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.

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

Cosmography can be considered as a sort of a model-independent approach to tackle the dark energy/modified gravity problem. In this review, the success and the shortcomings of the ΛCDM model, based...

Extended gravity cosmography

Cosmography can be considered as a sort of a model-independent approach to tackle the dark energy/modified gravity problem. In this review, the success and the shortcomings of the $\Lambda$CDM model, based on General Relativity and standard model of particles, are discussed in view of the most recent observational constraints. The motivations for considering extensions and modifications of General Relativity are taken into account, with particular attention to $f(R)$ and $f(T)$ theories of gravity where dynamics is represented by curvature or torsion field respectively. The features of $f(R)$ models are explored in metric and Palatini formalisms. We discuss the connection between $f(R)$ gravity and scalar-tensor theories highlighting the role of conformal transformations in the Einstein and Jordan frames. Cosmological dynamics of $f(R)$ models is investigated through the corresponding viability criteria. Afterwards, the equivalent formulation of General Relativity (Teleparallel Equivalent General Relativity) in terms of torsion and its extension to $f(T)$ gravity is considered. Finally, the cosmographic method is adopted to break the degeneracy among dark energy models. A novel approach, built upon rational Pade and Chebyshev polynomials, is proposed to overcome limits of standard cosmography based on Taylor expansion. The approach provides accurate model-independent approximations of the Hubble flow. Numerical analyses, based on Monte Carlo Markov Chain integration of cosmic data, are presented to bound coefficients of the cosmographic series. These techniques are thus applied to reconstruct $f(R)$ and $f(T)$ functions and to frame the late-time expansion history of the universe with no \emph{a priori} assumptions on its equation of state. A comparison between the $\Lambda$CDM cosmological model with $f(R)$ and $f(T)$ models is reported.

Extended Gravity Cosmography

The chemical abundance ratios and radial velocities for two stars in the recently discovered Triangulum II faint dwarf galaxy have been determined from high resolution, medium signal-to-noise ratio spectra from the Gemini-GRACES facility. These stars have stellar parameters and metallicities similar to those derived from their photometry and medium-resolution Ca II triplet spectra, and supports that Triangulum II has a metallicity spread consistent with chemical evolution in a dwarf galaxy. The elemental abundances show that both stars have typical calcium abundances and barium upper limits for their metallicities, but low magnesium and sodium. This chemical composition resembles some stars in dwarf galaxies, attributed to inhomogeneous mixing in a low star formation environment, and/or yields from only a few supernova events. One of our targets (Star40) has an enhancement in potassium, and resembles some stars in the unusual outer halo star cluster, NGC 2419. Our other target (Star46) appears to be a binary based on a change in its radial velocity (Delta v(rad) = 24.5 +/- 2.1 km/s). This is consistent with variations found in binary stars in other dwarf galaxies. While this serves as a reminder of the high binary fraction in these ultra faint dwarf galaxies, this particular object has had little impact on the previous determination of the velocity dispersion in Triangulum II.

Gemini/GRACES spectroscopy of stars in Tri II

In the present paper, we investigate the cosmographic problem using the bias–variance trade-off. We find that both the z-redshift and the $$y=z/(1+z)$$
 -redshift can present a small bias estimation. It means that the cosmography can describe the supernova data more accurately. Minimizing risk, it suggests that cosmography up to the second order is the best approximation. Forecasting the constraint from future measurements, we find that future supernova and redshift drift can significantly improve the constraint, thus having the potential to solve the cosmographic problem. We also exploit the values of cosmography on the deceleration parameter and equation of state of dark energy w(z). We find that supernova cosmography cannot give stable estimations on them. However, much useful information was obtained, such as that the cosmography favors a complicated dark energy with varying w(z), and the derivative $${\text {d}}w/{\text {d}}z <0$$
 for low redshift. The cosmography is helpful to model the dark energy.

