Constraining the Age of the NGC 4565 H I Disk Warp: Determining the Origin of Gas Warps
Bell, Eric F.; Holwerda, Benne W.; Monachesi, Antonela; Radburn-Smith, David J.; Bailin, Jeremy; de Jong, Roelof S.; Streich, David; Dolphin, Andrew E.; Dalcanton, Julianne J.; Stilp, Adrienne M.
United States, Germany, Netherlands
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})\times 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.