Molecular Gas Dynamics in NGC 6946: A Bar‐driven Nuclear Starburst “Caught in the Act”

Abstract

We present high angular resolution ($1 00 and 0B6) millimeter interferometric observations of the 12 CO(1À0) and 12 CO(2À1) line emission in the central 300 pc of the late-type spiral galaxy NGC 6946. The data, obtained with the IRAM Plateau de Bure Interferometer (PdBI), allow the first detection of a molecular gas spiral in the inner $10 00 (270 pc) with a large concentration of molecular gas (M H 2 $ 1:6 ; 10 7 M ) within the inner 60 pc. This nuclear clump shows evidence for a ringlike geometry with a radius of $10 pc as inferred from the position-velocity diagrams. Both the distribution of the molecular gas and its kinematics can be well explained by the influence of an inner stellar bar of about 400 pc length. A qualitative model of the expected gas flow shows that streaming motions along the leading sides of this bar are a plausible explanation for the high nuclear gas density. Thus, NGC 6946 is a prime example of molecular gas kinematics being driven by a small-scale, secondary stellar bar.

Molecular gas in NUclei of GAlaxies (NUGA)

“…It could well be that these torques take over the fueling of the nucleus inside the 300 pc where the gravity torques are not efficient anymore. Alternatively, an inner stellar bar could drive the gas further inward as in NGC 6946 (Schinnerer et al 2006); however, the current observations do not show any evidence of such a small inner bar.…”

Are Globular Clusters the Remnant Nuclei of Progenitor Disk Galaxies?

“…The center of each progenitor disk is occupied by a NC with ∼0.2% of the host mass. As long as the disk escapes merger activity, its NC grows in mass via a series of nuclear starbursts fueled by gas flow from the disk onto the nucleus, similar to those observed in nearby galaxies (e.g., Schinnerer et al 2003Schinnerer et al , 2006Schinnerer et al , 2007.…”

A Sinfoni View of Galaxy Centers: Morphology and Kinematics of Five Nuclear Star-Formation Rings

“…This is not a straightforward task, because maps and velocity fields of the molecular gas are difficult to obtain, especially for sources in the southern hemisphere, and reach the required resolution only in a few nearby galaxies (e.g. Schinnerer et al 2003Schinnerer et al , 2006. Lacking molecular gas observations, the best approach is to use high spatial resolution maps of the dust morphology, as demonstrated by Martini et al (2003).…”

“…Only recently has it become possible to study the molecular gas flows within a few tens of pc from the nucleus in a small number of nearby galaxies (e.g. Schinnerer et al 2003Schinnerer et al , 2006Schinnerer et al , 2007.…”