HerMES: SPIRE Science Demonstration Phase Maps

TL;DR

This paper details the creation and validation of high-quality sky maps from Herschel SPIRE data for the HerMES survey, using an iterative algorithm to preserve diffuse emission and minimize noise.

Contribution

Introduction of the SHIM iterative map-making algorithm for producing high fidelity, extended emission-preserving maps from Herschel SPIRE observations.

Findings

Maps have a transfer function close to unity on relevant scales.

The SHIM pipeline produces maps suitable for scientific analysis.

Validation tests confirm the maps meet HerMES science requirements.

Abstract

We describe the production and verification of sky maps of the five SPIRE fields observed as part of the Herschel Multi-tiered Extragalactic Survey (HerMES) during the Science Demonstration Phase (SDP) of the Herschel mission. We have implemented an iterative map-making algorithm (SHIM; The SPIRE-HerMES Iterative Mapper) to produce high fidelity maps that preserve extended diffuse emission on the sky while exploiting the repeated observations of the same region of the sky with many detectors in multiple scan directions to minimize residual instrument noise. We specify here the SHIM algorithm and outline the various tests that were performed to determine and characterize the quality of the maps and verify that the astrometry, point source flux and power on all relevant angular scales meets the needs of the HerMES science goals. These include multiple jackknife tests, determination of the map transfer function and detailed examination of the power spectra of both sky and jackknife maps. The map transfer function is approximately unity on scales from one arcminute to one degree. Final maps (v1.0), including multiple jackknives, as well as the SHIM pipeline, have been used by the HerMES team for the production of SDP papers.