Transcript Titulo do Artigo

A low-z test
for interacting dark energy
CosmoSur III – Córdoba, Argentina 03/08/15
R. S. Gonçalves, G. C. Carvalho, J. Alcaniz
Observatório Nacional - Brasil
Overview
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Theoretical model
Gas mass fraction
Simulations
Figure of Merit
Critical number of points
Relative error
Conclusions
Theoretical model
• Interaction between dark matter (CDM) and DE (Λ);
• Radiation and baryons are separetely conserved (Wang
X. and Meng U., 2005; J. S. Alcaniz and A. Lima, 2005)
Gas mass fraction
Standard equation (S. Sasaki, 1996; S. Allen 2002):
Low-z: (R.S.G, G. C.Carvalho, J. S. Alcaniz, 2015)
Obs:
- Interaction parameter is assumed constant;
- Marginalized over the nuisance paramters
Low-z
Observational data
Original data set:
(Allen et al. 2008)
42 galaxy clusters
0.063 < z < 1.063
Low-z data set:
27 galaxy clusters
0.063 < z < 0.399
Partial results
(R.S.G, G. C.Carvalho, J. S. Alcaniz, 2015)
Simulations
1.
We define the number of points in the set (N)
2.
We simulate N points of fgas equally spaced in the redshift
range (0.06 < z < 0.40);
3.
For each simulated point we assume a normal distribution
with a mean and error defined as the fiducial values;
4.
For the entire sample we make a chi-square analysis and
find the best fit values;
5.
We repeat this process 104 times and calculate the mean
and the standard deviation from the best fit distribution.
Figure of Merit
Definition used (D. Coe 2005): FoM =
Critical number
• We assume that the error on the matter density
parameter is negligible, compared with the error
on the interacting parameter.
• Fixed ΩM,0 = 0.28
• Number of points: 10 < N < 700
Critical number
Ncrit = 440
Relative error
of the fgas
Varying Ncrit
Conclusions
• Model with interaction in the dark sector
• Gas mass fraction at low-z
• Dispersion of 0.6 leads to a redshift range of
0.063 < z < 0.399 (i.e. low-z regime)
Conclusions
• Best-fit from the observational data
• Simulations: Number of points varying from 10-700.
• Critical number of points for the fiducial values in
the simulations equal to the observational ones is
440.
• This value decreases to 120 when the relative error
is 50% compared to the observational one.