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Galaxy Zoo Highlights from 2015

Following on from the excellent summary of the hi-lights in 2015 for the Radio Galaxy Zoo project, here’s a similar post about results from Galaxy Zoo.

This year we collected 4,755,448 classifications on 209,291 different images of galaxies. You continue to amaze us with your collective efforts. Thank you so much for each and everyone of of these classifications.

The year started with Galaxy Zoo scientists at Mauna Kea observing galaxies, and reported in this wonderful series of blog posts by (former) Zooniverse developer Ed Paget.

Ed, Chris, Sandor, and Becky in front of the telescope

Ed, Chris, Sandor, and Becky on Mauna Kea.

We celebrated 8 years of Galaxy Zoo back in July, with this blog series of all things 8-like about Galaxy Zoo.

An 8 for our 8th birthday!

An 8 for our 8th birthday!

Back in May we finished collecting classifications on the last of our Hubble Space Telescope images. At the AAS in Florida this week, Kyle Willett and Brooke Simmons presented posters on the planned data releases for the classifications.

We both launched and finished classifying the first set of images of simulated galaxies from the Illustris Simulation (read more here: New Images for Galaxy Zoo: Illustris and here: Finished with First Set of Illustris Images). We also launched our first set of images from the DECaLS survey, which is using the Dark Energy Camera (New Images for Galaxy Zoo: DECaLS)

We also launched a new Galaxy Zoo side project – Galaxy Zoo Bars (one of the first projects built on the new Zooniverse Project Builder software), measuring bar lengths of galaxies in the distant Universe. The entire set were measured in less than a year, so thank you to any of you who contributed to that, and if you missed it don’t worry, we have plans for more special projects this year.

We launched a new web interface to explore the Galaxy Zoo classifications.

Screenshot of the Visualisation Tool

Screenshot of the Visualisation Tool

Our contributions to the peer reviewed astronomical literature continue. Papers number 45-48 from the team were officially published in 2015. They were:
– Galaxy Zoo: the effect of bar-driven fueling on the presence of an active galactic nucleus in disc galaxies, Galloway+ 2015.
– Galaxy Zoo: Evidence for Diverse Star Formation Histories through the Green Valley, Smethurst+ 2015.
– Galaxy Zoo: the dependence of the star formation-stellar mass relation on spiral disc morphology, Willett+ 2015.

You can access all 48 team papers using your classifications at the Zooniverse Publication Page. Remember that all Zooniverse papers published in the Monthly Notices of the Royal Astronomical Society – which includes most of the Galaxy Zoo papers – are available open access to any reader, and if we happen to publish elsewhere we always make the post-acceptance version available on the arxiv.org.

All of our papers include a version of this acknowledgement to our classifiers: “The data in this paper are the result of the efforts of the Galaxy Zoo volunteers, without whom none of this work would be possible. Their efforts are individually acknowledged at authors.galaxyzoo.org.” We all hope you all know how grateful we are for each and every one of your classifications.

This year saw publication of the first paper on Hubble observations of Voorwerpje systems accompanied by an HST press release.

Montage of Hubble images of Voorwerpjes

Montage of Hubble images of Voorwerpjes

One of those papers from (mostly) outside the GZ team discussed a rare examples of double radio sources from spiral hosts, something Radio Galaxy Zoo will find many more of: “J1649+2635: a grand-design spiral with a large double-lobed radio source”, Mao et al. 2015.

Another exciting thing about this year has been the number of papers from non team members using the classifications which are now public (see data.galaxyzoo.org). To date almost 300 astronomical papers have been written which cite the original description of Galaxy Zoo (Lintott et al. 2008) and the two data release papers so far (Lintott et al. 2011 for GZ1 and Willett et al. 2013 for GZ2) have 164 and 34 citations respectively. The number of papers in the Astrophysics Data System which contain the words “Galaxy Zoo” (which you can search in ADS Labs) is an astonishing 700 (409 for refereed publications).

These are just some of the high-lights I’ve pulled together. If I’ve missed your favourite feel free to add it in the comments below. All in all it’s been a great year. Here’s to an equally good 2016!

Radio Galaxy Zoo Highlights from 2015

Happy New Year!  I hope everyone had a relaxing break. Radio Galaxy Zoo had a couple of highlights over the last year with new discoveries that will be out later this year.  Well done everyone!

