Back at IRAM 30m…
Hi all. I’m at the IRAM 30m telescope for the third time this year this time measuring the CO content in elliptical galaxies. This follows on from Kevin’s long-standing work of using blue elliptical galaxies to test whether or not AGN (Active Galactic Nuclei) are responsible for dispelling gas and thus putting an end to star formation. Theoretical models suggest that this must be the case and this ongoing project to measure exactly how much CO gas is in such galaxies is aiming to verify this. This is accomplished by measuring how much CO is in elliptical galaxies that show no signs of AGN activity and similar galaxies which do have signs of AGN activity. The theory is that, those galaxies with AGN activity will show low quantities of gas relative to their size.
The weather has been very good so far and we are on schedule here to get measurements for all 30 galaxies we asked for despite only being allocated about 3/4 the requested time! With so many measurements, we should hopefully get the statistical significance we need to confirm the theory.
Galaxy Zoo Paper on Dust in Spirals Submitted.
Before Kevin starts sending me friendly emails that I haven’t blogged about this yet, I want to announce the submission of the latest Galaxy Zoo paper (submitted to Monthly Notices on August 17th):
I’m delighted that I finally got this work submitted. Now I feel like I can properly call myself part of the Galaxy Zoo team. My first entry on the blog Blue Sky and Red Spirals was about this work, and you can also check out the scientific poster I made about it. I hinted several times over the past 8 months that we were very close to submission, so it’s great to be able to say it’s actually now in the referee process. I actually think this is one of the quickest papers I’ve ever written – only 10 months from when I started working on it, to submission of the paper. Fingers crossed for an equally smooth referee process.
Our main conclusions ended up being:
- Spiral galaxies are reddened as they become more inclined due to the presence of dust (this effect is explained in great detail in Blue Sky and Red Spirals)
- Spiral galaxies with large bulges are much redder than spiral galaxies with no/small bulges. This effect is larger than the dust reddening – face-on spirals with large bulges are redder than edge-on spirals with no bulge (on average).
- There is more dust reddening in spiral galaxies with small bulges than in those with large bulges.
- There is a peak in the dust content of spirals at moderate luminosities. Very luminous and very dim spirals both have less dust reddening. Very dim spirals are physically smaller, and make less dust than brighter ones. Very bright spirals usually don’t have a lot of recent star formation, and as dust is destroyed over time we may just be seeing that effect.
We compared the observed trends to a model published in 2004 (Tuffs etal. 2004: Attenuation of Stellar Light in Spiral Galaxies for the very keen!) and concluded that it works pretty well (especially considering how much you have to simplify a spiral galaxy to be able to model it), but there are some problems at the shortest wavelengths covered by SDSS – we see a lot less reddening there than the model predicts.
We finished by talking about the impact all these things have on galaxy surveys. It’s a fairly small effect, but because dust always dims galaxies that means that inclined spirals are often “left out” of samples which people use to study cosmology, or do galaxy evolution (just because you can’t see them, or they’re below a cut in brightness you needed to make). I don’t think I need to tell this crowd that spiral and elliptical galaxies are quite different objects, they also have different clustering properties. So if you preferentially leave out some of the spirals that could introduce some subtle biases, which when people are trying to use galaxy surveys to get percent level accuracy on cosmological parameters might actually start to matter!
Man vs Machine?
Manda’s paper on improving automatic galaxy classification seems to have caused quite a bit of concern and comment. Is the future of the Zoo portrayed above, with an out-of-control machine wrecking all we’ve come to hold dear? After all, we’ve always believed it important that we don’t waste your time by having you do tasks that computers are perfectly capable of completing. Are the Zookeepers putting the Zoo out of business?
Read More…
Machine learning paper now available
Just a quick note that Manda’s submitted paper on machine learning is now available on astro-ph.
Galaxy Zoo Supernovae from a technical standpoint
I’ve just finished writing up some of the more technical details associated with our recent supernova hunt. If you’re interested in how it all worked behind the scenes then head over here…
Cheers
Arfon
New supernovae found!
After a couple of exposures, we are happy to say that we believe the object mentioned previously is a young supernova. This is great news.
Mark and I thought we would give you better feel for what we are doing here by showing you something visual to have a look at. This our latest target, which we are confident is also a supernova from our raw data. What you can see here are the images of this object as they appear on the zoo. This is a great example of what a supernova will look like in the zoo images. The reason for this is that you can see some structure in the host of the supernova. In general if the transient object appears as in a blob, rather than a perfect circle, it is far more likely to be a real supernova, than a variable star. Although this is not a solid rule of supernovae screening, it is always good to know.
Thank you all for helping to make this observing run a real success. We will be sure to let you know our supernovae grand total soon enough but for now we are looking at in excess of 20 new supernovae. Let’s see if we can catch a few more!
Sarah
WHT supernovae finds update
Just over half way through or night and we are doing well again, in spite of some technical adversity early on. Our next target is a very exciting target. It is either a very new supernovae that has only been around for a few days, or it could be an asteroid. Here at WHT we are certainly hoping for this object to be a young supernovae.
So, why are new supernovae so good? Well, to begin with we want to know as much about supernovae as possible and the best way to do that is to catch them early and follow them. Certainly if this object is what we hope it is, it will be a good candidate for future follow up.
This really is some exciting science! Stand by for an update on what we find!
Sarah :0)
WHT second night prepped and ready to go!
One hour till sunset and Mark and I are ready for another fantastic night of supernovae observing. At the moment there is not a cloud in the sky, so let’s hope this good weather holds!
So far we have the Telescope set up and ready again, just waiting for darkness …
Sarah :0)
End of the night, and new supernovae confirmed
We’re nearing the end of the night now – and that cirrus that threatened earlier blew through quickly, leaving us with clear skies and generally excellent observing conditions.
We ploughed through 16 supernova candidates, which kept us on our toes, and a first look at the data shows that indeed many of them turned out to be supernovae as we had hoped, rather than other variables sources (such as variable stars). So excellent work!
Thanks to everyone who participated and helped to make a successful night of observation; we’ll try for a fuller report tomorrow on what we found. We also have one more night tomorrow night, when we’ll continue to look at candidates identified by the zoo, so keep checking in for updates!
Mark
Galaxy Zoo 
