TY - JOUR
T1 - Infrared-faint radio sources in the SERVS deep fields
T2 - pinpointing AGNs at high redshift
AU - Maini, A.
AU - Prandoni, I.
AU - Norris, R. P.
AU - Spitler, L. R.
AU - Mignano, A.
AU - Lacy, M.
AU - Morganti, R.
PY - 2016/12/1
Y1 - 2016/12/1
N2 - Context. Infrared-faint radio sources (IFRS) represent an unexpected class of objects which are relatively bright at radio wavelength, but unusually faint at infrared (IR) and optical wavelengths. A recent and extensive campaign on the radio-brightest IFRSs (S1.4 GHz? 10 mJy) has provided evidence that most of them (if not all) contain an active galactic nuclei (AGN). Still uncertain is the nature of the radio-faintest IFRSs (S1.4 GHz? 1 mJy). Aims. The scope of this paper is to assess the nature of the radio-faintest IFRSs, testing their classification and improving the knowledge of their IR properties by making use of the most sensitive IR survey available so far: the Spitzer Extragalactic Representative Volume Survey (SERVS). We also explore how the criteria of IFRSs can be fine-tuned to pinpoint radio-loud AGNs at very high redshift (z > 4). Methods. We analysed a number of IFRS samples identified in SERVS fields, including a new sample (21 sources) extracted from the Lockman Hole. 3.6 and 4.5 μm IR counterparts of the 64 sources located in the SERVS fields were searched for and, when detected, their IR properties were studied. Results. We compared the radio/IR properties of the IR-detected IFRSs with those expected for a number of known classes of objects. We found that IR-detected IFRSs are mostly consistent with a mixture of high-redshift (z ? 3) radio-loud AGNs. The faintest ones (S1.4 GHz ~ 100 μJy), however, could be also associated with nearer (z ~ 2) dust-enshrouded star-burst galaxies. We also argue that, while IFRSs with radio-to-IR ratios >500 can very efficiently pinpoint radio-loud AGNs at redshift 2 < z < 4, lower radio-to-IR ratios (~100-200) are expected for higher redshift radio-loud AGNs.
AB - Context. Infrared-faint radio sources (IFRS) represent an unexpected class of objects which are relatively bright at radio wavelength, but unusually faint at infrared (IR) and optical wavelengths. A recent and extensive campaign on the radio-brightest IFRSs (S1.4 GHz? 10 mJy) has provided evidence that most of them (if not all) contain an active galactic nuclei (AGN). Still uncertain is the nature of the radio-faintest IFRSs (S1.4 GHz? 1 mJy). Aims. The scope of this paper is to assess the nature of the radio-faintest IFRSs, testing their classification and improving the knowledge of their IR properties by making use of the most sensitive IR survey available so far: the Spitzer Extragalactic Representative Volume Survey (SERVS). We also explore how the criteria of IFRSs can be fine-tuned to pinpoint radio-loud AGNs at very high redshift (z > 4). Methods. We analysed a number of IFRS samples identified in SERVS fields, including a new sample (21 sources) extracted from the Lockman Hole. 3.6 and 4.5 μm IR counterparts of the 64 sources located in the SERVS fields were searched for and, when detected, their IR properties were studied. Results. We compared the radio/IR properties of the IR-detected IFRSs with those expected for a number of known classes of objects. We found that IR-detected IFRSs are mostly consistent with a mixture of high-redshift (z ? 3) radio-loud AGNs. The faintest ones (S1.4 GHz ~ 100 μJy), however, could be also associated with nearer (z ~ 2) dust-enshrouded star-burst galaxies. We also argue that, while IFRSs with radio-to-IR ratios >500 can very efficiently pinpoint radio-loud AGNs at redshift 2 < z < 4, lower radio-to-IR ratios (~100-200) are expected for higher redshift radio-loud AGNs.
KW - infrared: galaxies
KW - galaxies: high-redshift
KW - galaxies: active
UR - http://www.scopus.com/inward/record.url?scp=85005978100&partnerID=8YFLogxK
U2 - 10.1051/0004-6361/201629391
DO - 10.1051/0004-6361/201629391
M3 - Article
AN - SCOPUS:85005978100
SN - 0004-6361
VL - 596
SP - 1
EP - 18
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
M1 - A80
ER -