We now have over 1.45 million classifications and are at 48% complete.

Here are a few of our notable highlights:
Papers
Surprises
  • progress on the giant WAT is continuing to bring up more interesting information including our JVLA data – potentially 3 additional papers;
  • we obtained 4 hours to obtain a spectrum for four of our green DRAGN with the observations scheduled for March 2016; and
  • with all your work, RGZ has discovered over 100 new giant radio galaxies!
We are continuing to work away on the data that keeps coming in.  Keep your eye out for our next few projects:
  • matching of RGZ classifications to SDSS;
  • merging Galaxy Zoo data with Radio Galaxy Zoo data;
  • our observations with the JVLA on the hybrid radio sample is complete with 60 hours of observing time; and
  • we are working with the International Astronomical Union (IAU) to get the RGZ name official.
A big welcome to our new team members:
  • Martin Hardcastle (Hertfordshire)
  • Sarah White (ICRAR/Curtin)
  • Francesco de Gasperin (Leiden)
All of this could not have been accomplished without all of you – big THANK YOU! Looking forward to a great 2016!
Julie, Ivy and the RGZ team

Go West, Young (?) Astronomer

Sunset in Southern California

Many bargains must be made in pursuit of an academic career, and chief among them is an openness to a nomadic early-career life in exchange for a better chance at staying permanently put somewhere later. Grad students and postdocs move around. Not only do we travel all over the world sharing and discussing our research, but the relatively short duration of postdocs, and the fact that in astronomy doing at least 2 of them is now the norm, means we regularly pull up roots and dash off to live somewhere else. My friends have collectively done postdocs on all continents, including Antarctica. Including places thousands of miles from friends and family; including places where they can neither read nor speak any of the native languages.

In this context, I am so, so lucky. My first postdoc moved me only a medium distance (across just one ocean), and to a place where I could at least understand the words, even if I didn’t always get every nuance of meaning. At Oxford I made lifelong friends and built great collaborations, and I thought the research itself was pretty good, too.

Turns out NASA agrees with me. Last year I applied for and was awarded an Einstein Fellowship, which is an early-career award lasting 3 years, an independent postdoc that can be taken to any institution in the US. They’re very competitive (I had applied the previous year without success), and I was thrilled to be awarded one at my top-choice host institution. My first day was last week.

Here’s what the 2015 Fellows page has to say about my research plans:

Brooke uses a variety of multi-wavelength data, including highly accurate galaxy morphologies from the Galaxy Zoo project, to research the connection between supermassive black holes and the galaxies that host them. This connection appears to exist over many orders of magnitude in black hole and galaxy mass, but its fundamental origin is still a puzzle. As an Einstein Fellow at the University of California, San Diego, Brooke will investigate supermassive black hole growth in the absence of galaxy mergers, using a rare sample of galaxies which have never had a significant merger yet host growing black holes. These active nuclei, selected because their host galaxies lack the bulges which inevitably result from a galaxy merger, provide powerful leverage to disentangle the complex drivers of black hole growth and determine the origin of observed black hole-galaxy correlations.

During my fellowship I’m planning on moving forward with the research we first published in 2013 investigating bulgeless galaxies with growing black holes. That is: it’s Galaxy Zoo research.

Galaxy Zoo research brought me to Oxford, and now it has brought me to California. UCSD is a great place, and I’ve already made some really excellent scientists. UCSD is also part of the Southern California Center for Galaxy Evolution and has access to some of the world’s best telescopes, so the future is full of potential.

For now, though: I wouldn’t be here, watching sunsets from my office, without your contributions to Galaxy Zoo over the years. Thank you.

Searching for “tidal debris” in DECaLS images

This post was written with the help of Sugata Kaviraj, senior lecturer at the University of Hertfordshire in the UK. Sugata has been a member of the GZ science team for several years and is leading our analysis of tidal debris in the DECaLS images.

One of the biggest changes to the questions we’re asking for the new DECaLS images asks users to help us classify galaxies that are either merging and/or exhibiting “tidal debris”. While mergers have been part of Galaxy Zoo since our very first classifications, tidal debris is looking for something more specific, which the new DECaLS data is particularly suited for.

