Supernova Search Team Research Articles

New Hubble parameter data and possibility of more than one deceleration–acceleration transition redshift

It is quite believed that Universe has undergone a smooth transition from a decelerated phase to its present accelerated phase of expansion. There exists a wide consensus, based on robust observational indicating transition redshift z_{tr} around the unity. However our analysis on complete collection of reliable Hubble parameter H(z) data at intermediate redshift 0.07<z <2.36 , BAO, Pantheon data, give some hints that the universe may be transit more than one time from deceleration to acceleration phase in course of its evolution. Although we are agree with the results claimed by previous studies state the simplest cosmological models such as Lambda CDM and XCDM are consistent with Hubble data, but we doubt that they will be the best. We show that the chameleon cosmological model is more favored than the simple models and very well fits with the full Hubble data. Reconstructing the deceleration parameter based on best fitted parameters of the model indicates a new dynamic for the universe in which more than one transition occurs from deceleration to acceleration phase and the last transition occurs at z_{tr}simeq .43pm 0.04 which is close to that derived by the High-z Supernovae Search (HZSNS) team, z_{tr}=.43pm 0.07 (Riess et al. Astrophys. J. 659, 98–121, 2007).

Cosmological Distance Scale. Part 11. “Extraordinary” Evidence and the “Cosmic Jerk” Problem

A statistical test of the “extraordinary” evidence for the “accelerated expansion of the Universe” owing to the “cosmic jerk” over a range of red shifts z = 0.46 ± 0.13 and for z = 0.763 based on data from SN Ia supernovae for which photometric distances have been determined is carried out. The transition from “deceleration” to “acceleration” is treated as a “disruption”– a change in the structure and parameters of the model for the cosmological distance scale. It is shown that the data from different sources do not form a compositionally uniform set. “Discrepancies” in the model for the scale are discovered for z = 0.44–0.48 in a sample of 10 SN Ia over an interval from z = 0.30–0.97 according to data from the High-Z Supernovae Search Team and for red shifts z = 0.763–0.828 in a sample of 42 SN Ia over an interval from z = 0.172–0.83 according to data from the Supernovae Cosmology Project. The reason for these “discrepancies” may be an unbalanced and random distribution of the SN Ia over the observed range of red shifts for a scale with a clearly distinct non-metric character.

The Evidence for the accelerating universe: endorsement and robust consistency

The 2011 Nobel Prize in Physics was awarded to researchers from the Supernova Cosmology Project and the High-z Supernova Search Team for the discovery of the accelerating expansion of the universe. In this paper, I provide a historical analysis of the supernova cosmology evidence put forward by these teams for the accelerating universe, in terms of an iterative model of scientific progress developed by Hasok Chang in the context of his study of the development of measurement standards. I argue, using the key concept of epistemic iteration, that the iterative model adequately accounts for evidence production in experimental science as well. In order to apply Chang’s model to the experimental evidence for the accelerating universe, I introduce the concept of endorsement as a particular mode of progress, and argue that supernova scientists produced an endorsed measurement system to claim evidence for their discovery. Furthermore, I show that the credibility of the evidence was not based on a particular measurement, rather, what proved to be decisive was the “robust consistency” of many individual results.

Cosmological distances scale: Pt. 11. Extraordinary evidences and cosmically jerk problem

Statistical verification of the “extraordinary” evidence of “acceleration of the expansion of the Universe” due to the “cosmic push” at the redshift interval and at based on data on supernovae of type SN Ia, for which photometric distances were determined, was carried out. The transition from “deceleration” to “acceleration” is considered as a “breakdown” – a change in the structure and parameters of the model of the cosmological distance scale. It is shown that data from different sources do not form a compositionally homogeneous set. The scale model's “misalignment” (discord) was revealed for from a sample of 10 SN Ia obtained in the interval by the High-Z Supernovae Search Team, and for from a sample of 42 SN Ia obtained in the interval by the Supernovae Cosmology Project group. The reason for these “discrepancies” may be an unbalanced and random distribution of SN Ia over the observed range of redshifts with a clearly expressed non-metric character of the scale.

