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Yet more high-z galaxies from JWST…

Posted in The Universe and Stuff with tags , , , , , , , on December 19, 2023 by telescoper

I noticed a paper on arXiv yesterday, by Robertson et al., with the abstract:

You can click on this to make it larger if you find it difficult to read.

This is the latest in a number of studies by the JWST Advanced Deep Extragalactic Survey (JADES), which is aiming to detect galaxies that formed in the very early Universe; for a previous example see here. The latest batch can be seen in this figure:

There is an important caveat here, which is that these are photometric redshifts, based on the overall shape of the spectrum of the galaxy rather than on spectral lines which give a more accurate result. Follow-up spectroscopy is needed to firmly identify the redshift of the sources. Past experience suggests that some of these candidates may not actually be at as high a redshift as is claimed. If confirmed, however, the existence of large galaxies at redshifts of order 15 will put greater pressure on models of galaxy formation. A recent OJAp publication has shown that galaxies at redshift 10 are consistent with current theoretical ideas, but much larger will increase the tension on theorists. I can imagine quite a few people around the world replotting their graphs right now!

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Two New Publications at the Open Journal of Astrophysics

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , on December 14, 2023 by telescoper

As anticipated a couple of days ago, it’s now possible to announce another couple of new papers at the Open Journal of Astrophysics. These papers take us up to a total of 49  in Volume 6 (2023) and 114 in total since we started publishing.

It would be nice if we could make it to 50 in Volume 6 (2023), but I have already decided to close the publishing platform from 22nd December until 5th January (inclusive), so there there isn’t much time to get the single needed for our half-century.  While we will not be publishing new papers during this closure, the peer review platform will remain open for submission of new and revised manuscripts and the editorial processes will continue.

Whether or not we make 50 this year, it is worth remarking that 49 is already a significant figure, as it corresponds to the total number of papers we published in the previous three years: 15 (2020); 17 (2021); and 17 (2022). Things are definitely looking up!

Anyway, the first paper of the most recent pair – published on December 8th – is “The Million Quasars (Milliquas) Catalogue, v8”; its primary classification is Astrophysics of Galaxies and the author is Eric Wim Flesch from New Zealand. The Milliquas catalogue includes quasars from the literature to 30 June 2023, including quasars from the DESI-EDR and SDSS-DR18Q surveys.

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

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

The second paper was published on 11th December 2023 and is also in the folder marked Astrophysics of Galaxies.

The authors are all from various institutions in the USA:  Michael Grudić (Carnegie Observatories), Stella Offner (University of Texas at Austin); Dávid Guszejnov (Harvard);  Claude-André Faucher-Giguère (Northwestern University); and Philip F. Hopkins (Caltech).  The paper presents a comparison of full radiative magnetohydrodynamics simulations of the formation of star clusters with simple stochastic modelling showing the limitations of the latter.

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

 

 

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

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New Publication at the Open Journal of Astrophysics

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , on December 12, 2023 by telescoper

I was doing some work on the Open Journal of Astrophysics site and realized that there is a paper we published last week that I haven’t advertised on here yet, so I’m remedying that now.

The paper in question is the 47th so far in Volume 6 (2023)  and it’s the 112th altogether. This one was actually published on Tuesday December 5th. Two further papers are imminent; I’m just waiting for their metadata to be registered with Crossref.

The title of this one is “The SPHINX Public Data Release: Forward Modelling High-Redshift JWST Observations with Cosmological Radiation Hydrodynamics Simulations” and it represents  public data release of Sphinx20, a full box cosmological radiation-hydrodynamics simulation that provides a statistical sample of galaxies for comparison with those observed by JWST. It is in the folder marked Astrophysics of Galaxies.

There are 10 authors: Harley Katz (Oxford, UK); Joki Rosdahl (Lyon, France); Taysun Kimm (Seoul, Korea); Jeremy Blaizot (Lyon, France);  Nicholas Choustikov (Oxford, UK); Marion Farcy  and Thibault Garel (Geneva, Switzerland);  Martin G. Haehnelt (Cambridge, UK); Leo Michel-Dansac (Lyon, France); and Pierre Ocvirk (Strasbourg, France).

