Apsis: The ACS Science Analysis Pipeline
Current Release: v4.0
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.
Contact Information
Kenneth Anderson
Gerhardt Meurer meurer@pha.jhu.edu
