The spatial extension of extended narrow line regions in MaNGA AGN


In this work, we revisit the size–luminosity relation of the extended narrow line regions (ENLRs) using a large sample of nearby active galactic nuclei (AGNs) from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. The ENLRs ionized by the AGN are identified through the spatially resolved BPT diagram, which results in a sample of 152 AGN. By combining our AGN with the literature high-luminosity quasars, we found a tight log-linear relation between the size of the ENLR and the AGN [O III] λ5007 Å luminosity over four orders of magnitude of the [O III] luminosity. The slope of this relation is 0.42 ± 0.02 which can be explained in terms of a distribution of clouds photoionized by the AGN. This relation also indicates that the AGNs have the potential to ionize and heat the gas clouds at a large distance from the nuclei without the aids of outflows and jets for the low-luminosity Seyferts.

As part of the Sloan Digital Sky Survey, the MaNGA (Mapping Nearby Galaxies at APO) project is producing a catalog of integral field unit (IFU) spectra of nearby galaxies. IFU spectra provide detailed information about the light coming from different points in a galaxy. This is an invaluable tool for astronomy, and in particular, when these galaxies are hosts of Type II quasars, the IFU spectra can be used to calculate the [O III] size and luminosity, the quantities we modeled here. This paper uses MaNGA data to add many more points to the observed size/luminosity relationship, and among many other things, addresses whether that model holds water.

The short answer (which is all I’ll provide here) is yes. The following plot shows our model (adjusted for a slightly different definition of [O III] size) superimposed on the MaNGA data. We find quite a good fit over about four decades in [O III] luminosity. The model fits best when we use slightly higher cloud masses than the ones from our theory paper ($m_c \sim 10^7\,M_\odot$ here, compared to $m_c \sim 10^6\,M_\odot$ there). But in any case, the new data is certainly consistent with our model being an adequate description of the relevant physics.

Many thanks to Jianhang Chen and other collaborators for including me in this work. It’s always very satisfying to see theory match with data!