Undergrad Rotation curve of a gas disk in an elliptical galaxy

[Sofia Piol]

TL;DR

rotation curve of a gas disk in an elliptical galaxy

Hello, I'm Sofia and new here! I'm working on a project in which I'm trying to show that dark matter exists. It's about an elliptical galaxy with a rotating gas disk.

What I'm doing is comparing the theoretical calculation of the rotation curve with the actual measured rotation curve. It should be that the gas disc is actually rotating faster than predicted and therefore there is more mass there than you can see. I have already found a formula for the rotation curve, but I'm not sure if it makes sense.

I used the Jaffe profile for the mass distribution. I also don't know how it is possible to plot this predicted rotation curve without knowing the total mass and the scale radius "a". I would be very happy if someone could help me with this!

 

[Vanadium 50]

Can we back up a bit? Ellipticals are pressure-supported, so a "rotation curve" in the sense of spirals really doesn't exist. When you describe a "rotating gas disk" it sounds like you are talking about spirals with the elliptical in the role of the bulge.

Can you give an example or two of such galaxies?

 

[Vanadium 50]

Oh, and one other thing: ellipticals are thought to have originated through mergers. It is far from clear how much, if any, of the dark matter component remains.

 

[Sofia Piol]

Can we back up a bit? Ellipticals are pressure-supported, so a "rotation curve" in the sense of spirals really doesn't exist. When you describe a "rotating gas disk" it sounds like you are talking about spirals with the elliptical in the role of the bulge.

Can you give an example or two of such galaxies?

For example the elliptical galaxy NGC 5018 contains a rotating gas disk.

 

[Vanadium 50]

Thanks.

5018 is interacting with 5022, so you need to ensure that you are measuring what you think you are. I looked it up, and 5018 is quite the oddball. It's UV-poor, which implies little to no star formation, yet there have been three SNe seen in it.

You need to know the mass to predict the rotation curve. What you can do is look at the stars and the gas and show that that underpredicts the velocity. which would then allow you to invert the process and trace out the DM profile.

 

[ohwilleke]

TL;DR Summary: rotation curve of a gas disk in an elliptical galaxy

Hello, I'm Sofia and new here! I'm working on a project in which I'm trying to show that dark matter exists. It's about an elliptical galaxy with a rotating gas disk.

What I'm doing is comparing the theoretical calculation of the rotation curve with the actual measured rotation curve. It should be that the gas disc is actually rotating faster than predicted and therefore there is more mass there than you can see. I have already found a formula for the rotation curve, but I'm not sure if it makes sense.

I used the Jaffe profile for the mass distribution. I also don't know how it is possible to plot this predicted rotation curve without knowing the total mass and the scale radius "a". I would be very happy if someone could help me with this!

Is there a reason not to use the much easier example of a spiral galaxy?

Also, if you are looking for a reference to cite, rather than just some people on the Internet, the go-to textbook for this topic is Galactic Dynamics by Binney & Tremaine, which is currently in its second edition. The hard copy is pricey at a bit more than $100 USD (although you could get a copy for free from many college libraries or via interlibrary loan), but the e-textbook version is a lot cheaper.