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New Publication at the Open Journal of Astrophysics

Posted in Open Access, The Universe and Stuff with tags , , , , , , , on July 22, 2022 by telescoper

It seems we’re on a bit of a roll at the Open Journal of Astrophysics as we have yet another new paper for me to announce. I think with the end of teaching quite a few authors are finding time to make their revised versions (which I should also be doing, come to think of it….)

Anyway the new paper, published yesterday, is the 11th paper in Volume 5 (2022) and the 59th in all. The latest publication is entitled “Bayesian error propagation for neural-net based parameter inference” and is written by Daniela Grandón of the University of Chile and Elena Sellentin of Leiden University.

It being mainly about the application of parameter inference to cosmology, this is another paper in the Instrumentation and Methods for Astrophysics folder.

Here is a screen grab of the overlay which includes the  abstract:

 

You can click on the image to make it larger should you wish to do so. You can find the arXiv version of the paper here.

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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.

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New Publication at the Open Journal of Astrophysics

Posted in Open Access, The Universe and Stuff with tags , , , on July 17, 2022 by telescoper

Today is ten years to the day that I wrote the blog post that first proposed setting up the Open Journal of Astrophysics. It took a bit longer than I’d expected to get it going. The prototype site opened at the end of 2015 but owing to personal issues the project didn’t get going in full until after I moved to Maynooth in 2017.

It couldn’t have happened without enormous help from Arfon Smith, Chris Lintott, Adam Becker, Robert Simpson, Stuart Lynn and Mark Rohloff so many thanks to them for assistance in getting it off the ground. I also thank the staff at Maynooth University Library, especially Fiona Morley-Clarke, for their support and assistance. I also acknowledge financial support from the Gordon and Betty Moore Foundation.

I’d also like to thank the Editorial Team at OJAp, all unpaid volunteers, for their efforts and of course to all the authors who have trusted their research findings what was, at least at the start, an experimental venture.

Now seems an appropriate time to announce yet another new publication in the Open Journal of Astrophysics! This one, published last week, is the 10th paper in Volume 5 (2022) and the 58th in all.

The latest publication is entitled “V889 Her: abrupt changes in the magnetic field or differential rotation?” and is written by Teemu Willamo (Helsinki), Thomas Hackman (Helsinki), Jyri J. Lehtinen (Turku), Maarit Korpi-Lagg (Aalto) and Oleg Kochukhov (Uppsala). The first four of these are based in Finland and the last in Sweden.

This is another paper in the Solar and Stellar Astrophysics folder; the subject of the paper V889 Herculis is a young and very active dwarf star with some intriguing properties.

Here is a screen grab of the overlay which includes the (very short) abstract:

You can click on the image to make it larger should you wish to do so. You can find the arXiv version of the paper here.

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The (unofficial) 2021 Journal Impact Factor for the Open Journal of Astrophysics

Posted in Open Access, The Universe and Stuff with tags , , on July 16, 2022 by telescoper

Since a few people have been asking about the Journal Impact Factor (JIF) for the Open Journal of Astrophysics, I thought I’d do a quick post in response.

When asked about this my usual reply is (a) to repeat the arguments why the impact factor is daft and (b) point out that the official JIF is calculated by Clarivate so it’s up to them to calculate it – us plebs don’t get a say.

On the latter point Clarivate takes its bibliometric data from the Web of Science (which it owns). I have applied on behalf of the Open Journal of Astrophysics to be listed in the Web of Science but it has not yet been listed.

Anyway, the fact that it’s out of my hands doesn’t stop people from asking so I thought I’d proceed with my own calculation not using Web of Science but instead using NASA/ADS (which probably underestimates citation numbers but which is freely available, so you can check the numbers using the interface here); the official NASA/ADS abbreviation for the Open Journal of Astrophysics is OJAp.

For those of you who can’t be bothered to look up the definition of an impact factor for a given year it is defined the sum of the citations for all papers published in the journal over the previous two-year period divided by the total number of papers published in that journal over the same period. It’s therefore the average citations per paper published in a two-year window. Since our first full year of publication was 2019, the first year for which we can calculate a JIF is 2021 (i.e. last year) which is defined using data from 2019 and 2020.

I stress again we don’t have an official Journal Impact Factor for the Open Journal of Astrophysics but one can calculate its value easily. In 2019 and 2020 we published 12 and 15 papers respectively, a 27. These papers were cited a total of 193 times in 2021. The journal impact factor for 2021 is therefore … roll on the drums… 193/27, which gives:

If you don’t believe me, you can check the numbers yourself. For comparison, the latest available Impact Factor (2020) for Monthly Notices of the Royal Astronomical Society is 5.29 and Astronomy & Astrophysics is 5.80. OJAp’s first full year of publication was 2019 (in which we published 12 papers) but we did publish one paper in 2018. Based on the 134 citations received to these 13 papers in 2020, our 2020 Journal Impact Factor was 10.31, much higher than MNRAS or A&A.

Furthermore, we published 32 papers in 2020 and 2021 which have so far received 125 citations in 2022. Our Journal Impact Factor for 2022 will therefore be at least 125/32= 3.91 and if those 32 papers are cited at the same for the rest of this year the 2022 JIF will be about 7.5.

Who knows, perhaps these numbers will shame Clarivate into giving us an official figure?

With so much bibliometric information available at the article level there is no reason whatsoever to pay any attention to such a crudely aggregated statistics at the journal level as the JIF. One should judge the contents, not the packaging. I am however fully aware that many people who hold the purse strings for research insist on publications in journals with a high JIF. If there was any fairness in the system they would be mandating astronomy publications in OJAp rather than MNRAS or A&A.

