E. Aubourg

The Supernova Legacy Survey: Measurement of Omega_M, Omega_Lambda and w from the First Year Data Set

We present distance measurements to 71 high redshift type Ia supernovae discovered during the first year of the 5-year Supernova Legacy Survey (SNLS). These events were detected and their multi-color light-curves measured using the MegaPrime/MegaCam instrument at the Canada-France-Hawaii Telescope (CFHT), by repeatedly imaging four one-square degree fields in four bands. Follow-up spectroscopy was performed at the VLT, Gemini and Keck telescopes to confirm the nature of the supernovae and to measure their redshift. With this data set, we have built a Hubble diagram extending to z = 1, with all distance measurements involving at least two bands. Systematic uncertainties are evaluated making use of the multiband photometry obtained at CFHT. Cosmological fits to this first year SNLS Hubble diagram give the following results: {Omega}{sub M} = 0.263 {+-} 0.042 (stat) {+-} 0.032 (sys) for a flat {Lambda}CDM model; and w = -1.023 {+-} 0.090 (stat) {+-} 0.054 (sys) for a flat cosmology with constant equation of state w when combined with the constraint from the recent Sloan Digital Sky Survey measurement of baryon acoustic oscillations.

SALT2: using distant supernovae to improve the use of Type Ia supernovae as distance indicators

We present an empirical model of Type Ia supernovae spectro-photometric evolution with time. The model is built using a large data set including light-curves and spectra of both nearby and distant supernovae, the latter being observed by the SNLS collaboration. We derive the average spectral sequence of Type Ia supernovae and their main variability components including a color variation law. The model allows us to measure distance moduli in the spectral range 2500-8000 A with calculable uncertainties, including those arising from variability of spectral features. Thanks to the use of high-redshift SNe to model the rest-frame UV spectral energy distribution, we are able to derive improved distance estimates for SNe Ia in the redshift range 0.8

Limits on the Macho Content of the Galactic Halo from the EROS-2 Survey of the Magellanic clouds

The EROS-2 project was designed to test the hypothesis that massive compact halo objects (the so-called machos) could be a major component of the dark matter halo of the Milky Way galaxy. To this end, EROS-2 monitored millions of stars in the Magellanic clouds for microlensing events caused by such objects. (abridged)

Gemini Spectroscopy of Supernovae from the Supernova Legacy Survey: Improving High-Redshift Supernova Selection and Classification

We present new techniques for improving the efficiency of supernova (SN) classification at high redshift using 64 candidates observed at Gemini North and South during the first year of the Supernova Legacy Survey (SNLS). The SNLS is an ongoing 5 year project with the goal of measuring the equation of state of dark energy by discovering and following over 700 high-redshift SNe Ia using data from the Canada-France-Hawaii Telescope Legacy Survey. We achieve an improvement in the SN Ia spectroscopic confirmation rate: at Gemini 71% of candidates are now confirmed as SNe Ia, compared to 54% using the methods of previous surveys. This is despite the comparatively high redshift of this sample, in which the median SN Ia redshift is z = 0.81 (0.155 ≤ z ≤ 1.01). These improvements were realized because we use the unprecedented color coverage and light curve sampling of the SNLS to predict whether a candidate is a SN Ia and to estimate its redshift, before obtaining a spectrum, using a new technique called the SN photo-z. In addition, we have improved techniques for galaxy subtraction and SN template χ2 fitting, allowing us to identify candidates even when they are only 15% as bright as the host galaxy. The largest impediment to SN identification is found to be host galaxy contamination of the spectrum—when the SN was at least as bright as the underlying host galaxy the target was identified more than 90% of the time. However, even SNe in bright host galaxies can be easily identified in good seeing conditions. When the image quality was better than 055, the candidate was identified 88% of the time. Over the 5 year course of the survey, using the selection techniques presented here, we will be able to add ~170 more confirmed SNe Ia than would be possible using previous methods.

