2011A&A...527A..92C

We present ¹²CO(1-0) and ¹²CO(2-1) maps of the interacting barred LINER/Seyfert 2 galaxy NGC3627 obtained with the IRAM interferometer at resolutions of 2.1"x1.3" and 0.9"x0.6", respectively. We also present single-dish IRAM 30m ¹²CO(1-0) and ¹²CO(2-1) observations used to compute short spacings and complete interferometric measurements. These observations are complemented by IRAM 30m measurements of HCN(1-0) emission detected in the center of NGC3627. The molecular gas emission shows a nuclear peak, an elongated bar-like structure of ∼18" (∼900pc) diameter in both ¹²CO maps and, in ¹²CO(1-0), a two-arm spiral feature from r∼9" (∼450pc) to r∼16" (∼800pc). 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 1.6µm H-band 2MASS image of NGC3627 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 160µm images of NGC3627 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 NGC3627 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, ∼60pc in ¹²CO(2-1). If the bar ends at ∼3kpc, 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 NGC3627 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.