Tidal tail

A tidal tail is a thin, elongated region of stars and interstellar gas that extends into space from a galaxy. Tidal tails occur as a result of galactic tide forces between interacting galaxies. Examples of galaxies with tidal tails include the Tadpole Galaxy and the Mice Galaxies. Tidal forces can eject a significant amount of a galaxy's gas into the tail; within the Antennae Galaxies, for example, nearly half of the observed gaseous matter is found within the tail structures.^[1] Within those galaxies which have tidal tails, approximately 10% of the galaxy's stellar formation takes place in the tail.^[2] Overall, roughly 1% of all stellar formation in the known universe occurs within tidal tails.^[3]

Some interacting galaxy pairs have two distinct tails, as is the case for the Antennae Galaxies, while other systems have only one tail. Most tidal tails are slightly curved due to the rotation of the host galaxies. Those that are straight may actually be curved but still appear to be straight if they are being viewed edge-on.

The phenomena now referred to as tidal tails were first studied extensively by Fritz Zwicky in 1953.^[4] Several astrophysicists expressed their doubts that these extensions could occur solely as the result of tidal forces,^{[5] [6]} including Zwicky himself, who described his own views as "unorthodox".^[7] Boris Vorontsov-Velyaminov argued that the tails were too thin and too long (sometimes as large as 100,000 parsecs) to have been produced by gravity alone,^[8] as gravity should instead produce broad distortions. However, in 1972, renowned astronomer Alar Toomre proved that it was indeed tidal forces that were responsible for the tails.^[9]

Tidal tails have been observed in clusters as well as galaxies. There have been tidal tails identified around NGC 5466.^[10] These tails appear to be roughly 4 degrees in the sky, or 1 kpc in length.^[10] There have been other clusters observed with tidal tails as well,^{[11] [12]}

• NGC 2516, from tip of leading tail to tip of trailing tail, 380 pc.^[13]
• Theia 456 (COIN-Gaia 13), tidal tail spans 200 pc.^[13]
• NGC 752, estimates are less than 1.5 kpc to several kpc.^[13]
• ASCC 101, trailing tail is 100 pc, leading tail is hard to measure due to its position.^[14]
• Alessi 3, leading tail 120 pc, trailing tail 60 pc^[14]
• Blanco 1, both tails extend approximately 50-60 pc^[14]
• Collinder 350, both tails extend approximately 50pc^[14]
• Melotte 111, both tails span 50 pc^[14]
• Melotte 25, leading tail is 70 pc, trailing tail is 70 pc^[14]
• Roslund 6, both tails extend approzimately 100 pc^[14]
• Theia 517, leading tail is 120 pc and trailing tail is 150 pc.^[14]

These tidal tails are difficult to measure and different studies show different results. We can most accurately measure tidal tails close to Earth and in the correct orientation.

• Arc-shaped tidal tails in galaxy 3C186.[15]
  Arc-shaped tidal tails in galaxy 3C186.^[15]

^[1]

^[1]

• Interacting galaxies

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