Anisotropic Bianchi-V dark energy model under the new perspective of accelerated expansion of the universe in Brans–Dicke theory of gravitation

In this paper, we have proposed a cosmological model, which is consistent with the new findings of ‘The Supernova Cosmology project’ headed by Saul Perlmutter, and the ‘High-Z Supernova Search team’, headed by Brian Schimdt. According to these new findings, the universe is undergoing an expansion with an increasing rate, in contrast to the earlier belief that the rate of expansion is constant or the expansion is slowing down. We have considered spatially homogeneous and anisotropic Bianchi-V dark energy model in Brans–Dicke theory of gravitation. We have taken the scale factor $$a(t)=k t^\alpha e^{\beta t}$$ , which results into variable deceleration parameter (DP). The graph of DP shows a transition from positive to negative, which shows that universe has passed through the past decelerated expansion to the current accelerated expansion phase. In this context, we have also calculated and plotted various parameters and observed that these are in good agreement with physical and kinematic properties of the universe and are also consistent with recent observations.

The Accelerated universe. On the Nobel Prize in Physics 2011 awarded to Saul Perlmutter, Brian P. Schmidt, and Adam G. Riess

Since the end of the 1920s we have known that distant galaxies are receding from us. The observations that led to this conclusion were mainly those of Edwin Hubble. The history of the universe has been one of continuous expansion and cooling, marked by several critical events. In a matter-dominated universe, it is quite intuitive that the expansion will eventually slow down; in other words, the universe should decelerate. And yet two teams, the Supernova Cosmology Project and the High-z Supernova Search Team, used a subset of supernova-type Ia (SNIa)-and reached the same surprising result: the universe is accelerating. But what, then, is producing theobserved cosmological acceleration? This article discusses the 2011 Nobel Prize for Physics, awarded to Saul Perlmutter, Brian P. Schmidt, and Adam G. Riess for the discovery of the accelerating expansion of the universe through observations of distant supernovae, and reviews the cosmological context of the discovery and the use of supernovae as standard candles. Some of the consequences of the discovery are presented as well.

Transition redshift: new kinematic constraints from supernovae

The transition redshift (deceleration/acceleration) is discussed by expanding the deceleration parameter to first order around its present value. A detailed study is carried out by considering two different parametrizations, q=q0+q1z and q=q0+q1z(1 +z)−1, and the associated free parameters (q0, q1) are constrained by three different supernovae (SNe) samples. A previous analysis by Riess et al. using the first expansion is slightly improved and confirmed in light of their recent data (Gold07 sample). However, by fitting the model with the Supernova Legacy Survey (SNLS) type Ia sample, we find that the best fit to the redshift transition is zt= 0.61, instead of zt= 0.46 as derived by the High-z Supernovae Search (HZSNS) team. This result based in the SNLS sample is also in good agreement with the sample of Davis et al., zt= 0.60+0.28−0.11 (1σ). Such results are in line with some independent analyses and accommodate more easily the concordance flat model (ΛCDM). For both parametrizations, the three SNe Ia samples considered favour recent acceleration and past deceleration with a high degree of statistical confidence level. All the kinematic results presented here depend neither on the validity of general relativity nor on the matter–energy contents of the Universe.

The accelerating Universe and a limiting curvature proposal

We consider the hypothesis of a limiting minimal curvature in gravity as a way to constructa class of theories exhibiting late-time cosmic acceleration. Guided by the minimalcurvature conjecture we are naturally led to a set of scalar–tensor theories in which thescalar is non-minimally coupled both to gravity and to the matter Lagrangian. The modelis compared to the Lambda cold dark matter concordance model and to observational datausing the ‘gold’ SNeIa sample of Riess et al ((Supernova Search Team Collaboration),2004 Astrophys. J. 607 665 [astro-ph/0402512]). An excellent fit to the data isachieved. We present a toy model designed to demonstrate that such a new, possiblyfundamental, principle may be responsible for the recent period of cosmologicalacceleration. Observational constraints remain to be imposed on these models.

