Archive for JWST

A 13-billion-year-old Galaxy Spectrum

Posted in The Universe and Stuff with tags , , , , , on February 16, 2023 by telescoper

The Galaxy GN-z11 has been known for some time to have a very high redshift z~11 (hence the name) but you can now feast your eyes on the exquisite infrared spectrum of this object recently obtained using JWST:

It’s incredible to see so many clear emission lines for an object at such an enormous distance. The light from this galaxy set out towards us over 13 billion years in the past, when the Universe was less than 400 million years old, so it provides clues about the very early stages of cosmic structure formation. The spectral lines can not only be used to establish the redshift with great precision – it is z = 10.603 – but also to probe the physical properties of this source and its environment. The progress in this field is truly remarkable thanks to superb advances in observational technology.

For more details of this amazing result see the paper by Bunker et al now on the arXiv.

How big were the biggest galaxies in the early Universe?

Posted in Biographical, Cardiff, The Universe and Stuff with tags , , , , , , , on August 23, 2022 by telescoper

Once upon a time (over a decade ago when I was still in Cardiff), I wrote a paper with PhD student Ian Harrison on the biggest (most massive) galaxy clusters. I even wrote a blog post about it. It was based on an interesting branch of statistical theory called extreme value statistics which I posted about in general terms here.

Well now the recent spate of observations of high-redshift galaxies by the James Webb Space Telescope has inspired Chris Lovell (who was a student at Cardiff back in the day then moved to Sussex to do his PhD and is now at the University of Hertfordshire) and Ian Harrison (who is back in Cardiff as a postdoc after a spell in the Midlands), and others at Cambridge and Sussex, to apply the extreme value statistics idea not to clusters but to galaxies. Here is the abstract:

The basic idea of galaxy formation in the standard ΛCDM cosmological model is that galaxies form in dark matter haloes that grow hierarchically so that the typical size of galaxies increases with time. The most massive haloes at high redshift should therefore be less massive than the most massive haloes at low redshift, as neatly illustrated by this figure, which shows the theoretical halo mass function (solid lines) and the predicted distribution of the most massive halo (dashed lines) at a number of redshifts, for a fixed volume of 100 Mpc3.

The colour-coding is with redshift as per the legend, with light blue the highest (z=16).

Of course we don’t observe the halo mass directly and the connection between this mass and the luminosity of a galaxy sitting in it is likely to be complicated because the formation of the stars that produce the light is a rather messy process; the ratio of mass to light is consequently hard to predict. Moreover we don’t even have overwhelmingly convincing measurements of the redshifts yet. A brief summary of the conclusions of this paper, however, is that is some of the big early galaxies recently observed by JWST seem to be a big too big for comfort if we take their observed properties at face value. A lot more observational work will be needed, however, before we can draw definite conclusions about whether the standard model is consistent with these new observations.

ChorizoGate: an Accidental Hoax

Posted in Biographical, The Universe and Stuff with tags , , , on August 3, 2022 by telescoper

My Twitter account is usually a quiet backwater of social media, and that’s the way I like it, but there was an unexpected burst of activity and interest in it over the weekend. To amuse myself on Saturday morning I decided to post this on Twitter:

I thought a few people might find it funny, but it took off beyond my expectations. By my standards over 5000 likes counts as “going viral” (as you young people say). Most people saw the joke immediately – if you don’t get it, the image is of a slice of chorizo not an astronomical object – and some even joined in with puns and other jokes. Even funnier, some respondents earnestly shared their devastating insight that it was chorizo (or some variant thereof). I honestly didn’t think anyone would think that I was seriously trying to pass it off as a JWST picture; it was just meant to be silly. But there you go. That’s Twitter. I should also report that some people looked at the rainbow flags in my profile and proceeded to indulge in some casual homophobia. That’s Twitter too. Those people all got blocked.

Anyway, the day after I posted the image it seems a prominent French physicist called Etienne Klein who has many times more Twitter followers than I do, posted this embellished version. TRIGGER WARNING – it’s in FRENCH:

Notice the picture is exactly the same. What a coincidence! You might consider this plagiarism; I couldn’t possibly comment. I always regard anything I put on social media as being in the public domain so I’m not really bothered if other people “borrow” it. There’s quite a lot of plagiarism of stuff I’ve written on this blog out there, but life’s too short to get upset about it. Credit would be courteous, but one one learns that it isn’t generally to be expected.

As a matter of fact it’s not a new joke anyway. I didn’t make the picture and don’t remember where I got it from, though it was probably here.

Anyway, the funny thing is that this then got picked up by various other people:

and organisations:

There are others, e.g. here, here, here and here. Also here.

ChorizoGate all took off in a very surprising way. I’m not sure what the moral of this story is, other than if you make a joke no matter how obvious it is there will always be people who take it seriously…

Now a Galaxy at z>16?

