21 research outputs found
Type Ia supernova rate studies from the SDSS-II Supernova Study
No full textThe author presents new measurements of the type Ia SN rate from the SDSS-II Supernova Survey. The SDSS-II Supernova Survey was carried out during the Fall months (Sept.-Nov.) of 2005-2007 and discovered {approx} 500 spectroscopically confirmed SNe Ia with densely sampled (once every {approx} 4 days), multi-color light curves. Additionally, the SDSS-II Supernova Survey has discovered several hundred SNe Ia candidates with well-measured light curves, but without spectroscopic confirmation of type. This total, achieved in 9 months of observing, represents {approx} 15-20% of the total SNe Ia discovered worldwide since 1885. The author describes some technical details of the SN Survey observations and SN search algorithms that contributed to the extremely high-yield of discovered SNe and that are important as context for the SDSS-II Supernova Survey SN Ia rate measurements
Interactions between Dark Matter Substructure and Galaxies
No full textIn this thesis we study how subhaloes evolve and interact in the central regions of galactic dark matter haloes in a ΛCDM universe. We examine the effect that subhalo impacts have on disc galaxies and what visible signatures they leave behind. We use the Aquarius simulations, a set of high resolution simulations of Milky Way mass haloes, as the basis of the work in this thesis. We summarise the main properties of these haloes and show that they are typical haloes for most characteristics.
We develop a method to approximate the potential of host haloes that helps us understand how subhaloes evolve in the tidal field of their host. Using a basis function expansion method, we show that it is possible to create a time-evolving density/potential approximation of the late growth of simulated N-body dark matter haloes, and that particle and subhalo orbits can be integrated in this realistic, time-varying halo potential approximation at much lower computational cost than the original simulations.
Using samples of subhaloes extracted from the Aquarius haloes, we estimate the disc heating caused by substructure bombardment using the Benson et al. (2004) semi-analytical model. A critical evaluation of the model, however, finds that there are problems with the original implementation, including a numerical factor, that call into question its validity. We then approach the same problem using high resolution N-body simulations of subhalo interactions with discs. We find that only the most massive of subhaloes appreciably affect stellar discs, heating and thickening them, and that the majority of any heating occurs at early times and happens quickly. However, the substructure bombardment since redshift one is negligible in most of the haloes, and in the haloes that do show significant heating it is caused by a single massive subhalo
A Measurement of the Rate of Type Ia Supernovae at Redshift z ≈ 0.1 from the First Season of the SDSS-II Supernova Survey
No full textWe present a measurement of the rate of type Ia supernovae (SNe Ia) from the first of three seasons of data from the SDSS-II Supernova Survey. For this measurement, we include 17 SNe Ia at redshift z ≤ 0.12. Assuming a flat cosmology with m = 0.3 = 1 − , we find a volumetric SN Ia rate of [2.93+0.17 −0.04(systematic)+0.90 −0.71(statistical)]×10−5 SNe Mpc−3 h3 70 year−1, at a volumeweighted mean redshift of 0.09. This result is consistent with previous measurements of the SN Ia rate in a similar redshift range. The systematic errors are well controlled, resulting in the most precise measurement of the SN Ia rate in this redshift range. We use a maximum likelihood method to fit SN rate models to the SDSS-II Supernova Survey data in combination with other rate measurements, thereby constraining models for the redshift-evolution of the SN Ia rate. Fitting the combined data to a simple power-law evolution of the volumetric SN Ia rate, rV ∝ (1 + z) , we obtain a value of β = 1.5 ± 0.6, i.e. the SN Ia rate is determined to be an increasing function of redshift at the ∼ 2.5σ level. Fitting the results to a model in which the volumetric SN rate, rV = Aρ(t) + Bρ˙(t), where ρ(t) is the stellar mass density and ρ˙(t) is the star formation rate, we find A = (2.8 ± 1.2) × 10−14 SNe M−1 ⊙ year−1, B = (9.3+3.4 −3.1) × 10−4 SNe M−1 ⊙
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A Measurement of the Rate of Type Ia Supernovae in Galaxy Clusters from the SDSS-II Supernova Survey
