Ultra-luminous infrared galaxies

Definition

Ultra-luminous infrared galaxies (ULIRGs) are a class of galaxies that emit an exceptionally high amount of their energy in the infrared part of the electromagnetic spectrum, typically over 10^12 solar luminosities. These galaxies are often formed through intense star formation and are frequently linked to galaxy mergers, where the interaction between two or more galaxies can trigger significant bursts of star formation and activate their central supermassive black holes, resulting in the ULIRG phenomenon.

5 Must Know Facts For Your Next Test

1. ULIRGs can be several times more luminous than typical galaxies, primarily due to their intense star formation activity and dust absorption.
2. Many ULIRGs are found at higher redshifts, indicating that they are often seen in the earlier stages of the universe, which can provide insights into galaxy formation and evolution.
3. The merger of galaxies is a key factor in the formation of ULIRGs, as these interactions can compress gas and dust, leading to rapid star formation.
4. Most ULIRGs are thought to host an active galactic nucleus (AGN), where a supermassive black hole at the center emits large amounts of energy as it consumes surrounding material.
5. Infrared observations are crucial for studying ULIRGs because they can penetrate through dust clouds that obscure visible light, revealing the underlying processes occurring within these galaxies.

Review Questions

• How do ultra-luminous infrared galaxies relate to the processes of hierarchical merging and what impact does this have on their luminosity?
  • Ultra-luminous infrared galaxies are often the result of hierarchical merging, where smaller galaxies combine to form larger ones. During these mergers, gravitational interactions compress gas and dust, igniting intense star formation and resulting in high luminosities. This process significantly increases the total energy output in the infrared spectrum, making ULIRGs some of the most luminous galaxies observed.
• Discuss the role of star formation in ultra-luminous infrared galaxies and how it contributes to their classification.
  • Star formation plays a pivotal role in classifying ultra-luminous infrared galaxies. The extreme rates of star formation in ULIRGs lead to rapid consumption of gas and dust, resulting in high infrared luminosity. This burst of star creation is often driven by interactions during galaxy mergers, marking ULIRGs as critical for understanding the lifecycle of galaxies and the conditions necessary for intense star formation.
• Evaluate how studying ultra-luminous infrared galaxies enhances our understanding of galaxy evolution and cosmic history.
  • Studying ultra-luminous infrared galaxies provides significant insights into galaxy evolution and cosmic history by illustrating how interactions and mergers influence star formation rates and black hole activity. These galaxies are often located at high redshifts, allowing astronomers to observe conditions that prevailed during the early universe. By analyzing their properties and behaviors, researchers can better understand the mechanisms driving galaxy growth and evolution across different epochs.

Related terms

Starburst Galaxy: A galaxy experiencing an exceptionally high rate of star formation, often associated with interactions or mergers with other galaxies.

Active Galactic Nucleus (AGN): A compact region at the center of a galaxy that is significantly brighter than the rest of the galaxy, powered by a supermassive black hole accreting material.

Herschel Space Observatory: A space-based observatory that operated from 2009 to 2013, designed to observe the universe in the far-infrared and submillimeter wavelengths, crucial for studying ULIRGs.