Gasdynamics in NGC 5248: Fueling a Circumnuclear Starburst Ring of Super–Star Clusters

Abstract

Through observations and modeling, we demonstrate how the recently discovered large-scale bar in NGC 5248 generates spiral structure that extends from 10 kpc down to 100 pc, fuels star formation on progressively smaller scales, and drives disk evolution. Deep inside the bar, two massive molecular spirals cover nearly 180 in azimuth, show streaming motions of 20-40 km s À1 , and feed a starburst ring of super-star clusters at 375 pc. They also connect to two narrow K-band spirals that delineate the UV bright star clusters in the ring. The data suggest that the K-band spirals are young, and the starburst has been triggered by a bar-driven spiral density wave (SDW). The latter may even have propagated closer to the center where a second H ring and a dust spiral are found. The molecular and Hubble Space Telescope data support a scenario where stellar winds and supernovae efficiently clear out gas from dense star-forming regions on timescales less than a few Myr. We have investigated the properties of massive CO spirals within the framework of bar-driven SDWs, incorporating the effect of gas self-gravity. We find good agreement between the model predictions and the observed morphology, kinematics, and pitch angle of the spirals. This combination of observations and modeling provides the best evidence to date for a strong dynamical coupling between the nuclear region and the surrounding disk. It also confirms that a low central mass concentration, which may be common in late-type galaxies, is particularly favorable to the propagation of a bar-driven gaseous SDW deep into the central region of the galaxy, whereas a large central mass concentration favors other processes, such as the formation and decoupling of nuclear bars.

Explaining two circumnuclear star forming rings in NGC 5248

“…Comparison between the CO(2−1) emitting gas distribution presented here and the CO(1−0) distribution presented in Jogee et al (2002b) shows that CO(1−0) and CO(2−1) emission is both present in the two spiral arms that trace the outer circumnuclear star forming ring in the north and south. Inside the outer ring radius the two line emission distributions differ.…”

“…Also, the BIMA SONG data showed that CO(1−0) emission was constrained to this radius and in the dust spiral shown in Fig. 4a of Jogee et al (2002b) it does seem that the spiral's pitch angle changes significantly at this radius, indicating a change in gas/dust dynamics.…”

“…The BIMA SONG intensity distribution shows that the molecular gas density, as traced by the CO(1−0) flux intensity, increases towards the center, with an "S"-like shape, which is resolved into two spiral arms in the higher angular resolution CO(1−0) maps by Jogee et al (2002b). The main CO(1−0) emission structure extends out to ∼22 (1.4 kpc) from the nucleus.…”

“…Spiraling dust lanes between 6 (370 pc) and 90 (5.5 kpc) radius are seen in broad-band B and I − K images (Figs. 2 and 4a of Jogee et al 2002b). The CO(1−0) distribution mapped by the BIMA SONG survey (Helfer et al 2003) also shows some lowlevel CO emission at these positions (Fig.…”

The Fueling and Evolution of AGN: Internal and External Triggers

“…(1) Hydrodynamical simulations (Englmaier & Shlosman 2000) suggest that bar-driven shocks which exist near the ILRs can trigger gaseous SDWs which propagate inwards across the ILRs, and lead to grand-design two-armed nuclear dust spirals. Observational support for the model comes from detailed comparisons of the simulations with the data in NGC 5248 (Jogee et al 2002b; Fig. 11) which hosts a grand-design nuclear spiral.…”