J/MNRAS/519/4902 Radio sources at 6~>z~>4 with ASKAP in G23 (Shobhana+, 2023)
A search for missing radio sources at z ~> 4 using Lyman dropouts.
Shobhana D., Norris R.P., Filipovic M.D., Barnes L.A., Hopkins A.M.,
Prandoni I., Brown M.J.I., Shabala S.S.
<Mon. Not. R. Astron. Soc. 519, 4902-4919 (2023)>
=2023MNRAS.519.4902S 2023MNRAS.519.4902S (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies ; Active gal. nuclei ; QSOs ; Radio sources ; Redshifts ;
Spectroscopy ; Photometry ; Cross identifications ;
Positional data ; Optical ; Infrared ; References
Keywords: galaxies: active - galaxies: high-redshift - galaxies: starburst -
radio continuum: galaxies
Abstract:
Using the Lyman Dropout technique, we identify 148 candidate radio
sources at z ~> 4-7 from the 887.5 MHz Australian Square Kilometre
Array Pathfinder (ASKAP) observations of the GAMA23 field. About 112
radio sources are currently known beyond redshift z ∼ 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 µm 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, ∼10 per cent of our sample are found to have a
250 µm 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.
Description:
Motivated by the challenge of finding missing HzRSs, we make use of a
search technique different from conventional radio based techniques,
the Lyman Dropout technique to identify potential HzRSs at z ~> 4-7 in
the G23 field. We cross-match the used 887.5 MHz radio continuum
data of the G23 field procuded by ASKAP EMU observations with the KiDS
and the VIKING DR5 & CATWISE2020 catalogues (i.e section 2). The
results provide a selection of 146 radio source candidates as
presented in table7.dat including KiDS/VIKING and WISE W1 photometry
as well askap fluxes (i.e section 3). Also, we show published
radio-AGNs known at redshift z ~> 4 with their fluxes at 1.4 GHz in
tablea1.dat and tablea2.dat.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table7.dat 111 146 *z ~> 4-6 sample radio properties from ASKAP and
optical/IR phot. from KiDS, VIKING and CATWISE
tablea1.dat 222 112 List of published radio-AGNs known at redshift
z => 4
tablea2.dat 222 33 *Visually cross-matching SDSS DR12, FIRST and
NVSS catalogs to obtain sources at z ~> 4
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Note on table7.dat: Missing optical magnitudes indicate non-detection in that
respective filter. The missing WISE magnitudes (W1) indicate no counterpart
within 2 arcsec of the KiDS position.
Note on tablea2.dat: In each case the SDSS spectrum has been checked for
supporting evidence of the redshift, such as the Lyman break or other spectral
features.
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See also:
J/MNRAS/494/789 : NIR and MIR photometry of known z≥5 quasars (Ross+, 2020)
J/MNRAS/474/3875 : Galaxy And Mass Assembly (GAMA): DR3 (Baldry+, 2018)
J/MNRAS/455/2731 : Radio galaxies in ZFOURGE/NMBS (Rees+, 2016)
J/MNRAS/379/1442 : Multifrequency observations of 9C sources (Waldram+, 2007)
J/A+A/634/A1 : NGC 1068 GRAVITY reconstructed image (GRAVITY+, 2020)
J/ApJ/858/77 : DEIMOS 10K spectroscopic survey in COSMOS field
(Hasinger+, 2018)
J/ApJ/847/136 : Hβ to N2 line fluxes of nearby galaxies (Brown+, 2017)
J/ApJ/819/24 : z>4.5 QSOs with SDSS and WISE. I. Opt. spectra (Wang+, 2016)
J/ApJ/784/9 : SCUBA-2 high-redshift galaxies sample (Barger+, 2014)
J/ApJ/586/794 : Multiwavelength luminosities of galaxies (Bell, 2003)
