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Our last night at the telescope

The story so far: on the first night we were able to observe until 02:00 before the weather forced us to close. The following three nights we were confined to the Residencia, the place where they keep all the astronomers when they are not observing. Much to our surprise, this morning we awoke to a sky only sparsely covered by clouds, instead of being in the middle of one. Maybe we have a chance of observing something tonight?

== 19:30 ==

As the weather has cleared somewhat on Roque de Los Muchachos, La Palma, we have received permission to go to the telescope tonight. We’ve just arrived and started taking the first couple of calibration images with much enthusiasm. 

A bit about the telescope itself: we’re using a telescope called the Isaac Newton Telescope (INT). It is a Cassegrain reflector telescope with a ~2.5m primary mirror that weighs ~4000kg! 

We’re not great at selfies

It takes a while for the telescope to take all the calibration images (biases, arcs and flats), so we were able to enjoy the sunset right before -hopefully- a very busy night. 

== 22:00 ==

Unfortunately the weather has taken a turn for the worse. We cannot open the dome of the telescope as the humidity is too high. We’ve had our first cups of coffee and are settling in for the night, while keeping an eye on the humidity sensor.

As tonight will be our last night at the telescope and we’ve had bad luck with the weather the last couple of days, we are very hopeful to observe some galaxies tonight. So far we were able to observe only one galaxy before we had to close on the first night. At this point we will be grateful for any data that comes in, even one more galaxy would double our current sample size!

== 00:45 ==

We’re still not able to open, humidity is at 100% and we cannot see any stars. The highlight of the last couple of hours was exploring the library in the INT and listening to an old cassette tape of Joseph and the technicolour dream coat. None of the other tapes work.

== 04:00 ==

We’ve had a popcorn and pizza break, drank multiple cups of coffee and explored most of the telescope building. However, unfortunately we’ve not been able to use the telescope today – the weather gods seem determined to prevent us from getting any data. With any luck we’ll be back next year to try again.

Observing bars in La Palma

As some might remember, in our last paper (which can be found here), we studied differences between weak and strong bars. One of our results was that star forming galaxies with stronger bars have significantly higher star formation in their centres compared to galaxies with weaker bars. This might be due to differences in the gas flows induced by the different types of bars. To investigate this, we selected a sample of 21 galaxies from Galaxy Zoo, which we plan to observe over the next couple days. 

The relationship between galactic bars and star formation has long been up for debate. Galactic bars are vast structures of co-orbiting gas, dust and stars that form directly across the galactic nucleus. It is thought that gas flows along the arms of the bar into the centre, increasing the central gas density. As gas density increases, the star formation rate would also. So, that should be the answer then? However, in reality, it is not so simple.

There are many different kinds of bars, with varying characteristics such as strengths and orientations. A galaxy might contain a very strong bar – where it clearly dominates even over the galactic disk – or it could have a very weak bar – where the disk dominates over it. So, we need to ask ourselves further, is the gas flow and resultant star formation higher in galaxies with strong bars? What about weak bars? Does it even change at all if we compare either type of bar to galaxies which have no bars? 

These are the questions we are going to answer at the Isaac Newton Telescope, or INT, on the island of Santa Cruz de la Palma. With a sample of 21 galaxies characterised by Galaxy Zoo – 7 strongly barred, 7 weakly barred and 7 with no bars at all – we are investigating if any relation between star formation rate and bar strength exists. An example of each type of galaxy in our sample is shown below. On the left is a galaxy with no bar at all, while on the right is a galaxy with a strong bar. The strong bar clearly dominates over the disk of the galaxy. The middle panel shows a galaxy with a much weaker bar, where the disk dominates over the disk galaxy.

To investigate this, we must turn to spectroscopy. Rather than utilise images, such as the ones above, we align a spectroscopic slit along and perpendicular to the bar direction on the image. The spectroscope will split the incoming light into a spectrum of wavelengths, where we will be able to find any spectral signatures of elements within the bars themselves. 