In astronomy, “tides” are a type of force exerted on an object by the effect of gravity. Specifically, it refers to the gravitational force exerted by one body on another – since the force exerted by gravity depends on the distance to the object (specifically, it’s proportional to the inverse square of the distance), the nearer side of the object will feel a stronger force than the farther side of the object. On Earth, the differential force caused (mostly) by the gravity of our Moon acts on the liquid in the oceans, causing the rise and fall in sea levels each day.

Field tidal.svg
Example of how a solid body can be deformed under tidal forces. (“Field tidal” by Krishnavedala. Licensed under CC BY-SA 3.0 via Commons.)

When the object is a solid body (like a planet or moon), tidal forces can strain and compress the body, resulting in internal heat and sometimes driving geological activity. A galaxy isn’t a solid body, but composed of individual stars/gas clouds/dark matter particles bound within its own gravitational field. When a galaxy is subjected to tidal forces, it pulls the galaxy apart, causing irregularities in shape that can take many forms depending on the magnitude and direction of the forces involved.

One of the main reasons we want to identify tidal features specifically is to make better measurements of the merger history of galaxies. A complication is that the event of merging with a galaxy isn’t an instantaneous event – depending on the relative masses, velocities, and orientations of the merging galaxies, tidal forces strip out long tails of stars and gas from the galactic centers.

The Mice (NGC 4676): Colliding Galaxies With Tails of Stars and Gas
The Mice (NGC 4676): colliding galaxies with tails of stars and gas distorted by tidal forces. Source: Hubblesite.org

Ultimately, the nuclei of the two galaxies will fully merge; if that happened sufficiently far in the past for the orbits of stars to relax, then it’s difficult for observers to determine if an elliptical galaxy today was the result of a merger.

Tidal debris features, however, are longer-lived signals of a merger sometime in a galaxy’s past. If we only asked about mergers, we’d be restricting the sample to galaxies that we’re lucky enough to observe “right in the act” of merging. By identifying the tidal debris as well, we can make a more complete census of galaxies that had a merger at some point in their past. One project that this is critical for is looking at the history of galaxy populations, and trying to figure out whether star formation and/or active black holes might be powered by merger events.

Since tidal debris features can be very faint (ie, having low surface brightnesses), the deeper DECaLS images that we’re currently classifying are much better at picking out these features than SDSS. That’s the main reason we’re focusing on trying to detect them in the current set of images.

Tidal debris can come in many different forms, including extended light, faint shells, dust lanes, or satellites in the process of being assimilated to clearly distorted galaxies which have presumably have had a recent interaction. The features can definitely be faint, but we’d like to ask that when you reach this question, please take a careful second look at the area around the main galaxy and see if you can spot anything. Examples are also available in the help text, and we hope that you’ll discuss features you’re not certain about with the moderators, scientists, and other volunteers in Talk.

Example 2. Faint tidal debris extension is visible to the upper left of the main galaxy. Image courtesy DECaLS/Galaxy Zoo.

Example 1. Faint tidal debris extension is visible to the upper left of the main galaxy. Image courtesy DECaLS/Galaxy Zoo.

Example 3. Faint tidal debris is visible around the main galaxy in a shell-like shape. Image courtesy DECaLS/Galaxy Zoo.

Example 2. Faint tidal debris is visible around the main galaxy in a shell-like shape (see arrows). Image courtesy DECaLS/Galaxy Zoo.

Example 4. Faint tidal debris extension is visible to the left of the main galaxy. Image courtesy DECaLS/Galaxy Zoo.

Example 3. Faint tidal debris extension is visible to the left of the main galaxy (within red ellipse). Image courtesy DECaLS/Galaxy Zoo.

Ste

Example 4. A small satellite galaxy is merging into the larger one at the center, being ripped apart and causing tidal debris. Image courtesy DECaLS/Galaxy Zoo.

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Example 5. Tidal debris (within the red outline) extending to the top and left of the main galaxy. Image courtesy DECaLS/Galaxy Zoo.

3

Example 6. Faint tidal debris in a “shell” structure, extending in several directions from the main galaxy (comparable to Example 3). Image courtesy DECaLS/Galaxy Zoo.