Redshift-distance relations from type Ia supernova observations

Extinction due to intergalactic grey dust has been proposed as an alternative to accelerated expansion to account for the dimming of \s fluxes beyond $z \simeq 0.5$. The ``replenishing'' grey dust model, although fitting the observational data, does not seem to be based on physical assumptions. For this reason, in this paper we propose a new grey dust model whose dust distribution follows the comoving SFR density evolution, a reasonably established phenomenon. This new model is compared with the updated photometric data sample from the High Z Supernova Search Team (HZT). Also, using pairs of supernovae at different redshifts, the possibility of any ``patchy'' distribution proposed to explain the discrepancies between the ``high $z$'' dust model and the \s observations at very high redshift ($z \ge 0.9$) is ruled out. Finally, the data are compared with different models with and without dark energy and a best fit to a universe with adimensional parameters $\Omega_{\mathrm{m0}} = 0.31$ and $\Omega_{\mathrm{\Lambda 0}} = 0.69$ is obtained, from which an age of the universe of $t_{0} \simeq 14.6 \times 10^{9}$ years is derived. This age is compatible with the age of the globular clusters using an equation of state $\omega = -1$ and it obviates the need to resort to any kind of phantom energy.

Einstein’s Mistakes

Science sets itself apart from other paths to truth by recognizing that even its greate practitioners sometimes err.

Direct reconstruction of the quintessence potential

We describe an algorithm which directly determines the quintessence potential from observational data, without using an equation of state parametrization. The strategy is to numerically determine observational quantities as a function of the expansion coefficients of the quintessence potential, which are then constrained using a likelihood approach. We further impose a model selection criterion, the Bayesian Information Criterion, to determine the appropriate level of the potential expansion. In addition to the potential parameters, the present day quintessence field velocity is kept as a free parameter. Our investigation contains unusual model types, including a scalar field moving on a flat potential, or in an uphill direction, and is general enough to permit oscillating quintessence field models. We apply our method to the ``gold`` Type Ia supernovae sample of Riess et al. [A. G. Riess et al. (Supernova Search Team Collaboration), Astrophys. J. 607, 665 (2004)] confirming the pure cosmological constant model as the best description of current supernovae luminosity-redshift data. Our method is optimal for extracting quintessence parameters from future data.

CONSTRAINTS ON A NEW ALTERNATIVE MODEL TO DARK ENERGY

The recent type Ia supernova data suggest that the Universe is accelerating now and had decelerated in recent past. This may provide the evidence that the standard Friedmann equation needs to be modified. We analyze in detail a new model in the context of modified Friedmann equation using the supernova data published by the High-z Supernova Search Team and the Supernova Cosmology Project. The new model explains recent acceleration and past deceleration. Furthermore, the acceleration of the expansion of the Universe is almost zero in the future.

Weak lensing of the high-redshift SNIa sample

The current sample of high-redshift Type Ia supernovae (SNeIa), which combines results from two teams, the High-z Supernova Search Team and the Supernova Cosmology Project, is analysed for the effects of weak lensing. After correcting supernovae (SN) magnitudes for cosmological distances, assuming recently published, homogeneous distance and error estimates, we find that brighter SNe are preferentially found behind regions (5–15 arcmin radius) that are overdense in foreground, z∼ 0.1 galaxies. This is consistent with the interpretation that SN fluxes are magnified by foreground galaxy excess and demagnified by foreground galaxy deficit, compared with a smooth universe case. The difference between most magnified and most demagnified SNe is approximately 0.3–0.4 mag. The effect is significant at the >99 per cent level. Simple modelling reveals that the slope of the relation between supernova magnitude and foreground galaxy density depends on the amount and distribution of matter along the line of sight to the sources, but does not depend on the specifics of the galaxy biasing scheme.

Imaging and Demography of the Host Galaxies of High-Redshift Type Ia Supernovae

We present the results of a study of the host galaxies of high-redshift Type Ia supernovae (SNe Ia). We provide a catalog of 18 hosts of SNe Ia observed with the Hubble Space Telescope (HST) by the High-z Supernova Search Team, including images, scale lengths, measurements of integrated (Hubble-equivalent) BVRIZ photometry in bands where the galaxies are brighter than m ≈ 25 mag, and galactocentric distances of the supernovae. We compare the residuals of SN Ia distance measurements from cosmological fits with measurable properties of the supernova host galaxies that might be expected to correlate with variable properties of the progenitor population, such as host-galaxy color and position of the supernova. We find mostly null results; the current data are generally consistent with no correlations of the distance residuals with host-galaxy properties in the redshift range 0.42 < z < 1.06. Although a subsample of SN hosts shows a formally significant (3 σ) correlation between apparent V-R host color and distance residuals, the correlation is not consistent with the null results from other host colors probed by our largest samples. There is also evidence for the same correlations between SN Ia properties and host type at low redshift and high redshift. These similarities support the current practice of extrapolating properties of the nearby population to high redshifts, pending more robust detections of any correlations between distance residuals from cosmological fits and host properties.