There are two chemical signatures of star formation that we are looking for. The first, an indirect measurement, is looking for Hydrogen Alpha, or Hα. If there is a much higher abundance of Hα at the core of a galaxy with a strong bar, weak bar or not, it is very likely that there is a higher gas density. Ergo, there is a higher star formation. The second signature we are looking for is Oxygen III, or O[III]. O[III] is highly ionised only typically exists in areas where there are high rates of the star formation; the newly born stars being the cause of the ionisation. This would be direct evidence of higher star formation.

So, what do we find? Thus far, due to the adverse weather conditions caused by tropical storm Hermine on La Palma, we have set our spectroscopic observations on a single strongly barred galaxy. We have extracted the spectrum, removed any sources of contamination and reduced to only that of the bar and galactic nucleus. The top image is the spectrum from the slit at ninety degrees perpendicular to the bar direction and the bottom is aligned along it.

The top spectrum (perpendicular to the bar) appears to be almost empty, with only noise present. Along the bar, however, we get a very strong emission line at precisely 6562.801Å. Guess which wavelength Hα happens to rest at? Precisely the same! 

This is certainly a promising initial result. If the abundance of Hα is much higher along bars than not, then this is certainly a case for them enhancing star formation! The next steps are to confirm this finding by taking observations for the rest of our sample. Once the weather clears up on La Palma, we will be aiming to finally answer the question, what do galactic bars do for star formation? Enhance, prevent or nothing? Well, it looks like enhancing has won the first point!

We will keep you updated!

Cheers,
David, Tobias and Chris

In the News – Ringed Galaxies from GZ Mobile

Dear volunteers,

Thanks to you, we’ve found 40,000 new ringed galaxies – about six times more than all the ringed galaxies anyone has ever found before! The Royal Astronomical Society were impressed enough to share the news in a press release here.

Galaxy rings found by GZ Mobile volunteers (that’s you!)

I launched the Rings Challenge here on this blog ten months ago, asking for your help searching for galaxies with rings around them. I wasn’t sure if anyone would be interested in using the new mobile project we made. Ten months later, you’ve made a million swipes on 100,000 galaxies. I’m so grateful.

Rings are rare. To help you find them, I created an automatic assistant. I used the first half of your swipes to teach an artificial intelligence algorithm what rings look like. Then I set the algorithm searching a million DESI galaxies to find more rings. Finally, I took the galaxies the AI thought might have rings and asked you to check them with the second half of your swipes. This two step approach let us both search many galaxies quickly and have human eyes vet all of our discoveries.

This is the first major science result from the new GZ Mobile project. Making an app wasn’t part of the original plan – the first iPhone launched three weeks after GZ, 15 years ago this month – but it’s now a crucial tool for hunting specific galaxies quickly. I hope you’ll join us for the next search.

Cheers,

Mike

P.S

You can find more technical details on the machine learning on my personal blog.

P.P.S

Apologies to ChristineM, who many months ago correctly point out that I should technically call them “ringed” galaxies rather than “ring” galaxies.

Happy Birthday (& a belated announcement)

Firstly, happy 15th birthday to Galaxy Zoo and thank you to all those who have made it a success over the last decade-and-a-half. Whether you’re a regular on Talk, and original classifier, a member of the science team or someone who has been inspired by the project to find out a little more about science, thank you!

BBC News article announcing the launch of the project on 11th June 2007

Looking back at the BBC article that started everything, I notice we ‘hoped’ that 30000 people would take part in our project. We blew past that target early on, and haven’t looked back since. The results of the project have told us much about galaxy history, inspired novel machine learning approaches to science, helped us build the broader Zooniverse and much more. It still stuns me to think that there’s a Hubble Space Telescope program following up on Galaxy Zoo discoveries, and there is still much more science to come. (It’s not ridiculous to think that JWST, the new space telescope which will release its first image tonight, will soon follow up on a Galaxy Zoo discovery, or provide images for a future version of the project). My failure to anticipate this glorious feature came because we simply underestimated the passion, ability and enthusiasm of all of you to help learn a little bit more about the Universe.

