Hubble science results on Voorwerpjes – episode 1
After two rounds of comments and questions from the journal referee, the first paper discussing the detailed results of the Hubble observations of the giant ionized clouds we’ve come to call Voorwerpjes has been accepted for publication in the Astronomical Journal. (In the meantime, and freely accessible, the final accepted version is available at http://arxiv.org/abs/1408.5159 ) We pretty much always complain about the refereeing process, but this time the referee did prod us into putting a couple of broad statements on much more quantitively supported bases. Trying to be complete on the properties of the host galaxies of these nuclei and on the origin of the ionized gas, the paper runs to about 35 pages, so I’ll just hit some main points here.
Montage of Hubble images of Voorwerpjes
These are all in interacting galaxies, including merger remnants. This holds as well for possibly all the “parent” sample including AGN which are clearly powerful enough to light up the surrounding gas. Signs include tidal tails of star as well as gas, and dust lanes which are chaotic and twisted. These twists can be modeled one the assumption that they started in the orbital plane of a former (now assimilated) companion galaxy, which gives merger ages around 1.5 billion years for the two galaxies where there are large enough dust lanes to use this approach. In 6 of 8 galaxies we studied, the central bulge is dominant – one is an S0 with large bulge, and only one is a mostly normal barred spiral (with a tidal tail).<?p>
Numerical model of precessing disk of gas from a disrupted companion of NGC 5972
Incorporating spectroscopic information on both internal Doppler shifts and chemical makeup of the gas we can start to distinguish smaller areas affected by outflow from the active nuclei and the larger surrounding regions where the gas is in orderly orbits around the galaxies (as in tidal tails). We have especially powerful synergy by adding complete velocity maps made by Alexei Moiseev using the 6-meter Russian telescope (BTA). In undisturbed tidal tails, the abundances of heavy elements are typically half or less of what we see in the Sun, while in material transported outward from the nuclei, these fractions may be above what the solar reference level. There is a broad match between disturbed motions indicating outward flows and heavy-element fractions. (By “transported” above, I meant “blasted outwards at hundreds of kilometers per second”). Seeing only a minor role for these outflows puts our sample in contrast to the extended gas around some quasars with strong radio sources, which is dominated by gas blasted out at thousands of kilometers per second. We’re seeing either a different process or a different stage in its development (one which we pretty much didn’t know about before following up this set of Galaxy Zoo finds.) We looked for evidence of recent star formation in these galaxies, using both the emission-line data to look for H-alpha emission from such regions and seeking bright star clusters. Unlike Hanny’s Voorwerp, we see only the most marginal evidence that these galaxies in general trigger starbirth with their outflows. Sometimes the Universe plays tricks. One detail we learned from our new spectra and the mid-infared data from NASA’s WISE survey satellite is that giant Voorwerpje UGC 7342 has been photobombed. A galaxy that originally looked as if it night be an interacting companion is in fact a background starburst galaxy, whose infrared emission was blended with that from the AGN in longer-wavelength IR data. So that means the “real” second galaxy has already merged, and the AGN luminosity has dropped more than we first thought. (The background galaxy has in the meantime also been observed by SDSS, and can be found in DR12).
BTA Doppler maps of Voorwerpjes
Now we’re on to polishing the next paper analyzing this rich data set, moving on to what some colleagues find more interesting – what the gas properties are telling us about the last 100,000 years of history of these nuclei, and how their radiation correlates (or indeed anti-correlates) with material being blasted outward into the galaxy from the nucleus. Once again, stay tuned!
Radio Galaxy Zoo searches for Hybrid Morphology Radio galaxies (HyMoRS): #hybrid
First science paper on hybrid morphology radio galaxies found through Radio Galaxy Zoo project has now been submitted!
