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Unveiling the Distributions of Molecular Gas in Colliding Galaxies

Have you ever looked up to the sky at the starry night? Some people may think stars collide each other because they are too many. Actually, such an event occur very rare. But galaxies, which are made of about 10 billions of stars, collide and merge very often. During the collision, strong gravity force affects on each galaxies; their morphologies and kinematics are severely disturbed! Moreover, these galaxies (so called "Interacting Galaxies") produce significantly much more stars than usual galaxies. Such phenomena have been known from 1980's. Many astronomers eagerly studies to know how interacting galaxies produce stars but the its cause is still in a fog. Observations of interacting galaxies are difficult due to their distance.

A research group led by KANEKO Hiroyuki (University of Tsukuba) observed radio emission from carbon monoxide gas using NRO 45-m telescope and the multi-beam reciever BEARS and revealed the distribution of molecular gas of four interacting galaxies. They found that molecular gas is concentrated on the place which is apart from the centre of galaxies and molecular gas is distributed wider than stars. Simulations and other observations which are aimed at more advanced stage of the collision have showed that molecular gas converge to the centre of galaxies. This observation found out that molecular gas in interacting galaxies does not simply fall into the centre of galaxies.

Reference: Kaneko et al. (2013) PASJ 65, 20 

Figure: Each left figure represents the photograph (the distributions of stars) taken by The Sloan Digital Sky Survey (SDSS). The distributions of carbon monoxide gas obtained with this observation are shown in right figures. The observations were performed toward red rectangles. The strength of radio emission from carbon monoxide gas is frequently used to measurer the amount of molecular gas.
Top Left: Arp 84(NGC 5394 & NGC 5395), Top Right: VV 219(NGC 4567 & NGC 4568),
Bottom Left: VV 254(UGC 12914 & UGC 12915), Bottom Right: The Antennae Galaxies (NGC 4038 & NGC 4039)