Please let us know, here or on Talk, what questions you have. Thanks for your help in tackling a new and interesting scientific problem.

Radio Galaxy Zoo: conferencing in Italy (Day 1)

One of the best things about being a scientist is the opportunity to attend conferences – you get to visit a new place, meet your colleagues in person, learn about what they’ve been doing, and get a chance to share your exciting research with them. I’m lucky (through the assistance of the American Astronomical Society, the Italian National Institute for Astrophysics, and the University of Minnesota) to participate in a conference this week on the future of extragalactic radio surveys in Bologna, Italy. I’m getting my first chance to share results from Radio Galaxy Zoo and to learn about other, new results in the area of extragalactic radio science!

The conference is four days, from Tuesday – Friday; I’m going to try to make a blog post each day. I’m going to try give a quick overview of all talks/posters on the day, as well as more details on talks which I thought were particularly interesting. I know I won’t do justice to many of the interesting research topics being presented, but I won’t have time to give every topic the breadth they deserve.

The first day of the workshop started with several talks covering current and upcoming surveys in radio astronomy. These include radio telescopes in the Northern Hemisphere. The two main telescopes discussed were the Very Large Array (VLA) in New Mexico, USA, which will run surveys like VLITE (a low frequency survey which will run constantly on the telescope in parallel with other observations), and VLASS, a new all-sky survey with many similarities to the current FIRST data in Radio Galaxy Zoo. LOFAR is a low-wavelength radio telescope with stations centered around Europe; it will open up similar resources, but at significantly lower frequencies than the VLA and thus probing different physical phenomena. In the Southern Hemisphere, the EMU survey in Australia and the MIGHTEE survey in South Africa will carry out similar responsibilities.

I gave a talk at the end of this session on Radio Galaxy Zoo, covering our first accepted paper and some of our early science results. If you’re interested, I’ve put my talk online here.

Example slide from K. Willett's talk on Radio Galaxy Zoo at the Bologna workshop.

Example slide from Kyle Willett’s talk on Radio Galaxy Zoo at the Bologna workshop.

The afternoon had two sessions on science: one on radio continuum and star formation, and one on radio observations of the transient universe.

I think after the first day that I’m filled with a great sense of optimism about radio astronomy. We’ve got a fantastic new telescope being built in the next several years: the Square Kilometer Array. It’ll be the largest telescope ever built, addressing a huge number of scientific questions. We’re currently in the stage of building prototype telescopes, but those telescopes are already producing useful science – some of which I learned of today. We have a reasonable understanding about how things like magnetic fields affect both the formation and evolution of galaxies. Radio observations have a unique way of detecting and leveraging these detections; through polarization of the radio signal, we can measure the magnetic field and directly probe (through its signal) the interactions with matter between its source and our telescopes. New phenomena like fast radio bursts are, I think, a really neat way of measuring both the amount and distribution of matter in the Universe – this has implications for everything from star formation to cosmology.

Really excited for the rest of the week (including more Radio Galaxy Zoo results) – will post again tomorrow!

(Galaxy) Bars in the Summer

This is a guest post by Freya Pentz, who has spent much of this summer doing research with Galaxy Zoo.

Hi Galaxy Zoo volunteers!

I’m a summer student at the Zooniverse. I’m at university studying natural sciences about to go into my second year and for the past 5 weeks I’ve been working at the Zooniverse office here in Oxford. I wanted to let you know what I’ve been doing during that time.

I’ve been using data from the Galaxy Zoo: Bar Lengths project, writing code to process the information and making sure it looks sensible. Before I started working at the Zooniverse, I had done very little computing so I had to learn a lot! For those of you who are interested, I’ve been using python to extract the measurements you did on the galaxies and plotting graphs with all the data. Learning how to use python was like learning another language but it was definitely worth it.

The first thing I did was to find out how many of the galaxies that you’ve classified have bars. That meant looking at the answers to the first question about the galaxy in the Bar Lengths project ‘Does this galaxy have a bar’ and seeing for each galaxy if most people answered ‘Yes’ or if most people answered ‘No’.

Does this galaxy have a bar? Zooniverse interface

Remember this question?

