Infrared signature of active massive black holes in nearby dwarf galaxies

Abstract

Context. We investigate the possible presence of active galactic nuclei (AGN) in dwarf galaxies and other nearby galaxies to identify candidates for follow-up confirmation and dynamical mass measurements. Aims. We identify candidate active central massive black holes (CMBH) using their mid-infrared emission, verify their nature using existing catalogues and optical line emission diagnostics, and study the relationship between their mass and the mass of their host galaxy. Methods. We use the Wide-field Infrared Survey Explorer (WISE) All-Sky Release Source Catalog and examine the infrared colours of a sample of dwarf galaxies and other nearby galaxies in order to identify both unobscured and obscured candidate AGN by applying the infrared colour diagnostic. Stellar masses of galaxies are obtained using a combination of three independent methods. Black hole masses are estimated using the bolometric luminosity of the AGN candidates and computed for three cases of the bolometric-toEddington luminosity ratio. Results. We identify 303 candidate AGN, of which 276 were subsequently found to have been independently identified as AGN via other methods. The remaining 9% require follow-up observations for confirmation. The activity is detected in galaxies with stellar masses from ∼ 10 6 to 10 9 M ; assuming the candidates are AGN, the black hole masses are estimated to be ∼ 10 3 − 10 6 M , adopting L bol = 0.1L Edd . The black hole masses probed are several orders of magnitude smaller than previously reported for centrally located massive black holes. We examine the stellar mass versus black hole mass relationship in this low galaxy mass regime. We find that it is consistent with the existing relation extending linearly (in log-log space) into the lower mass regime. Conclusions. These findings suggest that CMBH are present in low-mass galaxies and in the Local Universe, and provide new impetus for follow-up dynamical studies of quiescent black holes in local dwarf galaxies.

AGN in dwarf galaxies: frequency, triggering processes and the plausibility of AGN feedback

“…If dwarfs do generically host IMBHs, as suggested by recent studies (e.g. Reines et al 2013;Mezcua et al 2016;Marleau et al 2017), then AGN feedback could offer solutions to several outstanding problems in this mass regime (e.g. Silk 2017).…”

Observational evidence for intermediate-mass black holes

“…MIR color searches rely on the different colors of dust when heated by AGN or by stars or non-active galaxies and have become a very common tool for identifying AGN, specially since the arrival of the Wide-Field Infrared Survey Explorer (WISE ; e.g., for the WISE bands W 1 and W 2 at 3.4µm and 4.6µm, respectively, AGN can be identified as having W 1 − W 2 ≥ 0.8, Stern et al 2012). Although several studies have made use of MIR colors cuts for selecting AGN in low-mass galaxies (e.g., Satyapal et al 2014;Marleau et al 2014), caution should be taken when using this selection technique as star-forming dwarf galaxies can show similar MIR colors to those of luminous AGN (Hainline et al 2016). Other MIR searches are based on the detection of the high-ionization emission line [NeV] 14 µm or the 24 µm line using Spitzer spectral observations.…”

Intermediate-mass black holes in dwarf galaxies out to redshift ∼2.4 in the Chandra COSMOS-Legacy Survey

“…The search for low-mass BHs (M BH 10 6 M ) in dwarf galaxies is mostly based on the detection of X-ray emission (e.g., Greene & Ho 2007a;Desroches et al 2009;Reines et al 2011;Dong et al 2012;Schramm et al 2013;Baldassare et al 2015Baldassare et al , 2017Lemons et al 2015;Secrest et al 2015;Pardo et al 2016;Chen et al 2017), in some cases spatially coincident with jet radio emission (e.g., Reines et al 2014;Nucita et al 2017), or the use of standard virial techniques to estimate the BH mass (e.g., Barth et al 2004;Greene & Ho 2004, 2007bPeterson et al 2005;Reines et al 2013;La Franca et al 2015;Bentz et al 2016;Onori et al 2017; see Mezcua 2017 for a review). Additional searches in the infrared regime have yielded a few more candidates (e.g., Satyapal et al 2007Satyapal et al , 2008Satyapal et al , 2009Satyapal et al , 2014Sartori et al 2015;Marleau et al 2017). Most of these samples are however incomplete, very local (z < 0.3), skewed toward high Eddington ratios, or skewed toward type 1 AGN in the case of optical searches (e.g., Greene & Ho 2004, 2007bReines et al 2013) which can hamper the detection of BHs lighter than 10 5 M if the size of the broad line region is controlled by BH mass (e.g., Chakravorty et al 2014).…”