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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.

The data available by the time I had to write up wasn't complete or as sensitive as it should have been. That data is described in the (so far) two resulting publications.

 

First-author publications :

Virgo 1

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. The raw data is available here (1.2 GB FITS cube).

 

Virgo 2

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. 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. Press release 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.

 

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 popula 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. Two spin-off papers are in preparation.

 

Spherical Cubes

3D data sets are often referred to as "cubes", even though in some cases they're rectangular. 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 the same as real distance (sometimes it is, but sometimes it isn't). 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 hell I went through to write it on my blog.

 

Check Out My Kinky Curves

Sadly this is not the tile 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 conditons under which such a kink could be mistaken for a galaxy, and, more importantly, when it couldn't. 

 

Co-authored publications :

Abell 1367 (Luca Cortese)

A fairly nearby galaxy cluster with some interesting HI detections with streams and without optical counterparts. The baryon fraction in nearby galaxies is shown to be constant. The raw data is available here (146 MB FITS cube).

 

NGC 7332/7339, NGC 1156 (Robert Minchin)

The galaxy pair NGC 7332 / 7339 are shown to be interacting, with NGC 7332 distorting the gas in NGC 7339. NGC 1156 is an isolated galaxy with a single companion (a paper on our full sample of isolated galaxies is in preparation). The raw data for NGC 1156 is available here (133 MB FITS cube) and NGC 7332 is available here (134 MB FITS cube).

 

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

 

Selected Posters :

Giant HI Streams (Vienna IAU 309, 2014)

FRELLED (Anchorage AAS, 2012)

Virgo Cluster (Boston AAS, 2011)

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