Apsis: The ACS Science Analysis Pipeline

Current Release: v4.0

Internal development pages (team only)

Introduction

The goal of the science data pipeline is to efficiently and consistently analyze the large volume of data acquired by the ACS GTO programs. Our goal is to produce a pipeline which accurately measures the relevant scientific parameters with as little human intervention as possible. Although the pipeline is designed for GTO data, it will also be useful for analyzing other data from GO and parallel programs.

Philosophy & Structure

Our philosophy is to use existing software whenever possible to leverage off the large amount of community effort which has already gone into creating software to effectively analyze HST data. We also plan to use a modular approach using such software as Python (or Pyraf ). Much of the pipeline software will run on an Unix cluster (possibly a Linux cluster using MOSIX.)

Pipeline requirements for individual GTO programs can be found here. A requirements document for the pipeline is now being prepared. A document describing the requirements for a grism science pipeline can be found here.

Galaxies and Clusters of Galaxies Program

The preliminary flowchart for the science pipeline for the Galaxies and Clusters of Galaxies GTO programs is given below.

Apsis Software Modules:

• The align module determines the relative x,y shifts and rotations, as well as the sky levels, of the input images of the dataset.
• The modules combDither and pyblot combine all exposures within each filter into a single geometrically corrected image while rejecting cosmic rays. This is done through the STSDAS Dither package drizzle-blot-drizzle cycle.
• The combFilter module combines the final filter images produced by combDither into a "detectionImage."
• The catalog modules, detectionCatalog and filterCatalog, create the source catalogs for the detection and filter images of the dataset by wrapping SExtractor which is used to detect, classify, and perform perform photometry of objects in astronomical images and will be used to create object catalogs [developed by Bertin & Arnouts]
• The colorCatalog module creates the photometry catalogs for the filters of the dataset.
• The photoz module is just the Apsis wrapper module to BPZ or Bayesian Photo-Z Estimation (see Benitez 2000, ApJ, 536, p.571). Produces the photometric redshift catalog from a dataset's filter photometry catalogs.
• GIM2D (Galaxy IMage 2D) is used to measure galaxy structural parameters. Developed by Luc Simard. Not yet implemented

Simulations

Rychard Bouwens has been working on developing a ACS simulator. His preliminary ACS signal to noise calculations can be found here. Also, Narcíso Benitez has put together some calculations regarding the best combination of filters and exposure times for accurate photometric redshift estimates here.

Operating procedure

Contact Information

Kenneth Anderson

Gerhardt Meurer meurer@pha.jhu.edu