Publications (10)6.02 Total impact
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Article: The BigBOSS Experiment
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ABSTRACT: BigBOSS is a Stage IV ground-based dark energy experiment to study baryon acoustic oscillations (BAO) and the growth of structure with a wide-area galaxy and quasar redshift survey over 14,000 square degrees. It has been conditionally accepted by NOAO in response to a call for major new instrumentation and a high-impact science program for the 4-m Mayall telescope at Kitt Peak. The BigBOSS instrument is a robotically-actuated, fiber-fed spectrograph capable of taking 5000 simultaneous spectra over a wavelength range from 340 nm to 1060 nm, with a resolution R = 3000-4800. Using data from imaging surveys that are already underway, spectroscopic targets are selected that trace the underlying dark matter distribution. In particular, targets include luminous red galaxies (LRGs) up to z = 1.0, extending the BOSS LRG survey in both redshift and survey area. To probe the universe out to even higher redshift, BigBOSS will target bright [OII] emission line galaxies (ELGs) up to z = 1.7. In total, 20 million galaxy redshifts are obtained to measure the BAO feature, trace the matter power spectrum at smaller scales, and detect redshift space distortions. BigBOSS will provide additional constraints on early dark energy and on the curvature of the universe by measuring the Ly-alpha forest in the spectra of over 600,000 2.2 < z < 3.5 quasars. BigBOSS galaxy BAO measurements combined with an analysis of the broadband power, including the Ly-alpha forest in BigBOSS quasar spectra, achieves a FOM of 395 with Planck plus Stage III priors. This FOM is based on conservative assumptions for the analysis of broad band power (kmax = 0.15), and could grow to over 600 if current work allows us to push the analysis to higher wave numbers (kmax = 0.3). BigBOSS will also place constraints on theories of modified gravity and inflation, and will measure the sum of neutrino masses to 0.024 eV accuracy.06/2011; -
Article: Spectra and Hubble Space Telescope Light Curves of Six Type Ia Supernovae at 0.511 < z < 1.12 and the Union2 Compilation
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ABSTRACT: We report on work to increase the number of well-measured Type Ia supernovae (SNe Ia) at high redshifts. Light curves, including high signal-to-noise Hubble Space Telescope data, and spectra of six SNe Ia that were discovered during 2001, are presented. Additionally, for the two SNe with z > 1, we present ground-based J-band photometry from Gemini and the Very Large Telescope. These are among the most distant SNe Ia for which ground-based near-IR observations have been obtained. We add these six SNe Ia together with other data sets that have recently become available in the literature to the Union compilation. We have made a number of refinements to the Union analysis chain, the most important ones being the refitting of all light curves with the SALT2 fitter and an improved handling of systematic errors. We call this new compilation, consisting of 557 SNe, the Union2 compilation. The flat concordance ΛCDM model remains an excellent fit to the Union2 data with the best-fit constant equation-of-state parameter w = –0.997+0.050 –0.054(stat)+0.077 –0.082(stat + sys together) for a flat universe, or w = –1.038+0.056 –0.059(stat)+0.093 –0.097(stat + sys together) with curvature. We also present improved constraints on w(z). While no significant change in w with redshift is detected, there is still considerable room for evolution in w. The strength of the constraints depends strongly on redshift. In particular, at z 1, the existence and nature of dark energy are only weakly constrained by the data.The Astrophysical Journal 05/2010; 716(1):712. · 6.02 Impact Factor -
Article: Spectra and Light Curves of Six Type Ia Supernovae at 0.511 < z < 1.12 and the Union2 Compilation
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ABSTRACT: We report on work to increase the number of well-measured Type Ia supernovae (SNe Ia) at high redshifts. Light curves, including high signal-to-noise HST data, and spectra of six SNe Ia that were discovered during 2001 are presented. Additionally, for the two SNe with z>1, we present ground-based J-band photometry from Gemini and the VLT. These are among the most distant SNe Ia for which ground based near-IR observations have been obtained. We add these six SNe Ia together with other data sets that have recently become available in the literature to the Union compilation (Kowalski et al. 2008). We have made a number of refinements to the Union analysis chain, the most important ones being the refitting of all light curves with the SALT2 fitter and an improved handling of systematic errors. We call this new compilation, consisting of 557 supernovae, the Union2 compilation. The flat concordance LambdaCDM model remains an excellent fit to the Union2 data with the best fit constant equation of state parameter w=-0.997^{+0.050}_{-0.054} (stat) ^{+0.077}_{-0.082} (stat+sys\ together) for a flat universe, or w=-1.035^{+0.055}_{-0.059} (stat)^{+0.093}_{-0.097} (stat+sys together) with curvature. We also present improved constraints on w(z). While no significant change in w with redshift is detected, there is still considerable room for evolution in w. The strength of the constraints depend strongly on redshift. In particular, at z > 1, the existence and nature of dark energy are only weakly constrained by the data.04/2010; -
