Extragalactic magnetism with SOFIA (SALSA Legacy Program) -- III: First data release and on-the-fly polarization mapping characterization

TL;DR

This paper introduces the first data release from the SALSA program, showcasing the on-the-fly mapping technique for polarimetric observations with SOFIA, which enhances efficiency and sensitivity in extragalactic magnetic field studies.

Contribution

It presents the implementation and benefits of the on-the-fly mapping mode for polarimetric data collection, significantly improving observational efficiency and sensitivity.

Findings

OTFMAP reduces observing overheads by a factor of 2.34.

Sensitivity is improved by a factor of 1.80 with OTFMAP.

Overall, OTFMAP increases science yield per hour by a factor of 2.49.

Abstract

We describe the data processing of the Survey on extragALactic magnetiSm with SOFIA (SALSA Legacy Program). This first data release presents 33% (51.34h out of 155.7h, including overheads) of the total awarded time taken from January 2020 to December 2021. Our observations were performed using the newly implemented on-the-fly mapping (OTFMAP) technique in the polarimetric mode. We present the pipeline steps to obtain homogeneously reduced high-level data products of polarimetric maps of galaxies for use in scientific analysis. Our approach has a general design and can be applied to sources smaller than the field-of-view of the HAWC+ array in any given band. We estimate that the OTFMAP polarimetric mode offers a reduction of observing overheads by a factor 2.34, and an improvement in sensitivity by a factor 1.80 when compared to previously obtained polarimetric observations using the chopping and nodding mode. The OTFMAP is a significant optimization of the polarimetric mode of HAWC+ as it ultimately reduces the cost of operations of SOFIA/HAWC+ by increasing the science collected per hour of observation up to an overall factor of 2.49. The OTFMAP polarimetric mode is the standard observing strategy of SALSA. The results and quantitative analysis of this first data release are presented in Papers IV and V of the series.