The eMERGE Survey – I: Very Large Array 5.5 GHz observations of the GOODS-North Field

Abstract

We present new observations of the GOODS-N field obtained at 5.5 GHz with the Karl G. Jansky Very Large Array (VLA). The central region of the field was imaged to a median r.m.s. of 3 µJy beam −1 with a resolution of 0.5 arcsec. From a 14-arcmin diameter region we extracted a sample of 94 radio sources with signal-to-noise ratio greater than 5. Near-IR identifications are available for about ∼88 percent of the radio sources. We used different multi-band diagnostics to separate active galactic nuclei (AGN), both radiatively efficient and inefficient, from star-forming galaxies. From our analysis, we find that about 80 percent of our radio-selected sample is AGNdominated, with the fraction raising to 92 percent when considering only the radio sources with redshift > 1.5. This large fraction of AGN-dominated radio sources at very low flux densities (the median flux density at 5.5 GHz is 42 µJy), where star-forming galaxies are expected to dominate, is somewhat surprising and at odds with other results. Our interpretation is that both the frequency and angular resolution of our radio observations strongly select against radio sources whose brightness distribution is diffuse on scale of several kpc. Indeed, we find that the median angular sizes of the AGN-dominated sources is around 0.2-0.3 arcsec against 0.8 arcsec for star-forming galaxies. This highlights the key role that high frequency radio observations can play in pinpointing AGN-driven radio emission at µJy levels. This work is part of the eMERGE legacy project.

The CO Luminosity Density at High-z (COLDz) Survey: A Sensitive, Large-area Blind Search for Low-J CO Emission from Cold Gas in the Early Universe with the Karl G. Jansky Very Large Array

“…The measured flux is compatible with the previously reported flux of 0.17±0.04 Jy km s −1 (Walter et al 2012). It is detected by the 5.5 GHz eMERGE survey with a flux of 14±3 μJy (Guidetti et al 2017) but is not detected at 1.4 GHz (Morrison et al 2010). This source is also detected at 850 μm with a significance of 7.1σ and a flux of 5.9±1.3 mJy (Geach et al 2017).…”

“…It is detected by the 5.5 GHz eMERGE survey with a flux of 9.6±1.7 μJy (Guidetti et al 2017). Its line flux is Figure 5.…”

A Census of Early-phase High-mass Star Formation in the Central Molecular Zone

“…At least one of these sources, C96, presents a double-lobe morphology, which may suggest radio lobes associated with AGNs. A recent VLA 5.5 GHz survey of the GOODS-North field detected 94 sources (including both star forming galaxies and AGNs) in an area of 150 arcmin 2 (Guidetti et al 2017), and 3 of them are above the flux threshold of 0.56 mJy (corresponding to five times the median rms of our observations). If this detection rate is representative for background sources of extragalactic origins, in the area of 1100 arcmin 2 covered by our observations, 22 extragalactic sources are expected.…”

An insight into the extragalactic transient and variable microJy radio sky across multiple decades

“…As shown in Figure 7, the VLA1996 data does not show the compact component which has appeared in the JVLA2011 epoch. The peak radio luminosity from the 2012 JVLA 5.5 GHz observations of Guidetti et al (2017) is 5.67 × 10 20 W Hz −1 and the spectral index of −0.71. This is a typical luminosity for core-collapse radio supernovae, which can range between 5 × 10 19 and 1.3 × 10 22 W Hz −1 (Weiler et al 2002).…”