Posted in The Universe and Stuff with tags , , , , , , on July 26, 2022 by telescoper

It’s less than a week since I posted an item about an object which is possibly the highest redshift galaxy ever observed (with z ~13) and now along comes a paper describing an object that may be of even higher redshift (with z~16.7). The abstract of the new paper – lead author of which is Callum Donnan of the University of Edinburgh – is here:

As with the previous object the redshift of this one is not obtained via spectroscopy (which usually involves the identification of spectral lines) but via fitting a spectral profile to photometric imaging data seen in different bands. The process for this galaxy is illustrated by this diagram from the paper:

There are 7 images along the top showing the source through various broad band filters. Suitably calibrated these can be converted to the flux measurements shown on the graph. Notice the first three images are significantly fainter than the others, so the first three points on the left of the graph are lower.

If this is a galaxy its spectrum is expected to possess a Lyman Break resulting from the fact that radiation of shorter wavelength than the Lyman Limit (912 Å) is absorbed by neutral gas surrounding the regions where stars are formed in the galaxy. In the rest frame of a galaxy this break is the ultraviolet region of the spectrum but because of the cosmological redshift it is observed in the infrared part of the spectrum for very distant galaxies. In this case the best fit is obtained if the break is positioned as shown, with the first three fainter points to the left of the break and the rest to the right. The break itself is straddled by two observational bands. Employing a number of different estimates the authors conclude that the redshift of this galaxy is z=16.7 or thereabouts.

There is no direct evidence for the sharp edge associated with the Lyman Break – and no spectral lines are observed either – so this all depends on the object being correctly identified as a high-redshift galaxy and not some other object at lower redshift. You have to assume this to get a redshift, but then all inferences are based on assumed models so there’s nothing unusual about this approach. The authors discuss other possibilities and conclude that there is no plausible alternative source. Take away the green template spectrum and you just see a spectrum that rises to a peak and falls again. The authors claim that there is no plausible low-redshift source with such a spectrum.

Anyway, here is a composite colour image of the source:

So is this now the earliest galaxy ever observed? And what object will I be asking this question about next week? One thing I can predict is that there are going to be many more such objects in the very near future!

The Earliest Galaxy we’ve seen?

Posted in Astrohype, The Universe and Stuff with tags , , , on July 20, 2022 by telescoper

The red smudge in the centre of this image is thought to be a galaxy with a redshift of around z=13, as seen by the NIRCam instrument on the James Webb Space Telescope. This redshift estimate is based on photometry so the object remains a candidate rather than a confirmed high-redshift galaxy, but if confirmed spectroscopically this would be the highest-redshift galaxy yet observed.

For more details on the observations and their implications see the preprint on arXiv here. It’s interesting (and challenging) that there are such bright galaxies at such an early stage of cosmic evolution, assuming of course that the redshift is correct. Photometric redshift estimates have been wrong before.

If we take the estimated redshift at face value and adopt the standard cosmological model, the lookback time to this galaxy (GLASS-z13) is about 97.6% of the current age of the Universe so we’re seeing it as it was just 330 million years after the Big Bang. It could therefore be the earliest galaxy we have seen. It isn’t very accurate to say that it is the oldest galaxy we’ve seen, as we are probably seeing it as it was when it was very young.

These observations come from JWST Early Science Release Programmes so are just a taster of what is to come. No doubt we’ll hear much more about high-redshift galaxies from JWST in future and there’s every chance that they will change our view of the high-redshift Universe in dramatic ways.

I’ll just mention here that I’m old enough to remember going to conferences where “high redshift” meant z=0.5! In those days the highest redshift objects were quasars, but they have long since been overtaken.

Characterization of JWST science performance from commissioning

Posted in The Universe and Stuff with tags , , , on July 14, 2022 by telescoper

I don’t suppose it will take very long for science papers based on the first data from JWST to start appearing on arXiv but I haven’t seen any yet. There is however a very important with an uncountable number of authors, led by Jane Rigby, that describes the commissioning process. Uncountable by me, that is.

Here is the abstract:

This document characterizes the actual science performance of the James Webb Space Telescope (JWST), as known on 12 July 2022. Following six months of commissioning to prepare JWST for science operations, the observatory is now fully capable of achieving the discoveries for which it was built. A key part of commissioning activities was characterizing the on-orbit performance of the observatory. Here we summarize how the performance of the spacecraft, telescope, science instruments, and ground system differ from pre-launch expectations. Almost across the board, the science performance of JWST is better than expected. In most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies.

Although it’s very long (60 pages) it’s well worth reading for an account of how meticulously the various calibrations etc were done. Various objects make cameo appearances, including Jupiter:

Those First Results from JWST

Posted in The Universe and Stuff with tags , , , , , on July 12, 2022 by telescoper

As promised in my post earlier today, we gathered in a small lecture theatre in Maynooth to watch the “reveal” of various new images and other data from the James Webb Space Telescope. The images are indeed wonderful and spectacular, but the video stream was excruciatingly bad to watch, with more technical glitches than I’ve had hot dinners. It was like an astronomical version of Acorn Antiques!