I’m also very proud of the PhD students who have worked with the Galaxy Zoo team to make use of our data, and help lead the project. Several generations have now successfully graduated, and there’s much more to come from the current cohort. Since September, the project has been led by the immensely impressive Karen Masters, who has taken over from me as Principal Investigator, with assistance from Brooke Simmons (Deputy PI), Sandor Kruk (Project Scientist), Becky Smethurst (Deputy Project Scientist), and Mike Walmsley (Technical Lead). With them the project is in excellent hands, and I’m looking forward to the next decade-or-so of galaxy science, powered by you, the wonderful denizens of the Zoo.

VV191: from Galaxy Zoo to JWST

Almost 15 years ago, what first attracted me to be involved with Galaxy Zoo was the ability of  participants to pick out rare galaxy types, especially silhouetted or overlapping galaxy systems. These highlight the effects of dust in the foreground galaxy on passing light, and offer ways to study the dust which are complementary to, for example, observations in the deep infrared where the dust itself shines, giving off the energy it absorbs from starlight. Visible-light measurements of backlit galaxies show us the dust no matter how cold it might be, where it can hide from IR detection, and at the high resolution available to optical telescopes (including the Hubble Space Telescope) rather than the more modest, wavelength-limited resolution we can achieve at longer wavelength. Better measurements of dust in galaxies affect our understanding of their energy output, stellar content, and even our view of the more distant Universe. Galaxy Zoo volunteers contributed to a catalog of nearly 2000 suitable galaxy pairs from the first iteration of the project, since expanded from Galaxy Zoo 2, GZ Hubble, and the most recent examinations using the Legacy Survey data. We have used this list for  number of followup studies – although, truth be told, I have also been distracted by other rare systems found by volunteers (cough, Hanny’s Voorwerp and the Voorwerpjes, for example).

The backlit-galaxy system VV191 was first reported in the Galaxy Zoo forum as a possible galaxy merger,  by user Goniners on November 2, 2007. Despite its near-perfect geometry for study of foreground dust, VV191 had eluded  our earlier searches because the inner regions, where one can see that this is a superposition of undisturbed galaxies rather a merging galaxy pair, are saturated in prints of the Palomar Sky Survey, which was the best visible-light survey before the Sloan Digital Sky Survey. At the time VV191 was selected for further study, catalogs showed a substantial redshift difference between the two galaxies, which is desirable so the two galaxies are unlikely to be physically  interacting with each other, and light from the background galaxy scattered by the dust becomes much fainter.  That has been revised by later data which put the redshifts closer; we can’t win them all, though the two galaxies are very symmetric and undisturbed in all our later data.

(Hubble red-light image of VV191, showing silhouetted dust in the foreground spiral arms)

We got a closer look with the STARSMOG project led by colleague Benne Holwerda, which was a Hubble snapshot program – one where short exposures are inserted into gaps in the telescope schedule, much like the Zoo Gems gap-filler project. STARSMOG drew promising overlapping-galaxy pairs from Galaxy Zoo forum posts and the GAMA (Galaxy And Mass Assembly) project. Over several years, it acquired images of 55 galaxy pairs of interest. Among those was VV191, generating a very detailed map of the dust silhouette of the spiral galaxy. This was one of the galaxy pairs analyzed in a project based on the master’s thesis work by Sarah Bradford at the  University of Alabama which went into a poster presentation at the January 2017 meeting of the American Astronomical Society in Texas. In fact, I used a low-contrast version of the VV191 image as the poster background. (The poster should still just be legible in this compressed  PNG version):

The data quality for VV191 stood out, because the background elliptical galaxy has its brightest region right behind the edge of the dust in the spiral. We then had a 2-dimensional map of how much light gets through the dust in the spiral at the wavelengths included in that single observation. The poster was viewed by my longtime collaborator Rogier Windhorst, who is one of the interdisciplinary scientists with the James Webb Space Telescope (JWST) project. In this capacity, he had an allocation of so-called GTO (guaranteed-time) observations, asked what we could do with JWST.  Rogier was struck by these images, and wondered what we could add to the science output with a little bit of JWST  observing time.

