TY - JOUR
T1 - The faint radio sky: VLBA observations of the COSMOS field
AU - Herrera Ruiz, N.
AU - Middelberg, E.
AU - Deller, A. T.
AU - Norris, R. P.
AU - Best, P. N.
AU - Brisken, W.
AU - Schinnerer, E.
AU - Smolčić, V.
AU - Delvecchio, I.
AU - Momjian, E.
AU - Bomans, Dominik J.
AU - Scoville, N. Z.
AU - Carilli, C
PY - 2017/11/28
Y1 - 2017/11/28
N2 - Context. Quantifying the fraction of active galactic nuclei (AGN) in the
faint radio population and understanding their relation with
star-forming activity are fundamental to studies of galaxy evolution.
Very long baseline interferometry (VLBI) observations are able to
identify AGN above relatively low redshifts (z> 0.1) since they
provide milli-arcsecond resolution. Aims: We have created an AGN
catalogue from 2865 known radio sources observed in the Cosmic Evolution
Survey (COSMOS) field, which has exceptional multi-wavelength coverage.
With this catalogue we intend to study the faint radio sky with
statistically relevant numbers and to analyse the AGN - host galaxy
co-evolution, making use of the large amount of ancillary data available
in the field. Methods: Wide-field VLBI observations were made of
all known radio sources in the COSMOS field at 1.4 GHz to measure the
AGN fraction, in particular in the faint radio population. We describe
in detail the observations, data calibration, source detection and flux
density measurements, parts of which we have developed for this survey.
The combination of number of sources, sensitivity, and area covered with
this project are unprecedented. Results: We have detected 468
radio sources, expected to be AGN, with the Very Long Baseline Array
(VLBA). This is, to date, the largest sample assembled of VLBI detected
sources in the sub-mJy regime. The input sample was taken from previous
observations with the Very Large Array (VLA). We present the catalogue
with additional optical, infrared and X-ray information.
Conclusions: We find a detection fraction of 20 ± 1%, considering
only those sources from the input catalogue which were in principle
detectable with the VLBA (2361). As a function of the VLA flux density,
the detection fraction is higher for higher flux densities, since at
high flux densities a source could be detected even if the VLBI core
accounts for a small percentage of the total flux density. As a function
of redshift, we see no evolution of the detection fraction over the
redshift range 0.5 1.5 we find that spiral galaxies become the most
prevalent (48%). The number of detections is high enough to study the
faint radio population with statistically significant numbers. We
demonstrate that wide-field VLBI observations, together with new
calibration methods such as multi-source self-calibration and mosaicing,
result in information which is difficult or impossible to obtain
otherwise.
The full Tables 2 and 3 are only available at the CDS via anonymous ftp
to http://cdsarc.u-strasbg.fr
(http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/607/A132
AB - Context. Quantifying the fraction of active galactic nuclei (AGN) in the
faint radio population and understanding their relation with
star-forming activity are fundamental to studies of galaxy evolution.
Very long baseline interferometry (VLBI) observations are able to
identify AGN above relatively low redshifts (z> 0.1) since they
provide milli-arcsecond resolution. Aims: We have created an AGN
catalogue from 2865 known radio sources observed in the Cosmic Evolution
Survey (COSMOS) field, which has exceptional multi-wavelength coverage.
With this catalogue we intend to study the faint radio sky with
statistically relevant numbers and to analyse the AGN - host galaxy
co-evolution, making use of the large amount of ancillary data available
in the field. Methods: Wide-field VLBI observations were made of
all known radio sources in the COSMOS field at 1.4 GHz to measure the
AGN fraction, in particular in the faint radio population. We describe
in detail the observations, data calibration, source detection and flux
density measurements, parts of which we have developed for this survey.
The combination of number of sources, sensitivity, and area covered with
this project are unprecedented. Results: We have detected 468
radio sources, expected to be AGN, with the Very Long Baseline Array
(VLBA). This is, to date, the largest sample assembled of VLBI detected
sources in the sub-mJy regime. The input sample was taken from previous
observations with the Very Large Array (VLA). We present the catalogue
with additional optical, infrared and X-ray information.
Conclusions: We find a detection fraction of 20 ± 1%, considering
only those sources from the input catalogue which were in principle
detectable with the VLBA (2361). As a function of the VLA flux density,
the detection fraction is higher for higher flux densities, since at
high flux densities a source could be detected even if the VLBI core
accounts for a small percentage of the total flux density. As a function
of redshift, we see no evolution of the detection fraction over the
redshift range 0.5 1.5 we find that spiral galaxies become the most
prevalent (48%). The number of detections is high enough to study the
faint radio population with statistically significant numbers. We
demonstrate that wide-field VLBI observations, together with new
calibration methods such as multi-source self-calibration and mosaicing,
result in information which is difficult or impossible to obtain
otherwise.
The full Tables 2 and 3 are only available at the CDS via anonymous ftp
to http://cdsarc.u-strasbg.fr
(http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/607/A132
KW - catalogs
KW - galaxies: active
KW - radio continuum: galaxies
U2 - 10.1051/0004-6361/201731163
DO - 10.1051/0004-6361/201731163
M3 - Article
SN - 0004-6361
VL - 607
JO - Astronomy & Astrophysics
JF - Astronomy & Astrophysics
ER -