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.
GZ1 used for the fractions of early-types in clusters
We’re happy to report that we have once again used your (now public) GZ1 classifications to find an interesting result.
We use the classifications in a study we just submitted to MNRAS (or see the arXiv entry for a copy) looking at the observed fractions of early-type galaxies (and spiral galaxies), in groups and clusters of galaxies.
Recent work (De Lucia et al. (2011), which posted to the arxiv in September), used sophisticated semi
analytic models to determine the properties of galaxies found in massive
clusters in the Millennium Simulation. They identified elliptical galaxies
(or more accurately early-type galaxies) in the simulation, and found that the fraction these
galaxies, remained constant with cluster halo mass, over the range 10^14 to
10^14.8 solar masses. They compared their results with previous
observational studies which each contained less than 100 clusters.
With GZ1 we realised we could put together a much larger sample. We
used galaxies with GZ1 classifications, cross matched with cluster and
group catalogues, to compare the above results with almost 10 thousand
clusters. We found that the fraction of early-type galaxies is indeed
constant with cluster mass (see the included figure), and over a much larger range of 10^13 to 10^15
solar masses (with covers small groups of galaxies to rich clusters), than previously studied. We also found the well known result (to astronomers) that outside of groups and clusters, the fraction of early-type galaxies is
lower than inside of groups and clusters.
Plot showing the fraction of early-type galaxies (red lines) as a function of halo mass. We used two different halo mass catalogues, and the agreement between them is excellent. We also examine the fraction of spiral galaxies with halo mass (blue lines)
This work suggests that galaxies change from spiral to early-type when individual
galaxies join together to form small groups of galaxies, but that going from groups to rich clusters does not significantly change the morphologies of galaxies.
Without the GZ1 results at our finger-tips, this work, which was devised,
implemented, and written up in less than 2 months, would have taken much
longer to complete.
Thanks again for making the Zoo such a wealth of information,
Ben Hoyle (on behalf of Karen Masters, Bob Nichol, Steven Bamford, and Raul Jimenez)
First look at Hubble's first look at the first Voorwerpje
The bits are still warm, having just been downlinked from Hubble overnight. There is still a good bit of processing to be done, cleaning up cosmic rays and so forth. But that said, here is our first look at SDSS 2201+11, first of the Galaxy Zoo AGN cloud galaxies (AKA voorwerpjes) to come up on the telescope’s schedule. As a reminder, as waveney just posted in yesterday’s Object of the Day, here it is in the SDSS images:
And now what we’ve all been waiting for! First up, the galaxy in a narrow filter that includes the strong [O III] emission from the clouds at this redshift:
emission”]![Hubble image of SDSS 2201+11 with [O III] emission](https://blog.galaxyzoo.org/wp-content/uploads/2011/11/sdss2201-hsto3.jpg)
And one in a filter including H-alpha emission, which is several times fainter in such highly ionized gas:
SDSS 2201+11 HST image with H-alpha
And finally, in the tradition of vacation photographs everywhere, a shot of just the galaxy (in this case a medium-width filter near the standard i band to show the stars and dust but not the gas):
SDSS 2201+11 Hubble i image
First inspection shows that the galaxy has been disturbed – the dust lanes twist. One of them trails right off into one of the gas clouds, adding to our evidence that ionized tidal debris often shows up in this way. That also suggests which cloud is on the near side, so we have a clue about the time delays experienced by the radiation we see from each one as it has been affected by possible changes in the nucleus. There are interesting holes and curlicues in the gas, as well.
Further processing will show us more. And there are six galaxies to go! (These should dribble in throughout 2012 – we just got an appetizer).
Galaxy Zoo 
