Most likely electron temperature gradient determined using the Bayesian linear regression with the MCMC sampling for different samples. The left panel shows the data and the most likely linear model in the dashed black line. The error bars are 1σ uncertainty in the derived electron temperature. The shaded yellow region represents the range of fits from 10 000 MCMC iterations. The black triangles represent the outlier data points which are flagged before the fitting, while the filled purple circles represent the data used for fitting. The right panel shows the corresponding corner plot displaying the one-dimensional (1D) histogram of the posterior distribution for each parameter (slope and y-intercept). The histograms represent the probability density functions (PDFs) of the Monte Carlo fit parameters, while the blue curves represent the scatter plot of the joint distribution between the two parameters. The solid orange lines indicate the peaks of the PDFs, representing the most likely fit parameters, and the dotted blue lines correspond to the 1σ confidence intervals. Top panel: Case 1: Consists of all 213 sources in our catalog excluding the Galactic center H II due to lack of reliable distance estimate. Bottom panel: Case 2: consists of 496 sources located within R_Gal range of 0.1–20.0 kpc from Quireza et al. (2006), Wenger et al. (2019), and our catalog. The electron temperature gradient for each sample is given in the plots.