Molecular Gas in NUclei of GAlaxies (NUGA)

XIV. The barred LINER/Seyfert 2 galaxy NGC 3627 ^⋆

¹ INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, 50125 Firenze, Italy
e-mail: [email protected]
² INAF - Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy
³ Observatoire de Paris, LERMA, 61 Av. de l’Observatoire, 75014, Paris, France
⁴ Observatorio Astronómico Nacional (OAN) - Observatorio de Madrid, C/ Alfonso XII 3, 28014 Madrid, Spain
⁵ IRAM - Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, 38406 Saint-Martin d’Hères, France

Received: 2 September 2010
Accepted: 4 January 2011

Abstract

We present ¹²CO(1–0) and ¹²CO(2–1) maps of the interacting barred LINER/Seyfert 2 galaxy NGC 3627 obtained with the IRAM interferometer at resolutions of and , respectively. We also present single-dish IRAM 30 m ¹²CO(1–0) and ¹²CO(2–1) observations used to compute short spacings and complete interferometric measurements. These observations are complemented by IRAM 30 m measurements of HCN(1–0) emission detected in the center of NGC 3627. The molecular gas emission shows a nuclear peak, an elongated bar-like structure of  ~18″ (~900 pc) diameter in both ¹²CO maps and, in ¹²CO(1–0), a two-arm spiral feature from r ~ 9″ (~450 pc) to r ~ 16″ (~800 pc). The inner  ~18″ bar-like structure, with a north/south orientation (PA = 14°), forms two peaks at the extremes of this elongated emission region. The kinematics of the inner molecular gas shows signatures of non-circular motions associated both with the 18″ bar-like structure and the spiral feature detected beyond it. The 1.6 μm H-band 2MASS image of NGC 3627 shows a stellar bar with a PA =  − 21°, different from the PA (= 14°) of the ¹²CO bar-like structure, indicating that the gas is leading the stellar bar. The far-infrared Spitzer-MIPS 70 and 160 μm images of NGC 3627 show that the dust emission is intensified at the nucleus and at the ansae at the ends of the bar, coinciding with the ¹²CO peaks. The GALEX far-ultraviolet (FUV) morphology of NGC 3627 displays an inner elongated (north/south) ring delimiting a hole around the nucleus, and the ¹²CO bar-like structure is contained in the hole observed in the FUV. The torques computed with the HST-NICMOS F160W image and our PdBI maps are negative down to the resolution limit of our images,  ~60 pc in ¹²CO(2–1). If the bar ends at  ~3 kpc, coincident with corotation (CR), the torques are negative between the CR of the bar and the nucleus, down to the resolution limit of our observations. This scenario is compatible with a recently-formed rapidly rotating bar which has had insufficient time to slow down because of secular evolution, and thus has not yet formed an inner Lindblad resonance (ILR). The presence of molecular gas inside the CR of the primary bar, where we expect that the ILR will form, makes NGC 3627 a potential smoking gun of inner gas inflow. The gas is fueling the central region, and in a second step could fuel directly the active nucleus.