The Spatially-Resolved Recent Star Formation History of the M81 Disk

@misc{rao2026spatiallyresolved,
  title = {{The Spatially-Resolved Recent Star Formation History of the M81 Disk}},
  author = {Vaishnav V. Rao and Eric F. Bell and Adam Smercina and Tobin M. Wainer and Andrew Dolphin and Benjamin Williams and Julianne J. Dalcanton},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.37661},
  eprint = {2610.37661},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.37661},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - The Spatially-Resolved Recent Star Formation History of the M81 Disk
AU  - Vaishnav V. Rao
AU  - Eric F. Bell
AU  - Adam Smercina
AU  - Tobin M. Wainer
AU  - Andrew Dolphin
AU  - Benjamin Williams
AU  - Julianne J. Dalcanton
PY  - 2026
DA  - 2026/10/27
PB  - arXiv
DO  - 10.48550/arxiv.2610.37661
UR  - https://arxiv.org/abs/2610.37661
AB  - The nearby M81 galaxy---a tidally interacting L^* spiral disk---offers a unique perspective on the interplay of secular and external processes in shaping galaxy properties. We present the most detailed, panoramic map of M81's stellar populations to date, using archival Hubble Space Telescope ACS photometry from the ANGST survey spanning the full optical extent of its disk. From color-magnitude diagram fitting, we recover spatially-resolved star formation histories (SFHs) over the last ∼180Myr. M81's global SFH is remarkably steady in the last ∼180Myr with slight enhancements seen ≲15Myr ago. The average SFR surface density rises toward the center before falling off within the innermost ∼4kpc. The disk is also notably lopsided, with the eastern half having formed ∼50% more stars than the western half over the same area---a trend missed by FUV-based SFR indicators due to dust systematics. Finally, the long-term SFHs of both M81 and M82 point to a pericenter passage ∼1Gyr ago. By identifying M81-M82 analogs in the TNG50 cosmological simulation, we rule out the more recent pericenter times of 150−220Myr predicted by some works, as such passages are inconsistent with M81's undisturbed SFH over the last ∼180Myr. With this work, M81 becomes only the third L^* spiral---after M31 and NGC 6946---to have its SFH spatially resolved across large areas of its disk.
ER  -