Hubble Zoo: Summer Research Starts!
Today’s guest post is from Anna Han:
Hi everyone!
My name is Anna Han, and I’m a sophomore undergrad at Yale studying black holes this summer. I’m currently working with images of galaxies observed by Hubble that you as members helped classify on Galaxy Zoo. So excited to be part of the community, and looking forward to sharing ideas with you all!
Galaxy Zoo Voorwerpjes – now with Hubble data!
Some of us continue to exult over the approval of our Hubble proposal to look at some of the “voorwerpjes” found through the GZ forum. These are clouds of gas ionized by an active galactic nucleus, similar to Hanny’s Voorwerp except for being smaller and dimmer (hence the Dutch diminutive form of the word). This has been a very fruitful project, going back to the first few possibilities posted for discussion in different contexts by Zooites. From these, I realized that such clouds could be spotted based on their unusual colors from the SDSS images, and with contributions from Waveney and laihro setting up the web interface and one of our source lists, the hunt was on! The results staggered us – within 6 weeks each of the 18,000 candidate galaxies had been examined by at least 10 Zooites. Seven of you looked at them all! Then we could examine the highest-scoring galaxies, in three sessions from Kitt Peak and Lick observatories, measuring spectra to see which ones really show gas ionized by an active nucleus. Once again, Drew, alias sdrew123, has done a lot of the data reduction and Python action in this part of the project. Our sample of giant AGN clouds now includes 19, each showing gas more than 10 kiloparsecs (32,000 light-years) from the galaxy core, so we get information on its history over at least that many years.
Why do we want to find these? From what we’ve learned about Hanny’s Voorwerp, we have the possibility of tracing the history of active galactic nuclei – how fast they can fade, how long they stay on at once, and maybe how they influence their surroundings. It’s hard to generalize from a single instance (though astronomers are notorious for trying), so we want enough of a sample for statistically defensible conclusions.
Which of our objects should we ask to look at, balancing the demand for Hubble time against the fact that very often more data are better? From our current point of view, investigating whether active nuclei shut down very often within time spans roughly 100,000 years, we want to concentrate on the ones that show evidence for a deficit of energy from the core compared to that needed to light up the gas we see. This gives us a set of 7 (plus NGC 5252, which has been known for many years and already has archival Hubble images). They are:
SDSS J143029.88+133912.0, the Teacup (Kevin started calling it that in honor of the handle-like loop of gas extending more than 15,000 light-years to the side). This is the most distant galaxy in the sample, at z=0.085.
UGC 7342 (also known in some Zoo threads as the Crab galaxy), with its enormous filaments of gas stretching more than 100,000 light-years on each side (fully half as large as Hanny’s Voorwerp, and at about the same distance).
Another new SDSS AGN, and new Zoo find for its gas clouds, is
SDSS J220141.64+115124.4 (which I tend to abbreviate to SDSS 2201+11 for my own sanity).
SDSS J151004.01+074037.1, with symmetric clouds around a type 2 Seyfert nucleus, is another SDSS//GZ discovery.
NGC 5972 is pretty close to us at z=0.0297. This galaxy attracted some brief notice in a 1995 paper by Mira Veron-Cetty and Phillippe Veron, who established that what look like spiral arms are purely ionized gas features, and noted that this AGN is surrounded by a double radio source.
UGC 11185 is part of a very disturbed interacting pair, with a bright spray of ionized gas seen to the east of the AGN. Note to self: we need to take care in where we center the Hubble images to avoid problems with scattered light from the annoyingly bright star.
Mkn 1498, as the name suggests, has a long-known AGN, but its ionized gas shows such strong radiation
reaching it that this one may have faded even to its observed brightness.
We based our observation request on what we learned from working on the Hanny’s Voorwerp data. The most valuable results for these will probably come from images in Hα and [O III] for these, the clouds sometimes extend into the galaxy, so we need red and green starlight images to distinguish stars and gas. Our filter selection depends on the galaxy redshift – the brand-new Wide-Field Camera 3 (WFC) has cleaner performance but only a limited set of narrow filters, while the decade-old Advanced Camera for Surveys (ACS) has ramp filters which can tune to any desired optical wavelength, but its CCD detectors are really showing the ill effects of damage from years in the space environment. So we use WFC where we can and ACS otherwise, emboldened by the release of Jay Anderson’s software for partially undoing the effects of that radiation damage. We end up using 3 orbits per galaxy – one for each emission line and the other for broad-band filters to map the structure and color of each galaxy’s starlight.
We know some of the things to look for in the data – regions of star formation, gas outflow, maybe shadowing effects from material near the galaxy nuclei. But the best is often in what we don’t know to look for beforehand…
Next up – detailed observation planning, at which point we get our first hints as to when each galaxy could be observed.
AAS 218: Black Hole Growth and Host Galaxy Morphology
Following Karen’s AAS 218 roundup, here is my talk from the Galaxy Zoo special session:
You can get the whole talk as a PDF or as a Quicktime movie.
Galaxy Zoo Lunch at the AAS
Following our session on “Cosmic Evolution from Galaxy Zoo“, a number of the Galaxy Zoo group went to lunch at a local Boston seafood place. Ivy (Wong) took a few photos, which I thought you might like to see.
