Galaxies without dark matter halos?

greywolf42 wrote in message news:...

Joseph Lazio wrote in message
...

{snip}

I just ran across a paper that measures both stellar motions and gas motions
in the galactic center. It is "Stellar Velocities and the Mass Distribution
in the Galactic Center," GH Rieke and MJ Rieke, July 1, 1988, APJ,
330:L33-L37

54 individual star motions were determined in this and contained referenced
papers. The motion of same was compared to the motions of gas around
Sagittarius A*. Final conclusion is that the motion of the stars is
"formally inconsistent" with the "dominant central-mass model" (i.e. black
hole) used to explain the motion of the gas.

The Rieke's note: "... the gas in the galactic center may be subject to
non-gravitational forces leading to high velocities, in which case the mass
in the region will be overestimated ..."

Which bears directly on this thread.

The paper is dated 1988. Does anyone know of any followup papers?

greywolf42
ubi dubium ibi libertas

(Slowly getting back to things ....)
"g" == greywolf42 writes:

g I just ran across a paper that measures both stellar motions and
g gas motions in the galactic center. It is "Stellar Velocities and
g the Mass Distribution in the Galactic Center," GH Rieke and MJ
g Rieke, July 1, 1988, APJ, 330: L33-L37

g 54 individual star motions were determined in this and contained
g referenced papers. The motion of same was compared to the motions
g of gas around Sagittarius A*. Final conclusion is that the motion
g of the stars is "formally inconsistent" with the "dominant
g central-mass model" (i.e. black hole) used to explain the motion of
g the gas.

g The Rieke's note: "... the gas in the galactic center may be
g subject to non-gravitational forces leading to high velocities, in
g which case the mass in the region will be overestimated ..."

g Which bears directly on this thread.

g The paper is dated 1988. Does anyone know of any followup papers?

I've already posted in sci.astro a list of authors to consult. Off
the top of my head, Sellgren, Genzel, Ghez, Goss, and Roberts come to
mind. For instance, Roberts, Yusef-Zadeh, & Goss (1996) find that the
ionized gas in Sgr A West implies a central mass of 3.5E6 solar
masses, fairly close to what the current stellar data suggest. Also,
Genzel has published multiple papers showing the mass estimates given
by different kinds of measurements (gas vs. stars).

--
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

(Slowly getting back to things ....)
"g" == greywolf42 writes:

g I just ran across a paper that measures both stellar motions and
g gas motions in the galactic center. It is "Stellar Velocities and
g the Mass Distribution in the Galactic Center," GH Rieke and MJ
g Rieke, July 1, 1988, APJ, 330: L33-L37

g 54 individual star motions were determined in this and contained
g referenced papers. The motion of same was compared to the motions
g of gas around Sagittarius A*. Final conclusion is that the motion
g of the stars is "formally inconsistent" with the "dominant
g central-mass model" (i.e. black hole) used to explain the motion of
g the gas.

g The Rieke's note: "... the gas in the galactic center may be
g subject to non-gravitational forces leading to high velocities, in
g which case the mass in the region will be overestimated ..."

g Which bears directly on this thread.

g The paper is dated 1988. Does anyone know of any followup papers?

I've already posted in sci.astro a list of authors to consult. Off
the top of my head, Sellgren, Genzel, Ghez, Goss, and Roberts come to
mind. For instance, Roberts, Yusef-Zadeh, & Goss (1996) find that the
ionized gas in Sgr A West implies a central mass of 3.5E6 solar
masses, fairly close to what the current stellar data suggest. Also,
Genzel has published multiple papers showing the mass estimates given
by different kinds of measurements (gas vs. stars).

--
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

In article , greywolf42
writes:

g I just ran across a paper that measures both stellar motions and
g gas motions in the galactic center. It is "Stellar Velocities and
g the Mass Distribution in the Galactic Center," GH Rieke and MJ
g Rieke, July 1, 1988, APJ, 330: L33-L37
^^^^
g The Rieke's note: "... the gas in the galactic center may be
g subject to non-gravitational forces leading to high velocities, in
g which case the mass in the region will be overestimated ..."

g The paper is dated 1988. Does anyone know of any followup papers?
^^^^
I've already posted in sci.astro a list of authors to consult. Off
the top of my head, Sellgren, Genzel, Ghez, Goss, and Roberts come to
mind.
And as I've noted several times before, anyone can post a list of authors.
But your list (posted several times now for different purposes), is not
necessarily relevant. And a list of *authors* is certainly not relevant
when the request was for references to *papers*. The question was whether
anyone knew of a DIRECT followup to Rieke's 1988 paper.

Research into the kinematics and dynamics of the galactic centre has
made ENORMOUS progress since 1988. Quite frankly, I can't see how an
observational paper from 1988 is even worth looking into if one wants to
understand what is going on at the galactic centre.

