Spatially resolved electron density in the narrow line region of z < 0.02 radio AGNs

Abstract

Context. Although studying outflows in the host galaxies of Active Galactic Nuclei (AGN) have become the forefront of extra-galactic astronomy in recent years, estimating the energy associated with these outflows have been a major challenge. Determination of the energy associated with an outflow often involves an assumption of uniform density in the Narrow Line Region (NLR), which span a wide range in literature leading to large systematic uncertainties in energy estimation. Aims. In this paper, we present electron density maps for a sample of outflowing and non-outflowing Seyfert galaxies at z<0.02 drawn from the Siding Spring Southern Seyfert Spectroscopic Snapshot Survey (S7) and understand the origin and values of the observed density structures to reduce the systematic uncertainties in outflow energy estimation. Methods. We use the ratio of the [S ii]λ6716,6731 emission lines to derive spatially resolved electron densities ( 50-2000 cm −3 ). Using optical Integral Field Unit observations from the WiFeS instrument, we are able to measure densities across the central 2-5 kpc of the selected AGN host galaxies. We compare the density maps with the positions of the H ii regions derived from the narrow Hα component, ionization maps from [O iii], and spatially resolved BPT diagrams, to infer the origin of the observed density structures. We also use the electron density maps to construct density profiles as a function of distance from the central AGN.Results. We find a spatial correlation between the sites of high star formation and high electron density for targets without an active ionized outflow. The non-outflowing targets also show an exponential drop in the electron density as a function of distance from the center, with a mean exponential index of ∼0.15. The correlation between the star forming sites and electron density ceases for targets with an outflow. The density within the outflowing medium is not uniform and shows both low and high density sites, most likely due to the presence of shocks and highly turbulent medium. We compare these results in the context of previous results obtained from fiber and slit spectra.

A close look at the dwarf AGN of NGC 4395: optical and near-IR integral field spectroscopy

“…Indeed, the N e map for NGC 4395 is consistent with the range of values derived for other Seyfert galaxies using IFS (e.g. Freitas et al 2018;Kakkad et al 2018). In a recent work, Kakkad et al (2018) presented electron density maps for the inner few kiloparsec of 13 nearby active galaxies, derived from IFS and obtained as part of the Siding Spring Southern Seyfert Spectroscopic Snapshot Survey (S7).…”

“…Freitas et al 2018;Kakkad et al 2018). In a recent work, Kakkad et al (2018) presented electron density maps for the inner few kiloparsec of 13 nearby active galaxies, derived from IFS and obtained as part of the Siding Spring Southern Seyfert Spectroscopic Snapshot Survey (S7). For all galaxies, they found highest values of N e at the nucleus and smaller values at the circumnuclear region.…”

Detections of [O iii] 88 μm in two quasars in the reionization epoch

“…Indeed, the size of the [Oiii] emitting region of the two quasars (≈ 2 − 3 kpc in FWHM) are reasonable for the size of stellar disks or extended NLRs. Ideally, one can separate the contribution based on spatially resolved diagnostics such as the BPT diagram (Baldwin et al 1981) as performed in local Seyfert and LINER galaxies (Kakkad et al 2018 Looze et al 2014). The authors present different empirical relations for e.g., metal-poor dwarf galaxies, starburst, the composite of star formation and AGNs, ULIRGs, and the entire sample.…”

The multiphase gas structure and kinematics in the circumnuclear region of NGC 5728

“…resolve the electron density distribution within individual galaxies at low redshift (e.g. Kakkad et al 2018;Nascimento et al 2019). At high redshift, stacks of the nuclear spectra from IFU surveys have produced estimates of the electron density for both HII regions and broad outflows (Förster Schreiber et al 2019).…”