ARCHANGEL Galaxy Photometry System

Abstract

Photometry of galaxies has typically focused on small, faint systems due to their interest for cosmological studies. Large angular size galaxies, on the other hand, offer a more detailed view into the properties of galaxies, but bring a series of computational and technical difficulties that inhibit the general astronomer from extracting all the information found in a detailed galaxy image. To this end, a new galaxy photometry system has been developed (mostly building on tools and techniques that have existed in the community for decades) that combines ease of usage with a mixture of pre-built scripts. The audience for this system is a new user (graduate student or non-optical astronomer) with a fast, built-in learning curve to offer any astronomer, with imaging data, a suite of tools to quickly extract meaningful parameters from decent data. The tools are available either by a client/server web site or by tarball for personal installation. The tools also provide simple scripts to interface with various on-line datasets (e.g. 2MASS, Sloan, DSS) for data mining capability of imaged data. As a proof of concept, we preform a re-analysis of the 2MASS Large Galaxy Atlas to demonstrate the differences in an automated pipeline, with its emphasis on speed, versus this package with an emphasis on accuracy. This comparison finds the structural parameters extracted from the 2MASS pipeline is seriously flawed with scale lengths that are too small by 50% and central surface brightness that are, on average, 1 to 0.5 mags too bright. A cautionary tale on how to reduce information-rich data such as surface brightness profiles. This document and software can be found at http://abyss.uoregon.edu/~js/archangel.