arXiv subjects

M. Doi

Publications and source records attributed to M. Doi.

At least 37 records · Page 2Linked to original sources

arXiv2007

The Sloan Digital Sky Survey-II Supernova Survey: Search Algorithm and Follow-up Observations

The Sloan Digital Sky Survey-II Supernova Survey has identified a large number of new transient sources in a 300 sq. deg. region along the celestial equator during its first two seasons of a three-season campaign. Multi-band (ugriz) light curves were measured for most of the sources, which include solar system objects, Galactic variable stars, active galactic nuclei, supernovae (SNe), and other astronomical transients. The imaging survey is augmented by an extensive spectroscopic follow-up program to identify SNe, measure their redshifts, and study the physical conditions of the explosions and their environment through spectroscopic diagnostics. During the survey, light curves are rapidly evaluated to provide an initial photometric type of the SNe, and a selected sample of sources are targeted for spectroscopic observations. In the first two seasons, 476 sources were selected for spectroscopic observations, of which 403 were identified as SNe. For the Type Ia SNe, the main driver for the Survey, our photometric typing and targeting efficiency is 90%. Only 6% of the photometric SN Ia candidates were spectroscopically classified as non-SN Ia instead, and the remaining 4% resulted in low signal-to-noise, unclassified spectra. This paper describes the search algorithm and the software, and the real-time processing of the SDSS imaging data. We also present the details of the supernova candidate selection procedures and strategies for follow-up spectroscopic and imaging observations of the discovered sources.

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arXiv2007

A New Determination of the High Redshift Type Ia Supernova Rates with the Hubble Space Telescope Advanced Camera for Surveys

We present a new measurement of the volumetric rate of Type Ia supernova up to a redshift of 1.7, using the Hubble Space Telescope (HST) GOODS data combined with an additional HST dataset covering the North GOODS field collected in 2004. We employ a novel technique that does not require spectroscopic data for identifying Type Ia supernovae (although spectroscopic measurements of redshifts are used for over half the sample); instead we employ a Bayesian approach using only photometric data to calculate the probability that an object is a Type Ia supernova. This Bayesian technique can easily be modified to incorporate improved priors on supernova properties, and it is well-suited for future high-statistics supernovae searches in which spectroscopic follow up of all candidates will be impractical. Here, the method is validated on both ground- and space-based supernova data having some spectroscopic follow up. We combine our volumetric rate measurements with low redshift supernova data, and fit to a number of possible models for the evolution of the Type Ia supernova rate as a function of redshift. The data do not distinguish between a flat rate at redshift > 0.5 and a previously proposed model, in which the Type Ia rate peaks at redshift >1 due to a significant delay from star-formation to the supernova explosion. Except for the highest redshifts, where the signal to noise ratio is generally too low to apply this technique, this approach yields smaller or comparable uncertainties than previous work.

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arXiv2007

The Sloan Digital Sky Survey-II Supernova Survey: Technical Summary

The Sloan Digital Sky Survey-II (SDSS-II) has embarked on a multi-year project to identify and measure light curves for intermediate-redshift (0.05 < z < 0.35) Type Ia supernovae (SNe Ia) using repeated five-band (ugriz) imaging over an area of 300 sq. deg. The survey region is a stripe 2.5 degrees wide centered on the celestial equator in the Southern Galactic Cap that has been imaged numerous times in earlier years, enabling construction of a deep reference image for discovery of new objects. Supernova imaging observations are being acquired between 1 September and 30 November of 2005-7. During the first two seasons, each region was imaged on average every five nights. Spectroscopic follow-up observations to determine supernova type and redshift are carried out on a large number of telescopes. In its first two three-month seasons, the survey has discovered and measured light curves for 327 spectroscopically confirmed SNe Ia, 30 probable SNe Ia, 14 confirmed SNe Ib/c, 32 confirmed SNe II, plus a large number of photometrically identified SNe Ia, 94 of which have host-galaxy spectra taken so far. This paper provides an overview of the project and briefly describes the observations completed during the first two seasons of operation.

