reflects the threshold for infall of gas out of a photo-ionized IGM. The observed gaps are typically bounded by deep absorption features as expected from the accumulation of swept-up gas on the bubble walls.

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arXiv2005

The H I opacity of the intergalactic medium at redshifts 1.6 < z < 3.2

We use high quality echelle spectra of 24 QSOs to provide a calibrated measurement of the total amount of Lyman-alpha forest absorption (DA) over the redshift range 2.2 < z < 3.2. Our measurement of DA excludes absorption from metal lines or the Lyman-alpha lines of Lyman limit systems and damped Lyman-alpha systems. We use artificial spectra with realistic flux calibration errors to show that we are able to place continuum levels that are accurate to better than 1%. When we combine our results with our previous results between 1.6 < z < 2.2, we find that the redshift evolution of DA is well described over 1.6 < z < 3.2 as A*(1+z)^gamma, where A = 0.0062 and gamma = 2.75. We detect no significant deviations from a smooth power law evolution over the redshift range studied. We find less H I absorption than expected at z=3, implying that the UV background is about 40% higher than expected. Our data appears to be consistent with an H I ionization rate of Gamma ~ 1.4E-12 1/s.

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arXiv2005

Quasar Spectrum Classification with PCA - II: Introduction of Five Classes, Artificial Quasar Spectrum, the Mean Flux Correction Factor dF,and the Identification of Emission Lines in the Ly alpha Forest

We investigate the variety in quasar UV spectra (1020-1600A) with emphasis on the weak emission lines in the Ly alpha forest region using principal component analysis (PCA). This paper is a continuation of Suzuki et al. (2005, Paper I), but with a different approach. We use 50 smooth continuum fitted quasar spectra (0.14 < z < 1.04) taken by the Hubble Space Telescope (HST) Faint Object Spectrograph. Three weak emission lines in the Ly alpha forest are identified as FeII 1070.95A, FeII+FeIII 1123.17A, and CIII* 1175.88A. Using first two standardized PCS coefficients, we introduce five classifications: Class Zero and Class I-IV. These classifications will guide us in finding the continuum level in the Ly alpha forest, and we discuss the characteristics of each class. We show weak emission lines in the Ly alpha forest become eminent for Class III and IV. By actively using PCS, we can generate artificial quasar spectra which are useful to test the detection of quasars, DLAs, and the continuum calibration. We provide 10,000 artificially generated spectra. We show that the power-law extrapolated continuum is inadequate to perform precise measurements of the mean flux in the Ly alpha forest because of the weak emission lines and the extended tails of Ly alpha and Ly beta/OVI emission lines. We introduce a correction factor dF such that the true mean flux can be related to that is measured by using power-law continuum extrapolation: = dF. The correction factor dF ranges from 0.84 to 1.05 with a mean of 0.947 and a standard deviation of 0.031 for our 50 quasars. This result means that we miss 5.3% of flux on average and we show that there are cases where we would miss 16% of flux using a power-law extrapolation.

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arXiv2004

The Kast Ground Based UV Spectral Survey of 79 QSOs at Redshift 2 for Lyman Alpha Forest and Metal Absorption

We present a moderate resolution (~1.15 Angstroms/pixel) survey of 79 quasars obtained using the Kast spectrograph on the Shane 3m telescope at Lick observatory. The spectra span the wavelength range of 3175-5880 Angstroms, and have typical signal to noise of 6-20 in the regions of the spectra showing Lyman alpha forest absorption. The quasars have a mean emission redshift of z=2.17, and nearly all cover the entire Lyman alpha forest between Lyman alpha and Lyman beta. Although the quasars were selected to avoid BAL, two quasars in the survey are BAL, one of which is a new discovery. We list the HI and metal ions observed in a total of 140 absorption systems. We also identify 526 emission lines, and list their observed wavelengths, along with new redshifts of the quasars. We determine the rest wavelengths of 3 emission lines or line blends in the forest to be 1070.95 +/- 1.00, 1123.13 +/- 0.51, and 1175.88 +/- 0.30 Angstroms.

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arXiv2004

Cosmological parameters sigma_8, the baryon density, and the UV background intensity from a calibrated measurement of H I Lyman-alpha absorption at z = 1.9

