Archive for Andrew Pontzen

Clusters, Splines and Peer Review

Posted in Bad Statistics, Open Access, The Universe and Stuff with tags , , , , , on June 26, 2012 by telescoper

Time for a grumpy early morning post while I drink my tea.

There’s an interesting post on the New Scientist blog site by that young chap Andrew Pontzen who works at Oxford University (in the Midlands). It’s on a topic that’s very pertinent to the ongoing debate about Open Access. One of the points the academic publishing lobby always makes is that Peer Review is essential to assure the quality of research. The publishers also often try to claim that they actually do Peer Review, which they don’t. That’s usual done, for free, by academics.

But the point Andrew makes is that we should also think about whether the form of Peer Review that journals undertake is any good anyway.  Currently we submit our paper to a journal, the editors of which select one (or perhaps two or three) referees to decide whether it merits publication. We then wait – often many months – for a report and a decision by the Editorial Board.

But there’s also a free online repository called the arXiv which all astrophysics papers eventually appear on. Some researchers like to wait for the paper to be refereed and accepted before putting it on the arXiv, while others, myself included, just put it on the arXiv straight away when we submit it to the journal. In most cases one gets prompter and more helpful comments by email from people who read the paper on arXiv than from the referee(s).

Andrew questions why we trust the reviewing of a paper to one or two individuals chosen by the journal when the whole community could do the job quicker and better. I made essentially the same point in a post a few years ago:

I’m not saying the arXiv is perfect but, unlike traditional journals, it is, in my field anyway, indispensable. A little more investment, adding a comment facilities or a rating system along the lines of, e.g. reddit, and it would be better than anything we get academic publishers at a fraction of the cost. Reddit, in case you don’t know the site, allows readers to vote articles up or down according to their reaction to it. Restrict voting to registered users only and you have the core of a peer review system that involves en entire community rather than relying on the whim of one or two referees. Citations provide another measure in the longer term. Nowadays astronomical papers attract citations on the arXiv even before they appear in journals, but it still takes time for new research to incorporate older ideas.

In any case I don’t think the current system of Peer Review provides the Gold Standard that publishers claim it does. It’s probably a bit harsh to single out one example, but then I said I was feeling grumpy, so here’s something from a paper that we’ve been discussing recently in the cosmology group at Cardiff. The paper is by Gonzalez et al. and is called IDCS J1426.5+3508: Cosmological implications of a massive, strong lensing cluster at Z = 1.75. The abstract reads

The galaxy cluster IDCS J1426.5+3508 at z = 1.75 is the most massive galaxy cluster yet discovered at z > 1.4 and the first cluster at this epoch for which the Sunyaev-Zel’Dovich effect has been observed. In this paper we report on the discovery with HST imaging of a giant arc associated with this cluster. The curvature of the arc suggests that the lensing mass is nearly coincident with the brightest cluster galaxy, and the color is consistent with the arc being a star-forming galaxy. We compare the constraint on M200 based upon strong lensing with Sunyaev-Zel’Dovich results, finding that the two are consistent if the redshift of the arc is  z > 3. Finally, we explore the cosmological implications of this system, considering the likelihood of the existence of a strongly lensing galaxy cluster at this epoch in an LCDM universe. While the existence of the cluster itself can potentially be accomodated if one considers the entire volume covered at this redshift by all current high-redshift cluster surveys, the existence of this strongly lensed galaxy greatly exacerbates the long-standing giant arc problem. For standard LCDM structure formation and observed background field galaxy counts this lens system should not exist. Specifically, there should be no giant arcs in the entire sky as bright in F814W as the observed arc for clusters at  z \geq 1.75, and only \sim 0.3 as bright in F160W as the observed arc. If we relax the redshift constraint to consider all clusters at z \geq 1.5, the expected number of giant arcs rises to \sim 15 in F160W, but the number of giant arcs of this brightness in F814W remains zero. These arc statistic results are independent of the mass of IDCS J1426.5+3508. We consider possible explanations for this discrepancy.

Interesting stuff indeed. The paper has been accepted for publication by the Astrophysical Journal too.

