Radio jets from AGNs in dwarf galaxies in the COSMOS survey: mechanical feedback out to redshift ∼3.4

Dwarf galaxies are thought to host the remnants of the early Universe seed black holes (BHs) and to be dominated by supernova feedback. However, recent studies suggest that BH feedback could also strongly impact their growth. We report the discovery of 35 dwarf galaxies hosting radio active galactic nucleus (AGN) out to redshift ∼3.4, which constitutes the highest redshift sample of AGNs in dwarf galaxies. The galaxies are drawn from the VLA-COSMOS 3 GHz Large Project and all are star forming. After removing the contribution from star formation to the radio emission, we find a range of AGN radio luminosities of L^AGN_1.4 GHz ∼ 10^{37}-10⁴⁰ erg s^-1. The bolometric luminosities derived from the fit of their spectral energy distribution are ≳10⁴² erg s^-1, in agreement with the presence of AGNs in these dwarf galaxies. The 3 GHz radio emission of most of the sources is compact and the jet powers range from Q_jet ∼ 10⁴² to 10⁴⁴ erg s^-1. These values, as well as the finding of jet efficiencies ≥10 per cent in more than 50 per cent of the sample, indicate that dwarf galaxies can host radio jets as powerful as those of massive radio galaxies whose jet mechanical feedback can strongly affect the formation of stars in the host galaxy. We conclude that AGN feedback can also have a very strong impact on dwarf galaxies, either triggering or hampering star formation and possibly the material available for BH growth. This implies that those low-mass AGNs hosted in dwarf galaxies might not be the untouched relics of the early seed BHs, which has important implications for seed BH formation models.