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- MILKYWAY GALAXY
- Astronomers often use the
Milky Way as a standard for studying how galaxies form and evolve. Since we’re
inside it, astronomers can study it in detail with advanced telescopes. By
examining it in different wavelengths, astronomers and astrophysicists can
understand its stellar population, its gas dynamics, and its other
characteristics in far more detail than distant galaxies.
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- MILKYWAY GALAXY
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- The Sloan Digital Sky Survey (SDSS), the
Two Micron All Sky Survey (2MASS), and the ESA’s Gaia mission are all prominent
examples. The Satellites Around Galactic
Analogs (SAGA) Survey is another, and its third data release features in three
new studies. The studies are all based on 101 galaxies similar in mass to the
Milky Way.
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- Research shows that galaxies form inside
gigantic haloes of dark matter, the elusive substance that doesn’t interact
with light. 85% of the Universe’s matter is mysterious dark matter, while only
15% is normal or baryonic matter, the type that makes up planets, stars, and
galaxies. Though we can’t see these massive haloes, astronomers can observe
their effects. Their gravity draws normal together to create galaxies and
stars.
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- SAGA is aimed at understanding how dark
matter haloes work. It examines low-mass satellite galaxies around galaxies
similar in mass to the Milky Way. These satellites can be captured and drawn
into the dark matter haloes of larger galaxies. SAGA has found several hundred
of these satellite galaxies orbiting 101 Milky Way-mass galaxies.
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- The Milky Way has been an incredible
physics laboratory. The comparison
between the Milky Way and the 101 others revealed some significant differences. The SAGA Survey’s third data release
includes 378 satellites found in 101 MW-mass systems, and the first paper
focuses on the satellites. Only a painstaking search was able to uncover them.
Four of them belong to the Milky Way, including the well-known Large and Small
Magellanic Clouds.
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- SAGA found that the number of satellites
per galaxy ranges from zero to 13. The
mass of the most massive satellite is a strong predictor of the abundance of
satellites. One-third of the SAGA
systems contain LMC-mass satellites, and they tend to have more satellites than
the MW. The Milky Way is an outlier in
this regard, it’s atypical.
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- The second study focuses on star formation
in the satellites. The star formation rate (SFR) is an important metric in
understanding galaxy evolution. The research shows that star formation is still
active in the satellite galaxies, but the closer they are to the host, the
slower their SFR. Is it possible that the greater pull of the dark matter halo
close to the galaxy is quenching star formation?
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- Our results suggest that lower-mass
satellites and satellites inside 100 kpc are more efficiently quenched in a
Milky Way–like environment, with these processes acting sufficiently slowly to
preserve a population of star-forming satellites at all stellar masses and
projected radii.
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- However, in the Milky Way’s satellites, only
the Magellanic Clouds are still forming stars, with radial distance playing a
role. What in the Milky Way caused
these small, lower-mass satellites to have their star formation quenched?
Perhaps, unlike a typical host galaxy, the Milky Way has a unique combination
of older satellites that have ceased star formation and newer, active ones –
the LMC and SMC – that only recently fell into the Milky Way’s dark matter
halo.
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- This is another reason that our galaxy is
atypical. What about the smaller dark
matter haloes around the satellite galaxies? They developed a new model for
quenching in galaxies with less-than-or-equal-to 109 solar masses. Their model
is constrained by the SAGA data on the 101 galaxies, and the researchers then
compared it to isolated field galaxies from the Sloan Digital Sky Survey.
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- Those surveys can hopefully answer
questions about the role internal feedback plays in the lower-mass satellites,
about their mass and gas accretion and the influence dark matter has on them,
as well as gas processes specific to the satellites.
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- SAGA provides a benchmark to advance our
understanding of the universe through the detailed study of satellite galaxies
in systems beyond the Milky Way.
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November 30, 2024 4628
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--------------------- --- Sunday, December 1,
2024
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