In the paper we have revised the definition of the hybrid morphology radio galaxy (HyMoRS or hybrids) class. In general, HyMoRS show different Fanaroff-Riley radio morphology on either side of the active nucleus, that is FRI type on one side and FRII on the other side of their infrared host galaxy. But we found that this wasn’t very precise, and set up a clear definition of these sources, which is:
”To minimise the misclassification of HyMoRS, we attempt to tighten the original morphological classification of radio galaxies in the scope of detailed observational and analytical/numerical studies undertaken in the past 30 years. We consider a radio source to be a HyMoRS only if
(i) it has a well-defined hotspot on one side and a clear FR I type jet on the other, though we note the hotspots may `flicker’, that is their brightness may be rapidly variable (Saxton et al. 2002), and, in the case the radio source has a very prominent core or is highly asymmetric,
(ii) its core prominence does not suggest strong relativistic beaming nor its asymmetric radio structure can be explained by differential light travel time effects. ”
Based on this we revised hybrids reported in scientific literature and found 18 objects that satisfy our criteria. With Radio Galaxy Zoo during the first year of its operation, through our fantastic RadioTalk, you guys now nearly doubled this number finding another 14 hybrids, which we now confirm! Two examples from the paper are below:
We also looked at the mid-infrared colours of hybrids’ hosts. As explained by Ivy in our last RGZ blog post (https://blog.galaxyzoo.org/2015/03/02/first-radio-galaxy-zoo-paper-has-been-submitted/), the mid-infrared colour space is defined by the WISE filter bands: W1, W2 and W3, corresponding to 3.4, 4.6 and 12 microns, respectively.
The results are below:
For those of you interested in seeing the full paper, we will post a link to freely accessible copy once the paper is accepted by the journal and is in press! 🙂
Fantastic job everyone!
Anna & the RGZ science team
First Radio Galaxy Zoo paper has been submitted!
The project description and early science paper (results from Year 1) for the Radio Galaxy Zoo project has been submitted!
We find that the RGZ citizen scientists are as effective as the science experts at identifying the radio sources and their host galaxies.
Based upon our results from 1 year of operation, we find the RGZ host galaxies reside in 3 primary loci of mid-infrared colour space. The mid-infrared colour space is defined by the WISE filter bands: W1, W2 and W3, corresponding to 3.4, 4.6 and 12 microns; respectively.
Approximately 10% of the RGZ sample reside in the mid-IR colour space dominated by elliptical galaxies, which have older stellar populations and are less dusty, hence resulting in bluer (W2-W3) colours. The 2nd locus (where ~15% of RGZ sources are found) lies in the colour space known as the `AGN wedge’, typically associated with X-ray-bright QSOs and Seyferts. And lastly, the largest concentration of RGZ host galaxies (~30%) can be found in the 3rd locus usually associated with luminous infrared galaxies (LIRGs). It should be noted that only a small fraction of LIRGs are associated with late-stage mergers. The remainder of the RGZ host population are distributed along the loci of both star-forming and active galaxies, indicative of radio emission from star-forming galaxies and/or dusty elliptical (non-star-forming) galaxies. See the figure below for a plot of these results.
Caption to figure: WISE colour-colour diagram, showing sources from the WISE all-sky catalog (colourmap), 33,127 sources from the 75% RGZ catalog (black contours), and powerful radio galaxies (green points) from (Gürkan et al. 2014). The wedge used to identify IR colours of X-ray-bright AGN from Lacy et al. (2004) & Mateos et al. (2012) is overplotted (red dashes). Only 10% of the WISE all-sky sources have colours in the X-ray bright AGN wedge; this is contrasted with 40% of RGZ and 49% of the Gürkan et al. (2014) radio galaxies. The remaining RGZ sources have WISE colours consistent with distinct populations of elliptical galaxies and LIRGs, with smaller numbers of spiral galaxies and starbursts.
In addition, we will also be submitting our paper on Hybrid Morphology Radio Sources (HyMoRS) in the next few days so stay tuned!
As always, thank you all very much for all your help and support and keep up the awesome work!
