The size–luminosity relationship of quasar narrow-line regions

Abstract

The presence of an active galactic nucleus (AGN) can strongly affect its host. Due to the copious radiative power of the nucleus, the effects of radiative feedback can be detected over the entire host galaxy and sometimes well into the intergalactic space. In this paper we model the observed size-luminosity relationship of the narrow-line regions (NLRs) of AGN. We model the NLR as a collection of clouds in pressure equilibrium with the ionizing radiation, with each cloud producing line emission calculated by Cloudy. The sizes of the NLRs of powerful quasars are reproduced without any free parameters, as long as they contain massive (10 5 M to 10 7 M ) ionization-bounded clouds. At lower AGN luminosities the observed sizes are larger than the model sizes, likely due to additional unmodeled sources of ionization (e.g., star formation). We find that the observed saturation of sizes at ∼ 10 kpc which is observed at high AGN luminosities (L ion 10 46 erg/s) is naturally explained by optically thick clouds absorbing the ionizing radiation and preventing illumination beyond a critical distance. Using our models in combination with observations of the [O III]/IR ratio and the [O III] size -IR luminosity relationship, we calculate the covering factor of the obscuring torus (and therefore the type 2 fraction within the quasar population) to be f = 0.5, though this is likely an upper bound. Finally, because the gas behind the ionization front is invisible in ionized gas transitions, emission-based NLR mass calculations underestimate the mass of the NLR and therefore of the energetics of ionized-gas winds.

Ionized gas outflow signatures in SDSS-IV MaNGA active galactic nuclei

“…These calculations yields total kinetic energy injection rates of E kin ∼ 2 × 10 38 erg/s and ∼ 5 × 10 × 10 39 erg/s for the low and high luminosity AGN samples, respectively. Although these calculations provide order-of-magnitude estimates at best, they show that (i) even in low/intermediate luminosity AGN, the positive correlation between AGN power and outflow energetics persists as expected from models (Dempsey & Zakamska 2018) and seen in observations (Fiore et al 2017, and references therein) but that (ii) the feedback processes in such low/intermediate luminosity, low redshift AGN probed by MaNGA are unlikely to have a significant impact on the evolution of their host galaxies, i.e. fully suppress star formation processes, as the kinetic coupling efficiencies E kin /L AG N are 1% and most of them even likely 0.1%.…”

The spatial extension of extended narrow line regions in MaNGA AGN

“…The scenario has been questioned before as some observations appeared to be in conflict with it (Schmitt et al 2003a;Greene et al 2011;Liu et al 2013), but our result over a large dynamic range of the AGN luminosity do not rule out the homogeneous gas model. Recently, Dempsey & Zakamska (2018) proposed a more detailed model of the ENLR. They modeled the (E)NLR as a collection of clouds in pressure equilibrium with the ionizing radiation and the emission line strength like [O III] is calculated by Cloudy (Ferland et al 1998;Stern et al 2014).…”

“…Lots of debates have focused on whether or not AGN outflows can suppress star formation of host galaxies (Shi et al 2009;Zhang et al 2016;Zubovas & Bourne 2017;Harrison 2017;Harrison et al 2018;Bing et al 2018;Gallagher et al 2019), even for the low luminous AGN (Cheung et al 2016;Penny et al 2018). AGN outflows may also affect the extension of the ENLRs by changing the distribution of the gas and dust Dempsey & Zakamska 2018). However, there may be a significant difference between the extent of the outflow and the extent of the ENLR.…”

“…For the more recent works, Sun et al (2018) At the high luminosity end of the size-luminosity relation, a flattening in slope has been observed (Netzer et al 2004;Hainline et al 2013Hainline et al , 2014Liu et al 2014), which is usually interpreted as a maximum size of the ENLR. Beyond that radius, the column density may be too low to support [O III] emission (Stern et al 2016) or photons are mostly obscured by the inner clouds (Dempsey & Zakamska 2018). Since we focused on low luminosity objects with a lower surface brightness cutoff, our results are not sensitive to this upper size limit.…”

“…The observed strong coronal lines in some Seyfert galaxies cannot be produced in these models (Dopita et al 2002;Groves et al 2004a), and the relationship between the ENLR size and the AGN luminosity has a slope that differs from the predicted value of 0.5 (Schmitt et al 2003b;Netzer et al 2004). More recent ENLR models replace the constant density with multicomponent gas densities or include the dust contribution (Dopita et al 2002;Groves et al 2004a,b;Dempsey & Zakamska 2018) which produce different slopes of the size-luminosity relation. A better constraint on the slope from the observation is required to distinguish different models.…”