M109 is an exquisite example of a symmetric barred spiral. Its strong stellar bar component has a rounded central bulge and is surrounded by an incomplete ring from which the two tightly wound spiral arms originate. Ring formation is strongly tied to barred structure and is believed to result from torque induced effects of mass distribution on the disk components of the galaxy. The galaxy shows a peculiar absence of bright HII regions and although knots of star forming regions are found in the outer spiral arms, star formation is peculiarly absent from the inner regions of the galaxy. It seems the outer spiral arms are rich in gas content (the progenitor matter of star formation) however there is a general absence of gas within the inner confines of the galaxy which may have been depleted by gas inflows driven by the large central bar. The effect of the bar on the distribution of gas in the galaxy is not straight forward but depends on the bars rotational velocity, its length, and the ratio of bar to disk mass. Simulations of galactic collisions show a tendency for bar formation in the merger remnants of galactic collisions. This phenomenon may help to explain the formation of nuclear bars.
M109 is a member of the Ursa Major Cluster
of galaxies. There are three galactic clusters that are all within
a similar distance of our galaxy, including the Virgo cluster,
the Fornax cluster, and the Ursa Major cluster. Unlike the Virgo
cluster which appears to concentrate towards a core, the Ursa
Major cluster is more dispersed without any core concentration.
Its loose structure has left it relatively undefined compared
to other clusters. It has about 79 known major galactic members
spread over about 3 million light years.