Now look at the key result, Figure 3:

I’ll leave aside the fact that there aren’t any error bars on the points, and instead draw your attention to the phrase “The curves are spline interpolations between the data points”. For the red curve only two “data points” are shown; actually the points are from simulations, so aren’t strictly data, but that’s not the point. I would have expected an alert referee to ask for all the points needed to form the curve to be shown, and it takes more than two points to make a spline.  Without the other point(s) – hopefully there is at least one more! – the reader can’t reproduce the analysis, which is what the scientific method requires, especially when a paper makes such a strong claim as this.

I’m guessing that the third point is at zero (which is at – ∞ on the log scale shown in the graph), but surely that must have an error bar on it, deriving from the limited simulation size?

If this paper had been put on a system like the one I discussed above, I think this would have been raised…

Stargazing (virtually) Live

Posted in Television, The Universe and Stuff with tags , , , , , , on January 18, 2012 by telescoper

I hope you’ve all been tuning in to the BBC’s astronomy jamboree Stargazing Live. There have been two episodes so far, with one last one to follow tonight, plus a huge range of activities across the country (including Wales) giving members of the public the chance to look at the sky through telescopes. The programmes and other activities have been getting an excellent response, especially from the younger generation, which is excellent news for the future of astronomy.

Working in a School of Physics & Astronomy makes one realise just how much public interest there is in astronomy, not just among schoolkids but in the numerous amateur astronomical societies, the members of which actually know the night sky better than many professionals! Most of us astronomers and astrophysicists are regularly asked to give public lectures and Cardiff in particular runs a  host of other outreach activities related to our astronomy research. Our colleagues in mainstream physics subjects such as condensed matter physics don’t get the same level of direct public interest – I don’t think there are any amateur semiconductor physics  clubs in the UK! – but many students attracted into universities by astronomy do turn to other branches of physics when they get here, because something else catches their imagination.

But important though that role is, let’s not forget that astronomy isn’t just about outreach. It’s actually real science, making real discoveries about the way our universe works. It’s worth doing in its own right as well as being good for other branches of physics.

Anyway, being a theoretical astrophysicist I usually feel a bit left out of these stargazing actitivies because I don’t really know one end of a telescope from the other. The other day I jokingly  asked whether Stargazing Live was ever going to include a theory component…

Last night’s episode actually did, in the form of a discussion of a numerical simulation of galaxy formation between the presenters and young Dr Andrew Pontzen from Oxford University. He even made a little video about the simulation, sort of virtual reality rendition of the formation of the Milky Way, as shown on the telly:

Apparently, making this required 300,000 CPU hours on 300 processors and it is based on 16 Terabytes of raw data. Phew!

It’s a very impressive simulation, but the use of the word simulation in this context always makes me smile. Being a crossword nut I spend far too much time looking in dictionaries but one often finds quite amusing things there. This is how the Oxford English Dictionary defines SIMULATION:

1.

a. The action or practice of simulating, with intent to deceive; false pretence, deceitful profession.

b. Tendency to assume a form resembling that of something else; unconscious imitation.

2. A false assumption or display, a surface resemblance or imitation, of something.

3. The technique of imitating the behaviour of some situation or process (whether economic, military, mechanical, etc.) by means of a suitably analogous situation or apparatus, esp. for the purpose of study or personnel training.

It’s only the third entry that gives the intended meaning. This is worth bearing in mind if you prefer old-fashioned analytical theory!

In football, of course, you can get sent off for simulation…

Echo of Creation – the Trailer

Posted in Education, The Universe and Stuff with tags , , , on May 27, 2011 by telescoper

Each day I find myself pressed for time and unable to think of anything to post, something seems to come along to rescue me. I found this on Twitter this morning and couldn’t resist sharing it, partly because it’s a cute video in its own right, and partly because it gives me the chance to advertise the event that it trails. Here’s the film …

..and it advertises a forthcoming event at the Cheltenham Science Festival, featuring the excellent Andrew Pontzen who is based at the Institute of Astronomy in Cambridge. Andrew is not only a whizzkid cosmology theorist but also an excellent public speaker, so do go and see his lecture if you can. Here’s the blurb:

Billions of years after the birth of the Universe, scientists realised they could tune into an echo of creation itself using nothing more sophisticated than a de-tuned television set. Andrew Pontzen explains the cosmos’ ‘background noise’ with hula hoops, beach balls and amazing telescopic pictures. But hold onto your hats: all is not as it seems with space and time…

Sounds fascinating! The talk is on Saturday 11th June 2011, 10am at the Town Hall in Cheltenham. You can book tickets here.

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