In particular, Genzel and colleagues have done some truly excellent work
in this area. If their conclusions contradict those of the 1988 paper,
don't believe the 1988 paper.

Specific papers:

http://www.arxiv.org/abs/astro-ph/0306214

http://www.arxiv.org/abs/astro-ph/0210426

http://www.arxiv.org/abs/astro-ph/0201031

In article , greywolf42
writes:

g I just ran across a paper that measures both stellar motions and
g gas motions in the galactic center. It is "Stellar Velocities and
g the Mass Distribution in the Galactic Center," GH Rieke and MJ
g Rieke, July 1, 1988, APJ, 330: L33-L37
^^^^
g The Rieke's note: "... the gas in the galactic center may be
g subject to non-gravitational forces leading to high velocities, in
g which case the mass in the region will be overestimated ..."

g The paper is dated 1988. Does anyone know of any followup papers?
^^^^
I've already posted in sci.astro a list of authors to consult. Off
the top of my head, Sellgren, Genzel, Ghez, Goss, and Roberts come to
mind.
And as I've noted several times before, anyone can post a list of authors.
But your list (posted several times now for different purposes), is not
necessarily relevant. And a list of *authors* is certainly not relevant
when the request was for references to *papers*. The question was whether
anyone knew of a DIRECT followup to Rieke's 1988 paper.

Research into the kinematics and dynamics of the galactic centre has
made ENORMOUS progress since 1988. Quite frankly, I can't see how an
observational paper from 1988 is even worth looking into if one wants to
understand what is going on at the galactic centre.

In particular, Genzel and colleagues have done some truly excellent work
in this area. If their conclusions contradict those of the 1988 paper,
don't believe the 1988 paper.

Specific papers:

http://www.arxiv.org/abs/astro-ph/0306214

http://www.arxiv.org/abs/astro-ph/0210426

http://www.arxiv.org/abs/astro-ph/0201031

In article ,
Phillip Helbig---remove CLOTHES to reply wrote:
[[observations of matter motion close to the center of the Milky Way]]
In particular, Genzel and colleagues have done some truly excellent work
in this area. [[...]]
Specific papers:

http://www.arxiv.org/abs/astro-ph/0306214

http://www.arxiv.org/abs/astro-ph/0210426

http://www.arxiv.org/abs/astro-ph/0201031

Another reference (a bit less technical):

@article{
PhysicsToday-Feb2003-BH-news,
title = "Infrared Adapti8ve Optics Reveals Stars Orbiting
Within Light-Hours of the Miliy Way's Center",
subtitle = "Orbital periods as short as 15 years clinch the case
sfor a supermassive black hole at the Galaxy's heart",
author = "Bertran Schwarzschild",
journal = "Physics Today",
year = 2003, month = "February",
volume = 56, number = 2,
pages = "19--21",
}

This is probably online somewhere at http://www.physicstoday.org,
but you may need to be a Physics Today subscriber to see it.

ciao,

--
-- "Jonathan Thornburg (remove -animal to reply)"
Max-Planck-Institut fuer Gravitationsphysik (Albert-Einstein-Institut),
Golm, Germany, "Old Europe" http://www.aei.mpg.de/~jthorn/home.html
"A survey of academic studies on the effects of passive smoking found that,
of the investigators with [financial] ties to the tobacco industry, 94%
claimed that it is not harmful, whereas 87% of those without such ties
claimed that it is." -- Jeremy Gunawardena, Nature 424, 489 (31.Jul.2003)

In article ,
Phillip Helbig---remove CLOTHES to reply wrote:
[[observations of matter motion close to the center of the Milky Way]]
In particular, Genzel and colleagues have done some truly excellent work
in this area. [[...]]
Specific papers:

http://www.arxiv.org/abs/astro-ph/0306214

http://www.arxiv.org/abs/astro-ph/0210426

http://www.arxiv.org/abs/astro-ph/0201031

Another reference (a bit less technical):

@article{
PhysicsToday-Feb2003-BH-news,
title = "Infrared Adapti8ve Optics Reveals Stars Orbiting
Within Light-Hours of the Miliy Way's Center",
subtitle = "Orbital periods as short as 15 years clinch the case
sfor a supermassive black hole at the Galaxy's heart",
author = "Bertran Schwarzschild",
journal = "Physics Today",
year = 2003, month = "February",
volume = 56, number = 2,
pages = "19--21",
}

This is probably online somewhere at http://www.physicstoday.org,
but you may need to be a Physics Today subscriber to see it.

ciao,

--
-- "Jonathan Thornburg (remove -animal to reply)"
Max-Planck-Institut fuer Gravitationsphysik (Albert-Einstein-Institut),
Golm, Germany, "Old Europe" http://www.aei.mpg.de/~jthorn/home.html
"A survey of academic studies on the effects of passive smoking found that,
of the investigators with [financial] ties to the tobacco industry, 94%
claimed that it is not harmful, whereas 87% of those without such ties
claimed that it is." -- Jeremy Gunawardena, Nature 424, 489 (31.Jul.2003)

Phillip Helbig---remove CLOTHES to reply
wrote in message ...
Research into the kinematics and dynamics of the galactic centre has
made ENORMOUS progress since 1988. Quite frankly, I can't see how an
observational paper from 1988 is even worth looking into if one wants to
understand what is going on at the galactic centre.