Cheers,
Julie, Ivy & the RGZ science team
Zooniverse at Mauna Kea, Day 6: This is the End
Part 1, Part 2, Part 3, Part 4, Part 5
I’m not sure if we’ve been especially unlucky or if this is the norm for observing trips, but we once again the weather is curtailing our telescope time. After a few hours of normal observing, clouds started to blow across the top of Mauna Kea, and now it’s raining outside the dome.
The Dip in the humidity (2nd from the top) represents when we were able to observe.
In the meantime, Becky and I shot a short video tour of the dome a couple days ago you can check out:
Tomorrow, we check out of Hale Pohaku and head down to Hilo for a night. Then I’m off to Chicago and Becky and Sandor are back to Oxford. Even with the bad weather, sleep deprivation, and static electricity, this trip has been a really great experience for me. I now know infinitely more about radio astronomy than I did before! I hope the people doing the real work were able to get all the data they needed.
A Few Notes:
This sums up the general mood
Zooniverse at Mauna Kea, Day 5: The Wind Strikes Back
Part 1, Part 2, Part 3, Part 4
After few good days of observations the wind has returned to ruin our fun. The CSO telescope is supposed to be closed when the wind is above 35mph. Curiously the telescope itself doesn’t have its own anemometer, so we have to rely on readings from the other telescopes on the mountain to decide if it is safe to open the telescope building.
Feeling this entire situation was quite unsatisfactory, I decided to build my own anemometer using a clipboard with a ruler and Becky’s boot, giving you the answer to Chris’s question from earlier tonight:
Shout out to Mrs Beck’s AP Physics for me understanding this
Using the above chart we tried to workout the wind speed. We had to do a bit of fudging. We decided the boot was a perfect cylinder (drag coefficient 0.82), and that it weighed about 300g. We also decided not to take into account lower air pressure. Finally when Sandor and I calculated it independently, we got wildly different results, so it was a futile exercise in the end. (Also CSO buy an anemometer)
Sandor doing the hard work!
Since then, we’ve been playing chicken with the wind. Sometimes having to close the dome. Sometimes thinking we can be open, only to have the telescope struggle to stay on target. Sometimes we hear Meg Schwamb‘s wind tracker say “Warning High Winds”. The conditions made us miss out on a second night of observing Comet Lovejoy, and everyone seemed pretty down for most of the night.
Around 1 or 2am the wind finally let up and we were able to start observing, so the night wasn’t a complete loss. Hopefully the weather tomorrow is better.
A Few Notes:
- It’s really hard to get enough sleep. Sleeping at altitude is hard anyway, and adding in trying to sleep during the day gives us all points for degree of difficulty. Everyone has lovely bags around their eyes.
- This is the last day Chris is with us. We’ll be all alone tomorrow night.
- Sandor is succumbing to the static curse now too.
- @GeertHub on Twitter wanted to me to post a screen shot of the telescope software:
- All the Sex & Drugs & Rock & Roll is helping us touch the sky.
Zooniverse at Mauna Kea, Day 4: Stand Back!
Tonight we took a brief break from observing galaxies to train the Caltech Submillimeter Observatory on comet Lovejoy. I was able to help out with the observation in a real life version of:
![Wait, forgot to escape a space. Wheeeeee[taptaptap]eeeeee](https://i0.wp.com/imgs.xkcd.com/comics/regular_expressions.png)
(turns out they have swinging ropes in the control room, who knew?). Sandor and Becky did the actual observing work. Sandor running the telescope, and Becky doing the data reduction to produce a nice graph Chris tweeted:
In the last post, I talked about how the telescope deals with the background noise from the Earth’s atmosphere by ‘chopping’ or alternating reading from its target and a point slightly off the target, then combining the readings to produce a measurement of the target with atmospheric interference removed. This works well for the distant galaxies we are observing, but not with the comet. Chris realized that the comet was too close and large (in a relative sense) for chopping to work. The telescope would take its noise reading while still pointing at the comet.
Instead, we used another, albeit less effective, technique for handling noise. We tuned the telescope to the frequency we were looking for (Carbon Monoxide) took a measurement, and then tuned it to another frequency to measure the background noise. Subtracting the noise measurement from the measurement of our target frequency gives us a clean(-ish) signal.
