(This post was co-written with Minnie Mao, an RGZ science team member and postdoc at the National Radio Astronomy Observatory in New Mexico.)
Thanks again for starting your work on the new images from the ATLAS survey! We wanted to talk more about how/why these images differ from the existing FIRST images, including details on the telescopes, survey data, and our science goals.
1. What kind of telescopes are used to take the new images?
The radio data in the new images is from the Australia Telescope Compact Array (ATCA), which is located in rural Australia outside the town of Narrabri. The ATCA has 6 separate radio dishes, each 22 meters in diameter. The Very Large Array (VLA), which took the FIRST images, has 27 dishes which are each 25 meters apiece; this means that ATCA has about 1/5th the collecting area of the VLA, and is less sensitive overall. The ATCA can still detect very faint radio objects, but they typically have to take longer exposures (integrate) than the VLA does.
The size of the arrays for the two telescopes is also different. The ATCA has a maximum baseline of 6km, which means that at 20cm (the wavelength used in RGZ images) you have a resolution of ~9 arcsec. This sets the smallest size of structures seen in the radio contours. The VLA has a longer maximum baseline of 36km, which means at 20cm you have a resolution of ~1.2arcsec. The configuration used for the FIRST images in RGZ has a resolution of about 5 arcsec, which is about twice as small as that in the new ATLAS data.
Finally, one of the biggest differences between the two telescopes comes from the arrangement of the dishes, not just their maximum size. The VLA is in a Y-shape which means imaging can be done in relatively short exposures, called ‘snapshots’. The ATCA is in a linear configuration running from east to west. Imaging with the ATCA requires observations over a large range of times so that observations are taken at a variety of earth rotation positions (filling the uv-plane). A full synthesis image with the ATCA requires 12 hours of observing.
The infrared data comes from the SWIRE survey carried out with the Spitzer Space Telescope. Spitzer is an infrared observatory launched by NASA in 2003 and is still operating today. One big difference between Spitzer and WISE is their relative sensitivities and field of view; Spitzer has a bigger mirror than WISE, but a much smaller field of view. Spitzer was designed mostly to study individual objects in detail and at very high sensitivity. WISE, on the other hand, was a survey telescope designed to sweep across the entire sky several times and detect all the infrared objects it could. So instead of mapping the whole sky, Spitzer carried out smaller observations of specific fields.
Spitzer had cameras that could image at a wide range of infrared wavelengths; the new images use Spitzer’s lowest-wavelength filter (3.6 microns) on the IRAC camera. This is almost exactly the same wavelength used for the WISE images (3.4 microns), so these are directly comparable. These near-infrared wavelengths are sensitive to emission from older/cooler stars, warm dust, and light from accretion disks that may surround black holes within galaxies.
2. Where in the sky were these new images taken?
The new images come from two fields in the Southern Hemisphere, called the Chandra Deep Field South (CDF-S) and the European Large Area ISO Survey South-1 (ELAIS-S1). If you know your constellations, these lie near Fornax and Phoenix, respectively.
These fields were chosen specifically so there weren’t bright radio sources in/near the fields. Moreover, these fields have tonnes of ancillary data! The CDF-S is one of the most intensely observed fields in the sky, with deep data from world-class telescopes from radio to gamma-ray! The CDFS (proper) is actually a MUCH smaller region than the ATLAS project observed… but the generally larger field-of-view from the radio telescope enabled a decent chunk of sky to be observed. This is critical to avoid problems such as cosmic variance.
Deep fields like CDF-S and ELAIS-S1 enable statistical properties of galaxies to be determined over cosmic time, and of course understanding how galaxies have formed and evolved is probably the most important extragalactic astronomy question :) These sorts of wide + deep observations also are great for discovering the ‘unknown’… :)
3. Why do these images look different than the ones already in RGZ?
This one is fun!! Mostly due to the VLA’s Y-shaped configuration, image artefacts tend to be hexagonally shaped (like a six-sided snowflake). Conversely, ATCA artefacts tend to look like radial spokes.
The ATLAS images also have ~10 arcsec resolution whereas the FIRST images have 5 arcsec resolution so the FIRST images might appear more ‘detailed’.
Both the ATLAS and SWIRE data are much more sensitive than the FIRST/WISE data because the telescopes integrated on this small part of the sky for much longer.
