Mapping the Excitation Mechanisms in the LINER I Active Galactic Nucleus NGC 5005: Positive Feedback and a Thin LINER Cocoon

Abstract

We present a spatially resolved Baldwin–Phillips–Terlevich analysis of the narrow-line region (NLR) in the low-ionization nuclear emission-line region (LINER) I galaxy NGC 5005 using Hubble Space Telescope narrowband imaging of [O iii ] λ 5007, H β , H α , and [S ii ] λλ 6717,6731. With a resolution of ≲0 $\mathop{.}\limits^{\unicode{x02033}}$ 1 (≲10 pc at z = 0.003), we dissect the NLR into H ii (star-forming), Seyfert, and LINERs across spatial scales extending up to r ∼ 8 kpc from the nucleus. Our results reveal a compact nuclear region exhibiting Seyfert-like emission, consistent with photoionization by a low-luminosity active galactic nucleus (AGN). Surrounding this Seyfert-like nucleus is a thin (∼20 pc thick) higher-excitation LINER-like cocoon, likely arising from shock-excited gas in the interstellar medium (ISM). Beyond this cocoon, a centrally localized extended ( r ∼ 1 kpc) LINER-like region surrounds the Seyfert-like nucleus and cocoon, likely ionized by the AGN, while a more extended ( r ≳ 2 kpc) LINER-like zone may be ionized by a combination of post-AGB stars and shocks from gas inflows. We also detect H ii –like regions at both small and large scales. In the inner 500 pc, these regions may be triggered by jet–ISM interactions, potentially inducing localized star formation. At r ∼ 4 kpc, we identify an outer H ii –like region tracing a large-scale star-forming ring, where ionization is dominated by young stars.

Keywords

• LINER galaxies