Multi-resolution HEALPix maps tools for multi-messenger astronomy

HEALPix -- the Hierarchical Equal Area isoLatitude Pixelization – is a standard for tessellating the sphere originally developed to improve the analysis of full-sky data sets. Thanks to its convenient geometric and algebraic properties it has now been adopted by multiple astronomical fields for various purposes, including the distribution of sky-localization probability maps by LIGO, Virgo and Kagra (LVK) and Fermi-GBM. As part of the Time-domain Astronomy Coordination Hub (TACH), in this contribution we present a series of tools that support the usage of multi-resolution maps and enable the use HEALPix to distribute sky-localization information and other astronomical data even by instruments with milliarcsecond resolution. This makes HEALPix a suitable candidate for a common format that can facilitate multi-messenger and multi-wavelength coordination and analysis. The tools include mhealpy, a general-purpose object-oriented Python library that provides an unified interface for single-resolution and multi-resolution HEALPix maps; a derived package to perform common operations needed to create and analyze sky localization probability maps; and healpix-alchemy, a package to add fast multi-resolution image arithmetic and set operations on sky regions to any PostgreSQL 14 database.