We identify a concordant model for the intergalactic medium (IGM) at redshift z=1.9 that uses popular values for cosmological and astrophysical parameters and accounts for all baryons with an uncertainty of 6%. We have measured the amount of absorption, DA, in the Ly-alpha forest at redshift 1.9 in spectra of 77 QSO from the Kast spectrograph. We calibrated the continuum fits with realistic artificial spectra, and we found that averaged over all 77 QSOs the mean continuum level is within 1-2% of the correct value. Absorption from all lines in the Ly-alpha forest at z=1.9 removes DA=15.1 +/- 0.7% of the flux between 1070 and 1170 (rest) Angstroms. This is the first measurement using many QSOs at this z, and the first calibrated measurement at any redshift. Metal lines absorb 2.3 +/- 0.5%, and LLS absorb 1.0 +/- 0.4% leaving 11.8 +/- 1.0% from the lower density bulk of the IGM. Averaging over Delta z=0.1 or 154 Mpc, the dispersion is 6.1 +/- 0.3% including LLS and metal lines, or 3.9 (+0.5, -0.7)% for the lower density IGM alone, consistent with the usual description of large scale structure. LLS and metal lines are major contributors to the variation in the mean flux, and they make the flux field significantly non-Gaussian. We find that a hydrodynamic simulation on a 1024 cubed grid in a 75.7 Mpc box reproduces the observed DA from the low density IGM with parameters values H_o=71 km/s/Mpc, Omega_Lambda=0.73, Omega_m=0.27, Omega_b=0.044, sigma_8=0.9 and a UV background that has an ionization rate that is 1.08 +/- 0.08 times the prediction by Madau, Haardt & Rees (1999).

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arXiv2003

Predicting QSO Continua in the Ly Alpha Forest

We present a method to make predictions with sets of correlated data values, in this case QSO flux spectra. We predict the continuum in the Lyman-Alpha forest of a QSO, from 1020 -- 1216 A, using the spectrum of that QSO from 1216 -- 1600 A . We find correlations between the unabsorbed flux in these two wavelengths regions in the HST spectra of 50 QSOs. We use principal component analysis (PCA) to summarize the variety of these spectra and we relate the weights of the principal components for 1020 -- 1600 A to the weights for 1216 -- 1600 A, and we apply this relation to make predictions. We test the method on the HST spectra, and we find an average absolute flux error of 9%, with a range 3 -- 30%, where individual predictions are systematically too low or too high. We mention several ways in which the predictions might be improved.

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arXiv2003

Relative Flux Calibration of Keck HIRES Echelle Spectra

We describe a new method to calibrate the relative flux levels in spectra from the HIRES echelle spectrograph on the Keck-I telescope. Standard data reduction techniques that transfer the instrument response between HIRES integrations leave errors in the flux of 5 - 10%, because the effective response varies. The flux errors are most severe near the ends of each spectral order, where there can be discontinuous jumps. The source of these errors is uncertain, but may include changes in the vignetting connected to the optical alignment. Our new flux calibration method uses a calibrated reference spectrum of each target to calibrate individual HIRES integrations. We determine the instrument response independently for each integration, and hence we avoid the need to transfer the instrument response between HIRES integrations. The procedure can be applied to any HIRES spectrum, or any other spectrum. While the accuracy of the method depends upon many factors, we have been able to flux calibrate a HIRES spectrum to 1% over scales of 200 A that include order joins. We illustrate the method with spectra of Q1243+3047 towards which we have measured the deuterium to hydrogen abundance ratio.

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arXiv2003

The cosmological baryon density from the deuterium to hydrogen ratio towards QSO absorption systems: D/H towards Q1243+3047

We report the detection of Deuterium absorption at redshift 2.525659 towards Q1243+3047. We describe improved methods to estimate the Deuterium to Hydrogen abundance ratio (D/H) in absorption systems, including improved modeling of the continuum level, the Ly-alpha forest and the velocity structure of the absorption. Together with improved relative flux calibration, these methods give D/H = 2.42^+0.35_-0.25 x 10^-5 cm^-2 from our Keck-I HIRES spectra of Q1243+3047, where the error is from the uncertainty in the shape of the continuum level and the amount of D absorption in a minor second component. The measured D/H is likely the primordial value because the [O/H] = -2.79 +/- 0.05. This absorption system has a neutral Hydrogen column density of 19.73 +/- 0.04 cm^-2, it shows five D lines and is mostly ionized. The best estimate of the primordial D/H is 2.78^+0.44_-0.38 x 10^-5, from the log D/H values towards five QSOs. The dispersion in the five values is larger than we expect from their individual measurement errors and we suspect this is because some of these errors were underestimated. We observe a trend in D/H with neutral H column density that we also suspect is spurious. The D/H corresponds to a baryon-to-photon ratio ETA = 5.9 +/- 0.5 x 10^-10 and a cosmological baryon density Omega_b h^2 = 0.0214 +/- 0.0020 (9.3%) that agrees with values from the pre-MAP measurements of the anisotropy of the Cosmic Microwave Background.

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arXiv2002

The UCSD HIRES/KECK I Damped Lya Abundance Database: IV. Probing Galactic Enrichment Histories with Nitrogen

We present 14 N^0 measurements from our HIRES/Keck database of damped Lya abundances. These data are combined with measurements from the recent and past literature to build an homogeneous, uniform set of observations. We examine photoionization diagnostics like Fe^++ and Ar^0 in the majority of the complete sample and assess the impact of ionization corrections on N/alpha and alpha/H values derived from observed ionic column densities of N^0, Si^+, H^0, and S^+. Our final sample of 19 N/alpha, alpha/H pairs appears bimodal; the majority of systems show N/alpha values consistent with metal-poor emission regions in the local universe but a small sub-sample exhibit significantly lower N/alpha ratios. Contrary to previous studies of N/alpha in the damped systems, our sample shows little scatter within each sub-sample. We consider various scenarios to explain the presence of the low N/alpha sightlines and account for the apparent bimodality. We favor a model where at least some galaxies undergo an initial burst of star formation with suppressed formation of intermediate-mass stars. We found a power-law IMF with slope 0.10 or a mass cut of ~5-8 Msolar would successfully reproduce the observed LN-DLA values. If the bimodal distribution is confirmed by a larger sample of measurements, this may present the first observational evidence for a top heavy initial mass function in some early stellar populations.

