New insights from deep VLA data on the potentially recoiling black hole
  CID-42 in the COSMOS field
  We present deep 3 GHz VLA observations of the potentially recoiling black
hole CID-42 in the COSMOS field. This galaxy shows two optical nuclei in the
HST/ACS image and a large velocity offset of ~ 1300 km/s between the broad and
narrow H beta emission line although the spectrum is not spacially resolved
(Civano et al. 2010). The new 3 GHz VLA data has a bandwidth of 2 GHz and to
correctly interpret the flux densities imaging was done with two different
methods: multi-scale multi-frequency synthesis and spectral windows stacking.
The final resolutions and sensitivities of these maps are 0.7" with rms = 4.6
muJy/beam and 0.9" with rms = 4.8 muJy/beam respectively. With a 7 sigma
detection we find that the entire observed 3 GHz radio emission can be
associated with the South-Eastern component of CID-42, coincident with the
detected X-ray emission. We use our 3 GHz data combined with other radio data
from the literature ranging from 320 MHz to 9 GHz, which include the VLA, VLBA
and GMRT data, to construct a radio synchrotron spectrum of CID-42. The radio
spectrum suggests a type I unobscured radio-quiet flat-spectrum AGN in the
South-Eastern component which may be surrounded by a more extended region of
old synchrotron electron population or shocks generated by the outflow from the
supermassive black hole. Our data are consistent with the recoiling black hole
picture but cannot rule out the presence of an obscured and radio-quiet SMBH in
the North-Western component.
