The SAMI Galaxy Survey: Cubism and covariance, putting round pegs into square holes

TL;DR

This paper introduces a novel methodology for combining irregularly sampled integral-field spectroscopic data that minimizes interpolation, preserves resolution, and effectively tracks covariance, demonstrated on the SAMI Galaxy Survey.

Contribution

The paper presents a new regularisation and combination technique for sparse, irregular spectroscopic data that retains image resolution and covariance information efficiently.

Findings

Achieves only 10% resolution degradation with subcritical sampling.

Tracks 90% of covariance information with minimal data volume increase.

Demonstrates effectiveness on the SAMI Galaxy Survey data.

Abstract

We present a methodology for the regularisation and combination of sparse sampled and irregularly gridded observations from fibre-optic multi-object integral-field spectroscopy. The approach minimises interpolation and retains image resolution on combining sub-pixel dithered data. We discuss the methodology in the context of the Sydney-AAO Multi-object Integral-field spectrograph (SAMI) Galaxy Survey underway at the Anglo-Australian Telescope. The SAMI instrument uses 13 fibre bundles to perform high-multiplex integral-field spectroscopy across a one degree diameter field of view. The SAMI Galaxy Survey is targeting 3000 galaxies drawn from the full range of galaxy environments. We demonstrate the subcritical sampling of the seeing and incomplete fill factor for the integral-field bundles results in only a 10% degradation in the final image resolution recovered. We also implement a new methodology for tracking covariance between elements of the resulting datacubes which retains 90% of the covariance information while incurring only a modest increase in the survey data volume.