EROS and MACHO Combined Limits on Planetary Mass Dark Matter in the Galactic Halo

The EROS and MACHO collaborations have each published upper limits on the amount of planetary-mass dark matter in the Galactic halo obtained from gravitational microlensing searches. In this Letter, the two limits are combined to give a much stronger constraint on the abundance of low-mass MACHOs. Specifically, objects with masses 10−7 Mm10−3 M make up less than 25% of the halo dark matter for most models considered, and less than 10% of a standard spherical halo is made of MACHOs in the 3.5×10−7 MThe EROS and MACHO collaborations have each published upper limits on the amount of planetary mass dark matter in the Galactic Halo obtained from gravitational microlensing searches. In this paper the two limits are combined to give a much stronger constraint on the abundance of low mass MACHOs.

Combined Analysis of the Binary Lens Caustic-crossing Event MACHO 98-SMC-1

We fit the data for the binary lens microlensing event MACHO 98-SMC-1 from five different microlensing collaborations and find two distinct solutions characterized by binary separation d and mass ratio q: (d,q) = (0.54,0.50) and (d,q) = (3.65,0.36), where d is in units of the Einstein radius. However, the relative proper motion of the lens is very similar in the two solutions, 1.30 km s-1 kpc-1 and 1.48 km s-1 kpc-1, thus confirming that the lens is in the Small Magellanic Cloud. The close binary can be either rotating or approximately static but the wide binary must be rotating at close to its maximum allowed rate to be consistent with all the data. We measure limb-darkening coefficients for five bands ranging from I to V. As expected, these progressively decrease with rising wavelength. This is the first measurement of limb darkening for a metal-poor A star.

Limits on Galactic dark matter with 5 years of EROS SMC data

Five years of EROS data towards the Small Magellanic Cloud have been searched for gravitational microlensing events, using a new, more accurate method to assess the impact of stellar blending on the efficiency. Four long-duration candidates have been found which, if they are microlensing events, hint at a non-halo population of lenses. Combined with results from other EROS observation programs, this analysis yields strong limits on the amount of Galactic dark matter made of compact objects. Less than 25% of a standard halo can be composed of objects with a mass between 2 10^-7 Msol and 1 Msol at the 95% C.L.

The core-collapse rate from the Supernova Legacy Survey

We use three years of data from the Supernova Legacy Survey (SNLS) to study the general properties of core-collapse and type Ia supernovae. This is the first such study using the rolling search technique which guarantees well-sampled SNLS light curves and good efficiency for supernovae brighter than i~24. Using host photometric redshifts, we measure the supernova absolute magnitude distribution down to luminosities 4.5 mag fainter than normal SNIa. Using spectroscopy and light-curve fitting to discriminate against SNIa, we find a sample of 117 core-collapse supernova candidates with redshifts z < 0.4 (median redshift of 0.29) and measure their rate to be larger than the type Ia supernova rate by a factor 4.5±0.8(stat.)±0.6 (sys.). This corresponds to a core-collapse rate at z = 0.3 of [ 1.42±0.3(stat.)±0.3(sys.)] ×10-4 yr-1(h_70-1 Mpc)-3.

The Type Ia Supernova Rate at z ≈ 0.5 from the Supernova Legacy Survey*

We present a measurement of the distant Type Ia 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 Ia in the redshift range 0.2 < z < 0.6. We derive a volumetric SN Ia rate of r_V((z) = 0:47) [0:42^(+0:13)-(-0:09)(syst:) ± 0:06(stat:)]x 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^(+0:048)_(-0:033)(syst:)^(+0:039)_(-0:031)(stat:) SN units. Using our rate alone, we place an upper limit on the component of SN Ia production that tracks the cosmic star nformation history of 1 SN Ia per 10^3 M_☉ of stars formed. Our rate and other rates from surveys using spectroscopic nsample confirmation display only a modest evolution out to z = 0:55.

Galactic Bulge microlensing optical depth from EROS-2

We present a new EROS-2 measurement of the microlensing optical depth toward the Galactic Bulge. Light curves of