THE VERY LARGE ARRAY 1.4 GHz SURVEY OF THE EXTENDED CHANDRA DEEP FIELD SOUTH: SECOND DATA RELEASE

130

167

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.

Section: Redshiftsmentioning

confidence: 99%

Section: The Sub-mjy Number Countsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Radio-faint AGN: a tale of two populations

Padovani

Bonzini

Kellermann

et al. 2015

130

167

“…A catalogue including sources down to peak flux density of five times the local rms noise has been extracted. A description of the survey strategy and the data reduction details are given in Miller et al (2013). The radio catalogue includes 883 sources.…”

Section: Radio Datamentioning

confidence: 99%

Star formation properties of sub-mJy radio sources

Bonzini

Mainieri

Padovani

et al. 2015

We investigate the star formation properties of ∼ 800 sources detected in one of the deepest radio surveys at 1.4 GHz. Our sample spans a wide redshift range (∼ 0.1 − 4) and about four orders of magnitude in star formation rate (SFR). It includes both star forming galaxies (SFGs) and active galactic nuclei (AGNs), further divided into radio-quiet and radio-loud objects. We compare the SFR derived from the far infrared luminosity, as traced by Herschel, with the SFR computed from their radio emission. We find that the radio power is a good SFR tracer not only for pure SFGs but also in the host galaxies of RQ AGNs, with no significant deviation with redshift or specific SFR. Moreover, we quantify the contribution of the starburst activity in the SFGs population and the occurrence of AGNs in sources with different level of star formation. Finally we discuss the possibility of using deep radio survey as a tool to study the cosmic star formation history.

“…163/177 (92%) of the 5.5 GHz sources have a 1.4 GHz match within 2 arcsec (FWHM of the synthesised beam of the VLA observations). The unmatched 5.5 GHz sources were inspected and four had counterparts in the 1.4 GHz image but weren't in the Miller et al (2013) catalogue. The 1.4 GHz flux density for these sources was measured manually with the MIRIAD task imfit.…”

Section: 4 To 55 Ghz Spectral Indicesmentioning

confidence: 99%

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

Huynh¹,

Bell²,

Hopkins³

et al. 2015

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.