After that the really exciting bit happened. I got to operate the telescope as we recalibrated it and got ready to point it at our first galaxy of the night. It was pretty easy, telescope operating. Even someone with a BS in Film, like me, can do it. The procedure for moving on our first source was to first pick a bright known object, aim the telescope at it, and have the telescope calibrate its positioning by taking five measurements around the source to figure out the source’s true location.
Once the positioning was calibrated, I ordered the telescope to ‘slew’ (using that new vocabulary) to the galaxy we’re observing, set the exposure time, and then had it ‘chop’. And then ‘chop’ again. And then ‘chop’ again. And again. And you get the idea. I’ve gotten to use a bunch of different cameras, but this was by far the coolest one I’ve operated.
That full-frame Red One is weaksauce next my 10m dish
A Few Notes:
- We ran into to computer glitch around 5 in the morning yesterday. Simon, the telescope manager, kindly helped us fix it.
- “Watts/Hertz or Watts*m^2/Hertz” I overheard Becky saying, triggering deeply repressed memories of doing unit conversion in High School chemistry.
- Sorry there haven’t been as many pictures recently. Stuff inside the control room doesn’t really seem to change that much from night to night.
- There was concern about our comet observation from a collaborator. It turns out the telescope was trying to compensate for the comet’s motion as though it were a distant galaxy, so the above graph still needs a few adjustments applied to it.
- We had some Comet Lovejoy themed music tonight . We didn’t even look at M83.
Zooniverse at Mauna Kea, Day 3: This line is not hidden in the RMS!
It occurred to me I haven’t talked much about the telescope itself. There haven’t been any pictures of it yet either. We’re at the Caltech Submillimeter Observatory which is basically a giant (10m) dish inside a sweet looking disco ball on top of a dormant volcano. It observes at wavelengths somewhere in between infrared and microwave.
The Dish (Astronomers for Scale)
We spend all of our time at the telescope in the control room with everyone hunched over a computer. I’ve learned a couple of the incantations they use to control the telescope. The first command ‘chop’ is what actually makes it record an observation. I wondered why it wasn’t called ‘listen’ or ‘observe’, but it turns out that ‘chop’ pretty accurately describes the motion of the telescope while it records.
The galaxies we’re observing are very distant and faint, and blend in to the background radiation in our atmosphere. To make up for this, the telescope will take a measurement of the source and then another slightly off the source. The controlling computer uses the second measurement to subtract the background noise from its measurement of the source galaxy.
The other command causes the telescope to move. It’s called ‘slew’. When I asked where that name came from, I was given a shrug by the so-called ‘experts’ in the room. So I turned to Google, and found the dictionary definition is to ‘turn or slide violently or uncontrollably in a particular direction’, which sounds like an accurate description of how the telescope’s movement feels from the control room. It’s also originally a nautical term which also feels appropriate.
Observing is serious business. Watching people observe is not!
A few notes from the second half of last evening and this:
- We had a small earthquake! It was exciting. It was shocking. It was only a 3.3! This is the second earthquake Chris, Sandor, and I have experienced and was Becky’s first. Pretty cool.
- Apparently the observations tonight have provided some confusing results. I tried to get Chris to explain what was odd about them. Mostly due to altitude (partly due to working on this), all I could grasp was that they wanted to compare their observations to a nice looking graph with a clear regression line, and the galaxies they are observing are way off in a corner instead of along the line.*
- Becky has a major problem with static electricity.
- Here are some of the songs we’ve been listening to tonight (presented without judgment).
- You can find more pictures of all the other telescopes at the top of Mauna Kea (post about all of them upcoming!) and other photos of the trip here.
* They misinterpreted the data and everything fits now!
Zooniverse at Mauna Kea Day 2: Take that Meteorologists!
(In which dismayed by forecasts of 100mph winds we go to beach and then end up observing anyway)
A brief update on last night, we were actually able to open the telescope in the wee hours of Thursday morning. Sandor and Becky got as far as pointing the telescope and starting to calibrate it when the wind picked back up and forced us to close.