Here is the overlay of the paper containing the abstract:

 

 

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

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The Return of Halley’s Comet…

Posted in Art, Literature, The Universe and Stuff with tags , , , on December 11, 2023 by telescoper

I was reminded at the weekend that Halley’s Comet has just passed its aphelion (furthest distance from the Sun) and is now falling back into the Solar System towards its next perihelion (closest distance to the Sun) in 2061, by which time I will almost certainly be retired.

Halley’s Comet last visited us in 1986 when I was 23 and living in Brighton. It will next appear in 2061, when I shall be 98 and lucky to be living at all.

This reminded me of a rather poignant cartoon I found a while ago on Facebook. I don’t know the name of the artist. If anyone does please let me know.

The comet’s orbital period of 75 years or so is brief by astronomical standards, as is the duration of a human life. As Quintus Horatius Flaccus (Horace to you and me) put it in one of his Odes (Book I, Ode 4, line 15):

Vitae summa brevis spem nos vetat incohare longam

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Do Black Holes have Singularities?

Posted in mathematics, The Universe and Stuff with tags , , , on December 7, 2023 by telescoper

A paper appeared on arXiv this week that has ruffled a few feathers. It’s by Roy Kerr (yes, him) and it has the abstract:

There is no proof that black holes contain singularities when they are generated by real physical bodies. Roger Penrose claimed sixty years ago that trapped surfaces inevitably lead to light rays of finite affine length (FALL’s). Penrose and Stephen Hawking then asserted that these must end in actual singularities. When they could not prove this they decreed it to be self evident. It is shown that there are counterexamples through every point in the Kerr metric. These are asymptotic to at least one event horizon and do not end in singularities.

arXiv:2312.00841

I don’t think this paper is as controversial as some people seem to find it. I think most of us have doubts that singularities – specifically curvature singularities – are physically real rather than manifestations of gaps in our understanding. On the other hand, this paper focusses on an interesting technical question and provides a concrete counterexample. The point is that the famous Penrose-Hawking singularity theorems don’t actually prove the existence of singularities; they prove geodesic incompleteness, i.e. that there are geodesics that can only be extended for a finite time as measured by an observer travelling along one. Geodesic incompleteness does imply the existence of some sort of boundary, often termed a trapped surface, but not necessarily that anything physical diverges there at that boundary. Though a singularity will result in geodesic incompleteness, the assertion that geodesic incompleteness necessarily implies the existence of a singularity is really just a conjecture.

For more details, read the paper. It’s technical, of course, but well written and actually not all difficult to understand.

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Euclid in the Media

Posted in Euclid, The Universe and Stuff with tags , , , , , on December 3, 2023 by telescoper

Yesterday came across the above “infographic” – as I’m told such things are called – showing the media traffic generated by last month’s Early Release Observations from the ESA Euclid mission. Some quite interesting facts emerge from it. The new observations were released n 7th November, hence the big spike in the left hand panel on that date.

I see that about 31% of the activity was on Twitter, which I am no longer on, with a slightly smaller amount on Facebook. Overall, social media account for about 60% of the “reach”, with mainstream media (including print, online, and TV/Radio) languishing far behind. Blogs (presumably including this one) account for a mere 1%.

The breakdown by country is interesting too; the table shows only EAS member states. The UK is way out in front, no doubt because BBC News ran a major item on the day of the release. France, Germany, Italy and Spain all have major scientific involvements in Euclid and correspondingly active public engagement activities.