This led to a plan of tracking the dust signature from ultraviolet to infrared in a single galaxy with a single technique. First Hubble had to do its part with more data, using not only its high resolution but UV sensitivity. We got Hubble images in filters around 2250 and 3360 Angstroms (0.22 and 0.34 microns) , with the short end limited mostly by the elliptical galaxy being so faint in the deeper UV that we couldn’t detect its light well enough in reasonable exposure times. These data have been processed, so we are ready  for the next step – JWST. Its near-infrared camera (NIRCAM) will observe this system in four filters from 0.9-4.0 microns wavelength (two at a time since the camera can use short- and long-wavelength channels simultaneously). The wavelengths are chosen to trace the way the dust effects fall off toward longer wavelengths, which is affected both by the sizes of the interstellar dust grains and how strongly they are clumped together. One filter matches one of the wavelengths at which small grains (or indeed large molecules, so-called PAH particles) emit, so we might be able to tell how they correlate with the larger particles blocking most of the light.

Because of the enormous sensitivity of JWST and NIRCAM, each filter is exposed for only 15 minutes to get very high measurement accuracy. (The telescope will probably take longer than that to point to VV191, depending on what it’s doing beforehand). Based on when JWST can view this part of the sky, these observations are most likely to be made between December 2022-March 2023, or May-July of 2023 (we should know more in a couple of weeks when the first year’s observation schedule is released). Watch this space…

Zoo Gems – Hubble does Galaxy Zoo(s)

Since mid-2018, the Hubble Space Telescope has taken occasional short-exposure images, filling what would otherwise be gaps in its schedule, of galaxies in the list from “Gems of the Galaxy Zoos” (otherwise known as Zoo Gems). The Zoo Gems project just passed a milestone, with acceptance of a journal paper describing the project, including how votes from Galaxy Zoo and Radio Galaxy Zoo participants were used to select some of the targeted galaxies, and acting as a sort of theatrical “teaser trailer” for the variety of science results coming  from these data. (The preprint of the accepted version is here; once it is in “print”, the Astronomical Journal itself is now open-access as of  last month). The journal reviewer really liked the whole project: “The use of the Galaxy Zoo project’s unique ability to spot outliers in galaxy morphology and use this  input list for a HST gap filler program is a great use of both the citizen science project and the Hubble Space Telescope” and “I think it is a wonderful program with a clever, useful, and engaging use of both SDSS and Hubble.” (We seldom read statements that glowing in journal reviews).

Zoo Gems got its start in late 2017, when the Space Telescope Science Institute (STScI) asked for potential “gap-filler” projects. Even with  what are known as snapshot projects, there remained gaps in Hubble’s schedule long enough to set up and take 10-15 minutes’ worth of high-quality data. We put together a shockingly brief proposal (STScI wanted 2 pages, originally to gauge interest) and were very pleased to find it one of 3 selected (the other two also deal with galaxies. Makes sense to me). We had long thought that the ideal proposal for further observations of some of the rare objects identified in Galaxy Zoo ran along the lines of “Our volunteers have found all these weird galaxies. We need a closer look”. That was essentially what the gap-filler project offered.

