Isolated, low-mass galaxies help researchers study the impact of reionization on their star formation histories (SFHs) without interference from large host galaxies. Few such galaxies are close enough to determine their SFHs accurately using detailed star photometry.
Leo P is such a low-mass isolated galaxy and a distant neighbor of the Milky Way.
In a new study, a team of researchers led by Kristen McQuinn, a scientist at the Space Telescope Science Institute and an associate professor in the Department of Physics and Astronomy at the Rutgers University-New Brunswick School of Arts and Sciences, used JWST observations. The team reported that Leo P “reignited,” reactivating during a significant period in the universe’s timeline, producing stars when many other small galaxies didn’t.
Leo P is a dwarf galaxy discovered in 2013, some 5.3 million light-years from Earth. It is far enough from the Local Group of galaxies, including the Milky Way, to be its neighbor without being affected by the gravitational fields of larger star systems.
Located in the constellation Leo, the galaxy is about the size of a star cluster within the Milky Way and about the same age. The “P” in Leo P stands for “pristine,” as the galaxy has few chemical elements besides hydrogen and helium.
The team looked into the past by studying about 13 billion years old stars. These ancient stars serve as “fossil records” of early star formation, and by examining them, they inferred what was happening in the early universe.
They discovered that Leo P initially formed stars but then stopped for a few billion years during the Epoch of Reionization. It took a few billion years after this period for the galaxy to reignite and start forming new stars again.
Kristen McQuinn/NASA’s James Webb Space Telescope
McQuinn said, “We have a measurement like this for only three other galaxies – all isolated from the Milky Way – and they all show a similar pattern.”
Observations of dwarf galaxies in the Local Group show that star production disappeared during the Epoch of Reionization, a significant period in the universe’s history between 150 million and one billion years after the Big Bang when the first stars and galaxies formed.
This contrast in star production suggests that it isn’t just the mass of a galaxy during reionization that determines whether it stops forming stars. The environment—whether the galaxy is isolated or a satellite of a larger system—also plays an important role.
How small galaxies sustain the formation of new stars?
McQuinn explained that these observations will help determine not only when small galaxies formed their stars but also how the reionization of the universe affected the formation of small structures.
“If the trend holds, it provides insights on the growth of low-mass structures that is not only a fundamental constraint for structure formation but a benchmark for cosmological simulations.”
The researchers discovered that Leo P is metal-poor, with only 3% of the sun’s metallicity. This means its stars contain 30 times fewer heavy elements than the sun, making Leo P similar to the primordial galaxies of the early universe.
McQuinn said the knowledge gleaned from these observations will help astronomers piece together the timeline of cosmic events, understand how small structures evolved over billions of years, and learn about the processes that led to the creation of stars.
Journal Reference:
- Kristen B. W. McQuinn, Max J. B. Newman et al. The Ancient Star Formation History of the Extremely Low-mass Galaxy Leo P: An Emerging Trend of a Post-Rionization Pause in Star Formation. The Astrophysical Journal. DOI 10.3847/1538-4357/ad8158
Source: Tech Explorist
