Kavli Affiliate: Kohei Inayoshi
| First 5 Authors: Anniek J. Gloudemans, Kenneth J. Duncan, Anna-Christina Eilers, Emanuele Paolo Farina, Yuichi Harikane
| Summary:
Radio observations can provide crucial insight into the nature of a new
abundant and mysterious population of dust-reddened active galactic nuclei
(AGN) candidates discovered by the James Webb Space Telescope (JWST), including
“Little Red Dots" (LRDs). In this study, we search for radio bright sources in
a large sample of $sim$700 JWST discovered AGN candidates ($zsim2-11$) in the
0.144-3 GHz frequency range, utilizing deep radio imaging in COSMOS, GOODS-N,
and GOODS-S. Only one source is significantly detected in our radio surveys,
which is PRIMER-COS 3866 at $z=4.66$. Its radio properties are consistent with
both an AGN and star formation origin with a spectral index of
$alpha=-0.76^{+0.11}_{-0.09}$ and a radio-loudness of $Rapprox0.5$. The
derived brightness temperature limit of PRIMER-COS 3866 of $T_b gtrsim 10^{3}$
K is too low to confirm its AGN nature. Our stacking results yield
non-detections in all fields with the most constraining 3$sigma$ limit
$L_{1.3text{GHz}} < 1.3times10^{39}$ erg s$^{-1}$ (rms of $sim$0.15 $mu$Jy
beam$^{-1}$ at $z_{text{median}}=6.1$) obtained for photometrically selected
AGN candidates in the COSMOS field. This result is still consistent with
expectations from the empirical $L_X – L_{text{H}alpha}$ and $L_X – L_R$
correlations established for local AGN. We conclude that current radio
observations have insufficient depth to claim JWST discovered AGN candidates
are radio-weak. We project that future surveys carried out by the SKA and ngVLA
should be able to obtain significant detections within a few hours, providing
crucial measurements of their brightness temperature, which would allow for
distinguishing between AGN and starburst-driven origins of this new abundant
population.
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