My Publications

This page contains all my academic publications. My popular outreach articles can be found via the Writings section. You can also find a complete list of my publications on ORCiD, but I don't like ORCiD, so please don't do that. A better alternative is this ADS library.

A note on data availability

All of the reduced FITS data used here was made publicly available as part of the AGES project. As per our internal policy, this happened upon the first publication from each data set. Unfortunately the whole Arecibo website is now defunct thanks to bloody stupid funding policies, but alternatives are being sought. In the meantime, I can probably provide any data on request.

First author

PhD Thesis : The Virgo Cluster Through The AGES
Or why you should never let your supervisor suggest the title of your thesis. Alternatives included : "The Arecibo Galaxy Environment Survey, or, How I Leaned To Stop Worrying And Love The Virgo Cluster" and "I Did My Thesis At Cardiff University And All I Got Were These Four Hundred Million Lousy Non-Detections".
The short version of this long-winded 189-page document is this : I looked at two areas in the Virgo Cluster, and found a bunch of galaxies. Some hydrogen detections don't have optical counterparts, which is weird. Some lenticular galaxies have hydrogen, and might have evolved from spiral galaxies. Lots of detections correspond to galaxies which no-one had noticed before. I wrote a program to find hydrogen more easily, which works very well, and did some fancy processing to try and increase sensitivity, which doesn't. Both of these will have dedicated pages here in due course.
The data available by the time I had to write up wasn't complete or as sensitive as it should have been. The final, full-sensitivity data is described in two main publications, VC1 and VC2, given below, as well as in various spin-offs.

AGESVC1

The first, largest area we looked at in the Virgo Cluster. Basically a descriptive write-up of the major results from my thesis, but more complete.

AGESVC2

The second, smaller area of the Virgo Cluster. The second area is pretty crappy compared to VC1, containing no new discoveries at all. But this is actually the more interesting paper, because here we try to interpret the results far more than in Virgo 1. Hydrogen detections without optical counterparts are shown to lie off the baryonic Tully-Fisher relation, and we describe some of the interesting objects behind the cluster (giant elliptical galaxies with stellar streams).

The Lonely Little Smurf

By sheer blind luck, we stumbled upon a nearby blue compact dwarf galaxy that no-one had noticed before. It really isn't very interesting, but it was worth reporting anyway. This was in the NGC 7448 field, more fully described in the paper below. Outreach version here.

Really Long HI Streams

We found a whole bunch of really long HI gas streams in a pretty much random part of the sky, which was made a lot easier thanks to FRELLED. Official press release here. Cynical version here.

FRELLED

Of course anyone viewing this website regularly will be aware that I've been developing FRELLED, a realtime volumetric data viewer for Blender, for years. The paper was a result of a minor tiff with some other astronomers who wrote that Blender wasn't suitable for data analysis, which prompted me to write this, which prompted an invite from Astronomy & Computing to submit a paper. Which I did. This is my first paper as sole author.

The dedicated FRELLED pages will be restored in due course. This has been completely re-written for Blender 2.79 and has greatly improved performance and expanded capabilities. Currently in the stages of final debugging.

Attack of the Flying Snakes

Yes, that's the real title of the paper. We catalogued all the known long hydrogen streams and isolated clouds that we could and used numerical simulations to try and explain them. We found that the most popular explanation for some clouds – tidal debris – really, really doesn't work, whereas dark galaxies seem to be pretty sensible. This is a very long paper, so outreach versions are here and here.

Spherical Data Cubes

3D data sets are often referred to as "cubes", even though in they're usually cuboids. In radio astronomy we map the brightness across the sky but also the frequency of the emission, and use this as the third axis – which is not usually the same as real distance. But at least those data sets usually have nice regular grids. In other cases even that isn't the case, especially in numerical simulations of discs. There the coordinates can be much more complicated. In this paper I describe a way to visualise data of (potentially) any coordinate system using Blender. This is my second sole author paper, and you can read about the minor hell I went through to write it on my blog.

With tremendous irony, this paper was developed as part of an interview process, for which I was ultimately unsuccessful. The paper itself has a paltry 2 citations, but it did get me another job offer... which I declined.

My Kinky Curves

Sadly this is not the title of the paper but I did manage to get the phrase "Kinky curves as fake dark galaxies" as a sub-heading, which is about all that one can hope for. This is a follow-up to the flying snakes paper. Previously we just looked at the effect of a galaxy cluster on stripped gas from galaxies, to see if it could produce strange velocity "kinks" in the streams that could be mistaken for rotating dark galaxies. In this paper (blog version here) we use more advanced simulations to include the formation process of the streams as well as their evolution. We look in much more detail at the precise conditions under which such a kink could be mistaken for a galaxy, and, more importantly, when it couldn't.

Will No-One Rid Me Of This Turbulent Sphere ?

Much to my annoyance the journal wouldn't let us this as the full title and didn't even like a slightly longer version, but insisted on this monstrosity. No matter. It describes a set of simulations to describe an alternative hypothesis proposed to explain the dark hydrogen clouds. Their high line width implies that they shouldn't last long enough to detect them, unless they're stabilised. Instead of rotation, as we explored in our other papers, the idea here is that they would have random, disordered motions but would be confined by the pressure of the intracluster medium. This was a clever idea, but when we tested it, it just didn't work. Outreach version here.

