The accretion history of the universe with the SKA

Jarvis, Matt J.; Rawlings, Steve

doi:10.1016/j.newar.2004.09.006

Cited by 93 publications

(102 citation statements)

References 75 publications

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“…Largely for these reasons, the cause of the upturn in the observed (Euclideannormalized) radio counts at ∼1 mJy was long debated in the literature (e.g., Georgakakis et al 1999;Gruppioni et al 1999;Jarvis & Rawlings 2004;Cowie et al 2004;Huynh et al 2005;Afonso et al 2005;Simpson et al 2006). The popular interpretation for years was that star-forming galaxies dominated the submilliJansky radio population.…”

Section: Introductionmentioning

confidence: 99%

The VLA-COSMOS 3 GHz Large Project: Multiwavelength counterparts and the composition of the faint radio population

Smolčić

Delvecchio

Zamorani

et al. 2017

A&A

171

255

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We study the composition of the faint radio population selected from the Karl G. Jansky Very Large Array Cosmic Evolution Survey (VLA-COSMOS) 3 GHz Large Project, which is a radio continuum survey performed at 10 cm wavelength. The survey covers a 2.6 square degree area with a mean rms of ∼2.3 µJy/beam, cataloging 10 830 sources above 5σ, and enclosing the full 2 square degree COSMOS field. By combining these radio data with optical, near-infrared (UltraVISTA), and mid-infrared (Spitzer/IRAC) data, as well as X-ray data (Chandra), we find counterparts to radio sources for ∼93% of the total radio sample reaching out to z 6; these sources are found in the unmasked areas of the COSMOS field, i.e., those not affected by saturated or bright sources in the optical to near-infrared (NIR) bands. We further classify the sources as star-forming galaxies or AGN based on various criteria, such as X-ray luminosity; observed mid-infrared color; UV-far-infrared spectral energy distribution; rest-frame, near-UV optical color that is corrected for dust extinction; and radio excess relative to that expected from the star formation rate of the hosts. We separate the AGN into subsamples dominated by low-to-moderate and moderate-to-high radiative luminosity AGN, i.e., candidates for highredshift analogs to local low-and high-excitation emission line AGN, respectively. We study the fractional contributions of these subpopulations down to radio flux levels of ∼11 µJy at 3 GHz (or ∼20 µJy at 1.4 GHz assuming a spectral index of -0.7). We find that the dominant fraction at 1.4 GHz flux densities above ∼200 µJy is constituted of low-to-moderate radiative luminosity AGN. Below densities of ∼100 µJy the fraction of star-forming galaxies increases to ∼60%, followed by the moderate-to-high radiative luminosity AGN (∼20%) and low-to-moderate radiative luminosity AGN (∼20%). Based on this observational evidence, we extrapolate the fractions down to sensitivities of the Square Kilometer Array (SKA). Our estimates suggest that at the faint flux limits to be reached by the (Wide, Deep, and UltraDeep) SKA1 surveys, a selection based only on radio flux limits can provide a simple tool to efficiently identify samples highly (>75%) dominated by star-forming galaxies.

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Section: Introductionmentioning

confidence: 99%

The VLA-COSMOS 3 GHz Large Project: Multiwavelength counterparts and the composition of the faint radio population

Smolčić

Delvecchio

Zamorani

et al. 2017

A&A

171

255

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“…Hopkins et al 1998). However, a growing number of studies are finding that lower luminosity AGN, both radio-loud and weakly radio emitting sources (radio-loud and radio-quiet AGN respectively), make a significant contribution to the sub-mJy population (Jarvis & Rawlings 2004;Huynh et al 2008;Seymour et al 2008;Smolčić et al 2008;Padovani et al 2009Padovani et al , 2011Bonzini et al 2013).…”

Section: Introductionmentioning

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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“…This raises the question of whether a significant population of apparently fainter USS sources either at even higher redshifts and/or with lower AGN power is being missed by these surveys. At sub-mJy levels the issue could actually become more complex, as the population mix of radio sources changes dramatically from that observed above a few mJy, with an increasingly large contribution from the evolving star-forming galaxy population (e.g., Jarvis & Rawlings 2004;Afonso et al 2005;Simpson et al 2006;Smolčić et al 2008;Wilman et al 2008). With the recent appearance of sensitive low-frequency radio facilities such as the Giant Metrewave Radio Telescope (GMRT), and with the Low Frequency Array (LOFAR) being commissioned, it has become viable to extend the search for and subsequent study of USS sources to the μJy regime (e.g., Bondi et al 2007;Owen et al 2009;Afonso et al 2009;Ibar et al 2009).…”

Section: Introductionmentioning

confidence: 99%

ULTRA STEEP SPECTRUM RADIO SOURCES IN THE LOCKMAN HOLE:SERVSIDENTIFICATIONS AND REDSHIFT DISTRIBUTION AT THE FAINTEST RADIO FLUXES

Afonso

Bizzocchi

Ibar

et al. 2011

ApJ

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Ultra steep spectrum (USS) radio sources have been successfully used to select powerful radio sources at high redshifts (z 2). Typically restricted to large-sky surveys and relatively bright radio flux densities, it has gradually become possible to extend the USS search to sub-mJy levels, thanks to the recent appearance of sensitive lowfrequency radio facilities. Here a first detailed analysis of the nature of the faintest USS sources is presented. By using Giant Metrewave Radio Telescope and Very Large Array radio observations of the Lockman Hole at 610 MHz and 1.4 GHz, a sample of 58 USS sources, with 610 MHz integrated fluxes above 100 μJy, is assembled. Deep infrared data at 3.6 and 4.5 μm from the Spitzer Extragalactic Representative Volume Survey (SERVS) are used to reliably identify counterparts for 48 (83%) of these sources, showing an average total magnitude of [3.6] AB = 19.8 mag. Spectroscopic redshifts for 14 USS sources, together with photometric redshift estimates, improved by the use of the deep SERVS data, for a further 19 objects, show redshifts ranging from z = 0.1 to z = 2.8, peaking at z ∼ 0.6 and tailing off at high redshifts. The remaining 25 USS sources, with no redshift estimate, include the faintest [3.6] magnitudes, with 10 sources undetected at 3.6 and 4.5 μm (typically [3.6] 22-23 mag from local measurements), which suggests the likely existence of higher redshifts among the sub-mJy USS population. The comparison with the Square Kilometre Array Design Studies Simulated Skies models indicates that Fanaroff-Riley type I radio sources and radio-quiet active galactic nuclei may constitute the bulk of the faintest USS population, and raises the possibility that the high efficiency of the USS technique for the selection of high-redshift sources remains even at the sub-mJy level.

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The accretion history of the universe with the SKA

Cited by 93 publications

References 75 publications

The VLA-COSMOS 3 GHz Large Project: Multiwavelength counterparts and the composition of the faint radio population

The VLA-COSMOS 3 GHz Large Project: Multiwavelength counterparts and the composition of the faint radio population

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

ULTRA STEEP SPECTRUM RADIO SOURCES IN THE LOCKMAN HOLE:SERVSIDENTIFICATIONS AND REDSHIFT DISTRIBUTION AT THE FAINTEST RADIO FLUXES

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