We estimated that we could identify 1100 particularly interesting galaxies (where short-exposure Hubble images would teach us something we could foresee) from Galaxy Zoo and Radio Galaxy Zoo.  We were allocated 300 by STScI, so some decisions had to be made. A key feature of our project was the wide range of galaxy science goals it could address, so we wanted to keep a broad mix of object types. Some types were rare and had fewer than 10 examples even from Galaxy Zoo, so we started by keeping those. When there were many to choose from, we did what Galaxy Zoo history (and STScI reviewers) suggested – asked for people to vote on which merging galaxies, overlapping galaxies, and so on should go into the final list. This happened in parallel for Galaxy Zoo and Radio Galaxy Zoo objects (the latter largely managed by the late Jean Tate, not the last time we are sadly missing Jean’s contributions as one of the most assiduous volunteers). Even being on that observing list was no guarantee – gap-filler observations are selected more or less at random, taking whichever one (from whichever project’s list) fits in a gap in time and location in the sky. The STScI pilot project suggested that we could eventually expect close to half to be observed; we are now quite close to that, with 146 observations of 299 (one became unworkable due to a change in how guide stars are selected by Hubble). These include a fascinating range of galaxies. From Galaxy Zoo, the list includes Green Pea starburst galaxies,  blue elliptical and red spiral galaxies, ongoing mergers, backlit spiral galaxies, galaxies with unusual central bars or rings, galaxy mergers with evidence for the spiral disks surviving the merger or reappearing shortly thereafter, and even a few gravitational lenses. From Radio Galaxy Zoo, we selected sets of emission-line galaxies (“RGZ Green”) and possibly spiral host galaxies of double radio sources (SDRAGNs, in the jargon, and so rare that we’ve more than doubled the known set already). Both kinds of RGZ selection  were largely managed by Jean Tate, who we are missing once again. By now, of 300 possible objects,  146 have been successfully observed. One can no longer be observed due to changes in Hubble’s guide-star requirements, and two failed for onboard technical reasons  (it was during one of those, a few months ago, that a computer failure sent the telescope into “safe mode”; I have been assured that it was not our fault).

Hubble images from Zoo Gems program.
Some favorite Zoo Gems images of Galaxy Zoo objects – a merger with surrounding spiral pattern, overlapping galaxy system with backlit dust, wheel-within-a-wheel bar and ring, two mergers, and a 3-armed spiral.

Zoo Gems images show that every blue elliptical galaxy observed shows a tightly wound spiral pattern near the core, so small that it was blurred together in the Sloan Survey images used by Galaxy Zoo, and broadly fitting with the idea that these galaxies result from at least minor mergers bringing gas and dust into a formerly quiet elliptical system.

There is much more to come as harvesting the knowledge from these data continues. Already, a project led by Leonardo Clarke  at the University of Minnesota  used Zoo Gems images to demonstrate that Green Peas are embedded in redder surroundings, possibly the older stars in the galaxies that host these starbursts.  Beyond these, these data can be used to examine the histories of poststarburst galaxies, dynamics and star-formation properties of 3-armed spirals, and nuclear disks and bars – some of these show galaxies-within-galaxies patterns where the central region nearly echoes the structure of the whole galaxy.

While going through some of the Zoo Gems images to see which should go in various montages in this paper, I considered the multilayer overlapping galaxy system including UGC 12281. It didn’t go into the paper, but the visual sense of deep space in this image is so profound that it became the 2nd most-retweeted thing I’ve sent out in more than 10 years.

From a Hubble Zoo Gems image: overlapping layers of galaxies behind the nearby edge-on spiral UGC 12281. Galaxies beyond galaxies, stretching away through space and time.

In presenting these data, we wanted to make the case for the value of wide-ranging, even short, programs such as this. These gap-filler projects are continuing with Hubble, until STScI starts to have trouble filling the gaps and needs to call for more projects. Premature as it seems, I can’t help musing that someone may eventually work out a low-impact way for the James Webb Space Telescope to make brief stopovers as it slews between long-exposure targets – we have suggestions…

Data from the Zoo Gems project (like the other gap-filler programs, Julianne Dalcanton’s program on Arp peculiar galaxies and the one on SWIFT active galaxies led by Aaron Barth) are immediately public, accessible in the  MAST archive under HST program number 15445 (the others are 15444 and 15446). Claude Cornen maintains image galleries for the Zoo Gems, Arp and SWIFT projects in Zoo Gems Talk. Our thanks go to everyone who helped draw attention to these galaxies, or voted in the Zoo Gems object selection.

