MRK 6: red-shifted HI absorption 5.5.0

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Overview

This example demonstrates a trickier spectral line data set. In this case, several radio bright active galaxies were observed to look for redshifted 21 cm absorption. The data were obtained using 4IF mode, which means that the full range of velocities were split into two spectral windows. Producing the data cube will require eventually stitching these windows back together.

Download your data from the VLA Archive; in this example we'll use the publicly available survey AB658. These data were published in Gallimore et al. (1999).

With the present archive defaults, you should have obtained the following VLA archive files.

'AB658_A921122.xp1'
'AB658_A921122.xp2'
'AB658_A921122.xp3'
'AB658_A921122.xp4'

This tutorial broadly follows the techniques described in the continuum survey tutorial and the 21 cm emission tutorial.