Galaxies without dark matter halos?

"g" == greywolf42 writes:

g Your original argument was that EM forces could not affect neutral
g hydrogen significantly -- directly or indirectly. I provided you
g with two physical mechanisms that can equalize the motion of
g neutral hydrogen with EM-driven motion of ionized hydrogen (which
g you apparently don't have a problem with).

Yes, you have "provided [...] two physical mechanisms that can
equalize the motion of neutral hydrogen with EM-driven motion of
ionized hydrogen." You have not shown that these physical mechanisms
operate or are important in the interstellar medium.

* You've asserted that there are plasma filaments with "typical widths
on the order of AU to thousands of AU," but you've provided no
observational evidence for them.

* You continue to confuse hydrogen atoms (from which rotation curves
are measured commonly) with hydrogen molecules. (See the response
to John Park on 2003-08-30, as well as various postings by me.)

* You continue to rely on pressure equilibrium, even though this is
widely known to be true only on average (for a striking
demonstration of the existence of pressure non-equilibrium in the
interstellar medium, see the massive work by Jenkins & Tripp in the
ApJS) and there are clear examples of shock waves in the ISM.

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greywolf42 ) writes:
Joseph Lazio wrote in message

* You continue to confuse hydrogen atoms (from which rotation curves
are measured commonly) with hydrogen molecules. (See the response
to John Park on 2003-08-30, as well as various postings by me.)

I'm not at all confused. The motion of ionized hydrogen (atoms) and the
motion of neutral hydrogen (molecules) are both measured. Hence, the
reference I gave you to Tayler.

Ionised hydrogen isn't an atom; it's a proton or, at best, a molecular ion.
Neutral H atoms are paramagnetic. H2 molecules are diamagnetic and don't
produce the 21 cm line; so how is their motion measured?

--John Park

greywolf42 ) writes:
Joseph Lazio wrote in message

* You continue to confuse hydrogen atoms (from which rotation curves
are measured commonly) with hydrogen molecules. (See the response
to John Park on 2003-08-30, as well as various postings by me.)

I'm not at all confused. The motion of ionized hydrogen (atoms) and the
motion of neutral hydrogen (molecules) are both measured. Hence, the
reference I gave you to Tayler.

Ionised hydrogen isn't an atom; it's a proton or, at best, a molecular ion.
Neutral H atoms are paramagnetic. H2 molecules are diamagnetic and don't
produce the 21 cm line; so how is their motion measured?

--John Park

"g" == greywolf42 writes:

g Joseph Lazio wrote in message
g ...

g Your original argument was that EM forces could not affect neutral
g hydrogen significantly -- directly or indirectly. I provided you
g with two physical mechanisms that can equalize the motion of
g neutral hydrogen with EM-driven motion of ionized hydrogen (which
g you apparently don't have a problem with).
Yes, you have "provided [...] two physical mechanisms that can
equalize the motion of neutral hydrogen with EM-driven motion of
ionized hydrogen." You have not shown that these physical
mechanisms operate or are important in the interstellar medium.

g I gave you the standard text by Tayler, and excerpts from same.

I finally had the chance to look at Tayler. I'll confess, I don't
understand why you reference it.

In Chapter 2 he discusses rotation velocities of stars and gas within
the Galaxy. He cites a couple of different estimates of stellar
rotational velocities, which are between 200 and 300 km/s. He also
provides rotation curves derived from gas motions, which are in the
range 220--240 km/s. No major discrepancy here, as Steve Willner has
already pointed out.

* You've asserted that there are plasma filaments with "typical
widths on the order of AU to thousands of AU," but you've provided
no observational evidence for them.

g What type of secondary 'observational' evidence would you accept,
g since we can't directly observe such without an interstellar probe?

Why can't you just provide what you think to be the evidence?
Moreover, Tayler describes magnetic fields in Chapter 6, citing values
similar to what John Park assumed (length scales ~ 100 pc and field
strengths ~ few microGauss). You've objected to both of these values,
arguing for much smaller length scales and higher field strengths, but
I'll have to confess I don't understand why.

* You continue to confuse hydrogen atoms (from which rotation
curves are measured commonly) with hydrogen molecules. (See the
response to John Park on 2003-08-30, as well as various postings by
me.)

g I'm not at all confused. The motion of ionized hydrogen (atoms)
g and the motion of neutral hydrogen (molecules) are both measured.
g Hence, the reference I gave you to Tayler.

