Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey

Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey
Name	Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey
Acronym	CANDELS
Start	2010
Telescope	Hubble Space Telescope
Instruments	Wide Field Camera 3, Advanced Camera for Surveys
Wavelength	Near-infrared, Optical
Fields	GOODS-North, GOODS-South, COSMOS, EGS, UKIDSS/UDS

Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey

The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey was a major Hubble Space Telescope program that obtained deep near-infrared and optical imaging across five extragalactic fields. The program complemented surveys undertaken by Spitzer Space Telescope, Chandra X-ray Observatory, Keck Observatory, Subaru Telescope, and Very Large Telescope to study galaxy formation and evolution across cosmic time. CANDELS data have informed research by teams associated with California Institute of Technology, Harvard University, University of California, Berkeley, Max Planck Society, and Space Telescope Science Institute.

Overview

CANDELS was executed with the Hubble Space Telescope using the Wide Field Camera 3 and the Advanced Camera for Surveys to obtain deep imaging in multiple filters over the GOODS-North, GOODS-South, COSMOS, EGS, and UKIDSS/UDS fields. The program built on legacy datasets from Great Observatories Origins Deep Survey, Hubble Ultra Deep Field, COSMOS survey, and Sloan Digital Sky Survey to create a contiguous archive useful to researchers from institutions including Princeton University, University of Cambridge, University of Oxford, Yale University, and Johns Hopkins University.

Goals and Scientific Objectives

CANDELS aimed to constrain the evolution of the galaxy luminosity function, stellar mass assembly, and star-formation histories through epochs sampled by redshifts probed by James Webb Space Telescope precursor work. Objectives included measuring morphological transformations relevant to the Lambda-CDM model, quantifying merger rates connected to studies by European Space Agency, and identifying high-redshift candidates contemporaneous with surveys from Atacama Large Millimeter/submillimeter Array, Herschel Space Observatory, GALEX. The program supported investigations into active galactic nuclei using comparisons with Chandra X-ray Observatory, black hole growth similar to work by Event Horizon Telescope collaboration, and reionization-era constraints related to observations from Planck collaboration.

Survey Design and Observations

The survey strategy combined deep and wide tiers, integrating observations from CANDELS-Deep and CANDELS-Wide fields to balance cosmic variance and depth similar to strategies used in Dark Energy Survey and CFHT Legacy Survey. Imaging was obtained primarily with the F125W and F160W filters on Wide Field Camera 3 and with F606W and F814W on Advanced Camera for Surveys, leveraging parallel observing modes similar to Hubble Frontier Fields. Target fields were selected for overlap with spectroscopic campaigns by DEEP2 Redshift Survey, VIMOS Ultra-Deep Survey, 3D-HST, and photometric catalogs from UKIRT Infrared Deep Sky Survey.

Data Reduction and Processing

CANDELS adopted pipelines building on calibration heritage from Space Telescope Science Institute and software tools developed by teams at Astrodeep, Astropy Project, SExtractor developers, and groups associated with STScI. Procedures included bias subtraction, flat-fielding, cosmic-ray rejection akin to methods in COSMOS survey processing, astrometric alignment to catalogs from Gaia and photometric zero-point calibration cross-matched with Spitzer Space Telescope and ground-based photometry from Subaru Telescope and VLT. High-level data products included mosaics, weight maps, segmentation maps, and multiwavelength catalogs used by researchers at University of Tokyo, Seoul National University, University of Toronto, and ETH Zurich.

Key Findings and Results

CANDELS produced constraints on the evolution of the galaxy stellar mass function that refined models from groups at Max Planck Institute for Astrophysics and Princeton University Observatory, provided measurements of size evolution for early-type and late-type galaxies complementary to studies by Kavli Institute for Cosmology and Royal Society-affiliated teams, and identified robust samples of galaxies at redshifts z>6 that informed follow-up by James Webb Space Telescope and ALMA. The survey enabled analyses of morphological quenching consistent with simulations from Illustris and EAGLE collaborations, measurements of galaxy clustering comparable to results from BOSS and VVDS, and studies of supernova rates tied to work by Supernova Cosmology Project and High-Z Supernova Search Team.

Legacy Data Products and Access

Final CANDELS products were released through archives maintained by Mikulski Archive for Space Telescopes and datasets interoperable with the NASA/IPAC Infrared Science Archive and European Space Agency archives. Delivered products included calibrated images, photometric catalogs, photometric redshifts used alongside spectroscopic redshifts from Keck Observatory, Very Large Telescope, and Gemini Observatory, and value-added catalogs produced by collaborations with Carnegie Observatories and Space Telescope European Coordinating Facility. The public release strategy mirrored practices from Hubble Legacy Archive and supported community-wide reuse by groups at Flatiron Institute and Lawrence Berkeley National Laboratory.

Collaborations and Instrumentation

The CANDELS consortium comprised investigators from institutions such as University of California, Los Angeles, Columbia University, University of Arizona, Imperial College London, University of Edinburgh, and included instrument teams from NASA and European Space Agency. Observations depended on the Wide Field Camera 3 infrared channel developed by teams at Goddard Space Flight Center and optical capabilities from Ball Aerospace and Lockheed Martin. Cross-facility synergy linked CANDELS to spectroscopic resources at W. M. Keck Observatory, millimeter-wave follow-up at Atacama Large Millimeter/submillimeter Array, and X-ray comparisons with Chandra X-ray Observatory programs.

Impact on Extragalactic Astronomy

CANDELS established legacy constraints used by theorists at Harvard-Smithsonian Center for Astrophysics, Institute for Advanced Study, University of Chicago, and Cambridge University to refine semi-analytic models and hydrodynamic simulations. The survey's catalogs underpinned student and postdoctoral research at Princeton University, University of California, Santa Cruz, Pennsylvania State University, and international groups at Max Planck Institute for Astronomy, influencing observing strategies of James Webb Space Telescope early release observations and informing proposals to National Science Foundation, European Research Council, and facilities like Subaru Telescope and ALMA.

Category:Astronomical surveys