Thanks to Prof. Karl Glazebrook FAA FASA,  Laureate Fellow & Distinguished Professor at the Centre for Astrophysics & Supercomputing, Swinburne University of Technology, for this article about recent discoveries made by the JWST of massive disk galaxies observed much sooner after the Big Band than expected. It is certainly an exciting time as we learn more about our Universe. He also touches on the enormous power of the JWST compared to ground based telescopes.

If you have any questions about this article, let us know and we will pass them on to Prof. Glazebrook,

Cheers,

Earl White

BINTEL

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I am sure many of the readers of this newsletter have been excitedly following the launch of the James Webb Space Telescope and the delivery of the first Webb images. I am fortunate enough to be leading a group of researchers at Swinburne University (https://jadc.swin.edu.au) who have been working hard on analysing the first precious data from Webb. It has been a busy, exhausting but also exhilarating time – we are part of an international team that has, since July, written over twenty scientific papers on the first Webb data. In particular we have pushed the ‘redshift boundary’ – finding galaxies at unprecedentedly high cosmic distances/early times – as well as getting clearer views of more ‘recent’ galaxies (lookback times of ‘only’ 10 billion years).

Everybody has seen all the wonderful Webb PR images, so I won’t repeat them here. However, I will share one comparison I made which demonstrates the stunning power of Webb:

This is a tiny field, only 30 arcseconds on the sky (about the apparent size of Jupiter) imaged at a wavelength of 2000 nanometres (about 3x longer than the human eye can see). It is near the giant galaxy cluster Abell 2744 in the southern sky. Webb is designed to observe in the infrared, so it can see the redshifted visible light from galaxies emitted a long way back in the history of the Universe. (For a primer on cosmological redshift see https://astronomy.swin.edu.au/cosmos/c/cosmological+redshift)

The image on the left is one of the deepest ground based images ever made at this wavelength. It is a 30 hour exposure on the Very Large Telescope (which has an 8m mirror) using the HAWK-I camera. The image on the right is the same wavelength and field, but using Webb’s near-infrared camera NIRCAM.  Just about everything seen here is a galaxy at lookback times of at least several billion years. Of course, you see the amazing increase in detail due to the lack of atmospheric blurring. This is particularly evident in the merging galaxy complex in the centre. But you also see a vast increase in the number of faint objects, Webb reveals many more and in fact the Webb image reaches 29th magnitude. The reason for this sensitivity is partly due to the sharper images but mostly due to the vastly lower background. The sky at 2000 nanometres is about 300x darker from Webb’s Lagrange 2 vantage point then it is from the Earth’s surface. This is like the difference when you observe from a dark site, compared to from the middle of Sydney, at night! I knew all of this intellectually, before Webb was even launched, but I still find such actual comparisons jaw dropping.

One really nice result that our Swinburne group has produced from the first data, is to use NIRCAM to make colour images of early galaxies in the ‘rest frame optical’. What does this mean? Basically we track the visible-wavelength light as it is redshifted, which we can do because NIRCAM covers 800-5000 nanometers, and we can make colour images of galaxies basically de-redshifted. So the colours correspond to those seen in nearby galaxy surveys such as those in the Sloan Digital Sky Survey (SDSS). Here is a montage one of our scientists, Dr Colin Jacobs, made:

 

This shows such pictures of galaxies at different cosmic epochs. (Technically these are synthetic RGB images using equivalent SDSS g,r,i filters).  In the first billion years galaxies do not contain much structure and have blue colours from young stars. But what surprised us most was that as soon as 2 billion years after the Big Bang we already see massive disk galaxies starting to appear, many with red central bulges. This had not been seen before by the Hubble Space Telescope due to its limited sensitivity and lack of infrared coverage – redder parts of galaxies are simply invisible in Hubble images.

A new early Universe is being revealed by Webb and the next few years will be quite exciting. Our group in Swinburne has just received some of the first Webb spectra – and again the comparison with ground-based spectra is utterly amazing. We are instantly identifying things that were impossible from the ground. I am very much looking forward to seeing what Webb finds, and I believe the most exciting results are still to come!

About Prof. Glazebrook

Karl Glazebrook is a world-leading astronomer whose research has led to major advances in our understanding of how galaxies and the Universe evolve over time. His ground-breaking work includes, establishing the existence of massive galaxies only three billion years after the Big Bang, and discovering the local analogues of primordial galaxies. Glazebrook has also pioneered near-infrared surveys and developed new award-winning instrumental techniques for carrying out ultra-deep spectroscopic surveys on the world’s largest telescopes. He has also been at the vanguard in the application of new observational techniques for quantifying the effects of dark energy on the accelerating expansion of the Universe.

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