The Unusual AGN Host NGC 1266: Evidence for Shocks in a Molecular Gas Rich S0 Galaxy with a Low Luminosity Nucleus

TL;DR

This study investigates the molecular gas and nuclear activity of NGC 1266, revealing shock-driven gas excitation, a low-luminosity AGN, and a starburst-dominated nucleus through multi-wavelength analysis and modeling.

Contribution

It provides detailed modeling of CO SLEDs with shock physics, constrains the AGN's low luminosity, and clarifies the starburst nature of NGC 1266's nucleus.

Findings

C-type shocks reproduce mid- and high-J CO observations.

The galaxy hosts a low-luminosity, obscured AGN.

Star formation rate is approximately 1.17 M$_{\ m\odot}$ yr$^{-1}$.

Abstract

NGC 1266 is a lenticular galaxy (S0) hosting an active galactic nucleus (AGN), and known to contain a large amount of shocked gas. We compare the luminosity ratio of mid-\emph{J} CO lines to IR continuum with star-forming galaxies (SFGs), and then model the CO spectral line energy distribution (SLED). We confirm that in the mid- and high-\emph{J} regions ($J_{\rm up}$ = 4--13), the C-type shock ($v_{\rm s}$ = 25 km s$^{-1}$, $n_{\rm H}$ = $5\times10^{4}$ cm$^{-3}$) can reproduce the CO observations well. The galaxy spectral energy distribution (SED) is constructed and modeled by the code {\tt X-CIGALE} and obtains a set of physical parameters including the star formation rate (SFR, 1.17 $\pm$ 0.47 \emph{M$_{\odot}$}yr$^{-1}$). Also, our work provides SFR derivation of [C\,{\sc ii}] from the neutral hydrogen regions only (1.38 $\pm$ 0.14 $M_{\odot}$yr$^{-1}$). Previous studies have illusive conclusions on the AGN or starburst nature of the NGC 1266 nucleus. Our SED model shows that the hidden AGN in the system is intrinsically low-luminosity, consequently the infrared luminosity of the AGN does not reach the expected level. Archival data from \emph{NuSTAR} hard X-ray observations in the 3--79 keV band shows a marginal detection, disfavoring presence of an obscured luminous AGN and implying that a compact starburst is more likely dominant for the NGC 1266 nucleus.