View down the table at lunch.
From right to left, Lucy, Kevin, Pamela, Carie and Chris.
From right to left, Alice, Brooke and me (busy talking).
By the way, the AAS abstracts are now up on the ADS, so I have put the links up on the previous post.
The Connection between AGN Activity and Bars in Late Type Galaxies AAS
At the center of every massive galaxy lies a supermassive black hole. In a small percentage of galaxies, so called Active Galactic Nuclei or AGN, these black holes are currently accreting gas and dust and shinning luminously as that material looses energy. It is thought that some galaxies have this AGN activity at their center and others do not because of the presence or absence of gas near-enough to the black hole to be accreted. But many questions remain, including how the gas which can live any where in the galaxy, gets down to the very central regions.
One solution to this problem could lie in the bar-like structures seen in many galaxies like this one from the Hubble Space Telescope:
Source: Hubblesite.org
These bar features are easy to form in a big disk galaxy and are likely transitory, first coming together and then dissipating. Most importantly, models suggest that these bars can drive gas inward towards the central regions of galaxies.
Whether or not these galactic-scale structures, which can transport gas towards the central regions of a galaxy, could be related to episode of AGN activity has been debated for decades. One of the simplest ways to approach this issue is to observer whether or not a bar feature in a galaxy is observed to correlate with the presence of accretion at the very center of the galaxy. In other words, if galaxies containing bars are more likely to host AGN, than we can hypothesize that the bar may be responsible for feeding gas to that AGN.
Because the scale of the central supermassive black hole is many orders of magnitude smaller than the regions into which the bar can transport gas, the connection is not as straightforward as the simple story seems to suggestion.
Before Galaxy Zoo, investigations looking into the connection between the presence of an AGN and that of a bar in galaxies suffered from being too small or looking at galaxies with only one particular color. Now With Galaxy Zoo we can search 10,000 galaxies and look at each for the presence of a bar, and use the spectroscopic data from SDSS to identify any AGN activity. We look at the votes from the viewers in galaxy zoo and assign a probability that a bar exists in a single galaxy by comparing the number of people who indicated a presence of a bar to the total number of people who viewed the galaxy. As the image below shows, we can accurately identify barred galaxies by selecting those where at least 50% of the classifiers identified a bar in the galaxy.
We found that both the presence of an AGN and the presence of a bar are tightly correlated with the color of a galaxy and its size. This explains why so many previous samples might have found contradictory results, depending on which types of galaxies in their sample contained AGN activity and which contained bars. However, because the sample of galaxies in Galaxy Zoo is so large, we can look at samples of galaxies with similar sizes and colors. And when we control for the effects of size and color, there is no longer a large correlation between the presence of a bar and central AGN activity.
This means that although the bar is responsible for driving gas inward in the galaxy, it doesn’t get it close-enough to the center to incite black hole accretion (or AGN activity). This result can have far reaching implications for models of galaxy evolution, which need to explain how galaxies (and their central black holes) grow. Unfortunately it rules out one popular idea: bars are not a key source of inciting black hole growth in galaxies.
Post starburst galaxies at the AAS.
At our AAS session, Ivy Wong (formerly of Yale, now back in her native Australia) talked about her work on post starburst galaxies. Post starburst galaxies are extremely rare, and in her paper (which is in the referee process at Monthly Notices), Ivy compares a sample of about 80 local post starburst galaxies to the parent sample they were drawn from which is made up of almost 50,000 of the galaxies you classifed in Galaxy Zoo 1.
The conclusion – post starburst galaxies are dominated by objects who have intermediate morphology (often half of you thought they were disks and half thought they were ellipticals – telling us that they are just hard to classify!). They are found in the low mass part of the “green valley” (ie. they are redder than most blue spirals, but bluer than most red ellipticals) and Ivy suggests this shows they are probably on the way to turning into the low mass end of the red sequence.
Ivy has provided the slides of her talk: Wong_AAS218talk.pdf.
Spheroidal Post Merger Systems at the AAS
I think Chris said it best – any session which is ended by a guy in a bowtie went well. And for our AAS Galaxy Zoo session, that guy in a bowtie was Alfredo Carpineti from UCL, who talked about his work on the properties of spheroidal post-merger systems selected with the help of the Galaxy Zoo merger classifications, and using a control sample of non-merging spheroidals (or ellipticals) also selected from Galaxy Zoo.
Alfredo provided me with the below description, and his slides are available to download at Carpineti_AAS218talk.pdf.
In this talk we discuss the properties subset of galaxies from the GZ mergers catalogue that are spheroidal ‘post-mergers’, where a single remnant is in the final stages of relaxation after the collision and shows evidence for a dominant bulge, making them plausible progenitors of early-type galaxies.
Our Galaxy Zoo Session at the Boston AAS
As many of you may know, several Galaxy Zoo scientists were at the recent meeting of the American Astronomical Society meeting in Boston, USA. This included Chris, Kevin, myself, Carie Cardamone and Brooke Simmons; Lucy Fortson (who recently did her first blog post about a review article we wrote), Alfredo Carpinati (from UCL) and Ivy Wong (who recently moved from Yale back to her native Australia).