4. Why does the RGZ science team want to cover these fields?<
One reason is that ATLAS is what's called a "pathfinder" mission for an upcoming survey called EMU. EMU will use another telescope in Australia, named ASKAP, to do a deep survey over the entire sky. This is the best of both worlds, combining the sensitivity of ATLAS with the sky coverage of FIRST, and will provide ~70 million radio sources! A pathfinder mission like ATLAS is a smaller version which tests things like hardware, data reduction, and feasibility of larger surveys. We plan on asking citizen scientists to help with the EMU data as well, and so starting on the ATLAS images is a critical first step.
Since the area covered in these images is also much, much smaller than the FIRST survey, it was possible for small groups of astronomers to visually go through and cross-match the radio and IR emissions. Those results were published several years ago (led by RGZ science team member Ray Norris). Getting your results for the same set will help us to calibrate the new data from FIRST, which has many more galaxies and for which we don’t have the same information yet. We also want to see what new objects are left to be discovered in ATLAS (giant radio galaxies, HyMORS, WATs, etc.) that astronomers may have missed!
Huzzah! We have now broken through the 1 million mark with Radio Galaxy Zoo as of January 16, 2015. It has taken all of you ~13 months to do 40 years worth of cross-identifications. Well done and a huge thank you to every single one of you out there who helped us along.
A big shout-out to the winners of our 1 millionth classification milestone competition. The winners are: @planetari7, @ChrisMolloy, @leonie van vliet, @antikodon, @BOSSARD louis michel and @JF45456. I will be e-mailing each of you soon.
My biggest thank you to every single Radio Galaxy Zooite who helped us get this far. We really could not have done this without you.
Ivy, Julie & the entire RGZ team
Seasons Greetings for the end of 2014, and many thanks for all the classifications you provided for us at Galaxy Zoo this year!
Hurray! Radio Galaxy Zoo has reached its first anniversary!
What a wonderful year it has been! In 1 year, we have completed ~30% of the project and have reached nearly 1 million classifications! In celebration of our anniversary, we are announcing that we will offer some special prizes to the first few citizen scientist(s) who take us to the 1 millionth classification and beyond! The top prizes we have to offer include a signed copy of “Bang! — the complete history of the Universe” signed by Brian May & Chris Lintott, a black ICRAR T-shirt (in your size), a CSIRO water bottle, CSIRO mugs, 3D telescope bookmarks and some Zooniverse stickers.
Using the current number of classifications of 931,029 and assuming that each classification took 5 minutes, this translates to a continuous working time of nearly 9 years! If we assume that one can only classify continuously over a standard 40-hour work-week, it’d take more than 37 years to complete what you all have so kindly done in 1 year!
In addition to matching the radio jets with their black holes, we (the citizen scientists & the science team) are making new discoveries of extreme types of radio galaxies. Just a few days after launch last year, @Dolorous_Edd and @antikodon discovered a very large nearby wide-angle tailed radio galaxy. They are currently working with Prof Rudnick and Prof Andernach on publishing their findings and analysis. Large teams of RGZ citizen scientists are also helping Dr Kapinska and Dr Mao with their search for Hybrids and S-DRAGNs, respectively!
Thank you all so very much for your support! We are most grateful for such a humbling effort by everyone. We hope that all of you have a wonderful holiday period and wishing you all a great upcoming year!
Best wishes, Ivy & Julie
(@ivywong & @42jkb)
You might be wondering what I’m doing on the Galaxy Zoo blog (normally you find me at Planet Four and Planet Hunters). Instead of studying planets and minor planets, a few weeks ago I was helping observe blue elliptical galaxies with some of Chris research group (his graduate students Becky and Sandor with help from Chris) using the Caltech Submillimeter Observatory (CSO). Chris wrote back in July about remote observing on CSO for a project looking at blue elliptical galaxies. Those nights in July were bonus nights. They got traded to us because the group observing needed better weather, and they kindly gave us the nights when the forecast was predicted to be not good enough for their main project in case we could do something useful with the time. We had just submitted the observing proposal to ask to use the CSO a few weeks before that. Those nights were good training for all of since we had never used the CSO before (and that was my first foray into submillimeter observing). In the fall, we learned that our proposal was accepted. We got awarded one night in November and 6 nights sometime in the the first part of 2015. We should know the exact dates when the observing calendar comes out in December.
The CSO is a single dish 10-m telescope located on Mauna Kea. The cool thing is that you can log in and drive the instruments and the telescopes remotely. On the night of November 18th in Hawaii (November 19 in the UK and Taiwan), I was logged in from Taipei, and Chris student’s Becky and Sandor were logged in from Oxford very very early in the morning commanding the telescope and instruments. This was Becky’s second run with the CSO, she co-observed during the July run. This was Sandor’s first time with the CSO and submilimeter observing.
