[Paper Review] Deep ATLAS radio observations of the CDFS-SWIRE field

R. P. Norris, J. Afonso+15 more|Oct 18, 2006

Radio Astronomy Observations and TechnologyPhysics and Astronomy117 citations

TL;DR

This paper presents deep radio observations from the ATLAS survey of the CDFS-SWIRE field, identifying 726 distinct radio sources, mostly associated with infrared and optical counterparts. A key finding is the detection of rare infrared-faint radio sources—bright in radio but undetected in optical, infrared, or X-ray bands—highlighting the power of wide, deep surveys for discovering unusual astrophysical populations.

ABSTRACT

We present the first results from the Australia Telescope Large Area Survey (ATLAS), which consist of deep radio observations of a 3.7 square degree field surrounding the Chandra Deep Field South, largely coincident with the infrared Spitzer Wide-Area Extragalactic (SWIRE) Survey. We also list cross-identifications to infrared and optical photometry data from SWIRE, and ground-based optical spectroscopy. A total of 784 radio components are identified, corresponding to 726 distinct radio sources, nearly all of which are identified with SWIRE sources. Of the radio sources with measured redshifts, most lie in the redshift range 0.5-2, and include both star-forming galaxies and active galactic nuclei (AGN). We identify a rare population of infrared-faint radio sources which are bright at radio wavelengths but are not seen in the available optical, infrared, or X-ray data. Such rare classes of sources can only be discovered in wide, deep surveys such as this.

Motivation & Objective

• To conduct deep radio observations over a 3.7 square degree field centered on the Chandra Deep Field South.
• To cross-identify radio sources with existing infrared (SWIRE) and optical photometry and spectroscopy data.
• To identify rare or unusual radio sources, particularly those faint or undetected at other wavelengths.
• To characterize the redshift distribution and nature (e.g., star-forming galaxies, AGN) of the detected radio sources.

Proposed method

• Conducting deep 1.4 GHz continuum observations using the Australia Telescope Compact Array (ATCA) over a 3.7 deg² region.
• Combining radio data with multi-wavelength data from the Spitzer Wide-Area Extragalactic (SWIRE) Survey for source cross-identification.
• Using optical spectroscopy and photometric redshifts to determine redshifts for radio sources.
• Applying source extraction and photometry techniques to identify 784 radio components from 726 distinct sources.
• Classifying sources based on their multi-wavelength properties, especially focusing on those undetected in optical, infrared, or X-ray bands.
• Using statistical analysis to assess the rarity and potential significance of infrared-faint radio sources.

Experimental results

Research questions

• RQ1 What is the distribution of radio sources in the CDFS-SWIRE field, and how do they correlate with infrared and optical counterparts?
• RQ2 What fraction of radio sources are undetected at optical, infrared, or X-ray wavelengths, and what does this imply about their nature?
• RQ3 What is the redshift distribution of the detected radio sources, and how does it compare to known populations of star-forming galaxies and AGN?
• RQ4 Are there any rare or previously undetected classes of radio sources in this deep, wide-field survey?
• RQ5 What are the properties of infrared-faint radio sources, and how do they differ from typical radio-loud galaxies?

Key findings

• A total of 726 distinct radio sources were identified from 784 radio components, with nearly all associated with SWIRE infrared sources.
• Most radio sources with measured redshifts lie in the redshift range 0.5–2, indicating a significant population of distant galaxies.
• A rare class of infrared-faint radio sources (IFRS) was detected—bright in radio but undetected in optical, infrared, or X-ray data.
• These IFRS are likely to be high-redshift or low-luminosity sources with unusual radio-to-infrared flux ratios, possibly powered by AGN or star formation in dust-enshrouded environments.
• The survey demonstrates the effectiveness of wide, deep radio surveys in uncovering rare and exotic astrophysical sources not detectable in shallower or narrower surveys.
• The cross-identification with SWIRE and ground-based spectroscopy enables robust classification of source types, including star-forming galaxies and AGN.