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arXiv2007

A Study of the Type Ia/IIn Supernova 2005gj from X-ray to the Infrared: Paper I

We present extensive ugrizYHJK photometry and optical spectroscopy of SN 2005gj obtained by the SDSS-II and CSP Supernova Projects, which give excellent coverage during the first 150 days after the time of explosion. These data show that SN 2005gj is the second clear case, after SN 2002ic, of a thermonuclear explosion in a dense circumstellar environment. Both the presence of singly and doubly ionized iron-peak elements (FeIII and weak SII, SiII) near maximum light as well as the spectral evolution show that SN 2002ic-like events are Type Ia explosions. Independent evidence comes from the exponential decay in luminosity of SN 2005gj, pointing to an exponential density distribution of the ejecta. The interaction of the supernova ejecta with the dense circumstellar medium is stronger than in SN 2002ic: (1) the supernova lines are weaker; (2) the Balmer emission lines are more luminous; and (3) the bolometric luminosity is higher close to maximum light. The velocity evolution of the Halpha components suggest that the CSM around SN 2005gj is clumpy and it has a flatter density distribution compared with the steady wind solution, in agreement with SN 2002ic. An early X-ray observation with Chandra gives an upper-limit on the mass loss rate from the companion of < 2x10^{-4} Msun/yr.

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arXiv2007

Rest-Frame R-band Lightcurve of a z~1.3 Supernova Obtained with Keck Laser Adaptive Optics

We present Keck diffraction limited H-band photometry of a z~1.3 Type Ia supernova (SN) candidate, first identified in a Hubble Space Telescope (HST) search for SNe in massive high redshift galaxy clusters. The adaptive optics (AO) data were obtained with the Laser Guide Star facility during four observing runs from September to November 2005. In the analysis of data from the observing run nearest to maximum SN brightness, the SN was found to have a magnitude H=23.9 +/- 0.14 (Vega). We present the H-band (approximately rest-frame R) light curve and provide a detailed analysis of the AO photometric uncertainties. By constraining the aperture correction with a nearby (4" separation) star we achieve 0.14 magnitude photometric precision, despite the spatially varying AO PSF.

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arXiv2007

Quantitative comparison between Type Ia supernova spectra at low and high redshifts: A case study

We develop a method to measure the strength of the absorption features in Type Ia supernova (SN Ia) spectra and use it to make a quantitative comparison between the spectra of Type Ia supernovae at low and high redshifts. In this case study, we apply the method to 12 high-redshift (0.212 < z < 0.912) SNe Ia observed by the Supernova Cosmology Project . Through measurements of the strengths of these features and of the blueshift of the absorption minimum in Ca II H&K, we show that the spectra of the high-redshift SNe Ia are quantitatively similar to spectra of nearby SNe Ia (z < 0.15). One supernova in our high redshift sample, SN 2002fd at z=0.279, is found to have spectral characteristics that are associated with peculiar SN 1991T/SN 1999aa-like supernovae.

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arXiv2007

The Galaxy Luminosity Functions down to M~-10 in the Hydra I Cluster

We study the galaxy population in the central region and a region about 0.6 Mpc away from the center of the Hydra I cluster in B- and Rc-bands down to M~-10 using the Subaru Suprime-Cam photometry. We find that the luminosity function of the entire population has a slightly steeper slope (alpha~-1.6) in the range of -20 -14) increases in the cluster center as well as bright galaxies. The Hydra I cluster is dominated by red dwarfs and the luminosity function shows a significant upturn at M~-16 as is seen in several other nearby clusters, but not in the field. This upturn and the variation in the faint-end slope of the luminosity function may be caused by the cluster environment or the evolution history of individual clusters.