No full textWe present measurements of the Type Ia supernova (SN) rate in galaxy clusters based on data from the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey. The cluster SN Ia rate is determined from 9 SN events in a set of 71 C4 clusters at z {le} 0.17 and 27 SN events in 492 maxBCG clusters at 0.1 {le} z {le} 0.3. We find values for the cluster SN Ia rate of (0.37{sub -0.12-0.01}{sup +0.17+0.01}) SNur h{sup 2} and (0.55{sub -0.11-0.01}{sup +0.13+0.02}) SNur h{sup 2} (SNux = 10{sup -12}L{sub x{circle_dot}}{sup -1} yr{sup -1}) in C4 and maxBCG clusters, respectively, where the quoted errors are statistical and systematic, respectively. The SN rate for early-type galaxies is found to be (0.31{sub -0.12-0.01}{sup +0.18+0.01}) SNur h{sup 2} and (0.49{sub -0.11-0.01}{sup +0.15+0.02}) SNur h{sup 2} in C4 and maxBCG clusters, respectively. The SN rate for the brightest cluster galaxies (BCG) is found to be (2.04{sub -1.11-0.04}{sup +1.99+0.07}) SNur h{sup 2} and (0.36{sub -0.30-0.01}{sup +0.84+0.01}) SNur h{sup 2} in C4 and maxBCG clusters, respectively. The ratio of the SN Ia rate in cluster early-type galaxies to that of the SN Ia rate in field early-type galaxies is 1.94{sub -0.91-0.015}{sup +1.31+0.043} and 3.02{sub -1.03-0.048}{sup +1.31+0.062}, for C4 and maxBCG clusters, respectively. The SN rate in galaxy clusters as a function of redshift, which probes the late time SN Ia delay distribution, shows only weak dependence on redshift. Combining our current measurements with previous measurements, we fit the cluster SN Ia rate data to a linear function of redshift, and find r{sub L} = [(0.49{sub -0.14}{sup +0.15}) + (0.91{sub -0.81}{sup +0.85}) x z] SNuB h{sup 2}. A comparison of the radial distribution of SNe in cluster to field early-type galaxies shows possible evidence for an enhancement of the SN rate in the cores of cluster early-type galaxies. With an observation of at most 3 hostless, intra-cluster SNe Ia, we estimate the fraction of cluster SNe that are hostless to be (9.4{sub -5.1}{sup +8.3})%
The SDSS-II Supernova Survey: Parameterizing the TYPE Ia Supernova Rate as a Function of Host Galaxy Properties
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Single Or Double Degenerate Progenitors? Searching For Shock Emission In The SDSS-II Type Ia Supernovae
No full textFrom the set of nearly 500 spectroscopically confirmed Type Ia supernovae (SNe) and around 10,000 unconfirmed candidates from SDSS-II, we select a subset of 108 confirmed SNe Ia with well-observed early-time light curves to search for signatures from shock interaction of the SN with a companion star. No evidence for shock emission is seen; however, the cadence and photometric noise could hide a weak shock signal. We simulate shocked light curves using SN Ia templates and a simple Gaussian shock model to emulate the noise properties of the SDSS-II sample and estimate the detectability of the shock interaction signal as a function of shock amplitude, shock width, and shock fraction. We find no direct evidence for shock interaction in the rest-frame B-band, but place an upper limit on the shock amplitude at 9% of SN peak flux (M-B > -16.6 mag). If the single degenerate channel dominates type Ia progenitors, this result constrains the companion stars to be less than about 6 M-circle dot on the main sequence and strongly disfavors red giant companions.Alfred P. Sloan FoundationNational Science Foundation 0847157U.S. Department of EnergyNational Aeronautics and Space AdministrationJapanese MonbukagakushoMax Planck SocietyHigher Education Funding Council for EnglandAmerican Museum of Natural HistoryAstrophysical Institute PotsdamUniversity of BaselUniversity of CambridgeCase Western Reserve UniversityUniversity of ChicagoDrexel UniversityFermilabInstitute for Advanced StudyJapan Participation GroupJohns Hopkins UniversityJoint Institute for Nuclear AstrophysicsKavli Institute for Particle Astrophysics and CosmologyKorean Scientist GroupChinese Academy of Sciences (LAMOST)Los Alamos National LaboratoryMax-Planck-Institute for Astronomy (MPIA)Max-Planck-Institute for Astrophysics (MPA)New Mexico State UniversityOhio State UniversityUniversity of PittsburghUniversity of PortsmouthPrinceton UniversityUnited States Naval ObservatoryUniversity of WashingtonESO New Technology Telescope at La Silla Observatory 77.A-0437, 78.A-0325
79.A-0715W. M. Keck FoundationDOE DE-FG02-08ER41562Astronom
Farmer willingness to pay for seed-related information: rice varieties in Nigeria and Benin
No full text"A typical private good is defined by its excludability and rivalry characteristics. Information embodied in a technology might not generate rivalry among its users. By contrast, excludability is certainly a characteristic of this kind of information and its delivery can generate incentives for private participation. This study examines farmers' preferences for seed of new rice varieties and their willingness to pay for seed-related information in villages of Nigeria and Benin. Conjoint analysis is used to estimate the structure of farmers' preferences for rice seed given a set of alternatives. Farmers are considered to be consumers of seed as a production input, preferring one variety over another based on the utility they obtain from its attributes, which depends on their own social and economic characteristics, including whether or not they sell rice. Contingent methods are used to elicit preferences and willingness to pay (WTP) for rice seed. The marginal values of attributes, with and without information about the seed, are estimated with an ordered probit regression. WTP for information is derived from the analysis of WTP for rice seed. The results have implications for the best way to finance research and extension services in the areas of intervention, particularly for new rice varieties. " Authors' AbstractWillingnes to pay (WTP), seed-related information, conjoint analysis, rice attributes, farmers' preferences, technology,
