Edge-on, bulgeless spiral - question
-
by
v3nom
This galaxy seems to be interesting. Quick question to experienced user / science team. Is it edge-on bulgeless spiral or cigar shaped elliptical? In my opinion it is edge-on spiral, but I would like to know your opinion.
Posted
-
by
ElisabethB
moderator
I'd go for edge on too !
Posted
-
by
vrooje
admin, scientist
Lovely #bulgeless #edge-on example in my opinion. Nice!
Posted
-
by
JeanTate
in response to v3nom's comment.
One thing I've learned is that if the elongated galaxy has pointy ends, then it's more likely a disk galaxy than an elliptical. Also, there's a quantitative means of saying 'how cigar-shaped?', a number called 'ellipticity'; a perfectly round elliptical is an E0, and the most cigar-shaped one is an E7. The number is related to the ratio between the length of the minor axis (b) and the length of the major one (a); an E7 galaxy has a b/a ratio of 0.3 (i.e. 7 = 10*(1-(b/a)) )1.
So, a highly elongated object subject (in the New! Upgraded! Talk, galaxies, stars and such are called "subjects", not "objects" 😮 ) like this can only be a disk galaxy.
Why a 'disk galaxy' and not a spiral? Because not all disk galaxies have (spiral) arms! The classic arm-less disk galaxies are the lenticulars, and it seems that even E7 'ellipticals' may be lenticulars too (perhaps even E6s too).
If you're interested in this sort of thing, the recent Galaxy Zoo blog Live Chat: Galactic Rings, Secular Evolution and The Good Old Days is on this topic. And the ultimate source is Ron Buta's Galaxy Morphology2, which contains hours and hours of happy reading. 😃
1 More on this in this GZ forum thread: What is the relationship between 'ellipticity' and 'axis ratio'?
2 the link takes you to the abstract; click on the PDF link (top right) to download
Posted
-
by
v3nom
in response to JeanTate's comment.
JeanTate, that is very detailed answer. Thank you 😉
EDIT: It is good to know, that I have provided classification, which is consistent with your opinions. I know there are often no correct answers, but opinion of people who possibly classified thousands of galaxies matters. Thanks!
Posted