I was pleasantly surprised at the significant amount of interest in Ireland, given that some bigger countries with far greater scientific involvement in Euclid (e.g. Denmark and The Netherlands) generated so little. As the only member of the Euclid Consortium in Ireland I could try to pretend that this was all down to me, but I rather think it’s more likely to be a result of the fact that many Irish people read the UK media so some of the Irish traffic could be spillover from the big UK spike. Still, I think one can interpret this as meaning that the Public in the Republic have an appetite for news about space, something that we have certainly noticed when organizing events in Maynooth.

I thought I’d mention another nice thing. Here is one of the PR images produced by ESA about the early release observations. The point about Euclid is that to achieve its science goals it has to have extremely good optical quality across a very wide field of view. The systems are currently being tested and fine-tuned to see how good their performance actually is, but so far it’s looking good.

The main thing that caught my eye, however, is the collection of little flags along the bottom. How nice it is to see Ireland’s among them!

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New Publication at the Open Journal of Astrophysics

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , on December 1, 2023 by telescoper

It’s Friday and I thought I’d take  the opportunity before the weekend to announce yet another new paper at the Open Journal of Astrophysics.

The latest paper is the 46th so far in Volume 6 (2023) – just four to go for a half-century – and it’s the 111th altogether. This one was actually published on Wednesday November 29th.

The title is “Optimization and Quality Assessment of Baryon Pasting for Intracluster Gas using the Borg Cube Simulation” and it presents an algorithm for adding baryons to gravity-only simulations via a “pasting” approach. It is in the folder marked Cosmology and Nongalactic Astrophysics.

There are 8 authors: F. Kéruzoré;  L. Bleem; M. Buehlmann;  J.D. Emberson; N. Frontiere; S. Habib; K. Heitmann; and P. Larsen;  all of them based at the Argonne National Laboratory, in Illinois (USA).

Here is the overlay of the paper containing the abstract:

 

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

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Hubble Tension Reviewed

Posted in The Universe and Stuff with tags , , on November 24, 2023 by telescoper

Just a quick post to pass on a reference to a paper on arXiv (to appear in Annual Reviews of Astronomy and Astrophysics) about the ongoing saga of the Hubble Tension. The authors are Licia Verde, Nils Schöneberg, and Héctor Gil-Marín, three members of the ICCUB which is hosting me during my sabbatical. I saw an earlier draft of this paper but didn’t want to blog about it before the final version appeared. The abstract (which I’ve slightly reformatted) reads:

The Hubble parameter H0, is not a univocally-defined quantity: it relates redshifts to distances in the near Universe, but is also a key parameter of the ΛCDM standard cosmological model. As such, H0 affects several physical processes at different cosmic epochs, and multiple observables. We have counted more than a dozen H0‘s which are expected to agree if a) there are no significant systematics in the data and their interpretation and b) the adopted cosmological model is correct. With few exceptions (proverbially confirming the rule) these determinations do not agree at high statistical significance; their values cluster around two camps: the low (68 km/s/Mpc) and high (73 km/s/Mpc) camp. It appears to be a matter of anchors: the shape of the Universe expansion history agrees with the model, it is the normalizations that disagree. Beyond systematics in the data/analysis, if the model is incorrect there are only two viable ways to “fix” it: by changing the early time (z≳1100) physics and thus the early time normalization, or by a global modification, possibly touching the model’s fundamental assumptions (e.g., homogeneity, isotropy, gravity). None of these three options has the consensus of the community. The research community has been actively looking for deviations from ΛCDM for two decades; the one we might have found makes us wish we could put the genie back in the bottle.

arXiv:2311.13305


You can read the full paper here to learn about the scientific arguments, but I’d like to draw attention to this excerpt which is of more general relevance and with which I agree wholeheartedly:

It is also fair to say that the developments of the last decade have changed the expectations and modus operandi of a big part of the community. The community now expects results to be reproducible, hence the data and key software to be publicly available in such a way that a practitioner not involved in the original analysis could still retrace and reproduce all important steps and findings. While research areas such as the CMB and large-scale structure made this transition to “open science” about two decades ago, this was not the case for other areas of extra-galactic astronomy, but this is now changing.

arXiv:2311.13305

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Challenging the Standard Cosmological Model

Posted in The Universe and Stuff with tags on November 20, 2023 by telescoper

I have been asked to use the medium of this blog to transmit information about a forthcoming event at the Royal Society – that’s English for Real Sociedad – next April.

