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Register a new userConstraining the dark energy and smoothness parameter with type Ia Supernovae and Gamma-Ray Bursts
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Vinicius Consolini Busti
Publication date
2012
fields
Physics
and research's language is
English
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The existence of inhomogeneities in the observed Universe modifies the distance-redshift relations thereby affecting the results of cosmological tests in comparison to the ones derived assuming spatially uniform models. By modeling the inhomogeneities through a Zeldovich-Kantowski-Dyer-Roeder (ZKDR) approach which is phenomenologically characterized by a smoothness parameter $alpha$, we rediscuss the constraints on the cosmic parameters based on Supernovae type Ia and Gamma-Ray Bursts (GRBs) data. The present analysis is restricted to a flat $Lambda$CDM model with the reasonable assumption that $Lambda$ does not clump. A $chi^{2}$-analysis using 557 SNe Ia data from the Union2 Compilation Data (Amanullah {it et al.} 2010) constrains the pair of parameters ($Omega_m, alpha$) to $Omega_m=0.27_{-0.03}^{+0.08}$($2sigma$) and $alpha geq 0.25$. A similar analysis based only on 59 Hymnium GRBs (Wei 2010) constrains the matter density parameter to be $Omega_m= 0.35^{+0.62}_{-0.24}$ ($2sigma$) while all values for the smoothness parameter are allowed. By performing a joint analysis, it is found that $Omega_m = 0.27^{+0.06}_{-0.03}$ and $alpha geq 0.52$. As a general result, although considering that current GRB data alone cannot constrain the smoothness $alpha$ parameter our analysis provides an interesting cosmological probe for dark energy even in the presence of inhomogeneities.
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The presence of inhomogeneities modifies the cosmic distances through the gravitational lensing effect, and, indirectly, must affect the main cosmological tests. Assuming that the dark energy is a smooth component, the simplest way to account for the influence of clustering is to suppose that the average evolution of the expanding Universe is governed by the total matter-energy density whereas the focusing of light is only affected by a fraction of the total matter density quantified by the $alpha$ Dyer-Roeder parameter. By using two different samples of SNe type Ia data, the $Omega_m$ and $alpha$ parameters are constrained by applying the Zeldovich-Kantowski-Dyer-Roeder (ZKDR) luminosity distance redshift relation for a flat ($Lambda$CDM) model. A $chi^{2}$-analysis using the 115 SNe Ia data of Astier {it et al.} sample (2006) constrains the density parameter to be $Omega_m=0.26_{-0.07}^{+0.17}$($2sigma$) while the $alpha$ parameter is weakly limited (all the values $in [0,1]$ are allowed even at 1$sigma$). However, a similar analysis based the 182 SNe Ia data of Riess {it et al.} (2007) constrains the pair of parameters to be $Omega_m= 0.33^{+0.09}_{-0.07}$ and $alphageq 0.42$ ($2sigma$). Basically, this occurs because the Riess {it et al.} sample extends to appreciably higher redshifts. As a general result, even considering the existence of inhomogeneities as described by the smoothness $alpha$ parameter, the Einstein-de Sitter model is ruled out by the two samples with a high degree of statistical confidence ($11.5sigma$ and $9.9sigma$, respectively). The inhomogeneous Hubble-Sandage diagram discussed here highlight the necessity of the dark energy, and a transition deceleration/accelerating phase at $zsim 0.5$ is also required.
