Re: Galaxies without dark matter halos?

greywolf42 wrote:

>Ulf Torkelsson <[EMAIL PROTECTED]> wrote in message
>news:[EMAIL PROTECTED]
>  
>
>>This is wrong.  The Hubble scheme for classification of galaxies is
>>purely morphological.  It does not depend on any form of distances.
>>As long as you can get a good picture of a galaxy you can determine
>>its Hubble typ.
>>    
>>
>
>We are not discussing the Hubble morphological classification scheme.  We
>are discussing the theoretical relationship between galactic type and
>absolute luminosity.  Absolute luminosity is not included in the Hubble
>classification.
>

  There is no such theoretical relationship as you imagine. For most
Hubble types you can find both small and large galaxies, and always
there is a significant spread in the luminosities.

>
>  
>
>>colonel_hack is then providing a brief, but accurate description of the
>>calibration of the Tully-Fisher and Faber-Jackson relations in modern
>>times, and nowhere in that process do you need to put in Hubble's
>>constant.  On the contrary these relations can be and have been used
>>to determine Hubble's constant.
>>    
>>
>
>Any calibration of a distance scale needs something to calibrate with.
>There are between 20 and 40 galaxies containing resolvable Cepheid variables
>(depending on study).  Galaxies beyond this range use the Hubble constant.
>The Tully-Fisher scheme was calibrated using "nearer"
>Hubble-constant-determined distances, in order to avoid them in the far
>distances.
>

  No, the Tully-Fisher scheme has never been calibrated based on the
Hubble constant, that is plainly wrong. There are also more distance
indicators than the Cepheids. May I suggest that you pick up the book:

Rowan-Robinson, M., 1985,
The cosmological distance ladder,
W. H. Freeman & Comp., New York

Rowan-Robinson describes in detail how you build up the cosmological
distance scale. You start with the primary indicators, cepheids,
supernovae, novae and RR Lyrae variables. You then use these to
calibrate new distance indicators, such as the size of HII-regions,
globular clusters, the brightest stars in the galaxies, the
Tully-Fisher relation and so on. In the end you can even use the
brightest cluster galaxies to determine the distances to clusters of
galaxies. Nowhere in this process do you use Hubble's constant.

Ulf Torkelsson

[Mod. note: quoted text trimmed and reformatted -- mjh]