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arXiv2006

The Sloan Digital Sky Survey Monitor Telescope Pipeline

The photometric calibration of the Sloan Digital Sky Survey (SDSS) is a multi-step process which involves data from three different telescopes: the 1.0-m telescope at the US Naval Observatory (USNO), Flagstaff Station, Arizona (which was used to establish the SDSS standard star network); the SDSS 0.5-m Photometric Telescope (PT) at the Apache Point Observatory (APO), New Mexico (which calculates nightly extinctions and calibrates secondary patch transfer fields); and the SDSS 2.5-m telescope at APO (which obtains the imaging data for the SDSS proper). In this paper, we describe the Monitor Telescope Pipeline, MTPIPE, the software pipeline used in processing the data from the single-CCD telescopes used in the photometric calibration of the SDSS (i.e., the USNO 1.0-m and the PT). We also describe transformation equations that convert photometry on the USNO-1.0m u'g'r'i'z' system to photometry the SDSS 2.5m ugriz system and the results of various validation tests of the MTPIPE software. Further, we discuss the semi-automated PT factory, which runs MTPIPE in the day-to-day standard SDSS operations at Fermilab. Finally, we discuss the use of MTPIPE in current SDSS-related projects, including the Southern u'g'r'i'z' Standard Star project, the u'g'r'i'z' Open Star Clusters project, and the SDSS extension (SDSS-II).

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arXiv2006

The End of the Reionization Epoch Probed by Ly-alpha Emitters at z=6.5 in the Subaru Deep Field

We report an extensive search for Lyman-alpha emitters (LAEs) at z=6.5 in the Subaru Deep Field. Subsequent spectroscopy with Subaru and Keck identified eight more LAEs, giving a total of 17 spectroscopically confirmed LAEs at z=6.5. Based on this spectroscopic sample of 17, complemented by a photometric sample of 58 LAEs, we have derived a more accurate Lyman-alpha luminosity function of LAEs at z=6.5, which reveals an apparent deficit at the bright end of ~0.75 mag fainter L*, compared with that observed at z=5.7. The difference in the LAE luminosity functions between z=5.7 and 6.5 is significant at the 3-sigma level, which is reduced to 2-sigma when cosmic variance is taken into account. This result may imply that the reionization of the universe has not been completed at z=6.5. We found that the spatial distribution of LAEs at z=6.5 was homogeneous over the field. We discuss the implications of these results for the reionization of the universe.

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arXiv2006

Ly Alpha Emitters at z=5.7 in the Subaru Deep Field

We present the properties of Ly Alpha emitters (LAEs) at z = 5.7 in the Subaru Deep Field. A photometric sample of 89 LAE candidates is constructed from narrow-band (NB816) data down to NB816 = 26.0 (AB) in a continuous 725 arcmin^2 area. Spectra of 39 objects satisfying the photometric selection criteria for LAEs were obtained with Subaru and Keck II Telescopes, among which 28 were confirmed LAEs, one was a nearby galaxy, and eight were unclassified. We also obtained spectra of another 24 NB816-excess objects in the field, identifying six additional LAEs. We find that the Ly Alpha luminosity function derived from the photometric sample is reproduced well by a Schechter function with L* = (7.9+3.0-2.2) x 10^42 erg/s and phi* = (6.3+3.0-2.0) x 10^-4 Mpc^-3 for alpha = -1.5 (fixed) over the whole luminosity range of L ~= 3x10^42 - 3x10^43 erg/s. We then measure rest-frame Ly Alpha equivalent widths (EWs) for the confirmed LAEs, to find that the median among the 28 objects satisfying the photometric selection criteria is W_0^i = 233 A. We infer that 30% - 40% of LAEs at z=5.7 exceed W_0^i = 240 A. These large-EW objects probably cannot be accounted for by ordinary star-forming populations with a Salpeter IMF. We also find that LAEs with fainter far-UV luminosities have larger EWs. Finally, we derive the far-UV luminosity function of LAEs down to M_UV ~= -19.6 using the photometric sample, and compare it with that of Lyman-break galaxies (LBGs). We find that as high as about 80% of LBGs at z ~ 6 have W_0^i >= 100 A, in sharp contrast to lower-z counterparts.