Announcing: Jan 13 press conference on Galaxy Zoo: Clump Scout results

I’m Nico, a PhD student with the Galaxy Zoo team, and I have an exciting announcement. About a year ago I wrote that classifications on the Galaxy Zoo: Clump Scout project had just finished. Now, with the first results nearing publication, the American Astronomical Society (AAS) has chosen Clump Scout to present its findings at an official press conference on Thursday, January 13 from 4:15-5:15pm Eastern Time (or 9:15-10:15pm GMT for our UK visitors). We’re very excited to finally share these results with our volunteers!

The press conference is free and open to all, so if you took part in the project, we encourage you to tune in to learn more about where your efforts have gone. (Or, if you’ve never heard of the Clump Scout project before, now is a great chance to learn!) I’ll spend a few minutes explaining why we created the project, and describe a few clues we’ve found as to the last 10 billion years of galaxy evolution. There will also be 4 other speakers presenting about their own citizen science work, so it will be a thorough tour of what’s going on in people-powered astronomy today.

We hope you can join us!

How to join:

You watch via YouTube live stream on AAS’s YouTube channel: https://www.youtube.com/c/AASPressOffice

PS. For more galaxies at the AAS (although not Galaxy Zoo directly), also see our PI Karen Masters talking about the completion of the MaNGA Galaxy Survey, Tue 11th Jan in the 2.15pm ET Press Conference. MaNGA the survey Galaxy Zoo: 3D was designed to help analyse; and look out for more crowd-sourcing projects to come from this complex data now it’s all publicly available, as well as much more use of the Galaxy Zoo: 3D classifications.

New Paper – Practical Galaxy Morphology Tools

Last year, we published the GZ DECaLS catalog: detailed morphology classifications for 314,000 galaxies. We classified so many galaxies by training AI models to learn from volunteers and work alongside them. This raises the question – what else can we do with those models?

It turns out that we can use them to make three new practical tools that will help both professional researchers and volunteers. You can read all about them in our new paper out today: https://arxiv.org/abs/2110.12735.

The first practical tool is a similarity search. You can type in the coordinates of a galaxy, and it will try to show you the most similar galaxies. Try it out on your favourite DECaLS galaxy. For now, it’s a simple demo website, but we hope to eventually integrate this into Galaxy Zoo.

The second is a new method for finding the galaxies most interesting to you personally. Imagine a website where you can rate galaxies by how interesting you find them. As you rate galaxies, the website shows you new ones for you based on your previous ratings – just like how Netflix suggests new series (I’m a big Bojack fan myself). The system is too complicated to create a simple demo to show you, but you can see some examples in the new paper. Thanks to funding from the Sloan Foundation, we’re making this even better and adding it as an official Zooniverse feature.

The third is about adapting the AI models to classify new kinds of galaxies. If a researcher wants a model that can find ringed galaxies, for example, they would usually have to start by gathering tens of thousands of examples of ringed galaxies with which to teach their new model. This takes a long time and a lot of effort, especially for rarer galaxies. However, a model already trained on Galaxy Zoo classifications needs just hundreds of example galaxies to learn to find rings as well. This will let researchers “fine-tune” models to help solve their own specific science problems. That includes me! I’m running a Galaxy Zoo Mobile project to make a new ring catalogue with this approach.

All these tools work because of your classifications. As well as using them directly in science catalogues, we need them to train better AI models. Thank you for your contribution.

If you have any spare time – maybe on the bus, or just sitting around scrolling – I would really appreciate your help finding ring galaxies by swiping left and right on Galaxy Zoo Mobile, part of our Zooniverse app (Apple, Android). I’m hoping to build the biggest catalogue of rings ever assembled so we can understand how they form. Please join in if you can.

Cheers,

Mike

P.S. You can find a few more technical details on my personal blog.

New Galaxy Zoo Mobile challenge – Ringed Galaxies

My name is Mike – I’m a researcher helping run the Zooniverse project Galaxy Zoo

I’m launching a new challenge within Galaxy Zoo Mobile, the version of GZ that runs on our mobile app (iOS, Android, scroll down to “Space” projects).

