Milky Way Rotation Curve

Can anyone point me to up to date data or plots of the Milky Way's
rotation curve, or alternatively to information about either velocity
data or data on the distribution of visible matter in the Milky way,
from which I can plot the rotation curve?


Regards

--
Charles Francis
substitute charles for NotI to email

Can anyone point me to up to date data or plots of the Milky Way's
rotation curve, or alternatively to information about either velocity
data or data on the distribution of visible matter in the Milky way,
from which I can plot the rotation curve?

You can find one sample rotation curve for
our galaxy in my notes at

http://spiff.rit.edu/classes/phys301...res/mw/mw.html

That page also contains a link to a paper with
rotation curves for a number of other spiral galaxies.

And, of course, you can always go to the ADS

http://adsabs.harvard.edu/abstract_service.html

and type "Milky Way rotation curve" into the Abstract
Words box, to get a large number of references.


Michael Richmond

Thus spake Stupendous_Man
Can anyone point me to up to date data or plots of the Milky Way's
rotation curve, or alternatively to information about either velocity
data or data on the distribution of visible matter in the Milky way,
from which I can plot the rotation curve?

You can find one sample rotation curve for
our galaxy in my notes at

http://spiff.rit.edu/classes/phys301...res/mw/mw.html

Many thanks. That is useful.

That page also contains a link to a paper with
rotation curves for a number of other spiral galaxies.

And, of course, you can always go to the ADS

http://adsabs.harvard.edu/abstract_service.html

and type "Milky Way rotation curve" into the Abstract
Words box, to get a large number of references.

Yes. 293 in fact. I have been trying this with arxiv, but this seems to
be a rather better database. I have churned up some useful stuff
thanks, including a couple more curves.

In so far as I can tell from my searches so far, the mass distribution
is not well constrained by observation. Is that right? This is rather
important for a comparison between theory and observation.


Regards

--
Charles Francis
substitute charles for NotI to email

In article , Oh No
writes:

In so far as I can tell from my searches so far, the mass distribution
is not well constrained by observation. Is that right? This is rather
important for a comparison between theory and observation.

The whole concept of dark matter revolves (pun intended) around the
concept that we can't detect it (i.e. "constrain the mass distribution
by observation") directly, but only indirectly, through the effects it
has on the motion of visible (in the broader sense of the term, i.e.
including radio observations) objects.

Of course, to determine the mass distribution at all, one has to specify
some theory, be it conventional gravity, MOND, or something else. Or,
perhaps, have some idea about the mass distribution from theory.

In the foreseeable future, we won't be able to say "here's the matter,
here are the observations, here's the theory, do they match?" but rather
"here are observations of visible matter and here is the theory, do they
match?". The answer is that they don't. Thus, one needs some
non-visible matter (dark matter) or a modified theory (e.g. MOND).

Personally, I'm rather agnostic on the matter. To some extent, MOND
shaves close with Occam's razor, explaining a lot from a little. On the
other hand, I don't think it would be particularly mysterious if most
matter were dark. A rough analogy: almost everything in our day-to-day
life is determined by the behaviour of electrons (chemistry, exclusion
principle preventing everything from being in one place at one time,
electricity, electronics etc), but we don't find it particularly
puzzling that most of the mass is in the nucleus (even though it takes
up much less space), not in the electrons. So, why should we be
surprised if most of the mass of the universe is not in a form which
interacts directly (i.e. electromagnetically) with our observational
instruments?

Phillip Helbig---remove CLOTHES to reply
wrote:

[...]
Personally, I'm rather agnostic on the matter. To some extent, MOND
shaves close with Occam's razor, explaining a lot from a little.

I'm not sure that's true. MOND typically involves an arbitrary
function that extrapolates between the low acceleration and high
acceleration regimes. The equation of motion is of the form
F(a/a_0)a = -del Phi
where F is a function such that F(x)~x for x1 and F(x)~1 for x1.
It's interesting that one can find a function (or actually a collection
of functions) for which this matches many observations; but freedom to
choose an arbitrary function isn't exactly a small assumption.

