The Andromeda Galaxy’s Devouring Nature: A Tale of Satellite Galaxies
The vast Andromeda Galaxy, a celestial behemoth, has a voracious appetite for its smaller companions. New research delves into the intricate process of how these satellite galaxies meet their fate, shedding light on the complex interplay between galaxies. The study, titled ‘The Lives and Deaths of Faint Satellite Galaxies Around M31’, explores the fate of these galaxies as they orbit their much larger host.
The Milky Way’s Hunger
Our own Milky Way galaxy is a master of consumption. It slowly devours the Large and Small Magellanic Clouds, leaving behind a long gas stream known as the Magellanic Stream. These clouds, lacking sufficient mass, succumb to the gravitational pull of the Milky Way, which strips away their gas.
The Milky Way’s appetite extends beyond the Magellanic Clouds. The ESA’s Gaia mission revealed that the Milky Way devoured the Gaia-Enceladus-Sausage dwarf galaxy billions of years ago. This evidence underscores the Milky Way’s role as a galactic cannibal.
Andromeda’s Satellite Galaxies
Andromeda, our galactic neighbor, is known for its extensive collection of satellite dwarf galaxies. These satellites have played a crucial role in Andromeda’s growth through mergers. The research focuses on understanding the intricate process of these mergers, aiming to unravel the mysteries of satellite galaxy evolution.
Thanks to the Gaia mission, astronomers now possess a treasure trove of data on the proper motions of over a billion stars within the Milky Way. This enables them to reconstruct the orbits of satellite galaxies into the past. Combined with the ability to resolve individual stars at great distances, astronomers can identify populations of stars that share a common origin, even if they are no longer gravitationally bound.
By utilizing this wealth of data, researchers can gain profound insights into how satellite galaxies are shaped by physical processes as they orbit their massive hosts. The study highlights the Local Group’s unique position, offering a rare opportunity to test galaxy evolution theories.
Quenching Satellite Galaxies
The research delves into the quenching of satellite galaxies, a critical phase in the merger process. The authors predict proper motions, infall times, and first pericentric passage times for 39 of Andromeda’s satellite galaxies. These predictions are based on cosmological N-body simulations and the properties of Andromeda itself.
The findings reveal that only the most massive satellites of Andromeda can sustain star formation for over 3 billion years after their pericenter. The pericenter is the point of closest approach to Andromeda, where the satellite’s stars are exposed to the galaxy’s powerful gravity.
The authors conclude that ‘ram-pressure, tidal stripping, and/or the cessation of gas accretion reliably quench dwarf galaxies with solar masses < 107.5 M⊙ upon becoming satellites of Andromeda.’ This quenching process is a critical aspect of the merger dynamics.
Early Quenching
Interestingly, the research indicates that a significant portion of lower-mass satellites are quenched long before they encounter Andromeda. The authors note that ‘the majority of the remaining lower mass satellites appear to have been quenched significantly before their first pericenter passage, with some of the least massive quenching up to 10 Gyr prior.’
Some satellites are quenched by reionization, where UV radiation heats the gas, providing it with sufficient kinetic energy to escape. However, most low-mass satellites quenched early are affected by ‘pre-processing.’ During this phase, the satellite galaxy spent time near a different host galaxy with lower mass than Andromeda, leading to gas heating and removal.
Comparing Andromeda and the Milky Way
The research team compared these findings with the Milky Way’s satellite galaxies. They discovered that the two galaxies exhibit distinct populations of satellite galaxies. The Milky Way’s satellites have generally been satellites for longer and have quenched more quickly after infall compared to Andromeda’s satellites.
Previous research supports this, indicating that the Milky Way’s satellites have old quenching times and infall times, accounting for 76% of the population. In contrast, Andromeda’s satellites display a wider and more even spread of both infall and quenching times.
This difference could be attributed to variations in observing and measuring the satellites of both galaxies. Alternatively, it might suggest that the Milky Way consumed its satellites earlier than Andromeda, with notable exceptions like the Large and Small Magellanic Clouds.
The Role of Environmental Effects
The authors emphasize that the properties of Andromeda’s satellites reflect the significant role of environmental effects, such as ram-pressure, tidal stripping, and gas accretion cessation, in quenching low-mass satellite galaxies throughout the universe.
This research provides valuable insights into the complex dynamics of galaxy mergers and the quenching of satellite galaxies, offering a deeper understanding of the universe’s galactic interactions.