J/ApJS/224/24 : The COSMOS2015 catalog (Laigle+, 2016)
J/A+AS/143/303 : Ultra steep spectrum radio sources catalog (De Breuck+ 2000)
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
VII/282 : T-RECS. Tiered Radio Extragalactic Continuum Simulation
(Bonaldi+, 2018)
V/147 : The SDSS Photometric Catalogue, Release 12 (Alam+, 2015)
II/365 : The CatWISE2020 catalog (updated version 28-Jan-2021)
(Marocco+, 2021)
II/284 : COSMOS Multi-Wavelength Photometry Catalog (Capak+, 2007)
Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
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1- 23 A23 --- n_ASKAP Notes for redshift subsamples (1)
25- 27 I3 --- Index Redshift subsample index number (Index)
29- 42 A14 --- ASKAP ASKAP designation name as JHHMMSS-DDMMSS (ASKAP)
44- 51 F8.4 deg RAdeg Right ascension (J2000) (RA)
53- 60 F8.4 deg DEdeg Declination (J2000) (DEC)
62- 67 F6.3 mJy S887.5 ASKAP flux density at 887.5 MHz coresponds to
radio continuum data of the G23 field (S887.5)
69- 74 F6.3 mag umag ? KiDs DR4.1 u optical AB magnitude from Kuijken
et al. 2019A&A...625A...2K 2019A&A...625A...2K (Mag_u)
76- 82 F7.4 mag gmag ? KiDs DR4.1 g optical AB magnitude from Kuijken
et al. 2019A&A...625A...2K 2019A&A...625A...2K (Mag_g)
84- 89 F6.3 mag rmag KiDs DR4.1 r optical AB magnitude from Kuijken
et al. 2019A&A...625A...2K 2019A&A...625A...2K (Mag_r)
91- 96 F6.3 mag imag KiDs DR4.1 i optical AB magnitude from Kuijken
et al. 2019A&A...625A...2K 2019A&A...625A...2K (Mag_i)
98-104 F7.4 mag Zmag ? VIKING Z NIR AB magnitude from Wright et al.
2019A&A...625A...2K 2019A&A...625A...2K, Cat. II/383 (Mag_Z)
106-111 F6.3 mag W1mag ? WISE W1 MIR magnitude in vega system from
CATWISE2020 of Marocco et al.
2021ApJS..253....8M 2021ApJS..253....8M, Cat. II/365 (W1)
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Note (1): Redshift subsamples are as follows:
z∼4 Sample (g dropouts) = 117 sources in our sample
z∼5 Sample (r dropouts) = 14 sources in our sample
z∼6 Sample (i dropouts) = 15 sources in our sample
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Byte-by-byte Description of file: tablea1.dat tablea2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Index Index raw number of the radio-AGN (Index)
5- 30 A26 --- Name The radio-AGN name (Name)
32- 40 F9.5 deg RAdeg Right ascension (J2000) (RA)
42- 50 F9.5 deg DEdeg Declination (J2000) (DEC)
52- 57 F6.4 --- z Redshift (z)
59- 66 F8.3 mJy S1.4 ? Flux density at 1.4 GHz frequency (S1.4)
68- 94 A27 --- Class Object class (class) (1)
96-120 A25 --- Aut Author's names of the reference paper (Ref)
122-140 A19 --- Bib Bibcode of the reference paper
142-162 A21 --- Cat Vizier catalog of the reference paper
164-222 A59 --- n_Bib Remarks of the reference paper
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Note (1): The object classes are as follows:
Infrared Faint Radio Source = IFRS class of radio-loud AGN,
3 sources in our samples
blazar = Blazar AGN, 11 sources in our sample
radio galaxy = Radio galaxy AGN,
14 sources in our samples
radio quasar = Radio quasar AGN,
84 sources in our samples
galaxy = 3 sources in our samples
hi-z cluster = 1 source in our samples
qso = Quasi-stellar object, 29 sources
in our samples
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History:
From electronic version of the journal
(End) Luc Trabelsi [CDS] 09-Feb-2026