Starburst galaxy

Definition

1. The rate at which the galaxy is currently converting gas into stars.
2. The available quantity of gas from which stars can be formed.
3. A comparison of the timescale on which star formation consumes the available gas with the age or rotation period of the galaxy.

• Continued star-formation where the current SFR would exhaust the available gas reservoir in much less time than the age of the Universe.
• Continued star-formation where the current SFR would exhaust the available gas reservoir in much less time than the dynamical timescale of the galaxy.
• The current SFR, normalized by the past-averaged SFR, is much greater than unity. This ratio is referred to as the "birthrate parameter".

  Triggering mechanisms

Types

• Blue compact galaxies. These galaxies are often low mass, low metallicity, dust-free objects. Because they are dust-free and contain a large number of hot, young stars, they are often blue in optical and ultraviolet colours. It was initially thought that BCGs were genuinely young galaxies in the process of forming their first generation of stars, thus explaining their low metal content. However, old stellar populations have been found in most BCGs, and it is thought that efficient mixing may explain the apparent lack of dust and metals. Most BCGs show signs of recent mergers and/or close interactions. Well-studied BCGs include IZw18, ESO338-IG04, and Haro 11.
• * Blue compact dwarf galaxies are small compact galaxies.
• * Green Pea galaxies are small compact galaxies resembling primordial starbursts. They were found by citizen scientists taking part in the Galaxy Zoo project.
• * Blueberry galaxies are dwarf starbursts that are low redshift counterparts of GPs and likely analogs of high redshift galaxies. While BBs have a low SFR, probably because of their youth and small masses, their sSFR is high and comparable to GPs.
• Luminous infrared galaxies. These galaxies are by definition extremely dusty objects with luminosities greater than. The ultraviolet radiation produced by the luminous young stars is absorbed by the dust and re-radiated in the infrared at wavelengths of around 100 micrometers. Dust absorbs blue and ultraviolet light better than red light, and this explains the extreme red colors associated with ULIRGs. Not all of the original UV radiation is necessarily produced purely by star formation, and some LIRGs are likely powered in part by active galactic nuclei.
• * Ultra-luminous Infrared Galaxies. These are more extreme versions of LIRGs with luminosities greater than. X-ray observations of many ULIRGs that penetrate the dust suggest that many starburst galaxies are double-cored systems, lending support to the hypothesis that ULIRGs are powered by star-formation triggered by major mergers. One well-studied ULIRG is Arp 220.
• * Hyperluminous Infrared galaxies are even more extreme versions with luminosities greater than.
• * Submillimeter galaxies are ULIRGs or HyLIRGs at redshift larger than 2. At these redshifts, the 100 micrometer infrared emission is observed at sub-millimeter wavelengths, making this wavelength range favorable for detecting distant ULIRGs.
• Wolf–Rayet galaxies, galaxies where a large portion of the bright stars are Wolf–Rayet stars. The Wolf–Rayet phase is a relatively short-lived phase in the life of massive stars, typically 10% of the total life-time of these stars, and as such any galaxy is likely to contain few of these. However, because the stars are both luminous and have distinctive spectral features, it is possible to identify these stars in the spectra of entire galaxies, and doing so allows good constraints to be placed on the properties of the starbursts in these galaxies.

  Ingredients

Examples

List of starburst galaxies