Examining the possibility of an ADAF as the main power source behind liner emissions

Abstract

Low-Ionization Nuclear Emission-Line Regions (LINERs) represent the low luminosity end of Active Galactic Nuclei (AGN). The main power source of LINERs is the subject of considerable debate in the scientific community today, despite the fact that some Liners show features of mass accretion into a super massive black hole (SMBH). Optical line-ratio diagrams are not conclusive diagnostic tools as they can be explained by different mechanisms, including shocks (Dopita et al. 1997[8]) and photoionization accompanied by outflow resembling accretion (Sabra et al. 2003[23]). This dissertation will examine the possibility of an Advection Dominated Accretion Flow (ADAF) as the main power source behind LINER emissions. I focus on a sample of LINER 1.9s that show Narrow Line Region (NLR) emissions with a signature of mass accretion: the broad Hα emission line. The scarcity of available observational data of UV spectra for this sample prompted us to look into IR line-ratios as an additional diagnostic. I compare IR emission line measures adopted from (Dudik et al. 2009[9]) for a set of LINER 1.9s and Optical and UV spectra for NGC 1052 (Dopita et al. 2015[7]) with sets of simulations of a single phase cloud excited by an ADAF source. The models are formed by varying the values of the photoionization parameter and the cloud density using Cloudy (c17.01, Ferland et al 2017[11]). I observe that line-ratios originating from the same element (Carbon and Neon) best fit in an area bounded by column densities ranging between 1022 to 1023 cm ́2 and photoionization parameters ranging between log(U) = -2.5 to -2 . Line-ratios involving Carbon versus Helium in the UV or Oxygen versus Neon in the IR are best fit inside these bounded areas, but only within a dusty metal-depleted model. I note that the [O III]5007 / Hβ line ratio of NGC 1052 diverge from the best fit scenario by about 1.2 dex. Optical and UV observations from a larger set of LINER 1.9s are required to better understand this deviation.