Cosmological Results from High‐zSupernovae

The High-z Supernova Search Team has discovered and observed 8 new supernovae in the redshift interval z=0.3-1.2. These independent observations, confirm the result of Riess et al. (1998a) and Perlmutter et al. (1999) that supernova luminosity distances imply an accelerating universe. More importantly, they extend the redshift range of consistently observed SN Ia to z~1, where the signature of cosmological effects has the opposite sign of some plausible systematic effects. Consequently, these measurements not only provide another quantitative confirmation of the importance of dark energy, but also constitute a powerful qualitative test for the cosmological origin of cosmic acceleration. We find a rate for SN Ia of 1.4+/-0.5E-04 h^3/Mpc^3/yr at a mean redshift of 0.5. We present distances and host extinctions for 230 SN Ia. These place the following constraints on cosmological quantities: if the equation of state parameter of the dark energy is w=-1, then H0 t0 = 0.96+/-0.04, and O_l - 1.4 O_m = 0.35+/-0.14. Including the constraint of a flat Universe, we find O_m = 0.28+/-0.05, independent of any large-scale structure measurements. Adopting a prior based on the 2dF redshift survey constraint on O_m and assuming a flat universe, we find that the equation of state parameter of the dark energy lies in the range -1.48<w<-0.72 at 95% confidence. If we further assume that w>-1, we obtain w<-0.73 at 95% confidence. These constraints are similar in precision and in value to recent results reported using the WMAP satellite, also in combination with the 2dF redshift survey.

On the Reality of the Accelerating Universe

Two groups recently deduced the positive value for the cosmological constant, concluding at a high (≥99%) confidence level that the universe should be accelerating. This conclusion followed from the statistical analysis of dozens of high-redshift supernovae. In this paper this conclusion is discussed. From the conservative frequentist's point of view, the validity of the null hypothesis of the zero cosmological constant is tested by the classical statistical χ2 test for the 60 supernovae listed in Perlmutter et al. This sample contains 42 objects discovered in the frame of the Supernova Cosmology Project and 18 low-redshift objects detected earlier. Excluding the event SN 1997O, which is doubtlessly an outlier, one obtains the following result: the probability for seeing a worse χ2—if the null hypothesis is true—is in the 5%-8% range, a value that does not indicate significant evidence against the null. Furthermore, if one excludes five possible outliers, as proposed by Perlmutter et al., then the sample of 54 supernovae is in excellent accordance with the null hypothesis. It also seems that supernovae from the High-z Supernova Search Team do not change the acceptance of the null hypothesis. This means that the rejection of the Einstein equations with zero cosmological constant—based on the supernova data alone—is still premature.

Optical Spectra of Type I[CLC]a[/CLC] Supernovae at [CLC][ITAL]z[/ITAL][/CLC] = 0.46 and [CLC][ITAL]z[/ITAL][/CLC] = 1.2

We present optical spectra, obtained with the Keck 10-m telescope, of two high-redshift type Ia supernovae (SNe Ia) discovered by the High-z Supernova Search Team: SN 1999ff at z=0.455 and SN 1999fv at z~1.2, the highest-redshift published SN Ia spectrum. Both SNe were at maximum light when the spectra were taken. We compare our high-z spectra with low-z normal and peculiar SNe Ia as well as with SNe Ic, Ib, and II. There are no significant differences between SN 1999ff and normal SNe Ia at low redshift. SN 1999fv appears to be a SN Ia and does not resemble the most peculiar nearby SNe Ia.

