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Open Access Publications from the University of California

Scholarly Works (7 results)

  • Article
  • Peer Reviewed
Lawrence Berkeley National Laboratory (2008)

We analyze the mean rest-frame ultraviolet (UV) spectrum of Type Ia Supernovae(SNe) and its dispersion using high signal-to-noise Keck-I/LRIS-B spectroscopyfor a sample of 36 events at intermediate redshift (z=0.5) discoveredby the Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS). Weintroduce a new method for removing host galaxy contamination in our spectra,exploiting the comprehensive photometric coverage of the SNLS SNe and theirhost galaxies, thereby providing the first quantitative view of the UV spectralproperties of a large sample of distant SNe Ia. Although the mean SN Ia spectrumhas not evolved significantly over the past 40 percent of cosmic history, preciseevolutionary constraints are limited by the absence of a comparable sample ofhigh quality local spectra. The mean UV spectrum of our z 0.5 SNe Ia and itsdispersion is tabulated for use in future applications. Within the high-redshiftsample, we discover significant UV spectral variations and exclude dust extinctionas the primary cause by examining trends with the optical SN color. Although progenitor metallicity may drive some of these trends, the variations we see aremuch larger than predicted in recent models and do not follow expected patterns.An interesting new result is a variation seen in the wavelength of selected UVfeatures with phase. We also demonstrate systematic differences in the SN Iaspectral features with SN lightcurve width in both the UV and the optical. Weshow that these intrinsic variations could represent a statistical limitation in thefuture use of high-redshift SNe Ia for precision cosmology. We conclude thatfurther detailed studies are needed, both locally and at moderate redshift wherethe rest-frame UV can be studied precisely, in order that future missions canconfidently be planned to fully exploit SNe Ia as cosmological probes.

    Cover page: Verifying the Cosmological Utility of Type Ia Supernovae: Implications of a Dispersion in the Ultraviolet Spectra
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2006)
    We present a method for selecting high-redshift Type la supernovae (SNe la) located via rolling SN searches. The technique, using both color and magnitude information of events from only two to three epochs of multiband real-time photometry, is able to discriminate between SNe la and core-collapse SNe. Furthermore, for SNe la the method accurately predicts the redshift, phase, and light-curve parameterization of these events based only on pre-maximum-light data. We demonstrate the effectiveness of the technique on a simulated survey of SNe la and core-collapse SNe, where the selection method effectively rejects most core-collapse SNe while retaining SNe la. We also apply the selection code to real-time data acquired as part of the Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS). During the period 2004 May to 2005 January in the SNLS, 440 SN candidates were discovered, of which 70 were confirmed spectroscopically as SNe la and 15 as core-collapse events. For this test data set, the selection technique correctly identifies 100% of the identified SNe II as non-SNe la with only a 1%-2% false rejection rate. The predicted parameterization of the SNe la has a precision of | Δz|/(1 + z spec) < 0.09 in redshift and ±2-3 rest-frame days in phase, providing invaluable information for planning spectroscopic follow-up observations. We also investigate any bias introduced by this selection method on the ability of surveys such as SNLS to measure cosmological parameters (e.g., w and Ω M) and find any effect to be negligible. © 2006. The American Astronomical Society. All rights reserved.
      Cover page: Photometric Selection of High-Redshift Type Ia Supernova Candidates
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2006)
      We show that Type Ia supernovae (SNe Ia) are formed within both very young and old stellar populations, with observed rates that depend on the stellar mass and mean star formation rates (SFRs) of their host galaxies. Models in which the SN Ia rate depends solely on host galaxy stellar mass are ruled out with >99% confidence. Our analysis is based on 100 spectroscopically confirmed SNe Ia, plus 24 photometrically classified events, all from the Supernova Legacy Survey (SNLS) and distributed over 0.2 < z < 0.75. We estimate stellar masses and SFRs for the SN Ia host galaxies by fitting their broadband spectral energy distributions with the galaxy spectral synthesis code PÉGASE.2. We show that the SN Ia rate per unit mass is proportional to the specific SFR of the parent galaxies - more vigorously star-forming galaxies host more SNe Ia per unit stellar mass, broadly equivalent to the trend of increasing SN Ia rate in later type galaxies seen in the local universe. Following earlier suggestions for a simple "two-component" model approximating the SN Ia rate, we find bivariate linear dependencies of the SN Ia rate on both the stellar masses and the mean SFRs of the host systems. We find that the SN Ia rate can be well represented as the sum of 5.3 ± 1.1 × 10-14 SNe yr -1M⊙-1 and 3.9 ± 0.7 × 10-4 SNe yr-1 (M⊙ yr-1) -1 of star formation. We also demonstrate a dependence of distant SN Ia light-curve shapes on star formation in the host galaxy, similar to trends observed locally. Passive galaxies, with no star formation, preferentially host faster declining/dimmer SNe Ia, while brighter events are found in systems with ongoing star formation. © 2006. The American Astronomical Society. All rights reserved.
        Cover page: Rates and Properties of Type Ia Supernovae as a Function of Mass and Star Formation in Their Host Galaxies
        • Article
        LBL Publications (2005)
          Cover page: The Supernova Legacy Survey: Measurement of Omega_M, Omega_Lambda, and w from the First Year Data Set
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2007)
          We present a progress report on a project to derive the evolution of the volumetric supernova Type Ia rate from the Supernova Legacy Survey. Our preliminary estimate of the rate evolution divides the sample from Neill et al. into two redshift bins: 0.2 < z < 0.4, and 0.4 < z < 0.6. We extend this by adding a bin from the sample analyzed in Sullivan et al. in the range 0.6 < z < 0.75 from the same time period. We compare the derived trend with previously published rates and a supernova Type Ia production model having two components: one component associated closely with star formation and an additional component associated with host galaxy mass. Our observed trend is consistent with this model, which predicts a rising SN Ia rate out to at least z = 2. © 2007 American Institute of Physics.
            Cover page: The Supernova Type Ia Rate Evolution with SNLS
            • Article
            • Peer Reviewed

