|Dec22-12, 03:12 PM||#1|
I have several question in this thread which is related to velocity dispersion as well as some other areas of galaxy formation and super massive black holes (SMBH)
(1) The sigma is used to calculate the speed of the star at the edge of the galaxy and there is a direct relationship with the SMBH. The heavier the black hole, the faster the stars move around. The M Sigma relation and the Sigma -- are they the same?
(2) The velocity dispersion measures the mass of a galaxy, by determining the kinetic energy and finally the potential energy of a stable system through 'virial theorem'. Is that correct?
(3) The M Sigma relation when plotted on a graph shows that the black hole mass M is directly proportional to the stellar velocity dispersion right?
(4) The numerical figure of M σ relation states:
What does '~~' means?
|Dec23-12, 12:12 AM||#2|
So, velocity dispersion is kind of an observational proxy for galaxy mass, and what the M-sigma relation is really saying is that SMBH mass correlates with host galaxy mass, suggesting that the evolution and growth of the galaxy with time is somehow related to the evolution of its central black hole.
|Dec23-12, 12:22 AM||#3|
Thank you very much. Yes the '~' is what you told, it is 'approximately equals to.'
|Dec23-12, 12:40 AM||#4|
Well, I have few more questions:
Hubble classification divides galaxies into the following forms:
(4) Other irregular galaxies
Our Milky Way is considered to be a spiral galaxy. Now,is there any relation between the type of galaxy with the formation of SMBH? I mean to say that does M-Sigma relation determines the galaxy size and SMBH between any type of galaxies mentioned above?
Secondly, what is a Local group? Going through Wikipedia I found that galaxies have been classified into spiral, elliptical ,irregular galaxies, dwarf elliptical, dwarf spheroidal. Now M110 and M32, denotes they are 'satellite of Andromeda'. Andromeda is a galaxy, I understand, but what does 'satellite of Andromeda' means?
|Dec23-12, 07:58 AM||#5|
Satellite galaxies are small galaxies that are gravitationally bound to a larger galaxy, e.g., our own Milky Way Galaxy or Andromeda Galaxy. The Large and Small Magellanic Clouds are satellite galaxies of the Milky Way. Satellite galaxies tend to be dwarf or irregular galaxies.
For example - http://en.wikipedia.org/wiki/Dwarf_spheroidal_galaxy
List of MW satellite galaxies - http://www.astro.uu.se/~ns/mwsat.html
A presentation on MW dward satellites - http://www.astro.uni-bonn.de/~mwhalo...t37-kroupa.pdf
|Dec23-12, 08:52 AM||#6|
Ok, thanks for the reply. That means the small galaxies are controlled by the main host galaxy? So Andromeda's satellite are those which are bound to Andromeda and Andromeda in turn is controlled by Milky Way? Is that so?
|Dec23-12, 09:55 AM||#7|
Here are some notes on the MW, Andromeda and other galaxies of the Local Group.
Local Group Galaxies (derived from Mateo 1999)
The Local Group of Galaxies
The Andromeda Galaxy is the largest member of the Local Group, bigger even than our Milky Way.
The observed properties of dwarf galaxies in and around the Local Group
Stardate (McDonald Observatory) has a statement that Milky Way may be a little smaller but more massive than M31.
Estimates of the masses of MW and Andromeda are found in N.W. Evans (Oxford), M.I. Wilkinson (Cambridge), The Mass of the Andromeda Galaxy, http://arxiv.org/abs/astro-ph/0004187, April 2000
"We find the halo of Andromeda has a mass of about 12 x 10^11 solar masses, together with a scalelength of roughly 90 kpc and a predominantly isotropic velocity distribution. For comparison, our earlier estimate for the Milky Way halo is 19 x 10^11 solar masses."
However on the BBC Universe site, there is:
Milky Way (notes and some discussion of rotation curve)
The Dynamics of the Galaxies in the Local Group
Roeland van der Marel (STScI), Main collaborators: Jay Anderson, Gurtina Besla, Nitya Kallivayalil, Tony Sohn
|Jan7-13, 08:00 AM||#8|
see plot on wikipedia http://en.wikipedia.org/wiki/M-sigma_relation
by the way, the validity of M-sigma relation being applicable to all galaxies is still under debate, there has been recent findings that this relation isn't applicable to BCGs (Brightest cluster galaxies) that reside within the center of galaxy clusters.
The M-sigma relation as i know it, usually only works well for Ellipticals if one considers the stellar dispersion of the whole galaxy.
|Jan7-13, 11:03 AM||#9|
Thanks once more for your insightful reply. Actually, I came a little bit later to the Faber-Jackson and Tully-Fisher relations. As you have pointed out above rightly, the m sigma relation works out properly with elliptical galaxies, but NOT in case of spiral galaxies.
But isn't that the Tully Fisher relation works out for Spiral galaxies?
Faber Jackson for Elliptical galaxies?
One more thing L is directly proportional to sigma^4. Is this the eqn.for Tully Fisher?
What is the eqn.for Faber Jackson relation?
Somehow, Faber-Jackson & Tully-Fisher are related. Is that both depicts a proportional relation?
Your answers would help me out.
|Jan7-13, 07:03 PM||#10|
Here you're mixing stuff, neither Faber-Jackson nor Tully-Fisher has any direct link to SMBH masses. They are as you know, just relations between stellar motion and the luminosity of the whole galaxy.
Tully–Fisher relation discusses the "luminosity-stellar rotation velocity"
Faber-Jackson relates the "luminosity-stellar dispersion"
I have to say that there is some connection between the Tully–Fisher relation and the BH mass, but it is not so trivial.
Please refer to this paper if you are interested in some more relations that are being used to estimate BH masses http://adsabs.harvard.edu/abs/2012MNRAS.424..224H
The introduction part should quite suffice to clear up some confusion.
Although we have some idea as to how these relations should be valid in theory, but still note that these relations are still more or less empirical and might as well break down for various extermes.
|Jan7-13, 11:39 PM||#11|
Yes, you are very right.
I was thinking that as the M-sigma relation helps to determine the speed of the star, then as heavier the black hole, the more faster the stars move, hence the M-sigma relation has direct relation with the BH.
As you have said that there is some relation with the Tully-Fisher model with the BH, what is that?
I have one more thing, that I need to ask you.
The equation for the Faber-Jackson relation: L is directly proportional to sigma^4.
What is the exact equation for Tully-Fisher? Some say L is directly proportional to V^4.
Is both Tully-Fisher and Faber-Jackson plotted, gives linear?
|Jan9-13, 05:59 AM||#12|
Hello, what is the exact equation form for Faber-Jackson and Tully-Fisher relation?
Wikipedia states: L is directly proportional sigma^4, but that it is in Faber-Jackson.
Can anybody please explain it?
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