On the bright-side we enjoyed a beautiful sunrise from the top the mountain.
We awoke late in the afternoon, to emails warning us that “Summit Conditions are Extremely Dangerous” and weather predictions of 100mph winds on the top of the mountain. Thinking it would be a lost night, Becky, Sandor, and I took off for Kona, hoping to checkout the ocean and maybe catch the sunset. Chris stayed behind to answer emails.
Sooo pretty (Photo by Becky)
It was awesome. Definitely a good decision.
Back at Mauna Kea, the predicted extreme winds never materialized, and Chris and Meg Schwamb were able to open the CSO’s doors for a bit of remote observing, while the beach bums rushed back to Hale Pohaku to join. After a brief wind scare, we made the trip up the mountain to observe on site.
Hard at work! (Photo by Ed)
It turns that radio astronomy is pretty similar to computer programming (my normal Zooniverse occupation), in that it mostly seems to involve typing obscure commands into a shell prompt and then waiting for things to happen. Unlike programming, it also involves stomach churning shifts, as the entire building moves to track the source.
During the waiting periods, I’ve tried to learn more about how the telescope works after being mesmerized by Simon’s, the telescope’s manager, technospeak. One part of the telescope he seemed most eager to show us was the heterodyne receiver. After asking the real astronomers what is was, I was very disappointed to learn that it wasn’t a Terminator weapon. Instead, it’s part of the telescope’s processing pipeline that transforms the signal from the telescope to a frequency where detectors are cheap(er). Anyway it’s certainly a cool looking piece of equipment.
It came form the Future to save the Present (Photo by Sandor)
That’s about it for me tonight. We’ll just be up here listening to some sick jams and looking at distant galaxies. Remember you can find a bunch of pictures of trip (not many of people observing yet though) here.
Zooniverse Goes to Mauna Kea, Day 1: High Winds
(…more like Day 1.5. We arrived late last night in Hilo, HI after about 24 hours of traveling for the Oxford contingent and mere 14 hours of travel for myself).
Chris, Becky, Sandor, and I are at Mauna Kea to use the CSO telescope to look for blue elliptical galaxies. Or at least they are. I’m just here with my American driver’s license to be the chauffeur. As the non-astronomer in the group, I think it’d be fun to give an outsider’s perspective into what an observing trip is like.
We’re staying at Hale Pohaku, just downhill from the observatories. It’s name means ‘Stone House’, referring to the original structure built by the CCC during the 1930s. It lets visiting observers acclimatize to the high altitude of Mauna Kea. (As Zooniverse readers may know, altitude sickness is not fun.)
Plotting their course of action
While the weather at Hale Pohaku has been beautiful, it is also amazingly windy. So amazingly windy that we weren’t able to start observing tonight when the sun set. Instead we’re reduced to sitting in the common room refreshing a page of anemometer readings hoping that it will drop down below the maximum 35 mph wind speed we can operate the telescope at.
struggling to open the car door in the wind
We did get to drive up to the summit of Mauna Kea to visit CSO with its manager Simon Redford. Driving the road up the mountain was quite the trip. It’s 5 miles of winding back and forth dirt road that ascends from 9,000ft (2,740m) to 13,000ft (3,960m), but it did give us a spectacular view.
The JCMT which is right next to the CSO
You can find more photos of the trip on our album. We’ll be adding to it throughout out stay. Hopefully tomorrow we’ll have some actual observing news to share.
ATLAS data and Radio Galaxy Zoo: more details
(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 six radio dishes of the ATCA, located outside of Narrabri, NSW, Australia. Image courtesy CSIRO/Ettore Carretti.
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.
A panoramic view of the near-infrared sky shows the distribution of galaxies beyond the Milky Way. SWIRE covers six small fields; two at the bottom right (Chandra-S and ELAIS-S1) are the ones now included in Radio Galaxy Zoo. Image courtesy NASA/T. Jarrett.
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!
Galaxy Zoo 