We show that peculiar velocities of Type Ia supernovae can be used to derive constraints on the sum of neutrino masses, $Sigma m_{ u}$, and dark energy equation of state, $w = w_0+w_a(1-a)$, from measurements of the magnitude-redshift relation, complementary to galaxy redshift and weak lensing surveys. Light from a supernova propagates through a perturbed Universe so the luminosity distance is modified from its homogeneous prediction. This modification is proportional to the matter density fluctuation and its time derivative due to gravitational lensing and peculiar velocity respectively. At low redshifts, the peculiar velocity signal dominates while at high redshifts lensing does. We show that using lensing and peculiar velocity of supernovae from the upcoming surveys WFIRST and ZTF, without other observations, we can constrain $Sigma m_{ u} lesssim 0.31$ eV, $sigma(w_0) lesssim 0.02$, and ${sigma(w_a)} lesssim 0.18$ ($1-sigma$ CL) in the $Sigma m_{ u}$-$w_0$-$w_a$ parameter space, where all the other cosmological parameters are fixed. We find that adding peculiar velocity information from low redshifts shrinks the volume of the parameter ellipsoid in this space by $sim 33$%. We also allow $Omega_{text{CDM}}$ to vary as well as $Sigma m_{ u}$, $w_0$ and $w_a$, and demonstrate how these constraints degrade as a consequence.
While the connection between Long Gamma-Ray Bursts (GRBs) and Type Ib/c Supernovae (SNe Ib/c) from stripped stars has been well-established, one key outstanding question is what conditions and factors lead to each kind of explosion in massive stripped stars. One promising line of attack is to investigate what sets apart SNe Ib/c with GRBs from those without GRBs. Here, I briefly present two observational studies that probe the SN properties and the environmental metallicities of SNe Ib/c (specifically broad-lined SNe Ic) with and without GRBs. I present an analysis of expansion velocities based on published spectra and on the homogeneous spectroscopic CfA data set of over 70 SNe of Types IIb, Ib, Ic and Ic-bl, which triples the world supply of well-observed Stripped SNe. Moreover, I demonstrate that a meta-analysis of the three published SN Ib/c metallicity data sets, when including only values at the SN positions to probe natal oxygen abundances, indicates at very high significance that indeed SNe Ic erupt from more metal-rich environments than SNe Ib, while SNe Ic-bl with GRBs still prefer, on average, more metal-poor sites than those without GRBs.
In this Comment we discuss a recent analysis by Yu et al. [RAA 11, 125 (2011)] about constraints on the smoothness $alpha$ parameter and dark energy models using observational $H(z)$ data. It is argued here that their procedure is conceptually inconsistent with the basic assumptions underlying the adopted Dyer-Roeder approach. In order to properly quantify the influence of the $H(z)$ data on the smoothness $alpha$ parameter, a $chi^2$-test involving a sample of SNe Ia and $H(z)$ data in the context of a flat $Lambda$CDM model is reanalyzed. This result is confronted with an earlier approach discussed by Santos et al. (2008) without $H(z)$ data. In the ($Omega_m, alpha$) plane, it is found that such parameters are now restricted on the intervals $0.66 leq alpha leq 1.0$ and $0.27 leq Omega_m leq 0.37$ within 95.4% confidence level (2$sigma$), and, therefore, fully compatible with the homogeneous case. The basic conclusion is that a joint analysis involving $H(z)$ data can indirectly improve our knowledge about the influence of the inhomogeneities. However, this happens only because the $H(z)$ data provide tighter constraints on the matter density parameter $Omega_m$.
Aims. We investigate the degree of improvement in dark energy constraints that can be achieved by extending Type Ia Supernova (SN Ia) samples to redshifts z > 1.5 with the Hubble Space Telescope (HST), particularly in the ongoing CANDELS and CLASH multi-cycle treasury programs. Methods. Using the popular CPL parametrization of the dark energy, w = w0 +wa(1-a), we generate mock SN Ia samples that can be projected out to higher redshifts. The synthetic datasets thus generated are fitted to the CPL model, and we evaluate the improvement that a high-z sample can add in terms of ameliorating the statistical and systematic uncertainties on cosmological parameters. Results. In an optimistic but still very achievable scenario, we find that extending the HST sample beyond CANDELS+CLASH to reach a total of 28 SN Ia at z > 1.0 could improve the uncertainty in the wa parameter by up to 21%. The corresponding improvement in the figure of merit (FoM) would be as high as 28%. Finally, we consider the use of high-redshift SN Ia samples to detect non-cosmological evolution in SN Ia luminosities with redshift, finding that such tests could be undertaken by future spacebased infrared surveys using the James Webb Space Telescope (JWST).
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