Spectral Map Making with SPHEREx

TL;DR

This paper introduces map-making techniques and preliminary spectral data cubes for SPHEREx, a NASA mission conducting an all-sky near-infrared spectral survey from 0.75 to 5.0 microns.

Contribution

It details the development of a map maker for SPHEREx data, addressing various spectral features, foreground mitigation, and systematics handling, with maps in tangent-plane and HEALPix formats.

Findings

Produced initial spectral maps of the sky in multiple formats.

Demonstrated methods to mitigate foregrounds and systematics.

Prepared for public release of specialized maps and tools.

Abstract

We present map-making methodologies and preliminary spectral data cubes for SPHEREx, a NASA Explorer mission that launched in March 2025 and has been performing an all-sky near-infrared spectral survey. The SPHEREx instrument observes from 0.75 to 5.0 microns with a spectral resolution ranging from 35 to 130 and a pixel size of 6.15". We define a nominal set of 102 wavelength channels, each of which maps the entire sky approximately twice per year. Among the main mission goals is an investigation of the cosmic history of galaxy formation through intensity mapping of the extragalactic background light (EBL), which is a primary motivation for the map maker described in this work. The SPHEREx dataset contains a wealth of additional mapping targets, e.g., resolved galaxies and nebulae and diffuse clouds of Galactic dust and gas, which display strong spectral features such as hydrogen recombination lines, molecular-hydrogen lines and emission from polycyclic aromatic hydrocarbons (PAHs). We describe how our map maker handles these various cases, how to mitigate foregrounds such as zodiacal light and upper-atmospheric emission and how to monitor and mitigate systematics and signal loss. Our maps are produced both in tangent-plane projection and in full-sky HEALPix format. Specialized maps will be released to accompany future publications from the SPHEREx Science Team, and a public mosaic tool will be made available by the NASA/IPAC Infrared Science Archive (IRSA).