{"id":26376,"date":"2020-04-23T11:43:02","date_gmt":"2020-04-23T01:43:02","guid":{"rendered":"http:\/\/astro3d.org.au\/?p=26376"},"modified":"2021-02-03T17:08:04","modified_gmt":"2021-02-03T06:08:04","slug":"hungry-galaxies-grow-fat-on-the-flesh-of-their-neighbours","status":"publish","type":"post","link":"https:\/\/astro3d.org.au\/hungry-galaxies-grow-fat-on-the-flesh-of-their-neighbours\/","title":{"rendered":"Hungry Galaxies Grow Fat on the Flesh of Their Neighbours"},"content":{"rendered":"

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Galaxies grow large by eating their smaller neighbours, new research reveals.<\/p>\n<\/blockquote>\n<\/div>

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Exactly how massive galaxies attain their size is poorly understood, not least because they swell over billions of years. But now a combination of observation and modelling from researchers led by Dr Anshu Gupta from Australia\u2019s ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) has provided a vital clue.<\/p>\n

In a paper published in The Astrophysical Journal, the scientists combine data from an Australian project called the Multi-Object Spectroscopic Emission Line (MOSEL) survey with a cosmological modelling program running on some of the world\u2019s largest supercomputers in order to glimpse the forces that create these ancient galactic monsters. <\/span>By analysing how gases within galaxies move, Dr Gupta said, it is possible to discover the proportion of stars made internally \u2013 and the proportion effectively cannibalised from elsewhere.<\/span><\/p>\n<\/div>

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Distribution of dark matter density overlayed with the gas density. This image cleanly shows the gas channels connecting the central galaxy with its neighbours. IMAGE CREDIT: Gupta et al\/ASTRO 3D\/ IllustrisTNG collaboration.<\/p>\n<\/div><\/div><\/div>

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\u201cWe found that in old massive galaxies \u2013 those around 10 billion light years away from us \u2013 things move around in lots of different directions,\u201d she said.<\/p>\n

\u201cThat strongly suggests that many of the stars within them have been acquired from outside. In other words, the big galaxies have been eating the smaller ones.\u201d<\/p>\n

Because light takes time to travel through the universe, galaxies further away from the Milky Way are seen at an earlier point in their existence. Dr Gupta\u2019s team found that observation and modelling of these very distant galaxies revealed much less variation in their internal movements.<\/p>\n

\u201cWe then had to work out why \u2018older\u2019, closer big galaxies were so much more disordered than the \u2018younger\u2019, more distant ones,\u201d said second author ASTRO 3D\u2019s Dr Kim-Vy Tran, who like Dr Gupta, is based at the UNSW Sydney.<\/p>\n

\u201cThe most likely explanation is that in the intervening billions of years the surviving galaxies have grown fat and disorderly through incorporating smaller ones. I think of it as big galaxies having a constant case of the cosmic munchies.\u201d<\/p>\n

The research team \u2013 which included scientists from other Australian universities plus institutions in the US, Canada, Mexico, Belgium and the Netherlands \u2013 ran their modelling on a specially designed set of simulations known as IllustrisTNG. This is a multi-year, international project that aims to build a series of large cosmological models of how galaxies form. The program is so big that it has to run simultaneously on several of world\u2019s most powerful supercomputers.<\/span><\/p>\n

\u201cThe modelling showed that younger galaxies have had less time to merge with other ones,\u201d said Dr Gupta.<\/p>\n<\/div>

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Distribution of dark matter density overlayed with the gas density. This image cleanly shows the gas channels connecting the central galaxy with its neighbours. IMAGE CREDIT: Gupta et al\/ASTRO 3D\/ IllustrisTNG collaboration.<\/p>\n<\/div>

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<\/i><\/i><\/span>MEDIA CONTACTS<\/span><\/a><\/h4><\/div>
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Dr Anshu Gupta is available for interview: anshu.gupta@unsw.edu.au; +61 405 220 778<\/p>\n

Dr Kim-Vy Tran is available for interview: kimvy.tran@gmail.com; +1 979 229 4414<\/p>\n

Further assistance: Andrew Masterson: andrew@scienceinpublic.com.au; +61 488 777<\/p>\n<\/div><\/div><\/div><\/div><\/div>

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<\/i>Paper available here<\/span><\/a><\/div>
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