Imaging extended emission-line regions of obscured AGN with the Subaru Hyper Suprime-Cam Survey

Abstract

Narrow-line regions excited by active galactic nuclei (AGNs) are important for studying AGN photoionization and feedback. Their strong [Out] lines can be detected with broad-band images, allowing morphological studies of these systems with large-area imaging surveys. We develop a new broad-band imaging technique to reconstruct the images of the [OIII] line, using the Subaru Hyper Suprime-Cam (HSC) Survey aided with spectra from the Sloan Digital Sky Survey (SDSS). The technique involves a careful subtraction of the galactic continuum to isolate emission from the [OIII]lambda 5007 and [OIII]lambda 4959 lines. Compared to traditional targeted observations, this technique is more efficient at covering larger samples without dedicated observational resources. We apply this technique to an SDSS spectroscopically selected sample of 300 obscured AGN at redshifts 0.1-0.7, uncovering extended emission-line region candidates with sizes up to tens of kpc. With the largest sample of uniformly derived narrow-line region sizes, we revisit the narrow-line region size-luminosity relation. The area and radii of the [Om] emission-line regions are strongly correlated with the AGN luminosity inferred from the mid-infrared (15 mu m rest frame) with a power-law slope of 0.62(-0.06)(+0.05) +/- 0.10(statistical and systematic errors), consistent with previous spectroscopic findings. We discuss the implications for the physics of AGN emission-line regions and future applications of this technique, which should be useful for current and next-generation imaging surveys to study AGN photoionization and feedback with large statistical samples.