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What do we know about cosmography

We present a cosmographic study designed to test the simplest type of accelerating cosmology: a flat universe with matter and a cosmological constant ($\Lambda$). Hubble series expansions are fit to the SCP Union2.1 supernova data set to estimate the Hubble Constant ($H_{0}$), the deceleration parameter ($q_{0}$), and the jerk parameter ($j_{0}$). Flat $\Lambda$CDM models always require $j_{0} = 1$, providing a single-parameter test of the entire paradigm. Because of convergence issues for $z \gtrsim 1$, we focus on expansions using the newer redshift variable $y$, and to estimate the effects of "model-building uncertainties" -- the dependence of the output results upon the fitting function and parameters used -- we perform fits using five different distance indicator functions, and four different polynomial orders. We find that one cannot yet use the supernova data to reliably obtain more than four cosmological parameters, and that cosmographic estimates of $j_{0}$ remain dominated by model-building uncertainties, in conjunction with statistical and other error sources. While $j_{0} = 1$ remains consistent with Union2.1, the most restrictive bound that we can place is $j_{0} \sim [-7.6,8.5]$. To test the future prospects of cosmography with new standard candle data, ensembles of mock supernova data sets are created, and it is found that the best way to reduce model-building uncertainties on lower-order Hubble parameters (such as $\{H_{0}, q_{0}, j_{0} \}$) is by limiting the redshift range of the data. Thus more and better $z \lesssim 1$ data, not higher-redshift data, is needed to sharpen cosmographic tests of flat $\Lambda$CDM.

Testing Lambda and the Limits of Cosmography with the Union2.1 Supernova Compilation

We present a cosmographic study designed to test the simplest type of accelerating cosmology: a flat universe with matter and a cosmological constant (Λ). Hubble series expansions are fit to the SCP Union2.1 supernova data set to estimate the Hubble Constant (H0), the deceleration parameter (q0), and the jerk parameter (j0). Flat ΛCDM models always require providing a single-parameter test of the entire paradigm. Because of convergence issues for we focus on expansions using the newer redshift variable y; and to estimate the effects of "model-building uncertainties"—the dependence of the output results upon the fitting function and parameters used—we perform fits using five different distance indicator functions, and four different polynomial orders. We find that one cannot yet use the supernova data to reliably obtain more than four cosmological parameters; and that cosmographic estimates of j0 remain dominated by model-building uncertainties, in conjunction with statistical and other error sources. While remains consistent with Union2.1, the most restrictive bound that we can place is To test the future prospects of cosmography with new standard candle data, ensembles of mock supernova data sets are created; and it is found that the best way to reduce model-building uncertainties on lower-order Hubble parameters (such as ) is by limiting the redshift range of the data. Thus more and better data, not higher-redshift data, are needed to sharpen cosmographic tests of flat ΛCDM.

https://iopscience.iop.org/article/10.1088/0004-637X/814/1/7/pdf

Testing lambda and the limits of cosmography with the union2.1 supernova compilation

product spokesperson: male vs. female) × 2 (gender affirmation: with vs. without) between-subjects design. 250 female Mturk workers participated in this study. In the gender affirmation condition, participants were asked to write about important qualities and values of women. In the control condition, participants were asked to list 20 everyday items that came to mind. Next, participants were told that they were browsing an online shopping platform and intended to buy underwear. They would see the underwear picture of a famous brand endorsed by a popular female star (vs. a popular male star) and then fill out the same product evaluation scale as above. We examined the interaction between gender of female-gender-imaged product spokesperson and gender affirmation. Specifically, when the female-gender-imaged product uses male endorsement, the product evaluation of the gender affirmation condition is lower than that of the control condition. Apart from the results from these were that both exclusivity and privacy of female-gender-imaged have significant interaction effects on the relationship between a

Menglu Dong

Papers

Testing Lambda and the Limits of Cosmography with the Union2.1 Supernova Compilation

Testing lambda and the limits of cosmography with the union2.1 supernova compilation

Does “male beauty” really work: The impact of male endorsements on female consumers' evaluation of female-gender-imaged product