We had really great weather and conditions. The opacity through the atmosphere in the submilimeter was stable and really low. You can see from the screen grab I took below
We were a bit too busy to blog during the night, but I thought I’d share some of the screen shots and photos we took that night including some of the computer interfaces we use to control the CSO and know the status of the telescope – Below is one of the orrery – it tells us where our target and other standard stars, Solar System planets, and other standard calibrators are in the sky. This is very handy when you’re looking for a pointing carbon star to go to tune and check the telescope pointing or if you want to double check a planet is observable for pointing and calibration. Below the orrery is the waveform for the secondary mirror telling us that it is indeed oscillating back and forth ,which is what we required for our observations.
This is the status window for the spectrographs. There are two that receive light at the same time. The bottom one covers a wider wavelength than the top one, but the wavelengths we’re interested in are captured on both.
We use carbon stars with strong CO emission features to tune the pointing of the telescope. You cans see the strong CO(2-1) line in the middle as the sharp peak.
Here’s a picture of Becky hard at work working checking that our calibration observation was centered at the right wavelength we were supposed to observing at.
A paper that uses Galaxy Zoo: Hubble to study whether supermassive black holes are fueled by galaxy bars beyond the local universe has recently been accepted! The paper will be published in MNRAS, but for a short summary, here is the original blog post.
First off, the science team for Radio Galaxy Zoo wants to thank our volunteers for their continued clicks, discussion on Talk, and continued participation in the project. As of today, we have 892,582 classifications on RGZ and over 45,000 subjects completed from the FIRST-SDSS sample. We absolutely could not do this without you, and we’re working hard on turning the data into interesting science.
We want to let you know of some particular galaxies that will be appearing slightly more often in the interface. One of the things I’ve been working on for Radio Galaxy Zoo over the last month is finding better and smarter ways of combining clicks from independent classifiers into the “final answer” for each galaxy. For past Zooniverse projects, we’ve been able to do this using relatively simple methods – users are weighted a little bit by their consistency with other volunteers, but the final data product is mostly just the vote fractions for various tasks. However, the task in RGZ is a bit more complex, and the simpler methods of combining classifications are proving very difficult. In order to accurately combine the information each volunteer gives us, we need to establish a bit more common ground than we currently have.
To calibrate the clicks across all citizen scientists, we need to look at galaxies that the same people have done. The science team has started this by labeling the correct morphologies (to the best of our abilities) for a smaller, “gold standard” sample. We use these as seed weights in our data reduction – that lets us calibrate users who have done the gold standard galaxies. These results are propagated outward to the full sample by looking at other galaxies done by both calibrated and uncalibrated users, and so on. Kind of like pulling ourselves up by the bootstraps. :)
What we’re missing right now, though, are galaxies that lots of citizen scientists have jointly classified. Since each galaxy is retired after 20 people classify it, the chances of seeing a particular galaxy is pretty low. Some members of the science team, including myself, recently sat down with a sample of 100 galaxies taken from a combination of random selection and ones you’ve identified on Talk as having interesting or non-trivial morphologies (bent jets, triple systems, giants, no IR counterparts, etc). These is what we’d like to use for calibration. However, only about a dozen users so far have done enough of this sample to give us enough data for calibration.
So, in order to help the accuracy of the data pipeline, we’ve chosen 20 “gold standard” galaxies that will eventually be shown to all volunteers. They won’t all be in one bunch (you should see one every five subjects or so) and you shouldn’t see any galaxies that you’ve classified before. We’ll label the galaxies on Talk – look for the hashtag #goldstandard. I hope that another positive outcome will be users getting to discuss interesting features in galaxies that they haven’t come across before. After you’ve done all 20 galaxies in the sample, your future classifications will be randomly selected as usual.
Please let us know on Talk if you have any questions about this, and I’ll be happy to discuss it further. Thanks again for all of your help – we hope this will let us produce a more accurate RGZ product and science papers in the coming year!
Meet Minnie Mao, leading the study of spiral double radio lobe AGNs (or S-DRAGNs) for Radio Galaxy Zoo.
Hello! My name is Minnie and I am a VLA postdoc at NRAO in Socorro, NM. Astronomers use a lot of acronyms, and often are not very creative with telescope names/ VLA stands for ‘Very Large Array’, which is where some of the Radio Galaxy Zoo radio images come from!