The challenge is to find galaxies with rings. I’ve picked out the 25,000 galaxies where some* volunteers voted for “Ring” on the final GZ question – “Does this galaxy have any rare features?”. Now it’s time to do a targeted search through these promising galaxies. Swipe left and right on GZ Mobile to tell us which ones you think have rings.

This is what galaxies with rings look like. I think these are easily the most beautiful galaxies we’ve ever shown on Galaxy Zoo, with glittering spiral arms and intricate structures. We’ve zoomed in each picture about 25% more than in Galaxy Zoo itself, so you’ll see all that fine detail.

We want to find galaxies with rings because they’re a mystery. Astronomers aren’t sure what causes rings. 

One leading theory is that they form from disk galaxies left undisturbed for hundreds of millions of years. Theoretical calculations and computer simulations suggest that the gravity of stars in the galaxy’s bar or bulge can cause the orbits of nearby stars to change, first making spiral arms and eventually a ring shape. Another theory is that rings are caused by head-on collisions where a small galaxy punches through the middle of a large disk galaxy, like a rock dropped into a pond.

The truth is that there are probably different kinds of ring, formed by different processes. Working out which processes form which rings will require many examples of each – and that’s where you come in. 

This targeted project is all about finding as many rings as possible. Once we know which galaxies have rings, we can follow up with future projects to divide them into different categories, and compare those categories to find out what creates each type of ring. 

As always with Galaxy Zoo, your classifications will be publicly shared with all researchers to help everyone investigate rings. We will also use your classifications to teach a new version of Zoobot, our galaxy-classifying AI, to find rings. Zoobot can then help find more rings in the million-or-so galaxies recently released by the DECaLS survey** that we haven’t yet uploaded to Galaxy Zoo. 

If you have any questions, come chat to our community and myself on the Galaxy Zoo Talk forum

Cheers,

Mike

* Specifically, galaxies where the fraction of volunteers answering “ring” is in the top third (typically about two or more volunteers).

** The published catalog from Galaxy Zoo DECaLS used images from Dark Energy Camera Legacy Survey data release 5 and earlier. The survey has since released more galaxy images, some of which have already been uploaded to Galaxy Zoo.

Stronger bars help shut down star formation

Hi everyone!

I’m Tobias Géron, a PhD student at Oxford. I have been using the classifications of the Galaxy Zoo DECaLS (GZD) project to study differences between weak and strong bars in the context of galaxy evolution. We have made significant amount of progress and I was able to present some results a couple of weeks ago at a (virtual) conference in the form of a poster, which I would love to share with you here as well.

To summarise: I have been using the classifications from GZD to identify many weakly and strongly barred galaxies. Some example galaxies can be found in the first figure on the poster. As the name already implies, strong bars tend to be longer and more obvious than weak bars. But what exactly does this mean for the galaxy in which they appear?

One of the major properties of a galaxies is whether it is still forming stars. Interestingly, in Figure 2 we observe that strong bars appear much more frequently in galaxies that are not forming stars (called “quiescent galaxies”). This is not observed for the weak bars. This suggests one of two things: either the strong bar helps to shut down star formation in galaxies or it is easier to form a strong bar in a quiescent galaxy.

In an attempt to answer this chicken or egg problem, we turn to Figure 3. Here, we show that the rate of star formation in the centre of the galaxy is highest for the strongly barred galaxies that are still star forming. This suggests that those galaxies will empty their gas reservoir quicker, which is needed to make stars, and are on a fast-track to quiescence. 

I’m also incredibly happy to say that we’ve written a paper on this as well, which has recently been accepted for publication! You can currently find it here. Apart from the results described above, we also delve more deeply into whether weak and strong bars are fundamentally different physical phenomena. Feel free to check it out if you’re interested!

It’s amazing too see all this coming to fruition, but it couldn’t have been possible without the amazing efforts of our citizen scientists, so I want to thank every single volunteer for all their time and dedication. We have mentioned this in the paper too, but your efforts are individually acknowledged here. Thank you!

Cheers,

Tobias