A Search for Missing Radio Sources at $z\gtrsim 4$ Using Lyman Dropouts

Abstract

Using the Lyman Dropout technique, we identify 148 candidate radio sources at $z\gtrsim 4-7$ from the 887.5 MHz Australian Square Kilometer Array Pathfinder (ASKAP) observations of the GAMA23 field. About 112 radio sources are currently known beyond redshift $z\sim 4$. However, simulations predict that hundreds of thousands of radio sources exist in that redshift range, many of which are probably in existing radio catalogues but do not have measured redshifts, either because their optical emission is too faint or because of the lack of techniques that can identify candidate high-redshift radio sources (HzRSs). Our study addresses these issues using the Lyman Dropout search technique. This newly built sample probes radio luminosities that are 1-2 orders of magnitude fainter than known radio-active galactic nuclei (AGN) at similar redshifts, thanks to ASKAP's sensitivity. We investigate the physical origin of radio emission in our sample using a set of diagnostics: (i) radio luminosity at 1.4 GHz, (ii) 1.4 GHz-to-3.4 $\mu$m flux density ratio, (iii) Far-IR detection, (iv) WISE colour, and (v) SED modelling. The radio/IR analysis has shown that the majority of radio emission in the faint and bright end of our sample's 887.5 MHz flux density distribution originates from AGN activity. Furthermore, $\sim 10\%$ of our sample are found to have a 250 $\mu$m detection, suggesting a composite system. This suggests that some high-$z$ radio-AGNs are hosted by SB galaxies, in contrast to low-$z$ radio-AGNs, which are usually hosted by quiescent elliptical galaxies.

arXiv commentAccepted for publication in Monthly Notices of the Royal Astronomical Society

References in corpus (52)

• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• The Eleventh and Twelfth Data Releases of the Sloan Digital Sky Survey: Final Data from SDSS-III
• The Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory
• The Herschel-SPIRE instrument and its in-flight performance
• The Cosmic Evolution Survey (COSMOS) -- Overview
• A luminous quasar at a redshift of z = 7.085
• A Cosmology Calculator for the World Wide Web
• The COSMOS2015 Catalog: Exploring the 1<z<6 Universe with half a million galaxies
• An 800-million-solar-mass black hole in a significantly neutral Universe at redshift 7.5
• Estimating Star Formation Rates from Infrared and Radio Luminosities: The Origin of the Radio-Infrared Correlation
• The First Release COSMOS Optical and Near-IR Data and Catalog
• EMU: Evolutionary Map of the Universe
• Gravitational Lensing Analysis of the Kilo Degree Survey
• Distant Radio Galaxies and their Environments
• A semi-empirical simulation of the extragalactic radio continuum sky for next generation radio telescopes
• The fourth data release of the Kilo-Degree Survey: ugri imaging and nine-band optical-IR photometry over 1000 square degrees
• The CatWISE2020 Catalog
• Resolved Molecular Gas in a Quasar Host Galaxy at Redshift z=6.42
• Discovery of three z>6.5 quasars in the VISTA Kilo-degree Infrared Galaxy (VIKING) survey
• Galaxy And Mass Assembly (GAMA): the G02 field, Herschel-ATLAS target selection and Data Release 3
• Science With The Australian Square Kilometre Array Pathfinder
• The DEIMOS 10k spectroscopic survey catalog of the COSMOS field
• A Sample of 669 Ultra Steep Spectrum Radio Sources to Find High Redshift Radio Galaxies
• HerMES: Far-infrared properties of known AGN in the HerMES fields
• The rapid assembly of an elliptical galaxy of 400 billion solar masses at a redshift of 2.3
• The role of star-formation and AGN in dust heating of z = 0.3-2.8 galaxies - I. Evolution with redshift and luminosity
• The Tiered Radio Extragalactic Continuum Simulation (T-RECS)
• A survey of luminous high-redshift quasars with SDSS and WISE. I. target selection and optical spectroscopy
• Herschel-ATLAS: The far-infrared--radio correlation at z<0.5
• First discoveries of z~6 quasars with the Kilo Degree Survey and VISTA Kilo-Degree Infrared Galaxy survey
• Spectroscopy of Ultra Steep Spectrum Radio Sources
• The first blazar observed at z>6
• Is There a Maximum Star Formation Rate in High-Redshift Galaxies?
• The discovery of a highly accreting, radio-loud quasar at z=6.82
• Discovery of a radio galaxy at z = 5.72
• Calibration of ultraviolet, mid-infrared and radio star formation rate indicators
• Measurements of resonant scattering in the Perseus cluster core with Hitomi SXS
• Cosmological Measurements with Forthcoming Radio Continuum Surveys
• The discovery of a typical radio galaxy at z = 4.88
• Modelling the luminosities and sizes of radio galaxies: radio luminosity function at z = 6
• Radio Detection of VIK J2318$-$3113, the Most Distant Radio-Loud Quasar ($z$=6.44)
• Deep Spitzer observations of infrared-faint radio sources: high-redshift radio-loud AGN?
• Some estimates of the source counts at Planck Surveyor frequencies, using the 9C survey at 15 GHz
• The Near and Mid-infrared photometric properties of known redshift $z\ge 5$ Quasars
• The radio core of the Ultraluminous Infrared Galaxy F00183-7111: watching the birth of a quasar
• Radio galaxies in ZFOURGE/NMBS: no difference in the properties of massive galaxies with and without radio-AGN out to z = 2.25
• Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). III. Discovery of a z = 4.72 Radio Galaxy with Lyman Break Technique
• The GLEAMing of the First Supermassive Black Holes
• A hyper luminous starburst at z=4.72 magnified by a lensing galaxy pair at z=1.48
• Star-Formation in the Ultraluminous Infrared Galaxy F00183-7111
• Herschel-ATLAS/GAMA: What determines the far-infrared properties of radio-galaxies?
• Infrared-Faint Radio Sources in the SERVS deep fields: Pinpointing AGNs at high redshift

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