A meta-analysis of distance measurements to M87

Abstract

We obtain the median, arithmetic mean, and the weighted mean-based central estimates for the distance to M87 using all the measurements collated in De Grijs et al (2020). We then reconstruct the error distribution for the residuals of the combined measurements and also splitting them based on the tracers used. We then checked for consistency with a Gaussian distribution and other symmetric distributions such as Cauchy, Laplacian, and Students-$t$ distributions. We find that when we analyze the combined data, the weighted mean-based estimates show a poor agreement with the Gaussian distribution, indicating that there are unaccounted systematic errors in some of the measurements. Therefore, the median-based estimate for the distance to M87 would be the most robust. This median-based distance modulus to M87 is given by $31.08 \pm 0.09$ mag and $31.07 \pm 0.09$ mag, with and without considering measurements categorized as "averages", respectively. This estimate agrees with the corresponding value obtained in DeGrijs et al (2020) to within $1\sigma$.