From Astrobites and The NASA/ESA/CSA James Webb Space Telescope: “Webb takes a peek at the first ever galaxies”

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National Aeronautics Space Agency/European Space Agency [La Agencia Espacial Europea] [Agence spatiale européenne][Europäische Weltraumorganisation](EU)/ Canadian Space Agency [Agence Spatiale Canadienne](CA) James Webb Infrared Space Telescope annotated, finally launched December 25, 2021, ten years late.

The NASA/ESA/CSA James Webb Space Telescope

Roan Haggar

Title: Panic! At the Disks: First Rest-frame Optical Observations of Galaxy Structure at z>3 with JWST in the SMACS 0723 Field

Authors: Leonardo Ferreira, Nathan Adams, Christopher J. Conselice, Elizaveta Sazonova, Duncan Austin, Joseph Caruana, Fabricio Ferrari, Aprajita Verma, James Trussler, Tom Broadhurst, Jose Diego, Brenda L. Frye, Massimo Pascale, Stephen M. Wilkins, Rogier A. Windhorst, Adi Zitrin

First Author’s Institution: University of Nottingham, Nottingham, UK

Status: Accepted to The Astrophysical Journal Letters, available on arXiv

Ever since the first data release of the James Webb Space Telescope (JWST) in July, it has become clear that this telescope is going to completely transform our view of the distant Universe. Galaxies that looked like featureless blobs when viewed through the Hubble Space Telescope can now be resolved in incredible detail (see Figure 1), despite the fact that Hubble has been one of the world’s leading telescopes for the past 30 years.

Figure 1: Four galaxies from the SMACS 0723 field (the focus of today’s paper), as seen by the Hubble Space Telescope (left) and the James Webb Space Telescope (right). Each one displays features that were undetected with Hubble, but can easily be seen with Webb. Credit: NASA/ESA/STScI.

Being able to measure the shapes of galaxies (known as their morphology) is vital if we want to understand how galaxies, including our own, were formed. Galaxies typically come in two shapes: thin, delicate disk-shaped galaxies, and spheroid-shaped elliptical galaxies, but it is still not really clear how and when these different galactic structures emerged. Today’s paper uses early JWST observations of a large galaxy cluster called SMACS 0723, to measure the shapes of very distant galaxies. With this exciting new data, the authors hope to expand our knowledge of galaxy evolution all the way to the very dawn of our Universe.

SMACS 0723 via Webb

Zooming in on the first galaxies

This photo of SMACS 0723 is one of the first images to be released from JWST. The cluster is located about four billion light years away at a redshift of 0.4, but today’s paper actually looks at even more distant galaxies, in the background of this image — many of these have been magnified by the gravitational lensing of the cluster.

Specifically, it looks at 280 background galaxies at redshifts between 1.5 and 8, meaning we are seeing them just 1-4 billion years after the beginning of the Universe.

The authors firstly measure galaxy shapes using quantitative properties of galaxies, such as their concentration and asymmetry. Their really exciting findings, however, come from classifying these galaxies by eye, splitting them into three categories: disks, spheroids, and “peculiars”.

Galaxies in this third class have an irregular shape, which can be caused by processes such as starbursts or tidal interactions. Alternatively, collisions between galaxies (known as “galaxy mergers“) that are currently in-progress can lead to these “peculiar” galaxies. These violent events are thought to play a major role in galaxy evolution: in the early Universe mergers allow large amounts of mass to clump together, which can later form a galactic disk. Later on, they can destroy these fragile disk structures, turning disk galaxies into featureless ellipticals.

It turns out that at high redshifts (between 3 and 6), about half of galaxies have a disk shape (Figure 2). This is much higher than we previously thought — the data from the Hubble telescope shows that it found a disk fraction of less than 10% at similar redshifts! Interestingly, according to JWST, the disk fraction also stays roughly constant across the whole range of redshifts.

Figure 2: Fraction of spheroid, disk, and peculiar galaxies at different redshifts, measured with JWST in today’s paper, and with Hubble (HST) in previous work. The trends found by Hubble had predicted the number of disks would decrease at redshifts greater than three, and that most galaxies would be peculiar. JWST shows that this is not the case. Figure 4 in today’s paper.

A less turbulent Universe?

