Lyman-alpha emitter

Some far away stars shine very bright.

These are young galaxies. They make a lot of new stars. This makes them glow with light.

This light comes from gas. The gas is part of the galaxy. The bright stars make the gas glow.

Sometimes dust hides the light. Dust can block the glow. But some light still escapes.

These galaxies are like clues. They help us see the past. They show us how the universe grew.

Some galaxies are very special. We call them Lyman-alpha emitters. These are young galaxies. They are often 200 to 600 million years old. They make stars very fast.

These galaxies glow with a specific kind of light. This light comes from hydrogen gas. Inside the galaxy, new stars make the gas glow. This process is called recombination. It happens when gas changes its state.

Sometimes it is hard to see this light. Dust inside the galaxy can block it. We call the amount of light that gets out the escape fraction. If there is a lot of dust, the light stays trapped. But light can still find a way out. Moving gas can help the light escape. Even uneven dust can leave small paths for the light.

These galaxies are important clues. They help us study the history of the universe. They might be the ancestors of our own Milky Way galaxy. By looking at them, we learn how matter moved in the early universe.

Lyman-alpha emitters are very special types of distant galaxies. These galaxies are often quite young. Most are only 200 to 600 million years old. They are famous for making stars at a very high rate. Scientists think these galaxies are the ancestors of modern galaxies like our Milky Way. Because light takes time to travel, seeing them shows us the history of our universe.

These galaxies glow because of a specific thing that happens with hydrogen gas. Inside the galaxy, new stars create a burst of star formation. This process ionizes the hydrogen gas. When the gas changes back, it releases a special kind of light. This is called Lyman-alpha radiation. This light comes from a process called recombination. It is a way for the gas to release energy.

People first thought about this light a long time ago. In 1967, Bruce Partridge and P. J. E. Peebles suggested this light could signal young galaxies. Today, astronomers use special searches to find them. They look for an excess of light at a specific wavelength. This wavelength is 1215.67 Å. By studying this light, scientists can track how matter moved in the early universe. They can even find dark matter halos.

These galaxies are usually small in mass. They typically have a mass between 10^8 and 10^10 solar masses. One hard job for scientists is seeing all the light. We call the amount of light that makes it out the escape fraction. Sometimes, dust inside the galaxy blocks the light. This makes the galaxy look less bright than it is. However, moving gas can help the light find a way out.

Studying these galaxies helps us understand the whole universe. They help us learn about a time called reionization. During this time, light from galaxies helped change the state of the universe. We can also use them to study sound waves from the early universe. These are called baryonic acoustic oscillations. Scientists use programs like the Lyman Alpha Reference Sample, or LARS, to study nearby galaxies. This helps them understand how light escapes from distant ones.

A Lyman-alpha emitter, or LAE, is a specific type of distant galaxy. These galaxies are characterized by their emission of Lyman-alpha radiation. This radiation comes from neutral hydrogen gas. Because light takes a finite amount of time to travel across space, observing these galaxies allows astronomers to glimpse the history of the universe. Many scientists believe these galaxies are the progenitors of modern galaxies like our Milky Way.

The glowing light from an LAE is created through a process called recombination. It begins with an ongoing burst of star formation within the galaxy. This intense star formation ionizes the interstellar hydrogen gas. As the hydrogen atoms recombine, they release energy in the form of Lyman-alpha radiation. This specific light occurs at a wavelength of 1215.67 Å. This process makes these galaxies stand out during narrow-band searches. Astronomers look for an excess of flux at this specific wavelength to identify them.

Lyman-alpha emitters possess very specific physical properties. They are typically low-mass galaxies. Their mass generally ranges from 10^8 to 10^10 solar masses. These galaxies are also quite young, usually between 200 and 600 million years old. Notably, they possess the highest specific star formation rate of any known galaxies. These combined traits suggest they represent an early, active stage of galactic evolution.

Scientists first identified this signature in 1967. Researchers Bruce Partridge and P. J. E. Peebles suggested that Lyman-alpha emission could signal the presence of young galaxies. Since then, the study of LAEs has become vital to cosmology. By observing the redshift of these emitters, researchers can trace dark matter halos. This helps them understand how matter was distributed throughout the early universe. They also help scientists study the faint end of the luminosity function at high redshifts.

One of the biggest challenges in studying LAEs is the Lyman-alpha escape fraction. This term describes the portion of light that actually escapes the galaxy to be seen by observers. This fraction varies greatly between different galaxies. Dust content within the interstellar medium is a major factor. Significant amounts of dust can obscure the brightness of a galaxy. Evidence shows that the escape fraction evolves with redshift, likely due to the buildup of dust.

However, other factors can help this light escape. Turbulence within the interstellar medium can play a crucial role. Moving gas can shift photons out of resonance. This reduces the chance that the light will be absorbed by neutral hydrogen. Additionally, a clumpy or uneven distribution of dust can create pathways for light. In some cases, varying velocities in the interstellar medium help photons bypass thick clouds of dust. Observations have even shown that luminous LAEs can amplify light in surrounding fainter galaxies by 3 to 9 times.

LAEs are also essential for understanding the Epoch of Reionization. This was a period when light from galaxies helped change the state of the universe. Simulations suggest that more luminous LAEs played a large part in this process. In fact, 90% of the escaping Lyman Continuum radiation in the interstellar medium can be credited to LAEs. Furthermore, these galaxies help scientists study baryonic acoustic oscillations. These are imprints of sound waves from the early universe. The three-dimensional distribution of these galaxies allows for a robust probe of cosmology.

To study these complex mechanisms, scientists use programs like the Lyman Alpha Reference Sample, or LARS. LARS focuses on several tens of nearby star-forming galaxies at redshifts between 0.028 and 0.19. These nearby galaxies serve as local analogs for the very distant LAEs. LARS has revealed that Lyman-alpha emission often forms large halos. These halos extend far beyond the actual regions of star formation. This happens most often in galaxies with low dust content.