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Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - HerMES: disentangling active galactic nuclei and star formation in the radio source population
AU - Rawlings, J. I.
AU - Page, M. J.
AU - Symeonidis, M.
AU - Bock, J.
AU - Cooray, A.
AU - Farrah, D.
AU - Guo, K.
AU - Hatziminaoglou, E.
AU - Ibar, E.
AU - Oliver, S. J.
AU - Roseboom, I. G.
AU - Scott, Douglas
AU - Seymour, N.
AU - Vaccari, M.
AU - Wardlow, J. L.
PY - 2015/10/1
Y1 - 2015/10/1
N2 - We separate the extragalactic radio source population above ˜50 μJy into active galactic nuclei (AGN) and star-forming sources. The primary method of our approach is to fit the infrared spectral energy distributions (SEDs), constructed using Spitzer/IRAC (Infrared Array Camera) and Multiband Imaging Photometer for Spitzer (MIPS) and Herschel/SPIRE photometry, of 380 radio sources in the Extended Chandra Deep Field-South. From the fitted SEDs, we determine the relative AGN and star-forming contributions to their infrared emission. With the inclusion of other AGN diagnostics such as X-ray luminosity, Spitzer/IRAC colours, radio spectral index and the ratio of star-forming total infrared flux to k-corrected 1.4 GHz flux density, qIR, we determine whether the radio emission in these sources is powered by star formation or by an AGN. The majority of these radio sources (60 per cent) show the signature of an AGN at some wavelength. Of the sources with AGN signatures, 58 per cent are hybrid systems for which the radio emission is being powered by star formation. This implies that radio sources which have likely been selected on their star formation have a high AGN fraction. Below a 1.4 GHz flux density of 1 mJy, along with finding a strong contribution to the source counts from pure star-forming sources, we find that hybrid sources constitute 20-65 per cent of the sources. This result suggests that hybrid sources have a significant contribution, along with sources that do not host a detectable AGN, to the observed flattening of the source counts at ˜1 mJy for the extragalactic radio source population.
AB - We separate the extragalactic radio source population above ˜50 μJy into active galactic nuclei (AGN) and star-forming sources. The primary method of our approach is to fit the infrared spectral energy distributions (SEDs), constructed using Spitzer/IRAC (Infrared Array Camera) and Multiband Imaging Photometer for Spitzer (MIPS) and Herschel/SPIRE photometry, of 380 radio sources in the Extended Chandra Deep Field-South. From the fitted SEDs, we determine the relative AGN and star-forming contributions to their infrared emission. With the inclusion of other AGN diagnostics such as X-ray luminosity, Spitzer/IRAC colours, radio spectral index and the ratio of star-forming total infrared flux to k-corrected 1.4 GHz flux density, qIR, we determine whether the radio emission in these sources is powered by star formation or by an AGN. The majority of these radio sources (60 per cent) show the signature of an AGN at some wavelength. Of the sources with AGN signatures, 58 per cent are hybrid systems for which the radio emission is being powered by star formation. This implies that radio sources which have likely been selected on their star formation have a high AGN fraction. Below a 1.4 GHz flux density of 1 mJy, along with finding a strong contribution to the source counts from pure star-forming sources, we find that hybrid sources constitute 20-65 per cent of the sources. This result suggests that hybrid sources have a significant contribution, along with sources that do not host a detectable AGN, to the observed flattening of the source counts at ˜1 mJy for the extragalactic radio source population.
KW - galaxies: active
KW - galaxies: ISM
KW - galaxies: nuclei
KW - infrared: galaxies
KW - radio continuum: galaxies
U2 - 10.1093/mnras/stv1573
DO - 10.1093/mnras/stv1573
M3 - Journal article
VL - 452
SP - 4111
EP - 4127
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
IS - 4
ER -