2007ApJ...662..304B

Propagating star formation in a collisional ring galaxy Arp 10 is investigated by a complex approach, which includes the broadband and narrowband photometry, long-slit spectroscopy, and scanning Fabry-Perot spectroscopy. The ionized gas velocity field obtained with best spatial resolution to date indicates a nonisotropic expansion of the outer ring with a maximum velocity 110 km/s. Strong vertical and noncircular motions are also seen in the vicinity of the inner ring. Our kinematic data suggest that Arp 10 has a small inclination i=22° and high total mass (10¹² M_☉ within a 50 kpc radius). The abundance of oxygen 12+log(O/H) in both star-forming rings is about 8.6. The analysis of spectral indices provides an estimate on the propagation velocities of both rings and metallicity of the precollision stellar population. A small ``knot'' near the nucleus of Arp 10 is unambiguously identified as the ``intruder.'' The intruder spectrum suggests that it was a spiral galaxy before the collision, and its present mass amounts to at least one-fourth of the total mass of Arp 10. We use a simplified two-dimensional hydrodynamic modeling of galaxy collisions to test a collisional origin of Arp 10. The sizes of the inner and outer rings, maximum expansion velocity of the outer ring, and radial profile of the gas circular velocity can be reproduced by a near-central collision with the intruder galaxy, which occurred approximately 85 Myr ago. We acknowledge that an apparent crescent-shaped distribution of Hα emission in the outer ring is caused by a star formation threshold in the gas disk of Arp 10.