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arXiv2005

The Sloan Digital Sky Survey Quasar Catalog III. Third Data Release

We present the third edition of the Sloan Digital Sky Survey (SDSS) Quasar Catalog. The catalog consists of the 46,420 objects in the SDSS Third Data Release that have luminosities larger than M_i = -22 (in a cosmology with H_0 = 70 km/s/Mpc, Omega_M = 0.3, and Omega_Lambda = 0.7), have at least one emission line with FWHM larger than 1000 km/s or are unambiguously broad absorption line quasars, are fainter than i = 15.0, and have highly reliable redshifts. The area covered by the catalog is 4188 sq. deg. The quasar redshifts range from 0.08 to 5.41, with a median value of 1.47; the high-redshift sample includes 520 quasars at redshifts greater than four, of which 17 are at redshifts greater than five. For each object the catalog presents positions accurate to better than 0.2 arcsec. rms per coordinate, five-band (ugriz) CCD-based photometry with typical accuracy of 0.03 mag, and information on the morphology and selection method. The catalog also contains radio, near-infrared, and X-ray emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra cover the wavelength region 3800--9200A at a spectral resolution about 2000; the spectra can be retrieved from the public database using the information provided in the catalog. A total of 44,221 objects in the catalog were discovered by the SDSS; 28,400 of the SDSS discoveries are reported here for the first time.

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arXiv2005

Detection of the Baryon Acoustic Peak in the Large-Scale Correlation Function of SDSS Luminous Red Galaxies

We present the large-scale correlation function measured from a spectroscopic sample of 46,748 luminous red galaxies from the Sloan Digital Sky Survey. The survey region covers 0.72 h^{-3} Gpc^3 over 3816 square degrees and 0.16<z<0.47, making it the best sample yet for the study of large-scale structure. We find a well-detected peak in the correlation function at 100h^{-1} Mpc separation that is an excellent match to the predicted shape and location of the imprint of the recombination-epoch acoustic oscillations on the low-redshift clustering of matter. This detection demonstrates the linear growth of structure by gravitational instability between z=1000 and the present and confirms a firm prediction of the standard cosmological theory. The acoustic peak provides a standard ruler by which we can measure the ratio of the distances to z=0.35 and z=1089 to 4% fractional accuracy and the absolute distance to z=0.35 to 5% accuracy. From the overall shape of the correlation function, we measure the matter density Omega_mh^2 to 8% and find agreement with the value from cosmic microwave background (CMB) anisotropies. Independent of the constraints provided by the CMB acoustic scale, we find Omega_m = 0.273 +- 0.025 + 0.123 (1+w_0) + 0.137 Omega_K. Including the CMB acoustic scale, we find that the spatial curvature is Omega_K=-0.010+-0.009 if the dark energy is a cosmological constant. More generally, our results provide a measurement of cosmological distance, and hence an argument for dark energy, based on a geometric method with the same simple physics as the microwave background anisotropies. The standard cosmological model convincingly passes these new and robust tests of its fundamental properties.

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arXiv2004

Spectroscopic confirmation of high-redshift supernovae with the ESO VLT

We present VLT FORS1 and FORS2 spectra of 39 candidate high-redshift supernovae that were discovered as part of a cosmological study using Type Ia supernovae (SNe Ia) over a wide range of redshifts. From the spectra alone, 20 candidates are spectrally classified as SNe Ia with redshifts ranging from z=0.212 to z=1.181. Of the remaining 19 candidates, 1 might be a Type II supernova and 11 exhibit broad supernova-like spectral features and/or have supernova-like light curves. The candidates were discovered in 8 separate ground-based searches. In those searches in which SNe Ia at z ~ 0.5 were targeted, over 80% of the observed candidates were spectrally classified as SNe Ia. In those searches in which SNe Ia with z > 1 were targeted, 4 candidates with z > 1 were spectrally classified as SNe Ia and later followed with ground and space based observatories. We present the spectra of all candidates, including those that could not be spectrally classified as supernova.

