Hector Galaxy Survey: Optical IFU and Chandra Reveal a Low-Luminosity AGN Behind Extended LINER Emission

Le résumé fourni par la source

We present evidence that the Hector Galaxy Survey galaxy C901005481609968 ($z_{\rm cl}=0.0553$), which exhibits spatially extended LINER-like emission in optical integral-field spectroscopy (IFS), hosts a low-luminosity active galactic nucleus (LLAGN) that contributes substantially to its ionization budget. Although the galaxy is not selected as an AGN by mid-infrared AGN color criteria, archival Chandra data reveal a compact nuclear X-ray source with $\log L_{\rm X}\approx41.46$ erg/s, supporting the presence of an LLAGN. Spatially resolved emission-line diagnostics show LINER-like line ratios across most spaxels with $\mathrm{S/N} \geq 3$, while spatially resolved $τ$ maps ($τ\equiv Q_{\rm pAGB}/Q_{\rm req}$) indicate a widespread photon deficit ($\logτ<0$ over most of the mapped region), even under the most optimistic pAGB normalizations, the nuclear region remains at $τ< 1$. Line-ratio--kinematic tests find no evidence for shock-dominated excitation as the primary driver of the extended emission, although a localized or sub-dominant shock contribution cannot be ruled out with the present data. We use this galaxy as a pilot case because the combination of Hector IFS and an independent nuclear X-ray constraint provides a stringent validation of the spatially resolved photon-budget framework. Our results indicate that evolved stellar populations alone cannot account for the observed emission, that an additional nuclear ionizing source is required at least in the inner region, and that a weak LLAGN likely contributes to the ionizing budget, particularly in the inner region. Our results demonstrate that extended LINER-like emission can conceal a substantial LLAGN contribution even when traditional optical and infrared AGN indicators are weak, and that spatially resolved photon-budget tests combined with X-ray constraints can effectively reveal such hidden activity.

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