Today’s guest blogger is Raul Jimenez who collaborated with us on an exciting paper on the spin (clockwise vs. counter-clockwise) of spiral galaxies.
The rate at which galaxies transform gas into stars as a function of time gives astronomers insight into the way galaxies formed and evolved. By using the SDSS spectra one can infer the past star formation history of a galaxy. We have been doing this using sophisticated statistical tools, take a look here. Much has been learned about the formation of galaxies using their star formation history, for example we know that the most massive galaxies assemble their stars early on, about 1-2 Gyr after the big-bang while small mass galaxies (100 to 1000 times smaller than the milky way) do it during the whole age of the universe. What we have done in our recent paper is to look at how the star formation history of galaxies correlates to the rotation direction of galaxies as measured by the galaxy zoo project. What we have found is that galaxies that had lots of star formation in the past do tend to rotate in the same direction in groups with lengths of about 10 to 20 Mpc.
Although this might sound surprising, it is not! If one reviews very old papers, almost 40-50 years ago, where people like Andrei Doroskievich worked out the way galaxies should rotate based on how they were formed in the past, one realizes that the correlation we have found arises naturally in these models of galaxy formation, so-called hierarchical models. What is happening is that in the past the cluster of galaxies was not yet formed and the spiral galaxies that the galaxy zoo has been classifying by morphology were coming down the filamentary structure into the proto-clusters. Because the proto-cluster already contains the big elliptical galaxies, they provide the same “pull” on all the spiral galaxies in the filament. So it is quite exciting to see this result from the galaxy zoo and the MOPED/VESPA catalogs. Now it is time to go back to theory and numerical simulations and understand better what it means for galaxy formation and evolution. This is something we will do next.
The paper has been submitted to MNRAS, and the pre-print is available for download on astro-ph.
Great work guys, thanks for sharing it.
Second that!
So do the way some galaxies are shaped by the actions of others average out to be equally CW or ACW? Or is there a bias towards one or the other, especially as distance increases?
I’m really impressed, I knew that galaxies rotated and everything, but now I realize how cool it really is from a point of view of us imagining it and knowing that, like the Earth, galaxies don’t stand still…they move. It’s like being in a train only this time we go in circles rather than in straight lines. As I write this, the Earth has moved from where it was just a minute ago because our galaxy rotates and so everything in it also moves from one place to another. And to think that some people out there don’t even know this stuff, that’s what makes Astronomy so fascinanting!
This is so very interesting!
Why is the “hierarchical” model so-called?
Are there other models?
What is SDSS spectra?
Is there someplace I can go to get a glossary for these technical terms?
Finally, thank you folks so much for this really excellent site!
Morry
A galaxy which rotates clockwise viewed from one side rotates anti-clockwise from the other,other than the obvious fact that galaxies have at least two differing views what possible logic is there in any statistical measurement of spin direction?
The underpinning assumption in the comments about rotation is that the term of reference is always from our Earth-view advantage position. So all rotational directions must be understood as relative to Earth, along our line of sight, surely? Hence the recent research of spin direction is making an observational determination.
What he is saying in his artical above is that locally (galatic neighborhood – a cluster) spins are influenced by some make up with in that galatic cluster. From our point of view the spin direction for galaxies in that cluster would be similar. From our point of view we would expect to see statistically equal number of galatic clusters favor CW spins as favor ACW spins.
I remember when I was categorizing the direction of spin of the galaxies in Zoo 1, I could not understand why we would need to do this, for similar reasons to billallen, but now you explain that you are looking at these galaxies in relationship to others near by and what they look like eg star formations taking place, it gives me an idea of what we are actually doing. thank you!
Is there an imaginary equator in the universe? If so perhaps the galaxies above spin one way and the ones below spin the other. This would require that we estimate our position in the cosmos and the possible equatorial line then, regardless of which galaxy you’re looking at you will know if behaving as it should. Of what use this is… I don’t know….. perhaps time travel. Cheers
Dan
Oh,crazy!I think I must study English more hard!
So when it comes to determining which way a galaxy is spinning, it seems to me that their orientation as viewed subjectively can be from just about any angle. How do you determine whether a galaxy is viewed from the top or bottom when determining it’s direction of spin?