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arXiv2002

The UCSD HIRES/KeckI Damped Lya Abundance Database III. An Empirical Study of Photoionization in the Damped Lya System Toward GB1759+7539

We investigate the ionization state of the damped Lya system at z=2.62 toward GB1759+7539 through an analysis of ionic ratios sensitive to photoionization: ArI/SII, FeIII/FeII, NII/NI, AlIII/AlII. Approximately half of the metals arise in a mostly neutral velocity component with HI/H > 0.9, based on FeIII/FeII < 0.013. In contrast, the remaining half exhibits FeIII/FeII~0.3 indicative of a partially ionized medium with HI/H~0.5. These conclusions are supported by the observed NII/NI, AlIII/AlII, and ArI/SII ratios. We assess ionization corrections for the observed column densities through photoionization models derived from the CLOUDY software package. In the neutral gas, the ionization corrections are negligible except for ArI. However for the partially ionized gas, element abundance ratios differ from the ionic ratios by 0.1-0.3 dex for (SiII, SII, NiII, AlII)/FeII ratios and more for (NI, ArI)/FeII. Independent of the shape of the photoionizing spectrum and assumptions on the number of ionization phases, these ionization corrections have minimal impact (<0.1dex) on the total metallicity inferred for this damped Lya system. Measurements on the relative elemental abundances of the partially ionized gas, however, have a greater than ~0.15 dex uncertainty which hides the effects of nucleosynthesis and dust depletion. We caution the reader that this damped system is unusual for a number of reasons (e.g. a very low ArI/SII ratio) and we believe its ionization properties are special but not unique. Nevertheless, it clearly shows the value of examining photoionization diagnostics like FeIII/FeII in a larger sample of systems.

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arXiv2001

New HST spectra indicate the QSO PG1718+4807 will not give the primordial deuterium abundance

The z ~ 0.701 absorption system towards the QSO PG1718+4807 is the only example of a QSO absorption system which might have a deuterium/hydrogen ratio approximately ten times the value found towards other QSOs. We have obtained new STIS spectra from the Hubble Space Telescope of the Lyman alpha and Lyman limit regions of the system. These spectra give the redshift and velocity dispersion of the neutral hydrogen which produces most of the observed absorption. The Lyman alpha line is too narrow to account for all of the observed absorption. It was previously known that extra absorption is needed on the blue side of the main H I near to the expected position of deuterium. The current data suggests with a 98% confidence level that the extra absorption is not deuterium. Some uncertainty persists because we have a low signal to noise ratio and the extra absorption - be it deuterium or hydrogen - is heavily blended with the Lyman alpha absorption from the main hydrogen component.

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arXiv2001

The Deuterium to Hydrogen Abundance Ratio Towards a Fourth QSO: HS0105+1619

We report the measurement of the primordial D/H abundance ratio towards QSO \object. The column density of the hydrogen in the $z \simeq 2.536$ Lyman limit system is high, \lnhi $= 19.422 \pm 0.009$ \cmm, allowing for the deuterium to be seen in 5 Lyman series transitions. The measured value of the D/H ratio towards QSO \object is found to be D/H$ = 2.54 \pm 0.23 \times 10^{-5}$. The metallicity of the system showing D/H is found to be $\simeq 0.01$ solar, indicating that the measured D/H is the primordial D/H within the measurement errors. The gas which shows D/H is neutral, unlike previous D/H systems which were more highly ionized. Thus, the determination of the D/H ratio becomes more secure since we are measuring it in different astrophysical environments, but the error is larger because we now see more dispersion between measurements. Combined with prior measurements of D/H, the best D/H ratio is now D/H$ = 3.0 \pm 0.4 \times 10^{-5}$, which is 10% lower than the previous value. The new values for the baryon to photon ratio, and baryonic matter density derived from D/H are $η= 5.6 \pm 0.5 \times 10^{-10} $ and \ob $=0.0205 \pm 0.0018$ respectively.

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arXiv2000

Review of Big Bang Nucleosynthesis and Primordial Abundances

Big Bang Nucleosynthesis (BBN) is the synthesis of the light nuclei, Deuterium, He3, He4 and Li7, during the first few minutes of the universe. This review concentrates on recent improvements in the measurement of the primordial (after BBN, and prior to modification) abundances of these nuclei. We mention improvement in the standard theory, and the non-standard extensions which are limited by the data. (abridged)

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