Luckily, the code could do that for me; otherwise I would have had to look at over 66000 answers! So far, 4960 galaxies have been classified out of a total of 8612 in the project. Your classifications show that 700 of these have a bar, meaning that the fraction of classified galaxies with a bar is around 14%. This is similar to the 10% bar fraction referred to in the study recently done by the Galaxy Zoo and CANDELS teams on bar fractions out to z=2 (blog post & paper). This number will probably change a little bit as more galaxies get classified, but it’s good that it is similar to known values so far.

The next thing was of course to find the lengths and widths of the bars. When you draw lines on the galaxy to mark the length and width, the database records this as coordinates. Each line has four coordinates, 2 x coordinates and 2 y coordinates. Once you have the coordinates, it’s fairly simple to turn them into lengths. All you need is some Pythagoras. When plotting a histogram of the lengths, the shape was a Gaussian distribution, or a bell curve. This shows that most of the galaxies have lengths between certain limits (5-15 kpc) and then as you go beyond these limits, the number of galaxies decreases.

During my time here, I found some interesting galaxies. When I first looked at the redshifts, there was a galaxy with a redshift of 4.25. I mentioned this to a couple of people on the Zooniverse team and they all said there wouldn’t be a galaxy with such a high redshift in the sample. I checked it out and this is the galaxy in question:

Image of a galaxy with lens-like-but-apparently-not-a-lens structure

The galaxy that fooled the computer into thinking it had a redshift of 4.25

You can see that there is a bright blue smudge in the top left of the galaxy. When I first saw this, I thought it was a lens. It looks like one, and you can just see a small bit of blue on the other side of the galaxy’s core, suggesting a lens even more. According to the experts in the Zooniverse however, this is probably not a lens, as the galaxy does not look massive enough to lens light. Also, the blue curve is well inside the galaxy, instead of being around the outside. Usually, all the mass of the galaxy is needed to lens an object so the light would appear around the edge. The blue curve is most likely an unusual feature of the galaxy itself, which can explain why the reported redshift is so high. The redshift for this galaxy was measured photometrically. This is where astronomers use galaxy colours across a wide range of wavelengths to predict the likely redshift. This method of measuring redshift is much more prone to error than spectrometry (where the absorption lines for certain elements in a galaxy are observed and the shift of these lines is measured) so the blue smudge could have easily made the telescope think the redshift was higher than it is. This redshift is therefore almost definitely a mistake. We also know this from the high resolution of the image. You normally wouldn’t be able to see a galaxy with even a redshift of 1 this well!

The reason telescopes have to use photometric redshifts sometimes even though they are often wrong is that there is not enough time to take a spectrum of every galaxy when you are conducting a large survey of the sky. Telescope time is expensive and photometric measurements allow you to get a bit of information about lots of galaxies which can sometimes be more useful that getting a lot of information about a few.

When running into problems like this it was really useful to be able to look at a picture of the galaxy on the Galaxy Zoo: Bar Lengths website. Looking at the galaxies and seeing in real life what the data on the graphs was telling me was probably my favourite part of my time at the Zooniverse. It’s so amazing that thanks to the Sloan Digital Sky Survey, the Hubble Space Telescope projects and other mass surveys of the universe, we can actually look at pictures of thousands of galaxies easily.

A cool barred galaxy you can see in Bar Lengths

A cool barred galaxy you can see in Bar Lengths

The Zooniverse is such a cool organisation and I’m lucky to have worked for them this summer. The great thing about them is that you can get involved too! I know from my work with Bar Lengths that even if a few people log on and classify in any of the projects, it can be really helpful. None of the science can be done without you providing the data.

Measure some galaxies here:

www.zooniverse.org/projects/vrooje/galaxy-zoo-bar-lengths/classify/

Or have a look at some of the other projects here:

www.zooniverse.org

Freya

New images for Galaxy Zoo! Part 2 – Illustris

We’re extremely excited to announce the launch of two new image sets today on Galaxy Zoo. Working with some new scientific collaborators over the past few months, we’ve been able to access data from two new sources. This blogpost will go into more details on where the images come from, what you might expect to see, and what scientific questions your classifications will help us answer. (See Part 1 of this post to learn about the other new images from the DECaLS survey).

