[Paper Review] The Hubble Legacy Fields (HLF-GOODS-S) v1.5 Data Products: Combining 2442 Orbits of GOODS-S/CDF-S Region ACS and WFC3/IR Images

G. D. Illingworth, D. Magee+8 more|arXiv (Cornell University)|Jun 2, 2016

CCD and CMOS Imaging SensorsEngineering19 citations

TL;DR

This paper presents the Hubble Legacy Fields (HLF-GOODS-S) v1.5 data release, a deep, multi-wavelength imaging survey combining 2,442 Hubble Space Telescope orbits over 13 years, merging ACS/WFC and WFC3/IR data across 10 optical and infrared filters. The dataset provides high-resolution (30–60 mas/pixel) co-added images and inverse variance weight maps for the GOODS-S/CDF-S field, creating a comprehensive, astrometrically aligned legacy resource for studying high-redshift galaxies and cosmic evolution.

ABSTRACT

We have submitted to MAST the 1.5 version data release of the Hubble Legacy Fields (HLF) project covering a 25 x 25 arcmin area over the GOODS-S (ECDF-S) region from the HST archival program AR-13252. The release combines exposures from Hubble's two main cameras, the Advanced Camera for Surveys (ACS/WFC) and the Wide Field Camera 3 (WFC3/IR), taken over more than a decade between mid-2002 to the end of 2016. The HLF includes essentially all optical (ACS/WFC F435W, F606W, F775W, F814W and F850LP filters) and infrared (WFC3/ IR F098M, F105W, F125W, F140W and F160W filters) data taken by Hubble over the original CDF-S region including the GOODS-S, ERS, CANDELS and many other programs (31 in total). The data has been released at https://archive.stsci.edu/prepds/hlf/ as images with a common astrometric reference frame, with corresponding inverse variance weight maps. We provide one image per filter of WFC3/IR images at 60 mas per pixel resolution and two ACS/WFC images per filter, at both 30 and 60 mas per pixel. Since this comprehensive dataset combines data from 31 programs on the GOODS-S/CDF-S, the AR proposal identified the MAST products by the global name "Hubble Legacy Field", with this region being identified by "HLF-GOODS-S". This dataset complements that of the Frontier Fields program. The total incorporated in the HLF-GOODS-S is 5.8 Msec in 7211 exposures from 2442 orbits. This is ~70% of a HST full cycle!

Motivation & Objective

• To create a deep, multi-wavelength imaging legacy of the GOODS-S/CDF-S field by combining data from 31 Hubble programs.
• To improve astrometric alignment and photometric consistency across diverse Hubble observations spanning over a decade.
• To produce a publicly accessible, high dynamic range, co-added dataset with calibrated inverse variance weight maps for scientific analysis.
• To complement the Frontier Fields by providing a deeper, broader view of the same region with enhanced depth and resolution.
• To enable high-precision studies of high-redshift galaxies, star formation, and cosmic structure formation.

Proposed method

• The data integration process combined 7,211 exposures from 2,442 Hubble orbits taken between 2002 and 2016.
• Images from the ACS/WFC and WFC3/IR instruments were co-added using a common astrometric reference frame to ensure alignment.
• Multiple pixel scales (30 and 60 mas/pixel) were produced for ACS/WFC data to support multi-resolution analysis.
• WFC3/IR data were co-added at 60 mas/pixel resolution per filter to maximize depth and dynamic range.
• Inverse variance weight maps were generated for each filter to enable optimal photometric measurements and noise estimation.
• The final data products were validated and released via MAST under the Hubble Legacy Fields project, with the GOODS-S region designated as HLF-GOODS-S.

Experimental results

Research questions

• RQ1 What is the optimal co-addition strategy for combining multi-epoch, multi-instrument Hubble data across a wide wavelength range in the GOODS-S field?
• RQ2 How does combining 2,442 orbits of Hubble observations improve the depth and dynamic range for detecting high-redshift galaxies?
• RQ3 To what extent does a common astrometric solution improve photometric accuracy and source extraction in deep extragalactic surveys?
• RQ4 How do the inverse variance weight maps enhance the reliability of photometric measurements in the HLF-GOODS-S dataset?
• RQ5 What is the total exposure time and number of unique exposures integrated into the HLF-GOODS-S v1.5 data release?

Key findings

• The HLF-GOODS-S v1.5 dataset combines 5.8 megaseconds of exposure time from 7,211 exposures across 2,442 Hubble orbits.
• The final data products include one co-added image per WFC3/IR filter at 60 mas/pixel and two co-added images per ACS/WFC filter at 30 and 60 mas/pixel.
• The dataset covers 10 filters: four ACS (F435W, F606W, F775W, F814W, F850LP) and five WFC3/IR (F098M, F105W, F125W, F140W, F160W).
• All images are co-added onto a common astrometric reference frame, enabling precise source matching and photometry.
• Inverse variance weight maps are provided for each filter, enabling optimal photometric extraction and error estimation.
• The dataset is publicly released via MAST under the Hubble Legacy Fields project, with the GOODS-S region designated as HLF-GOODS-S.