Our current idea that mergers assemble galaxies in the early Universe means that we would expect to find lots of peculiar galaxies and few disks at high redshift, as these disks are still in the process of forming. However, the near-constant disk fraction found in this study indicates that disk galaxies (like the Milky Way) have existed in a fairly stable state for more than 10 billion years, seemingly contradicting our old ideas.

So what’s going on? There are several ways to interpret these results. It could be that almost all mergers occur extremely early in the Universe, quickly forming disk galaxies, and that these disks survive until the present day because recent mergers are far less common than our current theories suggest. Alternatively, it could be that only some classes of galaxies are built up by mergers, or even that mergers are simply far less likely to destroy disk structures than we previously thought.

Whatever the case, it indicates that we may need to refine current theoretical ideas about how galaxies assemble and evolve through mergers, which is one of the key predictions of our widely-accepted model of the Universe (the Lambda cold dark matter, or ΛCDM, model).

Some articles based on this work have gone a step further, stating that this research disproves ΛCDM, or even the Big Bang. However, despite the homage to noughties emo-pop in the title of this paper, there’s really no reason to panic. Tuning and re-tuning theories to fit new data is a normal part of the scientific process. In fact, this paper is exciting: it tells us that we still do not truly know where galactic structure came from, but that new science carried out using this new telescope will finally give us a chance to understand the origins and lives of galaxies.

See the full article here.


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The NASA/ESA/CSA James Webb Space Telescope is a large infrared telescope with a 6.5-meter primary mirror. Webb was finally launched December 25, 2021, ten years late. The James Webb Space Telescope will be the premier observatory of the next decade, serving thousands of astronomers worldwide. It will study every phase in the history of our Universe, ranging from the first luminous glows after the Big Bang, to the formation of solar systems capable of supporting life on planets like Earth, to the evolution of our own Solar System.

The James Webb Space Telescope is the world’s largest, most powerful, and most complex space science telescope ever built. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it.

Webb telescope will be the premier observatory of the next decade, serving thousands of astronomers worldwide. It will study every phase in the history of our Universe, ranging from the first luminous glows after the Big Bang, to the formation of solar systems capable of supporting life on planets like Earth, to the evolution of our own Solar System.

Webb telescope was formerly known as the “Next Generation Space Telescope” (NGST); it was renamed in Sept. 2002 after a former NASA administrator, James Webb.

Webb is an international collaboration between National Aeronautics and Space Administration, the European Space Agency (ESA), and the Canadian Space Agency (CSA). The NASA Goddard Space Flight Center managed the development effort. The main industrial partner is Northrop Grumman; the Space Telescope Science Institute will operate Webb after launch.

Several innovative technologies have been developed for Webb. These include a folding, segmented primary mirror, adjusted to shape after launch; ultra-lightweight beryllium optics; detectors able to record extremely weak signals, microshutters that enable programmable object selection for the spectrograph; and a cryocooler for cooling the mid-IR detectors to 7K.

There are four science instruments on Webb: The Near InfraRed Camera (NIRCam), The Near InfraRed Spectrograph (NIRspec), The Mid-InfraRed Instrument (MIRI), and The Fine Guidance Sensor/ Near InfraRed Imager and Slitless Spectrograph (FGS-NIRISS). Webb’s instruments are designed to work primarily in the infrared range of the electromagnetic spectrum, with some capability in the visible range. It will be sensitive to light from 0.6 to 28 micrometers in wavelength.
National Aeronautics Space Agency Webb NIRCam.

The European Space Agency [La Agencia Espacial Europea] [Agence spatiale européenne][Europäische Weltraumorganisation](EU) Webb MIRI schematic.

Webb Fine Guidance Sensor-Near InfraRed Imager and Slitless Spectrograph FGS/NIRISS.

Webb has four main science themes: The End of the Dark Ages: First Light and Reionization, The Assembly of Galaxies, The Birth of Stars and Protoplanetary Systems, and Planetary Systems and the Origins of Life.

Launch was December 25, 2021 on an Ariane 5 rocket. The launch was from Arianespace’s ELA-3 launch complex at European Spaceport located near Kourou, French Guiana. Webb is located at the second Lagrange point, about a million miles from the Earth.

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Canadian Space Agency

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