Figure 2.
Left: net narrow-band Hα emission image, taken with the SOAR telescope, of the BGG in Abell 3581 after removal of continuum emission with the CTIO 6520/76 filter. Right: the unsharp masked Hα emission image. The initial image has been smoothed by a 2D Gaussian with σ = 1 arcsec, subtracted from the original and binned by 4 pixels (0.6 arcsec) in each direction.