Faint And Fading Tails : The Fate Of Stripped HI Gas In Virgo Cluster Galaxies

For some reason I will never fully understand this took more than a year of review and three referees, but finally sheer bloody-mindedness prevailed. After years of claiming that there were no streams in my Virgo cluster data, I realised I was completely wrong : there's plenty of short, faint streams if you know how to find them. Contains a rigorous statistical analysis proving beyond any reasonable doubt that the little buggers are real. Blog version here.

The Gassy Lion

For once, a paper that sailed through the review process without incident... thank you, kindly reviewer, you're lovely. In this paper we take a first look with AGES at the Leo Group, famed for its giant gassy ring. But the Ring itself turns out to be ferociously complicated, so we set that aside for now. Of more immediate interest are six little gas clouds, most without any sign of optical counterparts. While the obvious interpretation in a place like Leo is that these are tidal debris, most of these follow the standard baryonic Tully-Fisher relation for normal, rotation-dominated galaxies – and that's not really expected. Couple of blog entries about this : this one looking at how difficult constructing an accurate BTFR really is, and this one looking at the wider scientific interpretations.

Co-authored

Abell 1367 (Luca Cortese)
The first paper I was ever involved with (mainly for doing the follow-up observations to confirm the catalogued detections). A fairly nearby galaxy cluster with some interesting HI detections with streams and without optical counterparts. The main result is that the baryon fraction in nearby galaxies turns out to be constant.

NGC 7332/7339, NGC 1156 (Robert Minchin)
A couple of smaller AGES fields. Robert found that he galaxy pair NGC 7332 / 7339 are interacting, with NGC 7332 distorting the gas in NGC 7339. NGC 1156 describes the first results of the isolated galaxy sample, with NGC 1156 confirmed to be isolated as it has only a single companion.

NGC 7448 (Jonathan Davies)
A galaxy group with lots of interacting members. We found some new group members and use the whole survey to determine the HI mass function.

Isolated Galaxies (Robert Minchin)
Completion of the AGES study of apparently isolated galaxies. We found that they really are isolated – they don't have any gas-rich OR optically bright companions.

M33 (Olivia Keenan)
We spent five years observing the HI environment of the Triangulum galaxy M33. And... we found a giant HI cloud that's the largest detected there for over 30 years. Unusually, it's ring shaped, and we have no idea why. Check out the graphics-heavy blog post here.

Ram Pressure Stripping Made Easy (Joachim Köppen)
Galaxy clusters aren't just a bunch of galaxies hanging out for the sake of it – they're full of strippers. Or rather, clusters contain their own hot, very thin gas that isn't bound to any particular galaxy. If a galaxy moves fast enough, the ram pressure that builds up can completely strip its gas and eventually halt its star formation. Joachim found a neat way to model this very complicated process analytically, and even provided tools so you can try it yourself in a web browser. Blog post here.

Nazi Farmyard In Space (Frédéric Marin)
Frédéric specialises in X-ray polarimetry of active galactic nuclei, but, as a side project, he developed a code to calculate the population size required for an isolated human population to avoid inbreeding : i.e. the smallest population of a worldship. Then he took this a step further and calculated how much they'd need to eat.... blog post here.

A Giant Gassy Space Unicorn (Robert Minchin)
Although we haven't even finished analysing all of AGES, the successor survey WAVES (Widefield Arecibo Virgo Environment Survey) is well underway. This first field looks at the well-known Kent complex, a group of optically dark hydrogen clouds that, in this shiny new super-sensitive data, looks a lot like a rhino. And it's damn hard to explain how the thing got there too. Blog post here.

Fun With Filaments (Boris Deshev)
Everybody loves galaxy clusters – those crazy places where galaxies get smashed, slashed, and bashed. But are they perhaps just a little bit over-rated ? Might galaxies actually experience a significant measure of damage before they enter the cluster proper, or might some areas be worse than others ? Boris Deshev decided to do some fancy-schmancy Voronoi mapping to find out. Blog version here.

Deepening Darkness (Michal Bílek)
Just to make sure one of those dark gas clouds was really dark, and not just faint and annoying, Michal Bílek directed some impressively deep optical observations to look for any starlight that shallower surveys might have missed. We didn't find any. So yeah, there's definitely no stars or signs of tidal encounters in the optical. Short blog post here.

He who smelt it, dealt it (Robert Minchin)
Gas stripping, a.k.a. galaxy farts, can be a key part in shutting down star formation and thus galaxy evolution. Ideally we'd like to detect the stripped gas itself but sometimes this just isn't possible. Robert Minchin came up with a clever alternative : by looking for ionised carbon, we can see when galaxies are interacting with an external medium even when the "ram pressure" isn't strong enough to cause full-on stripping. So we don't need to see the stripped gas itself, it's enough to look at the chemistry, i.e. the smell... Public outreach version here.

A veritable plethora of blobs (Boris Deshev)
Returning to the very first paper I was ever on, 14 years later we finally completed a catalogue of the Abell 1367 cluster and its surroundings. This is mainly a catalogue paper (it's a rich field so this is a lot of work by itself) but Boris Deshev came up with some interesting ways to quantify gas loss from limited information. Plenty of spin-offs are expected from this in the fullness of time. Blog post here.

A couple of interactive features are also available : this one shows the distribution of galaxies detected with and without HI, while this one (caution, 55 MB file) shows the HI itself. Both are HTML files. If they don't open directly in the browser window, download them and open in any browser and they should work.