Anyway, it might annoy all the right people if I add a subtitle to the Open Journal of Astrophysics: “The World’s Leading Astrophysics Journal”…

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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:

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James Webb: the wrong name for a Space Telescope

Posted in History, LGBTQ+, The Universe and Stuff with tags , , , on July 13, 2022 by telescoper

Following yesterday’s excitement about the new images from the James Webb Space Telescope I thought I’d share this video documentary that explains why the choice of name for this facility is highly inappropriate and should be changed. This is a matter I’ve blogged about previously, in fact, but the video is new.

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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:

Carina Nebula
Stephan’s Quintet
Southern Ring Nebula
Slitless Spectroscopy of WASP 96-b

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.

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The First Deep Field from JWST

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

I have to say that I didn’t stay up to watch the live stream of last night’s preview of this afternoon’s release of the first images from the James Webb Space Telescope. It started very late and I got sick of listening to the dreary music on the feed so went to bed. Nevertheless here is the first picture:

Credits: NASA, ESA, CSA, and STScI

This is a deep field image taken using JWST’s NIRCAM (Near-Infrared Camera). Note that the artifacts you see around some objects are diffraction spikes which occur around bright sources; their six-fold symmetry reflects the hexagonal structure built into the JWST’s mirror assembly. Sources sufficiently bright and compact enough to cause these spikes in deep field images are foreground stars: the extended, fainter objects are all much more distant galaxies.

The description from the NASA page is:

NASA’s James Webb Space Telescope has produced the deepest and sharpest infrared image of the distant universe to date. Known as Webb’s First Deep Field, this image of galaxy cluster SMACS 0723 is overflowing with detail.

Thousands of galaxies – including the faintest objects ever observed in the infrared – have appeared in Webb’s view for the first time. This slice of the vast universe is approximately the size of a grain of sand held at arm’s length by someone on the ground.

This deep field, taken by Webb’s Near-Infrared Camera (NIRCam), is a composite made from images at different wavelengths, totaling 12.5 hours – achieving depths at infrared wavelengths beyond the Hubble Space Telescope’s deepest fields, which took weeks. 

The image shows the galaxy cluster SMACS 0723 as it appeared 4.6 billion years ago. The combined mass of this galaxy cluster acts as a gravitational lens, magnifying much more distant galaxies behind it. Webb’s NIRCam has brought those distant galaxies into sharp focus – they have tiny, faint structures that have never been seen before, including star clusters and diffuse features. Researchers will soon begin to learn more about the galaxies’ masses, ages, histories, and compositions, as Webb seeks the earliest galaxies in the universe

Here is a close-up of one of the distorted galaxy images and othe features produced by gravitational lensing:

We’re having a special viewing in Maynooth this afternoon of the press conference which will unveil more new images from JWST – nice telescope, shame about the name. I may add comments on here if anything particularly exciting turns up. You can watch it here:

Let’s hope this one starts on time!

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The Consequences of Decoupling

Posted in Politics, The Universe and Stuff with tags , , , on July 11, 2022 by telescoper
Cosmology

I was struck by the similarity between the UK’s export performance post-Brexit (left) and the behaviour of radiative perturbations in the post-recombination Universe (right). It seems that, in different ways, they are both consequences of some form of decoupling…

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Cosmological Constraints on Alternative Gravity Theories

Posted in The Universe and Stuff with tags , , , , , , , on July 11, 2022 by telescoper

The standard model of cosmology is based on Einstein’s theory of general relativity. In order to account for cosmological observations this has required the introduction of dark matter – which also helps explain the properties of individual galaxies – and dark energy. The result model, which I would describe as a working hypothesis, is rather successful but it is reasonable to question whether either or both of the dark components can be avoided by adopting an alternative theory of gravity instead of Einstein’s.

There is an interesting paper by Kris Pardo and David Spergel on arXiv that argues that none of the modifications of Einstein’s theory currently on the market is able to eliminate the need for dark matter. Here is the abstract of this paper:

It’s a more sophisticated version of an argument that has been going around at least in qualitative form for some time. The gist of it is that the distinctive pattern of fluctuations in the cosmic microwave background, observed by e.g. the Planck experiment, arise from coupling between baryons and photons in the early Universe. Similar features can be observed in the distribution of galaxies – where they are called Baryon Acoustic Oscilations (BAO) at a more recent cosmic epoch, but they are are much weaker. This is easily explicable if there is a dark matter component that dominates gravitational instability at late times but does not couple to photons via electromagnetic interactions. This is summed up in the following graphic (which I think I stole from a talk by John Peacock) based on data from about 20 years ago:

If there were no dark matter the coherent features seen in the power spectrum of the galaxy distribution would be much stronger; with dark matter dominating they are masked by the general growth of the collisionless component so their relative amplitude decreases.

The graphic shows how increasing the dark matter component from 0.1 to 0.3, while keeping the baryon component fixed, suppresses the wiggles corresponding to BAOs. The data suggest a dark matter contribution at the upper end of that range, consistent with the standard cosmology.

Of course if there are were no baryons at all there wouldn’t be fluctuations in either the CMB polarization or the galaxy distribution so both spectra would be smooth as shown in the graphic, but in that case there wouldn’t be anyone around to write about them as people are made of baryons.

This general conclusion is confirmed by the Pardo & Spergel paper, though it must be said that the argument doesn’t mean that modified gravity is impossible. It’s just that it seems nobody has yet thought of a specific model that satisfies all the constraints. That may change.

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