When midsize galaxies merge with giant ones, they drag so much of little galaxies with them, Eric Bell (University of Michigan, Ann Arbor) reported June ninth at the digital summer season assembly of the American Astronomical Society.
To examine the dwarf galaxy inhabitants of the Local Group during which the Milky Way and Andromeda galaxies reside, Bell and Richard D’Souza (Vatican Observatory, Italy) simulated the clouds of darkish matter during which Milky Way–mass galaxies reside. By following the interactions of 48 of these simulated haloes with smaller surrounding ones (stand-ins for dwarf galaxies), the astronomers found one thing attention-grabbing: Satellites tended to merge in teams with the massive galaxy, with smaller galaxies tagging alongside when a midsize one merged with the central leviathan. The impact didn’t improve the quantity of infalling galaxies; it solely modified when they fell in.
To check these predictions, the staff checked out when star formation shut off in real-life, smaller galaxies surrounding the Milky Way and Andromeda. Starbirth, the astronomers reasoned, is an efficient proxy for merger time, as a result of the little galaxies would probably be stripped of their star-forming gas once they fell into the massive, scorching halo of the central galaxy. And certainly, observations present that star formation shut off in the Milky Way satellites round two durations of time when a large galaxy was falling in — about 2 billion years in the past for the Large Magellanic Cloud and 10 billion years in the past for Gaia-Enceladus.
Conversely, there’s just one turn-off time for Andromeda satellites: about 6 billion years in the past. That means that Andromeda’s largest companion, M33, may need began its nosedive into Andromeda’s halo round then. The timeline would problematize others’ suggestion that M33 is on its first flyby past Andromeda and, like the LMC, had solely arrived in the final couple billion years. A more in-depth take a look at Andromeda’s satellite tv for pc household may elucidate simply when M33 confirmed up for its go to.
Astronomers are actually capable of discover the satellites of giant galaxies out to a number of tens of thousands and thousands of light-years from us, and if borne out, these outcomes might allow them to discern such galaxies’ histories extra clearly. The staff’s work seems in the July Monthly Notices of the Royal Astronomical Society.