I did my PhD at the University of Tasmania with Ray Norris (yup, THE Ray Norris), Jim Lovell, and Rob Sharp. We used optical data cross-matched with radio data from the ATCA (Australia Telescope Compact Array, where the rest of the RGZ radio images come from) to determine how galaxies have changed across cosmic time. A large chunk of the PhD was spent staring at images of radio galaxies, classifying their morphology, and determining their counterparts in optical/infrared images. While this can be a lot of fun, the Universe is rather large so I am glad I can now share this job with the wonderful zoo-ites!
One of my primary reasons for being involved in RGZ is because I am excited for the day when radio images become as familiar to people as optical images. To this end I hope you enjoy RGZ, because really, what is more fun than peering far back into the nether-reaches of the Universe?
Galaxy Zoo: Are Bars Responsible for the Feeding of Supermasssive Black Holes Beyond the Local Universe?
Supermassive black holes are thought to reside in the centers of most galaxies. These massive objects can produce powerful jets of energy that may significantly influence the evolution of their host galaxies. While we believe that black holes have an important role in galaxy evolution, a crucial unknown aspect about black holes is how they are fueled and turn into active galactic nuclei (AGN).
Among the proposed black hole fueling processes, bar-driven secular evolution is among the most popular. Bars are linear structures of stars that stretch across the centers of galaxies. They are theorized to fuel black holes by driving gas from the outskirts of galaxies into the very centers, where supermassive black holes lie.
Previous studies have tested whether bars can fuel black holes by examining whether there is an excess of bars among AGN hosts compared to non-AGN hosts. For the most part, those works found that there was not a significant enhancement of bars among AGN hosts, leading them to conclude that bars do not fuel black holes. But almost all these previous works were limited to the local universe, i.e., in the present, where the number of AGN is the lowest across cosmic time.
In this work, we investigate whether there is an excess of bars among AGN hosts beyond the local universe, i.e., in the distant past, up to 7 billion years ago. In this epoch, the number of AGN hosts is much higher, giving us a better glimpse of the identity of the black hole fueling mechanism. To conduct this experiment, we created two samples: 1) a sample of AGN hosts and 2) a carefully constructed control sample of non-AGN hosts that are matched to the AGN hosts. In order to create the largest samples possible, our experiment utilized three of the most popular extragalactic surveys: AEGIS, COSMOS, and GOODS-S. With these samples, we used the Galaxy Zoo: Hubble bar classifications to identify barred galaxies. Below is a gallery of 6 sets of AGN and their corresponding control galaxies, 2 sets from each survey.
Our main results are shown in the figure below. We have two probes of bar presence—bar fraction (left) and bar likelihood (right)—for the AEGIS, COSMOS, and GOODS-S surveys.
We find no statistically significant enhancement in the bar fraction or the bar likelihood in AGN hosts (green squares) compared to the non-AGN hosts (purple triangles). Our results, combined with previous works at the local universe, indicate that bars are not the primary fueling mechanism for supermassive black hole growth for the last 7 billion years. Moreover, given the growth of supermassive black holes over cosmic time, our results imply that bars are not directly responsible for the buildup of at least half the local supermassive black hole mass density.
Therefore, although among the most popular fueling mechanisms, it seems that bars do not fuel black holes. However, this result does narrow the search for the real black hole fueling mechanism.
One of our scientists Prof. Ray Norris put the call out to the Radio Galaxy Zoo community for a hunt on spiral galaxies hosting powerful radio sources. The first known galaxy of this type is 0313-192, a galaxy much like our Milky Way and has left astronomers baffled.
Figure 1: 0313-192 The wrong galaxy from the Astronomy Picture of the Day. Credit: W. Keel (U. Alabama), M. Ledlow (Gemini Obs), F. Owen (NRAO, AUI, NSF, NASA.
Here is Prof. Norris’ post:
Keep an eye out for any hourglass sources that seem to be hosted by galaxies that look spiral in the infrared. These objects are incredibly rare in the local Universe (only 2 or 3 known) and we may not see any in Radio Galaxy Zoo, but if someone does find one, that would be worth writing a paper about (with the discoverer as co-author, of course). The rarity of radio-loud spirals is thought to be because the radio jets heat up and disrupt the gas in the spiral, switching off star formation, and turning the galaxy into a “red dead” elliptical. But we might find one or two where the jets have only just switched on and haven’t yet destroyed the spiral. See The radio core of the Ultraluminous Infrared Galaxy F00183-7111: watching the birth of a quasar for another example of this process in its very early stage. So keep your eyes peeled and yell out (very loudly) if you find one!
We are pleased to announce that the Radio Galaxy Zoo community has identified over a dozen potential candidates and we are in the process of following these up.
Have you seen any? Head over to Radio Galaxy Zoo to join in on the hunt and let us know what you find.