Two-panel processed HST/WFC3 H-alpha image of the inner 500 pc of NGC 5005. Green contours mark H II-like excitation in both panels; the right panel also shows 1.5 GHz eMERLIN radio contours in purple, Seyfert-like contours in red, and analysis-defined cocoon-like contours in blue. A black X marks the optical centroid, and each panel includes a 0.2 kpc scale bar; north is up and east is left.

Research article · 2025

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

ApJ 986, 175 (2025)

Processed observational composite · Published Figure 5

Published-paper Figure 5. Continuum-subtracted, reddening-corrected HST/WFC3 F658N-derived H-alpha emission in the inner 500 pc of NGC 5005. Green contours mark H II-like pixels classified from processed spatially resolved BPT maps. The right panel adds full-resolution 1.5 GHz eMERLIN contours in purple and Seyfert-like and analysis-defined cocoon-like contours in red and blue. A black X marks the optical centroid; each panel includes a 0.2 kpc scale bar, with north up and east left. Spatial overlap suggests possible jet-ISM interactions but does not establish jet-triggered star formation or causal positive feedback.

Trindade Falcão et al. 2025, “Mapping the Excitation Mechanisms in the LINER I Active Galactic Nucleus NGC 5005: Positive Feedback and a Thin LINER Cocoon,” ApJ 986, 175, DOI: 10.3847/1538-4357/addc64, CC BY 4.0. Figure 5 rasterized, resized, and converted to WebP for web presentation. HST: NASA/ESA; eMERLIN contours: Baldi et al. 2018.

Research summary

Mapping excitation mechanisms across NGC 5005

HST/WFC3 narrow-band images of [O III] λ5007, Hβ, Hα+[N II], and [S II], processed for reddening and stellar-continuum subtraction, were used to construct spatially resolved [S II]-BPT classifications in NGC 5005. The F658N-derived Hα map assumes a spatially uniform 45% Hα contribution after [N II] removal; the paper also tests a conservative 30% lower limit. The maps resolve Seyfert-like emission near the nucleus, an approximately 10–20 pc-thick higher-excitation LINER-like structure, LINER-like emission on kiloparsec scales, and H II-like regions including an outer star-forming ring. “Cocoon-like” is an analysis-defined higher-[O III]/Hβ subset of LINER-like pixels, not a directly observed physical phase. Comparisons with archival 1.5 GHz eMERLIN and CO(1–0) contours motivate possible shock excitation, filtered AGN radiation, jet–interstellar-medium interaction, inflow shocks, post-AGB excitation, and jet-triggered star formation; these remain interpretations or alternatives and do not establish causal positive feedback. This study reports no new gas-kinematic measurement.