Deep, wide-field, global VLBI observations of the<i>Hubble</i>deep field north (HDF-N) and flanking fields (HFF)

Chi, Seungyoup; Barthel, Pieter; Garrett, M. A.

doi:10.1051/0004-6361/201220783

Cited by 39 publications

(97 citation statements)

References 54 publications

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“…Although limited in a statistical sense, our findings are supported by similar results by Herrera Ruiz et al (2016), who found VLBI cores in RQ QSOs in the COSMOS field. Further support comes from the 12 RQQ sources (according to the classification of Bonzini et al 2013) observed by Chi et al (2013), four of which were detected with VLBI.…”

Section: Discussionmentioning

confidence: 95%

Compact radio cores in radio-quiet active galactic nuclei

Maini

Prandoni

Norris

et al. 2016

A&A

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Context. The mechanism of radio emission in radio-quiet (RQ) active galactic nuclei (AGNs) is still debated and might arise from the central AGN, from star formation activity in the host, or from either of these sources. A direct detection of compact and bright radio cores embedded in sources that are classified as RQ can unambiguously determine whether a central AGN significantly contributes to the radio emission. Aims. We search for compact, high-surface-brightness radio cores in RQ AGNs that are caused unambiguously by AGN activity. Methods. We used the Australian Long Baseline Array to search for compact radio cores in four RQ AGNs located in the Extended Chandra Deep Field South (ECDFS). We also targeted four radio-loud (RL) AGNs as a control sample. Results. We detected compact and bright radio cores in two AGNs that are classified as RQ and in one that is classified as RL. Two RL AGNs were not imaged because the quality of the observations was too poor. Conclusions. We report on a first direct evidence of radio cores in RQ AGNs at cosmological redshifts. Our detections show that some of the sources that are classified as RQ contain an active AGN that can contribute significantly (∼50% or more) to the total radio emission.

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Section: Discussionmentioning

confidence: 95%

Compact radio cores in radio-quiet active galactic nuclei

Maini

Prandoni

Norris

et al. 2016

A&A

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“…Ten of them were previously detected with VLBI at 1.4 GHz by Chi et al (2013). VLBI cores are found to account for, on average, 30 percent of the total 1.6 GHz emission.…”

Section: 4 Ghz Vlbi Detectionsmentioning

confidence: 94%

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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“…We show the radio sources for which the submillimeter flux measurement at the radio position has a signal-to-noise ratio (S/N) ≥ 2 σ as circles with 1 σ uncertainties, and we show S/N< 2 σ as circles at the 2 σ limit with downward pointing arrows. We use colors to denote the sources classified as either compact (Chi et al 2013;cyan) or extended (Momjian et al 2010; red) from VLBI data. Finally, we denote with green shading the factor of two range found by Barger et al (2014) over which we expect the SFRs derived from the submillimeter fluxes to be consistent with the SFRs derived from the radio power, assuming the FIR-radio correlation with the radio emission dominantly powered by star formation.…”

Section: Vlbimentioning

confidence: 99%

A Submillimeter Perspective on the Goods Fields. Ii. The High Radio Power Population in the Goods-N

Barger

Cowie

Owen

et al. 2017

ApJ

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We use ultradeep 20 cm data from the Karl G. Jansky Very Large Array and 850 µm data from SCUBA-2 and the Submillimeter Array of an 124 arcmin 2 region of the Chandra Deep Field-north to analyze the high radio power (P 20 cm > 10 31 erg s −1 Hz −1 ) population. We find that 20 (42±9%) of the spectroscopically identified z > 0.8 sources have consistent star formation rates (SFRs) inferred from both submillimeter and radio observations, while the remaining sources have lower (mostly undetected) submillimeter fluxes, suggesting that active galactic nucleus (AGN) activity dominates the radio power in these sources. We develop a classification scheme based on the ratio of submillimeter flux to radio power versus radio power and find that it agrees with AGN and star-forming galaxy classifications from Very Long Baseline Interferometry. Our results provide support for an extremely rapid drop in the number of high SFR galaxies above about a thousand solar masses per year (Kroupa initial mass function) and for the locally determined relation between X-ray luminosity and radio power for star-forming galaxies applying at high redshifts and high radio powers. We measure far-infrared (FIR) luminosities and find that some AGNs lie on the FIR-radio correlation, while others scatter below. The AGNs that lie on the correlation appear to do so based on their emission from the AGN torus. We measure a median radio size of 1. 0 ± 0.3 for the star-forming galaxies. The radio sizes of the star-forming galaxies are generally larger than those of the AGNs.

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Deep, wide-field, global VLBI observations of theHubbledeep field north (HDF-N) and flanking fields (HFF)

Cited by 39 publications

References 54 publications

Compact radio cores in radio-quiet active galactic nuclei

Compact radio cores in radio-quiet active galactic nuclei

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

A Submillimeter Perspective on the Goods Fields. Ii. The High Radio Power Population in the Goods-N

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