Exploring the evidence for a large local void with supernovae Ia data
Abstract
In the present work we utilise the most recent publicly available SN Ia compilations and implement a well formulated cosmological model based on LTB metric in presence of cosmological constant $\Lambda$ ($\Lambda$LTB) to test for signatures of large local inhomogeneities at $z \leq 0.15$. Local underdensities in this redshift range have been previously found based on luminosity density data and galaxy number counts. Our main constraints on the possible local void using the Pantheon SN Ia dataset are  redshift size of $z_{\rm size}=0.068^{+0.021}_{0.030}$ and density contrast of $\delta\Omega_0/\Omega_0 = 10.5_{7.4}^{+9.3}\%$ in $68\%$ confidence intervals. Investigating the possibility to alleviate the tension between the measurements of present expansion rate $H_0$, coming from calibrated local SN Ia and high$z$ CMB data, we confirm previous findings that large local void alone is a very unlikely explanation for the $\sim9\%$ disagreement between the two estimates. However, constraints from our SN Ia analysis inside $1\sigma$ confidence regions of $z_{\rm size}\delta\Omega_0/\Omega_0$ plane allow a void of e.g. $z_{\rm size}=0.075$ ($320\,{h_{70}}^{1}$Mpc) and $\delta\Omega_0/\Omega_0=20\%$. Fitting Pantheon SN Ia from $0.023<z<0.15$ range, we find a $1.1\%$ shift towards lower $H_0$ value for $\Lambda$LTB model compared to modelindependent method with Taylor expanded distance formula. Analysing luminosity density data with $\Lambda$LTB model yields constraint on contrast of large isotropic void $\delta\Omega_0/\Omega_0 = 51.9\pm6.3\%$, which is in $\sim4\sigma$ tension with SN Ia results. More data is necessary to better constrain the local matter density profile and understand the disagreement between SN Ia and luminosity density samples.
 Publication:

arXiv eprints
 Pub Date:
 July 2019
 arXiv:
 arXiv:1907.11219
 Bibcode:
 2019arXiv190711219L
 Keywords:

 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 12 pages, 7 figures, 1 table, submitted to MNRAS. Comments are welcome