Article: Prospective Type Ia Supernova Surveys From Dome A
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ABSTRACT: Dome A, the highest plateau in Antarctica, is being developed as a site for an astronomical observatory. The planned telescopes and instrumentation and the unique site characteristics are conducive toward Type Ia supernova surveys for cosmology. A self-contained search and survey over five years can yield a spectro-photometric time series of ~1000 z<0.08 supernovae. These can serve to anchor the Hubble diagram and quantify the relationship between luminosities and heterogeneities within the Type Ia supernova class, reducing systematics. Larger aperture (>4-m) telescopes are capable of discovering supernovae shortly after explosion out to z~3. These can be fed to space telescopes, and can isolate systematics and extend the redshift range over which we measure the expansion history of the universe. Comment: 10 pages, 10 figures, accepted for publication in Astroparticle Physics02/2010; -
Article: Targeting Supernovae in Very High Redshift Galaxy Clusters with HST: Preliminary Results
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ABSTRACT: We demonstrate a novel approach to obtaining Type Ia supernovae (SNe Ia) at very high redshifts (z> 1) in dust-free environments. In a 219 orbit program (Perlmutter, PI), we have used the Advanced Camera for Surveys (ACS) and NICMOS on the Hubble Space Telescope (HST) to repeatedly observe a sample of 25 massive galaxy clusters at z> 1 to find and follow SNe. Clusters of galaxies are known to be dominated by nearly dust-free early type galaxies. SNe discovered in these galaxies are expected to have negligible dust extinction, the largest source of both statistical and systematic uncertainty in SNe derived distances. In addition, galaxy clusters contain a population of early type galaxies at a density much larger than that in the high redshift field, leading to a significantly higher rate of detection of SNe Ia in this well-understood host environment. The rolling nature of the search means we automatically follow field SNe, leading to a higher overall rate of SN discoveries compared to "blank field" surveys. The discovery rate we find is consistent with these expectations. Using pre-scheduled time on the Subaru, Keck, and VLT telescopes we have obtained either spectroscopic confirmations or host galaxy redshifts for most newly discovered candidates. This data set will significantly improve supernova constraints of dark energy both in terms of statistical uncertainty, and perhaps more importantly, of systematic uncertainty. This work has been supported by the Office of Science, U.S. Department of Energy, through contract DE-AC02-05CH11231 and in part by NASA through grants associated with HST-GO-10496.11/2006; 38:1025. -
Article: Decelerating and Dustfree: Targeting SNe in Very High Redshift Galaxy Clusters
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ABSTRACT: We present a novel approach to obtaining Type Ia supernovae (SNe Ia) at very high redshifts (z>1). In a 219 orbit cycle 14 program, we are using the Advanced Camera for Surveys (ACS) and NICMOS on the Hubble Space Telescope (HST) to repeatedly observe massive galaxy clusters at z>1 to find and follow SNe. Clusters of galaxies are known to be dominated by nearly dust-free early type galaxies. SNe discovered in these glaxies are expected to have negligible dust extinction, the largest source of both statistical and systematic uncertainty in SNe derived distances. In addition, galaxy clusters contain a population of early type galaxies at a density approximately five times that in the high redshift field, leading to a much higher rate of detection of SNe Ia in this well-understood host environment. With 20 scheduled half-nights on the Subaru telecope as well as multiple nights on the Keck telescope, we are obtaining spectroscopic confirmation and redshift of newly discovered SNe and their hosts. This data will significantly improve supernova constraints of dark energy both in terms of statistical uncertainty, and perhaps more importantly, systematic uncertainty. This sample of more than 20 galaxy clusters is also being studied for weak lensing, galaxy morphology, and color-magnitude relationship, as part of an entire program of cluster studies. This work was supported in part by the Office of Science, US DoE, under contract DE-AC03-76F00098 and in part by NASA through grants associated with HST-GO-10496.11/2005; 37:1459. -
Article: Supernova / Acceleration Probe: A Satellite Experiment to Study the Nature of the Dark Energy
