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The GLEAM 4-Jy (G4Jy) Sample: III. Further host-galaxy identification, and redshift assessment

Sarah V. White, Precious K. Sejake, Kshitij Thorat, Heinz Andernach, Thomas M. O. Franzen, O. Ivy Wong, Anna D. Kapinska, Joseph R. Callingham, Christopher J. Riseley, Nick Seymour, Randall Wayth, Lister Staveley-Smith, Rajan Chhetri, Natasha Hurley-Walker, John Morgan, Paul Hancock, Francesco Massaro, Abigail Garcia-Perez, Ana Jimenez-Gallardo, Harold A. Pena-Herazo

TL;DR

Paper III expands host-galaxy identifications and redshift assessment for the G4Jy sample, enabling a more complete multiwavelength view of bright southern radio sources. The authors compile and verify redshifts by combining newly identified hosts with spectroscopic data, photometric redshifts, and data-mined NED entries, across imaging from MeerKAT, VLASS, RACS, AllWISE, VHS, and optical surveys. They report $0.0<z<3.5699$ with 631 spectroscopic redshifts and 400 photometric redshifts (plus NED-derived redshifts for many sources), and present 127 new host identifications plus revisions to several others, aiming for 100% spectroscopic completeness. They also derive 151-MHz luminosities and linear sizes to characterize the radio properties and discuss implications for AGN evolution and multiwavelength follow-up (Paper IV provides deeper analysis).

Abstract

In this paper we present 127 new host-galaxy identifications for G4Jy sources (S_151MHz > 4 Jy), based on radio images from MeerKAT, the Very Large Array Sky Survey (VLASS), and the Rapid ASKAP (Australian Square Kilometre Array Pathfinder) Continuum Survey (RACS). This includes identifications that result from visual inspection of radio contours on K_s-band images, as opposed to the AllWISE-W1 images that were used for the original set of overlays when defining the G4Jy Sample (Papers I and II). Our aim is to achieve 100 per cent spectroscopic completeness for the sample, where all of the spectroscopy is available in digital form online. For now, we have gathered (i) digital optical spectroscopy for 34 per cent of the sample, (ii) photometric redshifts for an additional 21 per cent of the sample, and (iii) further redshifts found through the NASA/IPAC Extragalactic Database (but not recently verified). Our assessment of the redshifts includes visual inspection of all of the digital spectroscopy, and re-fitting redshift templates where necessary. The resulting redshift range is (currently) 0.0 < z < 3.6. We also present 151-MHz luminosities and linear sizes for the G4Jy Sample, based on initial analysis.

The GLEAM 4-Jy (G4Jy) Sample: III. Further host-galaxy identification, and redshift assessment

TL;DR

Paper III expands host-galaxy identifications and redshift assessment for the G4Jy sample, enabling a more complete multiwavelength view of bright southern radio sources. The authors compile and verify redshifts by combining newly identified hosts with spectroscopic data, photometric redshifts, and data-mined NED entries, across imaging from MeerKAT, VLASS, RACS, AllWISE, VHS, and optical surveys. They report with 631 spectroscopic redshifts and 400 photometric redshifts (plus NED-derived redshifts for many sources), and present 127 new host identifications plus revisions to several others, aiming for 100% spectroscopic completeness. They also derive 151-MHz luminosities and linear sizes to characterize the radio properties and discuss implications for AGN evolution and multiwavelength follow-up (Paper IV provides deeper analysis).

Abstract

In this paper we present 127 new host-galaxy identifications for G4Jy sources (S_151MHz > 4 Jy), based on radio images from MeerKAT, the Very Large Array Sky Survey (VLASS), and the Rapid ASKAP (Australian Square Kilometre Array Pathfinder) Continuum Survey (RACS). This includes identifications that result from visual inspection of radio contours on K_s-band images, as opposed to the AllWISE-W1 images that were used for the original set of overlays when defining the G4Jy Sample (Papers I and II). Our aim is to achieve 100 per cent spectroscopic completeness for the sample, where all of the spectroscopy is available in digital form online. For now, we have gathered (i) digital optical spectroscopy for 34 per cent of the sample, (ii) photometric redshifts for an additional 21 per cent of the sample, and (iii) further redshifts found through the NASA/IPAC Extragalactic Database (but not recently verified). Our assessment of the redshifts includes visual inspection of all of the digital spectroscopy, and re-fitting redshift templates where necessary. The resulting redshift range is (currently) 0.0 < z < 3.6. We also present 151-MHz luminosities and linear sizes for the G4Jy Sample, based on initial analysis.

Paper Structure

This paper contains 29 sections, 25 figures, 7 tables.

Table of Contents

  1. Introduction
  2. Paper outline
  3. Data
  4. Radio data
  5. Mid-infrared data
  6. Near-infrared data
  7. Optical spectroscopy
  8. Host-galaxy identification
  9. New identifications
  10. A tentative identification
  11. G4Jy sources that remain unidentified
  12. Revised identifications
  13. Cross-check with Massaro2023
  14. Cross-check with Maselli2022Maselli2024
  15. Cases of mistaken identities
  16. ...and 14 more sections

Figures (25)

  • Figure 1: An example overlay showing how different sets of radio contours (SUMSS [843 MHz] in blue, RACS-low1 [888 MHz] in purple, and MeerKAT [1300 MHz] in cyan) were used to assess the morphology of G4Jy 1444, with the respective beam-sizes of the different radio surveys shown in the upper right-hand corner. The underlying, inverted-greyscale image is a $K$-band image from VHS, with green plusses ('+') marking VHS catalogue positions within 3 arcmin of the radio-centroid position (red hexagon). This enabled us to identify the appropriate host galaxy of the radio emission (white '+'), which was followed by thorough checks against the literature (Section \ref{['sec:new_IDs']}) before being included in the updated G4Jy catalogue.
  • Figure 1: Continued -- Overlays of radio contours [and catalogue positions] from SUMSS/NVSS (blue), RACS-low1 (purple), TGSS (yellow) and MeerKAT/VLASS (cyan) on inverted grey-scale $K$-band images from VHS (unless otherwise stated). A white '+' marks the position of the galaxy hosting the radio emission.
  • Figure 1: Continued -- Overlays of radio contours [and catalogue positions] from SUMSS/NVSS (blue), RACS-low1 (purple), TGSS (yellow) and MeerKAT/VLASS (cyan) on inverted grey-scale $K$-band images from VHS (unless otherwise stated). A white '+' marks the position of the galaxy hosting the radio emission.
  • Figure 1: Continued -- Overlays of radio contours [and catalogue positions] from SUMSS/NVSS (blue), RACS-low1 (purple), TGSS (yellow) and MeerKAT/VLASS (cyan) on inverted grey-scale $K$-band images from VHS (unless otherwise stated). A white '+' marks the position of the galaxy hosting the radio emission.
  • Figure 1: Continued -- Overlays of radio contours [and catalogue positions] from SUMSS/NVSS (blue), RACS-low1 (purple), TGSS (yellow) and MeerKAT/VLASS (cyan) on inverted grey-scale $K$-band images from VHS (unless otherwise stated). A white '+' marks the position of the galaxy hosting the radio emission.
  • ...and 20 more figures