The second set of new data comes from the Illustris Project. Illustris is a state-of-the-art simulation of the Universe, led by a large team of researchers in the US, UK, and Germany. Large-scale cosmological simulations are a critical tool in astronomy; since we don’t have laboratories where we can replicate the conditions of processes like galaxy formation, we use computer simulations to investigate them instead. Such simulations start with what we believe conditions in the very early Universe were like (which we infer from the cosmic microwave background), and can include both dark matter and baryons (particles like protons and neutrons that eventually form the stars, dust and gas in galaxies). The simulation then tracks what happens to the matter and energy over billions of years as the Universe expands, evolving according to the laws of physics that are programmed into the simulation. This includes relations like the law of gravity, which dominates how dark matter moves, and hydrodynamics, which describe the motions of the gas. It’s truly amazing – scientists can watch galaxies form and evolve over huge scales of distance and time, and compare the results to real observations to test if the physics of the simulations are correct. Illustris is one of the largest and most detailed simulations ever run, taking more than 19 million CPU hours to run on powerful supercomputers.

A large-scale projection through the Illustris volume at redshift z=0, centered on a massive cluster. The left side of the image shows the density of dark matter, while the right side shows the density of the gas in cosmic baryons.

A large-scale projection through the Illustris volume at redshift z=0, centered on a massive cluster. The left side of the image shows the density of dark matter, while the right side shows the density of the gas in cosmic baryons. Image and text courtesy of the Illustris project.

This comparison to real data is the key feature that sparked the collaboration between Illustris and Galaxy Zoo. Once the simulation is run, astronomers analyze the results to see if their galaxies match the properties of those seen in the real Universe. This includes measurements like the total number of stars formed, the ratio of stars to dark matter, and the distribution of galaxies of different masses and luminosities. Another critical parameter we want to compare is galaxy morphology; measuring the ratio of ellipticals to spirals, for example, is an important test of whether the galaxy merger rate is correct, and if the simulation codes for star formation and gravitational interaction are correct.

The Illustris scientists have created images of the galaxies from their simulation that GZ volunteers will classify by their morphology. Our comparison data set for this will be the SDSS results from Galaxy Zoo 2, and the images are designed to match the Sloan images as closely as possible. This includes the same set of filters for the telescope, sizing the images so that the galaxies look like they’re at cosmic distance from the Milky Way, and setting them against backgrounds of stars and other galaxies. The quality of the simulations and images are amazing – these look to me like real galaxies in every way. It’s something that astronomers definitely couldn’t do ten years ago.

Two galaxies from the Illustris simulation evolving in time from left to right, from when the universe was a quarter its current age, to the present. The top galaxy shows a massive, red, elliptical-shaped galaxy forming after a series of mergers with other systems. The bottom galaxy reveals the formation of a smaller, bluer, disk-shaped galaxy forming after a less violent history of interactions. Images and text courtesy of the Illustris project.

Two galaxies from the Illustris simulation evolving in time from left to right, from when the universe was a quarter its current age, to the present. The top galaxy shows a massive, red, elliptical-shaped galaxy forming after a series of mergers with other systems. The bottom galaxy reveals the formation of a smaller, bluer, disk-shaped galaxy forming after a less violent history of interactions. Images and text courtesy of the Illustris project.

Although these images aren’t of “real” galaxies, we want to emphasize again how much your classifications will help scientists to do astronomical research. Simulations like Illustris are the only way that we can probe galaxy formation and evolution as it happens. Your classifications, both from Galaxy Zoo 2 and from the new Illustris data, provide vital tests for the output and will be fed back to the science teams in order to improve future versions of these sims.

If you have questions or want to discuss anything you see in the new images, please join the discussion with scientists and volunteers on Talk. The Illustris Project also has some amazing online tools if you want to learn more, including an interactive explorer of the simulation and videos of the evolving Universe. You also can explore specific galaxies you’ve classified via GZ:Examine. As always, thanks to everyone for your help!

New images for Galaxy Zoo! Part 1 – DECaLS

We’re extremely excited to announce the launch of two new image sets today on Galaxy Zoo. Working with some new scientific collaborators over the past few months, we’ve been able to access data from two new sources. This blogpost will go into more details on where the images come from, what you might expect to see, and what scientific questions your classifications will help us answer. Part 2 of this post will discuss the other set of new images from the Illustris simulation.