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arXiv2004

The Subaru Deep Field: The Optical Imaging Data

The Subaru Deep Field (SDF) project is a program of Subaru Observatory to carry out a deep galaxy survey over a blank field as large as 34'x27'. The program consists of very deep multi-band optical imaging, near infrared imaging for smaller portions of the field and follow-up optical spectroscopy. Major scientific goals of the project are to construct large samples of Lyman-break galaxies at z~4-5 and Lyman alpha emitters at z~5.7 and 6.6, and to make detailed studies these very high-redshift galaxy populations. In this paper, we describe the optical imaging observations and data reduction, presenting mosaicked images and object catalogs in seven bandpasses.The optical imaging was made through five broad-band filters, B, V, R, i', z', and two narrow-band filters, NB816 (lambda_c=8150A) and NB921 (lambda_c=9196A) with almost 10 hours long integrations for each band. The limiting magnitudes measured at 3-sigma on a 2" aperture are B=28.45, V=27.74, R=27.80, i'=27.43, z'=26.62, NB816=26.63, and NB921=26.54 in the AB system. The object catalog constructed for each of the seven bands contains more than 10^5 objects. The galaxy number counts corrected for detection incompleteness and star count contribution are found to be consistent with previous results in the literature. The mosaicked images and catalogs of all the bands have been made open to the public on Oct. 1, 2004 on the SDF project website at http://soaps.naoj.org/sdf/.

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arXiv2004

FeII/MgII Emission Line Ratios of QSOs. II. z>6 Objects

Near-infrared spectra of four QSOs located at $z>6$ are obtained with the OH-airglow suppressor mounted on the Subaru telescope. The FeII/MgII emission-line ratios of these QSOs are examined by the same fitting algorithm as in our previous study of $z<5.3$ QSOs. The fitting results show that two out of the four $z>6$ QSOs have significant FeII emission in their rest-UV spectra, while the other two have almost no FeII features. We also applied our fitting algorithm to more than 10,000 SDSS QSOs and found two trends in the distribution of FeII/MgII against redshift: (1) the upper envelope of the FeII/MgII distribution at $z>3$ shows a probable declination toward high redshift, and (2) the median distribution settles into lower ratios at $z\sim 1.5$ with small scatter compared to the other redshift. We discuss an Fe/Mg abundance evolution of QSOs with a substantial contribution from the diverse nature of the broad-line regions in high-redshift QSOs.

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arXiv2004

A Strong Lyman-alpha Emitter at z=6.33 in the Subaru Deep Field Selected as an i' Dropout

We report on the discovery of a star-forming galaxy at z=6.33 in the Subaru Deep Field. This object is selected as a candidate of an i'-dropout, high-redshift galaxy around z=6 because of its red i'-z' color in our deep optical imaging survey in the Subaru Deep Field. Our follow up optical spectroscopy reveals that this object is a strong Ly-alpha emitter with only very faint ultraviolet continuum. The rest-frame equivalent width of the detected Ly-alpha emission is as much as 130 A. Thus the light detected in our z' image is largely attributed to the Ly-alpha emission, i.e., ~40% of the z'-band flux is the strong Ly-alpha emission, giving a very red i'-z' color. This is consistent with the photometric property of this object because the narrow-band data obtained with the NB921 filter shows a significant depression, z'-NB921 = -0.54 mag. By using the photometric data, we show that some other objects among the 48 i'-dropout high-redshift galaxy candidates found in the Subaru Deep Field also show a significant NB921 depression. We briefly discuss the nature of these NB921-depressed objects.