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ABSTRACT: The Supernova / Acceleration Probe (SNAP) is a proposed space-based experiment designed to study the dark energy and alternative explanations of the acceleration of the Universe's expansion by performing a series of complementary systematics-controlled measurements. We describe a self-consistent reference mission design for building a Type Ia supernova Hubble diagram and for performing a wide-area weak gravitational lensing study. A 2-m wide-field telescope feeds a focal plane consisting of a 0.7 square-degree imager tiled with equal areas of optical CCDs and near infrared sensors, and a high-efficiency low-resolution integral field spectrograph. The SNAP mission will obtain high-signal-to-noise calibrated light-curves and spectra for several thousand supernovae at redshifts between z=0.1 and 1.7. A wide-field survey covering one thousand square degrees resolves ~100 galaxies per square arcminute. If we assume we live in a cosmological-constant-dominated Universe, the matter density, dark energy density, and flatness of space can all be measured with SNAP supernova and weak-lensing measurements to a systematics-limited accuracy of 1%. For a flat universe, the density-to-pressure ratio of dark energy can be similarly measured to 5% for the present value w0 and ~0.1 for the time variation w'. The large survey area, depth, spatial resolution, time-sampling, and nine-band optical to NIR photometry will support additional independent and/or complementary dark-energy measurement approaches as well as a broad range of auxiliary science programs. (Abridged) Comment: 40 pages, 18 figures, submitted to PASP, http://snap.lbl.gov05/2004; -
Article: N2O emissions from humid tropical agricultural soils: effects of soil moisture, texture and nitrogen availability
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ABSTRACT: We studied soil moisture dynamics and nitrous oxide (N2O) fluxes from agricultural soils in the humid tropics of Costa Rica. Using a split-plot design on two soils (clay, loam) we compared two crop types (annual, perennial) each unfertilized and fertilized. Both soils are of andic origin. Their properties include relatively low bulk density and high organic matter content, water retention capacity, and hydraulic conductivity. The top 2–3 cm of the soils consists of distinct small aggregates (dia. <0.5 cm). We measured a strong gradient of bulk density and moisture within the top 7 cm of the clay soil. Using automated sampling and analysis systems we measured N2O emissions at 4.6 h intervals, meteorological variables, soil moisture, and temperature at 0.5 h intervals. Mean daily soil moisture content at 5 cm depth ranged from 46% water filled pore space (WFPS) on clay in April 1995 to near saturation on loam during a wet period in February 1996. On both soils the aggregated surface layer always remained unsaturated. Soils emitted N2O throughout the year. Mean N2O fluxes were 1.04±0.72 ng N2O-N cm−2 h−1 (mean±standard deviation) from unfertilized loam under annual crops compared to 3.54±4.31 ng N2O-N cm−2 h−1 from the fertilized plot (351 days measurement). Fertilization dominated the temporal variation of N2O emissions. Generally fluxes peaked shortly after fertilization and were increased for up to 6 weeks (‘post fertilization flux’). Emissions continued at a lower rate (‘background flux’) after fertilization effects faded. Mean post-fertilization fluxes were 6.3±6.5 ng N2O-N cm−2 h−1 while the background flux rate was 2.2±1.8 ng N2O-N cm−2 h−1. Soil moisture dynamics affected N2O emissions. Post fertilization fluxes were highest from wet soils; fluxes from relatively dry soils increased only after rain events. N2O emissions were weakly affected by soil moisture during phases of low N availability. Statistical modeling confirmed N availability and soil moisture as the major controls on N2O flux. Our data suggest that small-scale differences in soil structure and moisture content cause very different biogeochemical environments within the top 7 cm of soils, which is important for net N2O fluxes from soils.Soil Biology and Biochemistry. -
Article: Prospective Type Ia supernova surveys from Dome A
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ABSTRACT: Dome A, the highest plateau in Antarctica, is being developed as a site for an astronomical observatory. The planned telescopes and instrumentation and the unique site characteristics are conducive toward Type Ia supernova surveys for cosmology. A self-contained search and survey over 5 years can yield a spectro-photometric time series of ∼1000z<0.08 supernovae. These can serve to anchor the Hubble diagram and quantify the relationship between luminosities and heterogeneities within the Type Ia supernova class, reducing systematics. Larger aperture (≳4-m) telescopes are capable of discovering supernovae shortly after explosion out to z∼3. These can be fed to space telescopes, and can isolate systematics and extend the redshift range over which we measure the expansion history of the universe.Astroparticle Physics. -
Article: Weak lensing from space I: prospects for the supernova/acceleration probe
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Institutions
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2010
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University of California, Berkeley
- Space Sciences Laboratory
Berkeley, CA, USA
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2006
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ucsc
Concepción, Region del Biobio, Chile
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