The Dark Energy Camera Legacy Survey (DECaLS) is a public optical imaging project that follows up on the enormous, groundbreaking work done by the various versions of the SDSS surveys over the past decade. The aim of DECaLS is to use larger telescopes to get deeper images with significantly better data quality than SDSS, although over a somewhat smaller area. The science goals include studies of how both baryons (stars, gas, dust) and dark matter are distributed in galaxies, and particularly in measuring how those ratios change as a galaxy evolves. By adding morphology from Galaxy Zoo, our joint science teams will explore topics including disk structure in lower mass galaxies, better constraints on the rate at which galaxies merge, and gather more data on how the morphology relates to galaxy color and environment.

DECaLS observations use the Blanco telescope, which is located at CTIO in northern Chile at an altitude of 2200m (7200 ft). The telescope has a 4-m aperture mirror, giving it more than three times the collecting area of the SDSS telescope. The camera used for the survey is named DECam, a large-area and extremely sensitive instrument developed for a separate program called the Dark Energy Survey. The camera has 570 megapixels and covers a 2.2 degree field of view – more than 20 times the apparent size of the full moon! The combination of the exquisite dark-sky observing site, a sensitive wide-field camera, and larger telescope all combine to generate the new images, which will eventually include more than 140 million unique sources on the sky when DECaLS is finished.

The Victor M. Blanco 4m telescope, located at CTIO in northern Chile. Image courtesy NOAO.

The Victor M. Blanco 4m telescope, located at CTIO in northern Chile, is carrying out the observations for the DECaLS survey. Image courtesy NOAO.

The DECaLS images in Galaxy Zoo are a smaller group taken from a catalog called the NASA-Sloan Atlas. We’re focusing on somewhat larger and brighter galaxies from the catalog. The reason is that although many of these galaxies have been classified in GZ already via their Sloan images, we’re particularly interested in measuring details like tidal tails from mergers, seeing fainter spiral structures, and separating galaxies that couldn’t be individually resolved in the Sloan data. Here’s a great example of a single galaxy in both SDSS and DECaLS – check out how much clearer the spiral arms are in the new images!

Left: an SDSS image of the galaxy J225336.34+000347.4. Right: a DECaLS image of the same galaxy.

Left: an SDSS image of the galaxy J225336.34+000347.4. Right: a DECaLS image of the same galaxy.

Almost all of the morphology and classification tasks are the same as they were for the Sloan images, so it should be familiar to most of our users. If you have questions or want to discuss anything you see in the new images, please join the discussion with scientists and volunteers on Talk. As always, thanks for your help!

Summer Research With Galaxy Zoo

The below blog post was written by Alex Todd, an Ogden Summer Intern who spent the summer working on Galaxy Zoo related research projects at the University of Portsmouth. Alex is now off to his next adventure – starting his undergraduate degree in Natural Sciences at the University of Bath.


Alex hard at work on his Galaxy Zoo project.

Alex hard at work on his Galaxy Zoo project.

 

I have been working with the Galaxy Zoo team at the Institute of Cosmology and Gravitation, in Portsmouth, for 8 weeks this summer. I have been analysing the results of Galaxy Zoo 2, and more specifically the region of the sky known as Stripe 82. In this area, the Sloan Digital Sky Survey (SDSS) took many images of the same patch of sky, instead of only one. These images were combined to produce a single, higher quality image, which showed fainter details and objects. Both these deeper images and the standard depth images of stripe 82 were put into galaxy zoo, and I have been comparing the resulting classifications. I learned to code in python, a programming language, and used it to produce graphs from the data I downloaded from the Galaxy Zoo website. I started by comparing the results directly, comparing the number of people who said that the galaxy had features in each of the image depths.

Screen Shot 2015-09-14 at 11.13.09

On the graph, each blue dot is a galaxy (there are around 4,000) and the red dashed line shows the overall trend. As you can see from the graph, when the proportion of people who see features is low, there is a good match between the two image depths. However, when the proportion is high, there is a much bigger difference between the two image depths, with the proportion being higher in the deep image. This is because fainter features are visible in the deeper image.

I then plotted graphs of the difference between the proportions (P(Features)) against the brightness of the galaxy. To measure the brightness, I used the apparent magnitude, a measure of how bright the galaxy appears to us (as opposed to how bright it actually is).

