Spectral index distribution between 74 MHz and 153 MHz. The difference in resolution is 80″ (VLSS) and the 25″ (GMRT) and multiple GMRT matches to a single VLSS source have been merged into one. The vertical line shows 5σ_avg, where σ_avg is the average rms noise in the GMRT mosaic. The diagonal dotted line indicates the incompleteness limit due to the sensitivity of VLSS. The horizontal dashed line shows the KM mean spectral index of −0.55. Error bars on individual points are not plotted for clarity, but a single bar in the top right indicates the maximum and minumum errors in the dataset.