Galaxies without dark matter halos?

"TS" == Thomas Smid writes:
TS Joseph Lazio wrote in message
TS ...

You're mixing up two different measurements. Within the optical
disk, I think gas and stars usually co-rotate. (....) Outside
the optical disk, no stars are detected so one has to rely on the
gas to trace the gravitational potential.

TS The fact remains that in most publications gas rotation curves are
TS used to support the hypothesis that stars are bound by dark
TS matter. Why ? Presumably because star rotation curves wouldn't be
TS as conclusive.

As a followup to my followup, I did some poking around. I discovered
a series of papers by Bottema, including Bottema et
al. (1991A&A...247..357B, URL:
http://adsabs.harvard.edu/cgi-bin/np...6A...247..357B )
in which the rotation curve is derived from stellar motions and
compared to the rotation curve derived from neutral gas (H I) (their
Figure 5). It looks to me like the two rotation curves agree to at
least 10%, and in some places better than 5%. In other papers Bottema
tries to reproduce the rotation curves using only stellar data and
concludes that at least some dark matter is required.

I have to conclude that stellar rotation curves show the same thing
that gas rotation curves do: There seems to be more matter in galaxies
than what we can see.

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