Physical Properties of the Circumnuclear Starburst Ring in the Barred Galaxy NGC 1097

Abstract

We report high resolution 12 CO(J = 2-1), 13 CO(J = 2-1), and 12 CO(J = 3-2) imaging of the Seyfert 1/starburst ring galaxy NGC 1097 with the Submillimeter Array to study the physical and kinematic properties of the 1-kpc circumnuclear starburst ring. Individual star clusters as detected in the HST map of Paα line emission have been used to determine the star formation rate, and are compared with the properties of the molecular gas. The molecular ring has been resolved into individual clumps at GMA-scale of 200-300 pc in all three CO lines. The intersection between the dust lanes and the starburst ring, which is associated with orbit-crowding region, is resolved into two physically/kinematically distinct features in the 1. ′′ 5×1. ′′ 0 (105×70 pc) 12 CO(J = 2-1) map. The clumps associated with the dust lanes have broader line width, higher surface gas density, and lower star formation rate, while the narrow line clumps associated with the starburst ring have opposite characteristics. Toomre-Q value under unity at the radius of the ring suggests that the molecular ring is gravitationally unstable to fragment at the scale of the GMA. The line widths and surface density of gas mass of the clumps show an azimuthal variation related to the large scale dynamics. The star formation rate, on the other hand, is not significantly affected by the dynamics, but has a correlation with the intensity ratio of 12 CO (J = 3-2) and 12 CO(J = 2-1), which traces the denser gas associated with star formation. Our resolved CO map, especially in the orbit-crowding region, for the first time demonstrates observationally that the physical/kinematic properties of the GMAs are affected by the large scale bar-potential dynamics in NGC 1097.

The NGC 1614 interacting galaxy

“…For NGC 1365, Sakamoto et al (2007) found five CO hot spots with line widths (FWHM) between 60 and 90 km s −1 that seem to be associated with SSCs of ∼10 6 M (Galliano et al 2005). Hsieh et al (2011) found many GMAs in the molecular ring (14 GMAs) and the dust lane (5 GMAs) of NGC 1097. They subdivided the GMAs in the molecular ring into two categories: GMAs with broad (σ > 30 km s −1 ) and narrow (σ < 30 km s −1 ) line dispersions.…”

“…These barred spirals are so-called twin-peak galaxies because they contain nuclear molecular rings that show a double-peak structure in their molecular gas distribution perpendicular to the stellar bar, where the starburst ring and the dust lanes connect (Sakamoto et al 2007;Hsieh et al 2011). NGC 1614 harbors an asymmetric ring and displays at least one connection point with its dust lanes.…”

“…One other property NGC 1614 shares with galaxies like NGC 1097 and NGC 1365 are hot spots (gas clumps and CO brightness temperature peaks, Sakamoto et al 2007;Hsieh et al 2011), so-called GMAs (Vogel et al 1988). For NGC 1365, Sakamoto et al (2007) found five CO hot spots with line widths (FWHM) between 60 and 90 km s −1 that seem to be associated with SSCs of ∼10 6 M (Galliano et al 2005).…”

“…1). Hsieh et al (2011) also determined the sizes of their GMAs by measuring the number of pixels above a certain intensity threshold and then assuming the GMAs to be spherical to obtain diameters of the individual GMAs. The sizes of GMAs located in the ring of NGC 1097 and outside the structure differ significantly.…”

Kinematics and dynamics of molecular gas in galactic centers

“…The presence of two velocity components is what is expected from the region being a convergent area of two types of gas orbits. Such double-peak line profiles have been observed in the x 1 -x 2 orbit-crowding regions of a number of barred galaxies (e.g., Regan et al 1999;Sakamoto et al 2007;Hsieh et al 2011).…”