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

Abstract

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 AGN out to redshift ∼3.4, which constitutes the highest-redshift sample of AGN 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 1.4GHz ∼ 10 37 -10 40 erg s −1 . The bolometric luminosities derived from the fit of their spectral energy distribution are 10 42 erg s −1 , in agreement with the presence of AGN in these dwarf galaxies. The 3 GHz radio emission of most of the sources is compact and the jet powers range from Q jet ∼ 10 42 to 10 44 erg s −1 . These values, as well as the finding of jet efficiencies ≥ 10 % in more than 50% 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 AGN hosted in dwarf galaxies might not be the untouched relics of the early seed BHs, which has important implications for seed BH formation models.

Dark Energy Survey identification of a low-mass active galactic nucleus at redshift 0.823 from optical variability

“…. BH mass versus redshift for DES J0218−0430 in comparison to optical and X-ray-selected low-mass AGN candidates in the literature (Filippenko & Ho 2003;Barth et al 2004;Greene & Ho 2004Reines et al 2011;Ho et al 2012;Secrest et al 2012;Reines, Greene & Geha 2013;Schramm et al 2013;Maksym et al 2014;Baldassare et al 2015;Lemons et al 2015;Reines & Volonteri 2015;Kawamuro et al 2016;Pardo et al 2016;Chang et al 2017;She, Ho & Feng 2017;Baldassare et al 2018;Chilingarian et al 2018;Ding et al 2018;Liu et al 2018;Mezcua et al 2018) as well as the low-mass AGNs of the Mezcua, Suh & Civano (2019) radio sample. This demonstrates DES J0218−0430 to be one of the lowest BH mass objects at similar redshift.…”

Feeding and feedback from little monsters: AGN in dwarf galaxies

“…X-ray or radio observations are however required to confirm the presence of AGN in these quiescent dwarf galaxies. Based on deep radio observations of the COSMOS field (Smolčić et al 2017), Mezcua et al (2019) found a sample of radio AGN dwarf galaxies whose radio jets have powers and efficiencies as high as those of massive galaxies. This indicates that AGN feedback could be as significant in dwarf galaxies as in more massive ones.…”

“…Satyapal et al 2008;Marleau et al 2017), on the detection of X-ray or radio emission indicative of AGN accretion (e.g. Schramm et al 2013;Lemons et al 2015;Mezcua et al 2016Mezcua et al , 2018aMezcua et al , 2019Reines et al 2020), or a combination of all (e.g. see review by Mezcua 2017;Greene et al 2019).…”

“…Recent studies are however starting to challenge this scenario. Both simulations (Smethurst et al 2016;Dashyan et al 2018;Barai & de Gouveia Dal Pino 2019;Koudmani et al 2019;Regan et al 2019) and observations (Bradford et al 2018;Penny et al 2018;Dickey et al 2019;Mezcua et al 2019) are starting to find that AGN feedback can be equally, or even more, significant than SN feedback in dwarf galaxies.…”

A status report on AGN variability

“…The most successful method to probe bona-fide IMBHs is to look for broad but weak emission Balmer lines, which together with the radius-luminosity scaling relations, has yielded masses for a few hundred sources after combing the whole SDSS (Liu et al 2018;Chilingarian et al 2018). The search for faint and compact radio sources ('radio cores') associated to the nuclei of galaxies in the COSMOS field has successfully determine the presence of AGN in 35 dwarf galaxies (Mezcua et al 2019), although their bolometric luminosities are found beyond that predicted by numerical simulations More recently, variability has shown to be able to identify many candidate IMBHs. Martínez-Palomera et al (2020) have selected galaxies which show rapid, low-amplitude variability in their nuclei and shown that this method increases the number density of IMBHs by a factor of 40-50, when compared with spectroscopic searches.…”