For a relativistic version like Bekenstein's TeVeS, it's even worse
-- you need a scalar and a vector interaction on top of the metric,
and an action that contains an arbitrary, and typically quite
complicated, function of the scalar field. Bekenstein's original
TeVeS action, for example, involves the function
F(x) = 3/8 x^{-2}{x(4+2x-4x^2+x^3) + 2ln[(1-x)^2]}
in the scalar fiels Lagrangian. I don't see why thr freedom to choose
such a function in the action is an improvement over an assumption of
dark matter.

Steve Carlip

In article ,
writes:

Phillip Helbig---remove CLOTHES to reply
wrote:

[...]
Personally, I'm rather agnostic on the matter. To some extent, MOND
shaves close with Occam's razor, explaining a lot from a little.

I'm not sure that's true. MOND typically involves an arbitrary
function that extrapolates between the low acceleration and high
acceleration regimes.

For a relativistic version like Bekenstein's TeVeS, it's even worse

That's correct, of course. However, on the purely astronomical side, it
does explain a lot from a little. As you point out, the theory itself
might be inelegant. On the other hand, that's true of dark matter as
well: saying "there must be dark matter" is at the level of the
phenomenological MOND, whereas it remains to be seen whether the theory
which explains this dark matter is elegant.

Thus spake
Phillip Helbig---remove CLOTHES to reply
wrote:

[...]
Personally, I'm rather agnostic on the matter. To some extent, MOND
shaves close with Occam's razor, explaining a lot from a little.

I'm not sure that's true. MOND typically involves an arbitrary
function that extrapolates between the low acceleration and high
acceleration regimes. The equation of motion is of the form
F(a/a_0)a = -del Phi
where F is a function such that F(x)~x for x1 and F(x)~1 for x1.
It's interesting that one can find a function (or actually a collection
of functions) for which this matches many observations; but freedom to
choose an arbitrary function isn't exactly a small assumption.

For a relativistic version like Bekenstein's TeVeS, it's even worse
-- you need a scalar and a vector interaction on top of the metric,
and an action that contains an arbitrary, and typically quite
complicated, function of the scalar field. Bekenstein's original
TeVeS action, for example, involves the function
F(x) = 3/8 x^{-2}{x(4+2x-4x^2+x^3) + 2ln[(1-x)^2]}
in the scalar fiels Lagrangian. I don't see why thr freedom to choose
such a function in the action is an improvement over an assumption of
dark matter.


I don't think MOND actually explains anything either. I think it
demonstrates a physical law which must be explained in a reasonable
approximation by some underlying theory, but it does not give an
explanation for the law. I think that gives a theorist something to aim
at, but because the interpolating function is not determined and the
data is fairly messy, any sensible theory which produces a reasonably
MOND like law would be a good candidate imv.

The teleconnection has a rationale and also eliminates the interpolating
function. It simply adds the MONDian inverse law to the Newtonian part,
but the MONDian part is seen as an effect of expansion on Doppler, not a
modification of dynamics (gtr is shown in the classical correspondence).

This does mean that the teleconnection is empirically distinguishable
from other MONDian models, because it gives greater orbital velocities
towards the centre of the galaxy. This is actually rather encouraging at
the moment, but I seem to have an awful lot of stuff to plough through
before I can make much of it. The fit to the Milky way seems much better
with the teleconnection law, but it is to a theoretical mass
distribution and I don't know how good that is. For distant Low Surface
Brightness galaxies (good for testing purposes) I have just discovered
that to get the MONDian fits they had to alter the angle of inclination
of about half the galaxies (sort of ok because it's a bit of a guess
anyway) in order to increase orbital velocities at the centre.