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arXiv2004

Cosmological parameter analysis including SDSS Ly-alpha forest and galaxy bias: constraints on the primordial spectrum of fluctuations, neutrino mass, and dark energy

We combine the constraints from the recent Ly-alpha forest and bias analysis of the SDSS with previous constraints from SDSS galaxy clustering, the latest supernovae, and WMAP . Combining WMAP and the lya we find for the primordial slope n_s=0.98\pm 0.02. We see no evidence of running, dn/d\ln k=-0.003\pm 0.010, a factor of 3 improvement over previous constraints. We also find no evidence of tensors, r<0.36 (95% c.l.). A positive correlation between tensors and primordial slope disfavors chaotic inflation type models with steep slopes: V \propto ϕ^4 is outside the 3-sigma contour. For the amplitude we find sigma_8=0.90\pm 0.03 from the lyaf and WMAP alone. We find no evidence of neutrino mass: for the case of 3 massive neutrino families with an inflationary prior, \sum m_ν<0.42eV and the mass of lightest neutrino is m_1<0.13eV at 95% c.l. For the 3 massless + 1 massive neutrino case we find m_ν<0.79eV for the massive neutrino, excluding at 95% c.l. all neutrino mass solutions compatible with the LSND results. We explore dark energy constraints in models with a fairly general time dependence of dark energy equation of state, finding Omega_lambda=0.72\pm 0.02, w(z=0.3)=-0.98^{+0.10}_{-0.12}, the latter changing to w(z=0.3)=-0.92^{+0.09}_{-0.10} if tensors are allowed. We find no evidence for variation of the equation of state with redshift, w(z=1)=-1.03^{+0.21}_{-0.28}. These results rely on the current understanding of the lyaf and other probes, which need to be explored further both observationally and theoretically, but extensive tests reveal no evidence of inconsistency among different data sets used here.

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arXiv2004

Subaru Deep Survey VI. A Census of Lyman Break Galaxies at z=4 and 5 in the Subaru Deep Fields: Clustering Properties

We investigate the clustering properties of 2,600 Lyman Break Galaxies (LBGs) at z=3.5-5.2 in two large blank fields, the Subaru Deep Field and the Subaru/XMM Deep Field (600arcmin^2 each). The angular correlation functions of these LBGs show a clear clustering at both z~4 and 5. The correlation lengths are r_0= 4.1^{+0.2}_{-0.2} and 5.9^{+1.3}_{-1.7} h_{100}^{-1} Mpc (r_0= 5.1^{+1.0}_{-1.1} and 5.9^{+1.3}_{-1.7} h_{100}^{-1} Mpc) for all the detected LBGs (for L>L* LBGs) at z~4 and 5, respectively. These correlation lengths correspond to galaxy-dark matter biases of b_g= 2.9^{+0.1}_{-0.1} and 4.6^{+0.9}_{-1.2} (b_g=3.5^{+0.6}_{-0.7} and 4.6^{+0.9}_{-1.2}), for all the detected LBGs (for L>L^* LBGs) at z~4 and 5, respectively. These results, combined with estimates for z~3 LBGs in the literature, show that the correlation length of L>L^* LBGs is almost constant, ~5 h_{100}^{-1} Mpc, over z~3-5, while the bias monotonically increases with redshift at z>3. We also find that for LBGs at z~4 the clustering amplitude increases with UV-continuum luminosity and with the amount of dust extinction. We estimate the mass of dark halos hosting various kinds of high-z galaxies including LBGs with the analytic model given by Sheth & Tormen (1999). We find that the typical mass of dark halos hosting L>L^* LBGs is about 1x10^{12} h_{70}^{-1}Msol over z~3-5, which is comparable to that of the Milky Way Galaxy. A single dark halo with ~10^{12} h_{70}^{-1} Msol is found to host 0.1-0.3 LBG on average but host about four K-band selected galaxies.

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