In particular, Genzel and colleagues have done some truly excellent work
in this area. If their conclusions contradict those of the 1988 paper,
don't believe the 1988 paper.

LOL! We don't get to pick and choose our data, in science. It's quite
funny to keep hearing that a 'newer' paper will allow us to ignore prior
papers that are irritatingly at odds with popular theory. The correct
approach is to evaluate the differences in the approach of the papers, to
see which is right.

Specific papers:

Thanks for the specific references.

http://www.arxiv.org/abs/astro-ph/0201031

"Stellar Orbits Near Sagittarius A*," Eckart, Genzel, Schodel, Jan 2002

Mixes data types:
Combines the high precision but shorter time scale NIRC/Keck data with the
lower precision but longer time scale SHARP/NTT data set;

"Adjusts" data:
Statistically corrects the observed accelerations for theoretical projection
effects;

Drops "contradictory" data:
Excludes star S8 from the analysis of the amount and position of the central
mass. ("... this star either was or is subject to a close interaction with a
different object or that its position measurements are influenced by the
emission of a different cluster star.")

http://www.arxiv.org/abs/astro-ph/0210426

"Closest Star Seen Orbiting the Supermassive Black Hole at the Centre of the
Milky Way", Oct 2002, Schodel et al.

23 authors (I'm afraid I'll always start out highly skeptical of such an
obviously political effort). One star as primary data. Mixing of VLBI and
infrared data. "Correcting" data to match theory (Sgr A* position was
'moved' to fit the theory). No mention of the other stars that don't seem
to be moving in this fashion.

http://www.arxiv.org/abs/astro-ph/0306214

"Stellar Dynamics in the Central arcsecond of our galaxy," June 2003,
Schodel et al Followup from 0210426. 6 Stars plotted. Retains the
"adjusted" data (postion of Sgr A*).


None of these address all the stars found in the Rieke's paper.
Specifically, instead of focusing on one or a few individual stars selected
for their apparent support of one theory, one needs to address the following
findings from Rieke and Rieke:

"The simplest model with a central black hole that dominates the mass within
2 pc would have a velocity dispersion increasing as r^-1/2; clearly there is
no indication of this trend in our data. A chi^2 analysis indicates there is
a 95% probability that the stellar velocity dispersion for r 0.5 pc ... is
less than 120 km s^-1. Perhaps the most important result of this letter is
that the upper limit of 120 km s^-1 ... is far below the velocities observed
for gas in this region, which vary over +- 300 km s^-1. ..."

greywolf42
ubi dubium ibi libertas

Phillip Helbig---remove CLOTHES to reply
wrote in message ...
Research into the kinematics and dynamics of the galactic centre has
made ENORMOUS progress since 1988. Quite frankly, I can't see how an
observational paper from 1988 is even worth looking into if one wants to
understand what is going on at the galactic centre.

In particular, Genzel and colleagues have done some truly excellent work
in this area. If their conclusions contradict those of the 1988 paper,
don't believe the 1988 paper.

LOL! We don't get to pick and choose our data, in science. It's quite
funny to keep hearing that a 'newer' paper will allow us to ignore prior
papers that are irritatingly at odds with popular theory. The correct
approach is to evaluate the differences in the approach of the papers, to
see which is right.

Specific papers:

Thanks for the specific references.

http://www.arxiv.org/abs/astro-ph/0201031

"Stellar Orbits Near Sagittarius A*," Eckart, Genzel, Schodel, Jan 2002

Mixes data types:
Combines the high precision but shorter time scale NIRC/Keck data with the
lower precision but longer time scale SHARP/NTT data set;

"Adjusts" data:
Statistically corrects the observed accelerations for theoretical projection
effects;

Drops "contradictory" data:
Excludes star S8 from the analysis of the amount and position of the central
mass. ("... this star either was or is subject to a close interaction with a
different object or that its position measurements are influenced by the
emission of a different cluster star.")

http://www.arxiv.org/abs/astro-ph/0210426

"Closest Star Seen Orbiting the Supermassive Black Hole at the Centre of the
Milky Way", Oct 2002, Schodel et al.