This sounds like a "Yes, you do. No, I don't" argument. I can't do
any more than say that, after re-reading your posts on Google, I
continue to think you do not make this distinction. Perhaps if you
were to supply a succinct summary of your idea it would clear up some
confusion.

* You continue to rely on pressure equilibrium, even though this is
widely known to be true only on average (...) and there are clear
examples of shock waves in the ISM.

g You asked for evidence that pressure could equalize the rotation
g rates of ionized and non-ionized gas. If -- as discussed in Tayler
g -- "ionized gas clouds and non-ionized gas clouds roughly maintain
g equal pressures between region boundaries," then the time scale for
g maintaining these equal pressures must be far less than the time to
g orbit the center of the galaxy. Otherwise, there wouldn't *be*
g different regions.

g Yes, it is the 'average' situation. And the average situation is
g what we look at when we measure overall galactic rotation curves.

The "average" that Tayler forms is over kiloparsec scales. You seem
to assert that pressure equilibrium continues to hold even on
sub-parsec scales. That's a huge extrapolation, and one for which we
have some evidence to the contrary.

Admittedly, I was browsing through Tayler's text after midnight last
night. I could have missed something. Perhaps you might provide a
succinct summary of your idea (and the evidence supporting it?) to
clear up the confusion?

--
Lt. Lazio, HTML police | e-mail:
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html

"g" == greywolf42 writes:

g Joseph Lazio wrote in message
g ...

g Your original argument was that EM forces could not affect neutral
g hydrogen significantly -- directly or indirectly. I provided you
g with two physical mechanisms that can equalize the motion of
g neutral hydrogen with EM-driven motion of ionized hydrogen (which
g you apparently don't have a problem with).
Yes, you have "provided [...] two physical mechanisms that can
equalize the motion of neutral hydrogen with EM-driven motion of
ionized hydrogen." You have not shown that these physical
mechanisms operate or are important in the interstellar medium.

g I gave you the standard text by Tayler, and excerpts from same.

I finally had the chance to look at Tayler. I'll confess, I don't
understand why you reference it.

In Chapter 2 he discusses rotation velocities of stars and gas within
the Galaxy. He cites a couple of different estimates of stellar
rotational velocities, which are between 200 and 300 km/s. He also
provides rotation curves derived from gas motions, which are in the
range 220--240 km/s. No major discrepancy here, as Steve Willner has
already pointed out.

* You've asserted that there are plasma filaments with "typical
widths on the order of AU to thousands of AU," but you've provided
no observational evidence for them.

g What type of secondary 'observational' evidence would you accept,
g since we can't directly observe such without an interstellar probe?

Why can't you just provide what you think to be the evidence?
Moreover, Tayler describes magnetic fields in Chapter 6, citing values
similar to what John Park assumed (length scales ~ 100 pc and field
strengths ~ few microGauss). You've objected to both of these values,
arguing for much smaller length scales and higher field strengths, but
I'll have to confess I don't understand why.

* You continue to confuse hydrogen atoms (from which rotation
curves are measured commonly) with hydrogen molecules. (See the
response to John Park on 2003-08-30, as well as various postings by
me.)

g I'm not at all confused. The motion of ionized hydrogen (atoms)
g and the motion of neutral hydrogen (molecules) are both measured.
g Hence, the reference I gave you to Tayler.

This sounds like a "Yes, you do. No, I don't" argument. I can't do
any more than say that, after re-reading your posts on Google, I
continue to think you do not make this distinction. Perhaps if you
were to supply a succinct summary of your idea it would clear up some
confusion.

* You continue to rely on pressure equilibrium, even though this is
widely known to be true only on average (...) and there are clear
examples of shock waves in the ISM.

g You asked for evidence that pressure could equalize the rotation
g rates of ionized and non-ionized gas. If -- as discussed in Tayler
g -- "ionized gas clouds and non-ionized gas clouds roughly maintain
g equal pressures between region boundaries," then the time scale for
g maintaining these equal pressures must be far less than the time to
g orbit the center of the galaxy. Otherwise, there wouldn't *be*
g different regions.

g Yes, it is the 'average' situation. And the average situation is
g what we look at when we measure overall galactic rotation curves.

The "average" that Tayler forms is over kiloparsec scales. You seem
to assert that pressure equilibrium continues to hold even on
sub-parsec scales. That's a huge extrapolation, and one for which we
have some evidence to the contrary.

Admittedly, I was browsing through Tayler's text after midnight last
night. I could have missed something. Perhaps you might provide a
succinct summary of your idea (and the evidence supporting it?) to
clear up the confusion?

--
Lt. Lazio, HTML police | e-mail:
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html