We present a sub-kpc localization of the sites of supermassive black hole ( SMBH ) growth in three active galactic nuclei ( AGN ) at z \sim 3 in relation to the regions of intense star formation in their hosts .
These AGNs are selected from Karl G. Jansky Very Large Array ( VLA ) and Atacama Large Millimeter/submillimeter Array ( ALMA ) observations in the HUDF and COSMOS , with the centimetric radio emission tracing both star formation and AGN , and the sub/millimeter emission by dust tracing nearly pure star formation .
We require radio emission to be \geqslant 5 \times more luminous than the level associated with the sub/millimeter star formation to ensure that the radio emission is AGN-dominated , thereby allowing localization of the AGN and star formation independently .
In all three galaxies , the AGN are located within the compact regions of gas-rich , heavily obscured , intense nuclear star formation , with R _ { e } = 0.4 - 1.1 kpc and average star formation rates of \simeq 100 - 1200 M _ { \odot } yr ^ { -1 } .
If the current episode of star formation continues at such a rate over the stellar mass doubling time of their hosts , \simeq 0.2 Gyr , the newly formed stellar mass will be of the order of 10 ^ { 11 } M _ { \odot } within the central kpc region , concurrently and cospatially with significant growth of the SMBH .
This is consistent with a picture of in-situ galactic bulge and SMBH formation .
This work demonstrates the unique complementarity of VLA and ALMA observations to unambiguously pinpoint the locations of AGN and star formation down to \simeq 30 mas , corresponding to \simeq 230 pc at z = 3 .