Nonparametric study of the evolution of the cosmological equation of state with SNeIa, BAO, and high-redshift GRBs

Journal Article · Mon Mar 10 00:00:00 EDT 2014 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/783/2/126· OSTI ID:22351547

Postnikov, S. ^[1]; Dainotti, M. G. ^[2]; Hernandez, X. ^[3]

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1. Nuclear Theory Center, Indiana University, Bloomington, IN (United States)
2. Physics Department, Stanford University, Via Pueblo Mall 382, Stanford, CA (United States)
3. Instituto de Astronomía, Universidad Nacional Autónoma de México, México D.F. 04510 (Mexico)

We study the dark energy equation of state as a function of redshift in a nonparametric way, without imposing any a priori w(z) (ratio of pressure over energy density) functional form. As a check of the method, we test our scheme through the use of synthetic data sets produced from different input cosmological models that have the same relative errors and redshift distribution as the real data. Using the luminosity-time L{sub X} -T{sub a} correlation for gamma-ray burst (GRB) X-ray afterglows (the Dainotti et al. correlation), we are able to utilize GRB samples from the Swift satellite as probes of the expansion history of the universe out to z ≈ 10. Within the assumption of a flat Friedmann-Lemaître-Robertson-Walker universe and combining supernovae type Ia (SNeIa) data with baryonic acoustic oscillation constraints, the resulting maximum likelihood solutions are close to a constant w = –1. If one imposes the restriction of a constant w, we obtain w = –0.99 ± 0.06 (consistent with a cosmological constant) with the present-day Hubble constant as H {sub 0} = 70.0 ± 0.6km s{sup –1} Mpc{sup –1} and density parameter as Ω{sub Λ0} = 0.723 ± 0.025, while nonparametric w(z) solutions give us a probability map that is centered at H {sub 0} = 70.04 ± 1km s{sup –1} Mpc{sup –1} and Ω{sub Λ0} = 0.724 ± 0.03. Our chosen GRB data sample with a full correlation matrix allows us to estimate the amount, as well as quality (errors), of data needed to constrain w(z) in the redshift range extending an order of magnitude beyond the farthest SNeIa measured.

• OSTI ID: 22351547
• Journal Information: Astrophysical Journal, Vol. 783, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
AFTERGLOW
CORRELATIONS
COSMIC GAMMA BURSTS
COSMOLOGICAL CONSTANT
COSMOLOGICAL MODELS
COSMOLOGY
DENSITY
ENERGY DENSITY
EQUATIONS OF STATE
LIMITING VALUES
LUMINOSITY
MAPS
MAXIMUM-LIKELIHOOD FIT
NONLUMINOUS MATTER
OSCILLATIONS
RED SHIFT
SATELLITES
SUPERNOVAE
UNIVERSE
X RADIATION