Circumnuclear star-formation and AGN activity: Clues from surface brightness radial profile of PAHs and [SIV]

TL;DR

This study investigates the relationship between star formation and AGN activity in nearby galaxies by analyzing MIR emission features at sub-kiloparsec scales, revealing a PAH deficit near the nucleus and insights into the AGN-star formation connection.

Contribution

It provides high-resolution measurements of PAH and [SIV] emissions in local AGN, highlighting the spatial distribution of star formation and its relation to AGN activity, which was previously less understood.

Findings

PAH emission is deficient within tens of parsecs from the AGN.

[SIV] emission often peaks beyond 1000 R_sub, indicating complex ionization structures.

The relation between AGN luminosity and star formation rate aligns with merger-driven galaxy evolution models.

Abstract

We studied the circumnuclear MIR emission in a sample of 19 local active galactic nuclei (AGN) with high spatial resolution spectra using T-ReCS (Gemini) and CanariCam (GTC), together with IRS/Spitzer observations. We measured the flux and the equivalent width for the 11.3 micron PAH feature and the [SIV] line emission as a function of galactocentric distance. This allowed to study the star formation (SF) at sub-kpc scales from the nucleus for a large sample of nearby AGN. The [SIV] line emission could be tracing the AGN radiation field within a few thousand times the sublimation radius (R_sub), but it often peaks at distances greater than 1000 R_sub. One possibility is that the SF is contributing to the [SIV] total flux. We found an 11.3 micron PAH emission deficit within the inner few tens of parsecs from the AGN. This deficit might be due to the destruction of the molecules responsible for this feature or the lack of SF at these distances. We found a sensible agreement in the expected shift of the relation of the AGN bolometric luminosity and the SF rate. This indicates that numerical models attributing the link between AGN activity and host galaxy growth to mergers are in agreement with our data, for most inner galaxy parts.