Merging Galaxies Make for Explosive Star Formation

The Gemini Observatory has unveiled a striking new image that shows star formation within the irregular galaxy NGC 4449. This galaxy is categorised as a “Magellanic-type” galaxy due to its similarities  with the Magellanic Clouds, although it is smaller in size. Surrounding NGC 4449 is a halo of smaller dwarf galaxies, two of which are currently merging with it. This merger is causing clouds of gas to collide, fuelling the surge in star formation observed in NGC 4449.

All stars, even the Sun, are born from vast clouds of gas and dust, and when they die, their remnants are recycled back into the galaxy, providing fuel for new stars. When the Universe began there was only hydrogen and a tiny amount of helium present but the fusion process inside stars creates new, heavier elements. This includes every atom inside you and me, the planets and even the computer screen you are reading this on. In a relatively nearby part of the Universe, 13 million light-years away in the constellation Canes Venatici, this cycle is beginning again at an extraordinary pace.

NGC 4449 (the four thousandth, four hundredth and forty ninth object in the New General Catalogue) is a fascinating galaxy and is well known for its high levels of star formation. It’s a member of the M94 group of galaxies and is surrounded by a halo of dwarf galaxies, two of which are currently merging with it. The Gemini Observatory has recently captured incredible images of NGC 4449, showcasing the processes and birth processes occurring within.

The stellar stream in the halo of the nearby dwarf starburst galaxy NGC 4449 is resolved into its individual starry constituents in this exquisite image taken with the 8.2-meter Subaru Telescope and Suprime-Cam. Image credit: R. Jay GaBany and Aaron J. Romanowsky (UCSC) in collaboration with David Martinez-Delgado (MPIA) and NAOJ. Image processed by R. Jay GaBany

The new image was captured with the 8.1 metre Gemini North telescope on Mauna Kea as part of its 25th year anniversary. The galaxy’s swirling red clouds and blue haze are prominent and the result of light from new stars. It has been classified as an irregular Magellanic-type galaxy as it has a loose spiral structure, similar to the Large Magellanic Cloud in southern hemisphere skies.

The Gemini North telescope on the summit of Mauna Kea (Gemini Observatory/AURA)

Deep within NGC4449, stars have been forming for billions of years. It’s producing stars now at a significantly accelerated rate leading to its re-classification as a starburst galaxy. Unlike others though, starbursts are usually restricted to central regions but NGC4449’s is much more widespread. The majority of hot young stars now found in the galaxy’s nucleus and surrounding regions. 

Such levels of star formation are reminiscent of the star formation in galaxies in the early Universe. The driving force here was galaxy mergers and accretions. It is thought the burst of activity in NGC4449 is the result of a galactic merger or interaction with a neighbour. 

One of them displays a faint stream of stars extending to the side of NGC4449 showing it is currently in the process of merging. The string (and satellite galaxy) are barely visible visually due to their low visual brightness but can be detected due to their interaction with NGC449. Another object that suggests previous interactions is a huge globular cluster. It seems to be embedded within the outer halo of NGC4449 and is now believed to be a nucleus from a previous satellite galaxy that has merged with its companion. 

These two interactions and others that have likely remained undetected to date create tidal interactions within the galaxy send shockwaves through the galaxy compressing the interstellar gas. The red that can be seen in the image reveals regions with high levels of ionised hydrogen and star formation. Significant quantities of hot young blue stars can be seen as they emerge from the star forming regions. It is thought, that the rate of star formation in NGC4449 is likely only to last for another billion years or so until the gas has been used up and the shockwaves subside. 

Source : Gemini North Captures Starburst Galaxy Blazing Bright With Newly Forming Stars