23 authors (I'm afraid I'll always start out highly skeptical of such an
obviously political effort). One star as primary data. Mixing of VLBI and
infrared data. "Correcting" data to match theory (Sgr A* position was
'moved' to fit the theory). No mention of the other stars that don't seem
to be moving in this fashion.

http://www.arxiv.org/abs/astro-ph/0306214

"Stellar Dynamics in the Central arcsecond of our galaxy," June 2003,
Schodel et al Followup from 0210426. 6 Stars plotted. Retains the
"adjusted" data (postion of Sgr A*).


None of these address all the stars found in the Rieke's paper.
Specifically, instead of focusing on one or a few individual stars selected
for their apparent support of one theory, one needs to address the following
findings from Rieke and Rieke:

"The simplest model with a central black hole that dominates the mass within
2 pc would have a velocity dispersion increasing as r^-1/2; clearly there is
no indication of this trend in our data. A chi^2 analysis indicates there is
a 95% probability that the stellar velocity dispersion for r 0.5 pc ... is
less than 120 km s^-1. Perhaps the most important result of this letter is
that the upper limit of 120 km s^-1 ... is far below the velocities observed
for gas in this region, which vary over +- 300 km s^-1. ..."

greywolf42
ubi dubium ibi libertas

greywolf42 writes:
[ ... ]
http://www.arxiv.org/abs/astro-ph/0201031

"Stellar Orbits Near Sagittarius A*," Eckart, Genzel, Schodel, Jan 2002

Mixes data types:
Combines the high precision but shorter time scale NIRC/Keck data with the
lower precision but longer time scale SHARP/NTT data set;

"Adjusts" data:
Statistically corrects the observed accelerations for theoretical projection
effects;

Drops "contradictory" data:
Excludes star S8 from the analysis of the amount and position of the central
mass. ("... this star either was or is subject to a close interaction with a
different object or that its position measurements are influenced by the
emission of a different cluster star.")

The three factors you bring up are *differences* between the Eckart
work and previous work by Ghez et al (2000). Despite this, the
results of Eckart and Ghez are consistent with one another, and with
the previous work by Genzel et al (2000). Furthermore the techniques
applied by the Eckart paper appear to be appropriate, and would tend
to *decrease* rather than increase observational biases. Therefore
your criticisms appear to be essentially irrelevant.



http://www.arxiv.org/abs/astro-ph/0210426

"Closest Star Seen Orbiting the Supermassive Black Hole at the Centre of the
Milky Way", Oct 2002, Schodel et al.

23 authors (I'm afraid I'll always start out highly skeptical of such an
obviously political effort). One star as primary data. Mixing of VLBI and
infrared data. "Correcting" data to match theory (Sgr A* position was
'moved' to fit the theory). No mention of the other stars that don't seem
to be moving in this fashion.

Your "political" comment is irrelevant. Your other comments imply
your disapproval. However, as the authors say, "

The remarkable consequence of the orbital technique is that the mass
can be determined from a single stellar orbit, in comparison to the
statistical techniques that use several tens to hundreds of stellar
velocities at 10 to 300 light days from SgrA* (Fig. 3). In addition,
the orbital technique requires fewer assumptions than the other
estimates (for example, equilibrium and isotropy of orbits), and
thus is less vulnerable to systematic effects.

The combination of VLBI and infrared data allows an extremely precise
alignment of the stars (IR) and Sgr A* (radio). The position of Sgr
A* can be considered a nuisance parameter since it is not relevant to
the mass determination (and in any case is within 1.6 sigma of the
previously determined position).



http://www.arxiv.org/abs/astro-ph/0306214

"Stellar Dynamics in the Central arcsecond of our galaxy," June 2003,
Schodel et al Followup from 0210426. 6 Stars plotted. Retains the
"adjusted" data (postion of Sgr A*).


None of these address all the stars found in the Rieke's paper.
Specifically, instead of focusing on one or a few individual stars selected
for their apparent support of one theory, one needs to address the following
findings from Rieke and Rieke:

"The simplest model with a central black hole that dominates the mass within
2 pc would have a velocity dispersion increasing as r^-1/2; clearly there is
no indication of this trend in our data. A chi^2 analysis indicates there is
a 95% probability that the stellar velocity dispersion for r 0.5 pc ... is
less than 120 km s^-1. Perhaps the most important result of this letter is
that the upper limit of 120 km s^-1 ... is far below the velocities observed
for gas in this region, which vary over +- 300 km s^-1. ..."


Genzel et al (2000) show, using an ensemble of stars, that the central
velocity dispersion is of order 280-350 km/s, and decreases with
radius between r^-1 and r^-0.5, so Rieke's findings appear to be
addressed. However, these statistical measurements really take second
place to a direct measurment of a Keplerian orbit around the central
mass, including both pericenter and apocenter, which both clinches the
mass of the central body, and highly constrains its density (since
pericenter is within 17 lt-hr = 120 AU).

CM

References
Genzel, R. et al 2000, MNRAS, 317, 348
Ghez, A. M. et al 2000, Nature, 407, 349