Massive black holes (MBHs) are ubiquitous in the Universe, and inhabit all massive galaxies (e.g. Ferrarese & Merritt 2000). MBHs are typically observed via their accretion-powered radiation as active galactic nuclei (AGNs), whose impact on to the host galaxy is invoked to explain massive galaxy quenching (e.g. Silk & Rees 1998; Di Matteo, Springel & Hernquist 2005) and the emergence of the MBH–galaxy correlations (Gültekin et al. 2009; Kormendy & Ho 2013). However, the demographics of MBHs are not yet well constrained (see e.g. Reines & Comastri 2016; Greene, Strader & Ho 2019, for reviews) and the role of AGN feedback in dwarf galaxies is just starting to be explored (Penny et al. 2018; Mackay Dickey et al. 2019; Manzano-King, Canalizo & Sales 2019). In particular, theoretical studies have shown that the MBH–halo occupation fraction can be low in dwarf galaxies (e.g. Greene 2012; Miller et al. 2015; Habouzit, Volonteri & Dubois 2017), and even in systems hosting MBHs, their growth is strongly suppressed because of the typically low gas densities in the host (compared to more massive disc galaxies) and the strong impact of supernova explosions, both at low and high redshift (Dubois et al. 2014; Anglés-Alcázar et al. 2017; Prieto et al. 2017; Trebitsch et al. 2018). Observationally, this could be partially reflected in MBHs in dwarfs being inactive for most of their life, hence in the small number of low-luminosity AGNs found (Reines, Greene & Geha 2013; Baldassare et al. 2016, 2018, 2019; Mezcua et al. 2016, 2018; Reines et al. 2019), although there are also strong observational biases that could make these AGNs difficult to find. On the other hand, if MBHs were present in many dwarfs, and efficiently grew, their feedback could significantly affect their host (see e.g. Penny et al. 2018; Mackay Dickey et al. 2019; Manzano-King et al. 2019), could play a role in the reionization of the Universe (Volonteri & Gnedin 2009), could help removing gas from massive disc progenitors (e.g. Peirani et al. 2012), and also mitigate the ‘too-big-to-fail’ problem (Garrison-Kimmel et al. 2013). Recently, Kaviraj, Martin & Silk (2019; K19 hereafter) tried to better assess the role of AGN feedback in dwarfs by jointly analysing the Hyper-Supreme Cam Subaru Strategic Program (Aihara et al. 2018b) and the WISE (Wright et al. 2010) surveys, finding that AGNs in dwarfs could exhibit very large bolometric luminosities, hence they could play a significant role in their host evolution. However, a clear consensus on the identification of AGNs in dwarfs is still missing (see e.g. Satyapal et al. 2014; Sartori et al. 2015; Marleau et al. 2017), in particular because of the low resolution of WISE (∼6  arcsec) relative to current optical surveys, resulting in a strong source overlap, and the possible contamination of infrared emission by star formation activity that could mimic AGN activity (Hainline et al. 2016; Satyapal, Abel & Secrest 2018), especially in dwarf galaxies (Hainline et al. 2016). In this paper, we build-up on the K19 work by re-analysing their dwarf sample in more detail in the aim at better disentangling plausible AGNs in dwarf from star-forming galaxies by taking into account possible source overlapping in the sample, and also assess the MBH properties.
Citation: Prieto et al. 2017
Citation function: Background; Background