Another Galactic Twin
It seems that finding our Milky Way’s twin has become a bit of an industry these days.
NASA/ESA have got in on the act today, releasing a press release about their favourite twin of the Milky Way, NGC 1073 and the below absolutely gorgeous Hubble Space Telescope image they’ve taken of it: Classic Portrait of a Barred Spiral.
Hubble image of NGC 1073: another possible Milky Way twin. Credit: NASA/ESA
And it does look a lot like what we think the Milky Way looks like – except perhaps for having slightly less tightly wound arms.
An artists impression of our Galaxy. Credit: NASA/JPL-Caltech/Robert Hurt (SSC-Caltech)
You might remember, back in September I posted a guest blog by Portsmouth A-level student, Tim Buckman, who spent his summer with us at Portsmouth finding the Galaxy Zoo galaxy we thought was most like the Milky Way: “A Summer Spent Finding our Galactic Twin “. His project in turn was inspired in part by an ESO press release about spiral galaxy NGC 6744 which was claimed to be a twin for the Milky Way (A Postcard from Extragalactic Space).
NGC 6744 – the previously proposed clone. Credit: ESO.
NGC 6744 is quite a lot more massive than our Milky Way however, so I thought we could do better with SDSS and Galaxy Zoo. Tim applied some mass cuts, then used your classifications to find a face-on 4 armed spiral which he thought matched the maps of the Milky Way (which has a bar, but perhaps a rather weak one which might not be obvious in the types of images we used for Galaxy Zoo).
Tim’s Milky Way clone based on your Galaxy Zoo classifications
I was interested to notice last month that one of the most popular press releases from the AAS this year was about finding a sample of galaxies like our Milky Way and using them to estimate what the colour of the Milky Way would be (BBC Article: Milky Way’s True Colours; AAS abstract it’s based on: What is the Color of the Milky Way?), especially interesting to me as it turns out the Milky Way might be on it’s way to being a red spiral (as has been suggested before, e.g. by Mutch, Croton, Poole (2011), or see New Scientist article about this paper: Milky Way Faces Midlife Crisis), which you might remember I’ve done a bit of work on! 😉
Today’s NASA/ESA release has already been picked up by the BBC: Hubble Snaps Stunning Barred Spiral Galaxy Image (they’d already used “Striking View of Milky Way Twin” on NGC 6744), and Space.com covers it as Hubble Telescope Spies Milky Way Galaxy Twin.
For Galaxy Zoo people, it should be of interest that the press release also says:
Some astronomers have suggested that the formation of a central bar-like structure might signal a spiral galaxy’s passage from intense star-formation into adulthood, as the bars turn up more often in galaxies full of older, red stars than younger, blue stars.
Well those astronomers are us – Galaxy Zoo results on bars, based on your classifications have shown that bars are more common in redder discs. Thanks again for the classifications which allowed us to do that work.
Meeting the Astronomy World
This guest post is from Anna Han, an undergrad working on the Hubble data from Galaxy Zoo:
I attended the AAS Conference in Austin, Texas with the Yale Astronomy and Physics Department to present the results from my research last summer. Many thanks to everyone in the department and Galaxy Zoo who gave me this opportunity and continue to support me through my work. It is because of their guidance that I was able to present a research poster at the conference this winter and enjoy a whole new experience.
The AAS Conference was fascinating, motivating, and overwhelming all at the same time. Starting from 9:00am every morning, I listened to various compact 10-minute talks given by various PhD candidates, post-docs, and researchers from around the world. Though I must admit some of the ideas presented went over my head, I learned more and more with each talk I heard.
The midday lunch breaks made up one of my favorite parts of the conference. Yes, the ribs in Texas are good. But no amount of delicious southern cuisine compares to how welcome and at ease I felt with fellow astronomers kind enough to invite me, a newbie sophomore undergraduate, to lunch. Lunch became my 2-hour my opportunity to talk one-on-one with other researchers and get informed on their work. When my questions ran out, I gladly took the chance to introduce my own research and use their feedback to better prepare for my poster presentation.
