The Star Formation History and Evolution of the Ultra-Diffuse M81 Satellite F8D1
Year: 2026
Type: article
Abstract: We present deep Hubble Space Telescope (HST) imaging of one of the nearest ultra-diffuse galaxies (UDGs) outside of the Local Group: F8D1, a satellite of M81 known to be tidally disrupting. UDGs are an enigmatic and diverse population, with evolutionary pathways ranging from tidal processing to bursty feedback and high initial angular momentum. To determine F8D1’s evolutionary drivers, we resolve stars in F8D1’s central ∼1 kpc and in a parallel field ∼6 kpc along its major axis to deep photometric limits, reaching below the red clump. We also image eight shallower fields along F8D1’s major and minor axes. We calculate the star formation history (SFH) in the two deep fields, finding that while currently quiescent, both regions experienced a substantial burst ∼2 Gyr ago and a smaller burst ∼500 Myr ago, which likely formed F8D1’s nuclear star cluster. In the shallow fields, using the ratio of evolved asymptotic giant branch and red giant branch stars out to ∼13 kpc along F8D1’s known stellar stream, we confirm that F8D1 was globally star-forming until at least ∼2 Gyr ago. We estimate a total progenitor stellar mass, including the stream, of ∼1.3 × 10 8 M ⊙ , with an average [M/H] ∼ −0.8. We compare F8D1’s properties to those of Local Group galaxies with similar initial stellar mass. We find that F8D1 is consistent with a progenitor star-forming galaxy similar to NGC 6822 that is in the midst of a transition to a Sagittarius-like system. Notably, this evolutionary sequence can be accomplished through tidal processing alone in galaxies that have experienced sufficiently bursty feedback to have created cored profiles.
Source: The Astrophysical Journal
Authors: Adam Smercina, Eric F. Bell, Benjamin F. Williams, Benjamin N. Velguth, Sarah Pearson, Jeremy Bailin, Tsang Keung Chan, Julianne J. Dalcanton, Roelof S. de Jong, Richard D’Souza, Andrew Dolphin, Puragra Guhathakurta, Kristen B.W. McQuinn, Antonela Monachesi, Colin T. Slater, Elisa Toloba, Daniel R. Weisz, Andrew Wetzel
Institutions: Tufts University, Space Telescope Science Institute, University of Michigan, University of Washington, Dartmouth College, University of Copenhagen, University of Alabama, Chinese University of Hong Kong, Flatiron Institute, Leibniz Institute for Astrophysics Potsdam, Vatican Observatory, RTX (United States), University of Arizona, University of California, Santa Cruz, Rutgers, The State University of New Jersey, University of La Serena, University of the Pacific, University of California System
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
Awards: RELICS OF STRUCTURE FORMATION: FROM DWARF GALAXIES TO THE OUTSKIRTS OF GALAXY CLUSTERS, G433322167, G4452337565, G4518818167, G4883711497, G58316358, G6273510985, G6506395156, G721019872, Collaborative Research: Estimating the Tempo of the Cambrian Explosion, G766669890, Collaborative Research: The Virgo Cluster as a Testbed for the Study of Galaxy Formation and Evolution, CENTRO DE ASTROFISICA Y TECNOLOGIAS AFINES (CATA)
OpenAlex ID: W4415310689