Regards

--
Charles Francis
substitute charles for NotI to email

In article , Oh No
writes:

I have two problems with cold dark matter. I don't have any problem with
the idea that dark matter exists in forms which we know about from
elementary particle physics. For example the neutrino only needs a small
mass to account for much more than observable baryonic mass. But we know
that the neutrino is not responsible for the phenomena associated with
CDM. My problem here is not simply that we have no theory in elementary
particle physics for CDM, but that the constraints on particles which
can exist are quite severe, and they do not even appear to allow a
theory of CDM.

Dark matter doesn't have to be "elementary particles" in the narrower
sense of the term. (Of course, it would be composed of elementary
particles in some sense, like everything else.) Some people have
suggested primordial black holes. (Although formed from baryonic
matter, they would have formed before baryogenesis, thus there is no
conflict with primordial nucleosynthesis etc.) However, this idea seems
inconsistent with microlensing observations. I think the dark matter
could even be bricks (except for the problem that bricks---as we know
them, Jim---are baryonic). Of course, this is not probable, there is no
mechanism etc. The point is, there are lots of forms the dark matter
could take which are not ruled out by current observations.

[...]
Personally, I'm rather agnostic on the matter. To some extent, MOND
shaves close with Occam's razor, explaining a lot from a little.

I'm not sure that's true. MOND typically involves an arbitrary
function that extrapolates between the low acceleration and high
acceleration regimes.

For a relativistic version like Bekenstein's TeVeS, it's even worse

That's correct, of course. However, on the purely astronomical side, it
does explain a lot from a little. As you point out, the theory itself
might be inelegant. On the other hand, that's true of dark matter as
well: saying "there must be dark matter" is at the level of the
phenomenological MOND, whereas it remains to be seen whether the theory
which explains this dark matter is elegant.

Probably you already know this , but MOND/TeVeS is NOT the only
alternative theory of gravity which explains galactic rotation curves
(without DM). If you see the recent conference on alternate theories
of gravity (which I sent a link at sci.physics.relativity) you will
note that both Moffat and Mannheim(and am sure others) have diff.
gravitational potentials to fit galactic rotation curves and these can
be derived from a much more elegant theory My guess is that if the
Pioneer anomaly is confirmed , then it may point to new gravitational
physics explanation for the dark matter problem. anyhow see
astro-ph/0505266 for more details.


[Mod. note: reformatted -- mjh]

Thus spake Phillip Helbig---remove CLOTHES to reply
LOTHESvax.de
In article , Oh No
writes:

I have two problems with cold dark matter. I don't have any problem with
the idea that dark matter exists in forms which we know about from
elementary particle physics. For example the neutrino only needs a small
mass to account for much more than observable baryonic mass. But we know
that the neutrino is not responsible for the phenomena associated with
CDM. My problem here is not simply that we have no theory in elementary
particle physics for CDM, but that the constraints on particles which
can exist are quite severe, and they do not even appear to allow a
theory of CDM.

Dark matter doesn't have to be "elementary particles" in the narrower
sense of the term. (Of course, it would be composed of elementary
particles in some sense, like everything else.)

Yes, but therein lies a problem, because the equations of sr and qm only
appear to allow the sorts of matte which we know about.

Some people have
suggested primordial black holes. (Although formed from baryonic
matter, they would have formed before baryogenesis, thus there is no
conflict with primordial nucleosynthesis etc.) However, this idea seems
inconsistent with microlensing observations.

Again, I have no philosophical problem with primordial black holes, but
as you say, observation is negative.

I think the dark matter
could even be bricks (except for the problem that bricks---as we know
them, Jim---are baryonic). Of course, this is not probable, there is no
mechanism etc. The point is, there are lots of forms the dark matter
could take which are not ruled out by current observations.

One form which does seem to be ruled out, however, is that lensing
observations do not permit haloes with profiles required by galactic
rotation curves. One finds an increasing number of papers commenting on
this salient fact, and yet no answer to it from those advocating CDM.



Regards

--
Charles Francis
substitute charles for NotI to email