Archive | June 2018
June 18, 2018  

Galaxy Builder Results

For the past few years, a new Galaxy Zoo project has been under development. This project allows the creation of models of galaxies inside the Zooniverse website (although in a slightly experimental fashion). Many of you helped trial this project in December of 2017, and some have classified since it was quietly launched in late April. I’d like to take this opportunity to share with you some of the early results we have obtained from your classifications!

From the beta

260 of you helped beta test and debug the project in our beta, providing invaluable feedback (most of which we hope we addressed!) and submitting over one thousand test classifications of our small test sample. One of the images in this sample was the SDSS r-band image of the galaxy below, catchily known as SDSS J104238.12+235706.8.

In this post we’ll look specifically at the spiral arms drawn on this galaxy, and how we can recover information about the shape of the spirals from your drawn arms. If we plot every spiral arm drawn on the galaxy, two distinct spiral appear:

There are a number of classifications which have either crossed the center of the galaxy, linking the two arms with one line, or which attempt to enclose the spiral (as in the GZ:3D project) rather than tracing along the center line. This confusion arose from the short tutorial and confusing help text present in the beta, which was flagged by our testers (thank you!).

Grouping Lines

We can make use of unsupervised machine learning techniques to cluster together these drawn arms, and extract points corresponding to each arm (while throwing away some lines which didn’t fit into our groups).

Cleaning up

Taking one arm as an example, we identify points which could be considered outliers, and remove them to improve our later fit (using another unsupervised machine learning technique called Local Outlier Factor). In the image below, red dots correspond to points identified as outliers, and the blue contours can be seen as a probability map, with points in regions of darker blue being more likely to be an outlier.

Fitting a spiral

Brilliant – we now have a load of (unordered) points which roughly resemble the spiral arm of our galaxy! We’ll fit a smooth line to obtain a “best guess” of the galaxy’s spiral properties, the result of which can be seen below:

 

What we’ve discovered from the beta trial is that we need at least 20 attempts at drawing spirals on a galaxy to get reliable answers, so we’re keen to get more people trying to build galaxies on Galaxy Builder.

If you’d like to help please join us at https://www.zooniverse.org/projects/tingard/galaxy-builder. If that’s not your thing we still need classifications on Galaxy Zoo: 3D, and the classic Galaxy Zoo is still live with all new images from the DECaLS survey.

June 4, 2018  

A Conference on Galactic Rings

A few of the Galaxy Zoo science team were in Alabama last week for a conference all about Galactic Rings. Results making use of your classifications were much in evidence, so we’ve collected some of the hi-lights for you in this blog post.
 The conference was timed to recognise the career of Prof. Ron Buta – one of the undisputed world experts in galaxy morphology (and especially galaxy rings) and someone who was personally trained by Gerard de Vaucouleurs (of the De Vaucouleur classification system) in classifying galaxies. One of the cool things about the meeting was the presence of an original hand drawn version (by De Vaucouleurs himself) of the classification scheme for Sb galaxies.

Paul Eskridge and Karen Masters help Ron Buta unwrap the De Vaucouleurs classification diagram. Photo credit: Bill Keel.

One of the first mentions of Galaxy Zoo classifications was by Ron himself, in the introduction to rings in galaxies. Of your classifications his verdict was “couldn’t have done it better myself”. A real endorsement from such an expert.

Ron Buta by the original diagram of the De Vaucouleur Classification Scheme for Sb galaxies. Gerard de Vaucouleur hand drew each galaxy in the diagram in pencil while clouded out on observing runs. Many of the structures discussed in this conference are clearly shown in this diagram. Photo credit: Bill Keel

 

There are various kind of rings we see in galaxies – nuclear, inner, outer, pseudo rings, collisional, accretion, maybe even disk instability at high redshift. We discussed how all of these are thought to form, and enjoyed a parade of beautiful images of ring galaxies.

A selection of ring galaxies. From left to ring: Hoag’s Object (an accretion ring), The Cartwheel Galaxy (a collisional ring) and NGC 3081 showing an inner and nuclear resonance ring (it also has an outer ring, not shown in this image). Image credits: Hubble Space Telescope for all three (composition by Karen Masters).

