CONSTRAINING THE AGE OF THE NGC 4565 H I DISK WARP: DETERMINING THE ORIGIN OF GAS WARPS

Abstract

We have mapped the distribution of young and old stars in the gaseous H i warp of NGC 4565. We find a clear correlation of young stars (<600 Myr) with the warp but no coincident old stars (>1 Gyr), which places an upper limit on the age of the structure. The formation rate of the young stars, which increased ∼300 Myr ago relative to the surrounding regions, is (6.3 +2.5 −1.5) × 10 −5 M yr −1 kpc −2. This implies a ∼60 ± 20 Gyr depletion time of the H i warp, similar to the timescales calculated for the outer H i disks of nearby spiral galaxies. While some stars associated with the warp fall into the asymptotic giant branch (AGB) region of the color-magnitude diagram, where stars could be as old as 1 Gyr, further investigation suggests that they may be interlopers rather than real AGB stars. We discuss the implications of these age constraints for the formation of H i warps and the gas fueling of disk galaxies.