Screen Shot 2015-09-15 at 13.41.56

The graph below shows the difference in P(Features) plotted against the apparent magnitude. The blue line is at y=0, and the green line represents the average value of the difference between P(Features). As you can see, there is not much difference between the values of P(Features) when the galaxy is particularly bright (Small apparent magnitude) or when it is particularly dim (large apparent magnitude). However, when the galaxy has an average brightness, the difference is quite substantial. We think this is because in bright galaxies, features can be seen in both images, whilst in dim galaxies they can be seen in neither. In medium brightness galaxies, however, they can only be seen in the deeper image. The fact that there are differences between the classifications means that it would be a good idea to classify deeper images of the rest of the sky, to hopefully improve the accuracy of the classifications.

I have greatly enjoyed my time working on at the ICG on galaxy zoo, and would certainly seize the opportunity to pursue it further.


 

It’s been a pleasure working with Alex this summer. He really impressed me with the speed at which he picked up programming languages. This information about the differences in perception of morphological features between deeper and shallower images is very useful to us as a science team as we plan for future generations of the Galaxy Zoo project with new, more sensitive images from current and ongoing astronomical surveys.

Eight years and 8 billion years of cosmic history

Next up in our series of eight blog posts celebrating eight years of Galaxy Zoo is this post from Tom Melvin, who was the lead author of the the first publication from Galaxy Zoo: Hubble, which looked at how the fraction of barred disk galaxies has evolved over the last eight billion years. Tom is also the first person to write a PhD thesis substantially based on Galaxy Zoo classifications, which he is in the process of completing final corrections for.

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Barred disc galaxies at high redshift identified by Galaxy Zoo Hubble. The redshift (‘z’) and the fraction of volunteers identifying a bar (‘Pbar’) are noted in each image.

This was the first time the Galaxy Zoo volunteers had been asked to classify galaxies taken by the Hubble Space Telescope, which provided beautiful images of galaxies whose light has taken up to eight billion light years to reach us!

With your classifications, we were able to select a sample of disk and barred disk galaxies, as shown above in Figure 1, and explore how the fraction of disk galaxies that are barred has evolved over the last eight billion years. We found that this bar fraction has been increasing as the Universe has grown older, doubling from 11% eight billion years ago to 22% four billion years ago, which is shown below in Figure 2. We also know from Galaxy Zoo 2 that this continues to increase, with around one third of disks having a bar in our local Universe. We were able to expand on this by showing that it was the most massive disk galaxies that were the driver of this evolution.

strong_bar_fraction_mod

Redshift evolution of the fraction of barred disc galaxies. Each point represents the observed bar fraction in a 0.3 Gyr bin, with the number of barred disc galaxies and total number of disc galaxies indicated. The grey shaded region indicates the error on the measurement. We show the mean bar fraction for the whole sample (fbar = 13.3 ± 0.7%) as the horizontal dot-dashed line, as well as a linear relationship between the bar fraction and the lookback time which is shown by the solid line.

As bars tend to only form in disk galaxies that are settled and relaxed, or ‘mature’, our results showing an increasing bar fraction over the last eight billion years tells us that the disk galaxy population has matured as the Universe has aged. As this evolution is being driven by the most massive disk galaxies, we were able to conclude that the most massive disk galaxies become mature sooner than their lower mass counterparts.

In addition to these results, we were able to identify a population of ‘red spiral’ galaxies thanks to your classifications. These red spirals’ would typically be omitted from other disk samples, as they would be classified as elliptical galaxies – but as you can see below, these are clearly beautiful red spiral galaxies! What is interesting about this population of disks is that their bar fraction of 45% is much higher than the bar fraction of the whole disk sample, which is roughly 14%.

galaxies2

Images showing 3 unbarred (images a − c) and 3 barred (images d − f) “red spiral” galaxies from Galaxy Zoo Hubble.

So, thanks to your help classifying the amazing images from the Hubble Space Telescope, we were able to track the evolving bar fraction of disk galaxies over the last eight billion years. There is plenty more to be done with this sample of galaxies, so keep an eye out for future results looking at how galaxies have evolved over the past eight billion years!

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