Continuing:
Thanatos January 11 Post#2701
I am still stuck on this [post 2628]
What do you mean by 'no redshift distances are needed' to calculate the PV72 value'? The 'V' in Vvir is, according to LEDA:
" . . . The heliocentric cz, v is computed from the data in the compilation of redshifts by rejecting outliers and measurements marked for their bad quality and computing a weighted average of the remaining measurements.
The heliocentric cz, v is used to compute the redshift in other reference frames: Namely in the Local Group referential, vlg, the Galactic referential, vgsr, the Virgo cluster referential, vvir, and the CMB referential, v3k."
Dgruss23 January 11 post#2702
There is a difference between a "redshift" and a "redshift distance". The redshift is specifically a shift of the observed spectral lines to longer wavelengths. The relative shift is typically expressed as "z" where:
Code:
z = Wavelength observed - wavelength actual Wavelength actual
This is the direct measurement of the amount of spectral shift. It is a redshift when the observed wavelength is longer than the actual wavelength.
Under the assumption that the observed wavelength shifts may be treated as velocities the spectral shift (z) may be multiplied by the speed of light (c) to get a velocity redshift:
Velocity = cz
In the conversation we're having here redshift may mean the spectral shift (z) or it may mean the velocity (cz). The "redshift" is not a distance.
In order to derive a "redshift distance" you must have a "redshift velocity" and a value for the Hubble constant (H0).
Then the redshift distance becomes:
Redshift Distance = cz/H0
But as I've previously explained, you don't need to calculate redshift distance to get a value for PV72. If you have a redshift independent distance (such as Cepheid's, TFR ...) you can still get a PV72 value by the following:
PV72 = Vvir - (Distance x H0)
where distance in the above equation may be derived from Cepheids, the TFR or any of the other secondary distance indicators.
For example, NGC 4535 has a Cepheid distance of 15.8 Mpc and a redshift velocity corrected to the Virgocentric reference frame of 2029 km s-1.
So plugging those numbers and a Hubble constant of 72 gives PV72 = +891 km s-1.
Thanatos January 12 post#2703
Would you agree that redshift is a measured value and redshift velocity is a derivation based on that measurement? I have no problem considering there may be discrepancies between the TF distance and redshift distances, just your resistance to making comparisons.
Dgruss23 January 12 post#2704
Of course. Mainstream astronomers use redshift velocity all the time. Are you suggesting multiplying the spectral shift by "c" introduces a problem? If so, then that's a mainstream problem too.
Thanatos, you're illustratingagain that you don't know what you're talking about. I have no "resistance" to calculating redshift distances. There simply is no need to calculate redshift distances because you get the exact same numbers if you calculate PV72 the way I did, that you would get if you first calculate a redshift distance a TF distance and then calculate the redshift discrepancy from the difference between the two.
If you want to calculate redshift distances, then this is how you will calculate the redshift discrepancy.
Redshift velocity difference = (Hubble distance - TFR distance) x H0
For NGC 4535 used in my last post the Vvir redshift velocity is 2029 km s-1. Divide this by a Hubble constant of 72 km s-1 Mpc-1 and you get a redshift distance of 28.18 Mpc. So then the redshift velocity difference (RVD) is:
RVD = (28.18 Mpc - 15.8 Mpc) x 72 km s-1 Mpc-1 = 891 km s-1
That may be compared with the PV72 value of 891 km s-1 calculated in the previous post.
Do you understand now?
Thanatos January 13 post#2705
I appreciate you taking the time to point out how I missed the boat with my naive questions.
Dgruss23 January 13 post#2706
Not "naive questions", but certainly too not questions asked without a bit of infused accusation. You say I'm resistant to calculating redshift distances when you never asked "Why don't you calculate redshift distances?" If that is what you wanted to know, just ask it instead of accusing me of resisting it, cherry picking ...
Thanatos February 1 post#2780
I admittedly did not understand that comment. I fail to see how any discrepancy between the TF distance and redshift distance of galaxies can be asserted without independently comparing the two.
TomT Feb 2 post #2781
Russell doesn't calculate redshift distances in his paper because he is working with the velocities to show that the results for Peculiar velocity lead to the conclusion that something more is needed to account for the results.
So he isn't asserting or emphasizing distance discrepencies, he is asserting discrepencies in what the velocities are telling us vs the mainstream interpretation.
Thanatos Feb3 post #2782
Tom, How do you derive a peculiar velocity without defining the difference between the 'z' and H0 components? The equations you cite are too inbred to make this distinction.
TomT Feb3 post#2783
I had thought that this had been discussed so many times, that it wasn't necessary to repeat it again. You have to have an independent, accurate measure of distance to the galaxy. That is what all the discussion and effort regarding Cepheid distances and Type Dependent - Tully Fisher equations was about.
Once you have your best independent measure of distance, D , it is converted to redshiftby z = (H0/c)*D. Call this zD. This is by mainstream definition, the part of the galaxy redshift due to cosmological expansion.
You have to have a value of the Hubble Constant to calculate this. The current best mainstream number for this is 72 + or - about 5. Note that LEDA uses 70 in the calculation of mucin.
Next, the value zD is subtracted from the total redshift. This remainder is thought by mainstream to be due only to the galaxy peculiar velocity. Russell takes a detailed look at this, and concludes that there is more to it than just peculiar velocity.
This is what the discussion the last 3 months has been about.
Thanatos March 4 post#2875
If it's any consolation, matt, I think I understand what you are saying. I'm otherwise a bit annoyed. I made provacative arguments about peculiar motions and nobody appears willing to admit their ATM notions might be flawed.
TomT March 4 post#2876
Could you expand a bit more on this so we know what you are referring to?
Thanatos March 5 post#2879
Deriving peculiar motion without invoking a redshift distance would be a good place to start.
This is an example of some of the mainstreamer absurdity that occurs in ATM when one presents an ATM case worthy of discussing. Note in this instance the fact that this specific issue is still being discussed is because a mainstreamer keeps bringing it up - and its not as if it was sufficiently explained in the first post.
We also have instances in Arp et al of mainstreamers simply ignoring rebuttals provided to the points they've made. Then later on someone brings up the supposed "problem" as if it was never responded to.
This sort of behavior is the reason I've had to keep taking breaks from BAUT. I invest too much effort into the posts I make to keep putting up with this kind of bad behavior by mainstreamers. I've observed enough instances during the last year of mainstreamers not being held to the same standard of discourse as ATMers. This is related to the points I made in the rules discussion thread a while back.
But after this latest rules change I've simply concluded that the forum is no longer what it used to be when I signed up. I'm not saying there are not valid reasons for changing, but the fact is that I'm quite tired of hearing "If ATMers ..." when my experience is that mainstreamers are guilty of all the bad behaviors ATMers are criticized for.
The reason most people don't see this is that very few ATM ideas have legs ... but when it comes to one that might it suddenly becomes apparent that mainstreamers are just as susceptible to flaws in dialogue as ATMers.