This is a scientific discussion meeting organised by Prof James Binney FRS, Dr Roya Mohayaee, Prof John Peacock FRS & Prof Subir Sarkar to be held from 15-16 April 2024, 09:00-17:00, The Royal Society, London SW1Y 5AG. Here’s a description:

Is the universe simple enough to be adequately described by the standard ΛCDM cosmological model which assumes the isotropic and homogeneous Friedmann-Lemaître-Robertson-Walker metric? Tensions have emerged between the values of cosmological parameters estimated in different ways. Do these tensions signal that our model is too simple? Could a more sophisticated model account for the data without invoking a Cosmological Constant?

The meeting is free to attend – both in-person and on-line attendance available. Advance registration is essential (an optional lunch is available to purchase during registration).

Meeting papers will be published in Philosophical Transactions of the Royal Society A.

For the full Chapter and Verse see the meeting website here.

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Thoughts of Retirement

Posted in Barcelona, Biographical, Maynooth, Open Access, The Universe and Stuff with tags , , , on November 19, 2023 by telescoper

I’ve been reviewing my situation while here in Barcelona. One of the themes that keeps popping into my head is well expressed by part of a little speech by Colonel Nicholson in The Bridge on the River Kwai:

But there are times… when suddenly you realize you’re nearer the end than the beginning. And you wonder, you ask yourself, what the sum total of your life represents. What difference your being there at any time made to anything – or if it made any difference at all, really. Particularly in comparison with other men’s careers. I don’t know whether that kind of thinking’s very healthy, but I must admit I’ve had some thoughts on those lines from time to time.

Healthy or not I’ve also had thoughts along those lines, and sometimes feel I should step aside and create a job opportunity for someone younger. I know my employer wouldn’t mind if I did that either. They’d much prefer replacing me with someone cheaper and more compliant than me. I think if I asked for early retirement they would probably jump at the chance. I’d miss the teaching and the students, of course,

The fact of the matter is though that I can’t afford to retire yet. I have a mortgage to pay and I’ve only had five full years of pensionable service in the Irish system, so won’t get much of a pension. I have the frozen residue of my UK pension, of course, but that is subject to an actuarial reduction if I take the benefit before I’m 65, which is also the standard retirement age for academic staff in Ireland. I can’t be made to retire here until I’m 70, in fact, but I think I’ll be well beyond my best-before date by then and am not keen to overstay my welcome.

So it looks like I’ll have to stay until I’m 65 at the earliest. In fact I won’t be able to collect the State Pension (SPC) until I’m 66, so I’ll probably have to stay another year. That means that when I get back from sabbatical I will have four or five years left until I can retire. I don’t know what I’ll be teaching when I return but I hope I get a chance to teach a few new modules before the end. In particular some cosmology or astrophysics would be particularly nice. All this is predicated on: (a) me living long enough; and (b) Physics at Maynooth not being closed down; neither of these is certain.

When I moved to the Emerald Isle in 2017 I supposed that I would carry on living in Ireland after retiring. Now I’m having some doubts about that. I have been advised by medical experts that my arthritis would be more tolerable in a warmer climate. And there’s the cost of living in Ireland, which is much higher than Spain. I can imagine living here, actually, though I think Barcelona itself might be a bit expensive for a pensioner. Somewhere in the surrounding countryside, or along the coast, might be nice. I’ve got a few years to think about that.

Another thing in my mind is what will happen to the Open Journal of Astrophysics when I retire? I would like some larger organization or community to take it over in the long term. It’s not expensive to run, actually, but someone would have to take over as Managing Editor. Moreover, I don’t think it’s really fair to expect one small University in Ireland to bear the full cost of a global astrophysics journal indefinitely.

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