The Molecular Cloud Content of Early Type Galaxies - Part Four - a Molecular Bar in NGC4691

Details The Molecular Cloud Content of Early Type Galaxies - Part Four - a Molecular Bar in NGC4691 The Molecular Cloud Content of Early Type Galaxies - Part Four - a Molecular Bar in NGC4691

Apr 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...271...71w&link_type=abstract

Astronomy and Astrophysics, Vol.271, NO. 1/APRI, P. 71, 1993

Astronomy and Astrophysics

Astrophysics

11

Scientific paper

Observations of the ^12^CO J = 1-0 and ,J = 2-1 emission in the SB0 galaxy NGC 4691 show a prominent molecular bar. Deconvolution using Lucy rectification and the method of Simulated Annealing' reveal that the molecular emission is distributed in several cloud complexes aligned with the stellar bar. Weak emission perpendicular to the bar suggests the presence of an inner Lindblad resonance at a radius of ~450 pc. The CO velocity field shows that NGC 4691 has an inclination ~0^deg^, which allows a determination of the molecular velocity dispersion in the z direction. The velocity dispersion is homogeneous across the molecular bar, with a mean value of 16 km s^-1^. A weak gas component with a velocity dispersion of 45 km s^-1^ is also found. The latter component appears to have different physical conditions than the former, and could indicate the presence of a molecular disk system, with its kinematics misaligned with that of the main emission component, or the presence of a thick molecular disk. A third possibility is outflowing molecular gas. The total molecular mass is ~9 x 10^8^ M_sun_, which is similar to the molecular gas mass derived from the FIR emission as well as to the HI mass. The ^12^CO(1-0)/^13^CO(1-0) ratio is ~8, indicating a high optical depth for the J = 1-0 line and a beam-averaged ^13^CO column density of ~ 10^15^ cm^-2^. The J = 2-1/J = 1-0 ratio has a minimum of ~0.7 at the most massive cloud complex, but is ~0.9 when averaged over the whole molecular bar.

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