Results from the High- z Supernova Search Team

We review the use of Type Ia supernovae for cosmological distance determinations. Low-redshift SNe Ia ( z≲0.1) demonstrate that (a) the Hubble expansion is linear, (b) H 0=65±2 (statistical) km s −1 Mpc −1 , (c) the bulk motion of the Local Group is consistent with the COBE result, and (d) the properties of dust in other galaxies are similar to those in the Milky Way. We find that the light curves of high-redshift SNe Ia are stretched in a manner consistent with the expansion of space; similarly, their spectra exhibit slower temporal evolution (by a factor of 1+ z) than those of nearby SNe Ia. The luminosity distances of our 16 high-redshift SNe Ia are, on average, 10–15% farther than expected in a low mass-density ( Ω M=0.2 ) universe without a cosmological constant. Our analysis strongly supports eternally expanding models with positive cosmological constant and a current acceleration of the expansion. We address many potential sources of systematic error; at present, none of them reconciles the data with Ω Λ=0 and q 0≥0. The dynamical age of the Universe is estimated to be 14.2±1.7 Gyr, consistent with the ages of globular star clusters.

Supernova Limits on the Cosmic Equation of State

We use Type Ia supernovae studied by the High-z Supernova Search Team to constrain the properties of an energy component that may have contributed to accelerating the cosmic expansion. We find that for a flat geometry the equation-of-state parameter for the unknown component, αx = Px/ρx, must be less than -0.55 (95% confidence) for any value of Ωm, and it is further limited to αx < -0.60 (95% confidence) if Ωm is assumed to be greater than 0.1. These values are inconsistent with the unknown component being topological defects such as domain walls, strings, or textures. The supernova (SN) data are consistent with a cosmological constant (αx = -1) or a scalar field that has had, on average, an equation-of-state parameter similar to the cosmological constant value of -1 over the redshift range of z ≈ 1 to the present. SN and cosmic microwave background observations give complementary constraints on the densities of matter and the unknown component. If only matter and vacuum energy are considered, then the current combined data sets provide direct evidence for a spatially flat universe with Ωtot = Ωm + ΩΛ = 0.94 ± 0.26 (1 σ).

Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant

We present spectral and photometric observations of 10 Type Ia supernovae (SNe Ia) in the redshift range 0.16 ≤ z ≤ 0.62. The luminosity distances of these objects are determined by methods that employ relations between SN Ia luminosity and light curve shape. Combined with previous data from our High-z Supernova Search Team and recent results by Riess et al., this expanded set of 16 high-redshift supernovae and a set of 34 nearby supernovae are used to place constraints on the following cosmological parameters: the Hubble constant (H0), the mass density (ΩM), the cosmological constant (i.e., the vacuum energy density, ΩΛ), the deceleration parameter (q0), and the dynamical age of the universe (t0). The distances of the high-redshift SNe Ia are, on average, 10%–15% farther than expected in a low mass density (ΩM = 0.2) universe without a cosmological constant. Different light curve fitting methods, SN Ia subsamples, and prior constraints unanimously favor eternally expanding models with positive cosmological constant (i.e., ΩΛ > 0) and a current acceleration of the expansion (i.e., q0 < 0). With no prior constraint on mass density other than ΩM ≥ 0, the spectroscopically confirmed SNe Ia are statistically consistent with q0 < 0 at the 2.8 σ and 3.9 σ confidence levels, and with ΩΛ > 0 at the 3.0 σ and 4.0 σ confidence levels, for two different fitting methods, respectively. Fixing a "minimal" mass density, ΩM = 0.2, results in the weakest detection, ΩΛ > 0 at the 3.0 σ confidence level from one of the two methods. For a flat universe prior (ΩM + ΩΛ = 1), the spectroscopically confirmed SNe Ia require ΩΛ > 0 at 7 σ and 9 σ formal statistical significance for the two different fitting methods. A universe closed by ordinary matter (i.e., ΩM = 1) is formally ruled out at the 7 σ to 8 σ confidence level for the two different fitting methods. We estimate the dynamical age of the universe to be 14.2 ± 1.7 Gyr including systematic uncertainties in the current Cepheid distance scale. We estimate the likely effect of several sources of systematic error, including progenitor and metallicity evolution, extinction, sample selection bias, local perturbations in the expansion rate, gravitational lensing, and sample contamination. Presently, none of these effects appear to reconcile the data with ΩΛ = 0 and q0 ≥ 0.