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Abstract From >1000 orbits of HST imaging, we present deep homogeneous resolved star color–magnitude diagrams that reach the oldest main-sequence turnoff and uniformly measured star formation histories (SFHs) of 36 dwarf galaxies (−6 ≥MV≥ −17) associated with the M31 halo, and for 10 additional fields in M31, M33, and the Giant Stellar Stream. From our SFHs, we find: (i) The median stellar age and quenching epoch of M31 satellites correlate with galaxy luminosity and galactocentric distance. Satellite luminosity and present-day distance from M31 predict the satellite quenching epoch to within 1.8 Gyr at all epochs. This tight relationship highlights the fundamental connection between satellite halo mass, environmental history, and star formation duration. (ii) There is no difference between the median SFH of galaxies on and off the great plane of Andromeda satellites. (iii) ~50% of our M31 satellites show prominent ancient star formation (>12 Gyr ago) followed by delayed quenching (8–10 Gyr ago), which is not commonly observed among the MW satellites. (iv) A comparison with TNG50 and FIRE-2 simulated satellite dwarfs around M31-like hosts shows that some of these trends (dependence of SFH on satellite luminosity) are reproduced in the simulations while others (dependence of SFH on galactocentric distance, presence of the delayed-quenching population) are weaker or absent. We provide all photometric catalogs and SFHs as High-Level Science Products on MAST.
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Relating the Diverse Merger Histories and Satellite Populations of Nearby Galaxies
Abstract We investigate whether the considerable diversity in the satellite populations of nearby Milky Way (MW)-mass galaxies is connected with the diversity in their host’s merger histories. Analyzing eight nearby galaxies with extensive observations of their satellite populations and stellar halos, we characterize each galaxy’s merger history using the metric of its most dominant merger,M⋆,Dom, defined as the greater of either its total accreted stellar mass or most massive current satellite. We find an unexpectedly tight relationship between these galaxies’ number ofMV< − 9 satellites within 150 kpc (NSat) andM⋆,Dom. This relationship remains even after accounting for differences in galaxy mass. Using the star formation and orbital histories of satellites around the MW and M81, we demonstrate that both likely evolved along theM⋆,Dom–NSatrelation during their current dominant mergers with the Large Magellanic Cloud and M82, respectively. We investigate the presence of this relation in galaxy formation models, including using the Feedback In Realistic Environments (FIRE) simulations to directly compare to the observations. We find no relation betweenM⋆,DomandNSatin FIRE, and a universally large scatter inNSatwithM⋆,Domacross simulations—in direct contrast with the tightness of the empirical relation. This acute difference in the observed and predicted scaling relation between two fundamental galaxy properties signals that current simulations do not sufficiently reproduce diverse merger histories and their effects on satellite populations. Explaining the emergence of this relation is therefore essential for obtaining a complete understanding of galaxy formation.
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- Award ID(s):
- 2007065
- PAR ID:
- 10486227
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 930
- Issue:
- 1
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 69
- Size(s):
- Article No. 69
- Sponsoring Org:
- National Science Foundation
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