Star formation in the outer resonance ring of NGC 1300

Surface photometry of the barred galaxy NGC 1300 in B and I bands reveals an outer pseudo-ring with star formation knots located at the positions of 108 M⊙ H I clouds previously mapped by M. England with the VLA. The age of the ring from the B-I colors is estimated to be ∼109 yr, and the age of the star formation knots is estimated to be ∼2 × 107 yr. Stability considerations suggest that the H I clouds formed by gravitational condensation along the ring periphery. If the outer extent of the ring is at the outer Lindblad resonance, then the bar ends slightly outside the inner 4:1 resonance and corotation is at the position of the break and dust lane crossing midway out in the spiral arms. © 1996. The American Astronomical Society. All rights reserved.