High-resolution studies of radio sources in the<i>Hubble Deep</i>and<i>Flanking Fields</i>

We study the Extended Chandra Deep Field South (E-CDFS) Very Large Array sample, which reaches a flux density limit at 1.4 GHz of 32.5 µJy at the field centre and redshift ∼ 4, and covers ∼ 0.3 deg 2 . Number counts are presented for the whole sample while the evolutionary properties and luminosity functions are derived for active galactic nuclei (AGN). The faint radio sky contains two totally distinct AGN populations, characterised by very different evolutions, luminosity functions, and Eddington ratios: radio-quiet (RQ)/radiative-mode, and radioloud/jet-mode AGN. The radio power of RQ AGN evolves ∼ ∝ (1 + z) 2.5 , similarly to star-forming galaxies, while the number density of radio-loud ones has a peak at z ∼ 0.5 and then declines at higher redshifts. The number density of radioselected RQ AGN is consistent with that of X-ray selected AGN, which shows that we are sampling the same population. The unbiased fraction of radiativemode RL AGN, derived from our own and previously published data, is a strong function of radio power, decreasing from ∼ 0.5 at P 1.4GHz ∼ 10 24 W Hz −1 to ∼ 0.04 at P 1.4GHz ∼ 10 22 W Hz −1 . Thanks to our enlarged sample, which now includes ∼ 700 radio sources, we also confirm and strengthen our previous results on the source population of the faint radio sky: star-forming galaxies start to dominate the radio sky only below ∼ 0.1 mJy, which is also where radio-quiet AGN overtake radio-loud ones.

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“…But many µJy sources are typically an arcsecond in size, so are partially resolved with a one or two arcsecond beam (e.g. Muxlow et al 2005).…”

Section: The Sub-mjy Number Countsmentioning

confidence: 99%

Radio-faint AGN: a tale of two populations

Padovani

Bonzini

Kellermann

et al. 2015

Mon. Not. R. Astron. Soc.

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“…Prandoni et al 2001) so we include it in our source count derivation, but we note it is derived from a brighter sample than our work (S1.4GHz > 0.4 mJy). The Muxlow et al (2005) sample goes to sub-100-µJy levels, but it comes from high resolution MERLIN and VLA imaging which may miss low surface brightness galaxies. We note that the resolution bias is negligible if the Muxlow et al (2005) size distribution is assumed.…”

Section: Source Size and Resolution Biasmentioning

confidence: 99%

“…The Muxlow et al (2005) sample goes to sub-100-µJy levels, but it comes from high resolution MERLIN and VLA imaging which may miss low surface brightness galaxies. We note that the resolution bias is negligible if the Muxlow et al (2005) size distribution is assumed.…”

Section: Source Size and Resolution Biasmentioning

confidence: 99%

The ATLAS 5.5 GHz survey of the extendedChandraDeep Field South: the second data release

Huynh¹,

Bell²,

Hopkins³

et al. 2015

Mon. Not. R. Astron. Soc.

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We present a new image of the 5.5 GHz radio emission from the extended Chandra Deep Field South. Deep radio observations at 5.5 GHz were obtained in 2010 and presented in the first data release. A further 76 hours of integration has since been obtained, nearly doubling the integration time. This paper presents a new analysis of all the data. The new image reaches 8.6 µJy rms, an improvement of about 40% in sensitivity. We present a new catalogue of 5.5 GHz sources, identifying 212 source components, roughly 50% more than were detected in the first data release. Source counts derived from this sample are consistent with those reported in the literature for S 5.5GHz > 0.1 mJy but significantly lower than published values in the lowest flux density bins (S 5.5GHz < 0.1 mJy), where we have more detected sources and improved statistical reliability. The 5.5 GHz radio sources were matched to 1.4 GHz sources in the literature and we find a mean spectral index of −0.35 ± 0.10 for S 5.5GHz > 0.5 mJy, consistent with the flattening of the spectral index observed in 5 GHz sub-mJy samples. The median spectral index of the whole sample is α med = −0.58, indicating that these observations may be starting to probe the star forming population. However, even at the faintest levels (0.05 < S 5.5GHz < 0.1 mJy), 39% of the 5.5 GHz sources have flat or inverted radio spectra. Four flux density measurements from our data, across the full 4.5 to 6.5 GHz bandwidth, are combined with those from literature and we find 10% of sources (S 5.5GHz 0.1 mJy) show significant curvature in their radio spectral energy distribution spanning 1.4 to 9 GHz.

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“…GOODS-N was observed previously at 1.4 GHz (Richards 2000;Muxlow et al 2005;Morrison et al 2010) and 8.5 GHz (Richards et al 1998) with the Karl G. Jansky Very Large Array (VLA). Preliminary observations at 5.5 GHz were obtained as part of the e-MERLIN commissioning (Guidetti et al 2013).…”

mentioning

confidence: 99%

“…Gruppioni et al 1999;Muxlow et al 2005;Simpson et al 2006;Bondi et al 2007;Seymour et al 2008;Smolčić et al 2009;Bonzini et al 2013;Smolčić et al 2017a). The unexpected detection in deep radio surveys of large numbers of RE-AGN (e.g Heckman & Best 2014), emitting over a wide range of the electromagnetic spectrum, from mid-IR (MIR) to X-rays, but typically radio-quiet, has opened the exciting prospect of studying the whole AGN population through deep radio surveys.…”

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confidence: 99%

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

Guidetti

Bondì

Prandoni

et al. 2017

Monthly Notices of the Royal Astronomical Society

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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.

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High-resolution studies of radio sources in theHubble DeepandFlanking Fields

Cited by 151 publications

References 54 publications

Radio-faint AGN: a tale of two populations

Radio-faint AGN: a tale of two populations

The ATLAS 5.5 GHz survey of the extendedChandraDeep Field South: the second data release

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

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