Anyway, you can find them all the new results together with explanations and descriptions here so Ill just put up a gallery here:

Those are the four results released today. This image was previewed last night and appeared in my post earlier today:

I couldn’t resist, however, adding this spectrum of a faint reddish galaxy in the above image:

This spectrum is taken using the NIRSpec instrument on JWST. The observed wavelength along the horizontal axis is measured in microns. If I’ve got the line identifications correct I think this galaxy is at an amazing redshift of about z=8.5. Amazing. High redshift galaxy spectra obtained are usually a lot rattier than this. I think this demonstrates that JWST is going to revolutionize the field of galaxy formation.

Merry JWSTmas!

Posted in The Universe and Stuff with tags , , , , on December 25, 2021 by telescoper

Well it’s 10.20am on Christmas Day and I’ve got up specially early in order to be ready for the launch at 12.20pm today (Irish Time) of the James Webb Space Telescope from Kourou in French Guiana. The JWST project has been almost thirty years in the making and it is great that it is finally going to be heading into space. The launch however is just the start – JWST has a very complicated journey in front of it – as demonstrated by the following little video.

In particular, JWST should separate from the Ariane 5 launcher at about 27 minutes after takeoff so look out for that.

I have no direct personal involvement with JWST but I am still feeling a bit nervous. I can’t imagine how it must feel to have spent decades working on it. I know a great many astronomers around the world who are waiting anxiously and hoping all goes well. Fingers crossed!

If you want to watch the launch live you can do so on Youtube here:

You can find alternative viewing options here.

The launch window opens at 12.20 UTC and lasts for 31 minutes but I understand they’re going to launch as early as possible within that so it looks like we’re in for a launch before lunch rather than the other way round.

I’ll update with any news as the day goes on.

UPDATE: 12.28pm Launched right on time, everything nominal as JWST leaves Earth’s atmosphere propelled by Stage One of the Ariane 5.

UPDATE: 12.31pm Stage One jettisoned, Stage 2 ignition. All still nominal.

UPDATE: 12.48pm JWST has separated from the launch vehicle and is on its way. The solar panel is deployed and is working. The spectacular onboard video showing the separation of JWST from the Ariane 5 launch vehicle and the deployment of the solar panels was supplied by Irish company Réaltra.

P.S. I still think JWST should have had a different name.

Top Ten JWST Facts!

Posted in The Universe and Stuff with tags , , on December 4, 2021 by telescoper

The James Webb Space Telescope looks nothing like the Hubble Space Telescope shown here.

As excitement mounts ahead of the launch of the James Webb Space Telescope (JWST) later this month I thought I would, as a service to the community, for the edification of the public at large, and despite popular demand, present my list of Top Ten JWST Facts.

  1. The JWST spacecraft will orbit the Sun near the Second Lagrange Point, L2, because it took so long to get built that tickets were no longer available for L1.
  2. JWST cost $10bn but its telescope is so sensitive that it can see back to redshifts greater than ten, meaning that it sees light that was emitted when its budget was less than $1 bn.
  3. To provide secure backup storage of the complete JWST data set, NASA has commandeered the world’s entire stock of 3½ inch floppy disks.
  4. As well as observing the Universe’s first galaxies and revealing the birth of stars and planets, JWST will look for signs that there might be intelligent life somewhere in the Universe.
  5. JWST’s unique 6.5m deployable mirror was  especially designed by experts from the IKEA company in Sweden who are famous for making items for ‘easy self-assembly’.
  6. The angular resolution of JWST is  0.1 arc seconds, which means  it could resolve a football at a distance of 550 km (or even further if it had Sky Sports).
  7. The Near-Infrared Spectrograph on JWST will be able to make simultaneous measurements of up to 100 sources while at the same time making a cup of coffee and washing the dishes.
  8. The BBC will be shortly be broadcasting a new 26-part TV series about JWST. Entitled WOW! JWST! That’s Soo Amaazing… it will be presented by Britain’s leading expert on infra-red astronomy, Professor Brian Cox.
  9. Er…
  10. That’s it.

The Curious Incident of the JWST and the Clamp Band…

Posted in The Universe and Stuff with tags , , , on November 23, 2021 by telescoper


Just a quick newsflash to pass on the news that the launch of the James Webb Space Telescope has been pushed back until at least 22nd December 2021 owing to an “incident” that occurred during preparations for its launch.

It seems the sudden release of a “clamp band” – or is it band clamp? – caused unwanted vibrations through the observatory and it now has to be thoroughly checked before it can be declared safe for launch.

This is not the news anyone wanted to hear, but the previous launch date was 18th December, so hopefully the few days’ delay won’t cause too much difficulty.

I was going say that for JWST to work there has to be something incident on its mirror, but on reflection I decided that wasn’t a very good joke.