Stellar Age Patterns Across the Disk of M101 with Narrowband Imaging

Using deep, narrowband imaging of the nearby spiral galaxy M101, I present stellar age information across the full extent of the disk of M101. Two of the narrowband filters on the 24/36-in Burrell Schmidt Telescope measure age-sensitive absorption features such as the Balmer lines and the slope of the continuum between the Balmer break and 4000 Å break. I interpret these features in the context of inside-out galaxy formation theories and dynamical models of spiral structure. In the relatively undisturbed main disk, I find that stellar ages get progressively older with distance across a spiral arm, consistent with the large-scale shock scenario in a quasi-steady spiral wave pattern. Unexpectedly, I find the same pattern across spiral arms in the outer disk as well, beyond the corotation radius of the main spiral pattern. I suggest that M101 has a dynamic, or transient, spiral pattern with multiple pattern speeds joined together via mode coupling to form coherent spiral structure. This scenario connects together the radial age gradient inherent to inside-out galaxy formation with the across-arm age gradients predicted by dynamic spiral arm theories across the full radial extent of the galaxy.

Dec 19, 2023 9:00 AM — 10:00 AM