NGC 1266: Characterization of the Nuclear Molecular Gas in an Unusual SB0 Galaxy

Abstract

With a substantial nuclear molecular gas reservoir and broad, high-velocity CO molecular line wings previously interpreted as an outflow, NGC 1266 is a rare SB0 galaxy. Previous analyses of interferometry, spectrally resolved low-J CO emission lines, and unresolved high-J emission lines have established basic properties of the molecular gas and the likely presence of an active galactic nucleus. Here, new spectrally resolved CO J = 5-4 to J = 8-7 lines from Herschel Space Observatory HIFI observations are combined with ground-based observations and high-J Herschel SPIRE observations to decompose the nuclear and putative outflow velocity components and to model the molecular gas to quantify its properties. Details of the modeling and results are described, with comparisons to previous results and exploration of the implications for the gas excitation mechanisms. Among the findings, like for other galaxies, the nuclear and putative outflow molecular gas are well represented by components that are cool (T_nuclear {=} 6⁺¹⁰_-2 K and T _outflow ~ 30 K), comprising bulk of the mass (log M_nuclear/M_⊙ {=} 8.3^+0.5_-0.4 and log M_outflow/M_⊙ {=} 7.6^+0.3_-0.3), and the minority of the luminosity (log L_nuclear/L_⊙ {=} 5.44^+0.22_-0.18 and log L _outflow/L _⊙ ~ 6.5) and warm (T_nuclear {=} 74⁺¹³⁰_-26 K and T _outflow > 100 K), comprising a minority of the mass (log M_nuclear/M_⊙ {=} 7.3^+0.5_-0.5 and log M _outflow/M _⊙ ~ 6.3) but the majority of the luminosity (log L_nuclear/L_⊙ {=} 6.90^+0.16_-0.16 and log L _outflow/L _⊙ ~ 7.2). The outflow has an anomalously high L _CO/L _FIR of 1.7 × 10^-3 and is almost certainly shock excited.