            The Type Ia Supernova Rate at z ≈ 0.5 from the Supernova Legacy Survey**Based on observations obtained with MegaPrime/MegaCam, a joint project of the Canada-France-Hawaii Telescope (CFHT) and CEA/DAPNIA, at CFHT, which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This work is based in part on data products produced at the Canadian Astronomy Data Centre as part of the Canada-France-Hawaii Telescope Legacy Survey, a collaborative project of NRC and CNRS. This work is also based on observations obtained at the European Southern Observatory using the Very Large Telescope on the Cerro Paranal (ESO Large Program 171.A-0486), and on observations (programs GN-2004A-Q-19, GS-2004A-Q-11, GN-2003B-Q-9, and GS-2003B-Q-8) obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperati

            UC Berkeley Previously Published Works (2006)
            We present a measurement of the distant Type la supernova (SN Ia) rate derived from the first 2 yr of the Canada-France-Hawaii Telescope Supernova Legacy Survey. We observed four 1° × 1° fields with a typical temporal frequency of (Δt) ∼ 4 observer-frame days over time spans of 158-211 days per season for each field, with breaks during the full Moon. We used 8-10 m class telescopes for spectroscopic follow-up to confirm our candidates and determine their redshifts. Our starting sample consists of 73 spectroscopically verified SNe la in the redshift range 0.2 < z < 0.6. We derive a volumetric SN Ia rate of r V(〈z〉 = 0.47) = [0.42 0.090.13(syst.) ± 0.06(stat.)] × 10 -4 yr -1 Mpc 3, assuming h = 0.7, Ω m -0.3, and a flat cosmology. Using recently published galaxy luminosity functions derived in our redshift range, we derive a SN Ia rate per unit luminosity of r L(〈z〉 = 0.47) = 0.154 -0.0330.048(syst.) 0.0310.039(stat.) SN units. Using our rate alone, we place an upper limit on the component of SN la production that tracks the cosmic star formation history of 1 SN la per 10 3 M ⊙ of stars formed. Our rate and other rates from surveys using spectroscopic sample confirmation display only a modest evolution out to z = 0.55. © 2006. The American Astronomical Society. All rights reserved.
              Cover page: The Type Ia Supernova Rate at z ≈ 0.5 from the Supernova Legacy Survey**Based on observations obtained with MegaPrime/MegaCam, a joint project of the Canada-France-Hawaii Telescope (CFHT) and CEA/DAPNIA, at CFHT, which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This work is based in part on data products produced at the Canadian Astronomy Data Centre as part of the Canada-France-Hawaii Telescope Legacy Survey, a collaborative project of NRC and CNRS. This work is also based on observations obtained at the European Southern Observatory using the Very Large Telescope on the Cerro Paranal (ESO Large Program 171.A-0486), and on observations (programs GN-2004A-Q-19, GS-2004A-Q-11, GN-2003B-Q-9, and GS-2003B-Q-8) obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperati
              • Article
              • Peer Reviewed
              UC Berkeley Previously Published Works (2009)
              In the next decade Type Ia supernovae (SNe Ia) will be used to test theories predicting changes in the Dark Energy equation of state with time. Ultimately this requires a dedicated space mission like JDEM. SNe Ia are mature cosmological probes --- their limitations are well characterized, and a path to improvement is clear. Dominant systematic errors include photometric calibration, selection effects, reddening, and population-dependent differences. Building on past lessons, well-controlled new surveys are poised to make strides in these areas: the Palomar Transient Factory, Skymapper, La Silla QUEST, Pan-STARRS, the Dark Energy Survey, LSST, and JDEM. They will obviate historical calibrations and selection biases, and allow comparisons via large subsamples. Some systematics follow from our ignorance of SN Ia progenitors, which there is hope of determining with SN Ia rate studies from 0
                Cover page: Type Ia supernova science 2010-2020
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