On Thursday morning, I tacked up my poster in the exhibit hall and stood guard, armed with organized details of my research and cookies as bait. Let me confess now that I have never been at or in a science fair, but I imagine it must be similar to what I experienced that day. Non-scientist citizens and experts in AGN alike perused my poster and asked questions. Every once in a while I recognized a familiar face: members from my research group, students I had befriended throughout the conference, and fellow researchers I had shared lunch with stopped by to see my poster. Explaining my research to someone who was interested (either in my work or the cookies) was an immensely rewarding experience. I felt proud of what I had accomplished and so thankful to the people who helped me do it. The encounters with other people also gave me ideas for future directions I could proceed in.
This semester, I plan to continue searching for multiple AGN signatures in grism spectra of clumpy galaxies. My experience at the AAS Conference has inspired me to develop a more systematic search for clumpy galaxies using Galaxy Zoo and explore in more detail the possibility of low redshift galaxies containing multiple AGN. To the citizens of Galaxy Zoo, thank you again, and I hope for your continued support!
The infrared properties of mergers
Another update from Alfredo Carpineti:
Following the previous post, we continue the analysis of galaxy mergers in the infrared.
We want to understand where our galaxies stand with respect to other mergers and other infrared luminous galaxies. Using infrared radiation we can extrapolate the number of stars produced by a galaxy every year, namely the star formation rate(SFR). This number is really important since the star content of a galaxy modifies both its colours and its intrinsic properties. The average star formation rate is around 15 solar masses per year, which is high, considered that the SFR for a common galaxy is of 1-2 solar masses per year.
Let’s compare now the SFR with the mass. We can use two parameters to define the mass of a merger: the total mass and the mass ratio. The total mass is the sum of the masses of the two galaxies while the mass ratio is the ratio between the two masses. If a merger had a mass ratio between 1:1 and 1:3 is called a major merger, otherwise it’s a minor merger.
From the plot you can see that we don’t find any correlation between SFR and mass ratio, while we see a clear trend with the total mass.
Another interesting parameter is the environment density. Density variations give way to difference in the tidal forces, approaching velocities and concentration of intergalactic gas and dust. These could lead to a dependence of the SFR on the environment. When we looked for it we found no such thing. The star formation rate seems independent of environment.
Galaxy overlaps at the AAS
Wednesday’s session at the Austin meeting of the American Astronomical Society will include new results from the Galaxy Zoo sample of overlapping galaxies. Extending the work in Anna Manning’s Master’s thesis, this marks an extension that helps us look ahead to comparison with the higher-redshift Hubble Zoo overlaps. Specifically, we compared visible-light data with ultraviolet data (from the GALEX satellite or a UV/optical monitor instrument on the European Space Agency’s XMM-Newton) to compare the amounts of optical and ultraviolet absorption in galaxies. This tells us, for example, how much we should correct Hubble measurements for high-redshift galaxies, where visible-light filters sample light which was emitted in the ultraviplet, to compare them with the rich SDSS data which see the visible range emitted by nearby galaxies. This is a key tool in trying to use backlit galaxies to search for changes in the dust content of galaxies over cosmic time, by comparing Hubble and Sloan results. Along the way, we see evidence that a common result – the flat so-called Calzetti extinction law in star-forming galaxies – results from the way dust clumps into regions of larger and smaller extinction that we usually see blurred together, since we see this in regions so far out in some galaxies that internal illumination by the galaxy’s own stars doesn’t matter. Here’s the poster presentation:
(That had to be shrunk to fit the blog size limits but should still be just legible – click for a bigger PNG). NGC 2207 is outside the SDSS footprint but had such good data that gave nice error bars that it wound up featuring a whole image series. Now to go back and apply that new set of analysis routines to more GZ pairs…
In other news, a Canadian astronomer working with NED found a new use for the overlap catalog including the “reject” list – to distinguish galaxies in pairs which are seen moving together or apart, since we often have both redshifts and from the dust we know which one is in front.
And to reiterate what it says at the end of the abstract – we thank all the Zooites who have contributed to the overlap sample and made this work possible!
