ASKAP commissioning observations of the GAMA 23 field

Edward N. Taylor ,Ian Heywood ,Maxim Voronkov ,G. Gürkan ,L. Wang,J. D. Collier,Matt S. Owers ,J. R. Allison,Ray Norris ,D. A. Leahy ,Kevin A. Pimbblet ,J. Liske,N. Seymour,Ángel R. López-Sánchez ,A. M. Hopkins,Craig S. Anderson ,J. Marvil,D. McConnell,Joss Bland-Hawthorn ,Wasim Raja ,Simon P. Driver ,Lisa Harvey-Smith ,M. J. I. Brown,Sarah Brough ,Benne W. Holwerda ,M. E. Bell ,Amanda J. Moffett ,Maciej Bilicki

doi:10.1017/pasa.2019.16

Abstract

AbstractWe have observed the G23 field of the Galaxy AndMass Assembly (GAMA) survey using the Australian Square Kilometre Array Pathfinder (ASKAP) in its commissioning phase to validate the performance of the telescope and to characterise the detected galaxy populations. This observation covers ~48 deg2 with synthesised beam of 32.7 arcsec by 17.8 arcsec at 936MHz, and ~39 deg2 with synthesised beam of 15.8 arcsec by 12.0 arcsec at 1320MHz. At both frequencies, the root-mean-square (r.m.s.) noise is ~0.1 mJy/beam. We combine these radio observations with the GAMA galaxy data, which includes spectroscopy of galaxies that are i-band selected with a magnitude limit of 19.2. Wide-field Infrared Survey Explorer (WISE) infrared (IR) photometry is used to determine which galaxies host an active galactic nucleus (AGN). In properties including source counts, mass distributions, and IR versus radio luminosity relation, the ASKAP-detected radio sources behave as expected. Radio galaxies have higher stellar mass and luminosity in IR, optical, and UV than other galaxies. We apply optical and IR AGN diagnostics and find that they disagree for ~30% of the galaxies in our sample. We suggest possible causes for the disagreement. Some cases can be explained by optical extinction of the AGN, but for more than half of the cases we do not find a clear explanation. Radio sources aremore likely (~6%) to have an AGN than radio quiet galaxies (~1%), but the majority of AGN are not detected in radio at this sensitivity.

Highlights

The moderate redshift Universe (0.1 z 1) has in the past decade become accessible for large surveys of galaxies at optical and IR wavelengths
The Evolutionary Map of the Universe (EMU) (Norris et al, 2011) is a wide-field radio continuum survey planned for the new Australian Square Kilometre Array Pathfinder (ASKAP) telescope (Johnston et al, 2008)
We have processed ASKAP commissioning observations of the Galaxy And Mass Assembly (GAMA) G23 field in two frequency bands centred at 936 MHz and 1320 MHz, and have demonstrated that ASKAP produces excellent image quality, allowing identification of radio sources down to ∼1 mJy with positions accurate to ∼ 5

Summary

Introduction

The moderate redshift Universe (0.1 z 1) has in the past decade become accessible for large surveys of galaxies at optical and IR wavelengths. Most radio surveys have sampled different populations from these, mainly because most bright radio sources represent the synchrotron emission from active galactic nuclei (AGN) (e.g. Heckman & Best 2014), which are relatively uncommon in optical and IR surveys. This is changing, as the largest area radio surveys are reaching the sensitivity where they are dominated by low-redshift star forming galaxies (SFG) (e.g. Norris 2017), in which the radio emission is powered by star formation processes. The Evolutionary Map of the Universe (EMU) (Norris et al, 2011) is a wide-field radio continuum survey planned for the new Australian Square Kilometre Array Pathfinder (ASKAP) telescope (Johnston et al, 2008). We report early EMU observations, taken during the commissioning phase of ASKAP, with the goal of characterizing the galaxy and radio galaxy samples

Objectives

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Discussion

Conclusion