Abstract
ABSTRACT We present an overview and description of the e-MERGE Survey (e-MERLIN Galaxy Evolution Survey) Data Release 1 (DR1), a large program of high-resolution 1.5-GHz radio observations of the GOODS-N field comprising ∼140 h of observations with enhanced-Multi-Element Remotely Linked Interferometer Network (e-MERLIN) and ∼40 h with the Very Large Array (VLA). We combine the long baselines of e-MERLIN (providing high angular resolution) with the relatively closely packed antennas of the VLA (providing excellent surface brightness sensitivity) to produce a deep 1.5-GHz radio survey with the sensitivity (${\sim}1.5\, \mu$ Jy beam−1), angular resolution (0.2–0.7 arcsec) and field-of-view (∼15 × 15 arcmin2) to detect and spatially resolve star-forming galaxies and active galactic nucleus (AGN) at $z$ ≳ 1. The goal of e-MERGE is to provide new constraints on the deep, sub-arcsecond radio sky which will be surveyed by SKA1-mid. In this initial publication, we discuss our data analysis techniques, including steps taken to model in-beam source variability over an ∼20-yr baseline and the development of new point spread function/primary beam models to seamlessly merge e-MERLIN and VLA data in the uv plane. We present early science results, including measurements of the luminosities and/or linear sizes of ∼500 galaxies selected at 1.5 GHz. In combination with deep Hubble Space Telescope observations, we measure a mean radio-to-optical size ratio of re-MERGE/rHST ∼ 1.02 ± 0.03, suggesting that in most high-redshift galaxies, the ∼GHz continuum emission traces the stellar light seen in optical imaging. This is the first in a series of papers that will explore the ∼kpc-scale radio properties of star-forming galaxies and AGN in the GOODS-N field observed by e-MERGE DR1.
Highlights
Optical and near-infrared (NIR) surveys have played a leading role in measuring the integrated star formation history ofC 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society e-MERGE: overview and survey description 1189 significant fraction of the integrated cosmic star formation has taken place in heavily dust-obscured environments, which can be difficult to measure fully with even the deepest optical/near-IR data (e.g. Barger et al 1998; Seymour et al 2008; Hodge et al 2013; Casey, Narayanan & Cooray 2014)
We have been conducting a multitiered survey of the extragalactic sky using the enhanced-Multi-Element Remotely Linked Interferometer Network (e-MERLIN), the UK’s national facility for high angular resolution radio astronomy (Garrington et al, in preparation), along with observations taken with the Very Large Array (VLA). This ongoing project – the eMERLIN Galaxy Evolution Survey (e-MERGE) – exploits the unique combination of the high angular resolution and a large collecting area of e-MERLIN, and the excellent surface brightness sensitivity of the VLA. The combination of these two radio telescopes allows the production of radio maps, which exceed the specifications of either instrument individually, and allows synchrotron emission due to both star formation activity and active galactic nucleus (AGN) to be mapped in the high-redshift Universe
We present a description of our updated e-MERLIN observations of the field, which along with an independent reduction of the Owen (2018) VLA observations and older VLA/MERLIN observations, constitute e-MERGE Data Release 1 (DR1)
Summary
Optical and near-infrared (NIR) surveys have played a leading role in measuring the integrated star formation history of. At 10 GHz, in contrast, the angular resolution of the VLA is θ res ∼ 0.2 arcsec (∼1.5 kpc at = 2), but the FoV shrinks to θ PB ∼ 4.5 arcmin This large (a factor ∼50 ×) reduction in the primary beam area greatly increases the cost of surveying deep fields over enough area to overcome cosmic variance (e.g Murphy et al 2017), given that the positive k-correction in the radio bands means that these observations probe an intrinsically fainter region of the rest-frame radio SEDs of highredshift galaxies to begin with. This ongoing project – the eMERLIN Galaxy Evolution Survey (e-MERGE) – exploits the unique combination of the high angular resolution and a large collecting area of e-MERLIN, and the excellent surface brightness sensitivity of the VLA The combination of these two radio telescopes allows the production of radio maps, which exceed the specifications of either instrument individually, and allows synchrotron emission due to both star formation activity and AGN to be mapped in the high-redshift Universe.
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