Galaxy Zoo volunteer and forum moderator, Alice was also there – and has written about some of it on the forum (under “why I’m going to be a bit quiet for 3 weeks“). Kevin has written some of his AAS highlights for the Planethunters blog.
But nothing has been written yet about our wonderful session on the science from Galaxy Zoo (except from the @galaxyzoo Tweets during the session), so I thought I’d take a bit of time to tell you about it.
It’s been a busy few weeks for me in the lead up to and following the session last Wednesday, so I hope you’ll forgive me for not doing this sooner.
Anyway, below is the title and description we came up with for the session when we proposed it to the AAS. You’ll this session was specifically aimed at highlighting the science results coming out of Galaxy Zoo.
Cosmic Evolution from Galaxy Zoo
Galaxy Zoo (www.galaxyzoo.org) is familiar to many as a hugely successful public engagement project. Hundreds of thousands of members of the public have contributed to Galaxy Zoo which collects visual classifications of galaxies in Sloan Digital Sky Survey images (and most recently Hubble Space Telescope) using an internet tool. Classifications from phase one of Galaxy Zoo (the basic morphology of SDSS galaxies) have recently been made public.
Galaxy Zoo has also shown itself, in a series of peer reviewed papers, to be a fantastic database for the study of galaxy evolution. In this session Galaxy Zoo team members will hi-light some of the most recent scientific results using Galaxy Zoo data, including the first results from phase two of the project (which collected more detailed morphologies).
We were given a 90 minute session during the meeting to do this in, and decided to have 6 speakers in this time. After some deliberation (and constraints based on who could come), we decided on the below speaker list, with Chris agreeing to act as session Chair (so he introduced the session, each of the speakers, and made sure we kept to time!).
- Barred Spirals on the Red Sequence – an important evolutionary stepping stone? – KLM (that’s me of course; ADS abstract)
- Bar Lengths in Nearby Disk Galaxies. – Ben Hoyle
- The Connection between AGN Activity and Bars in Late Type Galaxies – Carie Cardamone (ADS abstract)
- Black Hole Growth and Host Galaxy Morphology: Two Different Evolutionary Pathways – Kevin Schawinski (ADS abstract)
- Building the low-mass end of the red sequence with local post-starburst galaxies- Ivy Wong (ADS abstract)
- Properties of spheroidal post-mergers in the local Universe – Alfredo Carpineti (ADS abstract)
AAS abstract get posted on ADS, so when the links appear I’ll add them above (KLM June 6th: edited above to correct typos, and swapped talk titles).
We were in the “American Ballroom Central” at the conference venue, which was an absolutely massive room. After some technical difficulties with the microphone (very professionally dealt with by Chris), he introduced the session with his normal humour, saying something like “This is a session about the science from Galaxy Zoo. If you’re looking for something on exoplanets you can go to every other session here” (that’s my paraphrasing, with apologies to Chris if it’s not quite right!).
Then I started with a general overview of Galaxy Zoo, and Galaxy Zoo 2, going on to talk about our paper published earlier this year in which we showed bars were more likely to be found in redder disk galaxies (see the “bar” category on the blog). I talked a little bit about the implications this might have for galaxy evolution (“Do Bars Kill Galaxies” again), particularly in light of some results from an HST survey (arxiv link) which suggest that my favourite red spirals might not just be a rare curiousity, but actually be a phase that most galaxies might pass (briefly) through as they turn from blue star forming spirals into red passive ellipticals.
Unfortunately in the end Ben was unable to make it o Boston from Barcelona where he now works as a postdoc, but I was able to include a couple of slides about his main results from the bar drawing project showing that the bars in redder disk galaxies are longer, and that there is a difference in the colour of galaxies with a given length bar depending on if rings or spirals are present.
Then I showed some as yet unpublished results which Ramin Skibba has been working on which show that barred disk galaxies are more clustered than disk galaxies in general – this implies that bars are more likely to form in higher density regions (or in the types of galaxies found in those regions) which is quite interesting. You can expect to be hearing more about that in the next few months as we work on writing it up. Finally I talked about my plans to use the ALFALFA survey going on at Arecibo to make a census of the gas content of barred disk galaxies (the “fuel for future starformation”). There are some exciting early results in that comparison which I hope to be able to tell you about soon.
I have posted the pdf of my slides here.
I’m going to stop here for now, and plan to tell you more about the rest of the talks in session later.
Karen.
PS. Sorry about the “Zooiniverse” misspelling on the last slide. That’s a tough word to spell in a hurry!
Chandra X-ray Survey of Mergers Completed
Our Chandra programme to survey a sample of local merging galaxies found by you all to search for double black holes has just been completed. We’ve received the data for the final target. Now the data analysis can begin!
Talking about Galaxy Zoo on the Jodcast
I talk about Galaxy Zoo (specifically the red spirals and the results we had on bars in spirals) in the May 2011 Extra Edition of the Jodcast. I start talking about Galaxy Zoo about 6 minutes in. I linked just my interview below.
Hope you enjoy it, Karen.
Galaxy Zoo 