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Astron. Astrophys. 319, 450-458 (1997)

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A high-resolution 12 CO(1-0) study of the nucleus of NGC 5907

Observations and modelling

S. García-Burillo 1, M. Guélin 2 and N. Neininger 3

1 Observatorio Astronómico Nacional(OAN), Apartado 1143, E-28800 Alcalá de Henares, Spain (burillo@oan.es)
2 Institut de Radioastronomie Millimétrique, IRAM, F-38406 St. Martin D'Hères, France
3 Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, D-5321 Bonn, Germany

Received 10 July 1996 / Accepted 14 August 1996

Abstract

We have studied with the IRAM interferometer the 12 CO(1-0) emission around the nucleus of NGC 5907, an edge-on spiral at the center of which we had previously detected fast rotating molecular gas. The high angular resolution ([FORMULA], or 160 pc along the major axis) allowed an accurate determination of NGC 5907's kinematical center ([FORMULA], [FORMULA]).

Within [FORMULA] from the center, we detect molecular gas with velocities of [FORMULA] kms-1 (relative to the source systemic velocity [FORMULA] kms-1 (LSR)), and, within [FORMULA] from the center, velocities of up to [FORMULA] km/s. Part of the gas exhibits non-circular motions. We explain the gas kinematics by the presence of a stellar bar with an angular velocity ([FORMULA] =70 kmskpc-1) and of an Outer Inner Linblad Resonance (oILR) at r [FORMULA] 14". The dynamical mass inside the [FORMULA] pc region, estimated from the steepness of the apparent rotation curve, is [FORMULA]. It is comparable to the stellar mass derived from near IR photometry and [FORMULA] times larger than the mass of gas in the same region. The CO brightness distribution and, presumably, the molecular gas distribution are highly asymmetrical.

The interferometer, which filters out the smooth disk emission detected by the 30-m telescope, reveals two narrow structures parallel to the major axis. We identify those with spiral arms. From their position and velocities, we determine an inclination [FORMULA] of the plane of the galaxy. The thickness of the arms, perpendicularly to this plane, is found to be [FORMULA] ([FORMULA] 150 pc).

The large mass concentration near the nucleus and the flat rotation curve of NGC 5907 are more typical of early or intermediate-type spirals than of late type spirals. Yet, the large CO and HI luminosties, the conspicuous molecular arms, and the absence of visible bulge on optical photographs are more characteristic of Sc-Sd galaxies. NGC 5907 may thus be at a critical stage of galactic evolution.

Key words: galaxies: individual: NGC 5907 – galaxies: ISM – galaxies: kinematics and dynamics – galaxies: nuclei – radio lines: galaxies

Send offprint requests to: S. García-Burillo

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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998
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