X-ray observations of IC 2497 in the can!
As we tweeted about and as Chris noted in his blog post about the Zooniverse success at the American Astronomical Society meeting in Austin TX, half of the Chandra X-ray observations of IC 2497 (the galaxy next to Hanny’s Voorwerp) have been executed and so with bated breath we awaited the results.
From previous X-ray observations with Suzaku and XMM, we know that the quasar that lit up Hanny’s Voorwerp is dead, and that there’s just a weak source in the center of IC 2497 where the black hole lives and some evidence for hot gas. So we had turned to Chandra to figure out what was going on in the center of IC 2497. To puzzle apart the faint black hole at the center and the gas around, and Chandra has the sharpest X-ray eyes in the sky.
We got the notification from the Chandra X-ray Center that the observations had concluded and that we could have a preview of the raw frame. Bill and Chris happened to be near, so after Chris finished his talk on the latest Planethunters.org results (two new planets!), we got together in (possibly) the exact same spot where Chris and Bill viewed the first spectrum of the Voowerp at another AAS meeting in Austin four years ago.
Chris (left), Kevin (right)
From left to right: Bill, Kevin, Chris, all looking at the data.
So, without much further ado, here’s what we got:
Well that’s a bit underwhelming!
Or not!
First, we know that we have a bright source, so we can study the X-ray data in detail. Also, this is just a JPEG screenshot, so we can’t even zoom in and change the scaling to see if there’s anything else there. We don’t even know which way is North, so we don’t know where the Voorwerp is. So for now, all we can do is wait for the actual raw data to be available. This should take a few days. Stay tuned….!
Seeing mergers in a different light
Hello,
My name is Alfredo and I’m a Ph.D. student at Imperial College London. I’ve been asked to write a blog about how we take an idea and turn it into a paper, showing exactly what the man behind the scene does.
I’m working with galaxy mergers so the field from which we are going to pluck our idea has to be that one. Merger properties have been described extremely well by the Galaxy Zoo team, which used the Sloan Digital Sky Survey optical data so we thought it might be interesting looking at the GZ merger catalogue in different wavelengths, specifically in the infrared.
You can study pretty much every object in the infrared because what we call heat is simply the emission of infrared light. If you can measure it’s temperature then it radiates in the infrared. In astronomy infrared radiation allow us to see objects that are not too bright in the visible spectrum (cold stars, gas clouds), to probe regions that are obscure in the optical and to explore the early Universe. Our project will use the infrared fluxes to extrapolate interesting characteristics, mostly to do with the star formation process of the galaxies.
In the past, a huge number of papers have shown that galaxies which were very bright in the infrared ( called LIRGs – Luminous infrared galaxies, U(ltra)LIRGs and H(yper)LIRGs) were mostly mergers or post-mergers. We are going in the opposite direction: since we have a strong visually selected merger catalogue, thanks to your hard work, we can now see what’s the real connection between mergers and warm galaxies.
Galaxy Zoo on the "Curious" Podcast
Just wanted to put up a quick post to point out that the latest podcast from the people who run Ask an Astronomer @ Cornell discusses citizen science, and I’m interviewed on it about Galaxy Zoo stuff.
Link to the podcasts in iTunes.
Merry Christmas! Karen.
Galaxy Crash Debris: Post-merger Spherodials paper now out!
The specific subset we chose are the likely predecessors of elliptical galaxies, and we compared them to the general merger and an elliptical control sample to see how the properties of galaxies evolve along the merger. The SPMs are part of a sample classified by Galaxy Zoo as post-mergers. We looked at this sample again and we picked the ones which look mostly bulge dominated, a key feature of galaxies that are likely to be precursors of elliptical galaxies. You can see in the figure below how, even though these galaxies are similar in morphology to elliptical galaxies, they appear to be in the process of relaxing into relaxed ellipticals.
Post-starburst galaxies paper accepted!
Great news everybody!
The post-starburst galaxies paper has now been accepted by MNRAS. You can find the full paper for download on astro-ph.
Galaxy Zoo 