 While the conference was all about galactic rings, really all internal structures seen in spiral or disc galaxies were discussed – and the connections between them. It was a great mix of observers like ourselves, and theorists, working on state of the art models of galaxy morphology.
 Results from your classifications of Illustris galaxies were mentioned several times (Dickinson et al. 2018), revealing that the simulation, while doing OK for large galaxies, cannot reproduce the morphologies we see in the real Universe for lower mass galaxies – at least not yet. This was covered in the blog post: “Classifying Galaxies from Another Universe“
 The results from both Galaxy Zoo: Hubble, and Galaxy Zoo: CANDELS on how the bar fraction changes in disc galaxies as we look back across cosmic time came up several times. We’ve covered those on this blog here and here. Certain kinds of galactic rings (resonant rings) are thought to be created by bars, so understanding the evolution of bars in galaxies is important for understanding rings. What was really nice to see was this result presented with no mention that it came from Galaxy Zoo. That might sound odd at first, but we take it as recognition that Galaxy Zoo morphologies are now an accepted part of astronomical data and practice – used by astronomers for the excellent data they are – not because of (or in spite of) being created by citizen scientists, but because they provide useful information about how galaxies work.

 Spiral arms and how they form were a big discussion at the conference. Bill Keel (who you may now better for his work on overlapping galaxies found in the forum), presented work by the most recent Galaxy Zoo PhD – Dr. Ross Hart (who unfortunately could not make the meeting) on Galaxy Zoo constraints on spirals. This included results from a small side project Spiral Spotter. What is clear from this result (and many others presented at the meeting) on spirals – we really don’t understand which spiral arm formation mechanisms are the most important in galaxies, or how to tell in an individual galaxy which mechanism makes its spirals. There’s a dizzying array of possibilities – so lots of results to test with morphology. Overlapping systems did still get a mention – presented by Benne Holwerda.

Bill Keel presenting Galaxy Zoo results on spiral arms. Credit: Karen Masters

One especially strong and mostly new thing at the meeting – using the history of star formation in a galaxy (as unravelled from mostly resolved spectroscopy) to add information to dynamical histories. For example, if dynamics says nuclear rings are made only from gas funneled in along a bar, the ages of the oldest stars associated with that ring tell you that the bar was here at least that long ago. In one example, MUSE data suggest that NGC 4371 has a bar which formed about 10 Gyr ago, and this was compared to the highest-redshift bars found in Galaxy Zoo: CANDELS.

NGC 4371 and it’s clear bar (Credit: SDSS)

Galaxy Zoo has a link to the MaNGA survey (which covers many more galaxies than MUSE, but at much lower spatial resolution). Some of you may have contributed to Galaxy Zoo: 3D which is asking you to help us identify the locations of internal structures in galaxies observed by MaNGA. We saw some early results from this from Amelia Fraser-McKelvie, and Tom Peterken (both at Nottingham University), which we’ll be covering on the blog soon in more detail. Thanks for your classifications so far on GZ:3D – we could really use a lot more help on wrapping up that project if you have some time!
We heard from Bill’s PhD student Colin Hancock about interested 3-armed spirals. What’s curious about some of those is that they don’t seem to mind having strong bars. We’re all a bit confused how that’s possible, so stay tuned.
 Karen Masters gave one of the last talks of the conference, with an overview of Galaxy Zoo old and new. She wrapped up with live demos of both Galaxy Zoo: 3D and Galaxy Builder, both of which could use more expert (citizen, or professional scientist) classifications.

Karen Masters starting a talk with a review of 11 years of the Galaxy Zoo project. Credit: Bill Keel

Much was made at the conference that the last astronomy conference hosted in the same location had been in 1995, and many of the attendees present then were also present this year (although a Twitter poll established that most of the Twitter active attendees this time were still at school in 1995). Below a few attendees inspect the conference photo from 1995.
2018-05-31 08.27.14

A group of experts classify a photo of astronomers from 1995 (in the same location). Credit: Bill Keel.

It is possible most of the talks will be made available online eventually – we’ll keep you posted if that happens.
Blog post by Karen Masters, with significant input (and photos) from Bill Keel.