Infrared-Faint Radio Sources are at high redshifts

Abstract

Context: Infrared-Faint Radio Sources (IFRS) are characterised by relatively high radio flux densities and associated faint or even absent infrared and optical counterparts. The resulting extremely high radio-to-infrared flux density ratios up to several thousands were previously known only for High-redshift Radio Galaxies (HzRGs), suggesting a link between the two classes of object. Prior to this work, no redshift was known for any IFRS in the Australia Telescope Large Area Survey (ATLAS) fields which would help to put IFRS in the context of other classes of object, especially of HzRGs. Aims: This work aims at measuring the first redshifts of IFRS in the ATLAS fields. Further, we test the hypothesis that IFRS are similar to HzRGs, as higher-redshift or dust-obscured versions of these massive galaxies. Methods: A sample of IFRS was spectroscopically observed using the Focal Reducer and Low Dispersion Spectrograph 2 (FORS2) at the Very Large Telescope (VLT). The data were calibrated based on the Image Reduction and Analysis Facility (IRAF) and redshifts extracted. This information was then used to calculate rest-frame luminosities, and to perform the first spectral energy distribution modelling of IFRS based on redshifts. Results: We found redshifts of 1.84, 2.13, and 2.76, for three IFRS, confirming the suggested high-redshift character of this class of object. These redshifts as well as the resulting luminosities show IFRS to be similar to HzRGs. We found further evidence that fainter IFRS are at even higher redshifts. Conclusions: Considering the similarities between IFRS and HzRGs substantiated in this work, the detection of IFRS, which have a significantly higher sky density than HzRGs, increases the number of Active Galactic Nuclei in the early universe and adds to the problems of explaining the formation of supermassive black holes shortly after the Big Bang.

7 pages, 4 figures; version in print

References in corpus (10)

• The VLA-COSMOS Survey: II. Source Catalog of the Large Project
• The Massive Hosts of Radio Galaxies Across Cosmic Time
• Deep ATLAS radio observations of the CDFS-SWIRE field
• A Unified Catalog of Radio Objects Detected by NVSS, FIRST, WENSS, GB6, and SDSS
• The XMM-Newton survey of the ELAIS-S1 field. I: Number counts, angular correlation function and X-ray spectral properties
• Infrared-Faint Radio Sources: A New Population of High-redshift Radio Galaxies
• Multiwavelength characterization of faint Ultra Steep Spectrum radio sources : A search for high-redshift radio galaxies
• VLBI detection of an Infrared-Faint Radio Source
• Deep 610-MHz Giant Metrewave Radio Telescope observations of the Spitzer extragalactic First Look Survey field - III. The radio properties of Infrared-Faint Radio Sources
• The first VLBI image of an Infrared-Faint Radio Source

Cited by in corpus (12)

• Discovery of a radio galaxy at z = 5.72
• Infrared-Faint Radio Sources: A New Population of High-redshift Radio Galaxies
• A Spitzer survey of Deep Drilling Fields to be targeted by the Vera C. Rubin Observatory Legacy Survey of Space and Time
• The radio spectral energy distribution of infrared-faint radio sources
• The Redshift Distribution of Infrared-Faint Radio Sources
• Infrared-Faint Radio Sources in the SERVS deep fields: Pinpointing AGNs at high redshift
• Active galactic nuclei cores in infrared-faint radio sources: Very long baseline interferometry observations using the Very Long Baseline Array
• On the nature of infrared-faint radio sources in the SXDF and VLA-VVDS fields
• An Evolutionary Sequence of Young Radio Galaxies
• Infrared-faint radio sources remain undetected at far-infrared wavelengths. Deep photometric observations using the Herschel Space Observatory
• The Thermal Sunyaev-Zeldovich Effect of Primordial Recombination Radiation
• Multiwavelength Properties of Infrared-Faint Radio Sources Based on Spectral Energy Distribution Analysis