Single Epoch Cube Users Guide

VLASS Single Epoch Polarization Cubes

The VLASS single epoch cubes consist of up to 16 frequency channels of Stokes I,Q,U cubes for each square degree of the survey area. Science validation of the VLASS polarization cube products is detailed in VLASS Memo 18, available from the VLASS Memo repository.

The VLASS team has made available a demonstration release of cubes here.

Important notes for users

The number of cube planes that are made and pass QA varies depending on RFI. Frequently, spectral windows 3, 4 and 16 and 17 are rejected in QA. The rejected channels are available in the QA_REJECTED directory.

Cubes are produced at the native resolution for their frequency, and the central position of each cube (in the CRVAL1 and CRVAL2 keywords in the headers) differs slightly per channel due to the image-plane correction for w-terms (see VLASS Memo 14).

For the demonstration release only we will also provide the cubes regridded to the nominal image center and smoothed to the resolution of the lowest frequency channel. These are the *.com.fits images. These are made by the pipeline, but will be deleted before the cubes are archived due to the cost of storing them. A script linked here (and in the scripts directory of the release) has been made to align the cubes and convolve to a common beam.

Storing the individual channels in Stokes V is also too expensive, however we provide an averaged (with min/max pixel reject) plane from all the channels. The script that  produced these is also available in the scripts directory

Release contents

Top level directory:

scripts - scripts to align and convolve cubes and make the averaged Stokes V image.

VLASS2.1 - images from VLASS2.1

Tile directory:

<tilename>/<Individual image directories of the form VLASS2.1.cc.T10t02.J005000-023000.06.2048.v1>

QA_REJECTED - rejected cube planes

Image directories:

For each square degree the following files are provided inside the image directories (using T10t02.J005000-023000 as an example):

VLASS2.1.cc.T10t02.J005000-023000.06.2048.v1.spw[?].IQU.iter3.image.pbcor.tt0.subim.fits
- IQU image cube, one per spectral window.

VLASS2.1.cc.T10t02.J005000-023000.06.2048.v1.spw[?].IQU.iter3.image.pbcor.tt0.rms.subim.fits
- RMS IQU cube,one per spectral window.

VLASS2.1.cc.T10t02.J005000-023000.06.2048.v1.spw[?].IQU.iter3.image.pbcor.tt0.subim.com.fits
- IQU cube regridded to the nominal image center (in the filename) and convolved with the common beam.
(Note this product will not persist in the production release.)

VLASS2.1.cc.T10t02.J005000-023000.06.2048.V_mean_minmaxrej.subim.fits
- mean (with min/max reject) Stokes V image made from the common beam Stokes V images (which are not part of the release).

weblog.tgz - tarred and gzipped weblog

pipeline-<YYYMMDDTXXXXXX> - untarred weblog

placeholder.catalog.csv - empty file, will eventually contain source list

casa_pipescript.py - pipeline command script

casa_commands.log - list of equivalent CASA commands.

pipeline_manifest.xml - XML-formatted list of files

unknown.hifv_vlassSEIP.pprequest.xml - XML pipeline processing request

CCIP_parameter.list, SEIP_parameter.list - parameters used for running the cube and continuum pipelines, respectively.